The Mechanical Handling and Storing of Material

DISCHARGING BY MEANS OF SKIPS AND GRABS 419 the unloader depositing its load into this portable bunker, whilst Fig. 591 shows two unloaders in the same hold, one being open and the other closed. This illustration also shows the position of the driver’s cabin. Two such travelling bunkers are used so that one can be emptied into railway trucks whilst the other is being filled by the grab. The grab capacity is 17 tons of ore, and as the bunker holds 70 tons, it is practically filled by four grab loads. Three men are required to manipulate one machine. All movements of the grabs are controlled by one man. The travelling gear of the crane carriage, and the manipulation of the bunker, is under the control of the second man, whilst the third manipulates the under-carriage. The capacity of these latest Hulett unloaders varies from 500 to 1,000 tons per hour, depending upon the depth of the ore in the hold, and the construction of the ship to be un- loaded. As an example may be cited the unloading operations in the dock at Ashtabula, Ohio, in 1913, when eight 15-ton unloaders, working in sets of four, from two separate harbour basins, unloaded 70,000 tons of iron ore from eight steamers in twenty hours—an average of 437| tons per machine per hour. In this time calculation the berthing of the ships and the making fast in the docks is included. In this case the ore was deposited directly into railway wagons, 1,319 being re- quired, each containing 53 tons, that is, one wagon every fifty-five seconds. Up to the year 1914 fifty such unloaders had been Fig. 593. 10-Ton Grab of Hulett > Unloader. erected, and with the exception of two were engaged in unloading ore and handled over 50 per cent, of the total tonnage of ore shipped on the great American lakes. The Fig. 594. Hulett Unloader at Ashtabula. other two, which were erected in 1913 at Fort William, Ontario, in Canada, for the Canadian Pacific Railway Co., are for the unloading of coal. This latter plant consists of two automatic unloaders equipped with 8-ton scoops, a man-trolley stocking bridge carrying a 9-ton grab bucket, and a transfer car system with