球磨机变速器开裂的失效分析

Analysis on Cracking Failure of Ball Mill Speed Transmission

某矿山球磨机变速器圆锥齿轮使用10 d即发生开裂失效,为此,用直读光谱仪、拉伸试验机、维氏硬度计、金相显微镜、扫描电镜研究了球磨机齿轮的化学成分、力学性能、金相组织及断口形貌。结果表明:齿轮的金相、硬度、成分均符合技术要求,断口的裂纹源位于断口内部,裂纹源处有较多的O、Al、Ca、Na等夹杂物,这些夹杂物硬度较高,割裂了材料基体,使基体产生孔洞效应,受到外力时容易产生应力集中。根据断裂力学计算,夹杂物产生的应力集中约200 MPa,和淬火后的残余应力叠加,是导致齿部开裂的主要原因。采取的改进措施是将原材料由普通钢厂供应改为特殊钢厂供应,减少钢中夹杂物的含量。实践证明,改进措施彻底解决了齿轮的开裂问题。

The bevel gear of transmission of ball mill in a mine cracked affer 10 d of use,for this,the chemical composition,mechanical properties,microstructure and fracture morphology of ball mill gears were studied by means of direct reading spectrometer,tensile tester,Vickers hardness tester,metallographic microscope and SEM. Results showed that the metallographic,hardness and composition of the gear met the technical requirements. The crack source of the fracture was located in the inside of the fracture,and there were many O,Al,Ca,Na and other non-metallic inclusions in the crack source. These inclusions had high hardness,cut the material matrix,which made the matrix produce the hole effect and stress concentration when subjected to the external force. According to the fracture mechanics calculation,the stress concentration caused by inclusions was about 200 MPa,which was superposed with the residual stress after quenching. This was the main cause of tooth cracking for the gear. The improvement measure adopted was to change the raw material supply from ordinary steel plant to special steel plant,so as to reduce the content of inclusions in the steel. It was proved by practice that the cracking problem of gear was completely solved by the improvement measures.