Meeting LEV II, PZEV and Euro 4 with Viton® fluoroelastomers
With the introduction of tough new LEV II, PZEV and Euro 4 auto emissions regulations, DuPont Performance Elastomers offers the next generation of regulation-compliant fluoroelastomers — Viton® made with Advanced Polymer Architecture (APA).
Viton® made with APA is the result of a USD 50 million investment in proprietary new polymerisation and curing technology. Innovative specialty types of Viton® deliver significant performance improvements and meet rigorous automotive fuel system and powertrain sealing requirements, particularly by providing enhanced resistance to new fuel compositions, and by providing a highly effective barrier that controls evaporative emissions to low levels.
Applications of APA polymers in the automotive industry include fuel system seals and hoses, and air intake and engine oil gaskets.
Viton® types for automotive sealing
Viton® fluoroelastomers are available in different types to meet the exacting demands of each industry. Three types are recommended for automotive fuel system, air intake and engine oil sealing when compliance with emissions regulations is essential. All are produced via APA technology, and share easy processing with fast clean cures and good compression set resistance. (See Fig. 1. Viton® families and recommended applications).
Fig. 1. Viton® families and recommended applications
Viton® GF-S, Viton® GFLT-S and Viton® GBLT-S are high fluorine content FKM materials which have outstanding resistance to fuel and fuel-alcohol (including methanol) blends.
Viton® GF-S exhibits the lowest permeation and fuel swell of the three, but is not specifically designed for very low temperature sealing. When fully postcured, GF-S has a lower permeation rate than most 70% fluorine content products available today.
Viton® GFLT-S has the next best fuel resistance with improved low temperature capability to -24°C.
The ideal choice for air intake and engine oil gaskets
The virtues of GF-S and GFLT-S are combined in Viton® GBLT-S. This APA polymer has outstanding low temperature capability and low swell in high methanol containing flex fuels. It can seal statically to -40°C while maintaining that essential fuel-alcohol (methanol) resistance.
Why Fluoroelastomers?
Automotive fuel sealing needs have changed from the days when methanol flex fuels caused concern for sealing material manufacturers and specifiers. While methanol is less of a problem today, regulations directed toward seal performance present a much more complex challenge. Now, fuel system seals must seal for 15 years/150 000 miles without leaks and within fuel permeation limits — even at temperatures above 150°C, or as low as –40°C. They must also resist fuel and fuel/alcohol/ether blends including methanol, and "sour" gasoline.
In addition, the seals must be flexible and durable enough to absorb engine vibration for the lifetime of the vehicle. Which materials can survive in such a tough sealing environment and meet current LEV II, PZEV and Euro 4 automotive evaporative emissions requirements?
Silicone rubber (VQM) is highly permeable to hydrocarbons, has borderline compression set resistance (CSR) in synthetic oil, and long term (15 year) heat aging and compression set is marginal.
While hydrogenated nitrile rubber (HNBR) has better permeation performance than silicone, it is still 100 times more permeable than fluoroelastomers (FKM), and exhibits significantly poorer heat aging and long-term compression set.
Extensive testing by DuPont Performance Elastomers and independent tests by several leading fuels system OEMs reached the same conclusion — FKM has the best permeation performance of these elastomeric sealing materials, being 1000 times better than VMQ and 100 times better than HNBR. It also has better heat aging and CSR performance than either VMQ or HNBR. (See Fig.2. Permeation of Fuel Through Gasket Elastomers)
Fig. 2. Permeation of Fuel Through Gasket Elastomers
FKM is an ideal choice for air intake manifold and engine oil gaskets and fuel system seals. But there are many FKM products on the market. Which will do the best job in the engine compartment, and meet the latest emissions regulations? "Standard" fluoroelastomers are generally no longer up to the task. The performance high ground today is occupied by specialty fluoroelastomers, such as Viton® made with Advanced Polymer Architecture (APA) from DuPont Performance Elastomers.
SPECIAL NOTE:The information set forth herein is furnished free of charge and is based on technical data that DuPont Performance Elastomers believes to be reliable. It is intended for use by persons having technical skill, at their own discretion and risk. Handling precaution information is given with the understanding that those using it will satisfy themselves that their particular conditions of use present no health or safety hazards. Because conditions of product use and disposal are outside our control, we make no warranties, express or implied, and assume no liability in connection with any use of this information. As with any material, evaluation of any compound under end-use conditions prior to specification is essential. Nothing herein is to be taken as a license to operate or a recommendation to infringe on any patents. While the information presented here is accurate at the time of publication, specifications can change.
CAUTION: Do not use in medical applications involving permanent implantation in the human body. For other medical applications, discuss with your DuPont Performance Elastomers customer service representative and read Medical Caution Statement H-69237.