The Mechanical Handling and Storing of Material
Forfatter: A.-M.Inst.C E., George Frederick Zimmer
År: 1916
Forlag: Crosby Lockwood and Son
Sted: London
Sider: 752
UDK: 621.87 Zim, 621.86 Zim
Being a Treatise on the Handling and Storing of Material such as Grain, Coal, Ore, Timber, Etc., by Automatic or Semi-Automatic Machinery, together with the Various Accessories used in the Manipulation of such Plant
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ELEVATORS FOR MATERIAL IN BULK
27
hold one charge of the material
Fig. 23. Driving Gear for Worm
Elevator.
by the constant impact of the grain, not to mention heavier and harder substances.
A sheet of india-rubber about | in. thick secured to the point of impact will last longer
than a cast-iron plate of the same thickness. The shoots themselves should be at an
incline of say 5 to 10 per cent, greater than the angle of repose of the materials handled.1
Automatic Feeding Devices for Elevators.—If a system of feeding or
unloading is employed which is more or less intermittent, and if the material so unloaded
is to be handled further by elevators or conveyors so that the further progress is to be
continuous, the feed must be changed from an intermittent to a continuous one. The
importance of an even feed in all cases is obvious, as too rapid a heaping up of material
may lead to chokes, besides causing an unfair strain which might lead to breakages and
an undue consumption of power. If the material be delivered from railway or
contractors’ trucks, ropeway skips, or grabs, the load should be deposited in a hopper
(with an adjustable outlet or gate) sufficiently large to
to be conveyed. The feed of the succeeding ele-
vator or conveyor can be equalised in such a way
that the hopper pays out its contents at the rate
at which the elevator or conveyor can take it,
while the truck or grab brings the next load.
In some cases and with some materials it is
necessary to provide the exit of the hopper with
a mechanical feeding device in order to get uni-
form delivery. This is the case where the material
is not like grain, seedSj or small coal of uniform
size, but where large pieces of coal and ore are
mixed with the small. One effective device is an
inclined table which slides backwards and forwards
under the opening of the hopper and allows a
certain quantity to leave the hopper at each stroke,
which quantity can be adjusted by opening or
closing a vertical slide or gate in the side of the
hopper. A fairly uniform delivery can also be
obtained by having a short spout from the hopper
to the conveyor, the incline of which can be varied
to give a slower or faster feed. A good plan
frequently adopted in gasworks is to fit under the
hopper a pair of break rollers which reduce the size of the coal so that it can be more
easily handled by the succeeding elevators and conveyors; but even in such cases the
feeding devices here mentioned should be used, as the work of a breaker will always
improve in proportion to the uniformity of its feed.
Fig. 24 shows a mechanical feeding device for elevators in which a short Zimmer
conveyor is used, into which the coal falls through a receiving hopper above. In this
case the hopper is fed intermittently by narrow gauge trucks. By the use of a slide
or gate the quantity of material it is desired to convey can be regulated. This feeding
device can of course be used equally well for feeding other kinds of conveying appliances.
It is always well, where possible, to drive the feeding device from the machine which is to
be fed, so that when the elevator or conveyor is at a standstill the feed may also auto-
matically cease. This is of great importance, for if arranged otherwise the conveying
machine at its feed end would on starting be so full of material, that in attempting to
1 For inclines of shoots for delivery of coat see page 195.