Demagnetizing crank?
Posted: Mon Nov 22, 2021 10:03 pm
How do you demagnetize a crankshaft? I bought an EE crank that is in really good condition except that it is magnetized. Any ideas? Thanks, Dennis
Found this;
Demagnetize a Magnet by Heating or Hammering
If you heat a magnet past the temperature called the Curie point, the energy will free the magnetic dipoles from their ordered orientation. The long-range order is destroyed and the material will have little to no magnetization. The temperature required to achieve the effect is a physical property of the particular material.
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You can get the same effect by repeatedly hammering a magnet, applying pressure, or dropping it on a hard surface. The physical disruption and vibration shake the order out of the material, demagnetizing it.
Self Demagnetization
Over time, most magnets naturally lose strength as long range ordering is reduced. Some magnets don't last very long, while natural demagnetization is an extremely slow process for others. If you store a bunch of magnets together or randomly rub magnets against each other, each will affect the other, changing the orientation of the magnetic dipoles and lessening the net magnetic field strength. A strong magnet can be used to demagnetize a weaker that has a lower coercive field.
Apply AC Current
One way to make a magnet is by applying an electrical field (electromagnet), so it makes sense you can use alternating current to remove magnetism, too. To do this, you pass AC current through a solenoid. Start with a higher current and slowly reduce it until it's zero. Alternating current rapidly switches directions, changing the orientation of the electromagnetic field. The magnetic dipoles try to orient according to the field, but since it's changing, they end up randomized. The core of the material may retain a slight magnetic field due to hysteresis.
Note you can't use DC current to achieve the same effect because this type of current only flows in one direction. Applying DC might not increase the strength of a magnet like you might expect, because it's unlikely you'll run the current through the material in the exact same direction as the orientation of the magnetic dipoles. You will change the orientation of some of the dipoles, but probably not all of them, unless you apply a strong enough current.
A Magnetizer Demagnetizer tool is a device you can purchase which applies a strong enough field to change or neutralize a magnetic field. The tool is useful for magnetizing or demagnetizing iron and steel tools, which tend to retain their state unless disturbed.