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Metal finishing Q&As since 1989

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Clear anodizing that looks like gray paint.

Since switching from a caustic etch to an acid etch we have had issues with some clear class I material having a dark gray tint to it. It's random, sometimes several pieces on a load, sometimes as few as one piece. We have checked extrusion, tempering parameters and everything is as it should be. We finish 6063 alloy extrusions. Could someone give advice on what to look for.

James Justice
finisher - Midway, Tennessee
February 10, 2010

You should use caustic etching no acid etching.

Carlos Carrera
- Miami, Florida
February 22, 2010

First of two simultaneous responses --

If staying with your acid etch, you may need change your de-smut chemical (HNO3) to a strong de-oxide chemical, and 4 min immersion at least

John Hu
- Singapore
February 22, 2010

Second of two simultaneous responses --

If it is random on one rack, and the air agitation is not hitting the work, then it is contact reliability.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

February 22, 2010

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