Powder Coating

Nov2016

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POWDER COATING, November 2016 15 W ith the countless advance- ments in wood-based prod- ucts, and with medium density fiberboard (MDF) in particular, many manufacturers have been scrambling to find the right formula for applying paint and surface curing. Powder coat- ing heat-sensitive materials like wood products has never been easy. Manufac- turers are aware that the key to achiev- ing smoothly coated, durable products is finding the right formula of applica- tion and cure. "Wood-based product designers now have a huge range of creative flexibility. To optimize that flexibility, they need a powder system that promotes coverage of contours, slots or bores, complex edges, and even very sharp edges with no picture frame effect," says Judith Li- etzke, senior product manager at Carlisle Fluid Technologies. "Designers like the fact that they can put their imaginations to work and know that, chances are, whatever they conjure up on paper can be quality coated to meet their vision." Prepping, coating, and curing the MDF parts A quality finish requires multiple steps and good surface preparation. The sur- face preparation could be something as simple as blowing off the parts to re- move surface debris or it could be much m o r e c o m p l e x . O n c e t h e p a r t i s cleaned, the first step in powder coating MDF is to preheat the surface prior to coating. The powder is coated electro- statically, and a good quality electrosta- tic finish requires a good grounded work piece. Preheating the surface will induce moisture in the wood, which is needed to make the surface conductive and more accepting of the powder coat- ing. The recommended moisture range is a uniform 6 to 7 percent. The mois- ture generated in the wood by preheat- ing provides a good ground to draw the charged coating to the part while reduc- ing wasted material. In addition, the preheating process can help the small powder particles adhere better to the surface. Preheating will also release gases in the MDF material that could hinder a quality finish. Many manufacturers offer ovens in var- ious sizes and types that use minimal floor space to help preheat the product surface. Booster ovens are one type that will help heat the product surface to re- lease the gases and provide a uniform in- ternal moisture content. Oven options such as zoning the heat source creates an even surface temperature for geometri- cally complex shapes and sizes. The type and size of oven is dependent upon the application and floor space available, but choosing the correct oven for your needs is necessary to achieve a solid, smooth, and durable finish. The next step is applying the first coat- ing, or base coat, which supports the substrate. MDF materials have a natural inclination to swell and shrink, so the base coat is critical. The next layer, or covering coat, is what delivers the visible properties such as color, depth, protec- tiveness, brightness, and hardness. The application of these coatings can be ap- plied manually or, most typically, in an automated system. Many new powder coatings can eliminate the need for two coatings, and just one coat will suffice for a good application. However, it is al- ways best to work with your coatings provider when looking at new materi- als, processes, or applications. In an automated system, the parts can be moved through the pretreatment area to ensure proper moisture content all the way through to the final cure. Some manufacturers specialize in MDF product powder coating systems. A typ- ical such system incorporates special back electrodes to avoid build up on product edges and to control the lami- nation strength on the product's edges. Marek W. Urban, Ph.D. Clemson University IR Curing ShopTalk Infrared Equipment Division of IHEA This column is provided to you by members of the Infrared Equipment Division (IRED) of the Industrial Heating Equipment Association (IHEA). The group includes infrared (IR) curing equipment suppliers from throughout North America. We publish the column three times a year to give you the latest informa- tion about IR curing techniques and equipment. Contact information is at the end of the column. Most IR manufacturers offer testing for free or for a fee. Any IRED member can assist you in finding solutions to curing problems and best practices for finishing of coatings. This issue's column was submitted by IRED member Judith A. Lietzke, Carlisle Fluid Technologies, Scottsdale, Ariz. Powder coating MDF materials Photo 1

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