E-coating -- what is it?

A. Hi Jaipur. I believe that by "PT CED" you mean "Pretreatment" & "Cathodic Electrodeposition".

Pretreatment: any time you are applying any paint or organic coating you must first pretreat the surfaces to be coated. The pretreatment consists of cleaning, often followed by an acid dip, often followed by some form of phosphatization or phosphate coating. The pretreatment can be as simple as three stages (viz., a combined cleaning and iron phosphate, followed by two rinses, the last of which may contain a chromate or other chemical post treatment) or as complicated as seven to nine stages (separate cleaning, rinsing, acid dip, rinsing, possible grain refinement pretreatment, zinc phosphate, and several rinses, again the last of which may contain a chemical post treatment). These processes are not usually formulated from raw commodity chemicals by the user, but are usually purchased as a system from specialized suppliers.

Cathodic Electrodeposition: You will often see synonyms for this including e-coating, electrocoating, electropainting, electrophoretic lacquering, etc. I do not have deep knowledge of electrocoating, but I believe that when the technology was first introduced the approach was for the workpiece to be anodic, and thus AED or "Anodic Electrodeposition" was the predominant technology. I believe that almost all electrodeposition these days is done with the workpiece cathodic, thus CED. Sometimes electrocoating is the final finish as in "electrophoretic lacquering", and sometimes it is just a primer as is used on all automobiles frames/chassis these days.

An excellent starting point for your study is "The Metal Finishing Guidebook" which is on-line for free and lightly covers virtually every finishing technology. After that you can google using the keywords mentioned here.

Luck & Regards,

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 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.

A. Hi, Sanjay. Sorry but that is just so very broad :-) After a 50+ year career in metal finishing I still have only a passing acquaintance with many surface coating processes. I'd suggest starting with the Metal Finishing Guidebook -->
for an overview, and then look into stuff more specific to CED, phosphating, etc. There are also firms & institutions who can offer you a one or two week introductory course.

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 powder coating is more expensive. Perhaps a shop that offers both will confirm or refute this for me.

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

Q. How is monitoring of PT & CED done?

Q. Which one is better, e-coating or powder coating? Do they perform the same aside from powder coating being thicker? What are the advantages and disadvantages?

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 is a disadvantage. But "better" is only meaningful in terms of compliance with a detailed list of desired properties. If you tell us exactly what application you have in mind, I think people will be able to list advantages/disadvantages for that situation/ circumstance, and help you make an informed choice between the two, or to use the two coatings sequentially, which is also often done.

Attempting to suggest which one is "better", independent of the actual application, is usually wasted effort and often very misleading ... it's like trying to tell you whether you should travel by ship vs. by rail before you tell us whether a planned trip from Los Angeles is to Las Vegas, or to Hawaii.

Good luck.

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

Q. Hello everybody! What is the best method for treatment of a new replacement vehicle frame for a 59 Chevy. E-coating, powder coating - or a combination? What would You suggest? Thank You! Al

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.

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

! Mine is not a question but a comment about powder coating. I run a small job shop specialty coating service and use a Gema gun. The commercial guns have KV's ranging from 10-100 with the normal application amp set at 45 for powder attraction. I use a batch method with carts to handle large parts and racks for small parts. I think the application thickness would depend on the application KV's applied to the part for powder attraction, don't you?
Say for instance a tank holding 50 lbs of powder using an air mix and low KV's, I think with air blowing the powder around the tank as the parts passed through would flock the powder very proportionally and with low KV's the thickness could be adjusted.
Permits for E-coat and chemicals are very costly and a start up operation could start around $ 500,000.00 so I am told by suppliers.

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,

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

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

Advantages of electrodeposition over conventional powder coating

Q. We are in the business of light manufacturing for the shipping industries. Currently enclosures are coated with Epoxy (conventional powder coating). May I look for any alternative method to this electrodeposition (Typical Process offered by PPG- UK)? Are there any advantages or disadvantages? Are these two comparable with each on the performance?

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,

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

Q. Hi, I am purchasing a bumper for my Jeep Wrangler and I see most manufacturers use powdercoating and a few use the e-coating? Can you tell me which would be more durable and which would be more resistant to rust? Thank you.

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 :-(

I doubt that any bumper is only electrocoated, unless it is intended for repainting by the buyer, and the electrocoating is meant as only a primer. To the extent possible, please investigate customer satisfaction with the various brands and make your decision based on that.

Regards,

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

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 two 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 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,

Thank you, that'll help tremendously!

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 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,