GB531797A - Impact wrench - Google Patents

Abstract

531,797. Screwing-up nuts and bolts. CHICAGO PNEUMATIC TOOL CO. Aug. 2, 1939, No. 22416. Convention date, Oct. 14, 1938. [Class 83 (iii)] In an impact wrench having a rotatable impact hammer of substantial mass and moment of inertia with clutch teeth complementary with those on an anvil and driven by a continuously rotating spindle through a connection which permits limited axial movement of the hammer, and in which the hammer moves axially out of engagement with the anvil when the resistance to rotation of the anvil is excessive, the automatic means for moving the hammer axially into re-engagement with the anvil to deliver a rotational hammer blow is effected by centrifugal force. A shaft 16 rotated by an electric or pneumatic motor drives a spindle 17 having a recess 19 into which fits a cylindrical projection 20 on the anvil 21 to which the wrench socket 23 is connected. The spindle drives a rotary hammer 25 through a pair of balls 30 which each engage a pair of right and left hand spiral grooves 31R and 31L in the spindle and complementary pairs of right and left hand spiral shoulders 32R and 32L at the rear end of the bore 33 in the hammer 25. The hammer has a number of teeth 27 adapted to move into and out of driving engagement with teeth 28 projecting rearwardly from the anvil 21. Pivoted on ears 35 secured to the spindle 17 are a pair of centrifugal weights 38 with projections 39 abutting against a plate 40 pressing axially against the hammer 25 through a ball bearing 41 so as to press the hammer towards the anvil. When the nut or bolt becomes seated the resistance of the anvil to further rotation increases abruptly and further rotation of the spindle causes the hammer to be lifted out of engagement with the anvil under the action of the grooves 31R. balls 30, and shoulders 32R. The centrifugal weights are thus retracted. On release of the hammer from the anvil the hammer again rotates and overtakes the spindle due to the action of the centrifugal weights in forcing down the hammer in co-operation with the cam and ball arrangement. When the wrench is operated to loosen a nut &c. the balls 30 ride between the grooves 31L and shoulders 32L.