Coating Steel Fasteners

Q. I am a manufacturing engineer responsible for product development for a supplier of fasteners and fastener tools. We are currently exploring different coatings for screws and nails used in pressure-treated lumber-based building projects such as decks and other outdoor structures. We’re interested in different coating technologies with regard to corrosion resistance, and are getting ready to make a pretty big investment in a coating technology. We’re using this time to explore the various technologies on the market.

Our fasteners are made of steel, and they’re being used on and in treated lumber. There is sometimes interaction with other metal connectors. The big issue right now is finding a coating that can hold up to 1,000 hr of salt spray. ACQ (alkaline copper quaternary), used to preserve the lumber, plays a big role, too, because it accelerates corrosion. And cosmetics/aesthetics are important as well.

We’ve had the greatest amount of success with zinc nickel plating (400 hr in salt spray). At this point, we are interested in any coating technology, including plating technologies, organic technologies, or even a plating/organic hybrid technology. M. L.

 

A. I am not comfortable speaking about plating technologies. I can say, though, that I remember hearing a paper describing bulk finishing of small parts at a recent Electrocoat Conference. Electrocoated zinc alloy plated parts were able to withstand 1,000–1,500 hr of salt spray exposure. There is often a synergistic effect between electroplated surfaces and organic coatings that enhances corrosion resistance. It is the policy of Painting Clinic to withhold company names. However, suppliers of electrocoat paints are listed in the 2008 Products Finishing Directory and Technology Guide.