The adjustment and pre tightening of 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 radial or axial movement of another ring when one ring is fixed. Therefore, clearance is divided into two types: radial clearance and axial clearance.
When assembling rolling bearings, the clearance should not be too large or too small. Excessive clearance can lead to a reduction in the number of rolling elements that can simultaneously bear the load, resulting in an increase in the load on a single rolling element and a decrease in the rotational accuracy and service life of the bearing; If the clearance is too small, it will increase the friction force, generate more heat, intensify wear, and also reduce the service life of the bearing. Therefore, many bearings require strict control and adjustment of clearance during assembly.
Pre tightening is the process of applying axial force to the inner or outer race of a bearing during assembly, in order to eliminate bearing clearance and cause initial deformation at the contact between the rolling elements and the inner or outer race. Pre tightening can improve the stiffness and rotational accuracy of bearings in working conditions. For bearings that bear large loads and require high rotational accuracy, they mostly work in a state of no clearance or even a small amount of interference. In this case, it is necessary to pre tighten the bearing during assembly. The adjustment of clearance and pre tightening are usually achieved by making the inner ring of the bearing make 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 rotational accuracy can be improved, and the service life of bearings can be extended. But at the same time, it will intensify the friction of the bearing and increase the heat generation, so it is necessary to ensure good lubrication and heat dissipation while adjusting the clearance or pre tightening. If not adjusted properly or lubricated properly, it will in turn exacerbate bearing wear and reduce its lifespan. Therefore, when adjusting and pre tightening the clearance of rolling bearings correctly, attention should also be paid to the following issues:
The assembly technology requirements are the fundamental basis for selecting assembly process methods
Adjusting the clearance of rolling bearings can effectively improve their rotational accuracy, enhance their 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 certainly improve the rigidity and rotational accuracy of bearings, but at the same time, it will intensify friction, damage the lubricating oil film, and generate a large amount of heat. Therefore, the pre tightened bearings must be forcibly lubricated and cooled. This process method is limited to situations where the rigidity and rotational accuracy of the bearings are extremely high. It is a relatively special process method that is only used in the assembly of machine tool spindles in production practice, and is rarely seen in the assembly of bearings in other transmission mechanisms.
Whether to adjust the clearance and pre tighten in the assembly of rolling bearings should be determined according to the assembly technical requirements proposed in the technical documents. Specifically, in assembly technology requirements, there are generally requirements for adjusting bearing clearance or pre tightening for bearings that require high speed, heavy load, or high rotational accuracy. Conversely, bearing clearance will be maintained and only axial fixation is required during assembly. From the perspective of bearing types, 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, there is no need to adjust their clearance, only axial fixation is required.
To achieve the requirements of clearance adjustment and pre tightening under thermal equilibrium conditions
The ideal working clearance of rolling bearings is the clearance adjusted after the bearing temperature stabilizes. Therefore, the adjustment of bearing clearance should be carried out in two stages: first, adjust the bearing clearance at room temperature according to relevant operating specifications and technical requirements, until the clearance is appropriate, and rotate it by hand to feel flexible; Then, loosen the adjustment mechanism appropriately (to prevent the bearing from suddenly locking up due to temperature rise during testing), conduct an idle running test, and the idle running time from low speed to high speed should not exceed 2 hours. At the highest speed, the idle running time 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 bearings, friction will increase, and the heat generated will cause the temperature of the entire transmission system to rise. If the heat is not 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 take away a large amount of heat, control the temperature rise, and achieve thermal balance in the transmission system.
Before conducting the test, it is necessary to first check whether the oil supply to each part of the lubrication system is normal, especially for the pre tightened bearing parts, which need to pay special attention to their sufficient lubricating oil supply and good working condition.
In short, correctly assembling and using rolling bearings according to the process, carefully adjusting the clearance and pre tightening process of rolling bearings, is an effective means to improve the rotational accuracy and load-bearing capacity of bearings, and reduce the vibration and noise of transmission systems. In addition to meeting the general technical requirements of rolling bearing assembly, the impact of bearing temperature rise and lubrication on the adjustment work should also be carefully considered during operation. After conducting the idle running test, detailed inspection and secondary adjustment should be carried out patiently and meticulously.

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