Concept of bearing clearance:
Bearings are precision mechanical parts, and bearing assembly requires a high working environment and operating specifications, and requires orderly work in a clean and constant temperature environment. Bearing production is high-efficiency, high-precision machining, parts need to go through a long time, multiple processes to achieve a fairly high dimensional accuracy, rotation accuracy and surface roughness, in order to meet the standards and use of various performance requirements, to ensure that the bearing zero machining accuracy is not destroyed, which requires the bearing assembly not only to civilized production, but also the assembly process should be carried out under certain process regulations. There are many specialized technologies and supporting calculations in the process of rolling bearing assembly, which requires assembly workers to have considerable computing ability and a certain degree of proficiency in order to meet the assembly requirements of bearings.
The radial clearance of rolling bearings refers to the maximum clearance that can pass between the inner ring and the outer ring when the bearing is not installed on the shaft, and the radial clearance of rolling bearings is an important use characteristic, which has a great impact on the fatigue life, rigidity, vibration, temperature rise and mechanical normal operation accuracy of the bearing. The presence of radial clearance plays a crucial role in the performance and service life of the bearing.
Classification of radial clearances:
Design Clearance:The clearance specified in the product drawing.
Primitive Clearance:Actual clearance before bearing mounting.
The original clearance is the no-load clearance value, which is the actual clearance after the bearing is fitted with the sleeve, also known as the theoretical clearance or geometric clearance of the bearing, which should be guaranteed before leaving the factory.
Installing the clearance:The actual clearance after the bearing is installed, also known as the matching clearance.
After the inner ring of the bearing is installed on the shaft or the outer ring is installed in the bearing housing, due to the tight fit, the radial size of the bearing ring is elastically deformed, and the inner ring of the bearing expands due to interference fit, and the outer ring shrinks. As a result of interference fit, it is clear that the installation clearance is smaller than the original clearance, and the reduction varies depending on the bearing structure, size, shaft and housing shape. For bearings installed with both the inner and outer diameters of the interference fit, the outer raceway diameter is reduced, while the inner raceway diameter is increased, and the total clearance shrinkage is nearly half of the absolute sum of the interference fit of the two rings. It is generally believed that if the material of the shaft and the shaft shell bore fit of the bearing is steel, the total shrinkage of the clearance is 50% to 60% of the total interference fit of the inner and outer rings. If the material of the bearing housing fit is non-ferrous metal, the total shrinkage of the clearance is 20% to 30% of the total interference fit of the inner and outer rings.
Working Clearance:The clearance in the working state under actual operating conditions.
When the bearing is running at no load, the temperature rise will change the temperature difference between the inner and outer rings, which will reduce the clearance after installation. When the bearing is under load, the load makes the elastic deformation of the contact between the rolling element, the ring and the raceway, and the clearance increases, and the bearing clearance is the working clearance, and the working clearance is greater than the installation clearance under normal circumstances, in order to obtain satisfactory working performance, the appropriate working clearance should be selected.
The role of radial clearance:
First of all, radial clearance is a key factor in maintaining the flexibility of the bearing. During operation, friction will inevitably occur between the rolling elements inside the bearing and the inner and outer rings, and the appropriate radial clearance can ensure that the rolling elements will not be stuck due to friction during movement. In this way, the bearings can rotate smoothly without inflexibility or jamming.
Secondly, radial clearance has an important impact on the durability of bearings. The life of a rolling bearing depends mainly on the friction and wear inside it. The size of the radial clearance directly determines the contact area and friction between the rolling element and the inner and outer rings. The moderate radial clearance ensures the lubrication between the rolling elements and the inner and outer rings, thereby reducing friction and wear and increasing the service life of the bearing.
In addition, the radial clearance acts as a shock absorber. When the bearing is under load, the contact between the rolling elements and the inner and outer rings will produce elastic deformation, and the existence of radial clearance can provide a certain buffer space to absorb part of the shock and vibration, thereby reducing the damage to the bearing.
In general, the radial clearance of rolling bearings is an important factor to ensure their normal operation, improve service life and shock absorption performance. In practical applications, it is necessary to select the appropriate radial clearance size according to different use environments and working conditions to ensure that the bearing can exert the best performance and prolong the service life.