IR for Wood Finishing

How is infrared used in wood finishing applications?

There is an established history of infrared (IR) in the wood industry, and many of the products manufactured and produced in the furniture, flooring, siding and roofing industries involve IR in one or more of the operations. These operations might include drying and curing of varnishes, lacquers, primers, sealers, paints and finish coats; preheating of wood products for out-gassing; de-hydrating wood veneer in laminating processes, or drying/activating adhesives for laminations. In addition, IR is becoming a prominent player in the MDF industry, for the purpose of preheating prior to the application of low-temp powder coatings, and for the gel and cure of powder on fiberboard.

The reason IR is applied is because of the numerous advantages it has vs. other conventional methods of heat. Because IR heats the product and not the surrounding air, and generally has a faster response, it can be quickly directed to the product/substrate, allowing for shorter time cycles and greater uniformity of heat. Shorter cycles mean less time in the oven, helping to prevent drying or cracking of the wood. Also, the resulting oven footprint is less than convection systems, saving floor space. In most cases, IR penetrates the coating, and solvents are driven out from within, thus helping to reduce blistering problems. IR is a clean form of heat and has minimal air movement involved, thereby reducing the threat of contaminates, and reducing the amount of filtering and filter maintenance. Lastly, IR ovens are adapted to a variety of controls. Controlled IR ovens can easily and accurately provide product temperatures to within extremely close tolerances. Many of the aforementioned advantages will be discussed in greater detail in future articles in this column.

Most wood coating drying applications require a preheated flash-off prior to the heat cycle. The solvent/solid content of the particular wood coating being dried will usually determine the intensity of IR heat by which the coating can be dried without blistering. The wavelength of the emitters will vary according to the ratio of solids to solvents in the coating. In these applications, air circulation within the oven is recommended to drive off the solvents, even though the IR does not need air to flash-off and dry the coating.

IRED members have designed and manufactured IR oven systems for the wood finishing industry for many years. Examples include installations at manufacturers of display cabinets, pre-finished redwood siding, interior paneling, printed hardboard tabletops, panels for many types of furniture, plywood, wood shingles, wood flooring, and even caskets. As mentioned, MDF is now being powder coated, and IR enables the application of powder by preheating the board for out-gassing and for enabling the powder to adhere to the board prior to the gel and cure operation. IR also is recognized for its advantages in the gel and cure of powder on many substrates other than wood.

All IRED members have experience in wood applications, and are willing to discuss specific needs and design parameters. In addition, IRED members provide free testing, and are equipped to simulate most of the applications you might bring to them, to achieve the most efficient oven design.