ZWZ Bearing

ZWZ bearing belongs to a kind of rolling bearing. Rolling bearing is a precise mechanical component that changes the sliding friction between the running shaft and the shaft seat into rolling friction so as to reduce the friction loss. Rolling bearings are generally composed of inner ring, outer ring, rolling element and cage. The function of inner ring is to cooperate with the shaft and rotate with the shaft; the function of outer ring is to cooperate with the bearing seat and play a supporting role; the rolling element distributes the rolling element between inner ring and outer ring by means of the cage evenly, and its shape, size and quantity directly affect the service performance and life of rolling bearings. The cage can make the rolling body evenly distributed, prevent the rolling body from falling off, and guide the rolling body to rotate to play a lubricating role.
Precision bearing [1] requires high dimensional stability. The retained austenite in the inner structure of the ring after quenching (especially step quenching) is unstable. It will change continuously during storage and use, thus changing the bearing accuracy. Therefore, the cold treatment process can reduce the retained austenite in the structure and slightly improve the hardness of the parts. But we should also pay attention to the austenite content is not too small, otherwise it is not conducive to the increase of bearing life.
Cold Treatment Technology of Rolling Bearing
(1) Stay at room temperature after quenching:
After quenching, the inside and outside of the ring should be uniformly cooled to room temperature for treatment. Otherwise, it is easy to crack. Cold treatment (usually no more than 30 minutes) immediately after cooling to room temperature will stop the transformation of austenite to martensite.
(2) Cold treatment temperature: The temperature of cold treatment is mainly based on the termination temperature of martensitic transformation of steel. In addition, the influence of cold treatment on mechanical properties and technological factors should be considered.
(3) Heat preservation by cold treatment: Although a large amount of martensite transformation is completed at a certain temperature, in order to make the surface and center of a batch of rings reach the cold treatment temperature evenly, it needs a certain time of heat preservation, usually in about one and a half hours.
(4) Tempering of ZWZ rolling bearing after cold treatment: After cold treatment, the ring is put in air, and its temperature rises slowly to room temperature and tempers. Temperature should not be too fast, otherwise it is easy to crack and temper in time. Otherwise, the larger residual stress in the ring will lead to the cracking of the ring, which generally does not exceed two hours. Generally, the main defect of bearing rings after cold treatment is crack, which can be checked by magnetic testing method.
Defect Analysis of Rolling Bearing Cold Treatment
Causes:
After quenching, the ring is cold treated before it reaches room temperature, or after cold treatment, the temperature rises to room temperature in time.
Tempering.
Preventive methods: Before cold treatment, the ring must reach room temperature; after cold treatment, the ring should be tempered for 2 hours.