Metal finishing Q&As since 1989
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Final Visual Finish After Sulfuric Anodize and Dichromate Seal Type 2, Class 1
Need help on the Final Visual Finish After Sulfuric Anodize and Dichromate Seal type 2, Class 1 parts. I have no coloration; I'm told it should have coloration. Is this corect and is there a way to find out?
Adrian AlvarezBuyer - Fontana, California, USA
May 12, 2008
The Type 2 and Class 1 applies to the anodizing not the dichromate seal. The dichromate seal should leave a green-tellow tint.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
May 14, 2008
May 19, 2008
If dichromate seal is mandated by the callout, then it should appear a very distinct greenish-yellow tint that is unmistakable. If it is lacking in coloration then it is definitely not dichromate sealed. The problem is that not only have the Euros verbotten use of hexavalent chromium in products entering their borders but on our own soils OSHA has lowered the workplace PEL from 50 to 5 ug/m3: bottom line, borderline shops without engineering controls to permit continued use have ceased using dichromate (i.e. hexavalent chorme) solutions - particularly those heated to the extent of a seal! If the anodizing house certified that they dichromate sealed the parts and they're clear, they lie and I wouldn't trust the paper it's printed on, however, clear SEALED anodize can still meet the spec. Go back to your customer and explain the situation; get them to remove the "dichromate" requirement in favor of DI, nickel acetate or other seal which will still give the level of protection required (336 hours salt spray).
Milt Stevenson, Jr.
Syracuse, New York
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