Patent GB-227997-A (GB)
Title: Improvements in grabs
IPC: B66C3/06
Filed: 1924-01-14
Abstract: 227,997. Burke, N. I. D., and Somerville, T. P. Jan. 14, 1924. Grab-buckets.-Relates to single-rope grabs of the type in which the buckets are hinged to spreader arms 11 and to a lower frame which can be locked to or released from a lower block 2 moving vertically on telescopic guides 8, 7 extending from the lower frame to the grab-head. The invention includes trip mechanism for releasing the buckets in mid-air or by dumping with a safety device for preventing accidental release; means for taking up wear on the jaws 3a, 4a of the buckets, for adjusting the extent of opening of the buckets, for ensuring correct alignment of the lower and upper blocks, for preventing chafing of the hoisting rope, for preventing jamming of the telescopic guides, and additional guiding means for the lower block. (1) Figs. 4 and 5 show sectional and side elevations of the upper and lower blocks 1, 2 with the trip mechanism and looking device. When the block 2 is lowered on to the lower frame 6 with the buckets resting open upon the ground, an adjustable striking plate 27 bears on the inner ends of counterweighted catch-levers 21 pivoted on the frame and brings them into the position shown in Fig. 4 in which the hooked ends 25 engage flanges 26 on the block 2 so that the buckets will be closed when the block is lifted. The catches are locked in this position by a trigger lever 27<a> pivoted on the block 2 at 27b. The outer weighted arm of this lever is raised into the locking position shown in Fig. 5 by a plate 38 on a spring-pressed rod 29. The lever 27 is held in the locking position by frictional engagement with the lever 21, the rod 29 and plate 38 being depressed as shown in Fig. 5, when the grab is closed, by engagement with a stop, not shown, on the upper block. To prevent jamming, the spring 28 is placed around the rod 29 and the plate 38 bears against a roller 39<a> instead of a pin on the trigger lever. When the grab is raised to the discharging point, a spring- pressed rod 32 strikes a suspended plate, which may be mounted yieldingly to avoid shock, and is depressed so as to engage the upper end 31 of the lever 27a and releases the catch-levers 21. A safety locking-lever 44, 48 is normally held by a spring in the path of a rod 43 which acts as a stop to prevent accidental disengagement of the trigger lever, and the rod 32 in moving as described to release the trigger lever first turns the lever 48, 44 aside from the path of the rod 43. If the closed grab is lowered to the ground, the block 2 falls slightly and allows the rod 43 to rise sufficiently to release the trigger 27<a>. The outer end of the trigger lever falls by gravity, but if it is should be held up owing to friction between the parts 21 and 27a, the block 2 is lowered further until the plate 27 engages the ends of the catches 21. The idle travel of the rod 29 is sufficient to allow these movements without bring- ing the plates 38 into engagement with the roller 39<a>. If the trigger lever is to be released in mid-air by a hand-line 42, the safety device 48 &c. is first removed. (2) Metal strips 17 are secured to the lower edge of the upper block 1 and may be removed one by one as the jaws 3a, 4a of the brackets become worn, in order to ensure closure. (3) Toggle levers 12, Fig. 2, are pivoted to the spreader arms and to the buckets, several pivot holes being provided in the lower toggle levers so that the grab may be set to open to the desired extent. (4) Guide-plates 40, Fig. 4, are secured to the inner frame of the lower block in order to bring it into alignment with the upper block. (5) The hoisting rope 18 passes between guide rollers 19, Fig. 2, having their peripheries concave to encircle the rope. (6) The inner member 7 of the telescopic guides is fitted with rollers 9, Fig. 7, and the lower end of the outer member 8 is closed by a plug to keep out sand &c. (7) Pairs of rollers 9a, Fig. 4, on the lower block run on the guides 8, 7.