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E-coating a carbon steel candle holder for outdoor use

August 17, 2011

Hello sir,

I am now developing a item, which is a cast candle holder, material is carbon steel 35#, it will be used in outdoor environment. For a good looking surface, we decided to choose E-coating for surface treatment. Color is Black matte.

My question is what kind of test is required for the corrosion resistant? Neutral salt spray 5%? How many hours would be enough?

Thank you. I'm looking forward to your reply.

Andy Zhang
quality engineer - Fujian, China

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Hi, Andy.

Salt spray hours are not indicative of real life, and by asking for salt spray hours I think you may be doing the design of the finish a little backwards.

For outdoor exposure, start by choosing a robust finishing process. E-coat alone, even after a good zinc phosphate pretreatment, is probably not enough. I think you need to add a layer, either zinc plating under the e-coating or a polyurethane topcoat or a powder coating over the e-coating.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
August 18, 2011

Ted is 100% correct. When the UK had a car mf industry, most under-body parts were expected to conform to specs calling for very high physical and chemical performance (1000 hrs ASTM B117). This was achieved by using zinc phos followed by a coat of polyester semi matt black, 18-20 gloss. Belt and bracers used by some coater's included a e-coat as a primer.

Terry Hickling
Birmingham, United Kingdom
August 22, 2011