The adjustment and preload of the rolling bearing clearance is an important part of the rolling bearing assembly work. Accurately grasping the process concept of clearance adjustment and preload, and correctly using this process method in assembly work, is the guarantee of the quality of bearing assembly work.
The clearance of a rolling bearing refers to the maximum amount of movement of the other ring in the radial or axial direction when one ring is fixed. Therefore, the clearance is divided into two types: radial clearance and axial clearance.
When rolling bearings are assembled, the clearance should not be too large or too small. If the clearance is too large, the number of rolling elements that bear the load at the same time will decrease, and the load of a single rolling element will increase, thereby reducing the rotation accuracy of the bearing and reducing the service life; if the clearance is too small, the friction will increase, resulting in The increased heat will aggravate the wear and reduce the service life of the bearing. Therefore, many bearings must strictly control and adjust the clearance during assembly.
Preload means that when the bearing is assembled, an axial force is given to the inner or outer ring of the bearing to eliminate the bearing clearance and cause initial deformation at the contact between the rolling body and the inner and outer rings. Preload can improve the rigidity and rotation accuracy of the bearing under working conditions. For bearings with heavy loads and high rotational accuracy requirements, most of them work in the state of no clearance or even a small amount of interference. In this case, the bearings need to be preloaded during assembly.
The adjustment and preloading of the gap are usually done by making the inner ring of the bearing make an appropriate axial relative displacement to the outer ring.
It is not difficult to see from the above technological concepts that by adjusting the clearance of rolling bearings, the bearing capacity and rotation accuracy of the bearings can be improved, and the service life of the bearings can be improved. But at the same time, it will increase the friction of the bearing and increase the heat generation. Therefore, good lubrication and heat dissipation must be ensured while adjusting the clearance or preload. If it is improperly adjusted or poorly lubricated, it will in turn increase the wear of the bearing and reduce its life. Therefore, to correctly adjust and preload the clearance of rolling bearings, the following issues should also be paid attention :
Assembly technical requirements are the fundamental basis for selecting assembly process methodsThe adjustment of the clearance of the rolling bearing can effectively improve the rotation accuracy of the bearing, improve the bearing capacity of the bearing, prolong the service life of the bearing, and at the same time effectively reduce vibration and noise, but not all rolling bearings need clearance during assembly adjustment. While pre-tightening can improve the bearing rigidity and spin accuracy, but at the same time, it will increase the friction, destroy the lubricating oil film and generate a lot of heat. Therefore, the pre-tightened bearing must be forced to lubricate and cool. This process is limited to It is a relatively special process method that is used when the bearing rigidity and rotation accuracy are extremely high. In actual production, it is only used in the assembly of machine tool spindles, and it is hardly seen in the bearing assembly of other transmission mechanisms.
Whether to adjust the clearance and preload in the assembly of rolling bearings should be determined according to the assembly technical requirements proposed in the technical documents. Specifically, in the technical requirements of assembly, there is generally a requirement to adjust the bearing clearance or preload for bearings with high speed, heavy load or high rotational accuracy requirements, otherwise, the bearing clearance will be maintained, and only the shaft will be used during assembly can be fixed. From the perspective of bearing types, it is necessary to adjust the clearance for tapered roller bearings, angular contact bearings, and thrust bearings; for general low-speed, light-load radial ball bearings, it is not necessary to adjust the clearance in most cases. Adjustment, but only for axial fixation.
To meet the requirements of clearance adjustment and preload under thermal equilibrium conditions
The actual ideal working clearance of the rolling bearing is the clearance adjusted after the temperature rise of the bearing is stable. Therefore, the adjustment of the bearing clearance should be carried out in two stages: first, adjust the bearing clearance at room temperature according to the relevant operating specifications and technical requirements, until the clearance is appropriate and the rotation should be flexible by hand; then, adjust the adjustment mechanism properly. Back loose (to prevent the bearing from suddenly locking due to the temperature rise during the test run), carry out the idling test, the idling time from low speed to high speed is not more than 2 hours, and the idling time at the highest speed is not less than 30min, the bearing should run Flexible, low noise, working temperature does not exceed 50°C, and finally reset and lock the adjustment mechanism.
keep well lubricated
Good lubrication can not only reduce friction, but also cool the bearings and parts on the shaft. After the rolling bearing clearance is adjusted, the friction will increase, and the heat generated will increase the temperature of the entire transmission system. If the heat cannot be dissipated in time, the heat will change the size of the transmission parts, which will affect the change of the rolling bearing clearance, generate more heat, and form a vicious circle. Therefore, for the rolling bearings with clearance adjustment, it is necessary to maintain good lubrication to reduce friction, and more importantly, use the continuously circulating lubricating oil to take away a lot of heat, control the temperature rise, and achieve the heat balance of the transmission system.
Special notice
Before the dry running test, it is necessary to first check whether the oil supply to each part of the lubrication system is normal, especially for the preloaded bearing parts, it is necessary to pay special attention to the sufficient supply of lubricating oil and the working condition.
In short, the correct assembly of rolling bearings according to the process, reasonable use, and careful implementation of the adjustment and pre-tightening process of the rolling bearing clearance are effective means to improve the bearing rotation accuracy and load-carrying capacity, and reduce the vibration and noise of the transmission system. In addition to the general technical requirements, the influence of bearing temperature rise and lubrication on the adjustment work should also be considered, and careful inspection and secondary adjustment should be carried out after the dry running test, with patience and meticulousness.
