Hilustre Powder Coating Spray Painting and Glass Coating

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The Importance of Pre-Treatment.

The ultimate durability of any powder coating is based on the quality of the pre-treatment applied to the metal product prior to coating. Without pre-treatment corrosion will quickly attack the metal and spread under the powder coating. If the coating is damaged and the metal substrate is exposed to the elements moisture can penetrate to the base metal and begin to corrode (oxidize) the surface.

This can rapidly eat away under the surface coating. A quality pre-treatment provides a protective barrier to resist this corrosive attack and can add years to the life a product.

The pre-treatment process carries out two functions; cleaning and conversion coating.

On our conveyorised systems the parts are cleaned by in line high-pressure sprays of heated water and detergent. This removes oil and dirt from the surface of the item to be coated.

The next stage applies a ‘conversion coating’, this deposit is a microscopic film of iron or zinc phosphate crystals on the surface of the metal substrate. This aids in adhesion of the coating and provides the corrosion resistant layer.

Our newest powder coating line boasts an eight stage zinc phosphate pre-treatment system as used by all major car manufacturers. Zinc phosphate pre-treatment is the ultimate in corrosion protection on metal products. We current coat products for Ford and Holden on this line to comply with their stringent corrosion resistance specifications.

Our two other lines have iron phosphate pre-treatment systems, which have both provided excellent corrosion protection results on various metal substrates.

Corrosion Testing.
Corrosion is measured by a variety of testing methods, these are designed to accelerate the process of corrosion by exposure to heat, moisture, light and salt. One of the most common testing methods is by salt spray testing. in AS1111 by cutting thought (scribing) the coated layer back to the substrate metal then placing the test sample in a ‘Salt Spray Tank’. Here the sample is constantly sprayed with heated salt water 24 hours a day. Every 100 hours the sample is removed and the distance that the corrosion has travelled under the coating from the scribe line is measured. When the corrosion has travelled 2mm under the coating from the scribe it fails and is removed from the tank.

The results are rated from category 1 to 5. Category 5 passes after 1000 hours exposure in the salt spray tank!! It is suitable for use in harsh marine environments

There are many factors that can affect the efficacy of the pre-treatment process. The quality of the metal substrate is the most important factor. Clean lightly oiled bright steel is a good substrate that will clean easily and react well in a pre-treatment process. Rusty, black metal covered in mill scale and heavy deposits of grease and dirt will be difficult (or impossible) to clean and this will block the chemical reactions required for effective pre-treatment.

One aluminium panel coated on our zinc phosphate system achieved category 5 with no corrosion apparent after 1000 hours exposure in a salt spray tank. We have also achieved category 5 results on steel substrates.

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