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Resource-efficient paint processes

For car buyers, the finishing is of particular importance: the paintwork must be rich in tone, gleaming bright, and mirror-smooth. Customers also expect the coating to withstand many years’ exposure to ultraviolet light, harsh environmental conditions and extreme weather. At the same time, paint processes must be resource-efficient from the manufacturer’s point of view.

Due to the high requirements on the paintwork, today’s automotive coatings consist of multiple layers that demand complex and specialized treatments: degreasing, rinsing, phosphating, rinsing, electrocoating, rinsing, drying and top coat application. “As a result, surface finishing is an extremely energy- and water-intensive process. It accounts for up to 50 percent of the energy and close to 90 percent of the water consumed in production,” explains Oliver Bolk, an Eisenmann coatings specialist.

A few years ago, water consumption was around 800 liters per vehicle, but creative engineers have since cut that figure to some 300 liters. And today, it’s even possible to bring it close to zero. However, this saving is offset by higher energy consumption, which in largely water-rich Europe often plays a larger role in decision-making. “We’re working hard on in-line and closed-loop solutions for the pretreatment and painting processes.  With their help, we can continue to drive down water consumption and make more efficient use of energy and other resources,” stresses Bolk.

For example, flexible and intelligent conveyor systems such as VarioShuttle and E Shuttle can be deployed in production to move the bodies through the pretreatment and paint lines. Unlike conventional material handling equipment, these innovative systems rotate the bodies, which completely drain them of excess process fluid. In concrete terms, shuttle systems reduce carry-over by about 0.2 liters per square meter. Given that an average vehicle body has a surface area of about 100 square meters, this adds up to quite substantial quantities of fluid. And the conveyor systems not only save expensive chemicals, they also contaminate much less rinsing water in the next process step.

Although no water is consumed while the top coat is being applied, pretreatment still requires a certain amount of rinse water. This is because thorough degreasing, correct phosphating and optimum electrocoating are indispensable for a perfect finish. While it would be technically feasible to completely eliminate the need for water, the process would require extensive modifications and substantial amounts of energy. But Eisenmann’s plant engineers are coming closer to zero water consumption by a different route: by optimizing the entire painting process from start to finish.

“The water that’s used is recirculated. And we constantly clean this valuable resource using ultra- and nanofiltration and ion exchangers, as well as deploying cascade rinsing systems and evaporators. Separating particles as well as oil, we prolong the durability of the rinse water during the process step of degreasing in order to save water,” explains Dr. Peter Börgardts, sales manager for environmental technology at Eisenmann.

Electrocoating is followed by the actual surface finishing process, comprising primer, base coat and clear coat applications. This painting process requires no water, as wet scrubbing is now seldom used. “Our dry and electrostatic overspray removal systems recirculate the air, significantly reducing primary

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