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POWDER COATING, December 2016 5 Inclined plate flow. See Plate flow. Intercoat adhesion. A powder coat- ing's capability to adhere to previously applied films. L Lower explosive limit (LEL). The lower point for a range of concentrations of organic particles suspended in air that can be ignited by a sufficient energy source. Also called mini mum explosive concentration (MEC). M Melt mixing. A predominant process for the manufacture of powder coatings involving the continuous compounding of the pigments, fillers, catalysts, and resins at elevated temperatures. Melt point. The temperature at which a finely divided powder will begin to melt and flow. Micron/mil. Common units of measure- ment of coating thickness: 25 microns (micrometers) equals 1 mil (one thou- sandth of an inch). Minimum explosive concentration. See Lower explosive limit. N Nonelectrostatic deposition. A tech- nique of depositing powder onto a sub- strate, which may be heated above the melt point of the powder material. Some methods are flocking and fluidized bed. P Particle size. The average diameter of an object having irregular boundaries, which can be determined to have diam- eter through various test methods. Pill flow. See Plate flow. Plasma deposition technique. A method of applying powder by using compressed gas and by melting the pow- der in a flame before the powder im - pinges on the surface. Plate flow. The distance a powder coat- ing flows in the molten state before gel. Also called inclined plate flow, glass plate flow, and pill flow. Pourability. The capability of a dry powder to flow uniformly or to be contin- uously poured from a container at a steady rate. Powder coatings. Coatings that are protective, decorative, or both; and that are formed by the application of a coat- ing powder to a substrate and fused into continuous films by the application of heat or radiant energy. Coating powders are finely divided particles of organic polymer that generally contain pig- ments, fillers, and additives and that remain finely divided during storage under suitable conditions. R Reclaim. A process to recycle nonde- posited powder through the delivery sys- tem for reuse. Recovery. The process of removing non- deposited powder from the air before recirculating the powder through the delivery system. Repelling. See Back ionization. S Sintering. The tendency of some pow- ders and powder coating materials to agglomerate during storage. Spray/reclaim booth. A specially designed enclosure in which coating powders are introduced, contained, and recovered during the coating process. Storage stability. The capability of powder coatings to maintain uniform physical and chemical properties after being subjected to the manufacturer's specified storage conditions. Surface appearance. Generally refers to the smoothness and gloss of powder-coating films and the pres- ence or degree of surface defects. T Thermoplastic. A powder coating that will repeatedly melt when subjected to heat and solidify when cooled. Typical examples are vinyl (PVC), nylon, and polyolefin. Thermosetting. A powder coating designed to undergo an irreversible chemical change during the cure sched- ule. Typical examples are acrylic, epoxy, and polyester. Transfer efficiency. The ratio of the powder deposited compared with the amount directed at the part to be coated. Transportability. A powder coating's capability to be carried in an airstream and be passed through tubing and ducts designed to transfer the powder. Tribocharging. The process of creating a static electric charge on powder parti- cles by friction against a nonconductive material. V Virgin powder. Unsprayed powder as opposed to sprayed or reclaimed powder. Volatile content. The quantity, ex - pressed as a weight percent of the pow- der, that is lost under specified condi- tions of temperature and time. W Wrap. A characteristic of powder coat- ings in electrostatic application to seek out and adhere to parts of the substrate not in direct line of sight of the delivery system end point. Adapted with the kind permission of the Powder Coating Institute from Technical Brief #2. (Alexandria, Va.: Powder Coating Institute, 1986). POWDER COATING GLOSSARY