Adjusting and pre tightening the clearance of rolling bearings is an important part of the assembly work of rolling bearings. Accurately grasping the process concepts of clearance adjustment and pre tightening, and correctly applying this process method in assembly work, is the guarantee of the quality of bearing assembly work. The clearance of rolling bearings refers to the maximum movement of one ring in the radial or axial direction when the other ring is fixed. Therefore, the clearance is divided into two types: radial clearance and axial clearance.
When assembling rolling bearings, their clearance should not be too large or too small. If the clearance is too large, it will cause a decrease in the number of rolling elements that simultaneously bear the load, increasing the load on a single rolling element, thereby reducing the rotational accuracy of the bearing and reducing its service life; If the clearance is too small, it will increase the friction force, generate more heat, exacerbate wear, and also reduce the service life of the bearing. Therefore, many bearings require strict control and adjustment of clearance during assembly.
Pre tightening refers to applying axial force to the inner or outer rings of a bearing during assembly to eliminate bearing clearance and cause initial deformation at the contact between the rolling element and the inner and outer rings. Pre tightening can improve the stiffness and rotational accuracy of bearings under working conditions. For bearings that bear large loads and require high rotational accuracy, they mostly work in a state without clearance or even with a small amount of interference. In this case, it is necessary to pre tighten the bearings during assembly. The adjustment and pre tightening of clearance is usually achieved by making the inner ring of the bearing move axially relative to the outer ring.
From the above technological concepts, it is not difficult to see that adjusting the clearance of rolling bearings can improve the bearing capacity and rotation accuracy, and improve the service life of bearings. But at the same time, it will exacerbate bearing friction and increase heat generation. Therefore, when adjusting clearance or pre tightening, it is necessary to ensure good lubrication and heat dissipation. If adjusted improperly or poorly lubricated, it will in turn exacerbate bearing wear and reduce service life. Therefore, when adjusting and pre tightening the clearance of rolling bearings correctly, the following issues should also be noted:
Assembly technical requirements are the fundamental basis for selecting assembly process methods
Adjusting the clearance of rolling bearings can effectively improve their rotational accuracy, load-bearing capacity, extend their service life, and reduce vibration and noise. However, not all rolling bearings require clearance adjustment during assembly. Pre tightening can improve the rigidity and rotational accuracy of bearings, but at the same time, it can exacerbate friction, damage the lubricating oil film, and generate a large amount of heat. Therefore, the pre tightened bearings must undergo forced lubrication and cooling. This process method is only used when the rigidity and rotational accuracy of bearings are extremely high, and is a relatively special process method. In production practice, it is only used in the assembly of machine tool spindles, The assembly of bearings for other transmission mechanisms is almost invisible.
Whether to adjust and pre tighten the clearance during the assembly of rolling bearings depends on the assembly technical requirements proposed in the technical documents. Specifically, in the assembly technical requirements, there is generally a requirement to adjust the bearing clearance or pre tighten bearings that require high speed, heavy load, or rotational accuracy. Conversely, the bearing clearance will be maintained, and only axial fixation is required during assembly. From the perspective of the types of bearings, it is necessary to adjust the clearance of tapered roller bearings, angular contact bearings, and thrust bearings; For general low-speed and light load radial ball bearings, in most cases, it is not necessary to adjust their clearance, but only for axial fixation.
To meet the requirements of clearance adjustment and preloading under thermal balance conditions
The actual ideal working clearance of rolling bearings is the clearance adjusted after the temperature rise of the bearing stabilizes. Therefore, the adjustment of bearing clearance should be carried out in two stages: first, adjust the bearing clearance according to relevant operating specifications and technical requirements at room temperature, until the clearance is suitable and the rotation should feel flexible when turned by hand; Then, loosen the adjustment mechanism appropriately (to prevent the bearing from suddenly locking up due to temperature rise during testing) and conduct an idle running test. The idle running time from low speed to high speed should not exceed 2 hours, and the idle running time at the highest speed should not be less than 30 minutes. The bearing should operate flexibly, have low noise, and the working temperature should not exceed 50 ℃. Finally, reset and lock the adjustment mechanism.
Maintain good lubrication
Good lubrication not only reduces friction, but also has a cooling effect on bearings and shaft components. After adjusting the clearance of the rolling bearing, the friction will intensify, and the generated heat will increase the temperature of the entire transmission system. If the heat cannot be dissipated in a timely manner, it will cause changes in the size of the transmission parts, thereby affecting the changes in the clearance of the rolling bearings, generating more heat and forming a vicious cycle. Therefore, for rolling bearings that have undergone clearance adjustment, it is necessary to maintain good lubrication to reduce friction, and more importantly, to use continuously circulating lubricating oil to carry away a large amount of heat, control temperature rise, and achieve thermal balance of the transmission system.
Before the rotation test, it is necessary to first check whether the oil supply to all parts of the lubrication system is normal, especially for the pre tightened bearing parts. It is also necessary to pay special attention to the sufficient supply of lubricating oil and good working condition.
In short, the correct assembly and reasonable use of rolling bearings according to the process, as well as the careful implementation of the adjustment and pre tightening process of rolling bearing clearance, are effective means to improve the bearing rotation accuracy and bearing capacity, reduce the vibration and noise of the transmission system. In addition to meeting the general technical requirements of rolling bearing assembly, the operation should also focus on considering the impact of bearing temperature rise and lubrication on the adjustment work, And after conducting the idling test, detailed inspections and secondary adjustments should be carried out, patiently and meticulously.