Abstract
Atmospheric and half-tide immersion site trials on metal-sprayed and painted steel specimens have shown that flame sprayed zinc coatings can be successfully painted to give excellent protection to structural steelwork even under the most severe marine conditions. Choice of the correct primer and finishing paint becomes critical under severe exposure conditions. Best results were obtained with systems based on zinc tetroxychromate/polyvinyl butyral/phosphoric acid pretreatment primer. Of the finishing paints tested the two-pack polyurethane cured with an aliphatic isocyanate gave excellent protection and chlorinated rubber and aluminium-pigmented vinyl paints also gave good results.
A study of the process variables in metal spraying showed that air pressure pistol to work-piece distance and the use or non-use of a spreader nozzle have the most effect on the roughness of the applied coating. Exposure tests have indicated that rough coatings can have a marginally small deleterious effect on the performance of a paint system.
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