There are a variety of methods that will clean and remove
soils from metals. The pretreatment method used is determined by the part to be
coated (size, configuration, and material), the type of soil to be removed
(dust, wax, and oil) and the performance requirements of the finished
product. This process of pretreatment
requires three steps. The first two
steps are explained the previous pretreatment blog post, below is the final
pretreatment step.
CHEMICAL CONVERSION OF THE SURFACE
Phosphating, or
conversion coating, is the application of a phosphate coating to the
substrate. The most common conversion
coatings are iron and zinc phosphate which are applied for the following purposes:
- Provide temporary in-process corrosion protection before application of powder coating
- Converts the substrate into a uniform surface, promoting good adhesion of the powder coating
- Provide under-paint corrosion inhibitor to improve the life of the powder coating
The end product is the most important factor when deciding
between iron and zinc phosphate. Iron
works well for indoor use in non-corrosive environments and has several
economic and environmental advantages.
When undercoat protection is needed in a more demanding outdoor,
corrosive environment, zinc phosphate is the better option.
Pretreatment is
the base for powder coating. The highest quality powder coating will show you
excellent results ONLY if the pretreatment is done correctly, maximizing
the benefits of powder coating. Oily
patches, pin holes, rust spots, reduced resistance to weather, and overall poor
powder coating performance will result with improper pretreatment.
The following table compares iron and zinc phosphate processes in more detail.
Have a question about pretreatment? Contact our technical help today for
advice from an expert. Or you can always
reference our trouble
shooting guide online first.
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