GB847495A - Improvements relating to grabs - Google Patents

Abstract

847,495. Grab-buckets; opening and closing mechanism. PRIESTMAN BROS. Ltd. Oct. 30, 1957 [Nov. 15, 1956], No. 34986/56. Class 78 (4). So that a double chain grab can be hoisted in the open position by the closing chain 7 a tumbler 26 can be positioned by a sliding link 20 secured to the opening chain 6, when the grab is suspended by that chain, so that it prevents passage of a button 35 on the closing chain 7. In the construction illustrated the tumbler 26 comprises a forked member which normally falls about its pivot 22 on the grab to a position determined by a stop 25, in which a wide portion 31 of the yoke permits the button 35 on the closing chain 7 to pass to close the grab. When the grab is subsequently suspended from the opening chain 6 the link 20, which connects the chain 6 to the body of the grab and has a slot 21 sliding over the pin 22, is pulled upwardly against a spring 32 so that a slot 29 on it engages a pin 28 on the tumbler 26 to raise it to the position shown in which it bears against a stop 27. The grab can be opened in this position by slackening the closing chain 7 so that the button 35 slides down inclined surfaces 32 on the tumbler 26 and is diverted through the wider opening 31. When however the closing chain is subsequently drawn in the button 35 is too wide to pass through a narrower portion 30 of the tumbler 26 so that the grab is raised by the closing chain but held open. The tumbler 26 is subsequently released when the grab is lowered on to material to be picked up. The invention permits the grab to be slung between two derricks, one of which carries the opening chain and the other the closing chain, so that it can transfer material from a position below the derrick carrying the closing chain to a position below the derrick carrying the opening chain and yet be returned from the latter position, by hauling on the closing chain, without the grab closing.