Re: Anodizing question

"Barna Madau" wrote in news:bkar8v$rdleo$ snipped-for-privacy@ID-158944.news.uni-berlin.de:

We make a lot of soft anodized parts but rarely (never?) any that get threaded into each other. However, I can't imagine why this would be a problem. I know hard anodizing can sometimes add too much material to your threads and bugger them up if not planned for.

At my last job we used to make small anodized tubes that we'd screw together (camera lens extensions) and never had problems. Everything was soft anodized.

I think your boss is full of horse hockey. You don't specify what rationale he uses, but the only one I can even imagine is electrolytic coupling (sometimes called "Galvanic coupling") in which two materials with different electric potentials exchange electrons. That sets up chemical reactions that result in corrosion. Two LIKE materials anodized in the same fashion have no differences in electric potential (to speak of) and should therefore not set up Galvanic corrosion action. There are good reasons not to couple very different materials like (for example) stainless and aluminum in the presence of high moisture and/or an electrolyte (like chlorine), even if the aluminum is anodized. This is why typically brass pneumatic fittings are used with aluminum parts. But actually even stainless and aluminum in anything less than a harsh environment will hold up reasonably well. The aluminum will corrode eventually, but it will take a long time.

'Spork'

Barna Madau wrote:

seconded and well applied

swash

Hi

I use helicoil thread inserts.

steve

I am digging in the gray pits of my memory for this but "Diffusion Bonding" is sometimes referred to as "Cold Welding". It is a mechanism where tightly fitted parts made of similar metals or metals which are soluble in each other can diffuse into each other even at ambient temperatures. I don't think that aluminum, and especially anodized aluminum, would be prone to this because it has an oxide layer on the surface which acts as a diffusion barrier.

Confirm this before telling your boss what an idiot he is. A quick Google on "diffusion bonding" "cold welding" yields some pertinent information including a product used to induce the process in press fit parts by acting as an oxygen scavenger to reduce oxidation.

HTH,

JJ

My experience has shown me that two aluminum threaded parts, male and female, both anodized, tend to gall and can be problematic. Especially if the thread is to be used repeatedly. Hard coat anodizing usually builds up on the threads so we compensate with oversize taps on female threads. Whenever possible we will spec disimilar materials, sometimes Delrin.

I forgot to say that I always spec the use of loctite 222 this excludes moisture and helps with the dissimilar materials problem.

steve

The hydraulic manifolds I design are usually made from 6061 aluminum with an anodize finish. Some of the cartridge valves we thread into the manifold are anodized aluminum, although I'm not sure which grade aluminum is used. We haven't had any problem reported with these, but there are a couple instances that can be a problem. First electrical conductivity. Some solenoid valves use a single terminal with the valve body acting as the ground. We must wire brush any cavity threads to remove the anodizing to get a good ground. The second issue is using some of the various grades of Loctite; you must use the primer in order for the loctite to cure. It needs metal ions, or something like that, which it can't get from the anodized aluminum.

Al Peterson SunSource MEC

Hard anodizing can be used for an electrical insulator on heat sinks for power semiconductors.

Best regards, Spehro Pefhany

In our cameras we use a brass adjustment ring (for mounting the lenses) which has a black oxide finish. This threads into a black hard anodized aluminum front housing with a 1 3/8" x 32 thread. We do this to prevent galling, but I've always suspected this was overkill, and would like to use anodized alum instead of brass. The black oxide finish always gives us problems. (Anyone got a better finish for brass that won't create flakes or dust?)

bp

Anodized on soft or Anodized on Anodized works.

If you want to prove that soft aluminum male into a soft aluminum female does NOT work, just step out to the lathe and turn a couple threads that are minimal clearance and then try to screw them together a few times...if you can get past the first assembly.

Galling can be almost instantaneous if the parts are fresh cut, since no natural oxidation of the surface has had time to ocurr.

Some 300 series stainless will do the same thing if not passivated.

Bo

You dont say if this is a once off install or whether it is a reinstallable feature, if it is a once off then aluminum to aluminum no matter what the anodise should be ok, if it is a reinstallable feature I would use a helicoil insert to stop the female from wearing, especially if the female is in an expensive fitting or casting. When installing dissimilar metals together, especially in highly loaded joints or fatigue critical joints do a 'wet' install using sealant to prevent hydrogen embrittlement due galvanic action.

"Bo Clawson" a écrit dans le message de news: snipped-for-privacy@posting.google.com...

IIRC, has to be hard male into soft...

Sorry, friday, couldn't resist...

I would agree for use as a bearing, that hard + softer is more likely to work for a long time. Threads are not usually used that way.

For aluminum threads, anodized & unanodized, "soft" works, but indeed all aluminum naturally starts building an oxide layer on aluminum immediately after being cut or scratched & exposed to air, which is why aluminum works fairly well in exposed environments (without corrosive materials or galvanic corrosion).

Anodized on anodized has always worked well for me.

Bo

Yes there are sophisticated coatings for BeCu, brass & bronze which are used in molds and other places where hard surfaces are needed to resist wear.

Moldmaking Technology (paper copy only) has a table of coatings and properties for both Electroless and Electrolytic coatings for ferrous and nonferrous metals including ones infused with 'Teflon', and can get Rc 48- 68 (68 w/heat treatment) applied at below 212 F.

= latest issue, Aug 03. This issuse goes through a full page chart of 10 coatings supposedly all suitable for both ferrous and non-ferrous use.

Eastman published another chart of coatings in the early 90s as a part of info published on mold design.

There are a lot of choices, even for Brass, and it probably depends on the cost & features needed to decide what is really needed in each application.

Bo

Sporkman wrote in news: snipped-for-privacy@bigfootYETI.com:

right, i work in the alusector since years and we use to fit alu with stainless steel without problems. The prob begins if the final user works with iron (usually to trim costs). If u mixed alu with iron, it's very probably 99% that in you have corrosion in few months in reason to the Galvanic Pair. A good anodised Alu have no problem (with a minimum of 10-

15mic). xcuse my bad eng.

In mechanical engineering classes, our instructors always told us to use dissimilar metals (don't use the same steel for mating parts) when there were tight tolerances involved, due to the effect of the items "cold welding" themselves together.

It's been many years since I heard this, but it is a known problem with certain materials.

I agree with the poster below...don't make a fuss with your boss until you have some concrete facts to support your opinion.

Gerard