Patent GB-568014-A (GB)
Title: Improvements relating to wide span bucket grabs
IPC: B66C3/08
Filed: 1943-04-27
Abstract: 568,014. Grab buckets. CAULFIELD, W. J., and WESTWOOD & CO., Ltd., J. April 27, 1943, No. 6652. [Class 78 (iv)] In a wide-span grab of the kind in which the buckets 2, 3 are widelyseparated when open by spreader bars 9, 10, as the pivot 11 of the bars is lowered to open the grab stops, such as 12, 13, come into action to limit the opening or unfolding of the bars, and the folding movement of the bars, during the closing of the grab, does not commence until the buckets have completed a first part of their movement about their pivots 7, 8, the buckets being suspended from the bars by purchase gears 20, 21 constituting the means by which the effort to close the grab is transmitted thereto from the crane or winch operating the grab. In the construction shown in Figs. 1 and 2, applied to a tworope grab, the buckets 2, 3 are pivoted at 5, 6 to a head 1 and to the bars 9, 10 at 7, 8. The opening and closing rope or chain 15 is wound round a drum 14 mounted on the pivot 11 of the bars, this drum being fast with other smaller drums 17, 18 from which ropes 20, 21 pass round pulleys 22, 23 on the buckets to the ends of a compensating lever 24, 25 pivoted at 27 on the head 1. If the grab is open, a pull on the rope 15 unwinds this rope from the drum 14 and winds the ropes 20, 21 on their drums, thereby turning the buckets 2, 3 on their pivots 7, 8 until stops 28, 29 on the buckets abut against the bars 9, 10. Continued hauling on the rope 15 and the consequent further winding up of the ropes 20, 21 causes the pivot 11 to be raised and the bars folded together until the grab is closed, as shown in Fig. 1. The loaded grab is now raised by further hauling on the rope 15 and simultaneous hauling on a holding rope 30 as usual in a tworope grab. To open the grab, the rope 30 is held and the rope 15 paid out, the bars 9, 10 opening out until their stops 12, 13 abut, after which the buckets 2, 3 turn about their pivots 7, 8 until they reach the fully-open position shown in Fig. 2. The spreader bars 9, 10 may be in horizontal alignment when fully open, as shown, or they may be slightly inclined downwardly from their pivot 11. The following modifications are described: (1) A doublepurchase may be obtained by passing the ropes 20, 21 round the pulleys 22, 23, and round pulleys mounted on the ends of the lever 24, 25 to anchorages on the buckets. (2) In a singlechain grab, Fig. 6, the hoisting and operating chain 33 passes through the head 1 to a main drum 36 round which it is wound. Fixed to this drum are secondary drums 37, 38 from which chains 39, 40 pass over pulleys 41, 42 on the buckets, round pulleys 43, 44 on the ends of the compensating lever 45 pivoted at 46 to the head 1, and finally to anchorages 47, 48 on the buckets. The head 1 has the usual hook or hooks 49, 50 for engaging with a ring 51 suspended from the crane when the grab is to be opened by paying out the chain 33. (3) In a triple-rope grab, Fig. 8, the three ropes comprise a holding rope 54 and two operating ropes 52, 53 passing to separate buckets over pulleys 55 on the buckets, pulleys 57, 58 on the head 1 and round the pulleys 55 again, being finally secured to the ends of a compensating lever 59 mounted on the pivot 60 of the bars 9, 10. (4) In a single-chain grab, the holding hooks 49, 50, Figs. 9 and 11, have their pivots 64, 65 mounted on a cross-head 71, slidable in vertical slots 66, 67 in the grab head 1. Two pawls 62, 63 are also mounted on the pivots 64 and are formed with conical sockets 68 adapted to engage a conical surface on the button 61 formed on the grab chain. When the grab is closed and approaching the discharge ring 51, the parts are as shown in Fig. 9; the weighted hooks 49, 50 being kept in that position by stops 72, 73. As the hooks pass over the ring, they tilt and raise the.pivots 64 and cross-head 71, after which they fall back again into position to engage the ring and hold the weight of the grab. The grab chain is now paid out and the grab opens, the discharge ring lifting the hooks, the pawls and the cross-head to the top of the slots 66, 67. During the opening of the grab the button 61 passes through the grab head past the pawls 62, 63, which it turns aside from their normal horizontal position. To lift the grab empty and open the chain is hauled in until the button 61 engages the conical socket in the pawls and transmits the weight to the head through a tapered seating 70 in the cross-head 71. As soon as the hooks 49, 50 are clear of the ring, their weighted outer ends fall back against the stops 72, 73, leaving the ring free. The grab may now be lowered for the next load, and when it rests on the spoil the chain is payed out further and the button releases the pawls which fall to the position shown in Fig. 9, so that on hauling in the chain again the button passes through the pawls and the grab is closed by further hauling.