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Q & A: Magnetic sticky tape

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Most recent answer: 10/22/2007
Q:
I bought a large roll of magnetic 1/2" tape with a peel off sticky side. You use this roll to cut off a needed amount and stick it to an item that you want to hang magnetically but the roll is pretty old and it doesn’t seem to be as strong or magnetic as it should be. How can I re-charge this roll to make the magnet stronger? Can I set a very strong magnet on top of the roll? Any suggestions? Thanks, Bill
- Bill (age 62)
Morro Bay, CA
A:
I think you might just be out of luck on this one. But not necessarily!

The magnetic tape you talk about sounds as if it's made up of the same kind of stuff that makes up refrigerator magnets (it has to be flexible, after all, and have a magnetic field strong enough and varying in space enough to make stuff stick to it magnetically). It probably has alternating N and S poles along its length (try putting some iron filings on a strip of it to see where the field lines point).

Anyhow, if the roll of magnetic tape has been coiled up long enough, it can demagnetize itself, especially if repelling poles are forced to sit side by side for long periods of time. The tape was probably magnetized in the first place by magnetizing hot iron filings, cooled down past their Curie temperature (very hot!) in a magnetic field. Then these filings were mixed in with molten plastic or rubber, and this was cooled down in a field with alternating N and S poles along the length of the tape. The filings orient themselves along the applied magnetic field, and then get stuck in the cooled plastic. Over time, they will demagnetize. The best way to get them to remagnetize is to repeat the process that got them that way in the first place, but I'm afraid you'll make a sticky mess as all the gooey plastic melts, and you may burn it all before getting up to the Curie point of the iron.

Nonetheless, you could try putting it in an externally applied field, to see if that helps. I suspect it'll be tough going to get a good strength out of this, especially if you are reversing the direction of the existing residual magnetization.

I'd buy another roll of the stuff. It's gotta be easier that way. Probably cheaper too.

Tom

P.S. half-inch magnetic tape (not the sticky kind) is what lots of physicists used to record the data from their experiments! We still use wide magnetic tapes, but they are now wound up on spools inside plastic cartridges.

(published on 10/22/2007)

Follow-Up #1: Screwdriver magnetizer

Q:
I found this thing that magnetizes/demagnetizes at http://www.toolsforstagecraft.com/n322.htm (scroll down it should be on there somewhere). Would something like this work?
- Aaron H
Rochester NY USA
A:
Well, the magnetizing part of this gizmo should work for an ordinary steel screwdriver.  I really don't know how effective the de-magnetizing part will be, but for $6.95 you can take a chance.

LeeH

De-magnetizing can work if done carefully. It's usually done with an ac magnetic field that starts strong and gradually gets weaker. Mike W.

(published on 10/22/2007)

Follow-up on this answer.