Letter 14096

Help with blue dye over zinc plate [Minnesota] 

I am looking for advice on applying blue dye over zinc plated steel (for rack, not barrel). Should a chromate be applied before work is dyed? Does it matter if the zinc is plated from a chloride or cyanide bath? Is blue dye a difficult bath to control? Blue dye is applied by an immersion process and not electrolytically, correct? Are there any special waste treatment concerns with blue dye?

Any advice would be greatly appreciated.

Keith Rosenblum
- Fridley, MN, USA

The only blue dye I've seen applied to zinc plating has been to hardware in barrel plating lines; so I don't know if the uniformity will be good enough for rack work. But I know it is done on cyanide lines, and believe it works on acid zinc lines as well. You definitely have to chromate first because it is the chromate, rather than the zinc, which absorbs the dye. In the applications I'm familiar with it was quite easy, they just put the dye in the final hot rinse.

In terms of destroying the dye, unless the dye is unusual, I think you'll find that the sodium hypochlorite you would use for cyanide treatment makes short work of it.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

Yes, apply a TRI-VALENT BLUE BRIGHT, rinse and then the Blue Dye. Whether CN, alkaline, or acid does not matter so long as the plating solution film is completely removed in a "sour dip". Experiment first in a beaker to find the best dye concentration and pH for your application. Then call me and let's talk.

Robert H Probert Robert H Probert Technical Services Garner, NC, USA Editor's note:        Mr. Probert is the    author of Aluminum How-To

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