Advances to powder coating and the process mean an increase in profit for some.
According to The Fabricator:
“It’s a challenge nearly every fabricator faces—balancing the need to meet stringent OEM specifications for finished-product durability and appearance while minimizing finishing line cycle times, labor and equipment costs, and materials and energy consumption.
“As a way to meet both sets of challenges, many fabricators have installed powder coating operations in their plants. Powder coatings protect components, enhancing their resiliency, while reducing production costs over liquid paints. As an added benefit to the fabricator and its employees, powder coatings emit zero or very low volatile organic compounds (VOCs) and reduce shop floor solvent, which play an important role in a company’s sustainability program.
“To get the most out of powder coating technology, a shop must keep apprised of product enhancements that can add more to the bottom line. The technology is evolving rapidly, and recent innovations have contributed to increased line speed and density, improved transfer efficiency and film build control, as well as more consistent adherence of powder particles to substrate. Last, improved color-matching techniques can help a shop enhance its value to customers.
Two Coats, One Cure Reduces Cycle Time
“A high first-pass yield at accelerated speeds is completely achievable.
“For a finish with excellent flow characteristics, exceptional surface smoothness, and complete coverage, traditional powder coating systems require a four-step process: First, the primer is applied, followed by a post-primer cure, and then a topcoat is applied, followed by a second cure. This achieves the desired appearance and prevents problems that arise from nonuniform coverage, especially at corrosion-prone edges and corners. But, that four-step sequence can be inefficient, involving long cycle times. Part movement between spray booths and curing ovens alone can be time-consuming.
“Fortunately, coating chemistry and resin technologies advances have led to significant productivity gains. New one-cure coatings make it possible to eliminate one cure step (see Figure 1). After pretreatment, the dry primer and topcoat are applied sequentially, followed by a single curing step in which the powder particles melt and flow out to form a cross-linked film.
“This film delivers superior surface smoothness and part edge coverage, especially around vulnerable holes and other cutouts. The strong bond formed essentially eliminates intercoat adhesion failures that can occur between two independently cured layers.
“In general, all powder coatings provide all-over coverage because electrostatically charged powder particles are drawn to and deposit on surfaces of the grounded part, even those not directly in the spray gun’s path. The new two-coat, single-cure systems provide consistent film build, meaning that fabricators using the process can expect even less overspray and higher first-pass yields on their finished products.
“This new technology helps fabricators realize efficiencies. Cooling time is significantly reduced, thereby saving energy. Capital, operational, and maintenance expenses are reduced because a second curing oven is no longer necessary, and less conveyor equipment is needed. The shop floor footprint required for a three-stage process is smaller than for a four-step process. And with required cooling time reduced, work-in-process inventories will move faster through the shop.
Accurate Color Matching
“Powder coating color selection is broad, with a multitude of gloss ranges and textured appearances possible. New, significant breakthroughs in powder coating technologies have led to the development of color-matching systems that are designed to match the color of a sample to the closest available product. This reduces the time needed to create a match in a lab and helps applicators match and apply powder coatings more quickly.
“Color matching may sound simple, but it may not always be as easy as it sounds. Here’s an example. A customer presents a piece of fabric or plastic to a stamping shop and asks it to match the color for a metal part application. But a color sample from a piece of plastic can be composed of several dyes. The coating supplier must break that down and create a matching pigment and gloss for the powder coating for a metal part. Complicating the matter, the customer wants the color-matched powder coating ASAP.
“In the past, color matching typically would have required lab work, which would add significant time to the finishing process. The good news is that the process has been enhanced. Though the traditional process is still the case for more complex substrates and textures, digital platforms and color tools are making color matching simpler and faster than ever.
“New hand held digital color finder tools offer single-click color matching. The tool can connect via Bluetooth to a mobile phone app that stores up to 10,000 colors. As the closest matched color product is found, it is stored in the device’s memory to provide a reference for quality control when the color-matched powder is delivered for application.
“These tools are effective for reducing the amount of time needed to match a color through lab work and provide the closest match to a readily available existing color, allowing fabricators to move from matching to applying in less time.
Improved Transfer, Reduced Powder Waste, Better Finish
“Traditional methods used to achieve exceptionally smooth coatings of high quality and appearance have necessitated the use of very fine powders, which ultimately have resulted in increased powder consumption and problems. Fine powders are hard to fluidize; they can spit and spurt from the spray gun, causing defects on parts; they deposit unevenly across surfaces, leading to color variation; and they have very poor transfer efficiency, leaving powder particles drifting around the booth and falling on the floor. Higher applied costs, elevated reject rates, and powder on the floor detract from a finisher’s bottom line.
“Recent advances in technology have improved the application process, powder handling, and overall finish quality and film appearance without sacrificing coverage or protection. Specially tailored formulations used in conjunction with manufacturing processes that control particle size ensure uniform distribution of electrostatic charge on individual powder particles. The benefits are numerous: superb transfer efficiency, uniform coverage with reduced coating thickness, lower reject rates, less color variation across parts, and lower applied costs.
“Even the most experienced finishing lines on occasion may have problems applying a powder coating to a substrate successfully or producing parts without imperfections. The following techniques are likely to ensure that powder particles adhere consistently and decrease reject rates.
“First, the pretreatment prepares metal substrates of variable quality and cleanliness for powder coating. Shops should understand the specific pretreatment needs of each substrate and that additional approaches may need to be taken when substrates have surface imperfections such as laser cut edge oxidation, flash rust, or weld fill. Inadequate or insufficient pretreatment can lead to issues such as loss of adhesion, premature coating failure due to corrosion, pull-away from edges or weld areas, and pinholing/outgassing. Laser oxide should first be removed mechanically or by hand with a wire brush. An acid cleaner stage also can be added to the pretreatment sequence, but the shop should make sure the parts are well rinsed before they go into the washer/alkaline cleaner. Flash rust inhibitors that can be added after the rinse tank provide short-term rust prevention. Fabricators might consider using caulk or weld-through primer to fill the spaces between weld plates as this keeps out moisture and prevents corrosion.
“2Second, a shop would do well to re-examine its maintenance and spray techniques. Bad habits can lead to quality problems. Something seemingly minor such as hooks that have been insulated by powder buildup or an improperly grounded conveyor can cause grounding problems.
“Third, finishing personnel need to be properly trained in the most effective use of spray guns. Powder sprayed excessively or too quickly can cause powder to drift in the booth. In short, speed doesn’t pay off. Rather, a soft, even stream of powder emerging from the nozzle allows the powder to pick up the ionic charge from the gun’s electrode properly, providing the best finish.
Keeping the compressed air supply clean and dry by using a desiccant air dryer and filter can improve finish quality.
“Finally, it’s important to clean spray lines and guns thoroughly between projects. In some instances, dedicating hoses for specific jobs may be the best way to maintain quality and prevent rework (see Figure 2).
Additional Cost Savings
“A benefit of powder coating is that overspray can be reclaimed and reused. That stretches a fab shop’s coatings budget, reduces waste, and adds to its sustainability story. Yet, particle sizes change with each reclaim and reuse cycle. When particle size is smaller than optimal, poor transfer efficiency and rework result. Smaller particles don’t hold the proper charge for spraying; larger particles can bounce off targeted parts. Both reduce transfer efficiency. Developing a formula to maintain the ideal particle size by mixing virgin powder with reclaimed powder improves transfer efficiency.
“When looking at cost savings, it’s also important for shops to think about on-site storage. Powder absorbs moisture easily and may be damaged by excessive heat. Storing the powder inventory in a cool, dry atmosphere that meets a manufacturer’s prescribed standards will maximize a fabricator’s investment.
“New technologies, such as one-coat powder, digital color matching, and increased transfer rates, offer opportunities for enhanced profits. Fabricators can rely on the knowledge and technical expertise of their coatings supplier to take advantage of these benefits.”