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How to Anodize aluminum rivets



A. Although "barrel anodize" is a term that is out there, you can't exactly "barrel" anodize with a typical rotating plating barrel, Terry, because the anodized surface becomes non-conductive ... so once the current breaks, you can't get it back into the parts that way.

You can, however, "bulk anodize" or "basket anodize" by putting the rivets into a perforated basket, squishing a top onto the basket to hold all the pieces tightly in position, and then anodizing in bulk. There does tend to be a greater problem with contact marks, but specialists in bulk anodizing know from experience how to avoid most of the problems.

Considering the millions of rivets and other tiny components that are anodized, someone should probably build a bandolier style anodizing machine, or other continuous anodizer as an alternative --but I've never heard of one.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

A. I finally got around to reading the Dec Metal Finishing.

I would be interested in knowing whether anodizing rivets is even worthwhile. I assume the black would remain, but inasmuch as rivets are deformed during installation, would any protective nature remain or be of value?

I suppose, using Ted's bandoleer-style device, only the heads would be anodized and therefore it would be a worthwhile operation.

James Divine, PhD, PE, Chief Engineer
- West Richland, Washington

Multiple threads were merged: please forgive repetition, chronology errors, or disrespect towards other postings [they weren't on the same page] :-)

Q. My name is Juan Sandoval, I'm a Production Engineer working in the production department. Our company manufactures rivets (painted or non painted), depending on the application. We paint our rivets with a gun, but when the application is made, the paint comes off. Also, is very hard to control the parameters, because sometimes the flow is not constant in the gun. We are evaluating different options so we can paint our rivets in a different way. We have seen a little about anodizing, and we have found that the paint adheres very good. Someone told us that in order to get the anodizing done we have to hang every single rivet, which would make the process very expensive. I asked if the process could be done using barrels, and I got a no for an answer. That's why I would like to get some information on anodizing aluminum rivets (5052): the best recommended process, chemicals used, how to obtain colors (information you can send me so I can watch the whole process: pictures, photos, etc.), how do we hang the rivets (or if there is another way to do it).

Thanks a lot,

Juan Sandoval
- Medellin, Antioquia, Colombia

A. The rivets can be anodized in bulk, but not in a rotating barrel. Bulk anodizing involves snugging the components up very close in a perforated basket. Quality may not be as dependable as individual racking, and experience counts, but they may be good enough, especially if they will later be painted.

It is certainly theoretically possible to automatically feed them from a feeder bowl, orient them, and insert them into some kind of bandolier for continuous anodizing, but I have never actually heard of such an installation for rivets.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

A. Rivets will work very well bulk anodized, just make sure that you keep the rivets held tight, and be willing to pick out any burns or missed parts as some will inevitably turn out bad. With practice you can keep the burnt parts around 1%. Don't worry too much about contact marks, in general the rounded surface of rivets keeps them minimized.

Accurate Anodizing has been specializing in bulk anodizing for over 25 years and we have great success with rivets.

Good luck,

Jim Gorsich
Compton, California, USA

A. I would try Alocrom/Alodine as a pre-treatment prior to painting, this can be done in-house with a plastic bucket and a container of ready mixed alocrom/Alodine solution. You may find that you will need to acid etch the rivets prior to Alocroming.

Andrew Jones
- Wales, U.K.

Aluminum Rivets / Aluminum Channel

Q. We currently use an Aluminum Rivet with an anodize finish to assemble aluminum fishing boats. The anodize finish on the rivet helps prevent Galvanic Corrosion. My issue is that I have a new aluminum rivet that I need to use in a quantity too small to run through the anodize process. Is there a product, aerosol or otherwise on the market that will serve the same purpose as the anodize finish? Just so I can do a few hundred of these rivets. BTW the rivet itself is aluminum and the mandrel is steel. thank you!

Doug Williams
fastener distributor - Elkhart Indiana
September 17, 2020

A. Hi Doug. In the post just before yours,Andrew talks about Alochrome which is the British tradename for a Henkel product which is called 'Alodine' in the USA. Alodine, and a competitive product trade named Iridite, are 'chromate conversion coatings' or 'chem-film' processes, most frequently done in accord with MIL-DTL-5541 [on DLA]. So you can search the site or google for any of those terms to get a fuller understanding and sourcing regarding those processes.

They do not offer the full corrosion resistance of anodizing, but are capable processes for corrosion prevention of aluminum, and can be painted if you wish. The rivets can be chromate conversion coated by immersion or with a touchup swab. It should not be a major problem if stainless mandrels are used, although you'd probably be better all around if you could use aluminum mandrels. I wouldn't subject plain steel mandrels to the processes, and from my very limited experience I think sometimes a piece of the mandrel can get crimped into a rivet. You wouldn't really want stainless there, and definitely not carbon steel.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
September 2020

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