MECHANICAL CONVEYERS
We have already noticed band conveyers in connection with the transportation of grain. They are also used for handling coal, coke, diamond "dirt," gold ore, and other minerals, and for moving filled sacks. The belts are sometimes made of rubber or of balata faced with rubber on the upper surface, which has to stand most of the wear and tear—sometimes of metal plates joined together by hinges at the ends.
A modification of the belt is the continuous trough, with sloping or vertical sides. This is built of open-ended sections jointed so that they may pass round the terminal rollers. While travelling in a straight line the sides of the sections touch, preventing any escape of the material carried, but at the rollers the ends open in a V-shape.
Another form of conveyer has a stationary trough through which the substance to be handled is pulled along by plates attached to cables or endless chains running on rollers. Or the moving agency may be plates dragged backwards and forwards periodically, the plates hanging in one direction only, like flap valves, so as to pass over the material during the backward stroke, and bite it during the forward stroke. The vibrating conveyer is a trough which moves bodily backwards and forwards on hinged supports, the oscillation gradually shaking its contents along. As no dragging or pushing plates are here needed, this form of conveyer is very suitable for materials which are liable to be injured by rough treatment.