Relayer150, Thanks for the post!!
If you could provide a photo of this "splotchy, hazy" finish, I would probably be of more assistance. I will give it a try anyway.
First of all, what is the temperature? If below 50F, can you add some hot water to take the chill off of it? I am sure if you had a heater, you would be using, but "who heats chromates in a job shop?" If you cannot raise the temp to, let's say 60F, then try a longer immersion time (almost double what you would normally process).
Secondly, are you certain you are cutting the alkaline/brightener film over the cad plate? Have you changed out your "sour dip" or "post-dip" prior to the olive drab? Try making up a new "sour dip" if there is reason to think your current sour dip is contaminated or "old".
And last, what is the concentration of the Cr+6 in the olive drab and especially, what is the pH? Make sure the the Cr+6 is in parameter, then consider adding 10% of the makeup qty. of Part B and see if you overcome the "splotchy/hazy" look. Sometimes an imbalance of the two components will cause this appearance. Other times, it is a sure sign that the chromate is old, saturated with zinc or cadmium, and worst case, contaminated and the “law of diminishing returns” has set in.
I assume this is a 2-part chromate chemistry? You may very well just be out of ratio and are going to need to work delicately to get this back in sync. Most OD chromates are 1:1 Part A/Part B makeups, but this may not apply to your chemistry. Always refer to your Technical Data Sheet when troubleshooting your process chemistry, one mfg. may differ from the other.
Here are some bullets to re-consider, if you have not already:
-Chromate concentration.
-Acidity of chromate solution.
-Bath temperature.
-Immersion time.
-Drying temperature.
-Quality of plated finish.
-Load size processed.
-Agitation during chromating.
-Transfer times before and after chromating.
-Age of chromate solution.
-Impurities in chromate solution (drag-in).
-Rinsing before and after chromate.
Some variables will have only a slight effect, while others or a combination of several, will greatly effect the final finish. Most importantly, if you can work with your chromate on the level of a “bench test” in a beaker in the lab, or worst case, a 5 gal. pail or small tank. This can prove successful without the “wastefulness” of unnecessary chemistry being added to the process tank. And if you are successful, proportionally, you may make additions to your process tank.
Good luck!
Last edited by skelton (01/21/2010 - 04:34 PM)
Skelton, hOST
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