NITROCARBURIZING
NITROCARBURIZING
(OP)
We have a supplier who applies a wear/corrosion resistance surface finish to plain carbon steel bars. The problem is that when we receive the part, it has an objectionable black smut on the surface. The part is used in a medical environmenet. We believe that the process used is some variation of liquid salt bath nitrocarburizing. What is the black smut, and more importantly, how can it easily be removed?
grayseal
grayseal





RE: NITROCARBURIZING
What type smut are you seeing, loose or tightly adhering?
If it is loose the best way to remove ii is tumbling, vibratory finishing, or some other mechanical means like buffing.
If it is very tight one need to know the specifics of the applied process. One process I know leaves a variegated surface and the black areas are permanent.
RE: NITROCARBURIZING
Thanks for the reply. We have tried to have the supplier clean the parts with unacceptable (varied) results. Since I am not in Purchasing, I can't change supplier. We have tried tumbling, vibratory finishing, hot water wash, etc., again with unacceptable results. The smut is removed by simply wiping with a rag, but this is labor intensive.
I would like to know the specifics of the process, but this is proprietary information.
Thanks agian,
grayseal
RE: NITROCARBURIZING
One thing to try is tumbling with soft media like dry oak sawdust, corn cobs, walnut shells, or a mixture of one or the other with a plastic media.
http://www.black-walnuts.com/nutshell.asp
http://www.greenproducts.com/specifications.htm
If you could contact Mr Victor Briosi a Victor Metal Finishing he would put you on track and possibly do some samples.
http://www.vicmetals.com/
RE: NITROCARBURIZING
RE: NITROCARBURIZING
The parts are cold rolled bar 3/8" x 1" x 11". When we have tried tumbling, the bars tend to collide with each other removing all coating on the sharp edges.
swall,
You are exactly correct on the QPQ process. This is the process the supplier is supposed to be providing. I guess unclesyd has the best suggestion, find another supplier.
Thanks all,
grayseal
RE: NITROCARBURIZING
If the parts are going through a QPQ process, then they are going to be black. Changing suppliers won't change this fact. The oxidizing step after nitriding turns the surface layer black-- it is not a conventional smut, but an inherent part of the coating. Specify that the parts be nitrided only (no oxidizing step, no QPQ) if you do not want them to be black.
RE: NITROCARBURIZING
grayseal, it's certainly worth chatting with another vendor to see if they'll claim they can solve your problem. Realize that the surface finish of your original cold rolled may have something to do with the vendor's difficulties. If they're trying to nitrocarburize bars with scale still on them, maybe that's the source of the problem.
Best of luck!
RE: NITROCARBURIZING
All the parts I've seen, with the exception of some SS, with the QPQ process are very shinny and slick black.
RE: NITROCARBURIZING
Apparently you are currently handling each part individually to remove the smut. If you quantify the cost of smut removal, maybe purchasing will be given impetus to find another vendor even if the cost is greater. It certainly appears to be a processing problem which you should not have to solve in-house if it truely is a vendor problem.
RE: NITROCARBURIZING
RE: NITROCARBURIZING