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Technical Paper

A New Fluoroelastomer for Fuel System Seals

Fluoroelastomers (FKM) are known as premium sealing materials for automotive fuel systems. In specific, FKM-GFLT is known as one of the foremost FKM sealing materials, an elastomer that shows excellent hydrocarbon fuel, methanol and flex fuel resistance combined with good low temperature flexibility and sealing capability. Now a new fluoroelastomer alternative has been developed with many of the same attributes of GFLT, plus added features of -40°C dry static sealing capability, and part serviceability with little or no postcure of the elastomer. This paper will look at the new fluoroelastomer, VTX-8525, and compare it to current GFLT and other fuel system sealing materials. Fuel, alcohol, and ether resistance as well as low temperature sealing measurements will be reviewed with a specific focus on automotive fuel system end use requirements.
Technical Paper

Choosing the Right Elastomer for Air Intake and Engine Oil System Gaskets

More stringent evaporative emission loss and vehicle life requirements imposed by CARB LEV II and EPA Tier II regulations are necessitating replacement of highly permeable Air Intake and Oil System gaskets with low permeation elastomers. Low permeation, however, is not the only requirement for these gaskets. This paper presents data on fuel permeation, compressive stress relaxation and the low temperature sealing properties of the various elastomer candidates for these seals in order to help the sealing system engineer optimize the overall performance of these gaskets.
Technical Paper

New Cured-In-Place Gasket Technology Using UV-Cured High Performance Elastomers

Cured-In-Place Gaskets have been demonstrated as a viable, economical sealing choice for a number of automotive applications. Historically, this market has been limited by material choice, which has almost exclusively been the domain of liquid silicone (VMQ) and polyurethane (PU). New technology has been developed which expands the choices of elastomers that can be used in Cured-In-Place gaskets. Seals made with high performance elastomers such as ethylene acrylic elastomers (AEM) and fluoroelastomers (FKM) can now take advantage of this “efficient” process. These materials can be robotically dispensed using equipment similar to what is used in the “hot melt” adhesives industry and then cured with a UV-light source. These UV-cured seals exhibit mechanical properties similar to what their traditionally cured alternatives show and still maintain the excellent heat and fluid resistance of these polymers.
Technical Paper

Permeation and Stress Relaxation Resistance of Elastomeric Fuel Seal Materials

Today's fuel systems place many demands on the seals containing liquid and vapor hydrocarbons. California Air Resource's LEV II and EPA's Tier 2 demands require fuel systems which are essentially hermetically sealed with a robust, long term (12-15 year), life. Two properties which are key to long-term seal life are the material's ability to retain it's sealing force, and the ability to resist fuel permeation. To evaluate these two fuel seal properties, testing was conducted on a number of rubber compounds including HNBR, an HNBR-fluoroplastic alloy, FVMQ (fluorosilicone), an FKM-FVMQ blend, and FKM. To evaluate permeation through a seal, Thwing Albert cups were fitted with stainless steel lids and sealing gaskets prepared from the various test materials. Fuel losses through the gaskets were determined at elevated temperatures. Long term, >1000 hour, stress relaxation testing was conducted in “hot” 60°C fuel and “sour” fuel on these compounds.
Technical Paper

Reduction of Hydrocarbon Permeation through SORE Oil Seals and Fuel System Components

Environmental actions by the California Air Resources Board (CARB) may have a significant effect on emission requirements in the Small Off-Road Engine (SORE) segment. Meeting these new proposed standards will require material and design changes to engine seals, fuel hoses, and fuel tanks. New membrane filter technology is also being developed to manage diurnal emissions from fuel systems. This paper discusses what these options are in each of the critical application areas. Relative permeation rates of the various materials were determined by either a simple gravimetric cup method or a gas chromatographic technique that permits identification of the permeating species. Data from experiments of this type were shown to correlate well with results obtained on actual parts in the Sealed Housing Evaporative Determination Test (SHED).