The Mechanical Handling and Storing of Material

548 THE MECHANICAL HANDLING OF MATERIAL project at each side of cradle funder the top end of the shoot. When the cradle is elevated the shoot is also carried up with it to any desired level, and is held in that position by weighted pawls, which fall into vertical racks secured at each side to the frame. By holding these pawls disengaged from the racks, the shoot may be lowered with the cradle to any level. The shoot is also secured by a safety chain on each side, which is fixed in each new position by a clip. The two arms that lift the shoot are so balanced as to hang vertically and clear of the shoot when out of use, but when required they are thrown into action by pulling a small chain. The end of the shoot can also be raised or lowered in a similar manner, so as to give a greater or lesser fall, by means of two chains carried over pulleys at the top of the structure, and brought down the centre, one at each side, where they are secured to the frame by clips at the desired level. Whenever it is necessary to shift these chains they are pushed upon strong hooks fixed at the edge Fig. 772. Plan of Cardiff Tip. of the cradle, and then by lowering or raising the cradle the point of the shoot is raised or lowered as desired, and the chains are again fixed in a new position by the clips. In some dis- tricts, South Wales for instance, where the coal is very friable, it is necessary to take special precautions for reducing the loss by breakage, which occurs in discharging the coal wagons into the ship’s hold, and for this purpose the anti-breakage crane n has been intro- duced. For further development in this direction see description of the Penarth tips (page 557), in which full details of the Thomas Anti-Breakage Box1 are given. The receptacle used in conjunction with this crane n is the iron skip p, holding about 1 ton of coal. It is hopper-shaped, with a hinged flap door for discharging at the bottom, and is suspended from an independent light jib crane N, fixed at one side of the tip frame, and having hydraulic lifting and turning motions. In commencing to load a ship, this bucket is filled from the shoot e, then lowered to the bottom of the hold, and there emptied by pulling up the bolt which secures the flap door. This process is repeated until a conical heap of coal is formed sufficiently high to reach nearly to the hatchway, after which the shoot is allowed to discharge freely without the use of the bucket and delivers close down upon the heap, a vertical drop being thereby prevented. The point of the shoot is somewhat contracted so as to check the speed of the coal down the incline. At this point the discharging sometimes requires a little assistance by hand, and is thus kept under control whilst the bucket is being filled. The whole process is effected much quicker than it takes to describe it, the discharge of the bucket in the ship’s hold being self-acting, as the bolt which holds the flap door is fastened to a chain which is fixed to some portion 1 Other anti-breakage appliances are described and illustrated in the chapter, “ Loading Coal into Ships otherwise than by Tips” (page 595).