Letter 3746

Comparison Of Cold Blackening method Compared to Hot Blacking. 

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I would like to know about:

1. Room Temperature Blacking Method of Iron and Steel.
2. What are the Advantages and Dis advantages compared to Hot Blackening/Oxidization process.
3. Which web sites I can visit to know more about the process and the various manufacturers.

Hemant Manek
- Calcutta, India

The principal advantage of cold blackening is that it is far safer to operate than the hot process, which involves a boiling hot highly concentrated aqueous solution of caustic soda which, if not handled properly, can erupt and burn or kill people. The operating temperature of hot black oxide tanks is higher than the boiling point of water, such that when water is added to make good the evaporation losses, it has the potential of instantly flashing to steam and blowing the contents of the tank all over the place.

Cold blacking chemicals are more expensive, do not have equivalent corrosion resistance or the shiny uniform appearance of hot black oxide, and can rub off as an abrasive grit which can be a problem in certain manufacturing processes.

We have a FAQ on Black Oxide & Cold Blackening which may be helpful, and you can contact the companies in the banner ad at the top right corner of this page. Good luck.

(Sorry but this website, with its opportunities for technical information exchange and camaraderie among metal finishers, is only possible because of our supporting advertisers; it would be a disservice to them to spend their money printing contact info for their competitors).

 
Ted Mooney, P.E.
finishing.com - Brick, NJ

If properly rinsed after the black oxide bath, should a hot-process black oxide leave smut residue when handled?

Parts I am receiving from a supplier leave a black, greasy substance, and since the parts will be handled by a customer, I'd like to minimize this. It seems to be after finished in oil. Rinsing in isopropyl removes most of the smut but also some of the finish.

Thanks,
Jimmy

James Heisler
- Austin, TX, USA

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