The Story in a Magnet
What Makes an Electro Magnet Lift Things?
The working parts of an electric lift magnet are as follows:
A Shell.—This is a steel casting heavily ribbed on the top for strength, and also to assist in radiating the heating effect from the coil.
It is usually made circular in shape, the outside rim forming one pole, while the lug in the center forms the other. The coil fits in between these poles, thus making a magnet similar to the ordinary horseshoe type.
A Bottom Plate.—The under side of the magnet is closed by a very tough and hard non-magnetic steel plate, in order to protect the coil.
As well as being non-magnetic, this plate also has sufficient strength to resist the severe wear to which a magnet is necessarily subjected.
A Terminal Box.—A one-piece heavily-constructed steel casting bolted to the top of the shell, containing and protecting the brass sockets into which the wires from the coil terminate, forms the Terminal Box.
The sockets are made to receive plugs placed on the end of the conductor wire, by which the magnet is connected with the generator.
A Coil.—This consists of a round insulated wire which is passed, while being wound, through a cement-like substance, heavily coating each individual strand.
A low voltage of current is then passed through the coil, a sufficient length of time, to thoroughly dry out and bake the coating. This renders the magnet absolutely fireproof, eliminating all danger of short circuiting of the coil.
When finished it is well taped to protect the outside wire from becoming chafed.
The coil is made slightly smaller than the inside dimensions of the shell and the remaining space is filled with an impregnating compound, which hardens to the consistency of pitch.
This renders the coil thoroughly waterproof; also forms a cushion to prevent injury from the severe jars and shocks, received when dropping a magnet on its load.
A Controller.—The rapidity with which it is necessary to turn current on and off while operating a magnet, creates what is called a “back kick.” Unless this is dissipated quickly it is very destructive to the coil.
A special controller dissipates this back kick through a set of resistance coils placed in the controller. By means of an automatic arrangement, connection with these coils is made instantly upon breaking the current between the magnet and generator.
A system of control used prevents undue heating of the coil. This enables the magnet to lift as large a load after a long steady run as at the start.