Patent GB-522854-A (GB)
Title: Improvements in grabs
IPC: B66C3/12
Filed: 1939-01-10
Abstract: 522,854. Grab-buckets. SOC. FRANCAISE DE'CONSTRUCTION DE BENNES AUTOMATIQUES, and ALLARD, P. J. M. G. Jan. 10, 1939, No. 821. [Class 78 (iv)] Special opening and closing mechanism is provided for grabs of the type having a large spread and comprising scoops pivoted to opposite sides of a central body containing the opening and closing mechanism, the opening mechanism consisting of links pivotally connected to the scoops, and the closing mechanism consisting of auxiliary chains or cables running over pulleys mounted on the scoops. In the present construction the auxiliary closing chain 40 is secured at its ends to the drum 34, Fig. 13, carrying the hoisting rope. The chain 40 passes round pulleys 8 on the two scoops arranged symmetrically with respect to the vertical longitudinal plane of the grab, and mid-way of its length passes through the equalizing guide 42, Fig. 7. Thus, hauling on the hoisting-rope, rotates the drum 34, and the integral side drums 37 and so winds up the chain 40 on the drums 37 to close the grab. Stops 43 arrest the chain should one break, and prevent complete reopening of the scoops. To open the grab, the weight is transferred to the opening rope 25 which causes sectors 19, Fig. 5, to swing clockwise and impart a corresponding movement to arms 18 connected by links 20, Fig. 1 to the scoops. The sectors 19 cause a continuallyincreasing leverage to be applied to the scoops as the opening proceeds. A lever 28, pivoted at 27 and controlled by a spring 29 maintains the rope within the channelled guide forming the curved surface of the sector. The ropes 25 pass through guides 31, Fig. 1 pivoted at 32 to the central member and carrying a set of guide rollers arranged in a curved path. Fig. 12 shows means for holding the scoops open while lowering the emptied grab on to the material. The opening rope 25 is attached at 46 to one end of a pawl 44 pivoted at 45. As the sector 19 rotates to open the scoops, the rope passes the dead centre of the pivot 45 and thereafter rotates the pawl until finally its nose engages under the beak 49. Tension on the hoisting rope when lowering the opened grab then tends to turn the drum 34 in the direction to maintain contact between the pawl and beak, thus keeping the scoops open. As soon as the hoisting rope is slackened, the pressure on the pawl is relieved and the spring 48 then restores it, leaving the hoisting rope free to act to close the scoops. In the case where grabs are operated by double-drum winches in which the opening and hoisting ropes are wound on drums operated by separate motors, means are provided for nullifying the effect of undesirable tension in the opening rope caused by faulty timing during the operation of closing the scoops. Fig. 16 shows the hoisting and closing rope 35 passing to the drum 34 and thus rotating chain drums to which one end of chains 40 are secured. The other ends of the chains are secured at 56 to sectors 51 mounted loosely on the shaft and each carrying a projection 53 adapted to engage the opening sectors 54 connected to the scoops with a certain amount of lost motion. The opening ropes also are attached to the sectors 51 at the points 52. Thus a pull on the opening rope opens the scoops when the lost motion has been taken up. Operation of the hoisting-rope to close the scoops winds up the chains and also causes the ends 56 to rotate sector 51 counterclockwise so far as projection 53 will permit. Undesirable tension in the closing-rope during this operation first takes up the lost motion and eventually causes projection 53 to contact sectors 51 and draw the free ends of the. chains 40 inwards, thus completing the closing of the scoops. The Specification also describes pivots 3, Fig. 1, for the scoops of butt-hinge formation and various bracing and strengthening members both for the scoops and the central body, one of which, 6, Fig. 1, also protects the actuating mechanism from the material being handled. A barred overflow aperture is also provided on the scoops for preventing overloading when dealing with certain classes of material.