High-performance racing engines create a hostile environment with the presence of extreme temperatures and aggressive fluids. The polymers used for rubber seals and mouldings are often extremely costly, where even a simple O-ring can cost upwards of Â£35. However, recent advances in rubber compounding offer some lower cost alternatives.
For many years, automotive seals were manufactured from nitrile rubber because of its excellent resistance to mineral oils and petroleum solvents and fair resistance to heat and ageing. The introduction of smaller, higher revving, engines with elevated running temperatures has driven the switch to hydrogenated nitrile (HNBR) compounds with a higher top temperature range.
Today's modern lubricants are complex products, containing detergents, surfactants and viscosity-improving low-molecular polymer additives. Synthetic oils are widely accepted while transmission and power steering fluids increasingly contain aliphatic amines. These highlight gaps in HNBR’s performance envelope.
A new generation of optimised HNBR compounds addresses these problems, offering many applications in a performance envelope similar to perfluoroelastomers such as FFKM - at a significantly lower cost. These new polymers maintain HNBR’s high temperature performance while extending low temperature performance to –40Â°C, thereby expanding opportunities in extreme arctic weather conditions.
This fully-fluorinated perfluoroelastomer provides exceptional temperature and chemical performance, making it the material of choice for the harshest down-hole well drilling conditions. FFKM is a difficult material to mould but as more rubber moulders learn to master its production parameters, product prices are coming down, enabling increased use in oil and gas applications.
Originally formulated for aerospace applications, Viton soon found applications in automotive engineering because of its high temperature performance, exceptional resistance to mineral oils and chemicals, resistance to climatic factors such as ozone and sunlight, and low gas permeability. However, Viton exhibits long-term problems with high pH chemicals (bases), triggering premature failure.
The corrosion inhibitors designed to protect metal components use bases to counteract the long-term effects of acid build-up. Fortunately for designers, there is a new Viton (trade name Viton Extreme) that addresses this challenge and provides other advantages, including reduced manufacturing costs.
In addition to this enhanced base resistance, and Viton’s inherent fluid and chemical resistance, Viton Extreme offers improved tensile strength, superior compression set resistance and lower volume swell for longer seal life and wear resistance, making it ideal for use in the automotive and heavy duty/off-highway markets.
This fluoroelastomer also offers the moulder significant advantages: better mould flow, faster cure rates, improved mould release and reduce mould fouling, all of which should lead to more efficient manufacturing with reduced reject rates - and manufacturing costs.
Waiting in the wings
To respond to the requirements of engineering companies at the cutting edge of their technologies, seal manufacturers should be continuously investigating new rubber compounds through their on-going R&D programmes. These programmes should cover material flows, out gassing, residues, etc., that is, the material's moulding characteristics as well as its design performance.
For example, Teflon-coated rubber has been around for some time but the coating flakes and reduces flexibility; filling fluoroelastomer with nano-particle size Teflon shows immense promise. The resultant seal significantly reduces friction with none of the side effects of coatings, making it ideal for rotating seals in automotive, aerospace, oil and gas applications. It also exhibits reduced permeability, meaning reduced emissions to automotive manufacturers. Early indications are that it moulds well.
One seal manufacturer which specialises in providing customised solutions to customers seeking extreme performance without an extreme price tag, has successfully supplied seals and moulding to leading Formula One, WRC, Indy and Moto GP power plant developers. As a result of their efforts in this high tech market, the production parameters surrounding these exciting new materials have been mastered.
Written by Tom Sharp.