Fracture analysis of 20CrMnTi carburizing gear used in torque distribution gear box of double screw extruder

PAN Yuan

(Zhoushan Institute of Calibration and Tseting for Quality and Technology Supervision, Zhoushan 316021, China)

Abstract: In order to solve the fracture problem of 20CrMnTi carburized gear used in the torque distribution gearbox of the twin screw extruder, the fracture morphology analysis, microstructure observation and hardness gradient test were investigated to the study of fracture gear. After the analysis of the structure design and heat treatment process, the internal relations between failure mechanisms and gear strength was established. A method was presented to the improvement measures in design and technology and other aspects of the gear. The experimental results show that the distance between the keyway bottom and the root circle less than 2.5 mt is the main reason for the low strength and fracture of the gear; the large amount of residual austenite in the carburizing layer and the center network iron ferrite reduced the fatigue strength of the gear, fatigue crack is rapidly expanding along the line and plane of stress concentration; to reduce the stability of austenite cooling process, carburizing or quenching temperature not more than 950 ℃ and holding time less than 6 hours, can improve the fatigue strength of the gear.

Key words: twin screw extruder; torque distribution gearbox; 20CrMnTi; carburized gear; fatigue fracture