Barrel / Basket / Bulk Anodising

A. Hi rajendra.

It may not even be possible :-(

The principles of bulk anodizing are fairly simple: the parts must be packed so tightly with some sort of a lid that they cannot move, while still allowing excellent solution flow, and minimal part-to-part contact (because that creates non-anodized rack marks).

Then an inspection method and quality standard must be established which allow for the fact that anodizing this way cannot produce 100% perfect parts. Considering the smooth and uniform shape of these parts, together with the usual high quality requirements for aerospace processing, I wouldn't be very hopeful :-(

Luck & Regards,


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

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.

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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.

A. 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

A. This one is clearly loaded with semantics issues.

Some of us may be picturing a plating barrel when Jonathan says 'barrel' -- but perhap she may not care whether it's called a barrel or a basket or a rose 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 though.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - 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
- Madison Heights, Michigan

A. 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 A. 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 2µm thick transparent aluminium oxide film that can be coloured and works in slow rotating polypropylene barrels. Emmanuel Popesco - France Ed. note: Readers, you can read about the Decoral process in topic 2951, "Non-electrolytic blackening/coloring of aluminum: Decoral process"

A. Basket anodizing is going to have one or more contact marks with zero anodizing and thus zero dye. I do not think that this meets a normal definition of high quality. There are many kinds of tips for anodizing racks. Some are amenable to loading machines. while it does not meet the speed requirement, it will produce a high quality part and probably much faster than what you are currently using.

A. A variety of colors, yes. High quality, maybe, depending on the particular parts and the experience level of the anodizer. You'll have more, and more random, contact marks, and you may have some difficulties getting consistency.

A. Ability to dye - YES. High Quality - No.

All the rack manufacturers, some listed in finishing.com, sell baskets which tightly clamp small parts in a basket. Except for contact marks which will remain bare, the parts on the outside of the basket will get a good anodic thickness with ability to absorb dye. The parts closer to the inside of the basket will not get as much thickness as a function of current distribution and solution agitation.

Basket anodizing is suitable ONLY for color coding small parts and fasteners, leaving some lack of uniformity and a bare contact mark(s) on each part.

A. Scott,

The quality of basket anodizing does depend upon the configuration of the part, but that being said it is very possible to get a high quality finish on certain parts using basket anodizing. Furthermore, because of the bulk processing aspect, it is possible to do this at a much lower cost and shorter turn-around time then with conventional rack anodizing. Once anodized the parts can be dyed in the same manner as any other anodized part. Contact marks are left undyed, but (depending on the configuration of the part, parts with many or large flat surfaces are not good candidates) typically are very small and insignificant.

Jim Gorsich
Compton, California, USA

A. I agree with Mr. Gorsich that it's a question of what you are looking for and that a few contact marks don't obligate us to call a finish low quality. After all, virtually every plated or anodized part has at least one contact mark. If it was a watch case, contact marks would probably condemn it as low quality; but I have seen products such as hose barbs bulk anodized and they were fine for their purpose.

Robert Probert's comment about parts near the center of the mass getting less anodizing than those on the outside should also tell us that small loads are probably preferable to large ones.

A. You have not given us enough information to give a good answer. Anodize will cost more than phosphate! Your part is small so is going to be a little bit tough to rack. You might do basket anodizing, but you will have several contact points of various sizes on each part with no coating. Several anodizing choices. type 2 which is regular sulfuric anodizing, type 3 which is hard anodizing or what we refer to as type 2 1/2 which is a poor man's hard coat that is done with an additive and a higher temperature.
This quantity is not to be taken lightly for in-house work. You will need a significant dedicated facility. Can you run 24/7 or 24/5. If so, it can be downsized appropriately. Always leave room for increased production at a later time without a major rework of the facility. Since you are going to generate chemical fumes and a lot of moisture, even with a good exhaust system, it should be physically separated from the machining operation. Very doable, but not something that you jump right into without hiring a consultant or a very broadly based anodizing foreman and listen to him/her. A lot of engineering items to look at.

A. Perhaps you can tell me what machines I need to make the parts; I'm sure, just like you envision anodizing as simply "dipping", making the parts is nothing more than cutting up sheets of aluminum with tin snips and then bending them up with pliers (or something like that). Except that federal, state and local regulations on air emissions, discharging rinse water, hazardous chemicals such as concentrated sulfuric acid, and resulting hazardous wastes make the proposition of your anodizing much more inconceivable than my making machined aluminum parts! All kidding aside, you stick to "whittling" parts and I'll stick to "dipping" them. There are a number of good anodizing job shops in the mid-west which can be found at this website or other finishing based sites.

A. Bulk anodizing is perfect for that type of scenario, but I can't tell from your description whether your part is perfect for bulk anodizing or not. Because the location of contact marks can't be controlled during the bulk process, the best results are obtained with parts that predominantly curved surfaces (for example, rivets and screws - a combination of which my company does between 2000 and 4000 pounds per day).

Jim Gorsich
Compton, California, USA
2006

"I'm not expecting a perfect finish on these parts but I would like the whole part to take some color."

A. It depends. If they are flat parts, say washers, which will lay together, the answer is, probably, no. On the other hand, if they are formed enough that they make only point contact, the answer may be yes.

You'll have to try it and see.

A. Hi Shalem. Bulk/basket anodizing is surely the cheapest method, but there would not be other methods if one way was "best". It always "depends" on factors you haven't told us yet  :-)

How many parts do you have to do, what alloy are they, do you need dyed or non-dyed, how thick must the anodizing be and why, what reject ratio is acceptable? Please send a photo or drawing of the part to mooney@finishing.com for posting here, then hopefully the readers can suggest whether bulk/basket anodizing is worth pursuing or the parts must be racked. Thanks!

Regards,