Coal Mill 42CrMo Carburized Steel Gear

Coal mill is an important equipment in coal-fired units of thermal power plant, which breaks coal blocks into pulverized coal, mainly by means of crushing, crushing and grinding.Coal mill reducer is a two-stage planetary gear reduction drive structure. The motor drives the intermediate shaft to rotate through a pair of bevel gears meshing drive, then engages with planetary gear through toothed coupling, and finally outputs power.Gear is an important part of reducer of coal mill, which is used to transfer power and change running speed.During the meshing process, both rolling and sliding between the meshing teeth are required, as well as alternating stress. Therefore, adequate hardness and wear resistance are required on the gear surface.

A coal mill was put into operation in 2008 and overhauled in 2015. In the same year, the sun gear in planetary gear drive suffered serious teeth fracture, with a cumulative running time of about 40,000 hours.

According to the data, the diameter of the sun wheel is 190mm and the material is 42CrMoA, a high-quality alloy structural steel. The processing procedures of the gear are: blanking, forging, normalizing, machining, carburizing and quenching, low-temperature tempering and grinding.After carburizing and quenching, the hardness of the tooth surface reaches HRC60 + 2.

There are many reasons for gear failure, such as gear design, force, processing technology and precision, forging, heat treatment, gear installation and maintenance can cause gear teeth fracture.The failure analysis of gear is carried out from the aspects of stress analysis, morphology analysis, component analysis, metallographic structure analysis and mechanical property test, etc. to determine the cause of failure and provide solutions.