Author Topic: How magnets rust  (Read 12776 times)

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Eirbyte

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How magnets rust
« on: October 12, 2009, 02:42:53 AM »
Hi and well done on the upgrade to Fieldlines.


This is a short post on why not to use the polyester resin as you can see the nickel plated magnets have started to rust. This turbine is almost two years in the air and  this is the first time that it has been serviced.



Full story on our web site at http://www.buildyourownwindturbine.com/index.php/leitrim-workshops/89-servicing-workshop

« Last Edit: October 12, 2009, 02:42:53 AM by (unknown) »

wooferhound

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Re: How magnets rust
« Reply #1 on: October 12, 2009, 07:02:37 AM »
Do you think the polyester resin caused this ?

I looked at your linked story. My thought is that the magnet rotor was flexing and the resin cracked, being bonded to the magnets it pulled the nickel plating too causing the plating to crack also.


How thick is the steel that the magnets are bonded to ?

« Last Edit: October 12, 2009, 07:02:37 AM by wooferhound »

Capt Slog

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Re: How magnets rust
« Reply #2 on: October 12, 2009, 07:12:49 AM »
Interesting read.


Even though you say the resin is not waterproof, it seems odd that the magnets have corroded as they have.  Mine has been up for around two years too, and the magnets are not covered at all with resin, (they sit in holes in a plastic discs which are epoxied to the stator backs).  The magnet faces are still the same shiny surface as when they went in, despite being proud of the backing by around 2mm, they only have a thin film of paint and/or grease for protection.


Your magnets look almost to be undergoing some form of galvanic action, as if they are reacting with the metal of the disc. I wonder if the glue behind my magnets hence separating them from the iron of the disc by microns, is helping them in this way?


.

« Last Edit: October 12, 2009, 07:12:49 AM by Capt Slog »

Flux

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Re: How magnets rust
« Reply #3 on: October 12, 2009, 07:44:21 AM »
Difficult when you link to other sites, I didn't see the link until others mentioned it.


You have a very hostile site and corrosion is always going to be a big issue. Polyester is certainly not the best stuff but in your case you look to have negligible resin covering over the surface of the magnets. In a hostile environment you will need a significant thickness of coating over the magnet surface even if you use epoxy. This means more air gap and you probably need bigger or higher grade magnets to get the same performance as can be got in a dry environment.


I am not sure whether you have the chicken or the egg syndrome. My immediate reaction was that you have has a magnet rub on the stator and this would remove your very thin resin coating and damage the nickel plating, this would start a catastrophic corrosion problem and may still be the root cause.


Later I began to think that the rub came later as a result of the corrosion and expansion of the magnets. If this is the case then the lack of protection of magnets alone must have been the starting point.


Most people are fortunate not to have these sorts of environment or we should see very many more cases of this sort of problem. Neo is very problematic in this respect and in a marine environment the reaction goes ahead very rapidly once started.


I have never seen any need to pot magnets for mechanical reasons but except in very mild climates some form of protection from the weather seems essential.


In your environment I think you need epoxy and a decent thickness of it over the magnets probably with glass reinforcing. You most likely need over a mm of covering and this will have to be included in your air gap. Making sure you don't get a rub is also essential, or you will again damage the protective coating and it will happen again.


Thanks for posting, it is a warning for others in a hostile marine environment. Even here in the UK midlands magnet corrosion is something that concerns me a lot. Keeping magnets on is child's play but stopping corrosion is a significant issue.


Flux

« Last Edit: October 12, 2009, 07:44:21 AM by Flux »

Dave B

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Re: How magnets rust
« Reply #4 on: October 12, 2009, 12:37:53 PM »


First off, thank you for posting this. How many failures do we continue to see with poly as time moves on. Poly cracks, poly cracks, poly cracks, it is not an ADHESIVE. The Dans found this out years ago and posted many, many times about their switch to quality epoxy and glass and now, just for kicks and asthetics the steel banding besides prompted I am certain by their earlier failures with the pretty but cheap Bondo. IT DOES NOT WORK over time. Quality epoxy and glass, quality epoxy and glass, quality epoxy and glass.  I'm done, I promise to try not to comment on this anymore. Dave B.
« Last Edit: October 12, 2009, 12:37:53 PM by Dave B »
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oztules

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Re: How magnets rust
« Reply #5 on: October 12, 2009, 03:08:05 PM »
Hi Eirbyte,


You will find the real damage is between the resin and the disk itself. The back side of the magnet will be worse than the front you can see.


Yes..... sadly  I know this because I'm in a marine environment, and have recently discovered the same thing. The damage on the top is not as severe as the damage on the magnet/iron interface I found.


Best to pull the resin off and de-rust the disk, paint with epoxy etc and replace magnets (after iron brushing and tidying up) and re-pot . I believe you need to electrically isolate the nickel from the iron (sounds like a battery I know of). I'm using an epoxy paint for this, the Dans use powder coat.


Have no doubt, the water has capilliaried from the front of the magnet to the back and worked wonders beneath the resin where it doesn't dry out.....and can use the water as electrolyte to hasten things on .


Best with it.... listen to DaveB


.........oztules

« Last Edit: October 12, 2009, 03:08:05 PM by oztules »
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Flux

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Re: How magnets rust
« Reply #6 on: October 12, 2009, 11:57:31 PM »
Yes I am inclined to agree with this. I haven't had such a major failure but I have seen evidence of the rusting of the discs under the polyester. Any moisture in this region will certainly act as an electrolyte between the nickel coating and steel disc.


In the perfect world it is normally suggested you clean the discs to bare steel before sticking magnets on or potting. I have never removed the mill scale and in hindsight it may have held off much of the troubles I might have seen if I hadn't been so lazy.


For harsh marine environments I think galvanising or electro zinc plating of the discs would be a very good idea but zinc is not the easiest thing to stick things to. The idea of an insulating barrier between the disc and magnet is a good one even if it is not so good mechanically as sticking the magnets straight on. Mechanical problems are far less troublesome than this corrosion issue.


This may be why epoxy coated magnets seem to stand up better than the nickel ones and they may be a far better choice for this sort of environment. There is certainly evidence that the makers can't even keep the corrosion at bay under the nickel with all the elaborate precautions they take. I have seen new magnets with lumps under the plating.


Flux

« Last Edit: October 12, 2009, 11:57:31 PM by Flux »

Eirbyte

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Re: How magnets rust
« Reply #7 on: October 13, 2009, 12:46:26 AM »
Thanks for the feedback.

I did not build this machine so can't say what the mix of powder and resin was or how well the disks were cleaned before casting. And the amount covering the magnets is a bit light alright.


The site is some 30 miles from the sea and the magnet rotors are 8mm thick.


To get more value out of this machine rather than recasting it now with new magnets we are going to use some epoxy paint on the disks and see if we get another year or two or even just the winter before it stops producing any reasonable power.


Any thoughts on how long it might be before the magnets are completely gone? :)


And yes, oztules, I agree that the worst rot is at the back of the magnets. And as for the thought of electrolyte living there is frightening. But maybe someone can work out how to store power in the magnet rotor and do away with batteries :)

« Last Edit: October 13, 2009, 12:46:26 AM by Eirbyte »

oztules

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Re: How magnets rust
« Reply #8 on: October 13, 2009, 03:35:31 AM »
"To get more value out of this machine rather than recasting it now with new magnets we are going to use some epoxy paint on the disks and see if we get another year or two or even just the winter before it stops producing any reasonable power.


Any thoughts on how long it might be before the magnets are completely gone? :)"


......... once you seal the water and chemical soup in completely with the epoxy paint.... not very long at all before the magnets mysteriously increase in size..


What I meant was clean up these magnets, and see how long you can get away with it.


At the least, you should pull them off, clean the disk and paint them with good epoxy. Then place your clean and dried out  magnets back on, and, even if you only paint them with epoxy, you will do better than just sealing in the rot, which I think is what you are suggesting.


Whichever way you go, best of luck with it.


............oztules

« Last Edit: October 13, 2009, 03:35:31 AM by oztules »
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Warrior

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Re: How magnets rust
« Reply #9 on: October 13, 2009, 04:19:39 AM »
This is something that has always bogged my mind. I just don't like how exposed the magnets are in axial flux alternators. People in dry climates seem to do OK, but those in marine environments don't look to well.


The problem I see is galvanic action between the steel disc and the zinc plating.

The zinc plating is actually used as a sacrifice anode, meaning it slowly rusts away instead of the magnet. But once a galvanic reaction gets started you're doomed.


I have been really giving this a thought before building this type of alternator and have considered cleaning the steel rotor very thoroughly, leaving it bare steel and applying a coat of epoxy paint before gluing the magnets; this would isolate the zinc from the steel and in theory avoid any chemical reaction between them, even if water manages to get in between. What do you all think?

« Last Edit: October 13, 2009, 04:19:39 AM by Warrior »
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Warrior

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Re: How magnets rust
« Reply #10 on: October 13, 2009, 04:30:25 AM »
Meant to say nickel plating, not zinc in previous response. Sorry for the confusion...
« Last Edit: October 13, 2009, 04:30:25 AM by Warrior »
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Flux

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Re: How magnets rust
« Reply #11 on: October 13, 2009, 05:59:09 AM »
I think the real answer is to keep the moisture out. If you can't do this then yes an insulating barrier may help prolong the start of trouble. I am inclined to not use nickel coated magnets and try the epoxy coated ones.


Flux

« Last Edit: October 13, 2009, 05:59:09 AM by Flux »

DanB

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Re: How magnets rust
« Reply #12 on: October 13, 2009, 09:55:20 AM »
Interesting and thanks for posting.  I think my favorite postings here have to do secondly with folks building  stuff, and firstly postings about failures and problems that we all learn from.


There's been some discussion about galvanic reactions between Nickel and Iron, that may or may not be an issue I'm not sure.  I did build a battery a couple years ago with Nickel plated magnets and steel disks so I'm certain something goes on there... the steel is the sacrificial anode in that case and corrodes much more quickly but the Nickel will also 'go away' eventually I'm pretty sure.


In this case looking at your website the magnets were definitely rubbing the stator for a while and that likely caused the Nickel plate to fail ~ I expect that's the main problem.  There's a lot to be said for having a fair bit of mechanical clearance between the magnet rotors and the stators with these machines I think.


Good luck with it ~ the magnets (or some of them) look pretty rough ~ if it were me I'd rebuild the magnet rotors before I raised it again.

« Last Edit: October 13, 2009, 09:55:20 AM by DanB »
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oztules

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Re: How magnets rust
« Reply #13 on: October 14, 2009, 07:40:34 PM »
"In this case looking at your website the magnets were definitely rubbing the stator for a while and that likely caused the Nickel plate to fail ~ I expect that's the main problem."


I can't agree with this. If I could post this picture http://www.buildyourownwindturbine.com/images/stories/oneday-oct09/damagecup3.jpg (can't find the buttons) The scrubbing is insignificant, but the rot is monumental... this was not friction, it barely scuffed the enamel.


The scrubbing will have been from the pushed up resin and broken down magnet particles... mine did the same in a sea air environment... it happens pretty quickly in this humid salty air. In my case, I had a wide gap, and the magnets grew at least 3mm to just brush the stator. There was no bearing slop, and the stator did not warp... but the magnets grew considerably.


...........oztules

« Last Edit: October 14, 2009, 07:40:34 PM by oztules »
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Eirbyte

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Re: How magnets rust
« Reply #14 on: October 15, 2009, 11:03:08 AM »
oztules you are spot on the magnets did grow.

I know the best thing to do would be to recast with new magnets but it might not be that simple for some people regarding the price of magnets so lets see how long they last with some epoxy paint. And it might help someone to get longer from their magnets I think another year would be nice so lets see :)
« Last Edit: October 15, 2009, 11:03:08 AM by Eirbyte »

oztules

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Re: How magnets rust
« Reply #15 on: October 15, 2009, 03:01:10 PM »
I'd clean those magnets up with a wire brush, epoxy them and recast.... see how long that lasts. I can't begin to tell you what the magnet/iron interface area  looks like inside/under the resin... but it will accelerate quickly from here if you don't stop it.... painting over the disk will only increase the speed I think...locking in the moisture/cancer.


I pulled mine out and cleaned them up, they have remained in dry storage for a while now... and don't appear to be degrading further. During summer I will re-epoxy them, and then recast the rotors. I don't wish to lose 24 x 12mm x

50mm round magnets.


But it is your call.


...........oztules

« Last Edit: October 15, 2009, 03:01:10 PM by oztules »
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ghurd

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Re: How magnets rust
« Reply #16 on: October 15, 2009, 03:49:51 PM »
I have a neo with missing nickel stuck to the rail of the front porch where it can often get wet.  Been there since early April.

Have another in the house stuck to a paneling nail since then too.

Both look about like they did when I placed them.

No bare steel touching the exposed neo.

G-
« Last Edit: October 15, 2009, 03:49:51 PM by ghurd »
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oztules

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Re: How magnets rust
« Reply #17 on: October 16, 2009, 01:41:05 AM »
Ghurd,

I too have a few magnet pieces stuck to the shed wall outside. The corrugated iron has a factory green coating.


These magnets have survived a few years in the elements with no ill effect. (large pieces... left over from "playing" with magnets like you shouldn't). Surface rust on the open neo compound, and not much more than that... no sign of endemic cancer.


Whats the difference I wonder.


Hmmm... idea...

Hugh solved the eddy problems in the iron by having the steel disks rotate along with the magnets, so no eddy currents. This is easily proven by how well they freewheel.. so proven....


Question. If I'm generating 1 kw, I am pushing 50v@20A through lots of copper. This must generate a quite large back MMF. What happens to this field.


The wire usually termed dead wire (at the inner radius of the coil group, and the outer radius of the coils group, whose job it is to join the wires being cut by the magnetic field, are outside the influence of the permanent magnets... just when the EMF is the highest (N over one leg, S over the other.... neutral in the core area)


Does this mean that the fields generated in these wires are free to interact with the steel rotor... which is passing them........


Or is that bollocks..... perhaps it is more likely that we modulate the flux of the permanent magnets, and the fringing and repelling effects will actually change the return flux between the magnets on the rotor. This changing flux between magnets on the rotor (leakage induced from the back MMF??) may result in eddy currents being generated in the disk.... under the magnets.


If so does this cause localized warming from those eddy currents (speeds up reactions?), or an asymmetric electric field generated by those eddy currents (from the battery effect of the iron/nickel interface being modulated more one way than the other), which causes the horrific cancer in the magnets in this configuration....


Food for thought, but broken magnet pieces sure don't deteriorate very quickly exposed to sea air... but sure as hell do on an axial flux disk.


It might be I'm thinking too much too.......


Thoughts anyone?


.........oztules

« Last Edit: October 16, 2009, 01:41:05 AM by oztules »
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ghurd

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Re: How magnets rust
« Reply #18 on: October 16, 2009, 05:23:07 AM »
The neo field makes current, and current makes a field, so there has to be eddy currents in the disks. And neos.  Making some electrolysis?


Just pulled the end cap off a conversion with HD neos (obviously with 'compromised' nickel coating) .  Tested it, but never really flew it.

Neos epoxied straight to the bare armature.  Been sitting in my very damp basement for a few years.  The only thing it was not exposed to is long term eddy currents.

Looks about like it did when I made it.


VF's loose neo looks good after 3 years of storage too,

http://www.frontier.net/~bobwenn/diary/turbine/slipped2.JPG


I figure that only leaves electrolysis.

G-

« Last Edit: October 16, 2009, 05:23:07 AM by ghurd »
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Flux

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Re: How magnets rust
« Reply #19 on: October 16, 2009, 06:12:48 AM »
Yes I think electrolysis is the root of the problem and that is why there is big trouble in marine environments. Clean pure water is a poor conductor but salt water is a very different issue.


The potential between different metals is small and any voltage from eddies is also small. With clean water there is not going to be much reaction but with salt solution the process really gets under way the whole time. Once the nickel coating is damaged or dissolved you have other metal potentials from the components of the neo and you also have hydrogen decrepitation that wrecks neo.


To me the main thing is too keep the salt water out. Any insulating barrier between magnet and disc will also slow the start of the trouble but once the neo starts to rust I think you have lost the plot and total disintegration is only a matter of time and probably a very short one. So short that cleaning drying and coating with epoxy is probably a pointless exercise.


Flux

« Last Edit: October 16, 2009, 06:12:48 AM by Flux »

Eirbyte

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Re: How magnets rust
« Reply #20 on: October 18, 2009, 04:40:23 AM »
We have put it all back together if you want to see more this is the page.
http://www.buildyourownwindturbine.com/index.php/leitrim-workshops/91-servicing-workshop-page-2



A small brush like this is just the job

Again thanks for all the input.

« Last Edit: October 18, 2009, 04:40:23 AM by Eirbyte »

Dave B

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Re: How magnets rust
« Reply #21 on: October 19, 2009, 07:57:38 AM »
Eirbyte,


  I think that's about the best you could do to help seal the water out. Problem being as you well know is that there is no adhesion between the magnets and the poly. This gap around the magnets let the water in and it's all down hill after that. I don't know if your magnets were adhered first with any type of "glue" but it was common practice back when to use super glue or similar. With all your corrosion I'm sure this got under your magnets besides and super glue was never really anything more than to just hold the magnets during casting. It was assumed that casting the magnets then in poly would secure them.


 I hope you get plenty of life from this now but my main concern is that your magnets are not adhered to your disks. There is a huge amount of force being applied to the sides of the magnets under load and of course centripital force as well. If (when) the magnets move and or the disks flex the epoxy paint will crack and your water problems and corrosion will take off again. Maybe as Dan says a bit more time could be had also with a wider air gap so when the bubbling corrosion expands the magnets (there is always a huge force trying to pull these apart too) they won't rub on the stator as quickly. Good luck, let er run.  Dave B.

« Last Edit: October 19, 2009, 07:57:38 AM by Dave B »
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angus

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Re: How magnets rust
« Reply #22 on: November 16, 2009, 04:56:15 AM »
Hi. First let me thank Flux for his response to my post in Newbies.

  Now... Things rust. Fe is converted to FeO in the presence of water and oxygen.

  Both are necessary. Take a lump of steel and submerse it in water (even sea water- ref. the movie "Titanic") and you will get corrosion that will after a period of time stabilize- the Titanic has been under sea water for almost a century. The reason the Titanic is still down there is the lack of oxygen that is necessary for the process of oxidisation to continue. Had the Titanic "beach itself"  in shallow waters it would now be no more than FeO -that is rust - the brown stuff you see on your magnets.

 Those of you (and there are many) who have suggested GALVANIC REACTION are spot on. Those of you who are suggesting eddy currents / electrolosis are spot on also. All metals react sacrificially depending on their position in the periodic table.

 So HOW to AVOID it?

My thoughts are as follows-




  1. Have the rotor plates sand blasted ( or acid bathed) back to bare metal.

  2. Order yor your magnets as follows-



       a) Un-plated - ie. no nickle.

       b) Have two treaded holes (say 1/4 inch nf thread) machined into them - in say about 1/2 inch from each end of the magnets. Using two bolts will stop the magnets from turning on the steel rotor.




  1. Bolt these magnets to the rotors with S/Steel bolts .


  2. Send the rotors to your local plating company and have them "HARD CHROMED".




5.They will last for many years...(I am hoping to do this with my project).


PS to Flux.. about those two holes in the magnets and their impact upon the flux through the coils ??.

« Last Edit: November 16, 2009, 04:56:15 AM by angus »

Eirbyte

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Re: How magnets rust
« Reply #23 on: October 10, 2011, 07:30:40 PM »

shawn valpy

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Re: How magnets rust
« Reply #24 on: October 11, 2011, 02:33:38 AM »
Thanks for posting this I think everybody that has neos would be very interested in this post !
Trouble is now to replace them its goin to cost ya far more than two years ago this point alone makes me even more interested as my mags are just to much now so they have to live forever!!!
Good on the guys that are working on a ceramic alternater this has to be the only way to go from here I confess I am a sheep in the windmill building and am quietly waiting for hugh or the dans to build a simple to build ceramic mill then sell me the plans we need a ten footer,and a 13 footer guys.
I like the idear of putting it up and just checking berings now and then for years and years neos do not seem to do this.

clockmanFRA

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Re: How magnets rust
« Reply #25 on: October 11, 2011, 03:24:06 AM »
My actual professional life is the conservation of metals. Where they have been around a few hundred years, but retention of original surface polish and metal working concepts can, after treatment, still be visible.

When I first built my Hugh P's neo magnet 12 footer, I was surprised at the poor condition of the so called new neo magnets. The plating was poor with staining from the original plating bath acids, and poor plating adhesion.

I therefore treated each of the 32 magnets separately, and in total took me about 20 hours.
Using a stiff bristle brush and a soft 8 row brass brush only where corrosion was present.

First, all magnets. Corrosion chemically and physically removed. Stiff Bristle brushed with a rust removal jell, (normally a hydrochloric solution)
 Cleaning.
1.    All magnets, totally immersed and then bristle brushed in 8 deionised water to 1 Horolene (Concentrate of Ammonia & detergent, sniff it and your on your back) fluid for 18 minutes, this removes any corrosion or oil residues.
2.    All parts rinsed with light bristle brushing in Isopropyl Alcohol (a water neutraliser), for 13 minutes, Excess fluid removed with cotton swabs.
3.    All parts immersed in fine grit-o-cobs, synthetic absorber.
4.    All parts warm air-dried, for a minimum of 20 minutes.
5.    All parts soft brushed with French chalk, all parts then soft brushed.

Now the magnets are chemically so clean that even your finger print moisture will mark the magnet and corrosion will start.

This process repeated over and over again until no corrosion present. If you look at metal with a microscope you can see the surface is normally like a sponge, so the more you polish a surface correctly the less likely you will get ingress of moisture etc that then causes corrosion.

Ultrasonic cleaning is not recommended, as at very microscopic levels the metal can be damaged and more metal becomes porous.

I also treated my main magnet discs with the above treatment.

Once treated handle with cotton gloves and assemble as normal, I use Vinyl ester resin, but have stopped using Epoxy resin as this has caused problems where loading takes place, i.e. washers bolts etc, as the epoxy resin just chatters and then moisture can get in.

I have fume cabinets and all safety stuff, but please wear protective gloves and eye protection.

Results 3 years later;- Magnets look okay but staining colour present but no actual corrosion protruding from the magnets. Light Corrosion around the parts where the Epoxy resin has stressed/cracked due to mounting bolts.

My later turbines have the black coated Neo's and i could not find any problems with the coating.

« Last Edit: October 11, 2011, 03:34:23 AM by clockmanFRA »
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Flux

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Re: How magnets rust
« Reply #26 on: October 11, 2011, 04:54:19 AM »
Interesting to see a follow up on this problem.

Two years certainly goes quickly and as I suspected I have had trouble with 2 machines just as Eirbyte did. The polyester potting is worse than useless.  On the first failure the magnet damage was bad, I cleaned most up but had to replace 2. I used Hammerite rust inhibiting primer and lost of coats of decent paint. It is still working but I haven't had a close look at what is happening.

The latest failure was caused by the polyester block moving and stopping the machine. In that case the whole polyester block on both rotors came off with the magnets still stuck to the discs. The magnet plating is blistering but mainly intact.

I am trying POR15 as Chris Olson seems to have had good results with it, I don't have any faith in potting with vinyl ester or even epoxy, I think the differential expansion of the discs and a large block of resin is bound to cause trouble.

I think even the manufacturers have had great difficulty plating neo and probably haven't solved all the problems, even though they have got better at it.

The machines I haven't had any trouble with used some Early voice coil motor magnets I got cheap, these were epoxy coated and probably to some military spec. and most likely cost the earth in the first place. They are also used on drum type radial machines and have a lot more protection from the weather, I just gave them several coats of paint.  Too many variables to form any real opinion .

Flux

jlt

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Re: How magnets rust
« Reply #27 on: October 11, 2011, 08:54:01 AM »
I sand blast my rotors and paint them with automotive zinc chromite 2part epoxy. Then i install mags on the rotor.Then i use windshield urethane rubber sealant around them. Never had any problems so far.

Putting nickle mags on bare steel rotors makes a nickle iron battery.All you need Is some salt water.To make them work.

Also I clean the mags with some acetone to remove all the oils.   

fabricator

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Re: How magnets rust
« Reply #28 on: October 12, 2011, 07:55:51 PM »
Another reason to keep experimenting with ferrites.
I aint skeerd of nuthin.......Holy Crap! What was that!!!!!
11 Miles east of Lake Michigan, Ottawa County, Robinson township, (home of the defacto residential wind ban) Michigan, USA.

ChrisOlson

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Re: How magnets rust
« Reply #29 on: October 12, 2011, 08:23:20 PM »
Another reason to keep experimenting with ferrites.

I no longer experiment with them.  They work.  So I build with them.  And they're cheap too.  I've already seen all this with neos, and some people think that the place where you get them makes a difference in quality.  That may be.  But they're too expensive anymore to mess with, and even if the price comes down I'm done using them.
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Chris

electrondady1

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Re: How magnets rust
« Reply #30 on: October 12, 2011, 09:36:49 PM »
rather than try to seal the iron from oxygen with paint  another method to control corrosion is to completely and evenly oxidize the surface on purpose with a chemical oxidizing agent.
similar technique used in gun bluing which i believe turns the surface to iron nitrate

there is a waterborne paint called extend .
as well, there is paint by Benjamin moor called rust inhibitor.
ive used it on antique vehicles and any other junk i want to stop from rusting.
i did both rotors and hard drive magnets a few years ago with it
seem to be ok

the compound  turns the surface into iron sulphide.
smells like dog poo while it's curing but nothings too good for my windmills.
« Last Edit: October 12, 2011, 09:39:52 PM by electrondady1 »

Dutch John

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Re: How magnets rust
« Reply #31 on: October 13, 2011, 02:58:21 PM »
How I prepared the rotors: I superglued the magnets to the rotor. Then the sides of the magnets are extra glued to the rotors with windshield glue. No epoxy! Then the rotors got underbody coating and, after drying, a thin layer of grease. At each inspection new grease or oil is added.

My turbine is not up for years yet, but the combination underbody coating and grease has always worked very well for my cars in our wet salty climate. The trick is that the oil fills every crack, keeping the water out. Resin and paint crack over time. Oil is always at work.

Regards,
DJ

bob golding

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Re: How magnets rust
« Reply #32 on: October 22, 2011, 09:01:11 PM »
i am at the 2 year point as well. it does go quick. just checked  an im i got in october 2009 asking about corrosion. i have taken pics of my turbine that i have yet to post up but basicly what i have done is grind the rotors down to  bright steel then painted them with 3 coats of 2 pot epoxy. i did the same to the magnets using a sanding disc in the angle grinder. down to bright metal 3 coats of epoxy. i then stuck the magnets to the rotor with epoxy and painted the outside of them. one coat still to go. then i will encapsulate the whole lot in more resin. i have  got advice from the epoxy manufacturers about cure times ect. they said the epoxy resin should bond with the paint. it is used to paint  boat hulls and  bridges so should be ok. so hopefully i should get a bit longer out of the magnets. all the corrosion was on the front rotor. the back rotor was not  too bad. i managed to slide it off the  disc and  repainted it  and slid it back on. i used por15 on that disc. 
if i cant fix it i can fix it so it cant be fixed.