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topic 6158

Paint adhesion is poor on Welds


I have a situation where cold rolled steel is being welded and then painted with electrolytic dip process (e coat), however, there is no paint adhesion to the welds. I have been told that this is due to a "silicon" component of the metal rising and hardening on the surface of the weld. I wish to understand how accurate the analysis is or whether it is a generalization.

Chris Gardini
Dell - Austin, Texas US



There are many reasons why paint fails to adhere at welded locations, here are several I would investigate.

I would first look at the weld process and find out what electrode is being used. If the process is using an electrode high in silicon then you may want to use an electrode containing less silicon. As an example, in Gas Metal Arc welding, if the process is presently using an ER70S-6 electrode that contains considerable amounts of silicon then you may want to change to an ER70S-3 electrode containing less silicon.

Next, take a close look at the cleaning operation, and find out whether fabricating soils are being entrapped between the metals and determine whether the surface is being cleaned prior to and after welding to remove oxides, scale and those tenacious carbon residues. Carbon and silicon are adhesion killers and should be removed by power brushing.

That's all I have for now, good luck.

J. Regmont
- Warren, Michigan, USA

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