I’ve come across these things as promotional items, advertisments that get stuck on the fridge to remind people of who they did business with in the past but I’ve never understood the properties of flexible magnets that do not appear to have metallic properties.
Are these magnets just pieces of plastic or rubber mixed with some metallic material that’s magnetized? How’d they do that?
I did a websearch for ‘flexible amgnets’ and got 23.4 oodles of hits.
The magnetic medium is a powder that is turned into a slurry before being mixed with the bonding medium, which is also a powder.
The mixture is then extruded into sheets.
Yep, two powders mixed together one magnetic (barium ferrite typically) and the other rubbery (a thermoset polymer.) Heat 'em up, form 'em into shape while still hot and presto, you’ve got a refrigerator magnet.
Haj
I helped design an Engineering EXPO project last spring in which we conducted manufacturing of refrigerator magnets. Our presentation has an explanation behind some of the theory behind flexible magnets:
http://www.cae.wisc.edu/~tschohl/expo_01b.htm
The main difference between what we did and what commercial manufacturers do is that we cured and magnetized the magnets simultaneously, while manufacturers cure the elastomer compound first, then mix it with the magnetic powder and extured it into sheets. The unmagnetized sheets are passed over wide electromagnets that alternate N-S-N-S-… etc. across its width, turning the sheets into useable magnets.