How Can I Tell If it's Been E-Coated?

Ask an Expert From: Products Finishing, , from Ti6 Consulting International

Posted on: 11/21/2013

How do I know if the black car parts I buy from aftermarket dealers are e-coated for anti-corrosion protection?

Q. I own a car restoration business and buy quite a few aftermarket parts. I know that OEMs use e-coat  as an anti-corrosion treatment protection in their vehicles, but how do I know if the black parts I buy from aftermarket dealers are e-coated or not?—M.H.

A. Automotive body and repair shops around the world are supposed to be using replacement parts equivalent to the OEM-manufactured parts, but we know from experience that this is not always the case. Application of electrocoat requires facilities with high capital investment and a high degree of technical expertise to operate, which not all automotive aftermarket suppliers have. 

Write to the aftermarket part supplier and ask if the parts they supply to you are e-coated or not. If you get no response, then you can do the following:

A quick visual gloss evaluation could be the first indication of whether an aftermarket part was e-coated. Parts exhibiting extremely low gloss below 30 or high gloss above 70 probably were not e-coated. For typical automotive electrocoat paints, the application gloss falls between 30 and 70 depending on the technology, e-coat  supplier used and the application parameters, including cure temperature, time and p/b ratio. The low and high gloss extremes can be easily detected by a trained human eye.

For a more accurate test, the parts can be rubbed with a cloth or cotton tip impregnated with a solvent to see if the coating transfers from the part to the cotton tip or cloth. If after 40-50 rubs back and forth on the same spot you do not see any paint transfer to the cotton tip or cloth, then the chances are greater than 99 percent that the part was painted using e-coat . If you see paint transfer to the cotton tip or cloth, then the aftermarket part likely was painted with an imitation black paint. The rubbing must be vigorous while applying sufficient pressure on the rubbed surface. The solvent must be acetone, methyl ethyl ketone or methyl isobutyl ketone, which are very powerful and can dissolve any paint that is not cross-linked like electrocoat.

If a more scientific analysis is required, other expensive analytical techniques can be employed. Gas chromatography, liquid chromatography, mass spectrometry and other thermal and chemical identification techniques can be used to determine the chemical composition of the paint and whether it is electrocoat. 

Electrocoat is widely accepted in the automotive world because of its corrosion properties and its great chemical resistance to most automotive organic fluids such as gasoline, brake fluid, wiper solution, anti-freeze and organic solvents in general. Electrocoat paint develops this capability because, after application, the paint is cured at high temperatures ranging from 325 to 400°F, which enables the electrocoat epoxy paint to accomplish a high degree of polymerization and crosslinking to form a strong, chemically inert epoxy polymer.


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