GB244533A - Improvements in and relating to grabs - Google Patents

Abstract

244,533. Smith, W. Sept. 22, 1924. Grab-buckets. - Relates to the locking and tripping mechanism of grabs or excavators of the kind in which the lower sheaveblock 3 slides in guides connected with the grabhead 2 and is looked to the lower cross-beam 4 for closing and raising the grab by means of pawls 14, 15 pivoted on the member 3 and arranged to engage automatically with the head of a catch-pin 12 on the lower cross-beam for closing the buckets, and to be disengaged automatically when the buckets are lowered on to a dump, and the object is to permit of opening the buckets in mid-air either by manipulating the grab chain or by a hand-line. The sheave-block 3 moves between telescopic guides attached to the crossbeam and to the grab-head. The pawls 14, 15 are pivoted on a cross-head 11 on the sheaveblock and are locked in engagement with the pin 12 by a ring 25 pivoted in a ring-shaped lever 23 which is pivoted at 24 on the member 3. The lever 23 co-operates, as described below, with the tripping device 30, 26 and with a weighted lever 20 pivoted at 24. While the grab is closing, a gravity-catch 26 pivoted on the lever 23 passes above a catch-bar 30 attached to the links 7, and on supporting the grab and lowering the sheaveblock in the guides, the catch 26 is held by the bar 30 so that the pawls 14, 15 are freed from the locking-ring 25 and the buckets fall open. The locking-ring 25 may also be disengaged from the pawls 14, 15 to discharge the grab in mid-air by pulling on the line 37 connected to the lever 20 which is provided with a toe 20' engaging a pin 28 on the lever 23. If the closed grab is lowered on to the dump and the chain 31 is slackened. a weight 22 on the lever 20 lifts the locking ring 25 and the pawls 14, 15 fall free of the pin 12 so that buckets may be opened by hauling in the chain 31. When the open grab is lowered to the ground and the chain 31 payed out, the sheave-block 3 is lowered in the guides and a stirrup 19 suspended from the lever 20 comes against a bar 29 on one of the buckets, raising the weighted lever 20 to the position shown in Fig. 2, with the locking ring 25 resting on the ends of the pawls 14. 15. On further descent of the sheave-block 3, the lever 20 is raised, leaving the ring 25 free to fall and the ends 16 of the pawls 14, 15 come against bars 17 on the buckets so that the pawls are brought under the head of the pin 12 and are then locked bv the ring, and the grab can be closed and lifted. Specification 172,761 is referred to.