The Mechanical Handling and Storing of Material

CHAPTER XXXII UNLOADING VESSELS BY MEANS OF BARGE OR SHIP ELEVATORS AND MARINE LEGS BARGE ELEVATORS These are essentially elevators as fully described in Chapter II., page 10. They vary from those principally in the form of the elevator well, which is frequently not entirely enclosed but only made of skeleton work, so that the material to be handled can enter freely. The driving arrangements at the upper terminal necessarily differ from those of an ordinary stationary elevator, as the position of the terminal in relation to the driving shaft is constantly varied as the quantity of material in the barge is lessened. With regard to the suspension of the apparatus from . the supporting structure, this must be effected in such a way as not to burden the top pulley spindle with the weight of the elevator. Ihe simplest form of support is that which allows of merely an up-and-down motion. Such an installation would, however, only be suitable for very narrow canal barges, as through inability to rack the appliance from side to side of the barge a great deal of cargo trimming would be necessary. The more usual method of support is to suspend the elevator from a jib-like steel structure in such a way as to allow it a pendulum-like or racking motion so that it can be made to reach from side to side of the barge, hither of the above methods is suitable for barges in non-tidal rivers and canals. For tidal rivers where the barges are frequently compelled to take the ground at low tide, so that they become stranded and therefore a fixture, barge elevators are frequently fitted for such purposes to the end of a jib-like steel structure which allows of their slewing sideways and being luffed. In the former case applying to canals and non tidal rivers the barges are so moored that the elevator descends into the hold at one end, and the mooring is changed as the cargo is removed. With the latter type, which allows of a slewing action, a. greater reach is obtained to make up for the inability to move the barge when stranded. Barge elevators are generally used in connection with flour mills, breweries, and oil mills, as well as at small gasworks for handling material of small and uniform size. Grain and seeds, such as cotton or linseed, as well as small nuts and other small material, can readily be cleared out of a ship’s hold by lowering the elevator into the bulk of the material to be conveyed, when it will feed itself. All that is required on the part of the driver is to keep lowering the elevator as the vessel is cleared. For larger material barge elevators are subject to the same limitations as ordinary bucket elevators in regard to handling material containing larger fragments. Bar<>e elevators may either be supported from the factory building itself, from the end of&a steel gantry, or may be arranged portably on wheels to run along the quay wall; this latter method also overcomes the difficulties mentioned above for unloading stranded barges. For large capacities, say 40 tons per hour and over, pneumatic grain elevators are coming into more general use, owing to the great advantage of saving trimming expenses 451