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Gold Chem-Film Finishing Different Shades

January 14, 2009

Currently in our chemfilm line we dip our sheetmetal parts consisting of steel and aluminum and sometimes parts on the same rack will come out in different shades. Does anyone know the reason for this?

Josh Valliere
Shop Employee - Cedar Rapids, IA, United States
  ^- Privately contact this inquirer -^

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January 27, 2009

Hi, Josh. Solution agitation is important for consistent color. Do you have air agitation or solution spargers? Tell us more about the presence of steel in this bath.

Regards,

Ted Mooney, P.E. finishing.com Brick, New Jersey

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First of two simultaneous responses -- January 28, 2009

The reference to steel and chem film puzzles me as well, but I have found a good amount of variation in color due to alloy, surface finish (sanded vs blasted vs mill finish), and even though they go through the same process to clean, if one part had more in the way of soils or lubricants prior to clean, and now has some residues remaining in Chem-Film or affected prep in interim steps. More info would be good.

Paul Slater
- Cedar Rapids, IA, USA

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Second of two simultaneous responses -- January 28, 2009

Iron contamination in the chromate solution will degrade corrosion protection, enough will fail salt spray testing.

Robert H Probert Robert H Probert Technical Services Garner, North Carolina Editor's note:        Mr. Probert is the    author of Aluminum How-To / Aluminio El Como