How does a magnetizer/demagnetizer work?

[greypilgrim]

Hi.
These things can be used to magnetize/demagnetize tools, e.g. screwdrivers:

How do they work? I'm particularly interested in the demagnetizer part. How do the field lines look like?
And why is there this stair-like structure in the upper hole?

 

[berkeman]

I know how powered magnetizers and powered demagnitizers work, but I haven't seen effective unpowered versions. Can you provide a link to that product's datasheet or other info?

BTW, the search term for a powered demagnitizer is "DeGauss Coil". I'm assuming you know how a powered magnetizing coil works.

 

[Tom.G]

By sequentially using steps in the de-magnetize window, the device supplies progressively less magnetizing force when the tool is passed thru.
See this link for details:
https://www.quora.com/How-does-a-tool-demagnetizer-work

 

[berkeman]

By sequentially using steps in the de-magnetize window, the device supplies progressively less magnetizing force when the tool is passed thru.
See this link for details:
https://www.quora.com/How-does-a-tool-demagnetizer-work

This video does not exist

I wasn't able to watch the video, but does it show the tool being turned or in some other way being exposed to a decreasing alternating magnetic field?

 

[davenn]

yup, same problem as berkeman, video doesn't exist

 

[Tom.G]

This video does not exist

Hmm, so it doesn't. I didn't even try to watch it.
Here is one that exists, at least at the moment.

 

[davenn]

interesting

would love to know how the demag part works

 

[OmCheeto]

interesting

would love to know how the demag part works

After watching numerous videos of how the demagnetizer apparently doesn't work, I decided to build one last night.

Interesting project, and results.
What everyone missed, was that the paperclip/screw/metal thingy became magnetized when touched with a magnetized tool.
So even if they did successfully demagnetize their screwdriver, their metal test object would still be attracted to it.

Without actually having one, I had to guess as to how they work.
Here is my theory:

The explanation for example A is self apparent to me.
Example B displays over-demagnetization.
Example C kind of explains the stair-step structure of the demagnetizer: Just the correct reduced magnitude of a reversed field strength will theoretically demagnetize the screwdriver.

ps. I would wordsmith my explanation, but I'm late for an appointment with the coast. Ciao!