In the research of improving the quality of automobile gears, the priority should be given to the selection of materials, followed by the strict specification of heat treatment process, continuous innovation based on the existing, promotion of new heat treatment equipment and adoption of new technology. As a key process in the process of gear quality control, heat treatment still has a lot of room for progress in China’s application. The quality of automobile gear in China is far behind that of similar products in advanced countries, with low average service life, large energy consumption and low labor productivity.
1. Improvement of heat treatment equipment
There are many technical problems facing the heat treatment equipment in our country, such as the carburizing furnace can not realize the automatic control of carbon potential, the obvious fluctuation of carbon concentration on the product surface, the poor quality and low efficiency of carburizing gear, large energy consumption and high cost. In recent years, some improvements have been made in this problem. At present, the domestic gas dynamic software has been successfully applied to the carburizing furnace, but the control level needs to be further improved. Some equipment with great difficulty in manufacturing, such as IGBT transistor super audio power supply, this portable power supply can be self-sufficient and exported. Large horizontal marine crankshaft quenching machine, automatic crankshaft quenching device, non soft belt raceway quenching device and CVJ numerical control quenching machine have been designed and produced independently. Even some equipment, such as gear multi-purpose carburizing furnace, continuous carburizing furnace, isothermal normalizing furnace, large well type carburizing furnace with a diameter of 4m and corresponding supporting cooling medium, quenching cooling device and testing instrument, gear induction heating solid-state power supply and quenching machine tool, gear nitriding furnace, especially pulse ion nitriding furnace, have basically reached the international advanced level.
2. Improvement of heat treatment process
With the continuous improvement of the requirements of the mechanical industry for the quality and bearing capacity of gears, the heat treatment process of gears in China has developed gradually. In the 1970s, the gear design parameters of China’swere relatively low, and the technology of soft tooth surface tempering was the main technology. The large-scale research on the manufacturing technology of hard tooth surface began in the 1980s, mainly including the research on induction hardening of large , gear nitriding technology and gear carburizing potential control technology.
Zhang Guozheng et al. Analyzed the influence of temperature, cooling speed, time and carburizing potential on the post heat deformation of 20CrMnTi steel gear, taking 20CrMnTi steel as an example.
The production practice at home and abroad shows that the isothermal annealing treatment solves the problem of poor cold working performance of carburized steel, and the deformation after carburizing and quenching is also significantly reduced. Many automobile manufacturers prescribe different isothermal annealing processes for gear forging blanks of different materials. The application of induction hardening technology, such as shaft longitudinal induction hardening, has been expanded in the automotive and tractor industries. Many advanced quenching processes have been used in many domestic enterprises and are being improved continuously, such as no soft belt quenching of rotary bearing raceway, double frequency gear quenching, three column sliding set quenching, etc.
Qin Lili studied the practical effect of carburizing and carbonitriding heat treatment process in the production of automobile gear. The results showed that the process combined with gear hanger technology can not only achieve the purpose of simple organization and easy operation, but also obtain a certain amount of mixture of surface retained austenite and carbide, improve the strength of automobile gear and obtain excellent material plasticity and toughness, Thus, the anti fatigue life of automotive gears is improved.