Protective atmosphere heat treatment is a heat treatment carried out in an atmosphere or inert gas that does not oxidize the surface of materials or workpieces. In the current heat treatment of rolling bearing parts, the more advanced method is the heat treatment method of protective atmosphere heating and controllable atmosphere carburization. Protective atmosphere heating is necessary in the process of heat treatment, and carburizing is determined according to the requirements of the product.
The types of protective atmosphere heat treatment mainly include:
● endothermic (or exothermic) type of furnace: endothermic (or exothermic) type uses propane or butane gas as feed gas;
● drip injection type: methanol cracking gas is mainly used as carrier gas and propane gas as enriched gas;
● amino atmosphere type: mainly high-purity (99.7%) ammonia, supplemented by a small amount of methanol or acetone as raw materials.
Compared with ordinary heat treatment methods, the role of protective atmosphere heat treatment is:
● realize no oxidation and avoid decarburization. After such heat treatment, the decarburization layer on the metal surface is very thin, which can greatly reduce the grinding allowance. The test shows that the grinding allowance of bearing rings treated with protective atmosphere heat treatment can be reduced by 1 / 3-1 / 2.
● improve hardness and hardness uniformity;
● reduce surface cracks;
● keep the appearance of ferrule clean.