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topic 9747

Parts powdery after Chromic Anodize


Hello all,

I've been Anodizing for about a year and a half. So you can say that I am still very green! I have been very impressed with the answers given to a lot of questions here at this great site. So now it is my turn to ask one....

We have parts that are being Chromic Acid Anodized, then sealed with a Dilute Chrome Seal. The parts are coming out powdery.

What do you think it is?

A quick response would be very appreciated.

Randy A. Mattson
- Seattle, Washington, U.S.A.

First of two simultaneous responses -- 2001

Assuming you're anodizing it right, then that powdery stuff ('bohmite?') indicates that your parts are completely sealed.

Dado Macapagal
- Toronto, Ont

Second of two simultaneous responses -- 2001

Could be a couple of things.

1 The seal - check the conductivity etc - better still just dump it to remove from the trouble shooting loop.

2 Temperature.

If the parts are producing a white powder that comes back when you wipe it off, (normally the time taken to go from your place to the customer) temperature is the problem.

It is the solution getting too hot and driving the film dissolution reaction faster.

This results in bigger pore size in the anodic film and the pores are too big for the seal to fill.

The answer is to run the parts a little cooler, try different settings but only change by 2 C at a time, it will only take a small change.

The other thing may be the shape of the part causing solution to be held in an area where it then over heats, we had in side a part the size and shape of a top hat.

A jigging change and higher solution agitation solved this.

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England

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