风电齿轮箱小齿轮齿面剥落原因分析

某风场1.5 MW风电机组齿轮箱中速轴小齿轮失效.该齿轮箱设计寿命20 a,实际使用了5 a.齿轮的材质是20CrNiMo,齿面经过渗碳淬火.采用宏观观察,微观观察和断口分析并结合其它理化测试,分析了小齿轮失效的原因.现场宏观观察发现,大部分轮齿相对完好,只有两支轮齿失效,其中一支齿面剥落,另一支齿面硬化层开裂.经分析,齿面剥落和齿面开裂的原因相同.导致齿轮失效的原因是:齿面粗糙度较大,较深的加工刀痕在异常冲击载荷的作用下造成齿面开裂,随后在循环工作载荷的作用下,萌生了疲劳裂纹并不断扩展,最终导致齿面硬化层脱落.建议提高齿轮表面加工质量,降低表面粗糙度,同时改进齿轮箱制动技术,避免异常载荷冲击造成齿面过载.

Failure Analysis of Flakes Fell from Small Gear Surface in Wind Power Gearbox

Flakes fell from the tooth surface of the small gear in the gearbox of a 1.5 MW wind turbine in service. The design lifetime of the gear is 20 a. However, it failed 5 a later since it was installed into the gearbox. The material is 20CrNiMo and the gear was carburized and quenched during the manufacturing process. Macro- and micro-observation of the fracture surface as well as some necessary physical and chemical analysis were applied to analyze the cause for the failure of the small gear. Besides, results from the macro-observation showed that only two teeth failed, on the one of which flakes fell from the tooth surface only left some pits, and on the other tooth surface some cracks can be observed obviously. The results also showed that pits and cracks could be attributed to the same reason. Tool marks on the tooth surface increases the risk of cracking. In addition, the abnormal load introduced by emergency braking led to cracks occurred along the machining marks on the tooth surface. Then, fatigue cracks nucleated at the tip of the crack and extend slowly driven by the working load. Finally, the hardened layer fell from the tooth surface and left some pits. It was suggested that the machining quality and the braking technology should be improved in order to avoid the cracking of the teeth surface under the abnormal impact load.