Nearly every boy has had among his treasured possessions a small
horseshoe magnet, painted red, with bright ends, and has spent many
happy hours picking up needles, steel pins or other small objects, and
finally tired of it because of its small lifting capacity and dreamed of
one which would lift a hammer, or possibly even the family flatiron.
Little did he know at that time of the long and interesting history of
magnetism, the many stories and superstitions based on its strange
power; or of its intimate relation to the wonderful growth of
electricity within the last hundred years. His wildest dreams of lifting
power would be realized if he could see a modern electric lifting magnet
which has only come into use within the last ten years and is meeting
with instant approval in nearly every industry where iron and steel is
handled in any quantity.
[Illustration: FIG. 1]
There are three primary kinds of magnets: the lodestone or natural
magnets, the artificial or permanent steel magnet, and the electric
magnet. At present the lodestone is little used. The permanent steel
magnet is used for compass needles, as the familiar horseshoe magnet,
and in certain types of electric machinery. The electric magnet forms a
part of nearly every kind of electrical machinery and is by far the most
useful form of the magnet. The modern high-duty lifting magnet is a form
of the electric magnet.
The properties of the lodestone and the permanent magnet have been known
for thousands of years, while the electric magnet is a comparatively
recent discovery.
All magnets, whether natural, permanent or electric, possess the same
magnetic properties. Every magnet has two poles commonly called a north
pole and a south pole. It has also been found that when a magnet is
broken in two each piece becomes a magnet in itself with its own north
and south poles.
For practical purposes it has been found convenient to assume that
magnetism consists of a series of “lines of force” running through the
magnet from one end to the other and back again through the air. Each
one of these lines is assumed to have a certain strength, and the power
of any magnet is determined by the number of lines of force flowing
through it. These lines are clearly shown in Fig. 1, which was made by
sprinkling iron filings on a sheet of paper over a bar magnet, and
tapping the paper slightly so that the filings could arrange themselves
along the magnetic lines of force.
Since Oersted’s first electric magnet in 1820, electric magnets have
been made in a variety of forms and for many different purposes. The
simplest form of electric magnet is shown in Fig. 2. It consists of an
iron bar with an insulated electric wire wound around it carrying an
electric current.
[Illustration: FIG. 2]
Another form of the electric magnet is shown in cross-section in Fig. 3.
This consists of a short steel cylinder with a groove in its face for
the electric coil. The modern lifting magnet is a highly specialized
form of this type of electric magnet.
Although the use of a magnet for lifting purposes seems to be a very
simple idea and easily adopted, many difficulties had to be overcome and
years of experimenting done before the lifting magnet was a commercial
success. Nearly all electrical machinery may easily be protected from
rough usage and moisture, but the lifting magnet must be so strongly
designed that it will withstand the countless blows due to heavy pieces
of iron flying against it, and the banging it must get against the sides
of cars, ships, etc. All light parts must be placed inside of the magnet
or in such a position that they can never be knocked off or broken. To
moisture in some form or other nearly all lifting-magnet troubles can be
traced. Hence the importance of an absolutely moisture-proof
construction. The result of moisture in the interior of a magnet is to
weaken the effectiveness of the installation, leading eventually to
short circuits and burn-outs. It is necessary not only to guard against
moisture in the form of rain, snow or dew, but precaution must also be
taken against the entrance into the magnet of moisture-laden air, since
moisture so introduced will presently be condensed in the form of drops
of water.
[Illustration: FIG. 3]
[Illustration: A 43-INCH MAGNET HANDLING PIG IRON]
A very natural question is, how much such a magnet will lift. For a
given size of magnet, the lifting capacity varies greatly with the
nature of the load handled. With a magnet sixty-two inches in diameter,
this may vary from in the neighborhood of 1,000 pounds for light scrap,
to from 4,000 to 5,000 pounds for pig iron, and as high as 60,000 pounds
for a solid mass of steel or iron such as, for instance, a skull-cracker
ball or a casting affording surface for good magnetic contact.
The lifting magnet has been adopted for the handling of materials in all
branches of the steel and iron industry. It is used for handling pig
iron, scrap, castings, billets, tubes, rails, plates, for loading and
unloading cars and vessels, and for handling skull-cracker balls and
miscellaneous magnetic material.
Probably one of the best illustrations of the saving accomplished by
means of a lifting magnet is its use in unloading pig iron from
steamers. By the old hand method it required twenty-eight men, two days
and two nights, to unload a cargo of 4,000,000 pounds. When the lifting
magnet was introduced, the total time for unloading was reduced to
eleven hours, and was done by two men whose labor consisted in
manipulating the controllers in the cages of the cranes. Thus two men
and two magnets did the work of twenty-eight men in less than one-fourth
of the time. Furthermore, the vessels were enabled to double their
number of productive trips.
[Illustration: 36-INCH LIFTING MAGNET PICKING UP 3,500-POUND WINDING
DRUM]
In railroad work, lifting magnets are at the present time used
principally in scrap yards and around store-room platforms, where it is
necessary to handle iron and steel rapidly and economically. For this
class of work magnets are generally used in connection with a locomotive
crane, making a self-contained, self-propelled unit which may be
operated over the shop-yard tracks as required. The use of this
combination has reduced very greatly the cost of handling both new and
scrap material, both by reducing the actual expense of handling and by
enabling the material to be handled much more rapidly than was before
possible.
Probably the best possible endorsement of the waterproof construction of
the modern lifting magnet is the fact that one of them was successfully
operated seventy feet below the surface of the Mississippi River. At New
Orleans a large load of kegged nails was raised from a depth of seventy
feet. A load of steel cotton ties was raised near Natchez and a barge of
iron wire near Pittsburgh. And these are only a few instances of such
work.
The magnets used in this river work were three and one-half feet in
diameter. They were dropped into the stream, the current turned on, and
five or six kegs of nails or bundles of wire were raised each trip. The
nails weighed 200 pounds to the keg, so there were lifted each time,
from 1,000 to 1,200 pounds from the bed of the river.
The variety of uses to which these magnets may be put are shown by the
accompanying illustrations and there are many industries handling iron
and steel where the introduction of the modern, high-duty lifting magnet
will effect a great saving in time and labor.
[Illustration: 36-INCH MAGNET HANDLING HEAVY CASTINGS