非开挖反向回拉扩孔施工过程中时常出现钻杆正转而发生退扣，造成钻具孔内脱落事故的反常现象。
The dropping buckle usually occurs when reverse pulling is used for expanding the bore in the trenchless construction, thus causing the fall-off of the drilling tools.
公锥与正、反扣钻杆及其他工具配合使用，可实现不同的打捞工艺。
The taper tap can effect different fishing operations when equipped with RH thread or LH thread drill pipes and other tools.
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