The bearing capacity of the tooth surface should be related to the hardness of the tooth surface. The higher the hardness, the higher the bearing capacity. According to the hardness of the tooth surface, people usually divide gear transmission into two categories, namely hard tooth surface gear transmission and soft tooth surface gear transmission. Gear shaft, usually the tooth surface hardness of a pair of meshing gears is greater than 350HBS, which is called hard tooth surface gear, otherwise it is called soft tooth surface gear. The selection principle of gear accuracy is the working line speed, the required carrying capacity and the possibility of the company's equipment. For hard-toothed gears, the precision of the gears after grinding is generally 6 grades of precision. When the line speed is particularly high, choose grade 4-5. When there are special requirements for vibration and noise, the accuracy can currently be up to grade 3. 

 gear shaft

After the modulus of hardened gear is increased, or the diameter of quenched and tempered gear is increased, if the gear accuracy is not improved, the increase in strength caused by the increase in modulus and diameter will offset the increase in passive load. At this point, the experience and lessons of the failure of the previous quenched and tempered gear transmission in the cement and metallurgical industries can prove the necessity of improving the gear processing accuracy. After the gear diameter is increased, due to the volume effect of the workpiece after heat treatment, the hardness of the tooth surface from the tooth top to the tooth root is uneven, and the hardness difference reaches 20HB. In order to strictly control the gear manufacturing quality, from the introduction of the tooth surface hardness tester, the large-modulus gears are quenched with nitrate to improve the hardenability of the workpiece