Spiral bevel gear is the most widely used spiral gear in production. Because it has the characteristics of stable transmission, high bearing capacity, uniform wear, large overlap coefficient and high transmission quality, it has been widely used in differential box and reduction box of transportation machinery.
With the continuous development of mechanical industry, gear transmission devices are developing towards high power, small volume and high durability, especially for heavy machinery, automobile and other industries. Higher requirements are put forward for gear bearing capacity, service life, accuracy, surface roughness and noise control. This requirement also exists for spiral bevel gears. Forming hard tooth surface by heat treatment is one of the measures to meet this requirement. When the hardness of tooth surface is hrc58-63, it is generally called hard tooth surface. Increasing the tooth surface hardness has a great impact on the gear strength. With the increase of tooth surface hardness, the contact fatigue limit and bending fatigue limit of the gear increase significantly, so the bearing capacity and solution resistance of the gear can be significantly improved.
At present, the commonly used heat treatment methods for forming hard tooth surface are carburizing quenching, nitriding quenching, carbonitriding and so on. Due to a series of unstable factors such as grain direction, carburizing (nitrogen) concentration, carburizing (nitrogen) temperature and material permeability of gear blank forging, decarburization (nitrogen) deformation and black structure often occur on the part surface after carburizing (nitrogen) quenching of hard tooth surface materials. Due to the complex shape of spiral bevel gear, the deformation during heat treatment is more significant, especially in medium and small-scale factories, this problem is more prominent because the heat treatment process and equipment are not perfect. Although the level of heat treatment continues to improve, the accuracy of gears will still drop by 1-2 levels after hardening treatment, or even 3-4 levels in severe cases.
The deformation of spiral bevel gear after heat treatment leads to the shift of gear meshing position, the reduction of contact area, the great decline of motion accuracy and contact accuracy, the increase of working stress, vibration and noise in use, and the shortening of the service life of the gear. In this way, it is difficult to reflect the advantages of hard tooth surface. Therefore, in actual production, certain measures need to be taken to control and eliminate heat treatment deformation. Although the quenching press can control the deformation, it can not eliminate the deformation. If remedial measures are taken to compensate quenching deformation or correct error during rough machining of gear before heat treatment, it is very difficult and the cost is high. Therefore, another process method needs to be adopted to eliminate the heat treatment deformation of spiral bevel gear.
