Powder Coat Stainless Steel

Q. I work for an Indian company, a leading solar panel manufacturing company. We are required to powder coat stainless steel grade SS430, 2B finish. I would like to know what the process is for this and what would be the durability of such powder coat on stainless steel base. N. M.

A. I will assume the stainless steel parts you want to coat are used internal to the solar panel and not just external bracketry. Furthermore, I expect the color you are looking at is flat black to absorb the sun’s rays (i.e. black body light absorption). If these facts are true, then you must understand the following issues:

1. Internal temperatures of your solar panel can get quite hot. Most standard powder coatings (i.e. polyester, epoxy, hybrid, etc.) can be exposed to temperatures above 400°F for only a short period of time (i.e. a couple of hours). After prolonged exposure these standard powder coatings will breakdown and degrade. Therefore, you will want to use a high-temperature resistant powder coating, sometimes referred to as a dual resin powder coating. These materials are formulated for high temperature applications, like gas grilles and motor exhaust components and have a thermoplastic resin component (typically silicone). In use the thermoset resin will breakdown, as predicted, and the heat resistant thermoplastic resin will hold the material together and perform up to most expectations.
2. The next issue you must resolve in your design is to understand that most powder coatings are applied at 1.2–3.0 mils thickness. Coatings at this thickness tend to have poorer thermal transfer properties than thinner coatings, since they often act as thermal insulators. This can be a bad thing if you are trying to catch the sun’s solar rays and convert this light energy into thermal energy at maximum efficiency. Possibly an appropriate liquid coating applied at 0.2–0.5 mils will be a better fit for your application.
3. The next most important issue is to obtain maximum adhesion of the powder coating to the stainless steel substrate. Here you have two alternatives to evaluate. First you can use a surface wetting agent like Silane to improve powder adhesion. You would apply this as a liquid after scrupulous cleaning of the stainless steel surface to remove all soils. Another acceptable method to improve adhesion would be to roughen the surface using sanding or media blasting techniques to improve the surface “tooth” for the coating to “bite” onto. A 2B brushed stainless steel surface might bee too smooth to provide acceptable adhesion.
4. Lastly, you inquired about durability of the powder coating. Since your substrate is stainless steel, we don’t have much to worry about in the corrosion properties of the coating. Choose a UV-stable coating to ensure that the pigmentation does not breakdown and chalks the surface. This chalking will further reduce your heat transfer and solar absorption properties of the coating. Otherwise, look at a coating’s mechanical performance properties before selecting your material. Powder coatings can provide significant improvements in mechanical properties over liquid coatings. I would recommend that you discuss your application with several suppliers and develop your own coating material specifications before making a final selection.