Gear heat treatment method of planetary gear transmission

The weight of the planetary gear transmission is generally proportional to the weight of the gear, and the weight of the gear has a great relationship with its material and heat treatment hardness. For example, under the same power, the weight of the carburized and quenched gear will be about 1/3 of the weight of the quenched and tempered gear. Therefore, according to the structural characteristics of the planetary gear reducer and the load properties of the gears, hardened gears should be widely used. There are many heat treatment methods for obtaining hardened gears, such as surface quenching, overall quenching, carburizing and quenching, nitriding, etc., which should be selected according to the characteristics of the planetary gear reducer. 

1. Surface quenching Common surface quenching methods include high-frequency quenching (for small-size gears) and flame quenching (for large-size gears). Surface hardening works better when the hardened layer includes the base of the dedendum. The commonly used material for surface quenching is steel with a mass fraction of carbon of about 0.35%~0.5%, and the hardness of the tooth surface can reach 45~55HRC.

 2. Carburizing and quenching Carburizing and quenching gears have a relatively large load-carrying capacity, but the finishing process (grinding) must be used to eliminate heat treatment deformation to ensure accuracy. Carburizing and quenching gears are usually made of alloy steel with a mass fraction of carbon of 0.2%~0.3% before carburizing, and the hardness of the tooth surface is often in the range of 58~62HRC. If it is lower than 57HRC, the tooth surface strength will decrease significantly, and when it is higher than 62HRC, the brittleness will increase. The hardness of the tooth core is generally 310~330HBW. The hardness of carburized and quenched gears should gradually decrease from the surface to the deep layer of the gear teeth, and the effective carburizing depth is specified as the surface to the deep layer should gradually decrease, while the effective carburizing depth is defined as the depth from the surface to the hardness of 52.5HRC. The role of carburizing and quenching in the bending fatigue strength of gear teeth is not only to increase the hardness of the core, but also to have residual compressive stress on the surface, which can reduce the stress in the tensile stress area of the gear teeth. Therefore, the tooth root part cannot be ground when grinding the teeth, and the hob with the remaining grinding amount should be used when hobbing the teeth. 

3. Nitriding The use of nitriding can ensure that the gear teeth can achieve high tooth surface hardness and wear resistance under the condition of small deformation. After heat treatment, the post-finishing process can no longer be carried out, which improves the bearing capacity. This has special significance for internal gears that are not easy to grind. 

4. Combination of hardness of gears to be meshed When both the large and small gears have soft tooth surfaces, the tooth surface hardness of the small gear should be higher than that of the large gear. And when the two wheels are hard tooth surfaces and the hardness is high, the hardness of the two wheels is the same.