Patent GB-154952-A (GB)
Abstract: 154,952. Clark, C. J. J., and Woodbridge, W. E. June, 27, 1919. Grab-buckets.-In apparatus for digging graves, trenches, &c., in which the earth is loosened bv a frame furnished with cutters and with hydraulic hammer mechanism for driving the cutters into the ground, the loosened earth is removed by a grab which is closed by ropes passing down from fixed points on the grab sections round guide pulleys on the frame before being led away to the operating-mechanism. In the form shown in Figs. 1, 2, and 5, the grab 11 comprises four cooperating sections arranged in pairs on a common shaft 12. Hoisting-ropes 15 connect the shaft 12 to a drum 17, while closing-ropes 10 pass from the grab sections over pulleys 9, 13 on the frame and staging respectively, to drums 14, Fig. 5. Both the drums 14, 17 have other drums mounted on the same shafts which are connected by supplementary ropes to the ram of a hydraulic cylinder 29. On moving the hydraulic ram to the left in Fig. 5, the supplementary rope 19 is paid out. This allows the drums 17 to rotate under the weight of the grab to lower the same, while the drum 18 takes up the slack in the rope 19. The movement of the ram also withdraws the supplementary rope 34 from the drum 30, and thus rotates the drums 14 to take up the slack in the closing-ropes 10 caused by the lowering of the grab. When the grab rests on the ground and the ropes 10 are taut, the pulley 36 on the ram moves relatively to the rope 34 until a pin-andslot spring clutch 39 at the end of the rope is engaged with a moving truck 38 which is pushed along by the advancing ram. Further movement of the ram at this stage rotates the drum 30 forcibly, to operate the ropes 10 to close the grab. Conversely, the movement of the ram to the right hauls on the rope 19 and thus operates the drums 17 to raise the grab, while the slackening of the rope 34 permits the closing-rupes to be paid out as required. During this movement of the ram, the truck 38 lags behind the ram, since the only connexion therewith is by means of the rope 34 coiled round the pulley 37. When the grab arrives at the top of the frame, ropes 21, attached to the grab sections, and to the hoisting-rope, are squeezed together in fixed funnel-shaped members 20 to open the grab. This operation stops the hoisting rope and the corresponding supplementary rope 19, and thus the further paying out of the ropes 10, necessitated by the opening movement of the grab, is obtained by the inward movement of the truck 38 which takes up the previous lag with respect to the ram. Rings may be provided on the ropes 21 to keep the grab open during lowering. Fig. 7 shows a modification in which the various drums are driven by spur gearing on a common axially-movable driving shaft b. A spur wheel on the hoisting drum d can be engaged with a wheel b<4> for raising or lowering the grab. The closing ropes g<1> are wound on drums g which are operated indirectly through the medium of other drums h. The drums h are rotated by mutilated gears b<2> to raise weights which subsequently fall by gravity to drive the cutters into the earth. When the grab is to be closed, the drums g, h are moved axially by means of wedges i until they are connected by pawl-andratchet mechanism j, k. In this position the rotation of drums h, under the action of the falling weights, winds the ropes g<1> on to the drums g to close the grab.