How does a tool magnetizer and demagnetizer work?
These things (pictured below). I get how the magnetizer works: a permanent magnet magnetises the tool bit, but how is the magnetic fields arranged in the demagnetizer in order to demagnetize tools? These things are unpowered completely passive blocks, presumaly containing a magnet and some iron/steel parts.
The basic principle of magnetizing and demagnetizing tools is a process called “hysteresis loop”. To magnetize a tool (typically made of steel) you bring it orderly to the proximity of a strong magnet and then remove it. The magnetic field inside the tool increases, the tiny magnetic domains inside line up and when you remove the tool some of these tiny magnets remain in order. You can try that with a screw driver and a magnet: pass the magnet pole only in one direction, i.e. from back to front along the screwdriver.
The steel has gone through a loop of increasing and then decreasing magnetic fields but the withdrawal step leaves a residual field, thus when you plot the field in the steel you get a loop – that’s the hysteresis loop. If the material follows the arrows in the drawing below it ends up magnetized at the point Mrs.
To demagnetize, the tool is passed through a series of decreasing hysteresis loops, essentially going the opposite of the arrows by being exposed to magnets of successively lower strength or simply a series of larger distances from the magnet’s pole, as the device in your picture seems to do.
When the tool is magnetized, something called magnetic moments are aligned. They are basically the magnetic behavior of small areas of the tool. You can think of them as a field of arrows. When the tool is demagnetized all the arrows are random, resulting in an insignificant net magnetic field.
After the tools passes through the natural magnet several times, the magnetic moments are aligned and the net magnetic field is strong enough to pick up objects.
When the magnetized tool with aligned arrows is passed through the demagnetizing portion of the device, an opposite magnetic field is applied. But this time, instead of a straight magnetic field like this:
an irregular magnetic field is applied due to the step-like shape of this part. This magnetic field is not concentrated in a direction, so the magnetic moments are randomly spun around such that, once again, the net magnetic field is insignificant. This method of magnetizing tools is only temporary, because the material is paramagnetic. This means it responds to a magnetic field, but is not naturally magnetic. After a while, other magnetic fields and entropy will gradually return the magnetic moments to their natural state.
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