The tooth surface of the big gear after carburizing and quenching and tempering heat treatment

Gear materials do not meet 20CrNi2MoA steel alloy elements (especially Ni content is not enough), and in accord with 20CrMo steel alloy elements. Broken teeth material composition and standard steel alloy element contrast detection, tooth surface and core of Luo hardness test results /HRC, Rockwell hardness of gear core is about 36HRC, tooth surface Rockwell hardness is 56hrc around, relative to the bearing by heavy gear in terms of, low hardness of the tooth surface, should be about 60HRC. There are 2 main failure forms of the big gear of the failure: the broken tooth and the tooth surface. Gear tooth surface pockmark the main reason for tooth surface hardness and low load too high, resulting in lack of contact strength of gears, gear in the alternating contact stress, first on the tooth surface produce tiny micro crack and wear, said is pitting and pitting spalling to development, gradually caused by belt along the pitch circle of a shallow spalling, the further expansion of the spalling, eventually leading to tooth surface is large flaking, pitting. The main reasons for the large gear broken teeth are the load, the tooth surface and the installation or machining accuracy is poor (for example, such as the axis deflection, gear clearance), resulting in gear away from the 1 side of the coupling, the bending strength of the gear, the gear meshing condition is rapidly deteriorating, and in the case of periodic stress, fatigue, and eventually lead to broken teeth.

From the perspective of large gear material, the use of 20CrNi2MoA or better gear steel materials. From the heat treatment process point of view, the gear tooth surface after carburizing and quenching and tempering heat treatment, ensure that all tooth surface hardness is not less than 58HRC, and the thickness of the hardened layer processing residual thickness shall not be less than 1.5mm; re design and check the contact strength and bending strength of the gear, the safety factor to take a large number of. Improved gear lubrication state, in a long time after shutdown, restart best barring or add oil pump circulation, to start to improve the lubrication state. Macroscopic morphology of the fracture surface of composite fatigue or stress corrosion. The surface of broken teeth is banded, and this is the main evidence of fatigue fracture, which can determine the fracture properties of broken teeth. Material test in order to determine whether the material of the gear is in a gear steel 20CrNi2MoA, pick two broken teeth, by direct reading spectrometer to detect the material content of alloy elements.