Powder coating is no longer the new kid on the block, but it is still a growing technology in both the coating and equipment fields. Powder coaters are installing more automated systems, including PLCs, to minimize operating costs. Cyclone systems are also gaining in popularity because they afford quick color changes.
Formulators are creating powder coatings that cure at lower temperatures and others that withstand high temperatures. Still other powders give a special decorative look.
The following is a general summary of some new powder coating products and processes.
Low-Temperature-Cure Powder Coatings. Plastics are used more often in manufactured goods because they are lightweight and corrosion resistant. However, plastics distort at high temperatures and, therefore, are not powder coated often.
UV curable powders, such as those developed by Herberts/O'Brien, can be applied to plastic or metal substrates in the same manner as traditional powder coatings. After application, the powder is melted and allowed to flow out. Stoving with infrared may help; however cure speed is influenced by the number and type of UV lamps used.
Formulations for UV curable powder coatings are similar to current thermally cured powders. The main difference is a photoinitiator UV powder that is comparable to a catalyst in thermal cure powders. It is only activated when exposed to UV light.
Areas of application include plastic trim pieces and shock absorbers in the automotive industry; alloy wheels; bathroom fixtures and decorative hardware; plastics and sports equipment.
Compatible, Silicone Heat-Resistant Coatings. KOOLKOTE™ heat-resistant silicone powder coatings withstand temperatures in the 650 to 700F range. They are compatible with other epoxy, TGIC, hybrid and urethane powder coatings. The powder is practical for both OEMs and job shops.
Traditional silicone powders tend to contaminate in quantities as low as a few ppm, causing coating defects such as hazing, low gloss and fish eyes. KOOLKOTE does not cause such defects.
H.B. Fuller is developing additional powder coating colors in both high- and low-temperature ranges and lower-cure temperatures (the current curing schedule is 15 min at 400F). The coatings are now available in a low-gloss textured black and a medium-gloss smooth black. Additional colors will include blue, yellow, white and green.
A New Wrinkle in the Finish Line. Weather resistance and good mechanical properties come together in the Series 39 polyester wrinkle finishes for electronic cabinetry, lighting fixtures, metal toys and sporting goods. Twelve stock colors are available and other colors can be custom matched by Tiger Drylac, USA.
The matte texture hides small manufacturing and surface defects three to four mil under a single coating. The wrinkle finish is applied using manual or automatic electrostatic spray equipment. Cure time is approximately 10 min at 392F. Salt spray resistance according to ASTM B 117 is greater than 1,000 hrs.
Chrome Coatings. Corvel chrome coatings from Morton International Powder Coatings are weatherable, radiant, one-coat polyesters for use on exercise and sports equipment, furniture, medical mobility equipment and display fixtures. Cure cycles range from 10 to 15 min at 375 to 400F.
Film builds range from 1.5 to 3 mils. Salt spray resistance according to ASTM B 117 is 1,000 hrs plus. Pencil hardness as determined by ASTM D 3363 is two to four H.
Powder Coating Equipment
New Powder Coating Method. The tribo disc represents a new method of powder coating. It combines high transfer efficiency and the convenience of a liquid disc system with the coverage and surface benefits of tribo charging.
The disc is used on omega-loop conveyor systems, which convey parts in a circular route around an application device. Inside the unit, tribo charging tubes charge the powder as it moves through the tubes and onto the disc surface. The disc is capable of powder flow rates up to 180 lb per hr.
Two benefits of the Nordson tribo disc are the surface finish and coverage. Because no external electric field is applied, tribo charging creates no excess ions, which increase the chance of orange peel and surface roughness.
The tribo disc provides a horizontal, circular spray pattern. The dwell time of the part in front of the spray pattern is increased, so the part has more time for coating. The disc's reciprocating movement provides for improved coating uniformity. The disc builds up the powder slowly, providing for more complete coverage. The slow buildup and longer dwell time result in higher transfer efficiency.
Cyclone Recovery Systems. Cyclones are simple, economical, reliable and widely used. They can handle large flow rates with little risk of clogging. A cyclone separates powder from the containment air stream prior to reuse or disposal.
A high velocity air stream, moving anywhere from 2,800 to 5,000 fpm, enters the cyclone. Centrifugal and gravitational forces separate heavier powder particles from the air stream and force them to the bottom of the unit. The air stream exits at the top of the unit, but it should be filtered prior to entering the work environment.
When changing colors in a powder coating system that uses cyclone separators, it is important that all traces of color are removed. In the past, cyclones were large, bulky and difficult to clean. This made cleaning time-consuming and contamination a real possibility. High-pressure cleaning using compressed air or coarse particles can prevent color contamination.
Some improvements ITW Gema has made to the cyclone include high-pressure cleaning/introduction of coarse particles; access doors; combination cyclone/collector/multi-cyclone recovery unit.
A combination system uses a cyclone separator and a cartridge collector. During primary color runs, the recovered air/powder is directed into the cyclone. During secondary runs, the operator can close a door that directs the air/powder away from the cyclone and into a scrap cartridge collector.
A multi-cyclone recovery unit also makes for quick powder coating color changes. With this unit several small cyclones are arranged in parallel. The compact package connects directly to the booth. It eliminates ductwork, reducing contamination.
Powder Recycling Process. In the Powder-Plenum™ recycling process powder is manually sprayed into a tunnel. As air is drawn through the openings, oversprayed powder is carried to the collector and through the cartridge filter where powder is separated from the air stream. Clean air is drawn into the fan inlet and discharged through final filters back into the plant. This new recovery system is from Wagner Systems, Inc.
Color Change Flexibility. The Soft-Spray™ series of manual powder systems from Binks-Sames is designed for excellent application performance, color change flexibility and ease of operation. Color change is eased by the interchangeability of the fluidized feed hopper or vibratory box feed unit.
The fluidized feed hopper features a 55-lb stainless steel hopper. It is capable of delivering powder to two manual guns. The vibratory box feed unit allows you to use powder directly from the original shipping container.
The GCM-2000 gun control module allows operators to select and monitor the optimum operating parameters. The MPG-2000 powder coating gun has a two-stage trigger that allows the voltage output of the gun to be reduced to 60 pct of the setting to overcome Faraday cage.