PAINT PEELING FROM ZINC SURFACES
Q1. We manufacture a line of small utility vehicles and have been trying to upgrade our finish system. We previously applied a modified alkyd finish system over iron phosphated cold rolled steel. We are now using some smooth galvanneal steel on our vehicles.
We pretreat the metal with an iron phosphate and apply a two-component urethane primer and overcoat with an acrylic enamel. Adhesion to the cold rolled steel is excellent, but the new paint, which is very expensive, will not adhere to the galvanneal.
Can you help us? J.P.
A1. Your efforts to provide a first class finish system are all in vain. You are not getting your money’s worth because an iron phosphate is not the best pretreatment for galvanneal and other zinc surfaces such as galvanized and plated surfaces.
Although some iron phosphate products will pretreat zinc, they are not as good as the zinc phosphates. I suggest you change your pretreatment to a zinc phosphate or buy your galvanneal already pretreated and ready for painting.
Q2. We manufacture products using sheet steel. We do many operations such as sheet metal fabrication, painting, zinc plating and screen printing in our plant. We started making a new product calling for zinc-plated steel and we are facing the problem of paint peeling off from the zinc-plated parts.
Our customer is greatly distressed and so is my manager. Can you guide us to a suitable paint to be used on zinc plated surfaces? V.C.
A2. Zinc surfaces must be properly pretreated to accommodate paints. Here again an iron phosphate is a poor pretreatment choice.
Change your pretreatment system to a zinc phosphate. Your paint peeling problems will most likely go away, and you, your manager and your customer will be happy again.
Masking is employed in most any metal finishing operation where only a specifically defined area of the surface of a part must be exposed to a process. Conversely, masking may be employed on a surface where treatment is either not required or must be avoided. This article covers the many aspects of masking for metal finishing, including applications, methods and the various types of masking employed.
Specific questions about zinc phosphate and pretreatment are answered in one article...
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