Introduction of Planetary Gear Heat Treatment Process

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Gear reducer is a combination of reduction motor and large reducer. No couplings and adapters are required, and the structure is compact. The load is distributed on the planetary gears, so its carrying capacity is relatively high. 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, in view of the structural characteristics of the planetary gear reducer and the load characteristics of the gears, hardened gears should be widely used. There are many heat treatment methods to obtain hardened gears, such as surface quenching, overall quenching, carburizing quenching, nitriding, etc., which should be selected according to the characteristics of the planetary gear reducer.

1. Surface Hardening

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

2. Carburizing and Quenching

Carburized and hardened gears have relatively maximum load-bearing capacity, but finishing processes (tooth grinding) must be used to eliminate heat treatment deformation to ensure accuracy.

Carburized and hardened gears are commonly used alloy steels with a carbon mass fraction of 0.2% to 0.3% before carburizing, and their tooth surface hardness is often in the range of 58% to 62% HRC. If it is lower than 57HRC, the tooth surface strength will decrease significantly, and if it is higher than 62HRC, the brittleness will increase. The hardness of the tooth center is generally 310~330HBW.

The hardness of carburized and hardened gears should gradually decrease from the surface of the gear teeth to the deep layer, while the effective carburizing depth is specified as the surface to the deep layer should gradually decrease, and the effective carburizing depth is specified as the depth from the surface to the hardness of 52.5HRC.

The effect of carburizing and quenching on the bending fatigue strength of gear teeth not only increases the hardness of the core, but also lies in the residual compressive stress on the surface, which can reduce the stress in the maximum tensile stress area of ​​the gear teeth. Therefore, the root part of the tooth cannot be ground when grinding the gear, and the residual grinding hob is used when hobbing the gear.

3. Nitriding

Nitriding can ensure that the gear teeth achieve high surface hardness and wear resistance under the condition of minimum deformation. After heat treatment, the final finishing can not be carried out, which improves the load-bearing capacity. This is of special significance for internal gears that are not easy to grind.

4. Hardness Combination of Meshing Gear

When both the large and small gears have soft tooth surfaces, the hardness of the tooth surface of the small gear should be higher than that of the large gear. When both wheels have hard tooth surfaces and higher hardness, the hardness of the two wheels is the same.
Choosing a good planetary gear reducer material is conducive to improving the bearing capacity and service life of the gear reducer. For planetary gears, carburizing and quenching with 20CrMnTi is better than nitriding with 42CrMo. Generally, internal gears are nitrided with 42CrMo.

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