Magnetism – what is it?
Magnetism is an ever-constant and insidious enemy to horologists. The means by which a watch may be magnetized are so numerous today that it is important that the repairman form the habit of testing every watch for magnetism that comes in for regulation, examination or repair.
In testing for magnetism place a small compass not only over the balance but also over the winding wheel. The mainspring being subject to magnetization as well as other steel parts, has definite poles at the time the magnetic lines of force passes through the watch. These poles are split up into countless numbers as the mainspring unwinds. This constant alteration of the relative position of the poles between the mainspring, winding wheels, and the balance helps to explain the erratic performance of magnetized watches.
Theory of demagnetization
An alternating current is that type of electrical current that changes its direction constantly and when such current flows through a coil of wire the poles also change. Figure 1 shows a conception of an alternating current wave as it moves through time, and the complete wave is called a cycle. An alternating current of 60 such waves per second is said to have a frequency of 60 cycles.
When a steel rod is inserted in a demagnetizer and the flow of alternating current is suddenly cut off, the steel rod will be found to be magnetized, its poles being that of the last half cycle that was sent through the wire. However, if the current is left on and the rod gradually withdrawn, the result will be different. It will be repolarized for every cycle and each successive polarization will be weaker than the preceding one.
Wave form a alternating current
When withdrawn entirely from the field, the magnetism has disappeared.
Demagnetizing a watch
The procedure in demagnetizing a watch is much the same as explained above. Withdraw the watch, keeping it central with the opening and giving it a slight twist after leaving the opening. Continue the withdrawal until the watch is about three feet or more from the demagnetizer. If the first attempt fails to remove all magnetism repeat the operation.
Magnetized tools
The horologists’ tools are subject to being magnetized. Screw drivers and tweezers should be closely watched. Avoid placing such tools in a north-south position in or on the bench.
