DIPLOMA WORK ON THE TOPIC:
Pipe production
1. SORT AND REQUIREMENTS OF REGULATORY DOCUMENTATION FOR PIPES
1.1 Pipe range
KresTrubZavod OJSC is one of the largest pipe manufacturers in our country. Its products are successfully sold both domestically and abroad. The products manufactured at the plant meet the requirements of domestic and foreign standards. International quality certificates are issued by such organizations as: American Petroleum Institute (API), German certification center TUV - Rayland.
Shop T-3 is one of the main shops of the enterprise, its products meet the standards presented in table. 1.1.
Table 1.1 - Standards of manufactured pipes
The workshop produces pipes from carbon, alloyed and highly alloyed steel grades with a diameter of D = 28-89mm and a wall thickness of S = 2.5-13mm.
Basically, the workshop specializes in the production of tubing, general purpose pipes and pipes for subsequent cold processing.
The mechanical properties of the pipes produced must correspond to those indicated in table. 1.2.
1.2 Regulatory requirements
The production of pipes in the workshop T-3 KresTrubZavod is carried out according to various regulatory documents such as GOST, API, DIN, NFA, ASTM and others. Consider the requirements of DIN 1629.
1.2.1Sortment
This standard applies to seamless round pipes from unalloyed steels. Chemical composition steels used for the production of pipes are given in table 1.3.
Table 1.2 - Mechanical properties of pipes
Table 1.3 - Chemical composition of steels
Pipes made according to this standard are primarily used in various devices for the manufacture of tanks and laying pipelines, as well as in general mechanical engineering and instrument making.
The dimensions and maximum deviations of pipes are given in table 1.4., Table 1.5., Table 1.6.
The length of the pipe is determined by the distance between its ends. The types of pipe lengths are given in table 1.4.
Table 1.4 - Types of lengths and permissible length deviations
Table 1.5 - Tolerances for diameter
Table 1.6 - Permissible deviations in wall thickness
The pipes should be as round as possible. The roundness deviation must be within the tolerances for the outer diameter.
The pipes must be straight by eye, if necessary, special requirements for straightness can be specified.
The pipes must be cut perpendicular to the pipe axis and must be free of burrs.
The values for linear masses (weights) are given in DIN 2448. The following deviations from these values are allowed:
for a separate pipe + 12% - 8%,
for deliveries weighing at least 10t + 10% –5%.
The standard designation for pipes conforming to DIN 1629 indicates:
Naming (pipe);
The main number of the size standard DIN (DIN 2448);
Main dimensions of the pipe (outer diameter × wall thickness);
Main number of technical delivery conditions (DIN 1629);
Abbreviated name of the steel grade.
Example of a symbol for a pipe according to DIN 1629 with an outer diameter of 33.7 mm and a wall thickness of 3.2 mm made of steel St 37.0:
Pipe DIN 2448-33.7 x 3.2
DIN 1629 – St 37.0.
1.2.2 Technical requirements
Pipes must be manufactured in accordance with the requirements of the standard and according to the technological regulations approved in the prescribed manner.
On the outer and inner surfaces of pipes and couplings, there should be no captivity, sinks, sunsets, delamination, cracks and sands.
Cutting and cleaning of the indicated defects is allowed, provided that their depth does not exceed the maximum minus deviation in the wall thickness. Welding, caulking or sealing of defective spots is not allowed.
In places where the wall thickness can be measured directly, the depth of the defective places can exceed the specified value, provided that the minimum wall thickness is maintained, defined as the difference between the nominal pipe wall thickness and the minus deviation limit for it.
Some minor nicks, dents, risks, a thin layer of scale and other defects caused by the production method are allowed, if they do not bring the wall thickness beyond the minus deviations.
Mechanical properties (yield strength, tensile strength, elongation at break) should correspond to the values given in table 1.7.
Table 1.7 - Mechanical properties
1.2.3 Acceptance rules
Pipes are presented for acceptance in batches.
A batch must consist of pipes of the same nominal diameter, one wall thickness and strength group, of the same type and one design, and must be accompanied by a single document certifying that their quality meets the requirements of the standard and containing:
Manufacturer's name;
Nominal pipe diameter and wall thickness in millimeters, pipe length in meters;
Type of pipes;
Strength group, heat number, mass fraction of sulfur and phosphorus for all heats included in the batch;
Pipe numbers (from - to for each heat);
Test results;
Standard designation.
Each pipe of the batch must be checked for appearance, size of defects and geometric dimensions and parameters.
The mass fraction of sulfur and phosphorus must be checked from each heat. For pipes made from metal from another enterprise, the mass fraction of sulfur and phosphorus must be certified by a document certifying the quality of the metal manufacturer's enterprise.
To check the mechanical properties of the metal, one pipe of each size is taken from each heat.
To check for flattening, take one pipe from each heat.
An internal hydraulic pressure test shall be applied to each pipe.
When unsatisfactory test results are obtained for at least one of the indicators, repeated tests are carried out on a double sample from the same batch. Retest results apply to the entire batch.
1.2.4 Test methods
Inspection of the outer and inner surfaces of pipes and couplings is carried out visually.
The depth of the defects should be checked by filing or in another way in one to three places.
Checking the geometric dimensions and parameters of pipes and couplings should be carried out using universal measuring instruments or special devices that ensure the required measurement accuracy, in accordance with the technical documentation approved in the prescribed manner.
The curvature at the end sections of the pipe is determined based on the value of the deflection arrow, and is calculated as the quotient of the deflection arrow in millimeters by the distance from the measurement point to the nearest end of the pipe in meters.
Checking pipes by weight should be carried out at special means for weighing with an accuracy meeting the requirements of this standard.
The tensile test must be carried out in accordance with DIN 50 140 on short longitudinal specimens.
To check the mechanical properties of the metal, one sample is cut from each selected pipe. Samples should be cut along either end of the pipe using a method that does not change the structure and mechanical properties of the metal. It is allowed to straighten the ends of the specimen for gripping by the clamps of the testing machine.
The duration of the hydraulic pressure test must be at least 10 s. When tested, no leakage shall be found in the pipe wall.
1.2.5 Marking, packaging, transportation and storage
Pipe marking should be carried out in the following scope:
Each pipe, at a distance of 0.4-0.6 m from its end, must be clearly marked by impact or knurling:
Pipe number;
Manufacturer's trademark;
Month and year of issue.
The place of application of the marking should be circled or underlined with stable light paint.
The height of the markings should be 5-8 mm.
With the mechanical method of marking pipes, it is allowed to arrange it in one row. It is allowed to mark the heat number on each pipe.
Each pipe shall be marked with a durable light-colored paint next to the percussion or knurled markings:
Nominal pipe diameter in millimeters;
Wall thickness in millimeters;
Execution type;
Manufacturer's name or trademark.
The height of the markings should be 20-50 mm.
All marking signs must be applied along the generatrix of the pipe. It is allowed to apply marking signs perpendicular to the generatrix by the knurling method.
When loading, one wagon must contain pipes of only one batch. Pipes are transported in packages tightly tied in at least two places. The package weight should not exceed 5 tons, and at the request of the consumer - 3 tons. It is allowed to ship packages of pipes of different batches in one car, provided they are separated.
2. TECHNOLOGY AND EQUIPMENT FOR PIPE PRODUCTION
2.1 Description of the main equipment of workshop T-3
2.1.1 Description and brief technical characteristics of the walking hearth furnace (WB)
Walking hearth furnace of workshop T-3 is designed for heating round blanks with a diameter of 90 ... 120 mm, a length of 3 ... 10 m from carbon, low-alloy and stainless steel grades before piercing on TPA-80.
The furnace is located in the premises of the T-3 workshop on the second floor in aisles A and B.
The furnace project was carried out by Gipromez of the city of Sverdlovsk in 1984. Commissioning was carried out in 1986.
The furnace is a rigid metal structure lined from the inside with refractory and heat-insulating materials. Internal dimensions of the furnace: length - 28.87 m, width - 10.556 m, height - 924 and 1330 mm, operational characteristics of the furnace are presented in Table 2.1. Under the furnace is made in the form of fixed and movable beams, with the help of which the workpieces are transported through the furnace. The beams are lined with heat-insulating and refractory materials and framed with a special set of heat-resistant casting. The upper part of the beams is made of MK-90 mullite-corundum mass. The furnace roof is made suspended from shaped refractory materials and insulated with heat-insulating material. To service the furnace and conduct the technological process, the walls are equipped with working windows, a loading window and a metal unloading window. All windows are equipped with shutters. The furnace is heated by natural gas, which is fired by means of GR burners (low pressure radiation burner) installed on the roof. The furnace is divided into 5 heating zones with 12 burners each. Combustion air is supplied by two VM-18A-4 fans, one of which serves as a backup. Flue gases are removed through a smoke collector located on the roof at the beginning of the furnace. Further, through the system of metal lined chimneys and hogs with the help of two VGDN-19 smoke exhausters, flue gases are discharged into the atmosphere. A loop two-way tubular 6-section loop recuperator (SR-250) for heating the air supplied for combustion is installed on the chimney. For a more complete utilization of waste gas heat, the smoke removal system is equipped with a single-chamber mandrel heating furnace.
The delivery of the heated billet from the furnace is carried out using an internal water-cooled roller table, the rollers of which have a heat-resistant nozzle.
The oven is equipped with an industrial television system. Loudspeaker communication is provided between the control panels and the instrumentation and control panel.
The furnace is equipped with systems for automatic regulation of the thermal regime, automatic safety, units for monitoring the operating parameters and signaling the deviation of parameters from the norm. The following parameters are subject to automatic regulation:
Furnace temperature in each zone;
Gas-to-air ratio by zones;
Gas pressure in front of the furnace;
The pressure in the working space of the furnace.
In addition to automatic modes, a remote mode is provided. The automatic control system includes:
Furnace temperature by zone;
Temperature across the width of the oven in each zone;
Temperature of gases leaving the furnace;
Air temperature after the recuperator by zones;
Flue gas temperature in front of the recuperator;
The temperature of the smoke in front of the exhauster;
Natural gas consumption for the oven;
Oven air consumption;
Vacuuming in the hog in front of the exhauster;
Common manifold gas pressure;
Gas and air pressure in zone collectors;
Furnace pressure.
The stove is provided with a natural gas cut-off with a light and sound alarm when the gas and air pressure drops in the zone collectors.
| Natural gas consumption per furnace (maximum) nm 3 / hour | 5200 |
| 1 zone | 1560 |
| 2 zone | 1560 |
| Zone 3 | 1040 |
| 4 zone | 520 |
| 5 zone | 520 |
| Natural gas pressure (maximum), kPa before | |
| oven | 10 |
| burner | 4 |
| Furnace air consumption (maximum) nm 3 / hour | 52000 |
| Air pressure (maximum), kPa before | |
| oven | 13,5 |
| burner | 8 |
| Pressure under the roof, Pa | 20 |
| Metal heating temperature, ° С (maximum) | 1200...1270 |
| Chemical composition of combustion products in the 4th zone,% | |
| CO 2 | 10,2 |
| About 2 | 3,0 |
| CO | 0 |
| Combustion products temperature in front of the recuperator, ° С | 560 |
| Air heating temperature in the recuperator, ° С | Up to 400 |
| Delivery rate of workpieces, sec | 23,7...48 |
| Furnace productivity, t / hour | 10,6... 80 |
The audible alarm is also triggered when:
An increase in temperature in the 4th and 5th zones (t cp = 1400 ° C);
Temperature rise flue gas in front of the recuperator (t with p = 850 ° C);
An increase in the temperature of flue gases in front of the smoke exhauster (t cp = 400 ° C);
The pressure drop of the cooling water (p cf = 0.5 atm).
2.1.2 Brief technical characteristics of the hot cutting line
The line for hot cutting of the workpiece is designed for the task of the heated rod in the shears, cutting the workpiece to the required lengths, removing the cut workpiece from the scissors.
Brief technical characteristics of the hot cutting line are presented in table 2.2.
The equipment of the hot cutting line includes the shears themselves (SKMZ designs) for cutting the workpiece, a movable stop, a transport roller table, a protective screen to protect the equipment from thermal radiation from the PSHP unloading window. The scissors are designed for waste-free cutting of metal, but if, as a result of any emergency reasons, residual scrap is formed, then a chute and a box are installed in the pit, near the scissors to collect it. In any case, the work of the hot-cutting line must be organized in such a way as to exclude the formation of scrap.
| Parameters of the bar to be cut | |
| Length, m | 4,0…10,0 |
| Diameter, mm | 90,0…120,0 |
| Maximum weight, kg | 880 |
| Workpiece length, m | 1,3...3.0 |
| Rod temperature, О С | 1200 |
| Productivity, pcs / h | 300 |
| Transportation speed, m / s | 1 |
| Movable stop stroke, mm | 2000 |
| Video clip | |
| Barrel diameter, mm | 250 |
| Barrel length, mm | 210 |
| Rolling diameter, mm | 195 |
| Roller pitch, mm | 500 |
| Water consumption for a water-cooled roller, m 3 / h | 1,6 |
| Water consumption for a water-cooled roller with water-cooled axle boxes, m 3 / h | 3,2 |
| Water consumption per screen, m 3 / h | 1,6 |
| Sound level, dB, no more | 85 |
After the rod is heated and dispensed, it passes through a thermostat (to reduce the temperature drop along the length of the workpiece), reaches the movable stop and is cut into workpieces of the required length. After making the cut, the movable stop is lifted by means of a pneumatic cylinder, the workpiece is transported along the roller table. After its passage behind the stop, it is lowered into the working position and the cutting cycle is repeated. To remove scale from under the rollers of the roller table, hot cutting shears, a water descaling system is provided, to remove trimmings - a chute and a receiving box. After leaving the hot-cutting roller table, the billet goes to the receiving roller conveyor of the piercing mill.
2.1.3 Design and technical characteristics of the main and auxiliary equipment of the piercing mill section
The piercing mill is designed for piercing a solid workpiece into a hollow sleeve. TPA-80 is equipped with a 2-roll piercing mill with barrel-shaped or cup-shaped rolls and guide bars. The technical characteristics of the piercing mill are presented in Table 2.3.
In front of the piercing mill, there is a water-cooled roller table, designed to receive the workpiece from the hot cutting line and transport it to the centering machine. The roller conveyor consists of 14 water-cooled rollers with individual drives.
| Sizes of the workpiece to be sewn: | |
| Diameter, mm | 100…120 |
| Length, mm | 1200…3350 |
| Sleeve size: | |
| Outside diameter, mm | 98…126 |
| Wall thickness, mm | 14…22 |
| Length, mm | 1800…6400 |
| Main drive speed, rpm | 285…400 |
| Gear Ratio | 3 |
| Engine power, kW | 3200 |
| Feed angle, ° | 0…14 |
| Rolling force: | |
| Maximum radial, kN | 784 |
| Maximum axial, kN | 245 |
| Maximum torque on the roll, kNm | 102,9 |
| Working roll diameter, mm | 800…900 |
| Pressure screw: | |
| Greatest stroke, mm | 120 |
| Travel speed, mm / s | 2 |
The centering device is designed for knocking out a center groove with a diameter of 20 ... 30 mm and a depth of 15 ... 20 mm at the end of a heated workpiece and is a pneumatic cylinder in which a striker with a tip slides.
After centering, the heated billet enters the grate for its subsequent transfer to the groove of the front table of the piercing mill.
The front table of the piercing mill is designed to receive a heated workpiece rolling along the grate, align the axis of the workpiece with the axis of piercing and hold it during piercing.
On the output side of the mill, roller centering devices of the mandrel bar are installed, which support and center the bar, both before piercing and during the piercing process, when high axial forces act on it and its buckling is possible.
A stationary thrust-adjusting mechanism with an opening head is located behind the centering devices; it serves to perceive axial forces acting on a rod with a mandrel, to correct the position of the mandrel in the deformation zone and to pass the sleeve outside the piercing mill.
2.1.4 Design and technical characteristics of the main and auxiliary equipment of the continuous mill section
The continuous mill is designed for rolling rough pipes with a diameter of 92 mm and a wall thickness of 3 ... 8 mm. Rolling is carried out on a long floating mandrel with a length of 19.5 m. Brief technical characteristics of the continuous mill are given in table 2.4, in table 2.5. the gear ratios of the gearboxes are given.
During rolling, the continuous mill works as follows: the roller conveyor behind the piercing mill transports the sleeve at a speed of 3 m / s to the movable stop and, after stopping, is transferred to the grate in front of the continuous mill by means of a chain conveyor and rolls back onto the metering levers.
| Name | The magnitude | |
| Rough tube outer diameter, mm | 91,0…94,0 | |
| Rough pipe wall thickness, mm | 3,5…8,0 | |
| Maximum length of the rough pipe, m | 30,0 | |
| Diameter of mandrels of a continuous mill, mm | 74…83 | |
| Mandrel length, m | 19,5 | |
| Diameter of wolves, mm | 400 | |
| Roll barrel length, mm | 230 | |
| Roll neck diameter, mm | 220 | |
| Distance between the axes of stands, mm | 850 | |
| Stroke of the upper pressure screw with new rolls, mm | Up | 8 |
| Down | 15 | |
| The stroke of the lower pressure screw with new rolls, mm | Up | 20 |
| Down | 10 | |
| Lifting speed of the upper roll, mm / s | 0,24 | |
| Rotation frequency of main drive motors, rpm | 220…550 | |
If there are defects on the sleeve, the operator manually directs it into the pocket by manually activating the overlap and repulsive devices.
When the dispenser levers are lowered, a suitable sleeve is rolled into the chute, pressed by the clamping levers, after which a mandrel is inserted into the sleeve using the drive rollers. When the front end of the mandrel reaches the front edge of the sleeve, the clamp is released, and the sleeve is driven into the continuous mill using push rollers. In this case, the rotation speed of the pulling rollers of the mandrel and the sleeve is set in such a way that by the time the sleeve is gripped by the first stand of the continuous mill, the front end of the mandrel is extended by 2.5 ... 3 m.
After rolling on a continuous mill, the rough tube with a mandrel goes to a mandrel extractor, a brief technical characteristic is presented in table 2.6. After that, the pipe is transported by a roller conveyor to the area where the rear end is trimmed and comes to a stationary stop at the section where the rear end of the pipe is trimmed; the technical characteristics of the equipment of the POSC section are given in Table 2.7. Having reached the stop, the pipe is thrown by the auger ejector onto the grate in front of the leveling roller table. Next, the pipe is rolled along the grating onto the leveling roller table, comes to the stop that determines the trim length, and is transferred by the stacker from the leveling roller table to the grating in front of the discharge roller table, while the rear end of the pipe is trimmed during the movement.
The cut end of the pipe is transferred by a scrap conveyor to a scrap metal container located outside the workshop.
Table 2.5 - Gear ratio of continuous mill gearboxes and motor power
2.1.5 The principle of operation of the main and auxiliary equipment of the section of the reduction mill and refrigerator
The equipment of this section is designed to transport the rough pipe through the installation. induction heating, rolling on a reduction mill, cooling and further transporting it to the section for cold cutting saws.
Heating of rough pipes in front of the reduction mill is carried out in the heating installation INZ - 9000 / 2.4, consisting of 6 heating blocks (12 inductors) located directly in front of the reduction mill. The pipes enter the induction unit one after the other in a continuous flow. If there is no supply of pipes from the continuous mill (when the rolling is stopped), it is allowed to supply the deposited "cold" pipes to the induction unit one by one. The length of pipes to be installed in the installation should not exceed 17.5 m.
Reduction mill type - 24-stand, 3-roll with two support rolls and individual stand drive.
After rolling on the reduction mill, the pipe enters either the sprayer and the cooling table, or directly to the cooling table of the mill, depending on the requirements for the mechanical properties of the finished pipe.
The design and technical characteristics of the sprayer, as well as the parameters of cooling pipes in it are a trade secret of KresTrubZavod OJSC and are not presented in this work.
Table 2.8. the technical characteristics of the heating unit are presented, in table 2.9.– a brief technical characteristic of the reduction mill.
Table 2.8 - Brief technical characteristics of the heating unit INZ-9000 / 2.4
2.1.6 Equipment for cutting pipes to length
To cut pipes to measured lengths in the T-3 workshop, a Wagner batch saw, model WVC 1600R, is used, the technical characteristics of which are given in table. 2.10. The saws of the KV6R model are also used - technical characteristics in table 2.11.
| Parameter name | The magnitude | |
| Diameter of pipes to be cut, mm | 30…89 | |
| Width of cut bags, mm | 200…913 | |
| Wall thickness of cut pipes, mm | 2,5…9,0 | |
| Length of pipes after cutting, m | 8,0…11,0 | |
| Length of cut pipe ends | Front, mm | 250…2500 |
| Rear, mm | ||
| Saw blade diameter, mm | 1600 | |
| Number of teeth on a saw blade, pcs | Segmental | 456 |
| Carbide | 220 | |
| Cutting speed, mm / min | 10…150 | |
| The minimum diameter of the saw blade, mm | 1560 | |
| Circular saw support feed, mm | 5…1000 | |
| Maximum tensile strength of pipes, N / mm 2 | 800 | |
2.1.7 Equipment for straightening pipes
Pipes cut to length according to the order are sent for straightening. Straightening is carried out on leveling machines RVV320x8, designed for straightening pipes and rods made of carbon and low-alloy steel grades in a cold state with an initial curvature of up to 10 mm per 1 running meter. The technical characteristics of the RVB 320x8 straightening machine are given in table. 3.12.
| Parameter name | The magnitude |
| Single-row bag width, mm | No more than 855 |
| Opening width of the workpiece clamp, mm | 20 to 90 |
| Passage in the vertical direction of the workpiece clamping, mm | No more than 275 |
| Saw blade support stroke, mm | 650 |
| Saw blade feed speed (stepless) mm / min | No more than 800 |
| Fast return stroke of the saw blade, mm / min | No more than 6500 |
| Cutting speed, m / min | 40; 15; 20; 30; 11,5; 23 |
| Clamping length of the pipe package on the inlet side, mm | Not less than 250 |
| Clamping length of the pipe package on the outlet side, mm | Not less than 200 |
| Saw blade diameter, mm | 1320 |
| Number of segments on a saw blade, pcs | 36 |
| Number of teeth per segment, pcs | 10 |
| Diameter of processed pipes, mm | 20 to 90 |
| Parameter name | The magnitude | |
| Straightened pipes diameter, mm | 25...120 | |
| Wall thickness of straightened pipes, mm | 1,0...8,0 | |
| Straightened pipes length, m | 3,0...10,0 | |
| The yield strength of the metal of the straightened pipes, kgf / mm 2 | Diameter 25 ... 90 mm | Up to 50 |
| Diameter 90 ... 120 mm | Up to 33 | |
| Pipe straightening speed, m / s | 0,6...1,0 | |
| The pitch between the axes of the rolls, mm | 320 | |
| Diameter of rolls in the neck, mm | 260 | |
| Number of rolls, pcs | Drive | 4 |
| Singles | 5 | |
| Rolls installation angles, ° | 45 ° ... 52 ° 21 ' | |
| The greatest travel of the upper rolls from the upper edge of the lower, mm | 160 | |
| Roll rotation drive | engine's type | D-812 |
| Voltage, V | 440 | |
| power, kWt | 70 | |
| Rotation speed, rpm | 520 | |
2.2 Existing technology for the production of pipes at TPA-80 JSC "KresTrubZavod"
The billet in the form of rods arriving at the workshop is stored in the internal warehouse. Before being put into production, it is subjected to random inspection on a special rack and, if necessary, to be repaired. At the billet preparation area, scales are installed to control the weight of the metal put into production. The billets from the warehouse are fed by an electric bridge crane to the loading grate in front of the furnace and loaded into the heating furnace with a walking hearth in accordance with the schedule and rate of rolling.
Compliance with the workpiece stacking scheme is carried out visually by the metal planter. The billet is loaded into the furnace one by one into each one, through one or several steps of the guide plates of the movable beams, depending on the rate of rolling and the frequency of cutting. When changing the steel grade, melt and pipe size, the fitter separates the steel grades and heats as follows: with a billet length of 5600-8000 mm, heats are separated by displacing the first two rods along the width of the furnace; steel grades are separated by shifting the first four rods along the width of the furnace; with a billet length of 9000-9800mm, the separation of steel grades, heats from each other is carried out at landing with an interval of 8-10 steps, as well as by counting the amount of workpiece planted in the PSHP and issued, which are controlled by a metal heater PSHP and a hot-cutting shears cutter by means of verification with control panels ... TPA-80; when changing the size (reloading the mill) of the rolled pipes, the landing of metal in the furnace stops “5-6 steps” before the mill stops; when stopping for transshipment, the metal “steps back 5-6 steps”. The workpieces are moved through the furnace by three movable beams. In the pauses of the movement cycle, the movable beams are installed at the level of the hearth. The required heating time is ensured by measuring the step cycle time. Overpressure in the working space should be from 9.8 Pa to 29.4 Pa, the air flow rate = 1.1 - 1.2.
When billets of various grades of steel are heated in a furnace, the heating duration is determined by the metal with the longest residence time in the furnace. High-quality heating of the metal is ensured by the uniform passage of the blanks along the entire length of the furnace. The heated billets are delivered to the inner unloading roller conveyor, and they are delivered to the hot cutting line.
To reduce the cooling of the workpieces during downtime, a thermostat is provided on the roller table for transporting heated workpieces to the shears, as well as the possibility of returning (by turning on the reverse) an uncut workpiece into the furnace and finding it during the downtime.
Hot stopping of the oven is possible during operation. A hot stopping of a furnace is considered to be a stopping without shutting down the natural gas supply. During hot stops, the movable kiln beams are installed at the level of the fixed ones. The loading and unloading windows are closed. The air flow rate using the "fuel-air" unit is reduced from 1.1-1.2 to 1.0: -1.1. The furnace pressure at the hearth level becomes positive. When the mill stops: up to 15 minutes - the temperature in the zones is set at the lower limit, and the metal is “stepped back” by two steps; from 15 minutes to 30 minutes - the temperature in zones III, IV, V is reduced by 20-40 0 С, in zones I, II by 30-60 0 С from the lower limit; over 30 minutes - the temperature in all zones is reduced by 50-150 0 C compared to the lower limit, depending on the duration of inactivity. The workpieces "step back" 10 steps. With a downtime of 2 to 5 hours, it is necessary to free the furnace zones IV and V from the blanks. Workpieces from zones I and II are unloaded into a pocket. Metal unloading is carried out by a metal handler with PU-1. The temperature in zones V and IV is reduced to 1000-I050 0 С. At stops for more than 5 hours, the entire furnace is freed from metal. The temperature rise is carried out stepwise by 20-30 0 С, at a temperature rise rate of 1.5-2.5 0 С / min. With an increase in the heating time of the metal due to the low rate of rolling, the temperature in zones I, II, III is reduced by 6 0 C, 40 0 C, 20 0 C, respectively, from the lower limit, and the temperature in zones IV, V at the lower limits. In general, with stable operation of the entire unit, the temperature is distributed over the zones as follows (Table 2.13).
After heating, the workpiece enters the workpiece hot cutting line. The equipment of the hot cutting line includes the shears themselves for cutting the workpiece, a movable stop, a transport roller table, a protective screen to protect the equipment from thermal radiation from the unloading window of the walking hearth furnace. After the rod is heated and dispensed, it passes through the thermostat, reaches the movable stop and is cut into workpieces of the required length. After the cut is made, the movable stop is lifted by means of a pneumatic cylinder, the workpiece is transported along the roller table. After its passage behind the stop, it is lowered into the working position and the cutting cycle continues.
Table 2.13 - Distribution of temperature in the furnace by zones
The measured workpiece is transferred to the centering machine by the roller conveyor behind the scissors. The centered workpiece is transferred by the ejector to the grate in front of the piercing mill, along which it is rolled to the retainer and, when the exit side is ready, is transferred to the chute, which is closed with a lid. With the help of a pusher, when the stop is raised, the workpiece is set into the deformation zone. In the deformation zone, the workpiece is pierced on a mandrel held by a rod. The rod rests against the glass of the thrust head of the thrust-adjusting mechanism, the opening of which does not allow the lock. Longitudinal bending of the bar from axial forces arising during rolling is prevented by closed centering devices, the axes of which are parallel to the axis of the bar.
In the working position, the rollers are reduced around the rod by a pneumatic cylinder through a system of levers. As the front end of the sleeve approaches, the centering rollers are sequentially set apart. After the end of the blank piercing, the first rollers are brought down by a pneumatic cylinder, which move the sleeve from the rolls to be able to grip the rod by the interceptor levers, then the lock and the front head are folded back, the ejecting rollers are brought down and the sleeve at high speed is issued at high speed behind the thrust head onto the roller table behind the piercing mill ...
After flashing, the sleeve is transported along the roller table to the movable stop. Then the sleeve is moved by a chain conveyor to the inlet side of the continuous mill. After the conveyor, the sleeve is rolled along the inclined grate to the metering device, which retains the sleeve in front of the inlet side of the continuous mill. There is a pocket under the guides of the inclined grate for collecting defective sleeves. From the inclined grate, the sleeve is dropped into the receiving chute of the continuous mill with clamps. At this time, a long mandrel is inserted into the sleeve using one pair of friction rollers. When the front end of the mandrel reaches the front end of the liner, the liner clamp is released, two pairs of pulling rollers are brought to the liner, and the liner with the mandrel is set into a continuous mill. In this case, the rotation speed of the pulling rollers of the mandrel and the pulling rollers of the sleeve is calculated so that at the moment of the capture of the sleeve by the first stand of the continuous mill, the extension of the mandrel from the sleeve is 2.5-3.0 m. In this regard, the linear speed of the pulling rollers of the mandrels should be 2.25-2.5 times the linear speed of the liner pulling rollers.
Rolled tubes with mandrels are alternately transferred to the axis of one of the mandrel extractors. The mandrel head passes through the bearer of the extractor and is gripped by the gripper insert, and the tube into the bezel ring. As the chain moves, the mandrel exits the pipe and enters the chain conveyor, which transfers it to a double roller conveyor that transports the mandrels from both extractors to the cooling bath.
After removing the mandrel, the rough pipe goes to the saws to trim the rear loose end.
After induction heating, the pipes are fed into a reduction mill with twenty-four three-roll stands. In a reduction mill, the number of working stands is determined depending on the dimensions of the rolled tubes (from 9 to 24 stands), and stands are excluded, starting from 22 in the direction of decreasing the number of stands. Stands 23 and 24 participate in all rolling programs.
During rolling, the rolls are continuously water-cooled. When pipes are moved along the cooling table, there should be no more than one pipe in each link. When rolling hot-deformed pipes intended for the manufacture of tubing of strength group "K" from steel grade 37G2S, after the reduction mill, accelerated controlled cooling of the pipes in sprayers is carried out.
The speed of the pipes passing through the sprayer should be stabilized with the speed of the reduction mill. Control over the stabilization of speeds is carried out by the operator in accordance with the operating instructions.
After reduction, the pipes are fed to a rack cooling table with walking beams where they are cooled.
At the cooling table, pipes are collected in single-layer bags for trimming and cutting to length on cold saws.
Finished pipes go to the inspection table of the Quality Control Department, after inspection, the pipes are tied into packages and sent to the finished product warehouse.
2.3 Justification of design solutions
With the piece-by-piece reduction of pipes with tension on the PPC, a significant longitudinal difference in wall thickness of the pipe ends occurs. The reason for the end wall thickness of the pipes is the instability of axial tensions in unsteady modes of deformation when filling and emptying the working stands of the mill with metal. The end sections are reduced under conditions of significantly lower longitudinal tensile stresses than the main (middle) part of the pipe. The increase in wall thickness at the end sections, exceeding the permissible deviations, makes it necessary to trim off a significant part of the finished pipe
The norms of the end trim of the reduced pipes on the TPA-80 of JSC "KresTrubZavod" are given in table. 2.14.
Table 2.14 - Standards for trimming the ends of pipes at TPA-80 JSC "KresTrubZavod"
2.4 Justification of design solutions
With the piece-by-piece reduction of pipes with tension on the PPC, a significant longitudinal difference in wall thickness of the pipe ends occurs. The reason for the end wall thickness of the pipes is the instability of axial tensions in unsteady modes of deformation when filling and emptying the working stands of the mill with metal. The end sections are reduced under conditions of significantly lower longitudinal tensile stresses than the main (middle) part of the pipe. The increase in wall thickness at the end sections, exceeding the permissible deviations, makes it necessary to cut off a significant part of the finished pipe.
The norms of the end trim of the reduced pipes on the TPA-80 of JSC "KresTrubZavod" are given in table. 2.15.
Table 2.15 - Standards for trimming the ends of pipes at TPA-80 JSC "KresTrubZavod"
where PC is the front thickened end of the pipe; ЗК - rear thickened end of the pipe.
Approximately, the annual loss of metal in the thickened ends of the pipes in the workshop T-3 of JSC "KresTrubZavod" is 3000 tons. With a 25% reduction in the length and weight of the cut thickened pipe ends, the annual profit will be about 20 million rubles. In addition, there will be savings in the cost of batch saws, electricity, etc.
In addition, in the production of rework billets for drawing shops, it is possible to reduce the longitudinal difference in wall thickness of pipes; the saved metal due to a decrease in the longitudinal difference in wall thickness can be used to further increase the production of hot-rolled and cold-worked pipes.
Continuous tube-rolling mills are the most promising high-performance plants for the production of hot-rolled seamless pipes of the corresponding range.
The units include piercing, continuous mandrel and tension reduction mills. Continuity of the technological process, automation of all transport operations, long length of rolled pipes ensure high productivity, good quality of pipes in terms of surface and geometric dimensions.
In recent decades, the intensive development of the production of pipes by the method of continuous rolling continued: built and put into operation (in "" Italy, France, USA, Argentina), reconstructed (in Japan) continuous rolling shops, supplied equipment for new shops (in China), developed and projects for the construction of workshops were introduced (in France, Canada, USA, Japan, Mexico).
Compared to the units put into operation in the 60s, the new mills have significant differences: they mainly manufacture oil country tubular goods, in connection with which large sections are constructed in the shops for finishing these pipes, including equipment for their upsetting. ends, heat treatment, pipe cutting, production of couplings, etc .; The range of pipe sizes has significantly expanded: the maximum diameter increased from 168 to 340 mm, the wall thickness - from 16 to 30 mm, which became possible due to the development of rolling on a long mandrel, moving at a controlled speed, instead of a floating one, on continuous mills. The new tube rolling mills use continuously cast billets (square and round), which ensured a significant improvement in the technical and economic indicators of their work.
For heating billets, ring furnaces (TPA 48-340, Italy) are still widely used, along with this, walking hearth furnaces (TPA 27-127, France, TPA 33-194, Japan) are starting to be used. In all cases, the high productivity of a modern unit is ensured by installing one furnace of a large, unit capacity (capacity up to 250 t / h). For heating pipes before reduction (calibration), walking beam furnaces are used.
The main mill for the production of sleeves continues to be a twin-high helical rolling mill, the design of which is being improved, for example, by replacing fixed rulers with driven guide discs. In the case of using square billets, a screw rolling mill in the technical line is preceded by either a press roll mill (TPA 48-340 in Italy, TPA 33-194 in Japan), or a mill for sizing edges and a press for deep centering (TPA 60-245, France).
One of the main directions of further development of the continuous rolling method is the use of mandrels moving at a controlled speed during rolling, instead of floating ones. With the help of a special mechanism that develops a holding force of 1600-3500 kN, the mandrel is given a certain speed (0.3-2.0 m / s), which is maintained either until the pipe is completely removed from the mandrel during rolling (retained mandrel), or until a certain the moment from which the reference moves as a floating (partially held mandrel). Each of these methods can be used in the production of pipes of a certain diameter. So, for small-diameter pipes, the main method is rolling on a floating mandrel, medium (up to 200 mm) - on a partially retained, large (up to 340 mm and more) - on a retained one.
The use on continuous mills of mandrels moving at a controlled speed (held, partially held) instead of floating ones provides a significant expansion of the assortment, an increase in the length of pipes and an increase in their accuracy. Individual design solutions are of interest; for example, the use of a piercing mill rod as a partially retained mandrel of a continuous mill (TPA 27-127, France), outside insertion of the mandrel into the sleeve (TPA 33-194, Japan).
New units are equipped with modern reduction and sizing mills, most often one of these mills is used. Cooling tables are designed to receive pipes after reduction without preliminary cutting.
Assessing the current general state of the automation of pipe mills, the following features can be noted.
Transport operations associated with the movement of rolled products and tools throughout the unit are fully automated with the help of traditional local (mostly non-contact) automation devices. On the basis of such devices, it became possible to introduce high-performance units with a continuous and discrete-continuous technological process.
Actually, technological processes and even individual operations on pipe mills are clearly insufficiently automated, and in this part their level of automation is noticeably inferior to that achieved, for example, in the field of continuous sheet mills. If the use of control computers (CFM) for sheet mills has become practically a widely accepted norm, then for pipe mills examples are still rare in Russia, although the development and implementation of automated process control systems and automated process control systems has become the norm abroad. In the meantime, in a number of pipe mills, in our country there are mainly examples of industrial implementation of individual subsystems of automated control of technological processes using specialized devices made using semiconductor logic and elements of computer technology.
The noted condition is mainly due to two circumstances. On the one hand, until recently, the requirements for quality, and above all, for the stability of pipe dimensions, were met by relatively simple means (in particular, rational designs of mill equipment). These conditions did not stimulate more advanced and, naturally, more complex developments, for example, using relatively expensive and not always sufficiently reliable UVMs. On the other hand, the use of special non-standard technical means of automation turned out to be possible only for simpler and less effective tasks, while it required a significant investment of time and money for development and manufacture, which did not contribute to progress in the area under consideration.
However, the increasing modern requirements for pipe production, including the quality of pipes, cannot be met by traditional solutions. Moreover, as practice shows, a significant share of efforts in meeting these requirements falls on automation, and, at the present time, it is necessary to automatically change these modes in the process of pipe rolling.
Modern achievements in the field of control of electric drives and various technical means of automation, primarily in the field of mini-computers and microprocessor technology, make it possible to radically improve the automation of pipe mills and units, to overcome various production and economic limitations.
The use of modern technical means of automation presupposes a simultaneous increase in the requirements for the correctness of the formulation of problems and the choice of ways to solve them, and in particular, for the choice of the most effective ways of influencing technological processes.The solution of this problem can be facilitated by the analysis of the existing most effective technical solutions for the automation of pipe mills.
Studies of continuous tube-rolling units as objects of automation show that there are significant reserves for further improving their technical and economic indicators due to the automation of the technological process of rolling pipes on these units.
When rolling in a continuous mill on a long floating mandrel, the terminal longitudinal wall difference is also induced. The wall thickness of the rear ends of the rough pipes is 0.2-0.3 mm more than the middle. The length of the posterior end with a thickened wall is equal to 2–3 intercellular spaces. The thickening of the wall is accompanied by an increase in the diameter in a section spaced one inter-stand gap from the rear end of the pipe. Due to transient conditions, the wall thickness of the front ends is 0.05-0.1 mm less than the middle.When rolling with tension, the walls of the front ends of the pipes also thicken. The longitudinal difference in wall thickness of the rough pipes is preserved during subsequent reduction and leads to an increase in the length of the rear cut off thickened ends of the finished pipes.
When rolling in reduction stretching mills, the wall of the pipe ends thickens due to a decrease in tensions compared to the steady state mode, which occurs only when 3-4 mill stands are filled. The ends of pipes with a wall thickened in excess of the tolerance are cut off, and the associated metal waste determines the bulk of the total consumption coefficient at the unit.
The general character of the longitudinal difference in wall thickness of pipes after a continuous mill is almost completely transferred to finished pipes. This is confirmed by the results of rolling pipes with dimensions 109 x 4.07 - 60 mm at five tension modes on the reduction mill of the 30-102 YuTZ unit. During the experiment, at each high-speed mode, 10 pipes were selected, the end sections of which were cut into 10 pieces 250 mm long, and three pipes were cut from the middle, located at a distance of 10, 20, and 30 m from the front end. After measuring the wall thickness on the device, decoding the diagrams of the difference in wall thickness and averaging the data, graphical dependencies were built, shown in Fig. 54.
Thus, the noted components of the total wall thickness of pipes have a significant impact on the technical and economic indicators of the operation of continuous units, are associated with the physical characteristics of rolling processes in continuous and reduction mills and can be eliminated or significantly reduced only due to special automatic systems that change the setting of the mill during pipe rolling. The natural character of these components of the wall thickness makes it possible to use the program control principle at the basis of such systems.
Known other technical solutions to the problem of reducing end waste when reducing with the help of automatic control systems for the rolling process of pipes in a reduction mill with an individual drive stands (Federal Republic of Germany patents No. 1602181 and Great Britain 1274698). Due to the change in the speeds of the rolls during the rolling of the front and rear ends of the tubes, additional tension forces are created, which leads to a decrease in the terminal longitudinal wall thickness difference. There is information that such systems for programmed speed correction of the main drives of the reduction mill operate on seven foreign pipe-rolling units, including two units with continuous mills in Mühlheim (Germany). The units were supplied by Mannesmann (Germany).
The second unit was commissioned in 1972 and includes a 28-stand reduction mill with individual drives, equipped with a speed correction system. The speed changes during the passage of the pipe ends are carried out in the first ten stands stepwise, as an addition to the operating speed value. The maximum change in speed takes place on stand No. 1, the minimum - on stand No. 10. Photo relays are used as sensors for the position of the pipe ends in the mill, giving commands to change the speed. In accordance with the adopted speed correction scheme, the power supply of the individual drives of the first ten stands is carried out according to the antiparallel reversing scheme, the subsequent stands - according to the non-reversing scheme. It is noted that the speed correction of the drives of the reduction mill makes it possible to increase the yield of the unit by 2.5% with a mixed production program. With an increase in the degree of reduction in diameter, this effect increases.
There is similar information on equipping a twenty-eight cage reduction mill in Spain with a speed correction system. The speed changes are carried out in the first 12 stands. For this reason, various power supply circuits are also provided for the drives.
It should be noted that equipping reduction mills as part of continuous pipe-rolling units with a speed correction system does not completely solve the problem of reducing end waste during reduction. The efficiency of such systems should decrease with decreasing degree of diameter reduction.
Process control software systems are the easiest to implement and provide a large economic effect... However, with their help, it is possible to increase the accuracy of pipe dimensions only by reducing one of its three components - the longitudinal difference in wall thickness. As studies show, the main share in the total range of wall thicknesses of finished pipes (about 50%) falls on the transverse wall thickness. Variations in the average pipe wall thicknesses in batches are about 20% of the total variation.
At present, a decrease in the transverse wall thickness difference is possible only by improving the technological process of rolling pipes on the mills that are part of the unit. Examples of the use of automatic systems for these purposes are unknown.
Stabilization of average pipe wall thicknesses in batches is possible both by improving the rolling technology, design of stands and electric drive, and by means of automatic process control systems. Reducing the spread of pipe wall thicknesses in a batch can significantly increase the productivity of units and reduce metal consumption due to rolling in the field of minus tolerances.
Unlike software systems, systems designed to stabilize average pipe wall thicknesses should include sensors for monitoring the geometric dimensions of pipes.
Known technical proposals for equipping reduction mills with systems for automatic stabilization of the pipe wall thickness. The structure of the systems does not depend on the type of unit, which includes a reduction mill.
A set of control systems for the process of rolling pipes in continuous and reduction mills, designed to reduce end waste while reducing and increasing the accuracy of pipes by reducing the longitudinal difference in wall thickness and the spread of average wall thicknesses, forms the APCS of the unit.
The use of computers for production control and automation of the pipe rolling process was first implemented on the 26-114 continuous tube rolling mill in Mühlheim.
The unit is designed for rolling pipes with a diameter of 26-114 mm, wall thickness 2.6-12.5 mm. The unit includes an annular furnace, two piercing mills, a 9-stand continuous mill and a 24-stand reduction mill with an individual drive from 200 kW motors.
The second continuous-mill unit in Mühlheim, commissioned in 1972, is equipped with a more powerful computer, which is entrusted with broader functions. The unit is designed for rolling pipes with a diameter of up to 139 mm, a wall thickness of up to 20 mm and consists of a piercing mill, eight continuous stand mill and twenty-eight stand-alone reduction mill with an individual drive.
The continuous tube rolling mill in Great Britain, which started up in 1969, is also equipped with a computer that is used to plan the mill's load and as a information system continuously monitors the parameters of rolled products and tools. Quality control of pipes and billets, as well as the accuracy of mill settings, is carried out at all stages of the technological process. Information from each mill enters the computer for processing, after which it is issued to the mill for operational control.
In a word, they are trying to solve the problems of automating rolling processes in many countries, incl. and ours. To develop a mathematical model for the control of continuous mills, it is necessary to know the influence of the given technological parameters on the accuracy of finished pipes; for this, it is necessary to consider the features of continuous rolling.
A feature of pipe tension reduction is a higher product quality as a result of the formation of a lower transverse wall thickness, in contrast to rolling without tension, as well as the possibility of producing pipes of small diameters. However, with piece-by-piece rolling, there is an increased longitudinal difference in wall thickness at the ends of the pipes. Thickened ends during tension reduction are due to the fact that the front and rear ends of the pipe are not subjected to full tension when passing through the mill.
The tension is characterized by the magnitude of the tensile stress in the pipe (x). Most full description is the coefficient of plastic tension, which represents the ratio of the longitudinal tensile stress of the pipe to the resistance to deformation of the metal in the stand.
Typically, the reduction mill is set up so that the coefficient of plastic tension in the middle stands is evenly distributed. In the first and last stands, the tension increases and decreases.
To intensify the process of reduction and obtaining thin-walled pipes it is important to know the maximum tension that can be created in the reduction mill. The maximum value of the coefficient of plastic tension in the mill (z max) is limited by two factors: the pulling ability of the rolls and the conditions of pipe rupture in the mill. As a result of research, it was found that with a total reduction of the pipe in the mill up to 50-55%, the value of z max is limited by the pulling capacity of the rolls.
Shop T-3 together with EF VNIPI "Tyazhpromelektroproekt" and the enterprise "ASK" created the basis of the ACS-TP system on the TPA-80 unit. Currently, the following components of this system are functioning: UZN-N, UZN-R, ETHERNET communication line, all workstations.
3.2 Calculation of the rolling table
The basic principle of constructing a technological process in modern installations is to obtain pipes of the same constant diameter on a continuous mill, which makes it possible to use a workpiece and a sleeve of a constant diameter as well. Obtaining pipes of the required diameter is ensured by reduction. Such a system of work greatly facilitates and simplifies the setup of the mills, reduces the tool park and, most importantly, allows you to maintain high productivity of the entire unit even when rolling pipes of the minimum (after reduction) diameter.
We calculate the rolling table against the rolling course according to the method described in Art. The outer diameter of the pipe after reduction is determined by the dimensions of the last pair of rolls.
D p 3 = (1.010..1.015) * D o = 1.01 * 33.7 = 34 mm
where D p is the diameter of the finished pipe after the reduction mill.
Since a pipe of the same diameter comes out after a continuous mill, we take D n = 94 mm. In continuous mills, the calibration of the rolls ensures that in the last pairs of rolls the inner diameter of the pipe is 1-2 mm larger than the diameter of the mandrel, so that the diameter of the mandrel will be equal to:
H = d n - (1..2) = D n -2S n -2 = 94-2 * 3.2-2 = 85.6 mm.
We accept the diameter of the mandrels equal to 85 mm.
The inner diameter of the sleeve should provide free insertion of the mandrel and is taken 5-10 mm larger than the diameter of the mandrel
d g = n + (5..10) = 85 + 10 = 95 mm.
We accept the wall of the sleeve:
S g = S n + (11..14) = 3.2 + 11.8 = 15 mm.
The outer diameter of the sleeves is determined based on the value of the inner diameter and wall thickness:
D g = d g + 2S g = 95 + 2 * 15 = 125 mm.
The diameter of the workpiece used D z = 120 mm.
The diameter of the mandrel of the piercing mill is selected taking into account the amount of rolling, i.e. rise of the inner diameter of the sleeve, constituting from 3% to 7% of the inner diameter:
P = (0.92 ... 0.97) d g = 0.93 * 95 = 88 mm.
Elongation coefficients for piercing, continuous and reduction mills are determined by the formulas:
,
The overall stretch ratio is:
The rolling table for pipes with dimensions 48.3 × 4.0 mm and 60.3 × 5.0 mm is calculated in a similar way.
The rolling table is presented in table. 3.1.
| Finished pipes size, mm | Workpiece diameter, mm | Piercing mill | Continuous mill | Reduction mill | Overall stretch ratio | ||||||||||
| Outside diameter | Wall thickness | Sleeve size, mm | Mandrel diameter, mm | Draw ratio | Pipe dimensions, mm | Mandrel diameter, mm | Draw ratio | Pipe size, mm | Number of stands | Draw ratio | |||||
| Diameter | Wall thickness | Diameter | Wall thickness | Diameter | Wall thickness | ||||||||||
| 33,7 | 3,2 | 120 | 125 | 15 | 88 | 2,20 | 94 | 3,2 | 85 | 5,68 | 34 | 3,2 | 24 | 2,9 | 36,24 |
| 48,3 | 4,0 | 120 | 125 | 15 | 86 | 2,2 | 94 | 4,0 | 84 | 4,54 | 48,6 | 4,5 | 16 | 1,94 | 19,38 |
| 60,3 | 5,0 | 120 | 125 | 18 | 83 | 1,89 | 94 | 5,0 | 82 | 4,46 | 61,2 | 5,0 | 12 | 1,52 | 12,81 |
3.3 Calculation of the calibration of the rolls of the reduction mill
Roll sizing is important part of calculation of the mill operating mode. It largely determines the quality of pipes, tool life, distribution of loads in the working stands and the drive.
Calculation of roll sizing includes:
a) the distribution of partial deformations in the mill stands and the calculation of the average diameters of the calibers;
b) determination of the dimensions of the roll grooves.
3.3.1 Distribution of partial deformations
According to the nature of the change in the partial deformations, the stands of the reduction mill can be divided into three groups: the head one at the beginning of the mill, in which the reductions intensively increase in the course of rolling; sizing (at the end of the mill), in which deformations are reduced to a minimum value, and a group of stands between them (middle), in which partial deformations are maximum or close to them.
When rolling pipes with tension, the values of partial deformations are taken based on the condition of the stability of the pipe profile at the value of the plastic tension that ensures the production of a pipe of a given size.
The coefficient of total plastic tension can be determined by the formula:
,
where - axial and tangential deformations taken in logarithmic form; T is the value determined in the case of a three-roll caliber according to the formula
T = 
,
where (S / D) cp is the average ratio of wall thickness to diameter over the period of pipe deformation in the mill; k-factor taking into account the change in the degree of thickness of the pipe.
,
,
where m is the value of the total deformation of the pipe in terms of diameter.
.
,
.
The value of the critical partial reduction with such a coefficient of plastic tension, according to, can reach 6% in the second stand, 7.5% in the third stand and 10% in the fourth stand. In the first stand, it is recommended to take in the range of 2.5–3%. However, to ensure stable grip, the amount of reduction is usually reduced.
In the pre-finishing and finishing stands of the mill, the reduction is also reduced, but to reduce the loads on the rolls and increase the accuracy of the finished pipes. In the last stand of the calibrating group, the reduction is taken equal to zero, in the penultimate stand, up to 0.2 of the reduction in the last stand of the middle group.
V middle group of stands practice a uniform and uneven distribution of partial deformations. With a uniform distribution of reduction in all stands of this group, they are assumed to be constant. The uneven distribution of partial deformations can have several variants and be characterized by the following regularities:
the reduction in the middle group is proportionally reduced from the first stands to the last - falling mode;
in the first few stands of the middle group, partial deformations are reduced, and the rest are left constant;
the compression in the middle group is first increased and then decreased;
in the first few stands of the middle group, the partial deformations are left constant, and in the rest they are reduced.
With falling deformation modes in the middle group of stands, the differences in the value of the rolling power and the load on the drive, caused by an increase in the deformation resistance of the metal during rolling, due to a decrease in its temperature and an increase in the deformation rate, decrease. It is believed that a decrease in reductions towards the end of the mill also improves the quality of the outer surface of the pipes and reduces the transverse wall thickness.
When calculating the calibration of the rolls, we take a uniform distribution of reductions.
The values of partial deformations along the mill stands are shown in Fig. 3.1.
Compression distribution
Based on the accepted values of partial deformations, the average diameters of the calibers can be calculated by the formula
.
For the first stand of the mill (i = 1) d i -1 = D 0 = 94 mm, then
mm.
The average diameters of the calibers calculated according to this formula are given in Appendix 1.
3.3.2 Determination of roll groove dimensions
The shape of the calibers of three-roll mills is shown in Fig. 3.2.
An oval groove is obtained by outlining it with a radius r with a center offset from the rolling axis by the amount of eccentricity e.
Caliber shape
The values of the radii and eccentricity of the calibers are determined by the width and height of the calibers according to the formulas:
To determine the dimensions of the caliber, it is necessary to know the values of its semi-axes a and b, and to determine them - the value of the ovality of the caliber
To determine the ovality of the caliber, you can use the formula:
Power exponent q characterizes the possible amount of broadening in the caliber. When reducing in three-roll stands, q = 1.2 is taken.
The values of the semiaxes of the caliber are determined by the dependencies:
where f is a correction factor that can be calculated using the approximate formula
Let's calculate the dimensions of the groove according to the above formulas for the first stand.
For the rest of the stands, the calculation is carried out in the same way.
At present, the groove of the roll grooves is carried out after the rolls are installed in the working stand. Boring is carried out on special machines with a round mill. The boring scheme is shown in Fig. 3.3.
Rice. 3.3 - Gauge boring scheme
To obtain a caliber with the given values of a and b, it is necessary to determine the cutter diameter D f and its displacement relative to the plane of the roll axes (parameter X). D f and X are determined by the following mathematically exact formulas:
For three-roll mills, the angle a is 60 °. Di - ideal roll diameter, Di = 330mm.
The values calculated according to the above formulas are summarized in table. 3.2.
Table 3.2 - Calibration of rolls
| Cage number | d, mm | m,% | a, mm | b, mm | r, mm | e, mm | D f, mm | X, mm |
| 1 | 91,17 | 2,0 | 45,60 | 45,50 | 45,80 | 0,37 | 91,50 | 8,11 |
| 2 | 87,07 | 4,5 | 43,60 | 43,40 | 43,80 | 0,35 | 87,40 | 8,00 |
| 3 | 82,71 | 5,0 | 41,40 | 41,20 | 41,60 | 0,33 | 83,00 | 7,87 |
| 4 | 78,58 | 5,0 | 39,30 | 39,20 | 39,50 | 0,32 | 78,80 | 7,73 |
| 5 | 74,65 | 5,0 | 37,40 | 37,20 | 37,50 | 0,3 | 74,90 | 7,59 |
| 6 | 70,92 | 5,0 | 35,50 | 35,40 | 35,70 | 0,28 | 71,20 | 7,45 |
| 7 | 67,37 | 5,0 | 33,70 | 33,60 | 33,90 | 0,27 | 67,60 | 7,32 |
| 8 | 64,00 | 5,0 | 32,00 | 31,90 | 32,20 | 0,26 | 64,20 | 7,18 |
| 9 | 60,80 | 5,0 | 30,40 | 30,30 | 30,60 | 0,24 | 61,00 | 7,04 |
| 10 | 57,76 | 5,0 | 28,90 | 28,80 | 29,00 | 0,23 | 58,00 | 6,90 |
| 11 | 54,87 | 5,0 | 27,50 | 27,40 | 27,60 | 0,22 | 55,10 | 6,76 |
| 12 | 52,13 | 5,0 | 26,10 | 26,00 | 26,20 | 0,21 | 52,30 | 6,62 |
| 13 | 49,52 | 5,0 | 24,80 | 24,70 | 24,90 | 0,2 | 49,70 | 6,48 |
| 14 | 47,05 | 5,0 | 23,60 | 23,50 | 23,70 | 0,19 | 47,20 | 6,35 |
| 15 | 44,70 | 5,0 | 22,40 | 22,30 | 22,50 | 0,18 | 44,80 | 6,21 |
| 16 | 42,46 | 5,0, | 21,30 | 21,20 | 21,30 | 0,17 | 42,60 | 6,08 |
| 17 | 40,34 | 5,0 | 20,20 | 20,10 | 20,30 | 0,16 | 40,50 | 5,94 |
| 18 | 38,32 | 5,0 | 19,20 | 19,10 | 19,30 | 0,15 | 38,50 | 5,81 |
| 19 | 36,40 | 5,0 | 18,20 | 18,10 | 18,30 | 0,15 | 36,50 | 5,69 |
| 20 | 34,77 | 4,5 | 17,40 | 17,30 | 17,50 | 0,14 | 34,90 | 5,57 |
| 21 | 34,07 | 2 | 17,10 | 17,00 | 17,10 | 0,14 | 34,20 | 5,52 |
| 22 | 34,07 | 0 | 17,10 | 17,00 | 17,10 | 0,14 | 34,20 | 5,52 |
| 23 | 34,00 | 0 | 17,00 | 17,00 | 17,00 | 0 | 34,10 | 5,52 |
| 24 | 34,00 | 0 | 17,00 | 17,00 | 17,00 | 0 | 34,10 | 5,52 |
3.4 Calculation speed mode
The calculation of the high-speed operating mode of the mill consists in determining the number of revolutions of the rolls and, according to them, the numbers of revolutions of the engines.
When rolling pipes under tension, the value of plastic tension has a large effect on the change in wall thickness. In this regard, first of all, it is necessary to determine the coefficient of total plastic tension on the mill - z total, which would provide the necessary wall. The calculation of z total is given in clause 3.3.
,
where is the coefficient taking into account the effect of out-of-contact deformation zones:
;
l i - length of the capture arc:
;
- capture angle:
;
f - coefficient of friction, we take f = 0.5; a - the number of rolls in the stand, a = 3.
In the first working stand z z1 = 0. In subsequent stands, you can take z p i -1 = z z i.
,
;
;
.
Substituting the data for the first stand into the above formulas, we get:
mm;
;
;
;
; ;
mm.
Having carried out similar calculations for the second stand, the following results were obtained: z p2 = 0.42, S 2 = 3.251mm, z p3 = 0.426, S 3 = 3.252mm, z p4 = 0.446, S 4 = 3.258mm. At this point, we stop calculating z p i according to the above method, since the condition z п2> z total is satisfied.
From the condition of complete slip, we determine the maximum possible tension z z in the last deforming stand, i.e. z z21. In this case, we assume that z п21 = 0.
.
mm;
;
;
The wall thickness in front of the 21st stand, i.e. S 20 can be determined by the formula:
.
;
; ;
mm.
Having carried out similar calculations for the 20th stand, the following results were obtained: z z20 = 0.357, S 19 = 3.178 mm, z z19 = 0.396, S 18 = 3.168 mm, z z18 = 0.416, S 17 = 3.151 mm, z z17 = 0.441, S 16 = 3.151 mm. At this point, we stop calculating z п i, since the condition z z14> z total is satisfied.
The calculated values of the wall thickness along the mill stands are given in table. 2.20.
To determine the number of revolutions of the rolls, it is necessary to know the rolling diameters of the rolls. To determine the rolling diameters, you can use the formulas given in:
, (2)
where D in i is the diameter of the roll at the top;
.
If 
, then the calculation of the rolling diameter of the rolls should be carried out according to the equation (1), if this condition is not met, then it is necessary to use (2).
The value characterizes the position of the neutral line in the case when it is taken parallel (in plan) to the rolling axis. From the condition of the balance of forces in the deformation zone for such an arrangement of slip zones
,
Given the input rolling speed V in = 1.0 m / s, the number of revolutions of the rolls of the first stand was calculated
rpm
The revolutions in the remaining stands were found by the formula:
.
The results of calculating the speed limit are shown in Table 3.3.
Table 3.3 - Results of calculating the speed limit
| Cage number | S, mm | Dcat, mm | n, rpm |
| 1 | 3,223 | 228,26 | 84,824 |
| 2 | 3,251 | 246,184 | 92,917 |
| 3 | 3,252 | 243,973 | 99,446 |
| 4 | 3,258 | 251,308 | 103,482 |
| 5 | 3,255 | 256,536 | 106,61 |
| 6 | 3,255 | 256,832 | 112,618 |
| 7 | 3,255 | 260,901 | 117,272 |
| 8 | 3,255 | 264,804 | 122,283 |
| 9 | 3,254 | 268,486 | 127,671 |
| 10 | 3,254 | 272,004 | 133,378 |
| 11 | 3,254 | 275,339 | 139,48 |
| 12 | 3,253 | 278,504 | 146,046 |
| 13 | 3,253 | 281,536 | 153,015 |
| 14 | 3,252 | 284,382 | 160,487 |
| 15 | 3,252 | 287,105 | 168,405 |
| 16 | 3,251 | 289,69 | 176,93 |
| 17 | 3,250 | 292,131 | 185,998 |
| 18 | 3,250 | 292,049 | 197,469 |
| 19 | 3,192 | 293,011 | 204,24 |
| 20 | 3,193 | 292,912 | 207,322 |
| 21 | 3,21 | 292,36 | 208,121 |
| 22 | 3,15 | 292,36 | 209 |
| 23 | 3,22 | 292,36 | 209 |
| 24 | 3,228 | 292,36 | 209 |
According to table 3.3. a graph of changes in rolls revolutions is built (Fig. 3.4.).
Roll rotation frequency
3.5 Force parameters of rolling
A distinctive feature of the reduction process in comparison with other types of longitudinal rolling is the presence of significant inter-stand tensions. The presence of tension has a significant effect on the power parameters of rolling - the pressure of the metal on the rolls and the moments of rolling.
The force of the metal on the roll P is the geometric sum of the vertical P in and horizontal P g components:
The vertical component of the metal force on the rolls is determined by the formula:
,
where p is the average specific pressure of the metal on the roll; l is the length of the deformation zone; d is the diameter of the caliber; a - the number of rolls in the stand.
The horizontal component P g is equal to the difference between the forces of the front and rear tensions:
where z p, z z - coefficients of front and rear plastic tension; F p, F z - cross-sectional area of the front and rear ends of the pipe; s S - resistance to deformation.
To determine the average specific pressures, it is recommended to use the formula of V.P. Anisiforova:
.
The rolling moment (total per stand) is determined by the formula:
.
The resistance to deformation is determined by the formula:
,
where T is the rolling temperature, ° C; H — intensity of shear strain rates, 1 / s; e - relative compression; K 1, K 2, K 3, K 4, K 5 - empirical coefficients, for steel 10: K 1 = 0.885, K 2 = 7.79, K 3 = 0.134, K 4 = 0.164, K 5 = (- 2 ,eight).
The strain rate intensity is determined by the formula
where L is the degree of shear deformation:
t - deformation time:
The angular speed of the roll is found by the formula:
,
Power is found by the formula:
Table 3.4. the results of calculating the force parameters of rolling according to the above formulas are presented.
Table 3.4 - Force parameters of rolling
| Cage number | s S, MPa | p, kN / m 2 | P, kN | M, kNm | N, kW |
| 1 | 116,78 | 10,27 | 16,95 | -1,91 | -16,93 |
| 2 | 154,39 | 9,07 | 25,19 | 2,39 | 23,31 |
| 3 | 162,94 | 9,1 | 21,55 | 2,95 | 30,75 |
| 4 | 169,48 | 9,69 | 22,70 | 3,53 | 38,27 |
| 5 | 167,92 | 9,77 | 20,06 | 2,99 | 33,37 |
| 6 | 169,48 | 9,84 | 19,06 | 3,35 | 39,54 |
| 7 | 171,12 | 10,47 | 18,79 | 3,51 | 43,11 |
| 8 | 173,01 | 11,15 | 18,59 | 3,68 | 47,23 |
| 9 | 175,05 | 11,89 | 18,39 | 3,86 | 51,58 |
| 10 | 176,70 | 12,64 | 18,13 | 4,02 | 56,08 |
| 11 | 178,62 | 13,47 | 17,90 | 4,18 | 61,04 |
| 12 | 180,83 | 14,36 | 17,71 | 4,35 | 66,51 |
| 13 | 182,69 | 15,29 | 17,48 | 4,51 | 72,32 |
| 14 | 184,91 | 16,31 | 17,26 | 4,67 | 78,54 |
| 15 | 186,77 | 17,36 | 16,83 | 4,77 | 84,14 |
| 16 | 189,19 | 18,53 | 16,65 | 4,94 | 91,57 |
| 17 | 191,31 | 19,75 | 16,59 | 5,14 | 100,16 |
| 18 | 193,57 | 22,04 | 18,61 | 6,46 | 133,68 |
| 19 | 194,32 | 26,13 | 15,56 | 4,27 | 91,34 |
| 20 | 161,13 | 24,09 | 11,22 | 2,55 | 55,41 |
| 21 | 134,59 | 22,69 | 8,16 | 1,18 | 33,06 |
| 22 | 175,14 | 15,45 | 7,43 | 0,87 | 25,42 |
| 23 | 180,00 | - | - | - | - |
| 24 | 180,00 | - | - | - | - |
According to the table. 3.4 graphs of changes in the power parameters of rolling on the mill stands are built (Fig. 3.5., 3.6., 3.7.).
Change in mean specific pressure
Change in the force of the metal on the roll
Change in rolling moment
3.6 Investigation of the effect of transient speed modes of reduction on the value of the longitudinal difference in wall thickness of the end sections of finished pipes
3.6.1 Description of the calculation algorithm
The study was carried out in order to obtain data on the effect of transient speed modes of reduction on the value of the longitudinal difference in wall thickness of the end sections of finished pipes.
Determination of the inter-stand tension coefficient from the known roll revolutions, i.e. dependence Zn i = f (n i / n i -1) was carried out according to the method of solving the so-called inverse problem proposed by G.I. Gulyaev, in order to obtain the dependence of the wall thickness on the revolutions of the rolls.
The essence of the technique is as follows.
The established process of pipe reduction can be described by a system of equations reflecting the observance of the law of constancy of second volumes and the balance of forces in the deformation zone:
(3.1.)
In turn, as you know,
Dcat i = j (Zz i, Zp i, And i),
m i = y (Zz i, Zp i, B i),
where A i and B i are tension independent values, ni is the number of revolutions in the i-th stand, i is the stretch ratio in the i-th stand, Dcat i is the rolling diameter of the roll in the i-th stand, Zp i, Zz i - coefficients of front and rear plastic tension.
Taking into account that Zz i = Zp i -1 the system of equations (3.1.) Can be written in general form as follows:
(3.2.)
The system of equations (3.2.) Is solved with respect to the front and rear coefficients of plastic tension by the method of successive approximations.
Taking Zs1 = 0, we set the value of Zп1 and from the first equation of system (3.2.) By the iteration method we determine Zп 2, then from the second equation - Zп 3, and so on. ...
Knowing the coefficients of the front and rear plastic tension, we determine the wall thickness after each stand by the formula:
(3.3.)
where A is the coefficient determined by the formula:
;
;
z i - average (equivalent) coefficient of plastic tension
.
3.6.2 Study results
Using the results of calculating the tool calibration (p. 3.3.) And the high-speed setting of the mill (roll rotation speeds) with a steady reduction process (p. 3.4.) In the MathCAD 2001 Professional software environment, we solved the system (3.2.) And expressions (3.3.) With the purpose of determining the change in wall thickness.
It is possible to shorten the length of the thickened ends by increasing the coefficient of plastic tension by changing the revolutions of the rolls when rolling the end sections of the pipe.
At present, the TPA-80 reduction mill has created a control system for the speed mode of continuous non-corrosive rolling. This system allows you to dynamically adjust the speed of the rolls of the PPC stands when rolling the end sections of the pipes according to a given linear relationship. This regulation of the speed of the rolls when rolling the end sections of the tubes is called the "speed wedge". The revolutions of the rolls when rolling the end sections of the pipe are calculated by the formula:
, (3.4.)
where n i is the revolutions of the rolls in the i-th stand at steady state, K i is the reduction factor of the rolls revolutions in%, i is the number of the stand.
The dependence of the roll speed reduction factor in a given stand on the stand number is linear.
K i = (Figure 3.8.).
Dependence of the reduction factor of the rolls revolutions in the stand on the number of the stand.
The initial data for the use of this regulatory regime are:
The number of stands in which the speed setting is changed is limited by the length of the thickened ends (3 ... 6);
The amount of roll speed reduction in the first stand of the mill is limited by the possibility of an electric drive (0.5 ... 15%).
In this work, in order to study the influence of the high-speed adjustment of the PPC on the end longitudinal difference in wall thickness, it was assumed that the change in the speed adjustment when reducing the front and rear ends of the pipes is carried out in the first 6 stands. The study was carried out by changing the speed of rotation of the rolls in the first stands of the mill in relation to the steady rolling process (varying the angle of inclination of the straight line in Fig. 3.8).
As a result of modeling the processes of filling the PPC stands and the exit of the pipe from the pipe mill, we obtained the dependences of the wall thickness of the front and rear ends of the pipes on the change in the speed of rotation of the rolls in the first mill stands, which are shown in Fig. 3.9. and Figure 3.10. for pipes measuring 33.7x3.2 mm. Most optimal value“Velocity wedge” in terms of minimizing the length of the end trim and “hitting” the wall thickness in the tolerance range of DIN 1629 (wall thickness tolerance ± 12.5%) is K 1 = 10-12%.
In fig. 3.11. and fig. 3.12. shows the dependences of the lengths of the front and rear thickened ends of the finished pipes when using the "velocity wedge" (K 1 = 10%), obtained as a result of the simulation of transient processes. From the above dependences, the following conclusion can be drawn: the use of a “speed wedge” gives a noticeable effect only when rolling pipes with a diameter of less than 60 mm with a wall thickness of less than 5 mm, and with a larger diameter and wall thickness of the pipe, the wall thinning necessary to achieve the requirements of the standard does not occur.
In fig. 3.13 ... rolls K 1 equal to 5%, 10%, 15%).
Dependence of the wall thickness of the front end of the pipe on the value
"Speed wedge" for standard size 33.7x3.2 mm
Dependence of the wall thickness of the rear end of the pipe on the value of the "velocity wedge" for a standard size of 33.7x3.2 mm
Dependence of the length of the front thickened end of the pipe on D and S (with K 1 = 10%)
Dependence of the length of the rear thickened end of the pipe on D and S (with K 1 = 10%)
Dependence of the length of the front thickened end of the pipe on the diameter of the finished pipe (S = 3.5 mm) at different values of the "velocity wedge".
Dependence of the length of the front thickened end of the pipe on the diameter of the finished pipe (S = 4.0 mm) at different values of the "velocity wedge"
Dependence of the length of the front thickened end of the pipe on the diameter of the finished pipe (S = 5.0 mm) at different values of the "velocity wedge".
From the above graphs it can be seen that the greatest effect from the point of view of reducing the end wall thickness difference of finished pipes is provided by the dynamic regulation of the rotational speed of the PPC rolls within the range of K 1 = 10 ... 15%. Insufficiently intensive change in the “velocity wedge” (K 1 = 5%) does not allow thinning the wall thickness of the end sections of the pipe.
Also, when rolling pipes with a wall thicker than 5 mm, the tension arising from the action of the "speed wedge" is unable to thin the wall due to insufficient pulling ability of the rolls. When rolling pipes with a diameter of more than 60 mm, the elongation ratio in the reduction mill is small, therefore, the thickening of the ends practically does not occur, therefore, the use of a “speed wedge” is impractical.
The analysis of the given graphs showed that the use of the “speed wedge” on the TPA-80 reduction mill of JSC “KresTrubZavod” allows to reduce the length of the front thickened end by 30%, the rear thickened end by 25%.
As shown by the calculations of Mochalov D.A. for more effective application To further reduce the end trim, it is necessary to ensure the operation of the first stands in the braking mode with almost full use of the power capabilities of the rolls due to the use of a more complex nonlinear dependence of the roll speed reduction factor in a given stand on the stand number. It is necessary to create a scientifically based methodology to determine the optimal function K i = f (i).
The development of such an algorithm for the optimal control of the RRS can serve as a goal for the further development of the UZS-R into a full-fledged APCS TPA-80. As the experience of using such automated process control systems shows, the control of the number of rolls revolutions when rolling the end sections of pipes, according to Mannesmann (CARTA application software package), allows to reduce the size of the end trim of pipes by more than 50%, due to the system of automatic control of the pipe reduction process, which includes into itself as a subsystem for mill control and a measuring subsystem, as well as a subsystem for calculating the optimal reduction mode and process control in real time.
4. TECHNICAL AND ECONOMIC JUSTIFICATION OF THE PROJECT
4.1 The essence of the planned event
In this project, it is proposed to introduce an optimal speed mode for rolling on a stretching-reduction mill. Due to this measure, it is planned to reduce the consumption coefficient of metal, and due to a decrease in the length of the cut off thickened ends of finished pipes, an increase in production volumes is expected by 80 tons per month on average.
Capital investments required for the implementation of this project are 0 rubles.
The project can be financed under the item "current repairs", cost estimates. The project can be completed within one day.
4.2 Calculation of production costs
Calculation of the cost of 1t. products at the existing rates of trimming of the thickened pipe ends are given in table. 4.1.
The cost estimate for the project is shown in table. 4.2. Since the result of the implementation of the project is not an increase in production output, the recalculation of the consumption values for redistribution in the project cost estimate is not carried out. The profitability of the project lies in reducing the cost by reducing scrap waste. The trim is reduced due to a decrease in the consumption coefficient of the metal.
4.3 Calculation of design indicators
The calculation of project indicators is based on the cost estimate given in table. 4.2.
Cost savings per year:
Eg = (C 0 -C p) * V pr = (12200.509-12091.127) * 110123.01 = 12045475.08r.
Profit according to the report:
Pr 0 = (P-C 0) * V from = (19600-12200.509) * 109123.01 = 807454730.39r.
Profit for the project:
Pr n = (P-C n) * V pr = (19600-12091.127) * 110123.01 = 826899696.5 r.
The increase in profit will be:
Pr = Pr n-Pr 0 = 826899696.5-807454730.39 = 19444966.11 r.
The profitability of the products was:
Profitability of products for the project:
Cash flow for the report and for the project are presented in table 4.3. and 4.4., respectively.
Table 4.1 - Calculation of the cost of 1 ton of rolled stock in the shop T-3 of JSC "KresTrubZavod"
| N / a | Cost item | Quantity | Price for 1 ton | Sum |
| 1 | 2 | 3 | 4 | 5 |
| I | Specified in redistribution: 1. Blank, t / t; 2. Waste, t / t: substandard trim; |
|||
| I I | Redistribution costs 2. Energy costs: power electricity, kW / h steam for production, Gcal industrial water, tm 3 compressed air, tm 3 circulating water, tm 3 industrial storm water, tm 3 3. Supporting materials 7. Replaceable equipment 10. Overhaul 11. Work of transport shops 12. Other costs of the workshop Total redistribution costs |
|||
| Sh | General plant costs |
Table 4.2 - Design calculation of the cost of 1 ton of rolled stock
| N / a | Cost item | Quantity | Price for 1 ton | Sum |
| I | Specified in redistribution: 1. Blank, t / t; 2. Waste, t / t: substandard trim; Total given in redistribution minus waste and rejects |
|||
| P | Redistribution costs 1. Process fuel (natural gas), here 2. Energy costs: power electricity, kW / h steam for production, Gcal industrial water, tm 3 compressed air, tm 3 circulating water, tm 3 industrial storm water, tm 3 3. Supporting materials 4. Basic salary of production workers 5. Additional wages for production workers 6. Social contributions 7. Replaceable equipment 8. Current repairs and maintenance of fixed assets 9. Depreciation of fixed assets 10. Overhaul 11. Work of transport shops 12. Other costs of the workshop Total redistribution costs |
|||
| Sh | General plant costs Total production cost |
|||
| IV | Non-production costs Total full cost |
Improvement of the technological process will affect the technical and economic indicators of the enterprise as follows: the profitability of production will increase by 1.45%, the savings from reducing the cost will amount to 12 million rubles. per year, which will lead to an increase in profits.
Table 4.3 - Cash flow for the report
Cash flows |
Of the year | ||||
| 1 | 2 | 3 | 4 | 5 | |
| A. Cash flow: | |||||
| - Production volume, t | |||||
| - Product price, rub. | |||||
| Total inflow | |||||
| B. Cash outflow: | |||||
| -Operating costs | |||||
| -Income tax | 193789135,29 | ||||
Total churn: |
1521432951,34 | 1521432951,34 | 1521432951,34 | 1521432951,34 | 1521432951,34 |
| Net cash flow (A-B) | |||||
Coeff. Inversions |
0,8 | 0,64 | 0,512 | 0,41 | 0,328 |
| E = 0.25 | |||||
| 493902383,46 | 889024290,22 | 1205121815,64 | 1457999835,97 | 1457999835,97 | |
Table 4.4 - Project cash flow
| Cash flows | Of the year | ||||
| 1 | 2 | 3 | 4 | 5 | |
| A. Cash flow: | |||||
| - Production volume, t | |||||
| - Product price, rub. | |||||
| - Sales proceeds, rub. | |||||
| Total inflow | |||||
| B. Cash outflow: | |||||
| -Operating costs | |||||
| -Income tax | |||||
| Total churn: | 1526220795,63 | 1526220795,63 | 1526220795,63 | 1526220795,63 | 1526220795,63 |
| Net cash flow (A-B) | 632190135,03 | 632190135,03 | 632190135,03 | ||
Coeff. Inversions |
0,8 | 0,64 | 0,512 | 0,41 | 0,328 |
| E = 0.25 | |||||
| Discounted flow (A-B) * K inv | |||||
| Cumulative cash flow NPV | |||||
The financial profile of the project is shown in Figure 4.1. According to the graphs shown in Fig. 4.1. the cumulative NPV of the project exceeds the planned indicator, which indicates the unconditional profitability of the project. The cumulative NPV calculated for the project being implemented has been a positive value since the first year, since the project did not require capital investments.
Financial profile of the project
The break-even point is calculated using the formula:
The break-even point characterizes the minimum volume of production at which losses end and the first profit appears.
Table 4.5. presents data for calculating variable and fixed costs.
According to the reported data, the sum of variable costs per unit of production is Z per = 11212.8 rubles, the sum of fixed costs per unit of production is Z post = 987.7 rubles. The sum of fixed costs for the entire volume of the issue according to the report is 107780796.98 rubles.
According to the design data, the sum of variable costs Z lane = 11103.5 rubles, the sum of fixed costs Z post = 987.7 rubles. The sum of fixed costs for the entire volume of the issue according to the report is 108768496.98 rubles.
Table 4.5 - The share of fixed costs in the structure of planned and design costs
| N / a | Cost item | The amount according to the plan, rub. | Project amount, rub. |
Share of fixed costs in the structure of redistribution costs,% |
| 1 | 2 | 3 | 4 | 5 |
| 1 | Redistribution costs 1. Process fuel (natural gas), here 2. Energy costs: power electricity, kW / h steam for production, Gcal industrial water, tm 3 compressed air, tm 3 circulating water, tm 3 industrial storm water, tm 3 3. Supporting materials 4. Basic salary of production workers 5. Additional wages for production workers 6. Social contributions 7. Replaceable equipment 8. Current repairs and maintenance of fixed assets 9. Depreciation of fixed assets 10. Overhaul 11. Work of transport shops 12. Other costs of the workshop Total redistribution costs |
|||
| 2 | General plant costs Total production cost |
100 | ||
| 3 | Non-production costs Total full cost |
100 |
According to the reported data, the break-even point is:
TB from 
T.
According to the project, the break-even point is:
TB pr 
T.
Table 4.6. the calculation of proceeds and all types of costs for the production of sold products necessary to determine the break-even point was carried out. The graphs for calculating the break-even point for the report and for the project are shown in Figure 4.2. and Figure 4.3. respectively.
Table 4.6 - Data for calculating the break-even point
Calculation of the break-even point for the report
Calculation of the break-even point for the project
As a result, we can conclude that the measure proposed in the project will reduce the unit cost of manufactured products by 1.45% by reducing variable costs, which contributes to an increase in profit by 19.5 million rubles. with an annual production volume of 110 123.01 tons. The result of the project implementation is the growth of the cumulative discounted net income in comparison with the planned value in the period under review. Also, a positive moment is the reduction of the break-even threshold from 12.85 thousand tons to 12.8 thousand tons.
Table 4.7 - Technical and economic indicators of the project
| P / p No. | Indicator | Report | Project | Deviation | |
| Absolute | % | ||||
| 1 | Production volume: in kind, t in value terms, thousand rubles |
||||
| 2 | Cost of fixed assets, thousand rubles | 6775032 | 6775032 | 0 | 0 |
| 3 | Total costs (full cost): total issue, thousand rubles units of production, rub. |
||||
| 4 | Product profitability,% | 60,65 | 62,1 | 1,45 | 2,33 |
| 5 | Net present value, NPV | 1700,136 | |||
| 6 | Total investment, thousand rubles | 0 | |||
| 7 | For reference: break-even point Т.B., t, the value of the discount rate F, internal rate of return IRR maximum cash outflow K, thousand rubles |
||||
CONCLUSION
In this diploma project, a technology for the production of pipes for general use in accordance with DIN 1629 was developed. The paper considers the possibility of reducing the length of the thickened ends formed during rolling on a reduction mill by changing the speed settings of the mill when rolling the end sections of the pipe using the capabilities of the UZS-R system. Calculations have shown that the reduction in the length of the thickened ends can reach 50%.
Economic calculations have shown that the use of the proposed rolling modes will reduce the unit cost by 1.45%. This, while maintaining the existing production volumes, will allow to increase profit by 20 million rubles in the first year.
1. Anuryev V.I. "Handbook of the designer-mechanical engineer" in 3 volumes, volume 1 - M. "Mechanical engineering" 1980 - 728 p.
2. Anuryev V.I. "Handbook of the designer-mechanical engineer" in 3 volumes, volume 2 - M. "Mechanical engineering" 1980 - 559 p.
3. Anuryev V.I. "Handbook of the designer-mechanical engineer" in 3 volumes, volume 3 - M. "Mechanical engineering" 1980 - 557 p.
4. Pavlov Ya.M. "Machine parts". - Leningrad "Mechanical Engineering" 1968 - 450 p.
5. Vasiliev V.I. "Basics of designing technological equipment for motor transport enterprises" tutorial- Kurgan 1992 - 88 p.
6. Vasiliev V.I. "Fundamentals of designing technological equipment for motor transport enterprises" - Kurgan 1992 - 32 p.
480 RUB | UAH 150 | $ 7.5 ", MOUSEOFF, FGCOLOR," #FFFFCC ", BGCOLOR," # 393939 ");" onMouseOut = "return nd ();"> Dissertation - 480 rubles, delivery 10 minutes, around the clock, seven days a week
Kholkin Evgeny Gennadievich. Study local sustainability thin-walled trapezoidal profiles at longitudinal and transverse bending: dissertation ... Candidate of technical sciences: 01.02.06 / Kholkin Evgeniy Gennadevich; [Place of protection: Ohm. state tech. un-t] .- Omsk, 2010.- 118 p .: ill. RSL OD, 61 10-5 / 3206
Introduction
1. Review of stability studies of compressed plate structural elements 11
1.1. Basic definitions and methods for studying the stability of mechanical systems 12
1.1.1, Algorithm for studying the stability of mechanical systems by a static method 16
1.1.2. Static approach. Methods: Euler, Imperfect, Energetic 17
1.2. Mathematical model and main results of analytical studies of Euler stability. Stability factor 20
1.3. Methods for studying the stability of plate elements and structures of them 27
1.4. Engineering methods for calculating plates and composite plate elements. The concept of the reduction method 31
1.5. Numerical studies of Euler stability by the finite element method: possibilities, advantages and disadvantages 37
1.6. Review of experimental studies of the stability of plates and composite plate elements 40
1.7. Conclusions and objectives of theoretical studies of the stability of thin-walled trapezoidal profiles 44
2. Development of mathematical models and algorithms for calculating the stability of thin-walled plate elements of trapezoidal profiles: 47
2.1. Longitudinal-transverse bending of thin-walled plate elements of trapezoidal profiles 47
2.1.1. Problem statement, basic assumptions 48
2.1.2. Mathematical model in ordinary differential equations. Boundary conditions, imperfection method 50
2.1.3. Algorithm for numerical integration, determining the critical
tension and its implementation in MS Excel 52
2.1.4. Calculation results and their comparison with known solutions 57
2.2. Calculation of critical stresses for a single plate element
as part of a profile ^ .. 59
2.2.1. A model that takes into account the elastic conjugation of the profile plate elements. Basic assumptions and problems of numerical research 61
2.2.2. Numerical Study of Mate Rigidity and Approximation of Results 63
2.2.3. Numerical investigation of the buckling half-wave length at the first critical load and approximation of the results 64
2.2.4. Calculation of the coefficient k (/ 3x, / 32). Approximation of calculation results (A, /? 2) 66
2.3. Evaluation of the adequacy of calculations by comparison with numerical solutions by the finite element method and known analytical solutions 70
2.4. Conclusions and objectives of the experimental study 80
3. Experimental studies on the local stability of thin-walled trapezoidal profiles 82
3.1. Description of prototypes and experimental setup 82
3.2. Testing samples 85
3.2.1. Test procedure and content G. 85
3.2.2. Compression test results 92
3.3. Conclusions 96
4. Consideration of local stability in the calculations of load-bearing structures made of thin-walled trapezoidal profiles in plane longitudinal - transverse bending 97
4.1. Calculation of critical stresses local loss stability of plate elements and the limiting thickness of a thin-walled trapezoidal profile 98
4.2. The area of permissible loads without taking into account the local loss of stability 99
4.3. Reduction factor 101
4.4. Taking into account local buckling and reduction 101
Conclusions 105
Bibliographic list
Introduction to work
The relevance of the work.
The creation of lightweight, strong and reliable structures is an urgent task. One of the main requirements in mechanical engineering and construction is a reduction in metal consumption. This leads to the fact that structural elements must be calculated according to more precise constitutive relations, taking into account the danger of both general and local buckling.
One of the ways to solve the problem of minimizing weight is the use of high-tech thin-walled trapezoidal rolled profiles (TTP). Profiles are made by rolling thin sheet steel with a thickness of 0.4 ... 1.5 mm in stationary conditions or directly at the assembly site as flat or arched elements. Structures using load-bearing arched coverings from a thin-walled trapezoidal profile are distinguished by their lightness, aesthetic appearance, ease of installation and a number of other advantages over traditional types of coverings.
The main type of profile loading is longitudinal-transverse bending. Tone-
jfflF dMF " lamellar elements
profile experiencing
median compression
bones can lose places
new stability. Local
loss of stability
Rice. 1. An example of local buckling
Yam,
^ J
Rice. 2. Scheme of the reduced profile section
(MPA) is observed in limited areas along the length of the profile (Fig. 1) at significantly lower loads than the total buckling and stresses comparable to the allowable ones. With MPU, a separate compressed plate element of the profile completely or partially ceases to perceive the load, which is redistributed between the rest of the plate elements of the profile section. Moreover, in the section where the MPA occurred, the stresses do not necessarily exceed the permissible ones. This phenomenon is called reduction. Reduction
consists in reducing, in comparison with the real, the cross-sectional area of the profile when reduced to an idealized design scheme (Fig. 2). In this regard, the development and implementation of engineering methods for accounting for local buckling of plate elements of a thin-walled trapezoidal profile is an urgent task.
Prominent scientists were engaged in the issues of plate stability: B.M. Bro-ude, F. Bleich, J. Brudka, I.G. Bubnov, V.Z. Vlasov, A.S. Volmir, A.A. Ilyushin, Miles, Melan, Ya.G. Panovko, SP. Timoshenko, Southwell, E. Stowell, Winderberg, Khvalla and others. Engineering approaches to the analysis of critical stresses with local buckling were developed in the works of E.L. Ayrumyan, Burggraf, A.L. Vasil'eva, B. Ya. Volodarsky, M.K. Glouman, Caldwell, V.I. Klimanova, V.G. Krokhaleva, D.V. Martsinkevich, E.A. Pav-linova, A.K. Pertseva, F.F. Tamplona, S.A. Timashev.
In the above engineering calculation methods for profiles with a complex cross-section, the danger of an MPU is practically not taken into account. At the stage of preliminary design of structures made of thin-walled profiles, it is important to have a simple apparatus for assessing the bearing capacity of a specific standard size. In this regard, there is a need for the development of engineering calculation methods that allow in the process of designing structures from thin-walled profiles to quickly assess their bearing capacity. A verification calculation of the bearing capacity of a structure made of a thin-walled profile can be performed using refined methods using existing software products and adjusted if necessary. Such a two-stage system for calculating the bearing capacity of structures made of thin-walled profiles is the most rational. Therefore, the development and implementation of engineering methods for calculating the bearing capacity of structures made of thin-walled profiles taking into account the local buckling of plate elements is an urgent task.
The purpose of the dissertation work: study of local buckling in plate elements of thin-walled trapezoidal profiles during their longitudinal-transverse bending and development of an engineering method for calculating the bearing capacity taking into account local stability.
To achieve the goal, the following are set research objectives.
Extension of analytical solutions for the stability of compressed rectangular plates to a system of mating plates in the profile.
Numerical study of the mathematical model of the local stability of the profile and obtaining adequate analytical expressions for the minimum critical stress of the MPU of the plate element.
Experimental evaluation of the degree of reduction in the section of a thin-walled profile with local loss of stability.
Development of an engineering methodology for verification and design calculation of a thin-walled profile, taking into account local buckling.
Scientific novelty work is to develop an adequate mathematical model of local buckling for a separate plate
element in the profile and obtaining analytical dependencies for calculating critical stresses.
Reasonableness and reliability The obtained results are provided by basing on fundamental analytical solutions of the problem of stability of rectangular plates, correct application of the mathematical apparatus, sufficient for practical calculations coincidence with the results of FEM calculations and experimental studies.
Practical significance consists in the development of an engineering methodology for calculating the bearing capacity of profiles, taking into account local buckling. The results of the work are implemented in Montazhproekt LLC in the form of a system of tables and graphical representations of the areas of permissible loads for the entire assortment of produced profiles, taking into account local buckling, and are used for preliminary selection of the type and thickness of the profile material for specific design solutions and types of loading.
The main provisions for the defense.
A mathematical model of plane bending and compression of a thin-walled profile as a system of conjugated plate elements and a method for determining the critical stresses of the MPA in the sense of Euler on its basis.
Analytical dependences for calculating the critical stresses of local buckling for each plate element of the profile at plane longitudinal-transverse bending.
Engineering method for verification and design calculation of a thin-walled trapezoidal profile, taking into account local buckling. Approbation of work and publication.
The main provisions of the dissertation were reported and discussed at scientific and technical conferences of various levels: International Congress "Machines, Technologies and Processes in Construction" dedicated to the 45th anniversary of the Faculty of Transport and Technological Machines (Omsk, SibADI, December 6-7, 2007); All-Russian scientific and technical conference, "YOUNG RUSSIA: advanced technologies into industry" (Omsk, Om-GTU, November 12-13, 2008).
Structure and scope of work. The thesis is presented on 118 pages of text, consists of an introduction, 4 chapters and one annex, contains 48 figures, 5 tables. The list of references includes 124 titles.
Any engineering project relies on the solution of differential equations of a mathematical model of motion and equilibrium of a mechanical system. Drafting of a structure, mechanism, machine is accompanied by some manufacturing tolerances, and later on - imperfections. Imperfections can also occur during operation in the form of dents, gaps due to wear and other factors. It is impossible to foresee all the variants of external influences. The design is forced to work under the influence of random disturbing forces that are not taken into account in the differential equations.
Factors not taken into account in the mathematical model - imperfections, random forces or perturbations - can make serious adjustments to the results obtained.
The unperturbed state of the system is distinguished - the calculated state at zero perturbations, and the perturbed state, which is formed as a result of perturbations.
In one case, due to the perturbation, there is no significant change in the equilibrium position of the structure, or its motion differs little from the calculated one. This state of the mechanical system is called stable. In other cases, the equilibrium position or the nature of the movement differs significantly from the calculated one, such a state is called unstable.
The theory of stability of motion and equilibrium of mechanical systems deals with the establishment of signs that allow one to judge whether the considered motion or equilibrium will be stable or unstable.
A typical sign of the transition of a system from a stable state to an unstable one is the achievement of a value called critical by some parameter - critical force, critical speed, etc.
The emergence of imperfections or the impact of unaccounted forces inevitably leads to the movement of the system. Therefore, in the general case, one should investigate the stability of the motion of a mechanical system under disturbances. This approach to the study of stability is called dynamic, and the corresponding research methods are called dynamic.
In practice, it is often sufficient to restrict ourselves to a static approach, i.e. static methods of stability research. In this case, the final result of the perturbation is investigated - a new steady-state equilibrium position of the mechanical system and the degree of its deviation from the calculated, unperturbed equilibrium position.
The static formulation of the problem assumes not to consider the forces of inertia and the time parameter. This formulation of the problem often makes it possible to translate the model from equations of mathematical physics into ordinary differential equations. This greatly simplifies the mathematical model and facilitates the analytical study of stability.
A positive result of the analysis of the stability of the equilibrium by the static method does not always guarantee dynamic stability. However, for conservative systems, the static approach in determining critical loads and new equilibrium states leads to exactly the same results as the dynamic one.
In a conservative system, the work of the internal and external forces of the system, performed during the transition from one state to another, is determined only by these states and does not depend on the trajectory of motion.
The concept of "system" unites a deformable structure and loads, the behavior of which must be specified. Hence, two necessary and sufficient conditions for the conservatism of the system follow: 1) the elasticity of the deformable structure, i.e. reversibility of deformations; 2) conservatism of the load, i.e. the independence of the work performed by her from the trajectory. In some cases, the static method also gives satisfactory results for non-conservative systems.
For clarity of the above, we will consider several examples from theoretical mechanics and strength of materials.
1. A ball of weight Q is located in a depression of the bearing surface (Fig. 1.3). Under the action of the disturbing force 5Р Q sina, the equilibrium position of the ball does not change, i.e. it is stable.
With a short-term action of the force 5Р Q sina, without taking into account rolling friction, a transition to a new equilibrium position or oscillations around the initial equilibrium position is possible. When friction is taken into account, the oscillatory motion will be damped, that is, stable. The static approach allows you to determine only the critical value of the disturbing force, which is equal to: Ркр = Q sina. The nature of the motion when the critical value of the disturbing action is exceeded and the critical duration of the action can be analyzed only by dynamic methods.
2. Rod length / compressed by force P (Fig. 1.4). From the resistance of materials based on the static method, it is known that under loading within the elastic range, there is a critical value of the compressive force.
The solution of the same problem with a tracking force, the direction of which coincides with the direction of the tangent at the point of application, by the static method leads to the conclusion about the absolute stability of the rectilinear form of equilibrium.
Engineering analysis falls into two categories: classical and numerical methods. Using classical methods, they try to solve the problems of stress and strain fields distribution directly, forming systems of differential equations based on fundamental principles. The exact solution, if it is possible to obtain equations in a closed form, is possible only for the simplest cases of geometry, loads, and boundary conditions. A fairly wide range of classical problems can be solved using approximate solutions of systems of differential equations. These solutions are in the form of series, in which the lower-order terms are discarded after the convergence study. Like exact solutions, approximate ones require a regular geometric shape, simple boundary conditions, and convenient application of loads. Accordingly, these solutions cannot be applied to most practical problems. The fundamental advantage of classical methods is that they provide a deep understanding of the problem under study. A wider range of problems can be investigated using numerical methods. Numerical methods include: 1) energy method; 2) the method of boundary elements; 3) the method of finite differences; 4) finite element method.
Energy methods allow one to find a minimum expression for the total potential energy of a structure over the entire given area. This approach only works well for certain tasks.
The boundary element method approximates functions that satisfy the system of differential equations to be solved, but not the boundary conditions. The dimension of the problem is downsized because the elements represent only the boundaries of the modeled area. However, the application of this method requires knowledge of the fundamental solution of the system of equations, which can be difficult to obtain.
The finite difference method transforms the system of differential equations and boundary conditions into the corresponding system of algebraic -equations. This method allows solving problems of analysis of structures with complex geometry, boundary conditions and combined loads. However, the finite difference method is often too slow due to the fact that the requirement of a regular grid over the entire study area leads to systems of equations of very high orders.
The finite element method can be extended to an almost unlimited class of problems due to the fact that it allows the use of elements of simple and various shapes to obtain partitions. The sizes of finite elements, which can be combined to obtain an approximation to any irregular boundaries, sometimes differ in the partition by tens of times. It is allowed to apply an arbitrary type of load to the elements of the model, as well as to impose any type of fastening on them. The main problem is the increase in costs to obtain a result. One has to pay for the generality of the solution with the loss of intuition, since a finite element solution is, in fact, a set of numbers that are applicable only to a specific problem posed using a finite element model. Changing any significant aspect in the model usually requires a complete re-solution of the problem. However, this is an insignificant cost, since the finite element method is often the only one. possible way its solutions. The method is applicable to all classes of field distribution problems, which include structural analysis, heat transfer, fluid flow, and electromagnetism. The disadvantages of numerical methods include: 1) high cost of finite element analysis programs; 2) long training to work with the program and the possibility of full-fledged work only for highly qualified personnel; 3) quite often it is impossible to verify by a physical experiment the correctness of the result of the solution obtained by the finite element method, including in nonlinear problems. m Review of experimental studies of the stability of plates and composite plate elements
Profiles currently used for building structures are made from metal sheets with a thickness of 0.5 to 5 mm and are therefore considered thin-walled. Their faces can be both flat and curved.
The main feature of the operation of thin-walled profiles is that faces with a high value of the width-to-thickness ratio experience large buckling deformations under loading. A particularly intense increase in deflections is observed when the magnitude of the stresses acting on the face approaches the critical value. There is a loss of local stability, deflections become comparable to the thickness of the edge. As a result, the cross-section of the profile is greatly distorted.
In the literature on the stability of plates, a special place is occupied by the work of the Russian scientist SP. Tymoshenko. He is credited with developing an energy method for solving elastic stability problems. Using this method, SP. Timoshenko gave a theoretical solution to the problems of stability of plates loaded in the median plane under different boundary conditions. The theoretical solutions were tested in a series of tests on freely supported plates under uniform compression. Tests confirmed the theory.
To check the reliability of the results obtained, numerical studies by the finite element method (FEM) were carried out. Recently, numerical studies of FEM have found more and more widespread use due to objective reasons, such as the lack of test problems, the impossibility of meeting all conditions when testing on samples. Numerical methods make it possible to carry out research under "ideal" conditions, have a minimum error, which is practically impossible to implement in real tests. Numerical studies were carried out using the ANSYS program.
Numerical studies were carried out with samples: rectangular plate; U-shaped and trapezoidal profile element with a longitudinal ridge and without ridge; profile sheet (Figure 2.11). Samples with a thickness of 0.7; 0.8; 0.9 and 1mm.
A uniform compressive load sgw was applied to the samples (Figure 2.11) at the ends, followed by an increase in the Det step by step. The load corresponding to the local loss of stability of the flat shape corresponded to the value of the critical compressive stress σcr. Then, using the formula (2.24), the stability coefficient & (/? I, /? G) was calculated and compared with the value from table 2.
Consider a rectangular plate with a length of a = 100 mm and a width of 6 = 50 mm, compressed at the ends by a uniform compressive load. In the first case, the plate has a hinged fixation along the contour, in the second - a rigid fixation along the side edges and a hinge fixation at the ends (Figure 2.12).
In the ANSYS program, a uniform compressive load was applied to the end faces, the critical load, stress, and stability coefficient & (/?], /? 2) of the plate were determined. When hinged along the contour, the plate lost its stability in the second shape (two bulges were observed) (Fig. 2.13). Then the coefficients of resistance to, / 32) of the plate, found numerically and analytically, were compared. The calculation results are presented in Table 3.
Table 3 shows that the difference between the results of the analytical and numerical solutions was less than 1%. Hence, it was concluded that the proposed algorithm for the study of stability can be applied in the calculation of critical loads for more complex structures.
To extend the proposed method for calculating the local stability of thin-walled profiles to the general loading case, numerical studies were carried out in the ANSYS program to find out how the nature of the compressive load affects the coefficient k (y). The research results are presented in a graph (Fig. 2.14).
The next step in checking the proposed calculation methodology was the study of a separate element of the profile (Figure 2.11, b, c). It has a hinge fixation along the contour and is compressed at the ends by a uniform compressive load of the USL (Fig. 2.15). The sample was examined for stability in the ANSYS program and according to the proposed method. After that, the results obtained were compared.
When creating a model in the ANSYS program, to uniformly distribute the compressive load along the end, a thin-walled profile was placed between two thick plates and a compressive load was applied to them.
The result of the study in the ANSYS program of the element of the U-shaped profile is shown in Figure 2.16, which shows that, first of all, the loss of local stability occurs at the widest plate.
For supporting structures made of high-tech thin-walled trapezoidal profiles, the calculation is carried out according to the methods of permissible stresses. An engineering method is proposed for taking into account local buckling when calculating the bearing capacity of structures made of a thin-walled trapezoidal profile. The technique is implemented in MS Excel, is available for widespread use and can serve as a basis for appropriate additions to regulatory documents regarding the calculation of thin-walled profiles. It is built on the basis of research and obtained analytical dependences for calculating the critical stresses of local buckling of plate elements of a thin-walled trapezoidal profile. The task is divided into three components: 1) determination of the minimum profile thickness (limiting t \ at which there is no need to take into account local buckling in this type of calculation; 2) determination of the area of permissible loads of a thin-walled trapezoidal profile, within which the bearing capacity is ensured without local loss of stability; 3) determination of the range of permissible values NuM, within which the bearing capacity is ensured with local loss of stability of one or more plate elements of a thin-walled trapezoidal profile (taking into account the reduction of the profile section).
In this case, it is believed that the dependence of the bending moment on the longitudinal force M = f (N) for the calculated structure is obtained by the methods of resistance of materials or structural mechanics (Figure 2.1). The permissible stresses [t] and the yield stress of the material sgt are known, as well as the residual stresses sgstі in the plate elements. In the calculations after local buckling, the "reduction" method was applied. In case of loss of stability, 96% of the width of the corresponding plate element is excluded.
Calculation of the critical stresses of local buckling of plate elements and the limiting thickness of a thin-walled trapezoidal profile The thin-walled trapezoidal profile is divided into a set of plate elements as shown in Figure 4.1. In this case, the angle of mutual arrangement of neighboring elements does not affect the value of the critical stress of the local
Profile H60-845 CURVED buckling. Replacement of curved corrugations with straight-line elements is allowed. Critical compressive stresses of local buckling in the sense of Euler for an individual i-th plate element of a thin-walled trapezoidal profile with width bt at thickness t, material elastic modulus E and Poisson's ratio ju in the elastic stage of loading are determined by the formula
The coefficients k (px, P2) and k (v) take into account, respectively, the effect of the stiffness of the adjacent plate elements and the nature of the distribution of compressive stresses over the width of the plate element. The value of the coefficients: k (px, P2) is determined according to table 2, or calculated by the formula
Normal stresses in a plate element are determined in the central axes by the well-known formula for the resistance of materials. The area of permissible loads without taking into account local buckling (Fig. 4.2) is determined by the expression and is a quadrangle, where J is the moment of inertia of the section of the profile period during bending, F is the section area of the profile period, ymax and Utin are the coordinates of the extreme points of the profile section (Fig. 4.1).
Here, the sectional area of the profile F and the moment of inertia of the section J are calculated for a periodic element of length L, and the longitudinal force iV and the bending moment Mb of the profile refer to L.
The bearing capacity is provided when the actual load curve M = f (N) falls within the range of permissible loads minus the area of local buckling (Figure 4.3). Fig 4.2. The area of permissible loads without taking into account local buckling
The loss of local stability of one of the shelves leads to its partial exclusion from the perception of workloads - reduction. The degree of reduction is taken into account by the reduction factor
The bearing capacity is ensured when the actual load curve falls within the range of permissible loads minus the range of local buckling loads. At smaller thicknesses, the line of local buckling decreases the area of permissible loads. Local buckling is not possible if the actual load curve is located in a reduced area. When the curve of actual loads goes beyond the line of the minimum value of the critical stress of local buckling, it is necessary to rebuild the area of permissible loads, taking into account the reduction of the profile, which is determined by the expression
Rolling pipes in order to reduce their diameter (reduction) is very widely used in almost all workshops for the production of hot-rolled pipes, as well as in the manufacture of pipes by welding. This is due to the fact that the production of small-sized pipes is usually associated with tangible losses in the productivity of pipe-rolling or pipe-welding units and, consequently, with an increase in the cost of production. In addition, in some cases, for example, rolling of pipes to dia. less than 60-70 mm or pipes with a very large wall thickness and a small internal hole is difficult, since it requires the use of mandrels of too small a diameter.Reduction is carried out after additional heating (or heating) of pipes to 850-1100 ° C by rolling them on multi-stand continuous mills (with up to 24 stands) without using an internal tool (mandrel). Depending on the adopted system of work, this process can proceed with an increase in the wall thickness or with a decrease in it. In the first case, rolling is carried out without tension (or with very slight tension); and in the second - with a high tension. The second case, as a more progressive one, has become widespread in the last decade, since it allows a much larger reduction, and a decrease in the wall thickness at the same time expands the range of rolled pipes with more economical thin-walled pipes.
The possibility of wall thinning during reduction makes it possible to produce pipes with a slightly larger wall thickness (sometimes by 20-30%) on the main pipe-rolling unit. This significantly increases the productivity of the unit.
At the same time, in many cases, the older principle of operation - free reduction without tension - retained its significance. Basically, this refers to the cases of reduction of relatively thick-walled pipes, when even at high tensions it becomes difficult to significantly reduce the wall thickness. It should be noted that reduction mills are installed in many pipe rolling shops, which are designed for free rolling. These mills will be in operation for a long time and, therefore, tension-free reduction will be widely used.
Let us consider how the pipe wall thickness changes during free reduction, when there are no axial tension or back-up forces, and the stress state diagram is characterized by compressive stresses. B. JI. Kolmogorov and A. 3. Gleiberg, proceeding from the fact that the actual change in the wall corresponds to the minimum work of deformation, and using the principle of possible displacements, gave a theoretical definition of the change in wall thickness during reduction. In this case, the assumption was made that the non-uniformity * of deformation does not significantly affect the change in the wall thickness, and the forces of external friction were not taken into account, since they are much less than the internal resistances. Figure 89 shows the curves of the change in wall thickness from the initial SQ to the given S for low-strength steels depending on the degree of reduction from the initial diameter DT0 to the final DT (ratio DT / DTO) and the geometric factor - pipe fineness (ratio S0 / DT0).
At low degrees of reduction, the resistance to longitudinal outflow turns out to be greater than the resistance to inward outflow, which causes wall thickening. With an increase in the value of deformation, the intensity of wall thickening increases. However, at the same time, the resistance to the outflow inside the pipe also increases. At a certain amount of reduction, the wall thickening reaches its maximum and a subsequent increase in the degree of reduction leads to a more intensive increase in the resistance to outflow inward and, as a result, the thickening begins to decrease.
Meanwhile, only the wall thickness of the finished reduced pipe is usually known, and when using these curves it is necessary to set the desired value, that is, to use the method of successive approximation.
The nature of the change in wall thickness changes sharply if the process is carried out with tension. As already mentioned, the presence and magnitude of axial stresses are characterized by the rate conditions of deformation on a continuous mill, the indicator of which is the coefficient of kinematic tension.
When reducing with tension, the deformation conditions of the pipe ends differ from the deformation conditions of the middle of the pipe, when the rolling process has already stabilized. In the process of filling the mill or when the pipe leaves the mill, the ends of the pipe perceive only a part of the tension, and rolling, for example in the first stand until the pipe enters the second stand, proceeds without tension at all. As a result, the pipe ends always thicken, which is a disadvantage of the tension reduction process.
The amount of trim may be slightly less than the length of the thickened end due to the plus tolerance for wall thickness. The presence of thickened ends significantly affects the economy of the reduction process, since these ends must be cut and are a sunk production cost. In this regard, the process of rolling with tension is used only in the case of obtaining after reduction of pipes with a length of more than 40-50 m, when the relative losses in cuttings are reduced to a level characteristic of any other rolling method.
The above methods for calculating the change in the thickness of the stays ultimately make it possible to determine the stretch ratio both for the case of free reduction and for the case of rolling with tension.
With a reduction of 8-10% and a plastic tension coefficient of 0.7-0.75, the slip is characterized by a coefficient of ix = 0.83-0.88.
From consideration of formulas (166 and 167), it is easy to see how exactly the speed parameters must be observed in each stand in order for rolling to proceed according to the design mode.
The group drive of the rolls in the reduction mills of the old design has a constant ratio of the number of revolutions of the rolls in all stands, which only in a particular case for pipes of the same size can correspond to the free rolling mode. Reduction of pipes of all other sizes will take place with other hoods, therefore, free rolling will not be maintained. In practice, in such mills, the process always proceeds with a slight tension. The individual drive of the rolls of each stand with fine adjustment of their speed allows creating different tension modes, including the free rolling mode.
Since the front and rear tensions create moments directed in different directions, the total moment of rotation of the rolls in each stand can increase or decrease depending on the ratio of the forces of the front and rear tension.
In this respect, the conditions in which the initial and last 2-3 stands are located are not the same. If the rolling moment in the first stands as the pipe passes in the subsequent stands decreases due to tension, then the rolling moment in the last stands, on the contrary, should be higher, since these stands mainly experience back tension. And only in the middle stands, due to the close values of the front and rear tension, the rolling moment in the steady state differs little from the calculated one. When calculating the strength of the drive units of a rolling mill operating with tension, it should be borne in mind that the rolling moment increases for a short time, but very sharply during the period when the tube is captured by the rolls, which is explained by the large difference in the speeds of the tube and rolls. The resulting peak load, sometimes several times higher than the steady-state load (especially when reducing with a high tension), can cause breakdowns of the drive mechanism. Therefore, in the calculations, this peak load is taken into account by introducing the appropriate coefficient, taken equal to 2-3.
UDC 621.774.3
RESEARCH OF THE DYNAMICS OF CHANGE OF PIPE WALL THICKNESS DURING REDUCTION
K.Yu. Yakovleva, B.V. Barichko, V.N. Kuznetsov
The results of an experimental study of the dynamics of changes in the wall thickness of pipes during rolling, drawing in monolithic and roller drags are presented. It is shown that with an increase in the degree of deformation, a more intensive increase in the pipe wall thickness is observed in the processes of rolling and drawing in roller dies, which makes their use promising.
Key words: cold-deformed pipes, thick-walled pipes, pipe drawing, pipe wall thickness, quality of the inner surface of the pipe.
The existing technology for the manufacture of cold-deformed thick-walled small-diameter pipes from corrosion-resistant steels provides for the use of cold rolling processes at KhPT mills and subsequent safe drawing in monolithic dies. It is known that the production of pipes of small diameter by cold rolling is associated with a number of difficulties due to a decrease in the rigidity of the "rod-mandrel" system. Therefore, for the production of such pipes, a drawing process is used, which is mainly non-edging. The nature of the change in the wall thickness of the pipe during uncorrected drawing is determined by the ratio of the wall thickness S and the outer diameter D, and the absolute value of the change does not exceed 0.05-0.08 mm. In this case, wall thickening is observed when the ratio S / D< 0,165-0,20 в зависимости от наружного диаметра заготовки . Для данных соотношений размеров S/D коэффициент вытяжки д при волочении труб из коррозионно-стойкой стали не превышает значения 1,30 , что предопределяет многоцикличность известной технологии и требует привлечения новых способов деформации.
The aim of the work is a comparative experimental study of the dynamics of changes in the wall thickness of pipes in the processes of reduction by rolling, drawing in monolithic and roller dies.
Cold-deformed pipes were used as blanks: 12.0x2.0 mm (S / D = 0.176), 10.0x2.10 mm (S / D = 0.216) made of 08Kh14MF steel; dimensions 8.0x1.0 mm (S / D = 0.127) from steel 08X18H10T. All pipes were annealed.
Drawing in monolithic dies was carried out on a chain drawing mill with a force of 30 kN. For roller drawing, a VR-2 / 2.180 die with shifted pairs of rollers was used. Drawing in a roller die was carried out using the "oval - circle" gauge system. Reduction of tubes by rolling was carried out according to the "oval - oval" calibration scheme in a two-roll stand with rolls with a diameter of 110 mm.
At each stage of deformation, samples were taken (5 pieces for each variant of the study) to measure the outer diameter, wall thickness, and roughness of the inner surface. The measurement of the geometric dimensions and roughness of the pipe surface was carried out using a TTTTs-TT electronic caliper. electronic point micrometer, profilometer Surftest SJ-201. All instruments and devices have passed the required metrological verification.
The parameters of cold deformation of pipes are given in the table.
In fig. 1 shows the graphs of the dependence of the magnitude of the relative increase in wall thickness on the degree of deformation e.
Analysis of the graphs in Fig. 1 shows that during rolling and drawing in a roller die, as compared to the process of drawing in a monolithic die, a more intensive change in the pipe wall thickness is observed. This, according to the authors, is due to the difference in the stress state of the metal: during rolling and roller drawing, tensile stresses in the deformation zone have lower values. The location of the curve of change in wall thickness during roller drawing below the curve of change in wall thickness during rolling is due to somewhat higher tensile stresses during roll drawing due to the axial application of deformation force.
The extremum of the wall thickness change function observed during rolling on the degree of deformation or relative reduction along the outer diameter corresponds to the value S / D = 0.30. By analogy with hot rolling reduction, where a decrease in wall thickness is observed at S / D> 0.35, it can be assumed that cold rolling reduction is characterized by a decrease in wall thickness at S / D> 0.30.
Since one of the factors that determine the nature of the change in wall thickness is the ratio of tensile and radial stresses, which in turn depends on the parameters
No. of passage Pipe dimensions, mm S, / D, Si / Sc Di / Do є
Reduction by rolling (pipes made of steel grade 08Kh14MF)
O 9.98 2.157 O, 216 1, O 1, O 1, O O
1 9.52 2.2ZO O, 2Z4 1, OZ4 O, 954 1, OZ 8 O, O4
2 8.1O 2, Z5O O, 29O 1, O89 O, 812 1.249 O, 2O
Z 7, O1 2, Z24 O, ZZ2 1, O77 O, 7O2 1.549 O, Z5
Reduction by rolling (pipes made of steel grade 08X18H10T)
О 8, О6 1, О2О О, 127 1, О 1, О 1, О О
1 7, OZ 1.13O O, 161 1.1O8 O, 872 1, O77 O, O7
2 6.17 1.225 0.199 1.201 O, 766 1.185 O, 16
Z 5.21 1, Z1O O, 251 1.284 O, 646 1.4O6 O, 29
Reduction by drawing in a roller die (pipes made of steel grade 08Х14МФ)
O 12, OO 2.11 O, 176 1, O 1, O 1, O O
1 1О, 98 2,2О О, 2ОО 1, О4З О, 915 1, О8О О, О7
2 1O, O8 2.27 O, 225 1, O76 O, 84O 1.178 O, 15
З 9, О1 2, ЗО О, 2О1 1, О9О О, 751 1, З52 О, 26
Reduction by drawing in a monolithic die (pipes made of steel grade 08H14MF)
O 12, OO 2.11 O O, 176 1, O 1, O 1, O O
1 1O, 97 2.1Z5 0.195 1, O12 O, 914 1.1O6 O, 1O
2 9.98 2.157 O, 216 1, O22 O, 8Z2 1.118 O, 19
Z 8.97 2.16O O, 241 1, O24 O, 748 1.147 O, ZO
Di, Si - respectively, the outer diameter and wall thickness of the pipe in g-aisle.
Rice. 1. Dependence of the magnitude of the relative increase in pipe wall thickness on the degree of deformation
pa S / D, then it is important to study the influence of the S / D ratio on the position of the extremum of the function of changing the pipe wall thickness during the reduction process. According to the work data, at lower S / D ratios, the maximum value of the pipe wall thickness is observed at large deformations. This fact was investigated on the example of the process of rolling pipes with dimensions 8.0x1.0 mm (S / D = 0.127) of 08X18H10T steel in comparison with the data on rolling pipes with dimensions of 10.0x2.10 mm (S / D = 0.216) of 08X14MF steel. The measurement results are shown in Fig. 2.
The critical degree of deformation at which the maximum value of the wall thickness was observed when rolling pipes with the ratio
S / D = 0.216, was 0.23. When rolling pipes made of steel 08X18H10T, the extremum of the increase in wall thickness was not achieved, since the ratio of the pipe dimensions S / D, even at the maximum degree of deformation, did not exceed 0.3. An important circumstance is that the dynamics of an increase in the wall thickness during tube reduction by rolling is inversely related to the S / D ratio of the original tube, which is demonstrated by the graphs shown in Fig. 2, a.
Analysis of the curves in Fig. 2, b also shows that the change in the S / D ratio in the process of rolling pipes made of steel grade 08X18H10T and pipes made of steel grade 08X14MF has a similar qualitative character.
S0 / A) = O, 127 (08X18H10T)
S0 / 00 = 0.216 (08X14MF)
Deformation degree, b
VA = 0; 216 (08X14MF)
(So / Da = 0A21 08X18H10T) _
Deformation degree, є
Rice. 2. Change in wall thickness (a) and S / D ratio (b) depending on the degree of deformation during rolling of pipes with different initial S / D ratio
Rice. 3. Dependence of the relative roughness of the inner surface of pipes on the degree of deformation
In the process of reduction different ways the roughness of the inner surface of the pipes was also evaluated by the value of the arithmetic mean deviation of the microroughness height Ra. In fig. 3 shows the graphs of the dependence of the relative value of the parameter Ra on the degree of deformation during the reduction of pipes by rolling and drawing in monolithic diagrams
of the inner surface of the pipes in the r-th passage and on the original pipe).
Analysis of the curves in Fig. 3 shows that in both cases (rolling, drawing) an increase in the degree of deformation during reduction leads to an increase in the parameter Ra, that is, deteriorates the quality of the inner surface of the pipes. The dynamics of change (increase) in the roughness parameter with an increase in the degree of deformation in the case of re-
pipe ducting by rolling in two-roll calibers is significantly (approximately two times) higher than the same indicator in the process of drawing in monolithic die.
It should also be noted that the dynamics of changes in the roughness parameter of the inner surface is consistent with the above description of the dynamics of changes in the wall thickness for the considered reduction methods.
Based on the research results, the following conclusions can be drawn:
1. The dynamics of changes in the pipe wall thickness for the considered methods of cold reduction is of the same type - intense thickening with an increase in the degree of deformation, a subsequent slowdown in the increase in wall thickness with a certain maximum value at a certain ratio of pipe dimensions S / D, and a subsequent decrease in the increase in wall thickness.
2. The dynamics of changes in pipe wall thickness is inversely related to the ratio of the dimensions of the original pipe S / D.
3. The greatest dynamics of increasing the wall thickness is observed in the processes of rolling and drawing in roller dies.
4. An increase in the degree of deformation during reduction by rolling and drawing in monolithic die leads to a deterioration in the condition of the inner surface of the pipes, while the increase in the roughness parameter Ra during rolling occurs more intensively than during drawing. Taking into account the conclusions made and the nature of the change in the wall thickness in the process of deformation, it can be argued that for drawing pipes in roller dies, the
The increase in the Ra parameter will be less intense than for rolling, and more intense in comparison with monolithic drawing.
The information obtained on the regularities of the cold reduction process will be useful in the design of routes for the manufacture of cold-deformed pipes from corrosion-resistant steels. At the same time, the use of the process of drawing in roller dies is promising for increasing the pipe wall thickness and reducing the number of passes.
Literature
1. Bisk, M.B. Cold deformation steel pipes... At 2 pm Part 1: Preparation for deformation and drawing / M.B. Bisk, I.A. Grekhov, V.B. Slavin. -Sverdlovsk: Middle Ural. book publishing house, 1976 .-- 232 p.
2. Savin, G.A. Pipe drawing / G.A. Savin. -M: Metallurgy, 1993 .-- 336 p.
3. Shveikin, V.V. Technology of cold rolling and pipe reduction: textbook. allowance / V.V. Shveikin. - Sverdlovsk: Publishing house of UPI im. CM. Kirov, 1983 .-- 100 p.
4. Technology and equipment of pipe production / V.Ya. Osadchiy, A.S. Vavilin, V.G. Zimovets and others; ed. V.Ya. Despondent. - M .: Intermet Engineering, 2007 .-- 560 p.
5. Barichko, B.V. Fundamentals of technological processes of OMD: lecture notes / B.V. Barichko, F.S. Dubinsky, V.I. Krainov. - Chelyabinsk: SUSU Publishing House, 2008 .-- 131 p.
6. Potapov, I.N. Theory of pipe production: textbook. for universities / I.N. Potapov, A.P. Kolikov, V.M. Druyan. - M .: Metallurgy, 1991 .-- 424 p.
Yakovleva Ksenia Yurievna, Junior Researcher, JSC Russian Research Institute of the Pipe Industry (Chelyabinsk); [email protected]
Boris Barichko, Deputy Head of Seamless Pipes Department, Russian Research Institute of the Pipe Industry (Chelyabinsk); [email protected]
Kuznetsov Vladimir Nikolaevich, Head of the Cold Deformation Laboratory of the Central Plant Laboratory, OJSC Sinarsky Pipe Plant (Kamensk-Uralsky); [email protected]
Bulletin of the South Ural State University
Series "Metallurgy" ___________2014, vol. 14, no. 1, pp. 101-105
STUDY OF DYNAMIC CHANGES OF THE PIPE WALL THICKNESS IN THE REDUCTION PROCESS
K.Yu. Yakovleva, The Russian Research Institute of the Tube and Pipe Industries (RosNITI), Chelyabinsk, Russian Federation, [email protected],
B.V. Barichko, The Russian Research Institute of the Tube and Pipe Industries (RosNITI), Chelyabinsk, Russian Federation, [email protected],
V.N. Kuznetsov, JSC “Sinarsky Pipe Plant”, Kamensk-Uralsky, Russian Federation, [email protected]
The results of the experimental study of dynamic changes for the pipe wall thickness during rolling, drawing both in single-piece and roller dies are described. The results show that with the deformation increasing the faster growth of the pipe wall thiknness is observed in rolling and drawing with the roller dies. The conclusion can be drawn that the usage of roller dies is the most promising one.
Keywords: cold-formed pipes, thick-wall pipes, pipe drawing, pipe wall thickness, quality of the inner surface of pipe.
1. Bisk M.B., Grekhov I.A., Slavin V.B. Kholodnaya deformatsiya stal "nykh trub. Podgotovka k deformatsii i volochenie. Sverdlovsk, Middle Ural Book Publ., 1976, vol. 1.232 p.
2. Savin G.A. Volochenie trub. Moscow, Metallurgiya Publ., 1993.336 p.
3. Shveykin V.V. Tekhnologiya kholodnoy prokatki i redutsirovaniya trub. Sverdlovsk, Ural Polytechn. Inst. Publ., 1983.100 p.
4. Osadchiy V.Ya., Vavilin A.S., Zimovets V.G. et al. Tekhnologiya i obrudovanie trubnogo proizvodstva. Osadchiy V.Ya. (Ed.). Moscow, Intermet Engineering Publ., 2007.560 p.
5. Barichko B.V., Dubinskiy F.S., Kraynov V.I. Osnovy tekhnologicheskikh protsessov OMD. Chelyabinsk, South Ural St. Univ. Publ., 2008.131 p.
6. Potapov I.N., Kolikov A.P., Druyan V.M. Teoriya trubnogo proizvodstva. Moscow, Metallurgiya Publ., 1991.424 p.
Ilyashenko A.V. - Associate Professor of the Department of Structural Mechanics
Moscow State University of Civil Engineering,
candidate of technical sciences
The study of the bearing capacity of compressed elastic thin-walled rods with initial deflection and undergoing local loss of stability is associated with the determination of the reduced cross-section of the rod. The main provisions adopted for the study of the stress-strain state in the supercritical stage of compressed imperfect thin-walled rods are given in the works. This article examines the supercritical behavior of rods, which are represented as a set of jointly working elements - plates with initial deflection, imitating the operation of the shelves of angle, tee and cruciform profiles. These are the so-called shelf-plates with one resiliently clamped edge and the other free (see figure). In works, such a plate belongs to type II.
It was found that the breaking load, which characterizes the bearing capacity of the bar, significantly exceeds the load P cr (m), at which there is a local loss of stability of the imperfect profile. From the graphs presented in, it can be seen that the deformations of the longitudinal fibers along the perimeter of the cross section in the supercritical stage become extremely unequal. In the fibers far from the ribs, the compression deformations decrease with increasing load, and at loads close to the limiting ones, due to the sharp bending of these fibers due to initial deflections and the ever-increasing arrows of the longitudinal half-waves formed after local buckling, deformations appear and grow intensively stretching.
The sections of the cross-section with bent longitudinal fibers release stresses, as it were, are turned off from the operation of the bar, weakening the effective section and reducing its rigidity. So, the bearing capacity of a thin-walled profile is not limited to local loss of stability. The total load, perceived by the more rigid (less curved) sections of the cross-section, can significantly exceed the value of P cr (m).
We will obtain an effective, reduced section, excluding non-working sections of the profile. For this, we use the expression for the stress function Ф k (x, y), which describes the stress state of the k-th plate of type II (see).
Let us turn to the supercritical stresses σ kх (in the direction of the external compressive force), determined in the most unfavorable section of the bar (x = 0). Let's write them in general form:
σ kx = ∂ 2 Ф k (A km, y, f kj, f koj, β c, d, β c, d, j, ℓ, s) ∕ ∂ y 2, (1)
where the integration constants A km (m = 1,2,…, 6) and the arrows of the components of the acquired deflections f kj (j = 1,2) are determined from the solution of the system of resolving equations. This system of equations includes nonlinear variational equations and boundary conditions describing the joint operation of imperfect profile plates. Arrows f koj (j = 1,2, ..., 5) of the components of the initial deflection of the k-th plate are determined experimentally for each type of profile;
ℓ is the length of the half-wave formed at local loss of stability;
s is the width of the plate;
β c, d = cs 2 + dℓ 2;
β c, d, j = cs 4 + dℓ 2 s 2 + gℓ 4;
c, d, j - positive integers.
The reduced or effective width of the reduced section of the plate-shelf (type II) is denoted by s p. To determine it, we write down the conditions for the transition from the real cross-section of the bar to the reduced one:
1. The stresses in the longitudinal fibers at the initial face of the plate (at y = 0) adjacent to the rib (see figure) remain the same as those obtained by the nonlinear theory (1):
where F 2 kr = f 2 kr + 2f k0r f kr.
To determine the stress σ k2 = σ k max, it is necessary to substitute in (1) the ordinate of the most loaded longitudinal fiber, which is found from the condition: ∂σ kx / ∂y = 0.
2. The sum of internal forces in the plate during the transition to the reduced section in the direction of the compressive force does not change:
3. The moment of internal forces relative to the axis passing through the initial facet (y = 0) perpendicular to the plane of the plate remains the same:
It is obvious from the figure that
σ ′ k2 = σ k1 + y п (σ k2 -σ k1) / (y п + s п). (5)
Let us write down the system of equations for determining the reduced width of the plate s p. To do this, substitute (1) and (5) in (3) and (4):
where α = πs / ℓ; F kr, ξ = f kr f koξ + f kr f kξ + f kor f kξ;
r, ξ are positive integers.
The resulting system of equations (6) and (7) makes it possible to determine the reduced width s p of each of the plate-shelves that make up a compressed thin-walled rod that has undergone local loss of stability. Thus, the actual cross-section of the profile was replaced with a reduced one.
The proposed technique seems to be useful both in theoretical and practical terms when calculating the bearing capacity of compressed pre-curved thin-walled rods, in which local wave formation is permissible according to operational requirements.
