The vertical coal mill is shown in Figure 1.Reducer is an important part of coal mill and is mainly used as drive and deceleration device of coal mill in electric power industry.The reduction gear of coal mill is a two-stage reduction device with horizontal input and vertical output. The first stage is bevel gear drive and the second stage is planetary gear drive.As shown in Figure 2, a schematic representation of the reducer gear drive, the failed gear sun wheel is mounted on the upper end of the intermediate shaft.
It is known that the number of teeth of each gear in the reducer of the coal mill is bevel gear 1, z1=18, bevel gear 2, z2=62, sun gear 3, z3=20, planetary gear 4, z4=79, inner ring gear 5, z5=178, and the rated power of the motor of the coal mill is 650 kW.According to the analysis of tooth root fracture of intermediate shaft sun gear, the bending fatigue strength of tooth root of this gear is checked and the checking formula is as follows :
Where: B is tooth width; m is modulus; T1 is small wheel transfer torque, K is load factor; Z1 is pinion tooth number; YF is tooth coefficient.
Based on the given gear material and data, the bending fatigue strength of the solar gear root is obtained as follows:
The calculation results show that the bending fatigue strength of the solar gear tooth root is insufficient and the surface gear is prone to bending fatigue failure of the tooth root during the expected life.