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topic 28116

E-coat paint coating


A discussion started in 2004 but continuing through 2019

2004

Q. Are you familiar with a process called "E-coat"? And if so how is it different than powder coating? Also can powder coat be applied to galvanized metal?

JOHN JACKOWSKI
architect - CHICAGO, ILLINOIS, USA


2004

A. E-coat also goes by the terms electropainting, electrophoretic coating, electrodeposition and a few others. You may have seen it in old commercials; it's the process used on automotive chassis where the whole frame is dipped into a tank. The idea is that electricity converts the chemicals in the solution into a corrosion resisting primer right at the surface of the part. Because it forms an electrically resistive coating, as the prominent areas get coated, the electricity is diverted to the more recessed areas until everything is coated.

The powder coating process looks rather like electrostatic spray painting. What is sprayed, however, is dry powder that is heated and melts into a "paint". A big advantage is environmental friendliness because no solvents are needed.

Powder coating can be applied to galvanized metal. However, when galvanizing is intended to be the final finish it is chromated to help keep it bright and resist white rust. Powder coating and other finishes will not stick as well to this. If the galvanizing is to be powder coated, the chromate finish is omitted. Further, although galvanized metal can be powder coated, the right way is to zinc phosphate it as part of an integrated production process. Powder coating a galvanized surface of unknown history in situ presents additional adhesion issues. You can order instruction booklets about painting and powder coating of galvanized surfaces from the American Galvanizers Association at www.galvanizeit.org. Galvanizers sometimes call this (galvanizing followed by paint or powder coating) a duplex finish.

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



August 10, 2011

Q. What is the difference between e-coating and normal paint spray applications?

terry_smith
Terry Smith
- Cape Town, South Africa

August 30, 2011

A. Hi, Terry.

Don't confuse E-coating with electrostatic spraying. E-coating is a dip process rather than a spray process, but more significantly, the "paint" does not really become paint until the electricity is applied.

If you picture electroplating, you are not dipping the article into molten metal, rather you are dipping it into a metal salt, and the electricity reduces the metal ions to metal at the surface of the part. E-coating (also called electropainting, electrophoretic lacquering, CED coating) is similar in that the application of electricity reduces the ions that are dissolved in the solution into paint. Some advantages over other organic coating systems include very thin coatings and 100% coverage (because as the paint deposits, it is insulative, steering the electric current to uncoated areas).

Regards,

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



September 11, 2012

Q. How long can you let the paint stand still in a tank before it has to be replaced due to no agitation.

Nick Wood
- Australia

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Ed. note: Sorry your inquiry drew no reader response, Nick. Perhaps is was too vague for our readers.




September 19, 2012

Q. In autophoretic coating, all of the water soluble resins used have low pH (2-4). Above that value the bath has weak deposition efficiency.
Suppose we have resin soluble in water at high pH (6.5) ... is it suitable to deposit it from the above mentioned bath? You know if we add acid to lower the ph of this resin it will coagulate; it is only stable at ph 6.5.
How to solve this problem?

Ahmad Abo Awf
- Cairo, Egypt



November 9, 2012

Q. If I use E-coating to finish engine tin parts for an old Porsche I am restoring, is it considered a finish coat or do I need to apply a finish coat over the E-coat? If so what would be the recommended finish process. Thanks.

Mark Erbesfield
- Atlanta, Georgia, USA


November 12, 2012

A. Hi, Mark. E-coating is not so much a finish as a method by which to apply a finish. So there is, for example, e-coat priming which all automobile manufacturers use for the whole frame and body, and which proceeds wet painting and clear coating, but there is also e-coat lacquer which is either a finish coat or which is sometimes topped with polyurethane.

It's a matter of whether one layer gives enough corrosion protection and is aesthetic enough for you.

Regards,

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


December 28, 2012

A. Hello Mark,

I do a lot of hobby work on Car restoration; since I have a lot of electroplating facilities my life is a lot easier.

For internal engine compartment, Interior and under Chassis parts I use Zinc Nickel plating followed by E coat; for external body parts I use ductile zinc plating followed by E-Coat, followed by the leveling putty work followed by the final paint.

The thumb rule is epoxy based E-Coat should not be used as the final finish on exterior parts because of poor UV resistance.

The duplex coating of zinc nickel and E coat will ensure that you will never have to rework the parts as it lasts a lifetime; its not a very good idea to keep stripping and electroplating delicate old parts over and over again.

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

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Dipping in primer without electricity

September 7, 2019

Q. I understood that there is another dipping method with primer. Do you have any knowledge of this?

Brian Burke
restoration - Sherwood Park, Alberta, Canada


September 2019

A. Hi Brian. It's possible to apply paint by simply dipping into it, but you might also be referring to "autophoretic deposition" which is similar to electropainting except that the paint ions are sort of 'spring loaded', so they don't need electricity, just contact with metal for the reaction to occur.

Regards,

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


September 8, 2019

A. One of my former employers did this, its known as flow coating. Pretty primitive, coating thickness varies from top to bottom. Contaminants build up as coating continuously recycles.

Ron Zeeman
Coil Coating - Brampton Ontario Canada

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