Powder Coating

2019 Buyers Guide

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imately 300°F). After initial application and cooling, these materials will soften and flow again if exposed to heat. Examples of thermoplastic powder coatings are nylon, polytetrafluoroethy- lene (PTFE, or Teflon), polyethylene, and vinyl. Most thermoplastic powder coatings require a liquid primer to be applied to the part substrate to improve the marginal adhesion characteristic of these materials. These materials are normally used as functional coatings, providing corrosion protection, slip enhancement, detergent resistance, electrical insulation, and so on. Thermosetting powders. These coatings are the most common materials used in today's marketplace. They're chosen for both their excellent functional and appearance properties. Thermoset powder coatings are applied as dry par- ticulate, melted, and flowed when exposed to heat (above 250°F). After melting, the coating is then cured with heat or UV energy to form a densely crosslinked dur able coating. However, these coatings won't soften again when exposed to heat after initial application, cure, and cooling. Thermoset powder coatings come in a variety of formula- tions that include epoxies, polyesters, triglycidyl isocyanurate-based (TGIC- based) polyesters, acrylics, and hybrids. Powder coatings can be purchased in either spray grades or fluidized-bed grades. Matching the powder coating to the application method is important in achieving the desired results. For instance, fluidized beds should use flu- idized-grade powder coating formula- tions. These formulations are normally ground coarser than spray grades, resulting in a larger particle size that will aid the fluidization of this material. Con- versely, spray-grade powder coatings are ground finer than fluidized-bed grades, re sulting in a smaller particle size that will pump better and is more easily atomized to achieve thinner film builds. Powder application techniques. Powder coatings can be applied by using either fluidized-bed techniques or spray techniques. When choosing an application technique, you need to consider the following: • Does the coating need to be func- tional, decorative, or both? • How much film thickness control is needed? • What is your production rate? • How many color changes do you need to make? • Are there Faraday-cage 1 areas on the parts? • What is your product size? • What is your desired coating quality? Careful consideration of these issues will determine which application method makes the most sense for you. Fluidized beds have been used to apply powder coatings to parts since the 1950's. This method can use thermal attraction or electrostatic attraction to deposit the powder particles onto a given part. If you want to apply thick- film functional coatings (that is, more than 10.0 mils), then thermal attrac- tion is your best bet. Here you preheat the part to above 350°F and dip it into a fluidized bed of powder coating. The heat attracts the particulate to the part and may partially melt it onto the sur- Figure 3 A bi-level powder coating cure oven Photo courtesy General Fabrications Corp. Figure 4 Powder coating hoppers Photo courtesy Nordson. Figure 5 Corona-charging spray guns Photos courtesy Nordson. (a) Manual (b) Automatic 26 POWDER COATING, December 2018

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