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"Neodynium magnets rusting! :( " Topic


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1,070 hits since 31 Oct 2010
©1994-2014 Bill Armintrout
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Pajaro Muerto31 Oct 2010 11:48 a.m. PST

Hi all:

I've had several cases of planes that I have painted and sealed, and a year or two later I find that the magnets epoxied on them have rusted, so much that they come off easily. It appears that there ir a coating of a different metal that does not rust, but curves outward a little give way to the rust forming.

The process I do is this, to those who may help me with an explanation:
1. Epoxy the magnet (K&J Magnetics Grade 48 or 52 1/32" thick) onto the fuselage with a dark grey epoxy for metals.
2. Prime the mini with cheap (Harris Paint, maybe it's only sold in Puerto Rico) $2.19 USD Gray Primer.
3. Paint with Folk Art, Apple Barrel, DecoArt paints.
4. Krylon Crystal Clear gloss coat.
5. Decals, maybe a paint touch up.
6. Krylon Matte Finish or Crystal Clear.
7. Saved in furniture cushion foam-lined Plano fishing tackle boxes.

This has happened with planes that have had I think no chipping around the magnet, which I do not drill, but epoxy below the fuselage,

Any pointers? This is driving me mad!

Thanks,
Rolando

[crossposted from CY6! group]

highlandcatfrog Inactive Member31 Oct 2010 12:54 p.m. PST

Hi Rolando,

Saw this on the yahoo group but hadn't got around to responding, so I'll just do it here.

I've heard of very rare cases of lead rot caused by some chemical reaction between the metal of the magnet and the metal of the miniature being in contact. Might just be an urban legend; fear of it (combined with my natural bad luck) has caused me to always prime, then paint, then seal, then glue on the magnet, thus giving me a couple of layers of protection betwixt magnet and miniature to preclude something like that happening. I'm probably being way too over cautious, but if it happened to me there would be weeping and the gnashing of teeth!

Another cause might be moisture. Maybe some moisture is getting trapped next to the magnet, either from the epoxy or from humidity where you live (P.R. I think?). If there's moisture trapped, over time it might cause the magnet to rust. Maybe try a different glue – heck, I just use super glue. I'm sure the bond isn't quite as strong as with epoxy, but the super glue eats up any moisture present.

BTW, I've seen pics of some of your work. Absolutely stunning! If I had half of your skill I'd be a happy camper!

Mike G31 Oct 2010 2:04 p.m. PST

Rolando, I do everything that you do except one thing. I put on the magnet after I have painted the plane, so the magnet is not painted. Is the primer an enamel or acrylic? If it is acrylic, that has a water base. So you are in essence dipping the magnet in water with the first coat of paint.

Mike

Personal logo John the OFM Supporting Member of TMP31 Oct 2010 2:15 p.m. PST

Read this paper on corrosion of Neodymium magnets:
PDF link

Apparently, they are very sensitive to acidic conditions.

Top Gun Ace Inactive Member31 Oct 2010 2:25 p.m. PST

I haven't seen that before, but they make gold-plated ones, as well as ones coated in epoxy, so those might be a better option for you.

Of course, that doesn't solve the problem with the ones mounted on your aircraft.

Pajaro Muerto31 Oct 2010 3:41 p.m. PST

Oh… it's "Neodymium", with an "m"… oops…

highlandcatfrog (great name, by the way) and Mike:
Yeah, there's moisture for everyone and their mother here in Puerto Rico year round. The primer is oil-based enamel. But as I prime and then paint, a bit of primer gets chipped off during painting, where ACRYLIC paint goes on the magnet directly, I guess.

I don't glue the magnet afterwards for two reasons: aesthetics (I want it to blend in) and I think that with glues on harder to the metal than to a paint layer, I guess. It does say to clean well the metal surface before epoxying, on the label ;)

But, to contrast with those that rusted and fall off, other minis made during the same period are nice and pretty! I'm pretty sure that the primer chips off 90% of my magnets around the bottom edge, and THANK GOD there is no such rusting rate…

Has this rust happened to no one but me?

Rolando

show some respect for women Inactive Member31 Oct 2010 5:09 p.m. PST

I have done hundreds of miniatures and aircraft using Rare Earth Magnets -- some of these were Neodymiun.

Only used epoxy on my balloons. Otherwise used super glue. Generally do not paint magnets but did on my WWII 15mm stuff (about 70 figs).

So far, so good. No problems of any kind.

mjc

Personal logo John the OFM Supporting Member of TMP31 Oct 2010 6:11 p.m. PST

As with any alloy, the composition is important. Some cheaply made might be susceptible to rust, others may not.
Sintered or melted, acidic acrylics or not, coated or polished or not, acidic glue conditions or not…

BTW, chemists have a rather comprehensive and technical definition of "acidic", which laymen may not be aware of.

Timmo uk Inactive Member01 Nov 2010 1:54 a.m. PST

No problems here over a period of 4 years. I would at least switch your supplier of magnets.

Nobody else is reporting issues and yours is the first I have ever read of this happening so I don't think you are actually doing anything wrong in your process as it sounds pretty much like what of us do. My guess is that the problem lies with the quality of your magnets. I'd try another supplier and do a test ie try to make them rust and see how you go before you put them on your models.

Personal logo Randall Supporting Member of TMP01 Nov 2010 8:07 a.m. PST

I've switched to Amazing Magnets because of issues I've had with K&J. I haven't used Amazing Magnets enough to make a definitive statement (just a few projects so far), but I've been pleased so far.

Here's the website for Amazing Magnets:

amazingmagnets.com

CaptHobby01 Nov 2010 11:01 a.m. PST

Thanks for the link Randall.

Personal logo zippyfusenet Supporting Member of TMP01 Nov 2010 12:09 p.m. PST

Randall, what issues have you had with K&J?

Like Timmo, I've had magnets in use for four years with no problems.

Pajaro Muerto01 Nov 2010 11:22 p.m. PST

I do use K & J magnets… But guys here haven't had an issue with them, right?

Stopping to think about it, the rusting has happened only on Scotia planes—I THINK. I can't remember positively positively.

Personal logo zippyfusenet Supporting Member of TMP02 Nov 2010 4:15 a.m. PST

I use K&J magnets and have had no issues.

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