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Composite seal meets fuel vapour targets
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01/02/2007
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Fuel sender seals are one of the largest emission leak paths in automotive gasoline fuel systems and therefore a big focus of attention for design engineers, writes Roger Bishop.
Sender seals have to seal a large (typically 130mm) hole in the fuel tank, demanding an O-ring of 380mm circumference. Each vehicle requires at least one seal and many new vehicles have two.
A Canadian custom moulder, Poly-Nova of Ontario, has developed a two-component seal for the fuel tank/fuel sender unit interface that exploits the low-temperature resistance and vapour-tight sealability of fluoroelastomer overmoulded with a permeation-resistant plastic insert (mineral-filled nylon 6.6).
The company says it will comply with the partial zero emission vehicle (PZEV) evaporative emissions requirements of 5mg/day HC through the rubber.
Rick Valeriote, president and chief executive of Poly-Nova, says the design is currently undergoing extensive testing and is expected to meet the target of 1 to 2mg/day evaporative HC emissions, well below existing US LEV II and Euro 4 requirements .
Development engineers say long flow path to the sender seal mould required a material that flows easily, cures quickly and has good de-moulding characteristics. Viton GF-S elastomer was chosen, a material resulting from a $50 million investment in a new polymerisation and curing technology called Advanced Polymer Architecture. Materials cure quickly due to a proprietary monomer and its position along the polymer chain. The rate of cure can be tailored to particular applications by adjusting the peroxide level or type.
Other potential automotive applications for APA polymers include fuel system seals and hoses and air intake and engine oil gaskets.
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Author
Roger Bishop
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