Patent GB-618147-A (GB)
Title: Improvements relating to dumping grabs
IPC: B66C3/06
Filed: 1946-10-25
Abstract: 618,147. Grab-buckets. PRIESTMAN BROS., Ltd., PRIESTMAN, S. H., and PIPER, C. W. Oct. 25, 1946, No. 31763. [Class 78 (iv)] In a multiple purchase dumping grab the opening and closing mechanism comprises a spring-operated winding drum, a rope, one end of which is secured to said drum while its other end is adapted to support the grab, a tumbler which is raised by the closing movement of the jaws and allowed to fall as the jaws open, a button disposed. intermediately on the rope and adapted when raised to pass the tumbler freely when the jaws of the grab are open, but to engage beneath the tumbler when the jaws are closed, a ratchet device associated with the drum, and automatic trip mechanism operated by the button raising the tumbler, to disengage the ratchet device so that the drum is free to pay out the rope allowing the jaws to open. The jaws 8, Fig. 1, are pivoted to arms 10, the upper ends of which are-pivotally mounted on plates 15 secured to a cross-head 13 which has a central bell mouth opening 14. The jaws 8 are also pivoted to the frame 18 which carries the lower purchase sheaves 21; 22, the upper sheave 19 and the spring drum 26 being mounted between the plates 15. A rope 20 passes from its attachment to the drum 26 around sheaves 22, 19 and 21, and terminates at a connection 28 attached to a button 34 by a short rope 33, the button being suspended on a rope 36 attached to lifting ring 37. A pivoted tumbler 38, of the type described in Specification 23010/13, [Class 78 (iv)], is actuated by a cam member 39 connected with one jaw 8 by an adjustable link 41 and crankarm 42 arranged so that the tumbler falls when the jaws 8 open and allow the button 34 to freely pass therethrough. The grab is lowered on the spoil with the jaws open and is closed by withdrawing the rope in either one lift or a series of short lifts, after each of which the slack is taken up by the drum 26 which can rotate in a winding direction only when pawl 43, Fig. 4, engages ratchet 27. When closed, the grab is moved to the place of discharge and lowered on to the heap of material, after which the rope is paid out until ring 37 rests on bell mouth 14, and as the connection 28 cannot pass below the aperture 32 there is sufficient slack in ropes 36, 33 to allow button 34 to pass under the tumbler 38. The rope is now raised, the button 34 engages beneath the tumbler 38 which when raised lifts trip lever 46, and pin 47, which engages a projection 45 on the pawl 43, lifts the pawl out of engagement with the ratchet 27 and under the weight of the spoil the jaws open drawing down frame 18 and sheaves 21, 22 which causes the rope 20 to unwind from the drum 26, thus retensioning the spring. Opening of the jaws frees the tumbler 38 from the cam 39 so that when the grab is again lowered on to the spoil the button 34 and the tumbler 38 drop, and on rehoisting the button can pass freely through the tumbler. In a modification, the grab is discharged by hand, the pin 47 being withdrawn so that the pawl 43 is no longer tripped when lever 46 is engaged by tumbler 38, and a rope is attached to a tripping lever 51 having a cam surface 53 which engages a pin 50 on the pawl 43. To prevent discharge of the load before button 34 has passed under tumbler 38 a projection 55 on the lever 51 is engaged by a pin 56 on the trip lever 46, which latter, until tripped by tumbler 38, locks the lever 51. Pawl 43 is prevented from re-engaging the ratchet 27 on release of lever 51 by pawl stop lever 58 which engages the projection 45 on the pawl 43, which lever 58 is released by a pin 57 which strikes a projection 59 on said lever when the trip lever 46 and tumbler 38 fall after the grab has been lowered on to the spoil again. Spring 48 between the lever 46 and the lever 51 pulls back the lever 51 after tripping the pawl 43 and also assists the trip lever to press down the pawl stop lever 58.