注入头是连续油管作业机中驱动连续油管上提下放的关键设备。LG450型注入头作业期间发生故障，拆解后发现链传动系统损伤严重。对链传动系统进行宏微观形貌分析，发现轮齿外侧有弧形刮痕，齿面存在倾斜擦痕。对链轮轮齿进行化学成分检测、硬度试验及金相试验，结果显示材料达到工艺要求。对链轮和链条的啮合过程进行有限元仿真，结果显示接触压力分布与失效链轮齿面及侧面摩擦痕迹一致。揭示了该注入头链传动系统失效原因为链条滚子与链轮轴线空间交叉，滚子与轮齿非正常啮合。研究表明链轮链条的运动状态会对注入头工作安全性产生重要影响，对指导注入头设计和加工有重要意义。

The injection head is the key equipment to drive the coiled tubing in the coiled tubing operation machine. A fault occurred during the operation of a LG450 injection head, and it was found that the chain drive system was seriously damaged after disassembly. The macro and micro morphology analysis of the chain drive system shows that there are arc-shaped scratches on the outer side of the gear teeth and inclined scratches on the tooth surface. The chemical composition test, hardness test and metallographic test were carried out on the sprocket teeth, and the results showed that the material met the process requirements. The finite element simulation of the meshing process of the sprocket and the chain is carried out. The results show that the contact pressure distribution is consistent with the friction marks on the tooth surface and side of the failed sprocket. It is revealed that the failure reason of the chain drive system of the injection head is the spatial intersection of the chain roller and the sprocket axis, and the abnormal meshing of the roller and the gear teeth. This study shows that the motion state of the sprocket chain will have an important impact on the safety of the injection head, which is of great significance to guide the design and processing of the injection head.