Reformulation of paints and redesign of the paint shops have led to reduced emissions and more efficient operation at car manufacturers worldwide. But the paint shop in the newly opened Volkswagen plant in Chattanooga, TN, goes further than any other with a primerless process combined with an innovative method for collecting and recycling overspray.
The primer-free method has been proved by Volkswagen in its Mexican and Spanish plants. The recycling of paint overspray, however, uses a new, waterless scrubber called EcoDry, and the Chattanooga Volkswagen plant, where the Passat is built, is the first to have it.
The overspray is directed downward by the spray-gun system, where instead of dropping into a water filtration system it makes contact with a thick cloud of limestone powder, which resembles talcum powder. The cloud itself is produced by a pressurized air-spray system. During vehicle painting, bursts of compressed air direct the paint-coated cloud particles onto a filter. Then periodically during the process, air-spray bursts from the opposite side of the filter blow off the painted particles, which are directed out to a storage container. The surface cleaning will extend filter life to an estimated 2-3 years, according to Bobby Dean Parker, paint shop manager.
A truck delivers the fresh limestone powder, automatically unloading it into the EcoDry Scrubber’s dispenser, and at a later time a truck comes and automatically retrieves the storage containers holding the paint-laden limestone powder. No one at the factory touches the limestone powder before, during, or afterward. The paint-coated particles are used as an ingredient in concrete.
The paint shop has a highly efficient spray process, Parker said. An estimated 82% of the paint goes onto the car vs. a typical 70% for other OE plants at which he has worked. The limestone cloud is over 95% efficient at recovering the overspray, he added.
Water filtration is the long-used alternative to this new limestone powder cloud system. However, as Parker explained, “although water is an excellent filter, you have to chemically treat it to get the paint out. With our system we save 50,000 gallons of water a day, which equals 12.5 million gallons a year” (based on 250 days of annual operation). The EcoDry Scrubber also eliminates the need for a system of pumps to deliver the water and remove sludge from the water filtration process.
The paint shop’s waterless system (except, of course, for the use of water-based paint) also has a rainwater collection system on the roof. So the shop in a sense is a positive contributor to the water usage equation.
The shop “recycles” (filters and recirculates) up to 90% of its interior air to efficiently maintain temperature at 70°F (21°C) and 65% humidity in an area of the country that has a relatively warm, humid climate.
The primerless process saves over a half-hour in the painting of a car, and it provides several advantages for paint shop operation, Parker said. The system starts with a phosphate electrocoat immersion for corrosion prevention and then skips the primer coat and oven, going straight to application of a double-thick base (colorcoat)—between 25 and 30 µm (0.98 and 1.2 mil) thick. This compares with 12-15 µm (0.47-0.59 mil) for a colorcoat that is preceded by a primer. The thickest colorcoat for the U.S. Passat is for white, Parker explained.
The colorcoated body goes through a dehydration (drying) oven, which is controlled to 50°C (122°F) and humidity low enough (25%) to promote drying. Next is the conventional application of (double-thick) clearcoat, followed by the Volkswagen process of hot wax injection to seal cavities.
The paint shop was the first part of the plant on which construction began (in 2009, following site preparation the year before), and it was the last to be finished. It operates in a zero-dust atmosphere with 52 robots and 2.8 mi (4.5 km) of conveyor lines. Although the shop employs 154 employees, no one normally works in any of the booths.
Each vehicle is inspected for paint quality by a finesse team, which if necessary can manually correct any imperfections.
Environmental considerations obviously were a high priority for the entire plant, and Volkswagen estimates that the paint process reduces carbon dioxide emissions by 20%. Exterior lighting for the entire facility is with LED, and the interior uses various forms of energy-saving lighting controlled by motion sensors, for an overall reduction of 20% in electric energy usage for all lighting functions.
A total of 383 robots are deployed in the plant, which also has a body shop and assembly lines. The production process applies over 4700 spot welds and 107 ft (32.6 m) of sealer. Although the engines are imported, they are dressed at the plant.
The plant, which employs more than 1700 for openers, has an initial capacity of 150,000 units, but if needed capacity can be increased to 250,000.
Volkswagen estimates that U.S. content will be 85%. Many of the parts will be delivered from a supplier park on the site. Overall, Volkswagen estimates that its investment will be $1 billion and there will be a future total of 2000 employees working at the plant, plus 10,000 jobs nationwide with suppliers.
The site also holds a testing/engineering center and advanced training academy for employees.