The most widely used bearing in motor products is rolling bearing. Rolling bearings are standardized components that have the advantages of low friction, easy starting, and easy replacement. It is crucial for us to choose a reasonable and correct bearing fit during daily maintenance or mechanical design. There are many factors that affect the selection of rolling bearing fits. When choosing a fit, various factors must be considered comprehensively and combined with the analogy method of actual work to achieve the best fit state.

The correct selection of bearing matching is closely related to ensuring the normal operation of the motor, improving the service life of the bearings, and fully utilizing the bearing capacity. The selection of rolling bearing fit is mainly based on the nature and size of the bearing ring bearing load, and combined with factors such as bearing type, size, working conditions, material and structure of the shaft and shell, and working temperature.

One of the key factors affecting the operation of bearings is the working clearance of bearings. The main factors affecting the working clearance of bearings include the fit between the inner race and the shaft, the fit between the outer race and the bearing chamber, the clearance of the bearing itself under non assembly conditions, the operating state of the motor, and the turnover environment, among other objective factors. The same motor may have different fates under different usage conditions. To ensure the guarantee effect of bearings during motor operation, comprehensive consideration should be given to bearing selection, determination of fit relationship, understanding of working conditions, lubrication and maintenance, and other aspects.

Motor knowledge expansion

Is the bearing ring rotating

When the inner or outer ring of a bearing operates as a rotating ring, a slightly tight fit should be used, and the magnitude of its interference should ensure that the mating surface does not "crawl" under working load (commonly referred to as running ring), because once crawling occurs, the mating surface will wear and slide, causing the ring to rotate at a higher speed,

The more severe the wear is. When the bearing is in operation, if its inner or outer ring is a non rotating ring, for the convenience of disassembly and adjustment, it is advisable to choose a loose fit.

Due to different working temperature rises, the shaft neck or housing hole will experience different elongation in the longitudinal direction. Therefore, when selecting a fit, the principle is to achieve free movement of the bearing along the axial direction and eliminate internal stress in the support. However, excessive clearance can reduce the rigidity of the entire component, cause vibration, and exacerbate wear.

2. Bearing Load Types and Matching Relationships

The bearing ring bears radial load and can be divided into the following three types according to the relative motion relationship between the load and the ring.

Local load - Local load refers to the combined radial load acting on the bearing that is relatively stationary with the ring, meaning that the radial load is borne by the local raceway of the ring.

Cyclic load - Cyclic load refers to the combined radial load acting on the bearing and the relative rotation of the ring, that is, the radial load sequentially acts on the entire circumference of the ring raceway.

Swing load - Swing load refers to the combined radial load acting on the bearing and the relative swing of the ring in a certain area. The bearing bears a radial load that remains unchanged in one direction and a rotating load, and their combined radial load oscillates relatively in a section of the raceway of the fixed ring.

The ring that bears local load should choose a loose transition fit or a fit with smaller clearance, so that the friction torque between the ring raceways drives the ring to rotate, making the ring evenly stressed and extending the service life of the bearing. The collar that bears cyclic load should choose an interference fit or a tight transition fit, and the magnitude of the interference should be based on the principle of not causing crawling phenomenon on the surface of the collar and the shaft or shell hole. When bearing swing load, its coordination requirements are the same or slightly loose as the cyclic load.

3. Bearing load size and fit relationship

The minimum interference between the bearing ring and the journal and shell depends on the size of the load. Ferrules that bear impact loads or heavy loads are prone to deformation, causing uneven stress on the mating surface and causing looseness in the fit. Therefore, tighter fits should be selected, that is, the minimum interference should be greater; For rings that bear light loads, a loose fit should be selected.

4. The impact of other factors on coordination

● Working temperature - During bearing operation, due to friction heating and other heat sources, the temperature of the ring is higher than the temperature of its mating parts. The thermal expansion of the inner ring will cause it to loosen its fit with the journal, while the thermal expansion of the outer ring will cause it to tighten its fit with the casing hole. Therefore, when the working temperature of the bearing is high, appropriate adjustments should be made to the selected fit.

● Rotation accuracy and speed - For bearings that bear large loads and require high rotation accuracy, in order to eliminate the impact of elastic deformation and vibration, clearance fits should be avoided. For lightweight bearings of some precision machine tools, in order to avoid the impact of shape errors on bearing accuracy, clearance fits are often used. It is generally believed that the higher the rotation speed of the bearing, the tighter the fit should be.

● Conditions for installing and disassembling bearings - Considering the convenience of bearing installation and disassembly, a loose fit should be used, which is particularly important for large and oversized bearings used in heavy machinery. If convenient assembly and disassembly are required but tight fitting is required, separable bearings can be used, or bearings with tapered holes in the inner ring, tight sleeves, and withdrawal grooves can be used.

In addition, the bearing fit should be suitable for tightening in the following situations: larger bearings are more suitable than smaller bearings; Hollow journal compared to solid journal; Thin walled shells are more than thick walled shells; A light alloy shell is better than a steel or cast iron shell; The integral shell is better than the partial shell.