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Originally Posted On: Washer Wisdom: Common Finishes for Washers (mudgefasteners.com)
Washers can be plated or finished with a variety of coatings, ranging from the highly corrosion resistant DURA-CON coating to more simplistic metallic or painted finishes. Washers are sometimes coated for functional purposes, and sometimes for purely aesthetic reasons. Whatever the reason for using a particular coating or finish on a washer, we’re here to help to understand which would be best for your application. Let’s start with the three most common finished applied to washers.
Zinc / Trivalent Zinc
The most popular commercial platings, zinc is both economical and corrosion resistant, commonly used in environments where excessive moisture will not be present. On top of the zinc, a clear chromate finish is applied to create an additional layer of protection against white oxidation spots that can form in the presence of moisture. The most common way of applying zinc coatings to fasteners is through electroplating.
Black oxide is a “conversion coating”, meaning it is formed by a chemical reaction with the metal to form an integral surface, as opposed to an “applied coating” like zinc which bonds to the metal. A post-coating oil finish is typically applied to inhibit the development of rust.
Hot dip galvanizing can be highly effective as a method to apply a sufficient thickness of zinc for corrosion protection in particularly harsh environments. Steel reacts with molten zinc during the galvanizing process, which forms layers of zinc-iron alloy that are bonded metallurgically with the steel surface. The hard barrier created during this process not only resists mechanical damage, but also has a very low rate of corrosion.
If you have further questions about finishes for washers, please don’t hesitate to contact us for more information.