Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ

Paint adhesion on galvanised wire

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SUGGESTED GALVANIZING BOOKS
for Engineers, Shops, Specifiers

"Hot Dip Galvanizing of Steel Structures" by Kuklik & Kudlacek (2016)
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"Handbook of Hot Dip Galvanization" by Maass & Peissker (2011)
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"Galvanized Steel Reinforcement in Concrete" by Stephen Yeomans (2004)
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"Hot Dip Galvanizing -- A Guide to Process Selection & Galvanizing Practice" by M. J. Hornsby (1995)
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"Faults in Hot-Dip Galvanizing" by Dietrich Horstmann (in English, French & German)
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"User's Guide to Hot Dip Galvanizing for Corrosion Protection in Atmospheric Service" by NACE (1997 only rarely avail.)
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We manufacture components from 1.4 mm diameter bright hot dip galvanised steel wire. We coat this wire with about 10 micron thickness of a water based plastic paint, and cure at 250 °C. (Only takes a few seconds). Gloss and toughness is fine, but the paint will spall off on a very tight bend, as there is negligible adhesion of the paint to the zinc surface. Have tried cleaning the surface with white spirit, roughing of the surface with emery paper, results are identical. Any ideas on how to get a key would be much appreciated. The process is in-line at about 500 mm per second.

You need to spec that the galvanized coating is to be painted. Then the chromate conversion coating will not be included. The American Galvanizers Association at www.galvanizeit.com has free and nominally priced booklets on this finish which they call a "duplex" coating.

I'm surprised that emery paper didn't work as some readers have suggested that trisodium phosphate ⇦this on eBay or Amazon [affil links] applied with a tampico brush worked for them (on sheet rather than wire) -- but galvanized material which is destined to be painted or powder or plastic coated should be zinc phosphatized.