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Old 9th Sep 2017, 3:53 pm   #1
GW4FRX
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Default 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?
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Old 9th Sep 2017, 4:33 pm   #2
kalee20
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Default 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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Old 9th Sep 2017, 5:05 pm   #3
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Default Re: Re-anodising heatsinks?

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Originally Posted by kalee20 View Post
The alkaline solution of dishwasher tablets attacks aluminium, as you've found out! Depending on how bad the surface is, you may be lucky.
Oh well. I learned a lesson from that mistake. The surface feels very smooth so hopefully something can be done; I've e-mailed as you suggest and will see what transpires. Fingers crossed...
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Old 9th Sep 2017, 7:11 pm   #4
Craig Sawyers
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Default Re: Re-anodising heatsinks?

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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Old 9th Sep 2017, 7:19 pm   #5
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Default Re: Re-anodising heatsinks?

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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Old 9th Sep 2017, 7:54 pm   #6
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Default Re: Re-anodising heatsinks?

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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Old 9th Sep 2017, 8:33 pm   #7
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Default Re: Re-anodising heatsinks?

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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Old 9th Sep 2017, 9:24 pm   #8
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Default Re: Re-anodising heatsinks?

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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Old 9th Sep 2017, 10:32 pm   #9
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Default Re: Re-anodising heatsinks?

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Originally Posted by Bazz4CQJ View Post
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
I quite often put passivated steel chassis items for restoration (such as Racal receiver side panels or bottom chassis members) in the dishwasher. They come out looking like brand-new. But aluminium heatsinks evidently don't, alas.

Not sure the homebrew option would go down very well with Madam or the elf 'n' safety people nowadays....
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Old 9th Sep 2017, 10:37 pm   #10
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Default Re: Re-anodising heatsinks?

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Originally Posted by kalee20 View Post
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.
That would be ideal. There's no rush at all -- the PSU for this amplifier needs some re-design and a new PCB and there are still some components to source.
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Old 10th Sep 2017, 11:34 am   #11
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Default Re: Re-anodising heatsinks?

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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Old 10th Sep 2017, 12:27 pm   #12
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Default Re: Re-anodising heatsinks?

Quote:
Originally Posted by kalee20 View Post

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!
The DIY process I used about 5 years ago required the freshly anodised article, whether natural colour or dyed, to be immersed in boiling distilled water for 30 minutes to harden it, the piece I anodised has been outside now for that period and looks as good as it did when made.

John
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Old 11th Sep 2017, 5:43 am   #13
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Default Re: Re-anodising heatsinks?

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.

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Old 11th Sep 2017, 8:52 am   #14
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Default Re: Re-anodising heatsinks?

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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Old 11th Sep 2017, 5:57 pm   #15
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Default Re: Re-anodising heatsinks?

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Look forward to what South West Metal Finishers come up with.
Unfortunately they came up with a mildly snotty reply stating that they "...do not undertake this kind of work." Oh well. Back to the Yellow Pages.
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Old 12th Sep 2017, 8:00 am   #16
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Default Re: Re-anodising heatsinks?

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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Old 12th Sep 2017, 8:35 am   #17
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Default Re: Re-anodising heatsinks?

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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Old 12th Sep 2017, 4:34 pm   #18
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Default Re: Re-anodising heatsinks?

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.
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Old 12th Sep 2017, 6:11 pm   #19
Craig Sawyers
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Default Re: Re-anodising heatsinks?

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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Old 12th Sep 2017, 9:03 pm   #20
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Default Re: Re-anodising heatsinks?

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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