Selection and adjustment of rolling bearing clearance

First, the choice of rolling bearing clearance

 

  Bearing clearance has a great influence on bearing life, temperature rise, noise, etc. Therefore, it is necessary to select a suitable clearance according to working conditions and performance requirements. The clearance of the bearing is divided into radial clearance and axial clearance, which respectively indicate the displacement of one sleeve and the displacement of the other sleeve from one extreme position to the other in the radial direction and the axial direction. The radial clearance of the bearing, including the original clearance in the free state before the bearing is installed, the assembly clearance after loading the main shaft and the bearing housing, and the working clearance formed under the load during operation. For ball bearings, the optimum working clearance is close to zero; for roller bearings, a small amount of working clearance can be maintained. In parts requiring good support rigidity, the bearings should have a certain amount of preload. This is the principle for determining the radial clearance of the bearing. In the national standard GB4604-93, the radial clearance of the rolling bearing is divided into 5 groups, and the clearance value is from small to large, and 0 of them is the standard clearance. Bearings operating under special conditions such as high temperature, high speed, low noise, low friction, etc. should use a larger radial clearance; for bearings with precision spindles, a smaller radial clearance should be used. It should be noted that the working clearance after the bearing is installed is smaller than the original clearance before installation, because the bearing is subject to a certain load rotation, and the elastic deformation caused by the bearing fit and load. [2]

 

  For radial thrust ball bearings and tapered roller bearings, they are usually mounted face to face or back to back, and the internal clearance or preload is determined by the axial position of one of the bearing rings. Starting from the zero clearance condition, the specified clearance can be obtained by adjusting the thickness of the spacer on the outer ring of the bearing or loosening or tightening the backing on the shaft. There is a fixed relationship between the axial clearance and the radial clearance of such bearings, and it is sufficient to satisfy one of the values.

 

  When choosing a bearing clearance, you should also consider the following aspects:

 

  1. Bearing working conditions, such as load, temperature, speed, etc.;

 

  2. Requirements for bearing performance, such as rotation accuracy, friction torque, vibration and noise;

 

  3. When the bearing and the shaft and the housing hole are in an interference fit, the bearing clearance is reduced;

 

  4. When the bearing is working, the temperature difference of the inner outer ring causes the bearing clearance to decrease;

 

  5. The bearing clearance is reduced or increased due to the different expansion coefficients of the shaft and the outer casing material;

 

  6. Due to the large temperature difference between the inner and outer rings of the bearing, the deep groove ball bearing needs to withstand large axial load or need to improve the centering performance, and it is required to increase the limit speed and reduce the bearing friction torque;

 

  7. When the basic group cannot meet the usage requirements, the auxiliary group clearance should be selected. The large clearance auxiliary group is suitable for interference fit between the bearing and the shaft and the housing hole. The small clearance auxiliary group is suitable for the required high rotation precision, the axial displacement of the housing hole must be strictly controlled, and the vibration and noise need to be reduced. .

 

  Second, the adjustment of rolling bearing clearance

 

  The clearance of the rolling bearing is adjustable and not adjustable. Except for the angular clearance of angular contact ball bearings, tapered roller bearings, thrust ball bearings and thrust roller bearings, the bearing clearances of other categories are not adjustable. Bearings with adjustable clearance should be adjusted after installation and during use. Through adjustment during use, part of the bearing can be compensated for the increase of bearing clearance caused by bearing wear; bearings with adjustable clearance are Check the clearance after assembly and during use. According to the inspection results, it is decided whether it needs to be reinstalled, repaired or replaced.

 

  There is no large relationship between the axial clearance and the radial clearance, and the axial clearance is directly controlled during installation. To consider individual use or pairing separately. If it is used in a single bearing, since the bearing is separable, the axial clearance after installation needs to be controlled by itself. The axial limit position of the axis can be measured by the dial gauge (the amount of displacement of the push and pull limit positions); if it is used in pairs, it is only necessary to kill the inner and outer rings, and the channel in the manufacturing process Position to control the play.

 

  In the case of high precision and not very hot, you can use negative clearance. When you measure, you can push it negatively, but a process that gradually becomes smaller and negative. If it is suddenly too tight, it will cause the shaft to burn. If the accuracy requirement is not high, the axial clearance during installation is controlled between 0.1-0.3mm. If the shaft heat is serious, the clearance needs to be amplified.

 

  There are many adjustment methods for axial clearance of rolling bearings, such as gasket adjustment method, nut adjustment method, screw cover adjustment method and inner jacket adjustment method. Among them, the gasket adjustment method is the most commonly used adjustment method. When adjusting, generally do not add a gasket, and tighten the fixing screws of the side cover until the shaft can not rotate. At this time, there is no play in the bearing. Use a gauge to measure the distance K between the side cover and the end face of the housing, then add a spacer that is equal to the K value plus the axial clearance. It is important to note that the accuracy of adjustments made with this method depends on the quality of the side covers and gaskets. A set of gaskets should be composed of a variety of gaskets of different thicknesses. The gaskets should be smooth and smooth, and there should be no burrs on the inner and outer edges.

 

  Take the tapered roller bearing clearance adjustment as an example, the empirical method:

 

  1. Flatten the drive shaft and the inner and outer rings of the bearing are vertical;

 

  2. Rotate the shaft and observe the movement state of the roller at the same time, whether it is rolling or sliding. If 4 or 5 rollers are in the sliding state, the axial clearance is too large; if all the rollers are in the rolling state, the clearance is too small; It is ideal if there are 2 or 3 rollers in the sliding state.

 

  3. It is advisable to combine and contrast various adjustment methods. If they meet the requirements, the accuracy and reliability will be improved.

 

  In the process of adjusting the rolling bearing clearance, in addition to the general technical requirements for rolling bearing assembly, it is also necessary to consider the influence of bearing temperature rise and lubrication on the adjustment work, and also carry out detailed after the dry running experiment. Detection and secondary adjustment. Careful work attitude is also an indispensable quality for assembly fitters.