Conductive POM far exceeds standard for fuel delivery systems
01 August 2009
Bosch has been quick to realise the potential of BASF's new carbon nanotube containing polyoxymethylene (POM) for automotive fuel filtration and delivery systems where it actually exceeds the requirements of the current standard for specific resistance by no less than four orders of magnitude
BASF is believed to be among the first in the industry to introduce an engineering polymer containing carbon nanotubes for the automotive component market. Now available in commercial quantities throughout the world, the material - Ultraform N2320 C - is a polyoxymethylene (POM) that, with additives, acquires a high level of electrical conductivity without compromising its essential properties of toughness and dimensional stability.
Bosch is among the first of BASF's customers to find applications for the new material, which it is using in the production of fuel filter housings for the Audi A4 and A5 cars. For some time now, POM has been Bosch's material of choice for fuel pumps and fuel supply modules - materials such as non-reinforced Ultraform S2320 003 or glass fibre-reinforced Ultraform N2200 G43 being among the most popular.
For its filter unit, however, Bosch has to comply with the requirements of the Society of Automotive Engineers (SAE) standard J1645 (August 2006 version), which specifies electrically conductive materials for fuel related applications. This SAE standard recommends materials with a maximum specific volume resistance of one million ohm-cm, in order to eliminate any risk of electrostatic build-up and discharge under fuel flow conditions.
When measured according to ISO 3915 (four-point method), the conductive Ultraform N2320 C attains a value of just 30 ohm-cm, making it 30,000 times more conductive than necessary, and therefore easily meeting the requirements of SAE J1645.
Thanks to the type of additives and the way they have been incorporated, the new Ultraform is able to retain its POM-typical properties such as toughness, dimensional stability and elastic resilience. Moreover, when this material comes into contact with fuels, it is stronger and more creep-resistant than conventional POM, as well as being less costly than other conductive plastics.
As well as its excellent ESD properties, Ultraform N2320 C is also abrasion resistant, so easily lends itself to clean room manufacturing processes, which demand dust-free conditions as well as the elimination of any possibility of electrostatic discharges. According to BASF, the material is suitable for injection moulding and is easily joined using laser-welding techniques. The carbon nanotubes are securely contained within the plastic matrix, allowing the material to be handled safely throughout its life.
Ultraform N2320 C was optimised for the fuel filter housing application in a collaborative effort with Bosch. Various tools from BASF's laboratory played a role in the component design, including welding and burst-pressure experiments as well as creep-resistance tests. The fuel filter housing is now currently in production at Budweis in the Czech Republic.
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