Surface hardening technology of bevel gear

In the surface hardening technology of bevel gear, induction heating quenching is one of the four basic processes. Induction heating quenching technology is environment-friendly, energy-saving, high efficiency, good dimensional stability of heat treated workpiece, and convenient for automatic production.

Some data have compared the induction quenching process with the carburizing quenching process. In terms of energy consumption, quenching cooling medium consumption, plant and other equipment investment, the cost of adopting the induction quenching process is about 20% of the cost of carburizing quenching process. In terms of industrial pollution emission, the emission of “three wastes” of induction quenching process is also very low. In terms of heat treatment quality of bevel gear, compared with carburizing quenching, induction quenching bevel gear has less distortion and deeper hardening layer. Carburizing and quenching the gear, because the carburizing process takes a long time, resulting in large tooth warpage distortion and reduced gear accuracy. For high-precision gears, the later grinding will not only thin the hardened layer with high strength, but also lead to different depth of hardened layer and uneven hardness of tooth surface. This not only increases the cost, but also affects the gear accuracy and strength. For bevel gear, because its surface structure is more complex than ordinary spur gear, it is very difficult to grind teeth to correct its dimensional accuracy after carburizing and quenching.

In the surface induction hardening process of bevel gear, compared with the single frequency induction hardening process, the dual frequency induction hardening process can obtain the hardened layer distributed along the tooth profile. Due to the complex surface and convex concave structure of bevel gear, the tooth surface and tooth root can not be hardened at the same time during surface quenching with single frequency induction heating. Insufficient hardening of the tooth root will increase the residual stress at the tooth root. Too shallow hardening layer will cause insufficient bending fatigue strength, which may lead to tooth breakage during operation. Insufficient hardening of bevel gear tooth surface will lead to low hardness of bevel gear contact surface, insufficient contact fatigue strength and wear resistance of contact surface, and easy to produce pitting corrosion and other damage.

The dual frequency induction heating process can realize the uniform heating of the tooth root and tooth top of the bevel gear by adjusting the process parameters such as the frequency ratio of medium frequency and high frequency, and obtain the hardened layer distributed along the tooth profile. The latest synchronous dual frequency induction quenching technology (SDF) has been applied to production by many large enterprises at home and abroad. Considering the quality and environmental protection of bevel gear, Boeing adopts synchronous dual frequency induction quenching process to replace carburizing quenching process to carry out surface hardening treatment on bevel gear, eliminating the gear grinding process. Japanese Electric Industrial Corporation, BMW automobile manufacturer, Siemens and other companies have also adopted dual frequency induction quenching technology.

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