BMW F900R, 900XR's double-shell fuel tank uses Lanxess' Durethan polyamide

Do you know speciality chemicals company Lanxess has made a success of its new high-performance Durethan polyamide with BMW Motorrad, the two-wheeler arm of BMW? 

Lanxess says its new materials demonstrate a high level of tenacity and ductility, particularly in the event of a crash, offer high design flexibility for complex tank geometries, and should be cost-effective to process, a key requirement for motorcycle tanks that need to meet stringent requirements. This means, for example, that only very small amounts of fuel should be able to diffuse through the tank walls.

Lanxess says BMW Motorrad’s models F 900 R and F 900 XR have been able to meet all of these requirements thanks to Durethan BC550Z 900116 DUSXBL from Lanxess. The tanks in both machines are made from a single material. The unreinforced and impact-modified polyamide 6 is injection-moulded into two half-shells, which are then welded to form a tank by means of hot plate welding.

Dr. Klaus Kusters, business development manager blow molding in the High Performance Materials (HPM) business unit of Lanxess said: “Our material comfortably meets the stringent requirements of the United States Environmental Protection Agency (EPA) with regard to permeation. Since it is very easy to process in injection moulding, even complex geometries can be produced cost-efficiently. And when it comes to impact loading, this extremely tough material really shows its strengths. The tanks are a joint development of BMW Motorrad and Rochling Automotive Italia in collaboration with Lanxess.”

The German company says the monolayer solution with polyamide 6 offers several advantages over previously used tank materials. The design flexibility and the integration potential of this material are significantly higher in comparison to metals, such as sheet steel and aluminum. There is also no need for costly forming, stamping, joining steps and corrosion is also not a factor when polymers are used.

The Durethan from Lanxess is said to have significantly lower fuel permeation compared to other polymers, such as high-density polyethylene (HDPE). Although fluorination can further reduce permeation in HDPE tanks, it is advantageous to avoid this additional manufacturing step due to the costs involved and the chemically aggressive fluorine.

The material was originally developed for the blow moulding process and has proved its worth in the series production of fuel tanks over the course of several years now. Due to the increasing number of functions in motorcycles – for example, ASC (automatic stability control) – the installation space for fuel tanks is becoming increasingly fragmented and complex. These geometries are no longer suitable for the blow molding process.

Lanxess says for this reason in the current BMW Motorrad tanks, two halves are injection-moulded and then welded to form the tank. “With the injection moulding process, it is not only possible to produce more complex geometries, the wall thickness distribution can also be precisely controlled, which in turn facilitates a more precise tank design using CAE tools,” adds Kusters.

The welding properties of polyamide 6 are essential for reliable tank production. “This material is characterised by its excellent welding abilities. Our customers have a wide process window at their disposal to reproducibly create tight weld seams. A weld seam factor of 1 can be achieved easily,” said Frank Krause, expert in plastic welding at Lanxess.

Another special feature of this material solution is said to be its very high impact resistance. This means that the fuel bladder remains intact and no fuel escapes even in the event of a crash. Pendulum impact tests on aged tanks, for example, do not result in leaks at -20deg C or at 60deg C.

Due to its property profile, Lanxess says Durethan BC550Z 900116 DUSXBL is also suitable for tanks for small vehicles, such as quad bikes, snowmobiles, and ride-on mowers, and for petrol-powered garden tools, such as chainsaws and leaf blowers.