The Mechanical Handling and Storing of Material

436 THE MECHANICAL HANDLING OF MATERIAL links eg and cd a little beyond the straight line—or dead centre—thus forming a double deadlock to the system. One end of this block is connected to a system of links lettered c, n, e, f, g. In Fig. 611 the links D and e are nearly in a straight line, and thus the weight of the fall block, which is in position, as shown by the link f g, exerts no pressure on block b. What little pressure there is tends to keep b against its stop in the position there shown. Referring to Fig. 612, the tooth on b engages with a notch, and by means of link c pulls the two links d and E into the position shown. The hook k and the link f then descend, being dragged down by the weight of the fall-block. The hook is provided with a cam slot shown at h, in which engages a fixed pin. This cam slot is of such a shape that as the hook k descends it is swung to the left, as shown in Fig. 612, thus releasing the fall-block, which, on paying out the lifting rope, descends freely, completing the rotation of B, explained above. On raising the block again, striking pieces on it will come in contact with hook k, and raising the latter, will force up link f. The latter, by means of link e, will then pull over links c and d from the position shown in Fig. 612 into the position shown in Fig. 611, thus unlocking the traveller, and at the same time hook k comes again into position to suspend the load, as in Fig. 611. That is to say, the conditions of Fig. 611 are restored, except that the small pawl a now slopes up to the left instead of to the right, as there shown. It therefore follows that on slackening the rope, this pawl no longer catches on the beam, and the traveller is free to run down the latter on paying out the hauling rope. Generally the traveller is, in these circum- stances, allowed to run to the very end of the beam, where a projecting block of metal catches the tooth on the block b, which thus locks itself without any assistance from the small pawl, but the traveller can also be brought to rest at any intermediate point. When the traveller is locked to the beam, as shown in Fig. 612, lifting or lowering is accomplished by hauling in or paying out the rope in the ordinary way. If it be desired to release the traveller, the operator has only to haul in the rope until the fall- block has entered the bell, and in so doing has brought the mechanism of the traveller into the position shown in Fig. 611, when the traveller is free to move either up or down the beam. If it be desired to cause the traveller to move up the beam, the operator has only to continue to haul in the rope until the front part of the traveller has passed the point at which it is desired to lower, when by a reversal of the winch the traveller will engage with the first stop it encounters, and the load will be lowered. If the traveller is to descend the beam, all the operator has to do, after having released the traveller, is to pay out the rope and the traveller will descend along the beam— passing all the intermediate stops because the toggle has not been cocked and is therefore inoperative; the arresting of the traveller at the intermediate stop when moving down the beam is a very simple matter. It is only necessary to allow the carriage to pass the stop, when, by drawing it back in an upward direction, the toggle will become cocked, after which, as the rope is again paid out, the traveller will engage with a stop, and the load be lowered at that point. As the traveller moves up or down the track, the cam tooth can pass a stop with a clearance, but as the cam reaches the bottom stop it will, without the cocking of the toggle, automatically engage with it, and as the rope is paid out, the load will automatically be lowered. The mechanism for dumping and travelling, described below, is in reality the gear which deserves to be called automatic. Position a, Fig. 613, shows the dumping mechanism when the loaded skip is being lifted, the dumping mechanism of the fall- block having been thrown completely out of gear by the setting lever being placed in the position in which it is shown. On the fall-block entering the traveller, the dumping mechanism is brought into