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EMIM Magnet Nickel Plating - Anyone Re-Done it?

Discussion in 'Infinity Loudspeakers' started by Maxamillion, Feb 21, 2009.

  1. Maxamillion

    Maxamillion Super Member

    Messages:
    1,343
    Location:
    New Jersey, USA
    I'm in the process of upgrading my RSIIb's (outboard crossover, internal bracing, new wiring, etc.), and awaiting the news from Graz from Apogee Acoustics as to whether he can make new EMIM and EMIT diaphragms for us. Since the drivers are out of the speakers, I decided to disassemble one of the EMIMs and take a peek. All looks OK except that the plating on the magnets is peeling off (see pictures). In the second picture, the magnets on the right have been brushed lightly with a soft bristle brush on a Dremel to remove the peeling plating, the magnets on the left are as found. In a few places the peeling plating was actually contacting the diaphragm - not good!

    From reading on this subject I believe my EMIMs have the neodymium magnets, which are nickel plated. It seems like a simple solution to carefully remove as much of the loose material as possible, then have the magnet assembly re-plated at a local shop. I'm assuming that the plating can be done without removing (ungluing) all the magnets from the metal backing plate, as I'm sure that would break most if not all of them into pieces. I suppose an alternative would be to paint them with a thin coating of chrome paint, but I'd rather nickel plate them if that's what they had originally. I'm afraid the chrome paint might decrease the magnet strength versus plating them.

    Has anyone ever done this?? Any watchouts regarding the plating process, especially for magnets??
     

     

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  2. Maxamillion

    Maxamillion Super Member

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    1,343
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    Oops - forgot the pictures

    Here they are.
     

    Attached Files:

  3. Maxamillion

    Maxamillion Super Member

    Messages:
    1,343
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    Regarding painting the magnets, another thought I had was to just give them a thin coating of solvent-based polyurethane varnish. The poly is pretty waterproof, and from my understanding, the reason the Neo magnets are coated is because moisture ingression will cause them to decompose. If that's the case, a coat of waterproof varnish ought to do the trick, no? I don't really care if they don't look silver like the originals, just that they work the same.
     
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  4. Maxamillion

    Maxamillion Super Member

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    1,343
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    OK, so it seems I'm having this discussion with myself, but I've reached a decision. I used Minwax Wipe-on Polyurethane on the magnets; it went on nicely and didn't remove the glue, so I'm letting the first coat dry and then I'll put on another. It's a thinned polyurethane varnish specifically made for wiping; recoat time is fast (2-3 hours). It dries in very thin coats, so I may need a few - I can actually check for coating integrity with a multimeter, since no continuity = coated surface. I guess I won't need to put the thin plastic strip back on the magnets, either, since the poly will insulate them from the diaphragm traces.
     
  5. rabbit

    rabbit Well-Known Member

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    652
  6. Maxamillion

    Maxamillion Super Member

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    So far I have two coats of the wipe-on poly on the magnets and no adverse reactions. It really penetrates into all the nooks and crannies of the surface, but it will take forever to build up a decent layer at this rate. I just checked with a multimeter and there is still continuity,so the layer needs to get thicker.

    I'm thinking now that the wipe-on may be a good first step to seal/prepare the surface and get under any nickel plating that maybe loosening, followed up with a conformal coating of some type. I need to do a little more research on this, but I am familiar with urethane, acrylic and silicone conformal coatings, which are often applied to circuit boards to prevent corrosion and moisture ingression.

    Stay tuned.
     

     

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  7. Maxamillion

    Maxamillion Super Member

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    OK, 5 coats of the wipe-on poly are what it takes to get a coating thick enough that it doesn't conduct electricity across the magnet. Since I can re-coat every 2-3 hours, 5 coats can be done in 1 day.

    Tomorrow I will buy some conformal coating and coat that over the poly. Conformal coatings are typically used on circuit boards to protect the traces and prevent corrosion. That should give me a hard finish with high dielectric (1500V/mil) and excellent water resistance, assuming the poly accepts it as a topcoat. If that all works out, I'll do the other EMIMs as well.
     
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  8. oldstaffi

    oldstaffi New Member

    Messages:
    9
    NdFeB magnets, corrosion and plating

    I haven't done enough reading to know whether you have samrium cobalt or neodymium iron boron magnets in your drivers. NdFeB is a higher energy magnet, samarium cobalt is lower energy (but still very high) but much more corrosion resistant and also much more expensive. What I can tell you with pretty good certainty is that you won't be able to re-plate the magnets while they are still on the pole pieces of the drivers. Consequently, your "paint" approach is probably the best option. With regard to what kind of paint to use - some sort of magnet wire varnish (if you can find it) or a UV curable acrylate (like they stuff they use to protect both pre-recorded and writable CD's, DVD's, etc. or for optical adhesive) is probably about as good as you can do. Google UV acrylate adesives or go to www.norlandproducts.com for more info. If they are in fact NdFeB, you can buy new ones with good plating for a reasonable if not cheap price. All of these "hard" magnetic materials are also physically hard and very brittle, so you are correct regarding the potential for damage during dis-assembly. I have an extra EMIM that I've been meaning to take apart and this might push me into getting off my dead keester and doing it. I will let you know what I learn about the magnets once I do. I'll try to follow this thread, as I have a vested interest (Beta's) and also have a little knowledge of magnets and materials and would be happy to contribute to community if I can.
     
  9. Maxamillion

    Maxamillion Super Member

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    Yes, they are the NdFeB magnets. Others have looked for replacements but haven't been able to find the correct size, from what I have read here and on other sites. These are in a pretty mild environment, and even with the peeling nickel I haven't seen much corrosion on the magnets, so I'm hoping that a poly coating will be sufficient to keep them in good shape. Any help you can provide is appreciated.
     
  10. Maxamillion

    Maxamillion Super Member

    Messages:
    1,343
    Location:
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    I applied a urethane conformal coating tonight over the Minwax Wipe-on Poly, and it went on fine and seems to be sticking well. The magnets end up with a light yellow-amber color after the treatment. I used MG Industries Urethane Conformal Coating, and thinned it a bit with their solvent thinner, then brushed it on with the small brush MG supplies. The conformal coating dries very hard in minutes, and doesn't seem to affect the magnetic field strength much if at all. Lots of solvent fumes, though, so wear a mask or work in a well-ventilated area - it stinks!

    Does this solve the neodymium corrosion problem? Only time will tell, but it looks good so far!
     
  11. rabbit

    rabbit Well-Known Member

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    652
    Why not use transformer varnish or is that too thick ??
     

     

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  12. Maxamillion

    Maxamillion Super Member

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    Transformer varnish might work as well. I don't think there is any one answer to this. The key is to just seal the magnets against corrosion with some sort of coating that will stay adhered to them while not dissolving the glue holding them down. I picked the conformal coating because it is used for just that purpose on circuit boards for automotive and heavy industrial applications. I was afraid of the aggressive solvents attacking the glue, however, so that's why I applied the Wipe-on Poly coats first (the solvent in that is mineral spirits - much less agressive than the xylene and toluene in the conformal coating).

    As a side note, I talk to Bill Legall at Millersound about this (after I had done my urethane treatment) and he recommended removing the loose nickel plating with duct tape, then applying a light coating of super glue to the magnets.

    Probably many other effective treatments out there as well.
     
  13. rabbit

    rabbit Well-Known Member

    Messages:
    652
    Do all RSIIb's use the Nickel plated magnets in the EMIM's ??
     
  14. Maxamillion

    Maxamillion Super Member

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    I don't think so, as NdFeB magnets were only invented in 1984, so anything made before then would have SmCo. As it turns out, my particular RSIIbs had 4 Nd EMIMs and 2 SmCo EMIMS (no doubt some fiddling by the previous owner). I have managed to find someone who will trade me two Nd EMIMs for my two SmCo EMIMs so that I have a matching set. Now I just need to do the surface treament to the other five Nd EMIMs!

    Now I just need Graz to deliver on the new diaphragms, since I already have the EMIMs apart!:D but I'll probably want to test the new versus old diaphragms anyway....:yes:
     
  15. rabbit

    rabbit Well-Known Member

    Messages:
    652
    Maybe the RSIIa's had the earlier EMIM's with the Samarium Cobalt magnets.

    This raises an important question. Are the different EMIM's equivalent in their performance or have there been changes in the crossover to accommodate those differences ??

    I have notice on the some of the later EMIM's that the middle part of the diaphragm has a lighter coating of material and less rippling compared to the outside parts. I was wondering whether this was a mod to compensate for the higher field strength of the magnets or was it because they used Kapton instead of mylar ??

    The EMIM's on my RS4.5's don't have this so it looks like there might be two different types of diaphragm to contend with.
     
  16. Maxamillion

    Maxamillion Super Member

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    My Nd EMIMs use a Mylar diaphragm, not Kapton. The EMITs are Kapton. The material in the center you refer to is simply a strip of adhesive tape, probably there to help damp resonances.
    The crossover in my RSIIb matches the schematic on the Infinity Classic German website exactly, and that shematic is for both RSIIa and RSIIb, so I'd say the crossovers didn't change.
     

     

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  17. kmanusa

    kmanusa AK Subscriber Subscriber

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    Location:
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    I have wondered this myself and have asked the question here. The consensus at that time I thought was that there was little difference in performance across the range of standard EMIMs that Infinity outfitted on their loudspeaker systems from the late 1970s onward. I am beginning to question if this is indeed the case.

    I too have noticed that RS-IIa/b EMIMs have that different appearance that you describe and I have bought a few of these as backups for my RS-4.5s.
     
  18. Maxamillion

    Maxamillion Super Member

    Messages:
    1,343
    Location:
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    Since I have my Nd EMIMs apart now, I took a good look at them. The center of the diaphragm is a clear, uncolored material (with the traces glued to it). It spans the length of the diaphragm, but not the entire width. On the sides, it is joined to a more flexible, translucent material, that resonates like a drum skin when tapped (Mylar?), and appears to have been applied in 4 strips, almost like Scotch tape. These EMIMs have the widely spaced + and - terminals, without the screws.
    I think I'll take a picture of it tonight and send it off to Graz to make sure he has that type on his radar screen as well.
     
  19. rabbit

    rabbit Well-Known Member

    Messages:
    652
    Can you post the picture here ??
     
  20. Maxamillion

    Maxamillion Super Member

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    Location:
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    Very Interesting Journal Article

    From the Journal of Achievements in Materials and Manufacturing Engineering (2007) on the corrosion resistance of various coatings on NdFeB magnets, in water and 5% NaCl environments. To summarize: electrostatically painted polymer coatings such as polyester and epoxy were the best, sprayed on polyurethane and epoxy lacquers were the next best, and metallic coatings were the worst. In fact, nickel coating was found to have the least corrosion resistance of all the tested coatings!

    Looks like polyurethane wasn't such a bad choice after all - and the environment our speakers reside in is much milder than the test conditions (hopefully!!).

    http://www.journalamme.org/papers_vol20/1369S.pdf?PHPSESSID=6c84b0ced12c5c2de864470415be0210
     

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