The Metalworking Group installed a powder coating line so it could offer its customers a one-stop metalworking shop...
The Metalworking Group of Richards Industries, Cincinnati, Ohio, supplies sheet metal fabrication, CNC machining, stamping, die making, tooling, fixturing, blasting and liquid coating. However, when President Mike Kelley realized that many customers needed more than fabricating and liquid finishing, the company installed a powder coating line.
A preliminary study of the company's market indicated that customers needed a high-quality powder coating operation that could handle shorter runs. Adding powder coating allowed the company to offer a complete array of metalworking services and give its customers a competitive edge.
As part of the study, The Metalworking Group analyzed how it fabricated, machined and stamped parts; what oils, greases and coolants were used; material handling; and how it welded, ground, polished, cleaned and painted parts.
Chemicals and other substances used in the facility were analyzed to determine each one's contribution to effluent. Airborne particulates were also analyzed for their contribution to air pollution and part contamination. The company tested each substance to ensure that the cleaning solutions used prior to painting could remove them.
Substrate preparation. Aluminum and steel substrates are polished and buffed or blasted with glass beads prior to finishing. This first step eliminates rust, promotes adhesion and provides a blemish-free surface to paint.
Parts then proceed through a five-stage iron phosphate pretreatment system that includes an extra stage for aluminum etch/preparation. Stage one is an alkaline wash for steel, and stage two is an alkaline cleaner for aluminum parts. Stage three is a room-temperature rinse followed by iron phosphate, which is applied at 30 to 50 mg/sq ft. Stage five is a room-temperature rinse, and stage six is a room-temperature rinse with a non-chrome seal. All pretreatment chemicals are supplied by Texo, Inc.
The automated pretreatment system runs unattended. Overhead trolleys position the baskets of parts over each tank. A hydraulic cylinder lowers baskets into the tanks and provides mechanical agitation to aid cleaning. Parts are force-air dried at 300F using a combination of infrared and convection.
Following pretreatment, parts are inspected for phosphate coating thickness and a water-break-free surface. They also face a white glove test to assure that there are no organic deposits.
Finishing shop. The finishing shop is separate from the main building to provide a clean-room environment. As part of the company's drive toward cleanliness it sealed the shop floors with a urethane coating.
The Metalworking Group installed two dust-collection systems. Shop maintenance procedures were upgraded to eliminate dust, smoke, mist and oil. Shop walls and floors are vacuumed routinely with a Nilfisk vacuum to eliminate contaminants.
To separate the finishing department from as much potential contamination as possible, President Mike Kelley located the new line in an environmentally controlled shop. A.J. Dralle and Co., Lemont, Illinois, analyzed the room for dust and other airborne contaminants and made filtration recommendations. Filters remove all airborne particulates and special vacuums eliminate "blowing" dust.
Masked parts are hung on specially designed fixtures manufactured at the company. Cast aluminum parts are preheated to 425F prior to powder coating to eliminate trapped gases. These parts then cool to 180 to 200F before entering the powder coating booth. Because it is a manual powder coating line, line speed depends on the size of the parts. The line can run from one to eight fpm.
The system features three manual powder guns. The Iontech guns are equipped with "Multi-Mode," which allows painters to choose any of three spray modes to compensate for Faraday cage problems. It also has a special ring and pin electrode charging system that provides more powder at the charging surface. This maximizes transfer efficiency. The "swirl air" feature surrounds the part with powder and eliminates buildup at the gun tip.
Powders applied include epoxy, polyester TGIC, epoxy polyester hybrid, polyurethane and acrylic. Thickness ranges from 1.5 to 3.0 mils with non-textured powders and 2.5 to 4.5 mils with textured powders.
Of the three guns, one is dedicated to white powder, another to black, and the third gun is used to spray multiple colors. All compressed air lines in the paint facility have desiccant air dryers. These deliver air with a -40F dew point. This ensures that no moisture or oil is sprayed on the part. The dryer also has pre- and post-filters to remove oil, dirt and other submicron particulates.
The powder collection system in the powder booth features a Dust Hog cartridge-filter-collection system and reclaim unit. It contains a gage with a preset pressure-drop set point across the filters. As the filters fill with powder, the pressure drop rises and automatic high-energy cleaning nozzles blow off the filters. Booth walls and floors also contain high-pressure air nozzles that pulse on and off intermittently to blow powder off the walls and into the hoppers.
The Metalworking Group built the side-draft, polished stainless steel booth in its fabrication shop. The adjustable booth is a maximum four ft wide, five ft high and 10 ft long.
Curing. The oven is a combination infrared/convection from PED Technologies. It cures not only powder-coated parts, but liquid painted parts as well. It cures all parts consistently, regardless of shape, size or weight. A Datapaq Oven Tracker system is used to ensure oven temperature consistency and curing efficiency.
Hot air from the top of the oven is drawn into insulated recirculating ducts at the bottom of the oven. Parts first go through a three-min warm up. This is followed by three to four min of cure at 425F. Parts then cool down and are unracked.
The powder coating line has helped the Metalworking Group satisfy its customers' needs and created a new niche for the company. It is now a one-stop shop for forming, fabricating and finishing.