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Lacquering brake discs Eye-catching discs They look their best when they are at rest. It is particularly when the vehicle to which they are fitted is at a standstill that lacquered brake discs attract the eyes of car fans. At Audi, sophisticated technology from Sprimag and Festo is generating some striking impressions in the automotive“underworld”. he cheapest versions are cast, but those for well-heeled customers are cold-forged and precision-machined using CAD modelling and water-jet cutting machines. Aluminium wheels are the pride and joy of prestige-conscious drivers. Their unquestionably good looks also have a small disadvantage: more and more of the wheel interior is exposed to the critical gaze. This means that the hubs, in particular the brake discs, are exposed to the ravages of time. Even with the most exquisite alloy wheels, rusty steel will spoil the picture. T It is therefore fortunate that dedicated developers from Kirchheim in Southern Germany have found an elegant solution to the problem. The injection machinery manufacturer Sprimag Spritzmaschinenbau GmbH & Co. KG protects brake discs with lacquer technology to prevent corrosion, transforming them into a feast for the eye of motorists – including those driving the premium brand Audi. The clever feature of this process: proportional pressure control valves type VPPM controlled via Profibus by a valve terminal MPA are used to regulate the spray pressure so finely during the lacquering process that there is no need to mask the friction surface of the discs to protect them against lacquer mist. This innovative solution reduces the consumption of lacquer with semi- and fully-coated brake discs and makes the finishing process quick and cost-effective. Powerful valves: A dozen proportional valves VPPM regulate the spray pressure precisely. Minimised overspray At the heart of the lacquering process is the perfect implementation of computer programs by pneumatic components. Within the brake disc feed system, a laser probe identifies the type of brake disc and sends this information to the PLC. The system controller sends the appropriate data packet with the necessary parameters for the product specific spray pressure to the proportional valves VPPM. The cascade control system for these valves, with integrated multi-sensor control, adjusts the atomiser air, the spray jet and the pilot air to optimum settings and reduces overspray. This is the amount of lacquer which escapes during spraying applications into the environment in Fine nozzle: No need for protective masking of brake discs which are to be only partly lacquered. trends in automation Synergies 30 31 – Eye catcher: Brake discs on the Audi R8 GT. the form of spray mist. Minimising overspray not only improves the quality of the lacquer finish but also saves wear and tear on moving machine parts and reduces the consumption of lacquer. “Without Festo’s reliable technology and great capacity for innovation, we could not have realised the project in this form.” Georg J. Langer, Mechanical Design, Sprimag However, the Sprimag developers were not satisfied merely with precision. They also succeeded in making the throughput times extremely short. The lacquer coating is made especially weather resistant, shock and impact resistant by subsequent baking in a hot air oven. A round dozen A unique feature of this solution, not found anywhere else in the world, is the interaction of twelve Festo proportional valves VPPM. Each of the four painting robots has three valves, each of which provides a spray function. The first provides for perfectly metered atomising air, the second controls the spray jet and the third precisely regulates the amount of lacquer material. In comparison with a single regulator, the Festo proportional valves VPPM allow considerably higher control accuracy and more dynamic operation. The overall controlled section is subdivided into smaller subsections which can be controlled more accurately in accordance with task specific requirements; thus, not only the output pressure but also the diaphragm pressure is monitored in the valve. The two values can be evaluated together, leading to highly stable and precise control behaviour. The Sprimag system delivers lacquer finishes of consistently high quality. It requires no set up for changeovers from one product type to another and reduces the tubing and wiring in the two identical lacquering systems at Audi. The twin systems increase process reliability and ensure that the manufacturing process is not interrupted by malfunctions, failures or maintenance work. At times when demand is particularly high, both units are operated together for a higher production rate. ¢ www.festo.co.uk/proportional is infoservice 21-04 Proportional pneumatics brochure The Sprimag lacquering station at Audi finishes a brake disc. Sprimag Spritzmaschinenbau GmbH & Co. KG Henriettenstraße 90 D-73230 Kirchheim-Teck www.sprimag.com Area of activity: Manufacture of automated painting and lacquering machines for the external coating of series-produced workpieces and the internal coating of metal packaging