When Volkswagen opens its fully automatic paint shop for plastic parts at its Wolfsburg plant, it will be claimed as one of the most efficient units in the world.

Bumpers, fuel tank covers and small parts for the new Golf will be painted using mainly water-based paints in an environmentally friendly process delivering benefits right in line with the company’s Think Blue Factory concept, a philosophy that is driving environmental innovation throughout the company’s manufacturing process.

Hubert Waltl, member of the board of management of the Volkswagen Passenger Cars brand with responsibility for production and logistics spoke at length about the concepts at this year’s Think Blue Factory annual meeting, held at the Wolfsburg facility. “Think Blue Factory is an holistic approach that pools all the environmental activities of the Volkswagen brand plants,” he explains. “In brief, we have set two major goals for production: more sustainability and less environmental impact. Each plant has therefore produced an individual, tailormade development path for achieving our targets by 2018.” It includes cleaning and applying primer, the technology for base and clear coat application, as well as the oven and the workspace equipment. From the primer to the base coat, water-based paints are used, while the clear coat area uses a two-component solvent-based paint.

Eco robots help aim for a green target
The paint application is carried out by 24 Dürr EcoRP L033 robots. Through the application of SnowClean and flame treatment, plastic parts will be optimally prepared for painting; cleaning and activating the surface for paint adhesion. “The new KU (plastics) paint shop varnishes plastic components such as bumpers, for the Volkswagen Group,” Thomas Muller, project manager of the Wolfsburg paint shops explains. “It will start production in August 2013 and is designed for a capacity of up to 4000 bumper pieces per day. “It is built to deliver an innovative paint process that will result in minimal environmental burden while at the same time delivering high process reliability. During the KU paint process, we use the most modern techniques. This goes hand in hand with our Think Blue Factory initiative. The Volkswagen brand has set itself clear targets to reduce the environmental impact of all Volkswagen plants by 25%. The new KU paint shop is aiming to improve on this with the goal of a 50 % reduction in energy usage.

“The most modern techniques for varnishing and separation technologies are used in the KU paint process,” Muller says. “The selection of the techniques has been made within the planning for the Think Blue Factory initiative. So it is intended, by using the new KU paint shop, to cut the amount of energy used during the varnishing process of the bumpers at the Volkswagen plant in Wolfsburg by up to 50%.”

Humidity control the key to success
These environmental goals will come to life in the Wolfsburg plant. “The highlights of the painting process are the CO2 SnowClean paint process, the E-static application Ecobell 3, the cold intermediate drying system, dry precipitation under the painting cabins, as well as exhaust air treatment with adsorption wheel and thermal post-combustion.”

Before the implementation of SnowClean, the facility had operated a traditional chemical pre-treatment plant. As a result of SnowClean, Muller explains that the use of chemicals and water can be completely dispensed with. The procedure eliminates the risk of residual water on the part to be painted and therefore reduces the quality risk for subsequent painting. “The SnowClean purification is a fully automated, anhydrous cleaning process with a low space requirement,” Muller says. “In the case of a new building, this saves not only investments in the installation engineering and building but also cuts future operating costs.”

EcoBell3 atomisers in high rotation mode and without high voltage carry out the primer application of 2K water-based paint. In conjunction with the EcoLCC2 linear colour changer, minimal colour loss per colour change and optimum transfer efficiency can be achieved during painting. An EcoDryScrubber, for the dry separation of overspray, is also included in this line. This technology saves energy in the paint booth through air recirculation. The dehumidifying oven produces an additional energy savings effect through drying with cold, dry air.

This absorbs the moisture of the water-based paint more efficiently. In this case the oven is heated up to only 40 to 50°C in contrast to the usual 80°C. This eliminates the cooling zone downstream of the oven that, in addition to saving energy, also saves space as the line is shortened by 30%. Through the combination of SnowClean, EcoDryScrubber and dehumidifying drying, the painting of plastics is virtually free of process water.

Waterless process drives plastic perfection
Muller points out that the main advantages of the plant are gained by using the newest installation engineering resulting in a waterless cleaning process for all plastic parts. This, along with a high-efficiency oven for detailed components, and the energy-efficient intermediate drying of waterborne coating, delivers key advantages. Further benefits come from the anhydrous paint particle precipitation in the painting cabin as well as the highly effective precipitation of hydrocarbons and dust from the extracted air.

“In a conventional paint shop we would use, for example, a chemical wet cleaning and afterwards a blowing zone with wet dryer and hydrophilic venturi wet scrubber or air atomising application techniques,” Muller continues. “The difference between this and other paint shops in the Volkswagen Group does not come from the level of automation, but rather in the painting of plastics (for example bumpers) compared to metal structures (vehicle body).

“The waterborne coating fulfils the highest quality standards of the paint shop at the Volkswagen Group and contributes to the compliance with EU Directives concerning VOC (Volatile Organic Compounds) and new solvent regulations,” he says. Rather than being driven by any concerns over the use of the wet chemical cleaning process, the design decisions at Wolfsburg were an endorsement of the SnowClean purification process. “And this decision was made because of the high efficiency of the SnowClean purification process as well as the low investment and operating costs of the system,” Muller concludes.