Introduction to electrocoating, CED, ED, electropainting.
Q&A's, Problems & Solutions

A. Hi Dinesh.

I think it's most likely that the welded area is not spotlessly clean. If you can attach pics in email to mooney@finishing.com for posting here it would probably b helpful.

Luck & Regards,


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

SUGGESTED E-COATING, CED, E-PAINTING BOOKS
for Shops, Specifiers, & Engineers

"Electrocoat: Formulation & Technology" by Bruggemann & Rach (2020)
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"Electrophoretic Deposition (EPD)" by Nathan Bass (2017)
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"Electrocoating: a Guidebook for Finishers" by Electrocoat Association (2010)
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"Electropainting: A survey of principles and practice" by Reginald Leslie Yeates (1980)
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"Handbook of Electropainting Technology" by W. Machu (1978)
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A. Hi, Carlos.

E-coating is another name for electrocoating, electropainting, or electrophoretic lacquering. It is used to deposit a paint or lacquer coating (rather than metal, as is deposited by electroplating). It's more of an "application method" for paint or lacquer than a type of coating per se.

Parts are dipped into a vat of the lacquer or paint and are electrified in order to promote a reaction at the surface which deposits the paint. Depending on the chemistry, the workpiece can be anodic or cathodic, but these days it's usually cathodic, which has given the process still another common name "CED coating" (cathodic electrodeposition). It is used on very large parts, such as automobile bodies, to apply a primer coat that doesn't miss any spots, and it's also used on smaller parts such as lamps and jewelry to deposit a thin and durable lacquer (electrophoretic lacquer) as a decorative finish.

A. Yes, and no. E-coating is a process of using electricity to apply paint or lacquer, however, it is primarily used for smaller parts as a primer. I manage an e-coat facility that works parts from the size of a quarter to a rear axle on an 18 wheeler. E-coat is also a better choice over powder coat if thickness is a concern, the paint is distributed more evenly without fluctuation.

A. Dear friend, question needs to be elaborated and then answered.

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A. Hi, Sanjay. Indeed that is very broad :-) I'd suggest starting with the Metal Finishing Guidebook -->
for an overview, and then looking into stuff more specific to CED, phosphating, etc. There are also firms & institutions who can offer you introductory courses in metal finishing.

Luck & Regards,

A. E-coating is done with the parts immersed in a water-based solution. While you would need to get any relevant hazard information from the actual supplier, I've not heard of it being flammable or combustible and certainly wouldn't expect it to be.

Yes, powder coating is done with powders of thermoplastics or thermoset plastics.

A. That is a little difficult to answer, Scott, because there are different types of e-coats and powder coats, and some e-coats are intended only for use as a primer, and most powder coating requires some sort of pretreatment. But powder coating is generally far thicker than e-coating, involving the deposition of significantly more material, so it is probably reasonable to say that after discounting the capital costs, powder coating is more expensive. Perhaps a shop that offers both will confirm or refute this for us.

A. PT CED MEANS PRETREATMENT LINE & CED MEANS CATHODE ELECTRODE DEPOSITION LINE IN PAINT SHOP.

A. Hi Sureshkumar

All questions are welcome, but some can't be answered in the paragraph or two of a public forum. You would need to read an extensive article on PT such as phosphatizing and another one on CED (if not whole books on the subject) because, although they are easier questions than "how is an airline built", they are still multi-faceted and complex questions requiring many pages of exposition.

Luck & Regards,


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

A. Hi Leonardo. We've mentioned some general advantages of e-coating -- complete coverage and very thin coatings being the principal ones. Higher capital cost for e-coating and generally not as decorative are disadvantages. But "better" is only meaningful in terms of compliance with a detailed list of desired properties. If you tell us what application you have in mind and in detail, people will be able to list advantages/disadvantages for that situation/ circumstance, and help you make an informed choice between the two, or whether to use the two coatings sequentially, which is also often done.

Attempting to suggest which is "better", independent of the actual situation, is misleading ... it's a bit like trying to explain the advantages & disadvantages of travel by ship vs. by rail before you've told us whether the planned trip from Los Angeles is to Las Vegas, or to Hawaii.

Good luck.

A. Hello Alfons. Powder coating will not be able to cover all areas of the frame, whereas e-coating will -- and it is done by all OEMs. But both in sequence would actually be best. Good luck.

A. Hi Jimmy. Yes, there are clearly advantages to powder coating over e-coating, usually including lower capital cost as you mentioned, and also thicker coatings, the versatility to easily go from one color to another, and one type to another, apply multiple coats, etc.

But although you can vary the thickness of powder coating, no matter how thinly you apply it, you can't get it to melt and flow and cover at anything approaching the thinness and consistency of a e-coating with no missed spots in crimped areas, under spot welds, etc. 1 to 2 mils would be a common powder coating thickness and might still miss spots due to Faraday cage effects, whereas 2 tenths of a mil would be a common e-coating thickness and there would be no missed spots. Again, neither is "better" until we know what the application is. And I personally think they comprise an excellent relay team, with an epoxy e-coat under a powder coating topcoat.

Regards,

A. Hi, Ramachandra. Electrocoating can compete against powder coating, but it is often a complimentary process to powder coating rather than a competitive process. Electrocoating has the advantage of full coverage of the tiniest recesses and it is very thin. So electrocoating will often be a "prime coat" before powder coating. To the limit of my knowledge all automotive bodies are electrocoat primed.

Regards,

A. Ramachandra: Have you come across repeated cases where customers have complained of powder coating peeling off? If this has happened, then Electrocoating will go a long way in improving the quality. The epoxy primer coat gives the corrosion protection while a top coat of PU or PP powder coating will provide UV protection.

A. Although Ted is correct in that it is a complementary process to PC you have to be very careful that any recesses do not retain air. As EC is partially a dipping process with electrics... deep wells, unless facing up at an angle, will result in areas of no coating as the entrapped air will prevent this.

A. Thank you, Terry.

We can also note that, excellent as electrocoating is for good thickness distribution, it's doesn't do miracles -- people have observed lack of coating deep inside the hollow tubing of automobile frames.

Luck & Regards,


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

A. Hi, Jerry.

Regrettably, a manufacturer's sales spiel almost never reveals anything important about the finish because it is not intended to educate you, but to induce you to buy. But my guess is that you're actually looking at two different types of product --

I think that if a bumper is only electrocoated, the intention is for it to be repainted by the buyer, with the electrocoating intended as only a primer. If it's powder coated, it probably has its final intended finish on it.

To the extent possible, please investigate customer satisfaction with the various brands and make your decision based on that.

Regards,

A. Hi, Richard. The vehicles you mention would be first e-coated, then powder coated or wet spray painted. Obviously, the vehicle manufacturers do not think of e-coating as a replacement technology, but as a supplementary technology.

If your bike racks have tight interior corners or a bit of weld splatter, etc., e-coating can get you complete coverage whereas powder will not. But powder is thicker and probably more corrosion resistant and attractive. I think the powder coating is more durable. To do it best, apply e-coat and powder coat in sequence.

Regards,

A. Hello, Sandeep. This public forum is a good place to ask for a quick one-paragraph introduction to a technology you are unfamiliar with, and it's also a good place for answers to a highly specific question. But as you get into wanting detailed sequences for processes, with pictures, theories, etc., your needs will probably have to be met by books on the subject. We've suggested on this page the e-coating books that we are aware of.
But maybe one of the vendors of the process has a free brochure or CD that will help you. Good luck.

A. Hi, Srikanth. Here in America, a "silencer" is a device fitted on the barrel of a pistol to reduce the noise, and yes they can be e-coated. But I think what you call a "silencer" is what we call a "muffler" -- a device to reduce exhaust noise on motorcycles and automobiles?

As mentioned, the coating is thin but it is corrosion resistant. The biggest question I would immediately have would concern the operational and maximum temperature of the application. For high temperatures you usually need metals or ceramics rather than paint or organic coatings. Good luck.

A. Hi, Bob. The metallic colors to my knowledge are just post-treat dyes. Although I suppose it would be possible to do an aluminum vacuum metallizing before the e-coat, I haven't seen it. Finishing.com just completed a major study of corrosion resistant coatings for zinc die-castings for the International Zinc Association, and we found the metallic colors about equal to the solid colors in corrosion resistance. Polyurethane top-coating does significantly improve the corrosion resistance, but it adds significant thickness.

Regards,

A. Hi Chandresh. As mentioned immediately above, finishing.com's testing for IZA did not show evidence of your hypothesis leaning either way, although I can't rule them out since the amount of data we collected on that particular subset is scant, and really only had to do with metallic appearance, not actual metal particles. I am not familiar with e-coats containing metal particles.

Regards,

A. Hi, Dev.

Sorry, I've never heard of using e-coating on molds. I've only heard of using chrome, electroless nickel, and other hard metal or ceramic coatings, not paint. It's not that I claim to have heard of everything, just that I can't help.

Regards,

A. Hi Tracey.

To my limited knowledge the e-coat tank itself operates at about ambient temperature. But curing is usually required. The normal temperature for this is about 375° F, but there are low-temperature curing paints available that can be cured at 180 °F. It is also my understanding that there are UV curable e-coats.

Regards,

A. Hi, Wayne.

That one is probably better directed to auto body shops, who will be much more familiar and knowledgeable than we are with what is required to effect a robust repair. But I do note that I've never heard of e-coating being applied to a plastic component because it is an electrolytic process that can only be performed on a conductive surface, so the story sounds fishy to me.

Regards,

A. Hi Henry. While each extra layer of a coating has the potential to reduce corrosion, lack of e-coating is probably not the key issue here. Although it's not possible to do a failure analysis based on such limited verbal information, my bet is that the aluminum components used to be properly chromate conversion coated and no longer are chromated.

Step 1 is to find out if the parts are still chromate conversion coated, and to fix it if they're not.

opinion!   It is unfortunately common these days for inexperienced government regulators and wet-behind-the-ears environmental engineers in swivel chairs to steer industry toward implementing well-intentioned but foolish & wasteful substitutes for time-proven finishes in the erroneous belief that we "help the environment" by saving an ounce of chromate ... while consequently sending a ton of fabricated product to the junkyard. It's an environmental travesty and an assault on sustainability for manufacturers to supply products that last 2 or 3 years when we've known for decades how to easily & inexpensively make them last 15 years and a lot more.

Regards,

"No good decision was ever made from a swivel chair" -- General George S. Patton.

A. I suspect the chromate was too heavy, in which case the powder coat will peel off. Under powdercoat (or any organic finish) the chromate must be very thin, slightly iridescent, not bright gold.

A. Hi Praveen. In my opinion rinse tanks are for rinsing, they are not process tanks. Therefore, you should not add anything to them to control pH but should merely run an optimal amount of water through them, i.e., enough to guarantee quality without wasting water. Anything you add constitutes something that you are not rinsing off.

It is risky to take a tiny 2-letter acronym like ED and try to insist on what it means -- most of the world thinks it means 'erectile dysfunction' :-)
But in this context it presumably means "electrodeposition", and it additionally probably implies electrodeposition of paint rather than electrodeposition of metal (electroplating). Thus ED probably probably means the same thing as e-coating, electrocoating, electropainting, electrophoretic lacquering, etc.

Typical e-coating thicknesses are probably a couple to a few ten-thousandths of an inch. Good luck.

Regards,

A. Yes, you can process Aluminium parts in the same line. You have to be careful with the degreasing and phosphating baths. They will require additional controls.

A. Hi Ashvin. I doubt that e-coating without an additional layer of powder coating will survive 20 years of outdoor exposure, but there is unfortunately no good way to prove or disprove it in a short time. And, of course, you also have to make the assumption that the coating will not be scratched in 20 years of service.

Although it is possible to somewhat adjust the thickness of CED coatings, they are insulating, which inherently slows down the process at a rather low thickness (maybe 35 microns or so). I think CED coating is an ideal BASE for a 20-year coating system, but not an ideal topmost layer.

Regards,

A. Hi Bob. E-coating is paint, not metal. It is soft and certainly does not have the adhesion, hardness, or scratch resistance of metal. Poor pretreatment is the cause of most adhesion issues, i.e., the aluminum was probably not properly cleaned and chromated before e-coating.

Regards,