| 摘要 |
Pressure-air driven percussion device for a down-the-hole drill (1) with a hammer-piston (6) which is axially reciprocally movable in a hammer-piston chamber (18) through a driving device (9), said hammer-piston (6) in operation acting with a hammer-end (16) against an upper end (17) of a drill bit (2) which is positioned inside a chuck (3), wherein an air-cushion for reducing percussive power is arranged to be formed at the hammer-end of the hammer-piston in positions where the drill bit (2) has been moved passed a predetermined distance in the percussion direction. The drill bit (2) is sealingly slidingly supported in a drill bit bushing (5), and the hammer-end (16) of the hammer-piston (6) is formed so that it sealingly cooperates with the drill bit bushing (5) in said positions in order to form said air-cushion (19). The invention also concerns a down-the-hole drill (1).
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