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28 POWDER COATING, December 2016 change can be done literally in seconds by selecting the next color right at the gun, often by using a color selector panel and a feed center where numer- ous colors are waiting in individual hoppers. Since the collection system is a spray-to-waste design, cleaning the booth is unnecessary. What are the advantages of powder coating? This article started with several sweep- ing statements about this finishing technology. Now I'll provide testament to these statements. I'll discuss most of the misunderstandings and myths (see sidebar) that have surrounded this technology since it has gained promi- nence in the past 3 decades. Environmental issues. All powder coatings are reportable VOC 2 -free materials, and most of them are consid- ered landfill (non-hazardous) materials. Powder coatings contain no solvents and in most cases contain no heavy metals. In fact, only zinc-rich epoxy primers are considered hazardous for their heavy-metal content. Pigments have long been heavy-metal-free to ensure easy disposal of powder coating formulations. Imagine taking your waste coating materials, spray booth fil- ters, and gun parts, and simply throw- ing them away with your normal plant garbage. Powder coating end-users do just that every day in just about every municipality in North America. They may have to melt the powder to elimi- nate dust problems, but that normally is all the municipality requires. Safety issues. Powder coatings are remarkably safer than normal solvent- borne coatings. Solvent fumes readily catch fire and can be a health threat to plant personnel. Powder coating mate- rials aren't flammable but may com- bust in a very narrow concentration of powder and air. Insurance underwrit- ers rate powder systems much safer than liquid systems, resulting in lower premiums. Sprayers only have to wear personal protection categorized for nuisance-dust environments as opposed to clunky respirators required for most liquid paints. Coating performance issues. Ther- moset powder coatings have remark- ably better mechanical, corrosion, and chemical resistance when compared with all other organic finishes. This is mainly due to the molecular weight of the powder coating and dense cross - linking when fully cured. Further, because of the absence of solvent, a powder coating has less porosity than liquid paint. All these conditions make powder coatings more durable (that is, harder, more impact resistant, more flexible, etc.), more corrosion resistant (up to 5,000 hours salt-spray resis- tance on aluminum substrates), more chemical resistant, and more weather resistant than liquid coatings. Supe- rior coating performance properties have made powder coatings the pre- ferred choice by designers looking for a "bulletproof" organic coating. Operational cost issues. Powder coating processes are cheaper to oper- ate than other organic finishing pro- cesses. The most significant cost sav- ings is realized in lower coating mate- rial cost. Powder coatings are cheaper and can cover more area than just about all other organic finishes. With powder coatings, systems can be designed to accommodate denser pro - duct hang patterns allowing for higher productivity for each minute of run time compared with liquid systems. Powder coatings lend themselves well to automation, reducing operational labor costs. Because most powder coat- ings are non-hazardous and don't con- tain solvents, disposal costs are dramat- ically reduced and spray booth make-up air is eliminated. With no make-up air requirements and lower cure oven exhaust requirements, the powder coat- ing process requires less energy to oper- ate than liquid coating processes. Lower reject rates (typically under 4 percent) experienced with powder coat- ing systems mean you spend less time and money reworking bad products. Proven track record. Powder coat- ings have been used in the North American market since the late 1960's and in Europe even longer. Although no one knows for sure how many pow- der coating systems there are in the US, Canada, and Mexico, some say the number is in the tens of thousands. Powder coating is the fastest growing segment of all finishing technologies without dispute. Figure 11 Photo courtesy Deimco. Figure 12 A fast-color-change spray booth system Photo courtesy Nordson. An overhead conveyorized powder coating system