Metal finishing Q&As since 1989
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Is salt spray test applicable for chemically blackened parts?
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Q. Is salt spray test applicable for chemically blackened steel parts?
If so, If we do salt spray test for chemically blackened parts how many hours the parts will withstand without forming rust? Kindly clarify
- Chennai, Tamil Nadu, India
May 24, 2010
A. It is not a common test. You must comply with whatever the specification that you are blackening to and your customers purchase order.
James Watts- Navarre, Florida
A. Bhargavi,
What are you trying to prove with the salt spray test? Is this someone else's design or are you trying to emulate some exposure situation?
Black oxide has little corrosion resistance itself, but is usually used to help key other processes, such as oil retention (a small amount anyway) or a paint/varnish key etc.
The other thing to know about salt spray is that it cannot emulate realtime situations and is used only as a performance check.
Aerospace - Yeovil, Somerset, UK
A. Well bluing or blacking on steel is commonly black oxide. Black oxide has absolutely no resistance to sodium chloride and water. With that in mind I assume no one has ever bothered to salt spray test it. There really is no point as one knows what the outcome would be before conducting the test.
Rod Henrickson
gunsmith - Edmonton, Alberta, Canada
Q. That was a good point of knowing the black oxide has less resistance to the SST / Chloride.
However, the black oxide nut & screws are commonly used and there has been many incidences that the screw/nut/bolt get rusty along the way of the shipment.
Hence, one needs to know what will be the best test method to test the black oxide towards corrosion.
Regards.
- Malaysia
June 12, 2011
A. Hello Hussain.
It is mostly the wax or oil on the black oxide coating which resists corrosion. A black oxided nut or bolt is probably appropriate for naturally oily situations, like oil drain plugs, oil filler caps, but inappropriate for exposure to atmospheric conditions.
A properly oiled component can withstand a number of hours in salt spray, probably between 8 and 24. An un-oiled component can flash rust in 30 minutes in the general shop atmosphere.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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