| 摘要 |
A down hole hammer assembly comprising a reverse circulation hammer (11) having a drill bit (12) mounted to one end of a housing which accommodates a percussive hammer, the other end of the housing being adapted to be mounted to a drill string, the assembly further comprising a support member (14) receivable on the lower end of a bore hole casing (13) which is receivable over the drill string, said support (14) comprising a first part (15) adapted to be fixed to the lower end of the casing and a second part (16) rotatably received on the first part (15) and capable of limited axial slidable movement thereon, the second part (16) being engageable with the drill bit (12) to be rotatable with the drill bit (12) on rotation of the drill bit (12) in one direction and to be movable axially with the drill bit (12) the drill bit (12) being disengagable with the second part (16) to be able to be movable axially relative to the second part (16), flow passageways being provided between the drill bit and the second part to deliver fluid to the cutting face and the drill bit being provided on its outermost axial face with at least one opening (33) to receive the fluid and entrained cuttings.
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