Metal finishing Q&As since 1989
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How to evaluate trivalent clear chromate on steel while performing B117?
Our manufacturing plant has recently made the switch to tri-clear chromate plating for our steel products (approx. 4x6 in). We evaluate this plating by running a ASTM B117 and we have an engineering spec that says the part (flat surfaces) have to meet 120 hours before 'white corrosion' is seen. We typically check parts at 24 hr intervals. B117 makes mention of rinsing or cleaning parts with water. Is it proper to wipe off parts after each rinsing? We have some engineers in our company that think the 'white corrosion' is actually salt residue, and by wiping the part, it cleans all salt from the surface. We in test engineering would prefer to rinse the part and report what we see.
OK, my point is...what is the typical method of detecting when corrosion occurs? We have no way to tell if the 'white substance' is salt or white corrosion.
Also, what is the opinion of what the black spotting we see is, prior to this white corrosion? I've understood this to be the plating flaking off...HELP!
thanks,
- Iowa
2006
A. Your company needs tighter control of QA testing. ASTM B117 is pretty clear. No wiping. After water rinsing, remaining white stuff is zinc corrosion product. Chemically analyze for Zn if you want verification.
Option 1) Recall all parts shipped since the last verifiable, non-fraudulent salt spray results.
Option 2) Cut some fingers off the saboteurs, and require remedial courses in professional ethics.
- Goleta, California
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Tyler -
Can you give us more info about what the other layers are under your tri-chrome? Also, I would strongly say don't wipe the parts at all. A gentle rinse, dry, brief look at them and back into the chamber. Most likely the white stuff is corrosion product, not salt.
Terry
- Auburn, Washington
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