What is the difference between anodizing and e-coating?

"Electrocoating: a Guidebook for Finishers"
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A. Hi Dick. As you'll read on this thread, aluminum requires pretreatment before e-coating -- phosphating as a minimum, but chromate conversion coating ideally. My bet is that both is a salt spray test and in real life, chromating plus e-coating will outperform anodizing in corrosion resistance.

Luck & Regards,

A. Hello, Felix. Letter 11694 gives a pretty good intro to e-coating. Anodizing would apply only to aluminum or titanium, so if you are thinking of another metal, anodizing is off the list of possible finishes. What do you want to finish and what properties are important to you?

A. Felix,
Anodizing is an oxide layer that when sealed is often desirable against corrosion depending on exterior environment such as wind, sand and abrasion. Colored anodize does not do well under UV exposure. Anodizing applies mostly to aluminum. Fabrication of the aluminum after anodize will expose the raw material and subject it to oxidization.
E-Coating offers a thin coating that protects a surface but may wear with abrasion. E-Coating as a urethane, has excellent exterior UV protection, even with organic decorative dies. E-Coating can be used on any conductive metal. E-Coating as an epoxy, is used extensively in the automotive market as is not well suited for exterior applications.
Both e-coats are applied by submersion and offer coverage to all surfaces, including welds.

A. I hope someone will correct me if I am wrong, Dan, but while e-coat is a great coating, I don't think it's stand-alone. I believe the aluminum must be chromated (or at least phosphatized) before e-coating anyway.

I think I would look at it more like this: the aluminum should be chromated; then, if the shape is simple and free of faraday cages, spot welds, and crimped edges (such that paint or powder coating by itself will offer good corrosion protection) you are good to go. If the surface presents any of the problems I mentioned, you'll probably want to e-coat it after chromating and before powder coating. Good luck.

A. An e-coat coating is only as good as the pretreatment you put under it (and vice-versa). It's been my general experience that an e-coat coating on aluminum will not work that well (defined as resisting pitting corrosion leading to failure of a pressurized part) unless you have a good pretreatment under it.

Of course, this all depends on what you want the coating to do. If you want corrosion resistance, pure and simple, then a combination of pretreatment and e-coat is the best. If you value corrosion resistance and heat transfer equally, e-coat will definitely slow the heat transfer. In that case, pretreatment alone with a sealer may be better.

It also depends on how much performance you want. A simple etch/clean of aluminum with a good e-coat may be enough for your application. Then again, maybe not. You'd have to provide us with some idea of what you're trying to accomplish.

A. Ted is right again. My experience goes back to the mid 70's when I was employed by a large UK paint mfgr to carry out sales and tech service on the first white electrocoating system in Europe. The end product was extrusions for domestic double glazing -- so it had to last. What I can remember was (1) desmut using NaOH, rinse, (2) Chromate & rinse (3) apply coat and bake.
I have not touched E-coating since, but all the lit still suggests chromating prior to applying any surface coating to obtain the best results.

A. In China, E-coat as a topocat for aluminum is usually put onto an anodized surface, either in natural color or by electrolytic means. I do not think anybody use E-coat alone on aluminum without any kinds of pre-treatments.

A. Most of the articles and documentation I searched are in Chinese for this process. However, if you search "e-coating of aluminum" in Chinese yahoo, you will be able to obtain some of the information you want.

A. Hi, Leo.

This site doesn't recommend vendors or suppliers (why?), but that product is proprietary to Bulk Chemicals Inc., so you should probably start there. Good luck.

Regards,

A. Hello Mr Cullen,

It would not be advisable to put either a casting or stamping into water unless its fully molded over with plastic and you want the metal inside for additional strength.

In which case you want to go with E Coat and if you can afford it put a thick zinc plating on below the E Coat as well.

E Coat offers a highly adhesive surface and almost anything bonds over E- Coat like super-glue.

all the best,

A. Hi Sachin. E-coating produces a thin paint-like organic coating on the parts whereas anodizing is aluminum oxide, a ceramic-like coating which is much harder and more wear resistant. But anodizing is probably more costly and, because aluminum from the substrate forms the coating, the quality of the coating can be highly dependent on the alloy and quality of the extrusions.

It is probably best to detail the application as carefully as possible so experts in those technologies can advise us on their strengths and weaknesses in the particular situation because a paragraph or two in a public forum probably can't cover everything necessary to make sound choices for general cases.

Regards,

A. Hi Nandagopal. If you ask a more generic question, and supply the details of what kind of parts you are processing, etc., people can probably comment. But you are asking about a trade secret system, and only the vendor, Bulk Chemicals Inc., can advise of the proper process sequence for their proprietary processes. Good luck.

Regards,