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WHAT HAPPENED TO MY PARTS

 

I RECENTLY HAD SOME MACHINE PARTS RUN TRU THE BLACK OXIDE PROCESS. THESE WERE EXTREMELY CLOSE TOLERANCE PARTS +-.0001 OF AN INCH. IN SOME PLACES THE PARTS CAME BACK WITH AN ECTHED APPEARANCE AND MATERIAL WAS REMOVED APP. .0005 OF AN INCH. IS THERE ANY EXPLANATION FOR THIS.

DAVID MELLON
MELLON MACHINE - SAN DIEGO, California, USA

The most common problem would probably left in the acid etch tank too long. Stripped and reworked is a possibility also. You may have changed steel vendors or grade or hardness of the steel from what the vendor had set his process up for and was used to getting. A different cutting fluid could contribute to it also. The undersize could be a coverup in your shop also.

James Watts
- Navarre, Florida
 

I don't think that the black oxide caused the damage to your parts. Without seeing the parts, I would guess that they were put into a pickling tank prior to the black oxide (for activation) and were left in too long. Hot black oxide can create a slight (.0000020) swelling of the parts sometimes. The nature of the chemistry is caustic, so no etching should occur. I would contact the finisher and find out the process parameters used. Hope this gives you a place to start looking for answers.

Dan Brewer
chemical process supplier - Gurnee, Illinois