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Anodized Aluminium edges not taking dye very well

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Q. Good day. I have been having an inconsistent problem where some parts are not taking the colour dye very well on the edges. Any idea what the cause could be?


Denvor Tesmer
- South Africa
March 18, 2023

A. Hi Denvor. I'm not really understanding the picture in that I have no sense of scale (is this picture "actual size" or way smaller or way bigger? And I don't understand what the item is and why such ridges are considered acceptable, or maybe they're even desired.

But I think you're not going to get saturated dye on a thin ridge like this because you don't have good anodizing on small protuberances like those ridges because they're full of sharp inside corners where growing surfaces crash.
Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

A. I suspect
1. work hardening from a dull stamping/cutting tool,
2) and/or slivers of thin aluminum left behind by the same dull cutting tool, the slivers anodized, clear thru from side to side, then as 100% aluminum oxide, fell off and left bare metal.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

A. Hi Denvor,
Please have your customer do better deburring prior to sending for anodize. The sharp edges get attacked badly in the anodize tank and are not able to grow the same nice even crystalline structures as the rest of the part due to what we'd call 'burn' or 'scorch', and don't have the pore structure to take and hold dye correctly. This is a common defect. Removing the burr by buffing or some other means, or adding a 'break edge' instruction to the engineering sheet, will remedy it.

Rachel Mackintosh
- Greenfield, Vermont
June 9, 2023

thumbs up sign Good day Robert.
Thanks a lot for the reply.
The machining is of a very high standard so that will not be a problem.
The problem seems to be isolated to only parts dyed in red.
I have reduced the voltage and increased the anodizing time, which seems to have corrected the problem so far.

Denvor Tesmer [returning]
- South Africa
June 12, 2023

? Good evening Denvor, would you mind sharing what your dye process is? And what dye you are using?

Rachel Mackintosh
- Greenfield, Vermont

Q. Good day Rachel
The components are washed in a degreaser for 2 min; 40 sec in the brightener tank; 1 min in the desmut tank; anodized for an hour at 14 volts and a temp of 23 °C; and then the red dye tank at 50 °C for 20 min. The dye is a product supplied by MacDermid.
I was having this problem when I anodized for 45 min.

I hope that this info makes sense. Take care.

Denvor Tesmer
- South Africa
June 19, 2023

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