Conversion from Liquid to Powder
What are some tips for converting from liquid coating to powder coating?
Q. We make truck parts and other components used on service vehicles that are used for rough duty in outdoor environments all over the U.S. Some of our parts are coated before assembly by outside suppliers, but most of our products are painted after assembly with the belts, hydraulics, and other parts already in place. We have been asked by the local Department of Environmental Quality to consider powder coating to reduce our emissions, but we do not see how we can use powder coating on our assembled product with all of the temperature sensitive components.
Are there any low temperature cure powder coatings that we could use? Do we need to replan our manufacturing process and start coating all of our parts before assembly? If we need to coat the parts before assembly, will the powder coating be damaged when we fit the parts together during assembly? Our current liquid paint is not very durable and would not take the abuse of assembly. We are also wondering if the powder will provide better field performance than our current liquid paint. –B.S.
A. Typical powder cure temperatures are between 375°F and 400°F. There are some polyester formulas that will cure at lower temperatures, but they will still be above 300°F, a temperature that will most likely cause damage to rubber, plastic or other materials that you use in your assemblies. There are some powder coatings that can be cured at 250°F, but they are not resistant to sunlight.
In some cases, infrared (IR) curing is used to overcome heat sensitive elements inside an assembly. That can work well if the heat sensitive element is not exposed to the IR and the part geometry provides a good profile for IR absorption. For example, hydraulic cylinders with heat sensitive gasket material may work well with powder in an IR oven. IR does not work well if the part has a more complex shape or the heat sensitive component gets too much exposure. The good news is that you can coat before assembly and the powder is durable enough to take some abuse during assembly. It sounds like a big undertaking to change your manufacturing operation, but I can tell you from first-hand experience that it can be done, and there are substantial rewards in efficiency and quality when parts are coated on a high-production line instead of being painted as fully assembled units.
As far as field performance goes, that depends on the current liquid paint. If you are having some issues now, you may have a lower performance liquid coating and the powder will be better. For the toughness and durability that a single coat of powder can provide, you would usually need a primer and a superior liquid topcoat. Chances are your performance will be better with the powder.
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