ZWZ bearing belongs to one kind of rolling bearing. Rolling bearing is a kind of precise mechanical component which changes the sliding friction between the running shaft and the shaft seat into rolling friction, so as to reduce the friction loss. Generally, rolling bearing consists of inner ring, outer ring, rolling element and cage
It is composed of four parts. The inner ring is used to match the shaft and rotate with the shaft; the outer ring is used to match the bearing seat and play a supporting role; the rolling body is evenly distributed between the inner ring and the outer ring with the help of the cage, with the shape, size and quantity
It directly affects the service performance and service life of the rolling bearing; the cage can make the rolling body evenly distributed, prevent the rolling body from falling off, and guide the rolling body to rotate and play a lubricating role.
Precision bearing  has higher requirements for dimensional stability. After ring quenching (especially step quenching), there are still a lot of retained austenite in the internal structure. It is an unstable structure, which will change continuously in the process of storage and use
Bearing accuracy, therefore, cold treatment process is adopted, which can reduce the retained austenite in the structure and slightly improve the hardness of the parts. However, it should also be noted that the austenite volume should not be too small, otherwise it is not conducive to the improvement of bearing life.
Cold treatment process of rolling bearing
(1) stay at room temperature after quenching:
After quenching, the inner and outer of the ferrule should be evenly cooled to room temperature before treatment. Otherwise, it is easy to crack. If it is cooled to room temperature, it will be cold treated immediately (generally no more than 30 minutes) or the transformation from austenite to martensite will be terminated.
(2) cold treatment temperature: the temperature of cold treatment is mainly based on the martensitic transformation termination temperature of steel, in addition, the influence of cold treatment on mechanical properties and technological factors should be considered.
(3) cold treatment and heat preservation: Although the transformation of a large number of martensite is completed in a moment when it is cold to a certain temperature, in order to make a batch of ferrule surface and center reach the cold treatment temperature evenly, a certain heat preservation time is required, generally about one to one and a half hours.
(4) tempering after cold treatment of ZWZ rolling bearing: put the rings in the air after cold treatment, and the temperature will slowly rise to room temperature and then tempering. The temperature should not be too fast, otherwise it is easy to crack and temper in time, otherwise the large residual stress inside the ferrule will lead to the ferrule
Cracking, generally no more than two hours. In the quality inspection of cold treatment, the main defect of bearing ring after cold treatment is crack, which can be inspected by magnetic flaw detection.
Defect analysis of rolling bearing cold treatment
The ferrule is cooled before it is cooled to room temperature after quenching, or the temperature rises to room temperature after cold treatment and is not carried out in time
Prevention method: the ferrule must reach room temperature before cold treatment; tempering shall be carried out 2 hours after cold treatment.