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How To Get Grey Anodize To Match

March 9, 2009

We are a company that sends out parts to be machined by several different machine shops out of 6061-T6. The parts have the same surface finishing and anodizing specs, and they all go to the same plater afterwards to be anodized to Type II Class 2 Grey. However, none of these parts even remotely match each other, even if we leave a sample of what we are shooting for.

Does anyone know what we are doing wrong? Do they all need to be anodized in the same bath at the same time? Is Grey Anodize just a bad one to try to match? Should we give up and go back to Black or Clear Anodize?

Here is our note callout on all the parts:

1. GRAIN DIRECTION SHOWN
2. SATIN ETCH BATH
3. ANODIZE TYPE II CLASS 2 GREY TO MATCH SUPPLIED CHIP
4. NICKEL ACETATE SEAL

Any assistance would be greatly appreciated. Currently we are wasting a lot of time and money by stripping and re-trying whole batches of non-matching parts. Thank you.

Paul Costales
mechanical engineer - Santa Barbara, California

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Yes, the grays are very difficult to control, some dyes and some shades are more difficult than others. You, the anodizer, and the dye supplier need to sit down together and pick a dye and then tighten the controls (pH, concentration, temperature, alloy, anodize thickness, dissolved aluminum in the anodizing solution, galvanic stray currents in the dye tank, etc).

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

March 11, 2009