What is the preload of the bearing, the purpose of the preload of the rolling bearing

The preload of the bearing is the force applied in advance to enhance the reliability and tightness of the connection before receiving the working load (the connection mode and use are diverse), so as to prevent the gap or relative slippage between the connecting parts after receiving the load.

The amount of preload is limited not only by the strength of the screw material, but also by the strength of the material to be connected. When the material of the inner and outer threads is the same, only the strength of the external threads can be checked.

The strength of the thread should also be checked for the connection with short screw length, the connection composed of non-standard threaded parts, and the threaded connection with axial load with a large difference in the strength of the internal and external thread materials.

For example, for the fixation of elastic elements of a certain type of product, because the base material connected by the screw is die-cast aluminum alloy YL113, its strength is much lower than that of high-quality carbon structural steel 20, the strength of the thread profile on the aluminum alloy should be checked, mainly the shear stress and bending stress of the thread material.

The axial force exerted between the inner and outer rings of the bearing. Since there is more or less clearance (clearance) between the bearing ring and the rollers, applying a certain amount of preload can eliminate the clearance and reduce the noise and vibration during bearing operation. The preload should not be too large, otherwise it will accelerate the wear of the bearing, and in extreme cases, the bearing will be stuck.

In CNC machine tools, the bearing supporting the ball screw must apply preload to eliminate axial clearance, the purpose of which is to reduce the reverse error, improve the rigidity of the shafting system and the accuracy of rotation, and reduce vibration and noise.

Preloading is to make the bearing rolling element and the inner and outer rings produce a certain preload deformation, so as to keep the inner and outer rings of the bearing in a compressive state. In a spindle system, when the spindle system is not affected by external loads, the force exerted by the rolling elements on the outer ring of the bearing is called the bearing preload. The magnitude and direction of the preload force varies depending on the type of bearing, the mounting conditions and the operating condition.

Improve the axial and radial positioning accuracy, reduce the runout of the shaft, improve the rotation accuracy, improve the rigidity of the bearing and improve the gear meshing accuracy, inhibit the rotational sliding, revolving sliding and rotating sliding of the rolling elements, reduce abrasion, and prevent the bearing abnormal sound caused by vibration and resonance.

Constant pressure preload can be used to absorb changes in the load of the spring and shaft expansion and contraction caused by the temperature difference between the shaft and the housing during operation, so the preload change is small, and stable preload can be obtained, so it is advisable to use positioning preload when high rigidity is required. For thrust bearings that require high-speed rotation, prevent axial vibration and are used for horizontal shafts, it is advisable to use constant pressure preloading.

Precautions for rolling bearings.

When the bearing is loaded into the shaft, the outer ring of the bearing can not be directly knocked with a hand hammer, and the auxiliary tools are applied, and the force is acted on the inner ring through the auxiliary tools. When the bearing is fitted into the bearing bore, the force should be applied to the outer ring of the bearing. If you knock on the outer ring to let the outer ring be stressed in turn, so that the outer ring is gradually loaded into the hole, the outer ring will be unevenly stressed, resulting in tilting and scratching the hole wall.

For this reason, auxiliary tools are often used to exert force on the outer ring, so that the bearings are easy to fit in and do not damage the rolling bearings and raceways. The use of auxiliary tools can prevent dirt from entering the bearing during installation, and make the bearing stress position reasonable and uniform, and improve the assembly quality. Therefore, auxiliary tools should be used as much as possible for assembling rolling bearings.

The above method is used when the amount of interference is not large.

1. Eliminate bearing clearance;

2. Improve the rigidity of the bearing;

3. Improve the rotation accuracy of bearings.

Bearing preload refers to the axial or radial load pre-added to ensure the normal operation of the bearing, also known as preload.

The main purpose of high-speed precision spindle bearing preload is to improve the rotation accuracy of the bearing, avoid the sliding of the rolling elements at high speed, improve the rigidity of the bearing, reduce the axial and radial momentum of the support, improve the bearing damping, reduce noise and improve the service life of the bearing. Radial preload is generally achieved by adjusting the radial clearance of the bearing, and the purpose is also to ensure the normal operation of the bearing.

Bearing preload method:

1. Radial preload method.

The radial jacking method is mostly used in tapered bore bearings that bear radial loads, a typical example is a double-row precision short cylindrical roller bearing, which uses a nut to adjust the axial position of this bearing relative to the tapered journal, so that the inner ring has a suitable amount of expansion and obtains a radial negative clearance, this method is mostly used in machine tool spindles and jet engines.

2. Axial preload method.

The axial preload method can be roughly divided into two types: positioning preload and constant pressure preload.

1) In the positioning preload, the appropriate preload can be obtained by adjusting the size of the bushing or gasket; It can also be adjusted by measuring or controlling the starting friction torque to adjust the appropriate preload; It can also directly use the pre-adjusted preload of the paired double bearing to achieve the purpose of preloading, at this time generally do not need the user to adjust again, in short, where the bearing that has been preloaded axially, its relative position will certainly not change when used.

2) Constant pressure preloading is a method of using coil springs, disc springs, etc. to make the bearing get suitable preload. The rigidity of the preloaded spring is generally much less rigid than the bearing, so the relative position of the bearing with constant pressure and preload will change during use, but the amount of preload will remain roughly the same.

In order to prevent the nut from loosening during rotation, appropriate anti-loosening measures should be taken, and the bearing should be tightened with a grooved nut and a stop washer to prevent the nut from loosening. When tightening, the inner teeth of the washer should be placed in the keyway of the shaft, and then any external tooth should be bent into the mouth of the nut.

For the occasion of high bearing speed and large axial load, the end face of the nut in contact with the bearing ring should be perpendicular to the axis of rotation of the shaft, otherwise tightening the nut will destroy the correct installation position of the bearing, reduce the rotation accuracy and service life of the bearing, especially when the fit between the inner hole of the bearing and the shaft is loose, it should be strictly controlled.

The shaft is fastened with an elastic retaining ring in the case that the axial load is not large, the bearing speed is not high, and it is difficult to turn the thread on the journal, and the elastic retaining ring with a rectangular section can be used to fasten. This fastening method is easy to assemble and disassemble, occupies a small area, and has low cost.

The quality of bearing installation will affect the accuracy, life and performance of the bearing. Therefore, please thoroughly study the mounting of the bearing, that is, install the bearing according to the operating standards including the following items.

Preload refers to the use of the bearing at zero clearance by changing the relative position of the inner and outer rings before the bearing is loaded. The purpose of preload is to eliminate bearing clearance, improve bearing rigidity and bearing rotation accuracy.

The main function of preload is to improve the stiffness of the bearing and suppress vibration and noise.

However, excessive preload increases the friction of the bearing, increases the temperature, and reduces the noise life of the bearing. Therefore, it is important to choose the right preload.

Bearing in the installation process to control the amount of preload is mainly angular contact ball bearing, eccentric bearing, tapered roller bearing, taper bore double row cylindrical rollers, etc., in the final stage of these types of bearing installation, is to adjust the clearance more accurately, that is, to control the amount of preload (load), especially for the machine tool spindle and other shafts that have strict requirements for rotation accuracy, noise, temperature rise, not only in the initial installation to control the amount of preload (load) to adjust the clearance, but also in use also need to adjust. There are many ways to control the amount of preload, and here are several ways to control the amount of preload to adjust the clearance.

1) Measure the starting friction torque of the eccentric bearing, measure the relationship between the starting friction moment of the bearing and the axial load in advance, and adjust the preload by controlling the starting friction torque, which is often used for the axial preload of tapered roller bearings installed in pairs.

2) Measure the axial displacement of the bearing, and measure the relationship between the axial load and the axial displacement of the eccentric bearing in advance for the taper bore bearing, so as to control the axial displacement to adjust the preload.

3) Measure the deformation of the preloaded spring, measure the relationship between the load and the deformation of the spring in advance, and adjust the load of the constant pressure preload by controlling the deformation.

4) Measure the nut tightening torque, and adjust the preload amount by controlling the nut tightening torque when the nut is used to preload the bearing.

5), the use of bearing end cover padding, will cause one end to be tightened, the other end of the bearing is not put into the gasket, tighten the screw, when the shaft can not rotate freely, indicating that there is no clearance in the shaft system, with the thickness gauge equal to the end cover and the bearing seat end face clearance, the value plus the required clearance value is the thickness of the gasket.

6), the use of spacer, the length of the inner ring spacer sleeve can be calculated by the length of the outer ring spacer sleeve of the bearing and the size of the support, can also be measured to determine the detection of the eccentric bearing preload load is more difficult, a few with special instruments to detect, most of the axial with dial gauge to measure the axial, radial displacement or measurement of the starting friction torque to detect, some foreign bearing companies in order to make the preload load always in the best value, the use of special instruments and some structures to detect and adjust the preload load, to achieve the preload load can be controlled.

The preload of rolling bearings refers to the installation of bearings inward.

The gap between the rolling element and the inner and outer rings is eliminated, and a certain initial pressure and elastic deformation are formed, so as to reduce the actual deformation of the bearing under working load, so as to improve the supporting stiffness and improve the rotation accuracy. Preload is a preload or preload applied to a bearing before it is subjected to a working load. This preload not only improves the working performance of the spindle structure, but also extends.

Long bearing service life. Therefore, it can be said that the preload of angular contact ball bearings is an indispensable work, which directly determines the rotation accuracy of the bearing mounting components.