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topic 17450

Appearance of Chromate Finishes


2002

What final color should a steel screw look like having a finish of "zinc with clear chromate"? We have purchased the same part number (3M 3341-4 Jack Screw) from two different suppliers. One has a "silver" appearance and the other has a "gold tint" appearance. Are one of these yellow chromate? Is there a source for identifying various metal finishes? Thanks in advance for your help.

Regards,

Michael D. Zagnacky
- Cheswick, Pennsylvania, USA


2002

The "silver" finish is a clear chromate probably. The "gold" tint is a yellow chromate more than likely. However consider if parts are left in the clear chromate to long of a time, they could have a yellowish cast. If they are a yellow chromate, corrosion resistance is much greater than the clear or silver. Yellow chromate usually costs more on a finished part because it costs more for the chemistry. You may consider having parts with both finishes put in a salt spray chamber. You may get only 12-24 hours with clear before white corrosion. Yellow should achieve 96 hours. Problem-screws are almost impossible to trust the results. More than likely the heads of the screws, if flat, could be tested. Thickness of the zinc plate before chromate has a large impact on corrosion resistance.

Bill Hemp
tech svc. w/ chemical supplier - Grand Rapids, Michigan



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