LET THE SUN SHINE IN!
17 November 2004 - Bayer MaterialScience AG

The new Mercedes-Benz A-class was launched on the market from September 2004. The second generation compact car is the successor to the first A-class model which achieved sales of around 1.1 million in seven years of production. The pioneering metal louvre roof design of the first series has been further improved in the new A-class. Transparent, grey-tinted louvres made from Makrolon AG2677 from Bayer MaterialScience AG produce a light and agreeable interior even when the roof is closed. When opened, this type of roof – available as an option – gives the cars occupants an open-air experience, largely free from draughts.

This innovative principle of a panoramic louvred sliding sunroof creates a roof opening that is around 60% larger than conventional sunroofs. In the A-class, five louvres – produced by Freeglass GmbH & Co. KG based in Schwaikheim near Stuttgart – cover an area of around one square meter. The complete louvred roof comes from Webasto AG in Stockdorf, which is the system supplier. Frank Schiemann, Key Account Manager at Bayer MaterialScience, explains: “The key advantages of Makrolon are its transparency and high stone impact resistance. The polycarbonate roof, which replaces the previous type of louvre made from sheet metal, creates a lighter, open-air-effect interior. When the roof is open, the front louvre tilts upwards, acting as a wind deflector, while the other four louvres retract backwards to form one block, again at an angle. The low weight of polycarbonate permits a significant weight reduction of around 15% compared with the comparable standard sheet metal design in the previous A-class.”

At Freeglass, the louvres are produced using a two-component injection moulding process. The first part to be produced is the exterior side made from transparent grey-tinted Makrolon AG2677. Then black edging is applied by back-injecting a plastic all around the underside of the louvre. The component is then given a coating to protect against weathering and resist scratching. The black edging has various attachment aids which make it easier to glue on the aluminium profiles (lengthwise) and steel side panels (crossways) later. These metal profiles are fitted at Webasto. They give each louvre the stiffness necessary to withstand wind pressure. The aluminium profiles also have rubber sealing strips attached to them while the steel side panels carry the brackets for the adjustment mechanism.

In order to meet the diverse challenges faced by these components, experts from Bayer MaterialScience provided assistance to the developers at Freeglass, particularly with regard to the processing technology. Engelbert Meurer, Project Manager at Bayer MaterialScience, explains: “With these components for Mercedes-Benz it is very important to have a high level of dimensional stability and an excellent surface quality. Processing is an area where, working closely with Freeglass, we have been able to use our experience to ensure that the roof can be produced in the best way possible, using louvres made from Makrolon AG2677.”

The louvred sliding sunroof of the new A-class is just another example of the use of polycarbonate in automotive glazing. For example, the fixed rear side windows of the smart models, the front part of the panorama roof in the Smart Forfour and the transparent tailgate element of the Mercedes-Benz C-class sports coupé are all already made from Makrolon. Schiemann says: “We firmly believe that the trend towards more polycarbonate glazing in automobiles will continue. Makrolon not only offers greater design freedom than glass but, most importantly, offers the possibility of weight reduction. Another advantage is the high integration potential offered by plastic components. For example, it is possible to integrate entire antenna modules or blinds into the transparent panorama roofs. Complete roof modules made from plastic with integrated lighting elements or solar cells are also feasible.”

http://www.bayermaterialscience.com

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