By test and analysis,the direct reasons leading to failures are the defaults in designing coiler mandrel diameter change and controlling hydraulic system program but not the system parts themselves.

• 通过测试与分析,排除了液压系统元件本身的问题,认为卷筒变径设计缺陷和液压系统程序控制缺陷是故障产生的直接原因。