Yellow drip stain on Iridited aluminum

we've had a chronic problem with yellow stains on aluminum parts that get an Iridite coating. the stains look like the yellow color has dripped vertically down the part during or after the plating process. what causes this? what should the plater do to stop it? thanks! mda

This sounds like you are having a problem with your plater which sounds like a job shop rather than a captive one. I hesitate to get in the middle. Without being able to see exactly what you are talking about, I will make some guesses.

I will first guess that the "drips" are below holes, probably blind and probably about number 6 or 8. These will hold solution that will not rinse well and will run out as the part dries causing a stain. The worse case is that preprocess chemicals will drain out or be blown out. This stuff tends to strip the chem film (chromate) and is really ugly.

The next guess is that his rinse tanks are filthy.

The next guess is that he is not blowing the parts dry which is quite tedious and time consuming if you are not in Arizona.

I would investigate finding another plater and then give the current one a final chance to clean up his act(pun intended). Better rinsing and drying can eliminate the problem. It probably will cost more.