GB172449A - Improvements in self sustaining pulley blocks - Google Patents

Abstract

172,449. Willetts, C. Sept. 24, 1920. Winding pulley-blocks; geared pulley hoists; driving-gear; selfsustaining gear.-Driving-gear for pulley-blocks, cranes, &c. comprises two sets of worm gear, one set being either reversible or - irreversible and driving the pulley or drum in either direction for - hoisting or power lowering, while the other set is reversible and acts as a self-sustaining bear, as a means for permitting braked gravity lowering, and as a means for rapidly positioning the unloaded load chain or hook. As applied to a pulley-block, the apparatus comprises two wormwheels 1, 2, each formed integral with one of two chain sprockets 5, 6. The lower block carrying the load is suspended from two bights in the chain hanging from both sprockets, so that it can be manipulated by the rotation of either sprocket. Ordinary hoisting or lowering is performed by actuating the worm-wheel 1 through the medium of the hand chain-wheel 14. During the lifting movement a friction cone clutch 26 and ratchetwheel rotate together, but on the lifting-effort ceasing, the cone and ratchet form a selfsustaining gear for the load in so far as rotation of the sprocket 6 is concerned, and compel the worm shaft to overcome the friction of the cone clutch when the hand chain-wheel is rotated for lower. ing. The other worm-wheel 2, which also sup ports the load in part, is motionless during the operation of the worm-wheel 1, as the wormwheel is prevented from driving the worm 9 under the pressure of the load by a cone clutch member 15<a> engaging a non-rotating sleeve 22 to act as a self-sustaining brake for the sprocket 5. A lever 20 may be manipulated to move the member 22 axially to relieve this brake to permit braked gravity lowering, or rapid manipulation of the underloaded chain by direct hand haulage on the chain. A mechanical brake 30 mav be added to the apparatus to prevent the falling load from getting out of control.