THE MECHANICAL HANDLING OF MATERIALS 313
There are many o ther types of conveying machinery in more or less general use on gas-works, the following being the more important systems :—
(a) The travelling-tray conveyor.
(b) The swinging-tray conveyor.
(c) The push-plate conveyor.
(d) The gravity-bucket combined elevator and conveyor.
(e) Telphers.
Tipping or Travelling-Tray Conveyors
Band conveyors are not wholly suitable for conveying substances of a heavy ot abrasive nature, on account of the injury caused’to the material forming the belt. Owing to the advantages they offer, liowever, conveyors ■embracing the principle of the band are fre-quently preferred by many engineers, and the travelling-tray conveyor, whilst disposing of the perishable belt, retains the desirable features of the system. Figs. 229 and 230 illustrate typical examples of travelling-tray conveyors. This type of conveyor consists essentially of an endless chain to which. are attached a number ■of overlapping trough-like sections. Tlie chief objection to the employment of these conveyors is their inability in many cases to deliver at intermediate points in their length. In the type illustrated, however, a special tip-up bar enables the conveyor to deliver at any desired point in its course, or at several points simul-taneously, as well as over the extreme end. By a simple modification, moreover, th.e material eau be carried up a gradient much in excess of the limiting angle of the material on the trays. In discharging a friable material such as coke over the end, the drop is minimized by the preceding tray intercepting the fall of material from the tray following it. The power required is low in comparison with. types of conveyors such as the push-plate, and is usually under 5 per cent, of the weight of the moving parts. About 250 feet of conveyor carrying 20 tons of
Fio. 229.—Babcock & Wilcox Travelling-Tray Conveyor