Fracture Failure Analysis of the Output Gear Shaft for a Granulator Main Gearbox

Abstract

The output gear shaft of the main gearbox for polypropylene granulator main gearbox breaks during operation.Fracture reasons of the output gear shaft are investigated through fracture analysis, physical and chemical inspection, and strength check. The results show that the output gear shaft has early fretting tear, due to instantaneous impact caused by fracture of the corresponding screw shaft. Under the compound alternating load of the torque and the bending moment, the early crack initiates and propagates along the journal. When the effective bearing area of the output gear shaft reduces to the critical point that it cannot withstand the torsional torque generated by normal operation, the fracture of the output gear shaft occurs. It is easy to form stress concentration at the cutter back groove of the output gear shaft journal, which is also one of the cracking inducement.

Keywords

• Gear shaft;Fracture failure;Instantaneous impact;Fretting tear;Stress concentration