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Bad corrosion in magnet gap of 10" RCF driver
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digitallake View Drop Down
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Points: 56 		Post Options Post Options   Thanks (0) Thanks(0)   Quote digitallake Quote  Post ReplyReply Direct Link To This Post Topic: Bad corrosion in magnet gap of 10" RCF driver
    Posted: 26 February 2019 at 6:40pm
Hi all, interested in people's opinions on this, bad corrosion in magnet gaps causing coil rubbing etc.

Has anyone ever successfully (by successfully I mean reliably) repaired this kind of damage before reconing a driver?

I realise it's obviously possible to remove the corrosion with a lot of care, but surely when something starts to corrode then it will just continue sooner rather than later even if removed to start with.

Is it sensible to try to clean up this damage, maybe treat it with something to help prevent it returning, and then spend a fair amount of money on 4 recones? Or is not worth the risk and new replacement drivers the only sensible option?

The repair needs to be reliable not a bodge (needs to last for years)

Thanks
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jbl_man View Drop Down
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Points: 11155 		Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 27 February 2019 at 10:49am
The top plate (the outer side of coil) and the pole piece (inner side of coil) are badly corroded on all those above. yes,it can be cleaned, i have cleaned worse than that with fine emery paper soaked in WD40 to lubricate it,it does come off, but is time consuming and wearing on the finger tips,but half an hour on on each one would help matters. Make sure you vacuum the gap with the most powerful hoover you can find after.
Just store them somewhere warm and dry,the corrosion above is down to bad storage,not faulty drivers.
Be seeing you.
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or dissilve the rust with a mild acid such as vinegar or citric acid.

I keep on seeing these adds on facebook for amazing lazer machines that vaporise rust whilst leaving the metal unaffected.

surely the difficult bit is re-finishing the surface inside the gap so the corrosion does not begin again.

thinking about this, I'm not actually sure how a magnet can get rust - isn't ferrite already oxidised?
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Originally posted by snowflake snowflake wrote:


thinking about this, I'm not actually sure how a magnet can get rust - isn't ferrite already oxidised?

The parts we're seeing are the pole plates/pieces, which are typically steel, the magnet would be behind them in those views.

And they can't use stainless steel, as stainless steels are typically non-magnetic.
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I've had good results soaking in 50/50 vinegar and water fopr a few hours to loosen rust first then bircarb of soda wash to neutralise the acidity then doing exactly what jbl_man says. 

Edited by KDW32 - 27 February 2019 at 12:54pm
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APW View Drop Down
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Points: 1174 		Post Options Post Options   Thanks (0) Thanks(0)   Quote APW Quote  Post ReplyReply Direct Link To This Post Posted: 27 February 2019 at 3:02pm
how about trying something like Jenolite (or similar) Rust converter to neutralize the rust, and then clean it off as described above?




Edited by APW - 27 February 2019 at 3:04pm
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Originally posted by jbl_man jbl_man wrote:

The top plate (the outer side of coil) and the pole piece (inner side of coil) are badly corroded on all those above. yes,it can be cleaned, i have cleaned worse than that with fine emery paper soaked in WD40 to lubricate it,it does come off, but is time consuming and wearing on the finger tips,but half an hour on on each one would help matters. Make sure you vacuum the gap with the most powerful hoover you can find after.
Just store them somewhere warm and dry,the corrosion above is down to bad storage,not faulty drivers.

Try not to use WD40 anywhere near voicecoils. It degrades them and they eventually fall apart. (PD use WD40 to clean/desolve adhesive off the coil winding machine).
If you must use it clean the parts with acetone to remove all traces.
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snowflake View Drop Down
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I wouldn't use sandpaper at all because if you take off any of the unoxidised metal you will create metal dust that will stick to the magnet, especially in the gap. no vacuum is going to pull fine steel dust off a magnet. acid will dissolve the rust much quicker than metal but if it does dissolve any metal it becomes non-magnetic because magnetism depends on the crystal structure. dissolved metal can simply be washed away.

phosphoric acid in Jenolite will put a protective coating on the surface of steel. but this is best done once it is clean. otherwise it may fuse any grains of dust onto the surface and make it rough rather than smooth. be careful of other rustproofers - some contain latex and other stuff that you don't want in a coil gap.
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digitallake View Drop Down
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Points: 56 		Post Options Post Options   Thanks (0) Thanks(0)   Quote digitallake Quote  Post ReplyReply Direct Link To This Post Posted: 27 February 2019 at 6:53pm
Hi thanks guys for the suggestions, I'll have a good think about all that and try to put a plan together. Cheers :)
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concept-10 View Drop Down
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whatever you do the rust will be back very quickly as the coatings have gone, the plates, magnets and poles need to be separated 're coated and then re bonded then they will be as new, we have the shims to re align all the above parts, the correct adhesives for bonding and a partner who coats the pole and plates, if you choose to do the job yourself then I would be happy to advise you on anyway, good luck bud.
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digitallake View Drop Down
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Points: 56 		Post Options Post Options   Thanks (0) Thanks(0)   Quote digitallake Quote  Post ReplyReply Direct Link To This Post Posted: 27 February 2019 at 8:18pm
Well yes this is exactly what I'm concerned about, longevity / reliability following any repair.

Thanks for the offer, but at replacement cost of £150 per driver new, I'm assuming that the cost of the professional repair you describe and a recone would not be cost-effective compared to buying new drivers....



Originally posted by concept-10 concept-10 wrote:

whatever you do the rust will be back very quickly as the coatings have gone, the plates, magnets and poles need to be separated 're coated and then re bonded then they will be as new, we have the shims to re align all the above parts, the correct adhesives for bonding and a partner who coats the pole and plates, if you choose to do the job yourself then I would be happy to advise you on anyway, good luck bud.
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Young Croc
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Points: 1293 		Post Options Post Options   Thanks (0) Thanks(0)   Quote concept-10 Quote  Post ReplyReply Direct Link To This Post Posted: 28 February 2019 at 6:11am
Totally agree it will not be cost effective and new drivers is the answer, we usually only do this on rare or very expensive drivers.
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