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Old 12th Sep 2017, 8:10 pm   #21
M0FYA Andy
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Default Re: Re-anodising heatsinks?

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Originally Posted by Craig Sawyers View Post
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
What a silly idea! Heatsinks are intended to dissipate heat, not just look pretty. Obviously an audiophool idea................

Andy
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Old 13th Sep 2017, 6:13 am   #22
Craig Sawyers
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Default Re: Re-anodising heatsinks?

Didn't you see my earlier post regarding dissipation being almost all convection and hardly any through radiation for a temperature rise of less than 40C? The colour of the heatsink is pretty much irrelevant for a temperature rise of less than 100C.

There is another effect that reinforces this idea called the "view factor". Think about how much each part of a finned heatsink area sees of the environment, and is capable of thermally radiating. Before you get very deep into the profile, each area of the heatsink sees progressively less of the environment, and the more it sees of the adjacent fin. Since the adjacent fin is at the same temperature there can be no radiative energy transfer - it can only radiate if it sees a cooler environment which it can only peek through the gaps between the fins.

All of which says: the colour of the heatsink does not matter if you can touch the heatsink without burning yourself. Cooling is close to 100% convection.

The colour of a heatsink is traditionally black for decorative reasons only, and alas reinforces the pseudoscience argument that thermal radiation assists dissipation to a significant degree.

Here is a link to a heatsink manufacturer that says the same thing http://www.abl-heatsinks.co.uk/heats...ace-colour.htm

Quote "The heat transfer from the heatsink occurs by convection of the surrounding air, conduction through the air, and radiation. Heat transfer by radiation is a function of both the heat sink temperature, and the temperature of the surroundings that the heat sink is optically coupled with. When both of these temperatures are on the order of 0 C to 100 C, the contribution of radiation compared to convection is generally small, and this factor is often neglected. In this case, finned heat sinks operating in either natural-convection or forced-flow will not be effected significantly by surface emissivity."

Craig

Last edited by Craig Sawyers; 13th Sep 2017 at 6:41 am.
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Old 13th Sep 2017, 6:42 am   #23
M0FYA Andy
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Default Re: Re-anodising heatsinks?

OK Craig, I retreat defeated!

Andy
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Old 13th Sep 2017, 7:04 am   #24
Craig Sawyers
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Default Re: Re-anodising heatsinks?

And from the Aavid heatsink manufacturer https://www.aavid.com/product-group/...ons-na/anodize

"Relatively large extrusions and those used at low temperature rise, as in many high power applications, will only gain up to 10% by the addition of an anodized surface.

With forced ventilation (using a fan) convective cooling is about 3 times higher than in natural convection. This changes the proportion of heat transfer due to radiation. An anodized finish will only add 4 -8% to the overall cooling effect in forced air. This percentage again, depends on fin spacing and heat sink dimensions. The color of the anodized finish makes little impact on emissivity since most radiational heat loss occurs at wavelengths higher than visible light.

As a thumb rule, if anodize is not required for aesthetic or corrosion protection, we suggest it only for small, open finned heat sinks in natural convection."

Craig
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Old 13th Sep 2017, 7:09 am   #25
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Default Re: Re-anodising heatsinks?

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OK Craig, I retreat defeated!

Andy
Aplogies - my second post crossed with yours!

There is an application that needs 100% radiative cooling though - in space applications (where no-one can hear you scream!). Since it is in vacuum, the only method of getting heat out is via a radiator panel pointed at deep space (which is only about 2 Kelvin, so T1^4 - T2^4 is high). Each circuit board has a thermal layer connected to its housing. Each of those (there might be dozens or up to a hundred on a space vehicle) is coupled to the radiator panel with ammonia heatpipes.

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Old 13th Sep 2017, 7:28 am   #26
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Default Re: Re-anodising heatsinks?

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The color of the anodized finish makes little impact on emissivity since most radiational heat loss occurs at wavelengths higher than visible light.
You sometimes see heatsinks which have been painted black. I have always wondered about the trade off between the effect of the colour on improved radiation, and the thickness of a layer of paint reducing conductivity.

From what you say, it seems possible that painting something black could actually be detrimental from a thermal standpoint? Probably not a big effect, just a waste of time?

B
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Old 13th Sep 2017, 7:54 am   #27
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Default Re: Re-anodising heatsinks?

Well, back when I was involved in this from a production standpoint, anodising - particularly black - was a nightmare. Depending on the condition of the bath, and the repeatability of the dying and sealing processes you could get anything from a nice deep black right the way to almost a blueish tinted black.

What precise colour you get is also strongly dependent on the aluminium alloy - so that is another process to control if you aim to get colour uniformity.

In the end we had a sample and the plater had a sample. They (it wasn't Metro Plating, by the way) were told that if the batch was visually different to the sample to strip it and replate. And we did rigorous QC on goods inwards.

Powder coating can be much more predictable from a colour point of view, and with a much wider colour palette, but it is difficult to get uniform coating on sharp corners and into deep profiles (like a heatsink).

There is another sneaky problem with extruded heatsinks - they are always slighly banana shaped. It is inherent in the extrusion process. Aavid cheerfully own up to that, and say if flatness of the device mounting surface is important (and why wouldn't it be?) that it should be post-machined flat. And they will do it for you - at an additional cost.

Craig

Last edited by Craig Sawyers; 13th Sep 2017 at 8:03 am.
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Old 13th Sep 2017, 9:50 am   #28
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Default Re: Re-anodising heatsinks?

It's not just space-in-a-vacuum that denies cooling by convection: anywhere in zero-gravity experiences the same effect. There are lots of fans used for cooling in things like the ISS.

[Zero-gravity has other odd effects: a friend of mine is NASA's fire-suppression-in-space supremo. Without convection, fire behaves very differently in zero-G !]
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Old 13th Sep 2017, 1:21 pm   #29
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Default Re: Re-anodising heatsinks?

That is a good point. My experience is with unmanned space vehicles - I hadn't thought of cooling implications in manned zero g environments, and particularly the hazards of fire and how it behaves.
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Old 13th Sep 2017, 4:11 pm   #30
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Default Re: Re-anodising heatsinks?

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Originally Posted by M0FYA Andy View Post
Quote:
Originally Posted by Craig Sawyers View Post
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
What a silly idea! Heatsinks are intended to dissipate heat, not just look pretty. Obviously an audiophool idea................

Andy
Here is a selection of small heatsinks in a sample box from Aavid Thermalloy. There's black, red, blue, gold, natural, and plain. While the anodising may make only a small difference to performance, they sure do look pretty.

I used to work for a well-known power supply manufacturer, their approach with large heatsinks for highly-dissipating linear power supplies was to black powder-coat the heatsinks! As far as I know, there was no study done to determine whether plain, black anodised, or black powder-coated were best. I suspect not very much difference, as others have commented!
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Old 14th Sep 2017, 5:27 am   #31
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Default Re: Re-anodising heatsinks?

Old car engine oil is used in metalwork to give a black finish, the only problem is this is done by heating
said metal to cherry red. Easier to achieve with steel and iron than ali. Still might be worth experimenting with a blow torch. How big is said HS?

To be honest I'd just spray it black with bog standard spray paint, doubt it'll ever get hot enough to damage the paint. Think of a car roof in summer, gets hopping on one leg waving your hand about hot.

If that don't appeal here's - https://www.ebay.co.uk/sch/i.html?_f...paint&_sacat=0 various high temp paints as found on ebay. I've used both the barrel paint and SAS 59, works ok and have also used stove paint. Both the exhaust and stove paint comes off eventually, but then both hospital hot. I've had my burner glowing orange, not blacking can survive that.

Andy.
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Old 14th Sep 2017, 6:59 am   #32
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Default Re: Re-anodising heatsinks?

There's also a guy in Sweden who takes aluminium electrolytic capacitors, de-cans them and re-homes the innards in little hardwood housings. His web pages are quite lyrical about the improvements to be obtained and the effects of different woods. No mention of life-expectancy. I'm afraid I didn't bother to save the URL when I was pointed to it.

Couldn't be the same bloke, could it? I suppose he'd have gone for Iroko heatsinks.

At least the gold plate will have virtually no effect in either direction.

David
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Old 14th Sep 2017, 7:46 am   #33
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Default Re: Re-anodising heatsinks?

Would the recased electrolytics be any worse than old cardboard cased ones?
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Old 14th Sep 2017, 9:40 am   #34
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Default Re: Re-anodising heatsinks?

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There's also a guy in Sweden who takes aluminium electrolytic capacitors, de-cans them and re-homes the innards in little hardwood housings. His web pages are quite lyrical about the improvements to be obtained and the effects of different woods. No mention of life-expectancy. I'm afraid I didn't bother to save the URL when I was pointed to it.

Couldn't be the same bloke, could it? I suppose he'd have gone for Iroko heatsinks.

At least the gold plate will have virtually no effect in either direction.

David
Good grief. Sounds like the sort of hokum that gives rise to mains fuses filled with beeswax.

No - the guy I know's day job is at the Karolinska Institute carrying out research aiming at helping stroke patients recover more quickly and better by Transcranial Direct Current Stimulation.

His degree is in engineering Physics with majors in mathematics and computer science.

So a hard technologist - not a smoke and mirrors guy by any stretch

Craig
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Old 14th Sep 2017, 10:00 pm   #35
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Default Re: Re-anodising heatsinks?

That guy in sweden should rehouse some 3-1000A's in wooden cases!!!

The sound should be superb, especially in class A

Joe
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Old 15th Sep 2017, 6:22 pm   #36
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Default Re: Re-anodising heatsinks?

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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.
Just to wrap the thread up, I spoke to these and a few other companies but they all wanted a three-figure sum plus VAT to do the work. I eventually found an establishment in Manchester who would do it for considerably less and seemed to know what they were talking about, so the heatsinks are currently en route for treatment.

As seems to be usual on this forum, I learned a great deal about heatsinks and heat transfer from this thread and many thanks to all for the very valuable suggestions. Every day's a schoolday
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Old 15th Sep 2017, 7:08 pm   #37
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Default Re: Re-anodising heatsinks?

I'd be interested in who the company in Manchester is
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Old 15th Sep 2017, 11:08 pm   #38
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Default Re: Re-anodising heatsinks?

Yes - please share! (With a photo of the refurbished heatsinks!)
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Old 16th Sep 2017, 7:55 am   #39
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The company is Colour Anodising of Radcliffe, Manchester. I'll put up before-and-after pics of the results as soon as they return
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Old 16th Sep 2017, 10:19 am   #40
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Default Re: Re-anodising heatsinks?

I did a web search before you posted, found them, and discounted them - because the website looked so swish I was sure they had to be expensive!

But very interesting looking company.

Regarding gold plating, I also had a look around the UK and found http://www.goldplating1.co.uk/ in Bolton. Prices look really good - maybe I'll try a heatsink and see what they would quote for stripping and gold plating.
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