GB1184892A - Improvements relating to Impact Wrenches - Google Patents

Abstract

1,184,892. Impact wrenches. HOLMAN BROS. Ltd. 13 April, 1967 [18 April, 1966], No. 16867/66. Heading B3N. A compressed-air-driven impact wrench comprises a rotary hammer 30 Fig. 1, axially movable so as to engage an anvil 16 by pneumatic pressure, and a centrifugal shuttle valve 52, rotatable with the hammer, which is biassed towards an operative position, in which the pressure acting on the hammer is relieved, to allow it to be retracted, but which is held in the inoperative position by centrifugal force so long as the hammer rotates above a certain speed. Valve 52 has a shuttle with two pistons of different areas. A sleeve 28 is splined to the shaft 21 of a sliding vane rotor 20, and hammer 30 is rotatable with, and axially slidable in sleeve 28. The inner end of hammer 30 is formed as a piston 44, and air is supplied to move the piston against a spring 46, through a passage 22, and a port 50 in anvil shaft 12, and thence along a groove 51 formed in the bore of piston 44, air from the piston also passing to the two pistons of valve 52, when this groove is aligned with the port. The cylinder 45 of piston 44 can be vented at the required time through valve 52, so as to allow spring 46 to retract the hammer from the anvil. In operation, hammer 30 is retracted, and air motor shaft 21 is rotated, thus rotating sleeve 28 and hammer 30. Air is also supplied along bore 22 into shaft end 26. Hammer 30 and sleeve 28 accelerate, and the shuttle of valve 52 moves radially outwardly to close the valve, due to centrifugal force. Hammer 30 turns relative to shaft end 26 until slot 51 and port 50 are aligned, thus admitting air into cylinder 45. Hammer 30 is moved axially against spring 46 until the dogs 38 and 17 on the hammer and anvil engage. The fastener is tightened, and due to the slowing down of the parts of the wrench, the air that passes to the differential pistons of valve 52, overcomes the centrifugal force, the shuttle moves radially inwardly so as to vent the cylinder 45, and spring 46 retracts hammer 30. A further cycle commences, and impacts are thus produced until the motor stalls when the fastener is fully tightened. For loosening a fastener the motor is rotated in the opposite direction.