| 摘要 |
An overburden drilling device includes a drill bit body, a percussion element for applying impacts to the body, and a casing attached to the body. The casing is connected to the drill bit body by a casing shoe which comprises semi-cylindrical halves which are held together by a circular ring that is welded to the halves. The casing shoe and the drill bit body are interconnected by radially overlapping walls so that the drill bit body pulls the casing along during a drilling operation.
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