Better Coating Results With Pre-Treatments

5285693039_1c116d94ca_oClean metal by itself can be immediately powder coated but that will not give you superior performance and weathering characteristics. A good pre-treatment allows the powder coating to better bond physically to the metal, withstand exterior weathering, and prevents flash rust prior to powder coating.  Because of all the benefits associated with it, you should always consider adding metal pre-treatment to your coating process. There are a few of methods of pre-treatment. The first one is chemically etching the metal with an acid based product that promotes adhesion of the powder coating to slick or difficult to adhere to metals. Aluminium is typically a very slick substrate, so it needs some sort of surface treatment to remove oxidation and to etch the surface. Etching chemicals are usually more difficult to work with than the next method.

The second method of pre-treatment, phosphating, is used to improve the corrosion resistance of the product.  Iron phosphate is the oldest method of pre-treatment. It is a great way to improve the adhesion of the powder as well as doubling or tripling the corrosion resistance of powder by itself. In a pure steel fabrication process, it is the most common chemical pre-treatment. Zinc Phosphate is a more robust process that results in the best corrosion resistance for steel products that are meant for ships or near coastal areas. Besides etching and phosphating, a third method of pre-treatment is Zirconium Non-Phosphate pre-treatment. In essence, it is a combination etching chemical such as zirconium fluoride in a low solids acrylic sealer that bonds to the metal. This newer process is used for multi-metal operations and also combines well with cleaners for a 1-3 step spray system, depending on the chemical manufacturer. By using companies like envirotech-europe.com you can ensure that you have the right treatments for your metals whether this is aerospace or medical equipment.

If you are coating sheet steel, for example, you will usually only need light oil cleaning. Angle iron or castings often need sand/shot blasting to remove scale and surface rust. Aluminium is prepared differently than galvanised or regular steel; the oxidation layer of aluminum must be removed, which requires certain chemicals that provide a good etched layer for paint adhesion. Identifying which type of cleaning is right for your process is the first step in long-lasting, quality results.

Finally, your customer’s specifications will determine the cost and complexity of your pre-treatment process. If a tractor-trailer wheel needs to last 5-10 years on the road under heavy use in ice and snow, then the powder coater needs a superior pre-treatment process. A decorative base for an interior table would not need the corrosion resistance as the wheel, but might need a good etch or blast profile to prevent powder loss due to being bumped from time to time. An interior fluorescent light fixture would need neither improved adhesion or corrosion resistance, but would still need clean metal for the powder to be applied defect-free.

With all these questions answered, you’ll be able to implement a pre-treatment process that produces quality and consistent results for you and your customers.

Author: Marsha Bow

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