Generally speaking, the principles for selecting the design datum of bevel gear include: datum coincidence principle, datum unification principle, self datum principle, mutual datum principle, easy clamping principle and so on. Generally speaking, the bevel gear design will be developed and designed in strict accordance with these principles. After the design benchmark is set, it will be manufactured. Today we mainly talk about the preheating treatment of bevel gear blank in manufacturing.
     Proper preliminary heat treatment of bevel gear blank can not only obtain more uniform microstructure, but also eliminate stress and reduce distortion for final heat treatment.
     1. Normalizing + high temperature tempering process     It is suitable for low carbon medium alloy steels with high hardenability, such as 22CrMnMo, 20CrNiMo, 18crniwa and 20crni3. The hardness is 170-228hbw, and the metallography is tempered sorbite distributed on ferrite and ferrite matrix.
     2. Simple isothermal normalizing process     The equipment adopts two trolley type resistance furnaces. The process route is as follows: the gear blank is heated at high temperature (940-960 ℃) - discharged after heat preservation - air cooling for an appropriate time - enters No. 2 furnace for isothermal (550-650 ℃) - discharged air cooling. The isothermal temperature and time are determined according to the Austenite Isothermal Transformation Curve of gear blank steel to obtain normal normalized structure. This process is applicable to steels with high hardenability and easy to produce granular bainite, such as 18cr2ni4mo, 20cr2ni4, 20CrMnTiH, 20mncr5, 16MnCr5 and 22CrMoH steels. The hardness is 156-200hbw and the metallographic structure is pre eutectoid F + pseudo eutectoid P, but the effect of eliminating banded structure is not ideal.