| 摘要 |
A reverse circulation down-the-hole hammer drill actuated by a fluid such as compressed air comprises: an outer wear sleeve 1; a backhead 2 assembly for connecting the drill to a double-walled drill string; a fluid diverter 5 mounted inside the outer wear sleeve 1 adjacent to the backhead 2; an inner tube 9 concentric with the outer wear sleeve 1 and extending into the fluid diverter 5 and defining at least part of a central return passageway in the drill; a bit 10 located by a chuck 3 at the other end of the outer wear sleeve 1; an inner cylinder 6 mounted inside the outer wear sleeve 1 and defining a fluid communication passage 8 between the diverter and an annular piston chamber via porting means 26, 27; a piston 14 slidably disposed in the annular chamber so as to co-operate with the porting means 26, 27 and mounted over the inner tube 9 to reciprocate within the annular chamber and repeatedly strike the bit 10, the face 18 of the piston 14 adapted to strike the bit 10 being defined by a reduced diameter front end portion, the piston 14 also defining a shoulder 29 opposite the strike face of the piston to which a substantially continuous supply of pressure fluid is applied via the porting means 26, 27, the inner cylinder 6 extending only part-way into the said annular chamber, and the porting means 26, 27 being adapted to apply pressure fluid to the piston so as to maintain a downward force on shoulder 29 of 30 - 45% of the force on lift face 32 during the lift stroke. <IMAGE> |
