Views: 0 Author: WGT Publish Time: 2021-11-30 Origin: WGT
The weight of planetary gear transmission device is generally proportional to the weight of gear, and the weight of gear is closely related to its material and heat treatment hardness. For example, at the same power, the weight of carburized and quenched gear will be about 1 / 3 of that of quenched and tempered gear. Therefore, according to the structural characteristics of planetary gear reducer and the load properties of gear, hard gear should be widely used. There are many heat treatment methods to obtain hardened gears, such as surface quenching, integral quenching, carburizing quenching, nitriding, etc., which should be selected according to the characteristics of planetary gear reducer.
1. Surface quenching
There are two common surface quenching methods: high frequency quenching (for small size gears) and flame quenching (for large size gears). When the hardened layer of surface quenching includes the bottom of tooth root, its effect is good. The common material for surface quenching is steel with carbon content of about 0.35% ~ 0.5%, and the tooth surface hardness can reach 45 ~ 55HRC.
2. Carburizing quenching
Carburized and quenched gears have relatively large bearing capacity, but finishing process (gear grinding) must be used to eliminate heat treatment deformation to ensure accuracy.
Carburizing and quenching gears are usually made of alloy steel with carbon content of 0.2% ~ 0.3% before carburizing, and the tooth surface hardness is often in the range of 58 ~ 62Hrc. If it is lower than 57hrc, the tooth surface strength decreases significantly, and if it is higher than 62Hrc, the brittleness increases. The hardness of tooth center is generally 310 ~ 330hbw. The hardness of the carburized and quenched gear shall be gradually reduced from the gear tooth surface to the deep layer, while the effective carburizing depth is specified as the depth from the surface to the deep layer, 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 improves the core hardness, but also lies in the residual compressive stress on the surface, which can reduce the stress in the large tensile stress area of gear teeth. Therefore, the tooth root cannot be ground during tooth grinding, and the hob with grinding allowance shall be used during gear hobbing.
Nitriding can ensure high tooth surface hardness under the condition of small deformation, no finishing can be carried out after heat treatment, and the bearing capacity is improved. This is of great significance for internal gears that are not easy to grind teeth.
4. Hardness combination of meshing gears
When both large and small gears have soft tooth surfaces, the tooth surface hardness of small gear shall be higher than that of large gear. When both wheels have hard tooth surfaces and high hardness, the hardness of the two wheels is the same.
The selection of good planetary gear reducer materials is conducive to improve the bearing capacity and service life of the gear reducer.