某聚丙烯挤出机在运行中发生螺杆轴断裂, 采用断口宏观分析、扫描电镜观察、化学成分分析、显微组织检验、力学性能测试等方法对断裂轴开展失效分析。结果表明: 螺杆轴的断裂为扭转疲劳断裂, 裂纹起源于花键根部; 螺杆轴的疲劳强度低、花键槽根部应力集中、材料内部微孔聚集、材料组织不均匀等原因共同导致螺杆轴发生早期疲劳断裂; 建议采取改进热处理工艺、提高安装精度、检查表面缺陷等措施。

A fracture accident of a screw shaft of a polypropylene extruder occurred during operation. In order to find the fracture reasons, the failure analysis was carried out by means of macroscopic fracture analysis, scanning electron microscope observation, chemical composition analysis, microstructure observation and mechanical property testing. The results show that torsional fatigue was the cause of the fracture, and the cracks originated from the spline root. Low fatigue strength, stress concentration at spline root, micropore aggregation and uneven microstructure were the reasons together caused the screw shaft fatigue fracture in the early service life. Some measures, including improving heat treatment process and installation precision and examining surface defects, were suggested.