The Mechanical Handling and Storing of Material

DISCHARGING BY MEANS OF SKIPS AND GRABS 405 At the upper end of the framing is a second block e, containing another series of sheaves m, which in the construction illustrated are one less in number than the sheaves of the lower block or head c. The sheaves in the blocks c and e are set at an oblique angle to the framing, so that the sheaves and off-running portion of the operating rope shall come on the centre line of the top of the grab. Rope guides or eyes mn are provided on opposite sides of the block e, with centres corresponding to the centre lines of the grab. Hinged to the block E is the hoisting block g, having rope guides or eyes m ri at either side, being just opposite the guides or eyes mn on the block e. o is the rope whereby the grab is closed or allowed to open; it passes downward through the eyes m and ri, around the sheave in the upper block c, thence upward round a corresponding sheave in the upper block E, down around the next adjacent sheave in the block c, and so on around any remaining sheaves, when the outgoing portion of the mechanism is carried up through the eyes n and ri to the hoisting mechanism, r is the hoisting rope, which is reeved round the hoist block G, and connected with the winch in the usual manner. The grab is operated by lowering it on to the material by paying out both the hoisting and the operating ropes. When in proximity to the material the hoisting rope is held taut and the operating rope o is slackened. The block c being thus freed, will, by reason of its weight, descend within the framing or the housing of the grab, being guided vertically by the trunnion grooves, and at the same time carrying with it and depressing the pivoted inner ends of the jaws j j. It is evident that by this movement the said jaws being pivotally con- nected near their outer ends to the sliding blocks or pieces b and b, mounted on the guides T, said blocks will be forced outwardly along the track t, and carry with them the outer ends of the jaws jj, and the grab will thereby be opened. The contour of the track t is such that in connection with the vertical movement of the head c, the blades dd in their course in opening and closing will be constrained to describe any desired curve or course within the grab’s limits—such, for instance, as that indicated by the dotted lines in Fig. 573. In practice, particularly where material is to be taken from flat surfaces or from against the sides of a bin or barge, the path of the blade-like part d should at the initial movement of closing descend with a sharp curvature that diminishes as the jaws approach each other, whereby the material is first penetrated by the jaws to some depth to ensure a purchase and load, and is then scraped together within the jaws of the grab. As indicated by the drawings, the downwardly projecting pieces s' serve to prevent the escape of material at the sides where the jaws are closed, and by leaving the rear of said jaws unenclosed any surplus load above the capacity of the grab will be forced out without in any way crowding within the grab, and thereby interfering with its proper working. Both illustrations show the Brown grab with guide bars T (which are connected to the movable fulcrums of the jaws) in a straight line. These guide bars can, however, be made in any other shape, in which case the curve described by the cutting edges of the jaws will differ correspondingly. Hone’s Single-Chain Grab.—The first successful single-chain grab was un- doubtedly that on Hone’s patent, originally manufactured by the Thames Iron Works and Shipbuilding Co., Ltd., and now by Priestman Bros., Ltd., Hull. Although of compara- tively recent origin, this grab has undergone many changes in design. The original patent, which was obtained by George Hone in 1882, consisted essentially of an oblong bucket fitted with a shifting bail, which was worked by a spring manipulated by an attendant on the crane by means of a string. The bucket descended