Besides bringing unique shapes and great aerodynamics, the use of lightweight composite parts results in weight savings for the bus, translating into lower fuel cost and emissions.
VDL Bus & Coach has a reputation of building high quality passenger buses, featuring a modern look and a design tailored to specific end-customer needs. The company adopts a highly modular design in its products, which facilitates building custom-made buses, while simplifying bus repair, maintenance and spare parts supply.
VDL already has experience of using composites in its buses, but for the new Citea line it wanted to step up its efforts in weight reduction and manufacturing efficiency for the medium-sized production series. The company has been actively looking for composite technologies that better combine design flexibility, mechanical strength and light weight.
For VDL, moulding company OMB Composites, Czech Republic, made multiple composite components in a vacuum expansion process (VEX-technology), working with specially formulated resin compounds supplied by Büfa Composite Systems. After opening the mould, the mould surface is covered with a gel-coat, then reinforcement and resin are applied. After closing the mould the resin starts to foam and fill the mould. Depending on part design and end-use performance requirements, the vacuum expansion process with foaming resin enables the manufacture of large components up to 2 m x 6 m in size. With weight savings up to 45 % compared to parts made from conventional resin technologies, the system offers 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, the part surface can be very smooth, enabling the application of surface coatings for a perfect Class A finish.
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.
To develop the foaming resin compounds, Büfa worked closely with Aliancys to fine-tune resin composition and cure.
“Aliancys has a track record in the development of novel resins with unique chemistries and features,” comments Lothar Kempf, Commercial Director of Büfa. “Together we were able to optimise the resin system, delivering the right performance in the final part. We know that the great resin consistency of the Aliancys resins helps to ensure that our customers’ processes are stable and predictable, so their part manufacturing process is very reliable.”
The orthophthalic base resin used for making the foaming resin compound was tailored by Aliancys to the specific needs of the application.
“We like very much working together with our customers in the development of new process technologies,” explains Paul Vercoulen, CTO of Aliancys. “With this close collaboration, Büfa and Aliancys have been able push the limits of composites part performance and processing, delivering light weight, sustainability and great system cost.”
Industries: Mass Transport