thermoplastic coatings and remagnetising

edited July 2017 in Magnets
hello again, before i continue on my research on thermoplastic coatings i need your help, my plan now is to melt hdpe and make a mold for it then force the magnet in while forcing the molten hdpe whit it, then i will machine te thing to a nice disc. ok at this point the magnet has propably losen half of its potential, i got some large capacitors and im a master at electronics so i think i could make a pulse magnetiser whit caps, solenoid, coil but im unsure can i magnetise it again while its in a hdpe pellet and so on


  • May I suggest to start with HDPE foil and maybe ultrasonic weld the caps together.

    Anyway magnetizing the magnets should be as simple as exposing it to a very strong field for a brief moment. Like, ridiculously strong ( I found numbers suggesting 2.5 times the target). So my guess is you'll need high voltage equipment able to handle something like 100 to 300A. Sounds like a fun project. 

    You might want  to avoid crazy overheating in first place, maybe find a way to properly adhere the HDPE to the magnet. Maybe laser/ultrasonic welding seams with quick cooling.
  • Remagnetizing neodymium isnt trivial, but it's certainly doable. I work on a project where we do just that.

    Basically you want some huge capacitors and heavy duty thyristors. Charge them up as high as you can go and dump the whole thing through a coil.
  • Gave it a quick calculation. Using air coils you'd need something like a 20 turn coil which has an average radius of 10 cm. And you need to pump like 35kA through it for a moment. Not sure if it's that much of a great project to do at home. Handling that much current even for fractions of second is serious business. Even if you pull fancy tricks, getting like 50k Gauss is quite some effort. Not to mention the forces involved there.
  • @ThomasEgi

    I'll have to recheck my hardware, but that seems like WAYYYY too much to me. We magnetize SmCo magnets at full power with around 300 amps.

    Making smaller coils would certainly help too, why did you pick 10cm?
  • seemed like a practical choice. Well my calculation is just the air coil, no core material involved cause I had no numbers on maximum permeability for such crazy fields.
  • yeah sounds too easy for me at this point:D i have bunch of 40v 66000mf caps that i can series to get voltage high enough to be practical so i might try on 120v first and make a short thick wired coil for that. then i might try to paraller 400v caps

    im not home at this point so this can take a few weeks but i can hook some results of how much i can restore of the magneticity
  • @ThomasEgi Yeah, 10cm is definitively too big. It would be pretty realistic to go for a 1cm diameter coil. Probably even 5mm.

    That should massively reduce the current required.

    @dieselpwr The key point is to get the fastest discharge possible (since the peak current is the only thing that matters, even if it lasts for nanoseconds). Larger caps might slow it down so take that into account. But other than that, it's definitively doable.
  • i know, i might just go whit the high voltage way because like u said i want to dump the charge at one shot:D I just melted down some hdpe and holy cow its strong even in thin fibers !! if i succeed in this, might be a new way for these diy implants. its easy and cheap and if done right its easily going to last a lifetime. i got 3x1.5 and 3x0.7 sized magnets to try this on, 
  • @dieselpwr It goes without saying, but try to keep the plastic at the lowest possible temperature.

    If you get close to the curie temperature (above ~310C), the magnets wont be remagnetizable again because the internal structure changes.
  • just another idea: how about vacuum forming a thin film of hdpe around the magnet. With a the magnets pre-cooled and the low thermal capacity of a thin layer of HDPE no damage should be done. This way you'd only have to close a single seam of overlapping material. 
  • edited July 2017
    hmm that idea was in my mind while ago... i decided to go whit this way, i need a magnetiser for some other things too so im not doing it only for these little magnets

    edit: thanks for all help guys
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