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topic 5030

Barrel Anodising (bulk)


Q. Hello,

I am a graduate chemical engineer and have been working for an anodising company for 18 months. We anodise components for the Cosmetic industry, so, quality surface finish is paramount.

I have been asked to investigate barrel anodising. I understand the quality will not be as good as our rack anodising, but how do you barrel anodise gold without having lots of touch marks on the components? Is there a high level of rejects? Any information would be most helpful. Thank you.

Jonathan Holgate
Lancashire, UK


A. You cannot use a barrel to anodize!

You have to have excellent contact or the parts will make and break the connection and arc, destroying the parts. What you may be referring to is for small parts, they stuff them in a special titanium tube with lots of fine holes and literally squash the parts with a nut on the lid. You will have lots and lots of contact points that will show. Definitely not for a cosmetic finish.

James Watts
- Navarre, Florida


A. My company does all types of anodizing including BULK. You absolutely can anodize in a basket. We have done this for over 40 years & while, yes, you will have touch marks, many cosmetic parts are done in bulk anodize. Bulk anodizing is a specialty and the more experience you have doing it...the better the results.

David A. Kraft
- Long Island City, New York


Dave, My reply stated that you could do parts in BULK. The original letter stated that his parts were for the cosmetic industry, not cosmetic parts. Will you buy your best girl a compact that has a nice touch mark on the cover versus one that does not have any?

I have never met a customer that would accept contact marks anywhere but where it was covered by another part. The paintball industry will not accept it, the military generally will not accept it, the auto industry generally will not accept it, the archery industry will not accept it, the bicycle industry will not accept it, the electronics industry generally will not accept it, so, who will accept it on other than screws? Especially the COSMETIC industry.

James Watts
- Navarre, Florida


This one is clearly loaded with semantics issues.

A 'barrel' (to we in the finishing industry) is absolutely not the same thing as a basket--but perhaps Mr. Holgate may not care whether it's called a barrel or a basket as long as it permits bulk anodizing.

Then we have the term 'bulk', which to most people certainly induces visions of large containers of randomly oriented small parts which will make contact with each other, and consequently leave touch marks, at numerous points.

Then we have the question of 'cosmetic industry', which Mr. Holgate defines as a field where "quality surface finish is paramount".

My own feeling is that the chance of this project being a success is slim when he says quality surface finish is paramount.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. The shop where I once worked used to bulk anodize pencil ferrules (the metal band that holds the eraser) by the millions, when pencils were still made in the U.S. We bright dipped and gold anodized a large number, but the most popular color was Eberhard Faber's premium pencil, on which the ferrule was anodized black, where contact points would have been most noticeable. But contact points were not as much a concern as a lot of other issues. You obviously can't anodize in a traditional plating barrel, but you must use titanium baskets. Parts must be packed as tight as possible (An amazingly small percentage of parts bend). A doughnut-shaped basket is best for maximum circulation and best color uniformity, as you are packing a lot of surface area into a small,confined basket, hence a lot of amps, and hence a lot of watts of heat are generated, which can give you shades of gold across the whole dark-to- light spectrum.

Other problems include: Rinsing, rinsing, then more rinsing. Parts are best processed loose in all tanks except anodizing. Solution control is highly critical through the whole line. Load- to- load color matching is not at all easy.

We had to use an almost full-time inspector to pick out voids and bent parts (mostly voids), as no matter how hard you tighten the baskets, some parts will be loose.

The process is as much art as science, as in many types of metal finishing. Before you go out and buy the equipment to get into what can be a nightmare, I would recommend you have David or some bulk anodizer in your country anodize a drum full of your parts and send you back the loads uninspected, so you can see what to expect.

phil johnson
Phil Johnson
- Madison Heights, Michigan

sidebar 2000

Look into this for a way to keep rack plating your parts, but doing the racking and deracking at least twice as fast as by hand. Endura Corp. in Nokomis, FL builds a real neat racking machine. If you combine this with a modified multiple insert rack that I think Vulcanium makes (possibly Servasure) you should make life on your rackers a lot easier as well as a lot faster. I would guess that it could easily reduce rejects also. Really sounds like a win-win situation.

PS, both Endura and Vulcanium will be at Sur-Fin next month, so you could get hands on trial and face to face contact as to your needs. Sure beats faxes.

James Watts
- Navarre, Florida


I'm going to back James on his statement, Dick at Endura has an excellent machine for fast, production racking and unracking of small parts on compatible racks (he makes plating and painting racks too). Call him and ask him for the video he has, it shows you, in real life examples, how well this setup works. The cost around 5K for a manual machine and around 6-7K for a hydraulic. He stated to me at one time that if you have a lot of work that someone would be better off using the hydraulic units, less stress on the body = 's less fatigue = more production = more profit. Simple equation, wonderful idea. If I had a use for those things, I'd snatch a group of them up in a heartbeat.

Matthew Stiltner
- Toledo, Ohio


A. Mr.Holgate, You may consider the cold chemical oxidation of aluminum, a process (known as Decoral) which produces a 1 to 2 µm thick transparent aluminium oxide film that can be coloured and works in slow rotating polypropylene barrels.

Emmanuel Popesco
- France

Ed. note: You can read about the Decoral process in letter 2951, "Non-electrolytic blackening/coloring of aluminum: Decoral process".

September 24, 2013

Q. I want to start Anodizing specifically for Aluminum pencil ferrule in different colors please guide me with the process. Also if there is any other process to get different glossy finishes in different colors on aluminum.

Sohil Sheth
metal finishers - Gujarat, India

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