After the rolling bearing is installed, the rolling element and the ferrule race are in a proper pre-compacting state, which is called preloading of the rolling bearing. The purpose of bearing pre-tightening is to improve the rotation accuracy and support stiffness during operation, reduce vibration and noise, and reduce the relative sliding of the bearing rolling elements relative to the bearing and casing raceways caused by factors such as inertia torque. Angular contact bearings and shaftings that have high requirements for rotational accuracy and stiffness are usually preloaded.

The pre-tightening force is to use the external force applied during the assembly to give the bearing a proper preloading load. If the pre-tightening force is too small, there will be a gap when the bearing is working, resulting in a decrease in the support rigidity and the rotation accuracy, causing vibration and noise. The pre-tightening force increases the friction between the rolling element and the inner and outer ring raceways, and the temperature rises too fast during operation, which reduces the transmission efficiency and reduces the bearing life. Only by applying a suitable pre-tightening force can the axial clearance be eliminated, the reverse error can be reduced, the shafting rotation accuracy can be improved, and vibration and noise can be reduced. Give the bearing a proper pre-tightening force, even if the bearing after a certain period of operation, the relative position of the bearing changes slightly, the pre-applied load can still maintain the position of the inner and outer ring of the bearing, so the control of the pre-tightening force during installation is very important. of.

The usual axial pre-tightening method can obtain the appropriate pre-tightening amount by adjusting the size of the bushing or the gasket; the appropriate pre-tightening force can also be obtained by controlling the starting friction torque; and the pre-adjusting fixed pre-tightening amount can also be used. Pairs of double bearings come. Bearings that have been subjected to an axial preload will remain in their relative position during use. The bearing can also be applied with a suitable preload force using a coil spring, a fixed torque wrench or the like. Method for determining the preload in assembly:

1) Empirical testing

The empirical test method relies on the technical worker's ability to sense the torque in practice to judge the preload of the bearing. During the shafting assembly process, a preload is applied to the bearing, the spindle is manually rotated, or the shafting is placed in a low speed drive test system. The flexibility of the spindle rotation is sensed by the resistance torque of the two hands. The resistance torque received by the hands is the pre-tightening torque of the bearing on the shaft. Although this method is rough, it is simple to use and has been extensively assembled. Used by workers, it can be used as a primary test method for product assembly accuracy. However, this method has low efficiency and high labor intensity, and is not suitable for occasions with high precision requirements, and the maximum load on the shaft cannot be determined. This method is only suitable for experienced operators.

2) Measuring the rotational moment method

Use a spring balance or a simple force gauge to secure the bearing to the rotating shaft during assembly and to ensure that the shaft can rotate, then place the spring balance or simple force gauge on the shaft. Use a spring balance to apply tension along the tangential direction of the shaft. The inner ring and the shaft rotate together. When the reading is in a steady state, the final measurement result is obtained. By measuring the magnitude of the force, multiply the tangent to the axial distance value, that is, the spindle. Bearing preload torque value.

The angular contact ball bearings used in the pair have frictional torque requirements. In the case of bearing form, internal parameters and lubrication methods, the frictional moment of the bearing has a certain correspondence with the axial load, so the pre-tightening force can be determined. Refer to the frictional torque of the bearing. Therefore, by calculating the friction torque of the pair of bearings subjected to the preload load, the calculation result is compared with the measured value of the actual friction torque value to determine whether the preload force inside the bearing meets the requirements.

3) Pre-measurement preload method

Before the bearing is installed, the bearing is pre-installed using a test system similar to the actual installation, the bearing is installed in the mechanism, the axial preload force F required for the conversion is applied, and the actual distance d of the bearing is measured. The measured value is the actual required size value after the pre-tightening force is applied to the bearing. This includes the actual distance of the bearing and the clearance adjustment dimension after the bearing applies the pre-tightening force. The length of the spacer is processed according to d.

In the actual installation process, strictly control the inner bore of the bearing and the shaft, the fit of the inner ring of the bearing at the journal is not loose, and it can move flexibly in the axial direction. When assembling the inner and outer rings, it is most appropriate to push the fit with the thumb of both hands at the journal and the housing hole. Then adjust the size of the sleeve and the size of the outer end bearing cap to ensure the actual assembly size d. If necessary, a fixed-size adjustment gasket can be added during the size adjustment process to ensure that the value of the bearing pre-tightening force is compared with the predicted value. Close.

4) Measurement control method for bearing deformation

Pre-measure the relationship between the bearing friction torque and the axial load, and place the bearing on the round seat body. By formula conversion, a load equal to the pre-tightening force can be applied to the inner ring of the bearing by gravity or spring pressure control. After the bearing is stressed, the axial difference between the inner and outer rings is ΔK1 and △K2, and the value is measured by a lever dial gauge. When assembling the bearings, the pre-tightening force of the drive shaft bearings for each assembly shall be checked with a dedicated dial gauge. If the applied preload is insufficient, a washer can be added to adjust the clearance of the bearing to ensure that the preload is within a fixed range.

5) Use a fixed torque wrench

In order to eliminate the gap between the inner and outer rings of the bearing, the bearing that is axially fixed by the nut can be pressed against the inner ring of the bearing by the torsion of the nut to reach the target of the preload of the bearing. This method is a more general method, its structure is simple, and its applicability is strong, so that the pre-tightening force of the pre-tightening bearing is easy to control, and the defect is that there is no quantitative data. However, by measuring the final assembly axial dimension and adding the appropriate gasket, the preload force can be adjusted. In order to improve production efficiency and assembly accuracy, assembly is usually done in the production with a fixed torque wrench. The main feature of the fixed torque wrench is that the torque can be set and the torque can be adjusted. The fixed torque wrench can be tightened or tightened. It is used to adjust the torque and tighten the bolts. During the assembly of the bearing, pre-assembly can be carried out to obtain the tightening torque required for the pre-tightening force and then assembled.

6) Sensor method

In the demanding assembly process, we can use the sensor to achieve measurement and control. The rapid advancement of modern sensor technology has made measurement more and more simple. A torque sensor can be used during the assembly of the bearing. The torque sensor is to apply a special torsion strain gauge to the elastic shaft to be tested, and form a strain bridge. The current is supplied to the strain bridge to measure the electrical signal of the elastic shaft, and the strain signal is obtained. After amplification, after conversion, it becomes a frequency signal that is proportional to the twist. The obtained signal can be processed by the relevant instrument or computer to display the torque value. Using the previous installation method, the fixed shaft rotary bearing housing is used for measurement. By clamping with a mechanical clamp dedicated to the torque sensor, the bearing housing body can be rotated together with the measuring machine under the driving of the driving device, and the reaction torque value of the clamping device, that is, the bearing pre-tightening torque value can be measured. A common drive motor can be used as a drive to power the drive.

The control method proposed in this paper to study the preload force of bearing installation has practical significance for the installation of bearings. The adjusted spindle can be inspected by the test run method until it meets the requirements.

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