Thermal compounds

thijsco19

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Jun 18, 2012
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So I have to remove the inner anodizing layer for the best heat transfer between the heatsink and the body, I will use some thermal compound (some basic pc stuff) between it.

What's the best methode to remove a anodization layer?
 

CTS

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Nov 20, 2012
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The best method to remove the anodizing is a carbide cutter on the end of a boring bar. It's pretty tough.

If you don't have a lathe, you're down to sanding it out. Oven cleaner will work on decorative anodizing but doesn't really touch hard anodizing. Plus you risk ruining the exterior that you want to keep.

If you can find one, get one of those expanding rubber cylinder arbors that sanding sleeves slip over. Mount it in a drill press and run it up and down. Those arbors usually have short shanks. I have an extension that I made out of a Milwaukee spade bit extender that's cut down to about 4" long. Don't use a drum much more than half the diameter of the tube ID. Any larger and it will begin orbiting the ID rather than rotating against it. The drill press isn't moving so you are. If it doesn't drop away freely when tilted at an angle, it's likely going to catch, the force will cause the other end do orbit in a larger radius and the tube will break a few finger. Or worse. you can accomplish the same with a drill in a vice or clamped to a table top.

Your best bet is a press fit. The surfaces should be as smooth as possible. If not, you have tiny contact points and alot of air. Even a tiny fraction of a MM is an effective insulator, so the better the contact, the better the heat conductivity. Thermal paste is better than not if you can't get a good interference fit. It's going to be tough to get uniform application with a tight fit so you're back to doing what you can to get the best metal to metal fit possible. The alternative would be to have a larger gap and fill it with a thermal adhesive.

You have to determine how far you want to go and that depends on what you're trying to accomplish. If you're using an XML in a Mag and have an inch-tall heat sink, remove the anodizing and goop it up. If you're putting 10 amps into an SST90 in that mag, find a good machinist.

You can do the basic math for each material interface, beginning at the diode and ending at the exterior of the tube. The numbers are only going to be relative but the exercise will show you where the thermal bottlenecks are. Unless you do that, you're just guessing- and maybe wasting time, effort and money. Nothing is worse than investing in something you enjoy and not being happy with the results. And it's very avoidable. It's a hobby- it should be fun.
 

moderator007

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The chemical in those drain cleaners you are looking for is caustic soda. I use Roebic drain cleaner 100% caustic soda. Will eat through maglite anodizing in minutes with very little caustic soda in water.
 

BIGWOOD

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The substance in all those products (Grease Lightning, Drano, Liquid Plumber) is Lye, also known as sodium hydroxide (NaOH), or potassium hydroxide, or the household term, caustic soda. If you are using one of these products, make sure you read the MSDS. The MSDS will tell you what % of lye is contained in the product so you know which product will be more effective compared to the other. Also wear gloves and eye protection. The stuff is seriously alkaline and caustic. It'll give your hands a really nice chemical burn.
 

Luciaro

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Arctic Silver 5 is not a glue, I use it for inserting heat sink to flashlight body, so it's removable.

The two parts Arctic Silver is excellent thermo glue, better than Fujik or Arctic Alumina, I use it for glue down led star

Fujik is non conductive, I use it for potting drivers.



I don't know Céramique 2, never used it.

Thank you ;)
 

CTS

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If you attempt the chemical method and are just looking to remove the finish from the tube ID, I would avoid masking the finish using any sort of tape. You might want to try coating the exterior of the tube in a coat of grease. I'd use what is commonly called "red grease" That's not the real name, but everywhere you might find it will know what you're looking for- any parts store/Walmart/Etc. After coating, you can wrap in saran to keep the mess down. The reason I suggest red grease is that it doesn't have additives in it that stain your hands or whatever you might get it on. Any grease will work.

Also, if you go with the chemical method, you'll need to smooth up the surface of the bore as the NaOH will etch the surface. Rough surface equals poor thermal conductivity.

Remember there are two components in that anodized finish- the anodizing and the coloring. They anodize them and then dye them whatever color they might use. As I'm guessing you want to go slow and not eat up the tube ID, don't go too slow and only remove only the color. It's very difficult to tell when you have bare aluminum. Probably the best test would be sandpaper. If it's still got anodize on it, the paper won't really bite too well. If it's aluminum you'll get that silver-grey loading in the paper very quickly. I'd suggest 600 grit.
 
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