AUTOMATIC WEIGHERS
Scarcely less important than the rapid transference of materials from
one place to another is the quick and accurate weighing of the same. If
a pneumatic grain elevator were used in conjunction with an ordinary
set of scales such as are to be found at a corn dealer's there would be
great delay, and the advantage of the elevator would largely be lost.
Similarly a mechanical transporter of coal or ore should automatically
register the tonnage of the mineral handled, to prevent undue waste of
time.
There are in existence many types of automatic weighing machines, the
general principles of which vary with the nature of the commodity
to be weighed. Finely divided substances, such as grain, seeds, and
sugar, are usually handled by _hopper_ weighers. The grain, etc., is
passed into a bin, from the bottom of which it flows into a large pan.
When the proper unit of weight--a hundredweight or a ton--has nearly
been attained, the flow is automatically throttled, so that it may be
more exactly controlled, and as soon as the full amount has passed,
the machine closes the hopper door and tips the pan over. The latter
delivers its contents and returns to its original position, while the
door above is simultaneously opened for the operation to be repeated.
A counting apparatus records the number of tips, so that a glance
suffices to learn how much material has passed through the weigher,
which may be locked up and allowed to look after itself for hours
together. The "Chronos" automatic grain scale is built in many sizes
for charges of from 12 to 3,300 lbs. of grain, and tips five times a
minute. Avery's grain weigher takes up to 5-1/2 tons at a time.
For materials of a lumpy nature, such as coal and ore, a different
method is generally used. The hopper process would not be absolutely
accurate, since the rate of feed cannot be exactly controlled when dust
and large lumps weighing half a hundredweight or more are all jumbled
together. Therefore instead of a pan which tips automatically as soon
as it has received a fixed weight, we find a bin which, when a quantity
roughly equal to the correct amount has been let in, sinks on to a
weigher and has its contents registered by an automatic counter, which
continuously adds up the total of a number of weighings and displays
it on a dial. So that if there be 10 lbs. in excess of a ton at the
first charge, the dial records "one ton," and keeps the 10 lbs. "up
its sleeve" against the next weighing, to which the excess is added.
Avery's mineral scale works, however, on much the same principle as
that for grain already noticed, a special device being fitted to render
the feed to the weighing pan as regular as possible. His weigher is
used to feed mechanical furnace stokers. The quantity of coal used
can thus be checked, while an automatic apparatus prevents the stoker
bunkers from being overfilled.
_Continuous weighers_ register the amount carried by a conveyer
while in motion. The recording apparatus comes into action at fixed
intervals, _e.g._ as soon as the conveyer has moved ten feet. The
weighing mechanism is practically part of the conveyer, and takes the
weight of ten feet. The steelyard is adjusted to exactly counterbalance
the unloaded belt or skips of its length, but rises in proportion to
the load. As soon as the conveyer has travelled ten feet the weight on
the machine is immediately recorded, and the steelyard returns to zero.
_Intermittent weighers_ record the weight of trucks or tubs passing
over a railway or the cables of aerial track, the weigher forming part
of the track and coming into play as soon as a load is fully on it.
Some machines not only weigh material, but also stow and pack it. We
find a good instance in Timewell's sacking apparatus, which weighs
corn, chaff, flour, oatmeal, rice, coffee, etc., transfers it to sacks,
and _sews the sack up_ automatically. The amount of time saved by such
a machine must be very great.
NOTE.--The author desires to express his indebtedness to Mr. George
F. Zimmer's _The Mechanical Handling of Material_ for some of the
information contained in the above chapter; and to the publishers,
Messrs. A. Crosby Lockwood and Son, for permission to make use of the
same.