The transporter-crane is an enormous struc ture resembling a gantry crane, having a large trussed framework or steel tower, which sup ports a long trussed arm that serves as a rail way for a car or carrier that does the convey ing. This is useful in loading and unloading vessels at docks, and can be used to pass the merchandise completely over low buildings or other obstructions.
A spiral chute is often used to deliver sacks of material to a lower level by gravity. The inclination of the spiral invites friction which prevents the sacks from descending too rapidly. A perpendicular tube is sometimes used for a similar purpose by placing alternate inclines on the sides so that the sack or other object is thrown by gravity alternately to either side, and so descends at a sufficiently delayed speed to prevent its being damaged by the fall.
About 1910 a new type of conveyer appeared on the market, which permitted the transporta tion of loose material, as ashes, broken stone, etc., around a right angle. Nearly all other conveyers are restricted to a straight line of operations, subject only to slight variation in grade, or sometimes to swinging in the arc of a circle. The Zimmer conveyer, and others of
its type, is a rectangular trough of wood or iron, with an oscillating mechanism for moving the bottom boards or sections of the trough. Power is applied to these bottom boards so as to reciprocate them slowly in a forward direc tion with a quick return. The slow forward motion not only advances the material in the trough, but raises it slightly., and before the material can fall the bottom is pulled down by a quick-acting spring to first position. The material is thus thtown forward by a series of slight jumps, so that it appears to move slowly onward in a mass, and may be made to turn a right-angled corner or any other shorter sharp angle. The Norton and Marcus conveyers em ploy the same principle. See EXCAVATOR ; TEL PHERAGE. Consult Zimmer, 'Mechanical Hand ling and Storing of Material) (1916).