0 ft. per minute. The driving gear must
always be placed at the delivery terminal, so that the loaded strand is
in tension. Such appliances are often used as sorting tables or picking
bands, for instance, for coal, cement, minerals, &c.

In another modification of the metal band conveyor, the _travelling
trough_ conveyor, the sides of each plate are turned up so as to form
the conveying surface of the band into a continuous trough. With this
arrangement intermediate delivery is impossible, as the sides of the
trough will not allow the use of a scraper. As compared with push-plate
conveyors (which consist of scrapers mounted on endless travelling
chains that run usually in troughs), travelling trough conveyors are
gentle handlers of material.

A conveyor which is capable of dealing with many different kinds of
material is known as the _vibrating trough_ conveyor. It is so far like
the band and travelling trough conveyor that the material it conveys
from one point to another is conveyed without the use of any stirring or
pushing agent, such as belong to worm, push-plate and cable trough
conveyors. For materials requiring gentle treatment, this type of
conveyor is eminently suitable. There are different kinds of vibrating
trough conveyors. In one type the trough is caused to make a
reciprocating motion by means of a crank and connecting rod, the trough
itself being supported on rollers. In another type the trough is
actuated by a cam, or by cranks with some kind of quick return motion.
In the appliance known as the Zimmer or swinging conveyor the trough is
supported in its reciprocating motion by means of laminated spring legs
set obliquely to the trough. These legs are securely bolted at one end
to the floor or any other solid support, and at the other end to the
trough itself; hence no lubrication is required, as would be the case
with supporting rollers. Moreover the combined action of the
reciprocating motion of the crank and the rocking of the spring legs has
the effect of causing the material to travel faster in the trough with a
given stroke of the crank than would be the case with any other support.
The material to be conveyed is not carried along with its support as in
the case of a band or travelling trough conveyor, but is caused to move
in a series of hops, to use popular language.

[Illustration: FIG. 8.--Swinging or Zimmer Conveyor.]

The action will be sufficiently explained by the appended diagram
(