Water pump seals of DuPont™ Viton® GFLT-600S resist aggressive coolants and greases where HNBR fails

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Chart: DuPont
Chart illustrates marginal loss of elongation at break of Viton® GF-600S and Viton® GFLT-600S, versus dramatic loss of properties for a bisphenol grade of fluoroelastomer (FKM) after aging in the coolant.


DuPont™ Viton®, the most specified fluoroelastomer for automotive seals, hoses, O-rings, gaskets and shaft seals, is the subject of continuous evolution and development.

At DKT 2012, DuPont Performance Polymers (DPP) showcased an application based on Viton® GFLT-600S, an exceptionally fast curing, low temperature resistant fluoroelastomer with enhanced processibility and water resistance, based on DPP's proprietary Advanced Polymer Architecture (APA)—the result of a USD 50 million investment in polymerization and curing technology.


Peroxide-cured Viton® GFLT-600S is a key example of the benefits of APA technology, best demonstrated in newly commercialized grease and coolant-resistant automotive water pump seals developed in close collaboration between DPP, OEMs and part manufacturers.


Water pump seal challenge


Automotive water pumps employ a two-lip seal, one to seal against monoethylene glycol coolants and the other to seal against high temperature grease containing polymeric urea, both aggressive to many rubbers and elastomers. Hydrogenated nitrile butadiene rubber (HNBR) seals traditionally used for water pump applications leaked when subjected to today's higher heat (125°C+) requirements imposed by automotive manufacturers.


The failure was attributed to the poor temperature resistance of HNBR. A standard bisphenol cured fluoroelastomer also failed to seal satisfactorily in field tests, and a standard high fluorine content peroxide cured fluoroelastomer did not meet the low-temperature requirements of this application.


Following extensive failure analysis and in-depth evaluation of Viton® grades after 2,000 hours at 125°C in the specified coolant liquid, and 2,000 hours at 150°C in the high performance polyuria-stabilized greases, only peroxide-curable, low-temperature Viton® GFLT-600S provided the required chemical and temperature resistant properties.


Benefits for processors and end-users


Viton® GFLT-600S is one of a broad family of Viton® fluoroelastomers made with APA technology, encompassing standard peroxide, improved low-temperature, expanded fluid resistant and improved base resistant types. Compared with standard fluoroelastomers, it combines superior low-temperature sealing performance with improved resistance to automotive fuels, acids, methanol, hot water and steam.


Benefits to processors, resulting from the optimized injection, compression, transfer and extrusion processing performance of APA grades, include an exceptionally fast and high state of cure with improved mold flow and release, low mold fouling properties and less shear sensitivity. These characteristics lead to shorter cycle times, less waste and improved productivity of seals, hoses, O-rings, gaskets, extruded tubing and profiles, and easier overmolding onto plastic inserts or carriers.


For OEMs and end-users, Viton® GFLT-600S meets new performance criteria in an era of longer warranties, hotter engines and more aggressive lubricants that shorten the life of many existing elastomers. The DuPont fluoroelastomer provides an effective solution to tough lubricant and fuel system sealing applications where additional low-to-high temperature flexibility (from -40°C to +230°C) and life-of-the-vehicle durability is required.


In addition, the excellent resistance of Viton® GFLT-600S to heat, swell, permeation and degradation when in contact with aggressive gasoline, diesel, new biofuels and acid condensates from blow-by or exhaust gas recirculation helps automotive OEMs meet current Euro 5 and forthcoming Euro 6 evaporative emissions regulations.