1. Specifications
Ball screws, such as NBS, are characterized by strict quality control carried out during each production process.
The high performance of the screws allows to reduce the torque of up to 70% relative to the traditional trapezoidal screws, both in the applies of general purpose (the transformation of the rotational movement into the translational movement) and in special applications (transformation transportation in the rotational movement).
1.1 Contact Geometry
Gothic arch creates a significant strength of the screw, while simultaneously providing accuracy and low torque values.
2. Parameters for selecting ball screws (with ball circulation) NBS
2.1 Accuracy class
In stock There are ball screws (with ball circulation) NBS with the following accuracy classes:
CO. C1. C2. C3. C5. C7. C10
Each accuracy class is due to the following parameters:
E. E. Ezoo. E2π.
The graph below provides a description of their values.
| Term | Link | Definition |
| Movement compensation | T. | Compensation of the length of the movement is between the theoretical and nominal length; The slight compensation value (if matched with a nominal move) often It is necessary to compensate for elongation caused by an increase in temperature or external loads. If this compensation is not necessary - the theoretical move is equal to the nominal. |
| The actual length of travel | - | The actual length of the stroke is an axial offset between the screw and the nut. |
| Middle length | - | The average length of the stroke is a straight line that is greatest approaching the actual length of the stroke; The average length of the stroke is the slope of the actual length of the stroke. |
| Deviation of the average stroke | E. | The deviation of the average stroke - is the difference between Middle and theoretical stroke length. |
| Change travel | E. Ozoo E2P |
Changes in the course called a band with two parallel lines of the average stroke. Maximum range of changes on the length of the stroke. The range of changes measured at the length of the usual part of the course of equal to 300mm. Battery error, change range at one turn (2 radian). |
| Accuracy class | C0. | C1. | C2. | C3. | C5. | C7. | C10 | |||||||
| Length Stroke [mm] |
from: | before: | ± E. | e. | ± E. | e. | ± E. | e. | ± E. | e. | ± E. | e. | e. | e. |
| 100 | 3 | 3 | 3.5 | 5 | 5 | 7 | 8 | 8 | 18 | 18 | ± 50 / 300mm. |
± 210 / 300mm. |
||
| 100 | 200 | 3.5 | 3 | 4.5 | 5 | 7 | 7 | 10 | 8 | 20 | 18 | |||
| 200 | 315 | 4 | 3.5 | 6 | 5 | 8 | 7 | 12 | 8 | 23 | 18 | |||
| 315 | 400 | 5 | 3.5 | 7 | 5 | 9 | 7 | 13 | 10 | 25 | 20 | |||
| 400 | 500 | 6 | 4 | 8 | 5 | 10 | 7 | 15 | 10 | 27 | 20 | |||
| 500 | 630 | 6 | 4 | 9 | 6 | 11 | 8 | 16 | 12 | 30 | 23 | |||
| 630 | 800 | 7 | 5 | 10 | 7 | 13 | 9 | 18 | 13 | 35 | 25 | |||
| 800 | 1000 | 8 | 6 | 11 | 8 | 15 | 10 | 21 | 15 | 40 | 27 | |||
| 1000 | 1250 | 9 | 6 | 13 | 9 | 18 | 11 | 24 | 16 | 46 | 30 | |||
| 1250 | 1600 | 11 | 7 | 15 | 10 | 21 | 13 | 29 | 18 | 54 | 35 | |||
| 1600 | 2000 | 18 | 11 | 25 | 15 | 35 | 21 | 65 | 40 | |||||
| 2000 | 2500 | 22 | 13 | 30 | 18 | 41 | 24 | 77 | 46 | |||||
| 2500 | 3150 | 26 | 15 | 36 | 21 | 50 | 29 | 93 | 54 | |||||
| 3150 | 4000 | 30 | 18 | 44 | 25 | 60 | 35 | 115 | 65 | |||||
| 4000 | 5000 | 52 | 30 | 72 | 41 | 140 | 77 | |||||||
| 5000 | 6300 | 65 | 36 | 90 | 50 | 170 | 93 | |||||||
| 6300 | 8000 | 110 | 60 | 210 | 115 | |||||||||
| 8000 | 10000 | 260 | 140 | |||||||||||
| 10000 | 12500 | 320 | 170 | |||||||||||
| Accuracy class | C0. | C1. | C2. | SZ | C5. | C7. | C10 |
| e Zoo | 3.5 | 5 | 7 | 8 | 18 | 50 | 210 |
| e 2π. | 2.5 | 4 | 5 | 6 | 8 |
2.2 Preload and axial gap
The preload and axial clearance of NBS ball screws are shown in the table below.
| Preload class | P0. | P1 | P2. | RZ | R. |
| Axial gap | Yes | Not | Not | Not | Not |
| Preload | Not | Not | Easy | Middle | Strong |
The tables below lists the main instructions when choosing the accuracy class, preload and axial gap of ball screws (with ball circulation) NBS.
| Accuracy class | Preload and axial gap | Type of nut | Type of running screw |
| From 10 | RO (with axial gap) | Single | Rolling |
| With 7. | P1 or ro. | On demand | Rolling or straightened |
| With 5. | On demand; Standard 0TNBS-P2 |
On demand | Shag errors |
| With 3. | On demand; Standard 0TNBS-P2 |
On demand | Straightened with a certificate of control Shag errors |
| Model | Single nut | Double nut |
| 1605 | 1 ± 3 n | 3 ± 6 N |
| 2005 | 1 ± 3 n | 3 ± 6N. |
| 2505 | 2 ± 5 n | 3 ± 6N. |
| 3205 | 2 ± 5 n | 5 ± 8N. |
| 4005 | 2 ± 5 n | 5 ± 8N. |
| 2510 | 2 ± 5 n | 5 ± 8N. |
| 3210 | 3 ± 6 N | 5 ± 8N. |
| 4010 | 3 ± 6 N | 5 ± 8N. |
| 5010 | 3 ± 6 N | 8 ± 12 N |
| 6310 | 6 ± 10 n | 8 ± 12 N |
| 8010 | 6 ± 10 n | 8 ± 12 N |
2.3 Pitch thread
The choice of the screw step depends on the following formula:
where:
Pp \u003d screw step [mm]
Vmax \u003d Maximum speed of moving system [m / min]
n Mach \u003d maximum screw rotation mode [min 1]
In the event that the result of the equation is not a whole result, you should select the value rounded to the large side, choosing between the steps available.
Given the possible variability of axial loads caused by, for example, the presence of inertia forces, the load value is indicated, as the "average dynamic load PM", which defines the same variable load coefficients.
2.4.1 Middle Dynamic Load
To calculate the ball screw, exposed by variable working conditions, are used average values \u200b\u200bof PM and N M:
P M \u003d average dynamic axial load [n]
n m \u003d average speed [min -1]
Under continuous load and variable speed conditions, you can reach the following values:
Under the conditions of variable load and continuous speed, you can reach the following values:
Under the conditions of variable load and variable speed, you can reach the following values:
The selection of the screw depending on the affecting and (or) the in-demand thrust is due to the following values:
Soa values \u200b\u200bare given in dimensional tables.
2.5.1 The static stock ratio A s The static static reserve coefficient A s (or the static strength factor) is determined by the following equation:
2.5.2 Fitness Firm F H
The hardness coefficient takes into account the surface hardness track tracks:
where:
hSV10 track hardness \u003d actual rolling track hardness, expressed in vickers units with test load equal to 98.07 N
700HV10 \u003d hardness equal to 700 Vickers units at a test load equal to 98.07 (700HV10 ≈ 60 HRC)
2.5.3 Precision Factivity F AC
The accuracy ratio takes into account the tolerance of the screw processing, and therefore the accuracy class corresponding to the standard.
The table shows some examples.
The need for a static reserves of the strength A S\u003e 1 is made possible by the presence of impact and (or) vibrations, starting and stopping moments, random loads that can lead to system malfunction.
The table below shows the values \u200b\u200bof the static strength of strength taking into account the type of application.
Values \u200b\u200bwith A are given in dimensional tables.
2.7 Nominal resource L
The nominal resource L (this theoretical mileage, made at at least 90% of the indicative number of identical ball screws (with the circulation of balls), exposed to the same load conditions, without showing signs of material fatigue) is determined by the following conditions:
2.7.1 Nut without preload
For ball screws (with the circulation of balls) with a nut without preload, the calculation of the nominal resource, expressed among the revolutions, is determined by the following formula:
where:
P M \u003d average used dynamic axial load [N]
where:
a 1 \u003d reliability factor
2.7.2 Coefficient A 1
The coefficient A 1 takes into account the possibility of non-rotation c%.
| C% | 80 | 85 | 90 | 92 | 95 | 96 | 97 | 98 | 99 |
| a 1. | 1.96 | 1.48 | 1.00 | 0.81 | 0.62 | 0.53 | 0.44 | 0.33 | 0.21 |
It should be noted that for C% \u003d 90 a 1 \u003d 1.00
2.7.3 Nut with a pretension
The reality of subsequent formulas is due to maintenance of constant preload; Otherwise, you should consider the case with a nut without preload.
For ball screws (with ball circulation) with a pretension nut, the calculation of the nominal resource, expressed among the revolutions, is determined by the following formula:
where:
L 10 \u003d Nominal resource [Turns]
L 10 B - (with A / PM 2) x 10 6
L 10A and L1 0B Nominal resources for two halves of the nut.
In the event that the operating conditions do not correspond to the above conditions, the following formula should be used:
where:
L 10 \u003d Nominal resource [Turns]
L 10 A \u003d (C A / P M1) 3 x 10 6
L 10 B - (with A / PM 2) x 10 6
a 1 \u003d reliability coefficient;
f HO \u003d Hardness Coefficient (See Static Static Reserve A S)
f AC \u003d accuracy coefficient (see the static stock of A S static stock
P M1 and P M2 - medium axial dynamic loads for two halves of nut;
P R \u003d pretension force [n]
2.7.4 Nominal service life in hours LH
Having L 10 (nomineeRears, expressed among the revolutions), one can calculate the nominal resource in the hours of operation L H;
where:
L M \u003d Duration [Clock]
n m \u003d average speed [min -1]
m i \u003d speed [min -1]
qi \u003d percent distribution [%]
2.7.5 Nominal service life in km LKM
Having L 10 (nominal resource, expressed among the revolutions), you can calculate the nominal resource of the distance traveled in KM L KM.
where:
L km \u003d nominal resource [km]
P H \u003d screw step [mm]
The following table shows the instructions of the Typical Ball Screw Work Resource for General Use Applications.
2.8 Fastening Method
As a rule, there are the following types of fastening of the ball screw:
The applied fastening method is the function of the application conditions, which ensures the rigidity and the required accuracy.
2.9 Critical speed of rotation
The maximum rotation speed of the ball screw should not exceed 80% of the critical speed.
The critical speed of rotation is a point in which the screw begins to vibrate, producing a resonant effect caused by the coincidence of the vibration frequency with the natural frequency of the screw.
The value of the critical speed depends on the inner diameter of the driving screw, the method of fastening the edges and the length of the free magnitude of the deflection.
Critical speed is measured by the following formula:
where:
n Cr \u003d Critical Speed \u200b\u200b[Min -1]
f KN \u003d fastening method coefficient
d 2 \u003d internal diameter of the running screw [mm]
l n \u003d free value of the deflection [mm]
Depending on the type of fastening, the values \u200b\u200bof F Kn are supplied:
where:
DO \u003d nominal diameter [m m]
Da \u003d diameter of balls [mm]
A \u003d Contact angle (\u003d 45)
The length of the free magnitude of the deflection L n is determined depending on:
-Gike without preload
l n \u003d distance between attachments [mm] (in the case of fastening "in-point - free", the distance between the free edge of the screw and the nest should be taken into account)
-Nut with preyagoma
l n \u003d The maximum distance between half nuts and the mounting [mm] (in the case of the "LOVE-free" attachment, should consider the maximum distance between a half nut and the free edge of the screw)
n Mach \u003d Maximum Screw Rotation Speed \u200b\u200b[Turns / Min]
Critical load is the maximum axial load that the screw may be subject to without disturbing the stability of the system; In the event that the current maximum axial load reaches or exceeds the value of the critical load, it is created. new form The impact on the screw, which is called a "peak load", causing additional deflection in addition to simple compression.
This phenomenon associated with the elastic properties of the component becomes more sensitive when the high length of the swivel of the screw of the screw will have decent attention to the value relative to its cut. The value of the critical load is determined by the following formula:
where:
P Cr \u003d Critical Load [N]
f kp \u003d fastening method coefficient
d 2 \u003d Inner diameter of the driving screw [mm] (see Critical Speed)
l Cr \u003d Length of the free value of the deflection [mm]
Depending on the type of fastening, the values \u200b\u200bof FKP are supplied:
| Low-permanent - deline | f Kr \u003d 40.6 | |
| Local - support | f KP \u003d 20.4 | |
| Support - support | f KP \u003d 10.2 | |
| Local - free | f KP \u003d 2.6 | |
To calculate the critical load, the value of La is determined by the maximum distance between a half nut and fastening.
For greater safety, the maximum allowable axial load should be considered as equal to half of the critical load:
P max \u003d maximum allowable axial load [n]
2.11 Stiffness
The axial rigidity of the displacement system equipped with a ball screw is determined by the following formula:
where:
K \u003d axial rigidity system
P \u003d axial load [n]
e \u003d axial deformation of the system [μm]
The axial rigidity of the system K is the function of the axial stiffness of the individual components, which make it: the chassis screw, nut, supports, connecting support elements and nut.
where:
K s \u003d axial rigidity of the running screw
K n \u003d axial rigidity nut
K \u003d axial rigidity supports
K H \u003d axial stiffness connecting support elements and nuts
2.11.1 KS- axial rigidity of the running screw
The KS stiffness value is the functions of the fastening system.
Fastening Method: Low-Purpose - Local
where:
d 2 \u003d Inner diameter (see Critical speed of rotation)
l S \u003d Distance between the middle axis of two mounts
Fastening Method: Local - Support
where:
d 2 \u003d internal diameter [mm] (see Critical Speed)
l s \u003d The maximum distance between the average axes of the attachment and the nut [mm].
2.11.2 K N - axial rigidity nuts
Double nut with preload
where:
K \u003d tabular rigidity
F PR \u003d preload force [n]
Simple nut without preload
The value K n is determined by the following formula:
where:
P \u003d axial load [N]
C A \u003d Load Dynamic Ability [N]
2.11.3 kV - axial rigidity supports
The axial rigidity of the screw support is caused by the rigidity of bearings.
In the case of rigid radial bearing bearings with angular contact, the following formulas are used:
where:
bV \u003d axial bearing strain
Q \u003d load on each ball [n]
β \u003d contact angle (45 °)
d \u003d diameter of balls [mm]
N \u003d number of balls
The stiffness of the connecting support elements and nuts is the characteristic of the machine, and therefore does not depend on the screw system, nuts, supports.
2.12 Operating temperature
In the case of fastening the type "is in-point-permanent", a possible thermal extension, caused by increasing the screw temperature during operation, such an extension, if provided according to the appropriate way, has an additional axial load on the system, which can cause a system to solve the system. To solve Problems It is necessary to perform sufficient screw preload.
where:
Al \u003d change of length [mm] A \u003d thermal expansion coefficient
(11.7 x 10 -6 [° С -1])
L \u003d Screw Length [mm]
AT \u003d temperature changes [° C]
2.13 Lubricant
For lubrication of ball screws, NBS needs to be taken into account the following instructions.
2.13.1SMazing with liquid lubricant
This type of lubrication should be preferred if operating at high speeds of rotations. Lubricating liquid substances that can be applied are endowed with the same characteristics as the substances used to lubricate rolling bearings (from VG 68 to VG 460). The viscosity selection is the function of operating characteristics and the working environment: temperature, rotation speed, existing loads; Only for screws with low rotation mode, high viscosity classes are recommended (about VG 400).
In this case, it is not necessary to pay special attention to maintenance with the exception of constant security in the lubricating oil system (intervals for re-lubrication are shorter than in the installations using greased lubrication).
In any case, the instructions of the manufacturer of liquid oil should be followed.
2.13.2 Consystem grease
Lubrication with grease is intended for low rotational speeds.
When choosing a grease, the prescriptions applied to lubricating rolling bearings should be taken into account; Therefore, it is recommended to use a lithium soap-based consistent lubricant, and not lubricants with solid additives (as, for example, MOS2 or graphite lubricants), with the exception of very low rotation modes; However, it is recommended to adhere to the instructions of the consistency grease manufacturer.
3. Moment and rated power
To approximate the calculation of the torque and engine power values \u200b\u200bfor the transformation of the rotational movement into a straight movement, you need to use these formulas:
where:
Pmax \u003d Maximum active load [H]
Pp \u003d step of thread [mm]
ɳ V \u003d Mechanical CPD of the screw (OK 0.9)
ɳ T \u003d Mechanical Engine Transmission efficiency - Screw
(transmissions with gear wheels ɳ T \u003d 0.95 + 0.98);
z \u003d gear ratio engine - screw
In the case of direct engine connection - screw, z \u003d 1 and ɳ 2 \u003d 1.
where:
Nm \u003d Rated engine power [kW]
Mm \u003d nominal torque [nm]
Pmach \u003d maximum screw rotation mode [min]
z \u003d gear number Engine - screw (PTC x z \u003d n Motor)
In the case of the transformation of the straight line in the rotational motion, there is:
M R \u003d moment of load [nm]
P MAX \u003d Maximum active load [H]
P H \u003d Thread Pitch [mm]
ɳ R \u003d mechanical efficiency (approx. 0.8
4. Montaja examples
| Nut type code | Direction Screw |
Nominal diameter Screw [mm] |
Step [mm] | Type of flange | Processing code | Class Accuracy |
General length Screw [mm] |
The code preload |
||
| Single or Double |
Flange or Not flanse |
A type | ||||||||
| V \u003d single W \u003d Double |
F \u003d flange C \u003d flange |
U. I. E. TO M. |
R \u003d Right L \u003d left |
_ | - | N \u003d without cut S \u003d single slice D \u003d double slice |
C \u003d straightened F \u003d rolled |
With 0. With 1. With 2 With 3. With 5. With 7. From 10 |
- | P0. P1 P2. RZ P4 |
6. NBS calculation program for ball screws (with ball circulation)
In our online store you can purchase yourself
Or, by contacting our specialists for the free phone number 8 800 700 72 07
As well as sending a request to email [Email Protected]website
Herotor couples
In this article, I want to tell about the principle of operation of screw (or gerotrious) pumps. The pumps of this type are widespread in industry, and the description of their work is far from everywhere.
With the same appearance, these pumps may have completely different operating parameters.
Let's try to figure out what the difference is.
The figure shows a typical screw pump in the context:
Where: 1. Bearing node, 2. Shaft seal, 3. Hinges, 4. Railing, 5. Screw (rotor), 6. Oboem (stator).
Herotor pair (working body screw pump), Call a pair of rotor stator (or screw-clip). When rotating the rotor in the stator, the liquid moves along the spiral stator channel. Thus, there is a pumping of fluid.
The stator is an internal N + 1-nicer spiral made, as a rule, from elastomer (rubber), inseparable (or separately) connected to a metal rope (sleeve).
The rotor is an external N-n-naochety, which is manufactured, as a rule, from steel, followed by or without coating.
It is worth indicating that the most common aggregates with a 2-nicer stator and a 1-hot rotor, such a scheme is classical for almost all manufacturers of screw equipment.
An important point is that the centers of rotation of the spirals, both the stator and the rotor are shifted by the amount of eccentricity, which allows you to create a pair of friction in which when rotoring the rotor inside the stator is created closed hermetic cavities along the entire axis of rotation. In this case, the number of such closed cavities per unit length of the screw pair determines the final pressure of the unit, and the volume of each cavity is its performance.
Difference of the pumps from each other is precisely the use of different geometry of tower steam.
There are four main types of tower steam, which are taken to indicate the letters of the Latin alphaate: S, L, D, P.
In our country and neighboring countries, so far pumps are produced only with pairs S and L. more complex pair D and P are made only abroad, for example in Germany.
Types of hetero pairs:
1. Geometry "S":
Turns: 1/2
Performance: 100%
Differ. Pressure: 12 bar
Benefits of geometry S:
Very smooth feed
Compact dimensions Despite a large number of steps
big square Entrance cross sections
Low flow rate / high suction ability
Possible pumping compressed particles
Pumping large particles
It should be noted that the clip with geometry "S" will be "locking", i.e. Through it, with a stopped pump, the fluid will not flow.
2. Geometry "L":
Turns: 1/2
Productivity: 200%
Differ. Pressure: 6 bar
Advantages of geometry L:
Good volumetric characteristics with a long interremant period due to the long contact line between the rotor and the stator
Compact dimensions at high performance
Less friction speed
The clip of this type is a "unmarked". When the pump is stopped, the fluid can flow through the gauge pair. 
3. Geometry "D":
Turns: 2/3
Productivity: 150%
Differ. Pressure: 12 bar
Benefits of geometry D:
very small dimensions when high pressure and productivity
Almost idle passchka
High accuracy of delivery
4. Geometry "P":
Turns: 2/3
Productivity: 300%
Differ. Pressure: 6 bar
Benefits of geometry P:
Compact sizes with very high performance
Almost no ripple
High accuracy of delivery
Good volumetric indicators, long interremant period due to the long contact line between the rotor and the stator
We led examples of geometry of tower pairs of the same length. From the drawings it can be seen that the number of turns of the pairs of "s" is twice as high as the "L" pair with a single length. This affects the maximum pressure of the trootor pair. Than pain turns, the higher the maximum pressure.
As you can see, each gauge pair gives a certain maximum pressure (if you consider the pairs of the same length).
The question arises: what to do if the output pressure needs more (or less) than one or another pair issues.
In this case, they increase (decrease) the length of the geerot pair. For example, the increase in the length of the pair "s" is twice, leads to an increase in the macquimal pressure of the pump by 2 times, i.e. Pressure will increase to 12 atmospheres.
Screw pumps can also be manufactured in different versions To work in various conditions.
Pump layout options:
1. Classic horizontal layout with bearing rack 
2. Horizontal layout without bearing rack 
3. Additional subference screw 
4. Bunker and auger feeder 
5. Additional proceedor (chopper) 
Video work of the barrel screw pump
The screw pair is two parts (screw and nut) connected via the screw surface. The screw pair is used to convert the rotational movement to the translational, or vice versa.
Screw pairs are with a triangular, rectangular and round profile of the screw surface.
In the technique, the screw surface is often called carvings. Threads with a triangular profile are divided into metric, inch, trapezoidal and stubborn.
The main geometric parameters of the metric thread according to GOST 9150-81 (Fig. 5.3):
N. - height of the source profile (equilateral triangle);
d., d. 2 , d. 1 - the diameters of the outer, medium and internal;
Fig. 5.5.Screw pairs with rectangular and triangular carvings:
in - screw, g - nut, Rand d. 2 - Step and medium thread diameter
step R - the distance between the nearest similar contour points along the line parallel to the thread axis;
profile angle \u003d 60;
the angle of lifting the screw thread line (Fig. 5.4).
P
Fig. 5.6.Screw pair: v. t. and v. a. - district and durability of the nut; d. r - outer diameter of nut; - The angle of lifting the screw line
or 
Here t. - The period of rotational movement.
Rotational Movement Nut
where I. n. - Corner speed and speed of nut.
Speed \u200b\u200bof progressive nail
Consider a screw pair with a rectangular thread profile (Fig. 5.7). We assume that the axial load F. but the screw focuses on one turn and that the nut reaction is applied in the middle of the thread, i.e. by d. 2 .
Fig. 5.7.To the definition of friction forces in a screw pair with a rectangular thread profile
The movement of the screw over the screw can be considered as the movement of the slide along the inclined plane with the angle of inclination (Fig. 5.8).
With a uniform movement of the slider, the following equilibrium equation is valid:
where F. t. = M./r. 2 - horizontal force acting on the slider (nut), M. - torque pair of forces attached to the nut at a distance r. 2 from the screw axis in the plane perpendicular to the axis (in the horizontal plane).
From the plan (Fig. 5.9) it can be seen that driving force F. t. necessary for the uniform movement of the slider upwards on the inclined plane is associated with the size of the axial force F. but By relationship
F. t. = F. but TG ( + ),
and torque M. Couples attached to the nut will be
M. = F. t. r. 2 = F. but TG ( + ) r. 2 .
From the law of Kulon Amonton follows
F. T \u003d. f. N. = N. TG .
From the plan of the forces we define the power of friction acting in the screw pair:
Sharing the numerator and denominator of this expression on COS and considering that f. \u003d TG , get
In a screw pair with triangular threads Normal power N. > F. but (Fig. 5.10), therefore the force of friction F. T is greater than in the screw pair discussed above with a rectangular thread profile. Respectively
Fig. 5.10. Ratosities between normal with axial forces in screw pairs with triangular and rectangular thread profiles
the angle of friction and the coefficient of friction f. w. a screw pair with triangular thread will be greater than in a screw pair with a rectangular thread profile.
In a screw pair with triangular thread, the coefficient and the friction angle will be
and 
.
Received for a screw pair with a triangular thread profile coefficient f. And the angle friction is called the resulting coefficient and angle of friction.
To create software with software numerical control, it is necessary to use ball-screw pairs. They differ not only external speciesbut also design. To select a specific model, you should familiarize yourself with the structure and components of the SCVP.
All types of CNC machines for CNC machines are designed to convert the rotational movement to the translational. Constructively consist of a housing and a running screw. Differ from each other with dimensions and technical characteristics.
The main requirement is to minimize friction during operation. For this, the surface of the components undergoes a thorough grinding process. As a result, during the movement of the running screw, there is no sharp jumps of its position relative to the hull with bearings.
Additionally, to achieve a smooth stroke, no friction is applied relative to the pin and the case, but combustion. To obtain this effect, the principle of ball bearings is applied. Such a scheme increases the overload characteristics of the SVP for CNC machines, significantly increases efficiency.
Basic components of ball-screw transmission:
Despite all the advantages of this design, ball-screw transmissions for CNC are used only for medium and small machines. This is associated with the possibility of a screw deflection when the housing is locally in its middle part. Currently, the maximum allowable length is 1.5 m.
Similar properties have the transfer of a screw-nut. However, this scheme is characterized by rapid wear of components due to their constant friction.
Relative ease of design and the possibility of making ball-screw transmission with various characteristics Expands its area of \u200b\u200buse. Currently, the ball-screw pairs are essential components of homemade milling machines with numeric software control. Well, on this area of \u200b\u200bapplication is not limited.
Due to its universality, the SVP can be installed not only in CNC machines. Smooth stroke and practical zero friction make them indispensable components in accurate measuring instruments, medical installations, in mechanical engineering. Often, for the configuration of homemade equipment take spare parts from these devices.
This became possible due to the following properties:
However, the disadvantages of the CNC equipment should also be taken into account. First of all, it includes the complex design of the case. Even with insignificant damage of one of the components, the ball-screw transmission will not be able to perform its functions. Restrictions on the rotational speed of the screw are also superimposed. Excess this parameter can lead to vibration.
To reduce the axial clearance, the assembly is performed with a tension. To do this, the balls of increased diameter or two nuts with axial displacement can be installed.
To select the optimal model of ball-screw transmission for machine tools with numeric software, you should familiarize yourself with the technical characteristics. In the future, they will affect the operational qualities of the equipment and the time of its fierce operation.
The main parameter of the SVP for CNC machines is the accuracy class. It determines the degree of error of the position of the movable system according to the calculated characteristics. The accuracy class can be from C0 to C10. The error of movement should be given by the manufacturer, indicated in the technical passport of the product.
| Accuracy class | C0. | C1. | C2. | C3. | C5. | C7. | C10 |
| 300 μm error | 3,5 | 5 | 7 | 8 | 18 | 50 | 120 |
| One turnover error | 2,5 | 4 | 5 | 6 | 8 |
In addition, when choosing, you need to consider the following parameters:
These data must be predetermined. It should be remembered that the actual characteristics of the SVP for CNC equipment cannot differ from the calculated one. Otherwise, this will lead to the wrong operation of the machine.
The number of turns of balls for one circle will determine the degree of transmission of torque from the shaft of the case. This parameter depends on the diameter of the balls, their quantity and sections of the shaft.
After selecting the optimal model, you must think through the SVP installation scheme to the CNC machine. For this, the design drawing is pre-drawn, other components are purchased or manufactured.
During work, not only should be taken into account. specifications Ball-screw transmission. Its main purpose is the movement of the machine elements on a certain axis. Therefore, it is necessary to think in advance to the mounting of the processing unit to the CPU machine to the CNC machines. It is necessary to verify the size of the seating holes, their location on the housing. It should be remembered that any mechanical processing of ball-screw transmission may entail negative changes to its characteristics.
Installation of installation in the CNC machine housing.
After that, you can perform the first trial launch of the equipment. In the process of work there should be no oscillations and vibrations. If they appear to perform additional calibration of components.
When the SVP breakdowns during the operation of the CNC machine, the transmission can be made independently. To do this, you can order a special kit. With the peculiarities of restoration work, you can get acquainted in the video material:
Most compressor manufacturers declare a warranty overhaul Compressor up to 40,000 hours. For ideal conditionsthat are not in real exploitation.
The lifetime of modern supporting bearings of the screw pair has not yet reached the level when the intervention and their replacement are not required during this time. On average and honest, bearings work from 10,000 to 20,000 hours, depending on the quality of bearings installed in the screw unit at the factory and regularity maintenance At the owner of the compressor. After the operation of this time, there is noise under load in the screw pair, increasing as the wear increases another 5000-15000 thousand hours. As a result, the compressor begins to overheat and the screw unit clinics due to the changing gaps in the screw pair. In case of serious overheating, the ends of the screw pair are "welded" to the body, which dramatically increases labor costs to repair the screw block. Or bearings fall apart, leaving for them unpredictable damage - from the local overheating of the screw pair, to the jackets and the cooler screw shanks.
In any of these cases, we will perform the following work:
Replacing the support bearings of the screw pair.
- Replacing the glands of the screw shafts.
- Setting the working gaps of the screw block.
- Restoring the working ends of the screws.
- Restoring the profile of screws.
- Restoring the shank of the drive screw shaft.
- Restoration of the housing of the screw block.
Works are carried out equally successfully, regardless of the manufacturer of the screw block, be it: Ceccato, Aerzener, Ghh-Rand, Rotorcomp, Fini, Enduro, Tamrotor, Termomeccanica, VMC, domestic arsenal or any other manufacturer.
An example of work, click on the title to view:
Dual screw block with direct transmission through the gearbox. The unit regularly worked for 5 years, after which, after which the increasing, noise and vibrations appeared during the operation of the screw block. The weight of 1100kg and the size of the unit inspires respect to anyone who stands next to this work of engineering thought.
After coordinating the volume of work with the customer, the screw block was defecting with a complete disassembly:
The autopsy showed the complete wear of the support bearings of both screw steam, one piece is slightly larger, the second is slightly smaller, and small local loans on one of the screw blocks. Apparently, the abundant power of this unit saw and ate some very hard garbage:
Bearing wear approached the critical that in addition to the Musor, also affected the ends of the screw rotors:
In the crankcase and closed cavities, a metal chip was present, which spoke about the limit wear of bearings and the upcoming overheating and jamming. If it were not for the accuracy and attentiveness of the serving staff of the compressor, then a little more and the volume of repair would be resolved at times:
After the results of the defectation, they ordered new bearings for screw pairs, made them replace, as well as replacing the gearbox bearings. Collected the entire metal chips, the crankcase was rinsed, removed all the loops on the rotors and covers. Carefully collected and most accurately and carefully configured both screw blocks to avoid doss-load at work.
Now the next 4-5 years, the customer is not about what is worried, besides the timely replacement of oil and filters on this unit.
Screw block S. toothed transmission. The trouble sneaks from the Siemens electric motor, which broke its bearings and, accordingly, the gear gearbox, which led to the jam. The swords on the toothed gears did not cut and happened that it should have happened - the split small gear and the shank of the leading rotor.
An analysis of the material of the screw pair showed that this is an ordinary cast iron. Effective from the point of view of friction, but poorly repaired. It also explains why the steel key is not cut and makes the repair only more interesting.
Killed gear:
Damage to the lead shaft shank:
Given the fact that the cost of the new screw block is 4-5 times more expensive to repair, the decision by the client was made immediately.
Restored shank and keypads. Once again, we draw attention to the material of the screws - cast iron:
Ordered and installed a new gear:
Of course, the support bearings were changed, simultaneously improving the design - instead of one stubborn-radial bearing installed two, which fixed the working clearance in the screw pair and made it even more reliable than when released from the factory:
The Rotorcomp screw unit from the RENNER-Kompressoren compressor arrived at the repair base in a robust state, honestly spent its 5 years since 2007:
Despite regular service The compressor time took its own, wear of the support bearings reached critical tolerances, the oil no longer helped in cooling the screw pair and the screw rotors were overlapped into the working surface, welded to it. This type of repair is always unpredictable by volume of work and receiving a blank-blanche card started disassembling the screw block. It was decided to disassemble slowly and gently to minimize damage with the connector of the welded parts. After the persistent struggle for safety, the screw pair surrendered with minimal losses for the customer's wallet:
The damage to the cover of the screw block is also minimized:
Restored the working surfaces of the ends of the screws and the plane of the lid with the help of welding, turning and milling machines, as well as the invaluable knowledge and experience of our mechanics. Replaced the support bearings of the screw pair. Collected and configured the screw block. They returned to the customer with comments to whom to contact and what to do, when after 4-5 years of rigid operation of the compressor, the working temperature of the oil will begin to grow again.
