Re-anodising heatsinks?
I found out the hard way today that putting anodised aluminium heatsinks in the dishwasher to clean them is a very bad idea. They're now a sort of streaky grey with black areas where the devices were mounted. "Mortified" is the word.
Is it possible to get heatsinks re-anodised? |
Re: Re-anodising heatsinks?
The alkaline solution of dishwasher tablets attacks aluminium, as you've found out!
Depending on how bad the surface is, you may be lucky. Take a few photos and email South West Metal Finishers. No connection apart from a satisfied customer in the day job! |
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Black anodising is essentially cosmetic for a heatsink that is not running stinking hot.
The majority of heat transport from a heatsink is via convection, not radiation, for typical heat rise of say 40C. In that case the difference between a black anodised heatsink and a shiny aluminium one is negligible that for typical heat rise. Rather than pay for a small quantity to be stripped to bare metal and re-anodised, I'd be tempted to spray paint them black. |
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Per Craig: If you use VHT [AKA Very High Temperature] spray paint there is no chance that this will lift or bubble .... this stuff is used by car restorers etc. on exhaust manifolds. (It goes under then name of VHT / 'Firecote' etc. Retailed by CarPlan - made by Tetrosyl Ltd. Bury, Lancs. BL9 6RE. Tel. 0161 764 5981.)
They'll be fine .............. |
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That's interesting -- thank you. Does this type of paint work well on aluminium? I seem to recall reading horror stories about needing etch primer or exotic surface preparation to make paint adhere properly.
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For an outlay of 15 shillings, anodising can be done in the average home...according to PW in 1962 (see attached)!
I wonder how big your heatsink(s) are? PM me if you consider any "homebrew" option. As for dish washers, I have put the odd item of agricultural engineering in them, but never any item of radio/electronics. B |
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Worth trying for some fun!
I believe after dyeing, commercial anodising features a further electrolytic operation which hardens the oxide coating and makes it more dense. This is missing from the PW article. But I may be wrong on this. Hopefully someone will correct me! Look forward to what South West Meatl Finishers come up with. If time is not of the essence, they may offer to wait till a big batch of something arises, and put it in at the same time for a nominal sum. |
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Not sure the homebrew option would go down very well with Madam or the elf 'n' safety people nowadays.... |
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Being amphoteric, it's difficult to predict how the aluminium oxide will have reacted, but there's a fair chance that it's just the dye which has been leached out. I'd be inclined to dump the heatsink in a hot dye bath for a few hours before contemplating anything more drastic.
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John |
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My understanding is that the conditions chosen for anodising intentionally create a porous oxide layer and the dye goes in to the pores. That is then is sealed in by the action of the subsequent immersion in boiling water which "seals" the pores, though I guess the same could be done electrolytically.
B |
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The reason that anodised aluminium cannot be used in ultra high vacuum systems is the pores. These give rise to what is known as a "virtual leak". In other words it has the characteristics of a leak, preventing the vacuum level to be attained, but in fact it is something in the chamber outgassing. And anodised aluminium outgasses pretty much forever.
The aluminium treatment for UHV use is electropolishing. For decorative use (ie not vacuum use!) electropolishing and then anodising (and dying) gives a superb mirror like finish. |
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I've used these guys on a number of occasions, and found them to be pretty good. Perhaps worth a try. Based in Uxbridge.
http://www.metroplating.co.uk/ |
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That's an excellent link Craig - if you click on the various services they offer, they give some very good concise descriptions of each of the anodising processes.
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Hello
This sounds like something that motorbike customizers or restorers would need doing. Perhaps if you could get a read of the adds in a 'bike magazine there might be some firms that would do a small job. Just a ramdom thought. Will |
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A guy I know in Sweden has a plater that takes a black anodised heatsink, strips the anodising and then gold plates it. Must ask him who does this, hopefully in a cost effective way.
This is what his gear looks like |
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We use metro plating, they are a friendly bunch, worth having a chat at tea time (10 am) outside (fag break) for a "private job". One of the cleanest plating plants I have ever seen.
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