What Is Powder Coating?

Conversion Coating for Mild Steel

The most common types of conversion coating include zinc phosphate coating and iron phosphate coating

Zinc phosphate coating is crystalline heavy coating gray in colour. While iron phosphate coating is amorphous conversion coating that ranges in color from iridescent blue to gray.
Iron phosphate coating gives minimum sludge formation and hence smoother finish than zinc phosphate. Apart from this the bonding characteristics are also good.

Iron phosphate processes are much easier to operate than zinc phosphate processes and require fewer process stages (zinc phosphate coating requires a predip in activation chemical prior to phosphating to have micro crystalline grain structure), but iron phosphates do not provide the degree of corrosion protection imparted by zinc phosphates.
Iron phosphate systems are therefore used for a range of products requiring a durable finish that are not exposed to severely corrosive environments.

Zinc phosphating processes have been developed to provide exceptional painted part durability in corrosive requirements. Typical industries using zinc phosphate processes include automotive, appliance and truck and bus.
Post Treatment

After a metal surface receives a conversion coating, the surface is water rinsed to remove unreacted conversion coating chemicals and a post-treatment is applied. The post-treatment can provide a two- to ten-fold increase in corrosion resistance and humidity resistance when compared to conversion coatings without final rinses. Post-treatments are generally based on chromic acid.

Learn more about the process

Powder coating is an advanced method of applying a decorative and protective finish to a wide range of materials and products that are used by both industries and consumers. The powder used for the process is a mixture of finely ground particles of pigment and resin, which is sprayed onto a surface to be coated. The charged powder particles adhere to the electrically grounded surfaces until heated and fused into a smooth coating in a curing oven. The result is a uniform, durable, high-quality, and attractive finish

What is Pretreatment for Powder Coating?

Pretreatment means surface preparation. Here by pretreatment, we mean metal pretreatment as the powder coating is predominantly applied to metals.

Surface Preparation Includes:

Mechanical cleaning includes for (Applied Powder Coatings) aluminum oxide blasting. This by abrasive action not only removes the surface impurities but also eliminates scratches and surface irregularities. Cleaning is very good, however, coating must be done immediately because the cleaned surface is in a highly reactive state and corrosion occurs very soon. Chemical cleaning includes removal of dirt, oil and grease, and the oxidation products present on the surface by means of chemicals. The chemicals may be applied by wiping, spraying or dipping. The nature of chemicals used depends upon the base metal and will be discussed later in detail.

Application of Conversion Coating

Conversion coating. â€“ These are applied for three purposes: 1) provide temporary in process corrosion protection before application of powder coating. 2) promote good adhesion of the powder coating to the substrate. 3) impart under paint corrosion & thereby improve the life of the powder coating. The type of the conversion coating used also depends upon the base metal and will be discussed later.

APC

Conversion Coating for Mild Steel