| 摘要 |
PROBLEM TO BE SOLVED: To pull out a drilling bit, keeping the wall surface of a drilled hole as much as possible from crumbling when the drilling bit is in a jamming state in a drilling device for drilling a rock-bed or the like with the drilling bit mounted through a rod to the tip of a shank rod accommodated in a drifter, by striking the shank rod forward while rotating it. SOLUTION: A reverse striking piston 8 is mounted in a longitudinally slidabld manner on the front side of a collar part 3a on a shank rod 3. Advance side and retreat side working chambers 24, 25 are provided for advancing or retreating the reverse striking piston 8. Only the retreat side working chamber 25 is put in a high pressure state by a hydraulic supply circuit C, and the shank rod 3 is retreated by the reverse striking piston 8 into a position where it can be struck by a normal striking piston 9. The retreat side working chamber 25 is alternately changed into the high pressure state and low pressure state to directly apply backward impact to the shank rod 3 by the reverse driving piston 8.
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