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RED FINISH ON BLACK OXIDE

I AM OPERATING A 200 GAL HOT BLACK OXIDE TANK AND CONTINUE TO EXPERIENCE A RED FLASH RUST ON THE SURFACE OF THE PART WHEN THE PARTS ARE MOVED FROM THE BLACK TANK TO THE RINSE TANK.THE PART ACTS AS A HEAT SINK AND WHEN DIPPED TO RINSE IT HAS A QUENCHING EFFECT. OPERATING TEMP IS 280-290F AND TRANSFER TIME IS ONLY SECONDS. WE ARE HAVING TO HAND RUB EACH PART TO REMOVE THIS REDDISH FINISH . WE HAVE CLEANED OUR TANKS BUT ARE STILL SEEING THIS SMUT! ANY SUGGESTIONS?

DAN MORPHEW
- COOKEVILLE,TN
2000

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Got a suspicion...only that. Wonder if you use tap water to make up this bath? Tap water contains Chlorides, and you evaporate off a lot of water, I suspect, and I wonder if the Chlorides are causing this flash rusting?

Chloride has such a profound effect on all of metal finishing, that it always is a suspect, especially when corrosion is occurring.

Rudy Sedlak
Mountainview, California
2000

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Dan -

It sounds like your parts are too hot, causing the iron freeze. Another cause could be that your tank needs rectifying - it has too much insoluble iron in it. Be sure to skim it every morning too - this will take out the floating iron when the bath is below it's operating temp.

Dan Brewer
chemical process supplier - Gurnee, Illinois
2000