Supporting VDL Bus & Coach in Making Light-Weight Passenger Buses
Passenger bus manufacturer, VDL Bus & Coach, has introduced its new Citea series of busses to the market, incorporating multiple light-weight composite components. These components are made by applying a foaming resin formulation supplied by BÜFA on the basis of resin from AOC. Besides bringing unique shapes and great aerodynamics, the use of low density composite parts results in major weight savings for the bus, translating into lower fuel cost and emissions.
Public transport companies need to carry passengers comfortably and safely to their destination. At the same time, they want fleet operating expenses associated with fuel consumption and maintenance to be as low as possible. With the aim to achieve sustainable mobility, low CO2 emissions are becoming a very important selection criterion for these companies when purchasing new buses.
VDL Bus & Coach has a reputation of building high quality passenger busses, featuring a modern look and a design tailored to specific end-customer needs. The large window areas, modern colors, along with many other great details, provide passengers a feeling of comfort and space. VDL Bus & Coach chooses to adopt a highly modular design in its products. This modular approach facilitates building custom-made busses, while simplifying bus repair, maintenance and spare parts supply.
VDL already has a good experience using composites in its busses. Yet for its new Citea busses it wanted to step up its efforts in reducing weight and manufacturing efficiency for the medium-sized production series. The company has been actively looking for composite material technologies that better combine design flexibility, mechanical strength and light weight.
Easy Processing and Light Weight
Molding company OMB Composites (Psáry, Czech Republic) made for VDL multiple composite components in a vacuum expansion process (VEX-technology), working with specially formulated resin compounds supplied by BÜFA Composite Systems. After opening the mold, the mold surface is covered with a gelcoat, then reinforcement and resin is applied. After closing the mold the resin starts to foam and fill the mold.
Depending on part design and end-use performance requirements, the vacuum expansion process (VEX-technology) with foaming resin allows to make large components up to 2 x 6 m. With weight savings up to 45 % compared to parts made from conventional resin technologies, the technology enables to have a cycle time of only 3 hours per part. Using Hand lay-up production techniques results in a much longer production time. With this new technology, part surface can be very smooth, enabling the application of surface coatings for a perfect Class A finish. A demonstration of the technology is available on video. When using the BÜFA®-Firestop Foaming Resin System, it is also possible to increase rescue times through improving fire protection and smoke development at a level typical for the rail vehicle industry.
Finding the Perfect Resin
When developing the special foaming resin compounds, BÜFA worked closely together with AOC to fine-tune resin composition and cure. “AOC has a track record in the development of novel resins with unique chemistries and features. Together we were able to optimize the resin system, delivering the right performance in the final part”, comments Lothar Kempf, Commercial Director of BÜFA. “We know that the great resin consistency of the AOC resins helps to ensure that our customers’ processes are stable and predictable, so their part manufacturing process is very reliable.”
The special Orthophthalic base resin used for making the foaming resin compound was tailored by AOC to the specific needs of the application. “We like very much working together with our customers in the development of new process technologies”, comments Paul Vercoulen, CTO of AOC. “With this close collaboration, BÜFA and AOC have been able push the limits of composites part performance and processing, delivering light weight, sustainability and great system cost.”