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"Problem is dyeing then grinding Hard anodizing"

December 8, 2010

Dear Sir,
We seeking for advice to improve black color dye penetration for hard anodizing process at 80 microns thickness and then grind down to 50 micron as requirement stated. We could not manage to maintain the black color after grind down more than 30 microns as we are using immersion black dye at 55 degree heat up. Is it possible for the black dye penetrating more the 30 micron of 80 micron thickness for hard anodizing?

Arthur Koo
Plating employee - Hong Kong

December 10, 2010

55 C seems a bit low for a good black dye. Remember that the pores in hard anodize are much smaller and the cells tighter packed which will limit the penetration of the dye.
Can you put on less anodize and thus grind off less?
Have you tried to re dye the part?
Are you using a high quality metal based dye from a very reputable OEM. There are only 2 in my book. Have you talked with the dye MFG tech services. They may have seen this before.

James Watts
- Navarre, Florida

December 12, 2010

Dear Sir,
Thanks for your previous reply.
We are using Japan's branded dye stuff, at what recommended temperature does do the job and not seal the pores? We have not tried re dye the parts, how is this being done?

Arthur Koo
- Hong Kong

First of two simultaneous responses -- December 13, 2010

Have you tried a 3-5 min HN03 (25% vol) agitated soak after anodize, prior to dyeing? In the past I've found that to be very helpful when dyeing hard anodized parts, although these parts were not ground afterwards.

I agree with James in that you should be approx. 20° F higher in temperature for most of the dyes I'm familiar with.

Marc Green
Marc Green
anodizer - Boise, Idaho

Second of two simultaneous responses -- December 13, 2010

I missed the no seal part. 55° C will partially seal the anodize, but very little. As you take the temperature up, sealing becomes more complete till you get to 90+ C which is as complete as you will practically get.

Parts will not stay black forever if they are not sealed, so you have a significant problem there.

Hard anodizing does not take dye very well to start with.

RE dye? Take a scrap part that you have anodized, dyed and ground and put it in the dye tank same as the original dye work. Be sure to get before and after measurements. See what it looks like.

I do not think that dying after grind will work as your surface finish will change. Dimensions may change also. Since some of the pores will have cutting fluid in them, I think the appearance would be bad, poor at best.

James Watts
- Navarre, Florida

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