With the increasing demand for coal mine output, the TBM model has higher and higher requirements for gear quality and performance. The gear is deformed and cracked in the process of heat treatment and the gear box pushing gear occurs from time to time in coal mining excavation. Here, the technical and quality problems and solutions encountered in the process of gear heat treatment are described as follows.
There are two common heating methods for gear heat treatment: 1) overall heating; 2) Surface induction heating. Commonly used carburized gear materials are 20CrMo, 20CrMnTi, 20Cr2Ni4A steel, etc.
1. Overall quenching of carburized gear
1) The purpose is to require high strength, hardness and wear resistance on the surface, high comprehensive mechanical properties on the heart, and integral quenching is commonly used for gears with large load, high speed and wear resistance on the tooth surface.
2) When the requirements for strength, hardness and impact resistance of the carburized gear core are high, the quenching temperature shall be higher. The quenching temperature shall be 840 ± 10 ℃ and the tempering temperature shall be 200 ± 10 ℃. The metallographic structure obtained after quenching is [surface M + Fe3C. Low carbon m in the core], and the amount of low carbon m is high.
3) When the surface strength, hardness and wear resistance of carburized gear are high, the quenching temperature shall be lower. The quenching temperature shall be 800 ± 10 ℃ and the tempering temperature shall be 180 ± 10 ℃. After quenching, the metal structure is [surface M + Fe3C. Core low carbon M], and the amount of low carbon m is low.
2. Carburizing gear tooth surface quenching
The purpose is to require the gear tooth surface to have high strength, hardness and wear resistance, while the comprehensive mechanical performance of the heart is not high, and the gear with small load often adopts tooth surface quenching.
3. Quenching and tempering gear tooth surface
The purpose is to require the gear tooth surface to have high strength, hardness and wear resistance, and the heart to have good comprehensive mechanical properties. Commonly used quenched and tempered gear materials are 35CrMo, 40Cr, 42CrMo, steel, etc. This treatment is often used for gears with large load, low speed and low wear resistance.