Powder Coating Not Just for Motorcycles Anymore

In the past, powder coating was used only for metal. This was mostly due to the facts that wood had moisture related to their sap content, have low conductivity, and exposure to high temperatures caused the gain or fibers to rise and the wood to be distorted or charred. However, because of the development of UV-powder coating and thermosets, materials such as wood, plastic, and preassembled parts can now also be powder coating.

The process for coating wood using the new UV or thermoset powders is similar to those using conventional powder coatings for metal. When thermosets are used, they are heated to the powder's melting point until the coating particles fuse into a continuous coat. With UV-powder coating, the powder is heated in a melt flow oven, and then cured for a few seconds under UV lamps. When powder coating wood, the application steps are as follows:

1.Preconditioning is required, which involves the wood product being heated in an infrared or convection oven in order for the wood to reach the required conductivity, and release gasses. The surface temperature is equalized between 200 and 220oF before it enters the spray booth. The moisture in wood must remain equalized over the entire surface at approximately 4 to 6% or greater in order to maintain conductivity for the powder to adhere to the surface. Because heat causes evaporation of moisture, carefully controlled preheating is mandatory.

2.The application of the powder coating is the same as with conventional powders with the use of either a Corona or Tribo spray system.

3.The curing process depends on if UV powders or thermosets were used. UV powders are initially melt flowed in infrared ovens or in convention ovens, then cured under UV light for a few seconds, whereas thermosets are cured by infrared or convention ovens. Curing times, temperatures, settings, and wavelengths will vary with film and substrate thickness, powder, and substrate size and shape.

4.The cooling process can occur in the open air, or thermosets may be placed in a forced air tunnel.

Once the wood product has been coated, recovery systems that use cyclones or filtration to recover overspray can successfully recover approximately 99.9% of the oversprayed powder. The reclaimed powder can be reused as is, thus adding to the economical benefits of UV-powder coating.