Metal finishing Q&As since 1989

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Zinc-coated galvanized tractor

Dear sir,

I am a sales engineer in Thailand. I have a problem with finding the zinc-coated galvanize tractor. I have a beach cleaning product which is zinc-coated galvanized which is no problem with using in sea water, but this machine also have to work with a towing tractor. As my searching for several weeks, one of the tractor supplier has answered me there is no tractor with zinc-coated are supply by any manufacturers. They also told me that two coat acrylic paint is used on the tractors. This paint is applied in two coats a primer and a top coat, with both coats being oven dried. The total thickness of the two paint coats will be 0.6 & 0.7 mm. They also claimed that this is design to with stand the most extreme conditions of climate including working in salty conditions at sea level.

I have no knowledge about painting or coating, so if you can answer my question weather those 2 layer of paint coats will protect tractor from corrosion or getting rust in sea water working condition.

If there is any suggestion please don't hesitate to advise me.

Best Regards,

Skitha Virunanond
- Bangkok
2001

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The 2-layer paint system will provide good protection to the steel. The paint will only fail if there are any holes in the paint that get down to the base metal. Having thick layers and more than one layer reduces any microscopic holes from the paint being porous. The paint will need to be durable enough to withstand abrasion, chipping, wear, and any other physical damage. If the paint is damaged, the exposed metal will rust immediately.

Zinc platings and coatings protect sacrificially. Even if a small hole appears in the coating or plating, the exposed metal still has electrochemical protection. However, zinc coatings are usually not very thick. A zinc coating may also not survive abrasion, chipping, and wear as well as the paint can.

You might want to look at a system with paint on top of a zinc plating. This would provide both barrier and sacrificial protection. You may want to test some samples using a salt spray test ( ASTM B117 ).

Tim Neveau
Rochester Hills, Michigan
2001