Extreme environments demand extreme solutions. Andrew Piper describes some new rubber compounds that meet these demands - but not at an extreme price Products designed for hostile environments - oil exploration, sub-sea cabling, high-performance engines - demand seals and mouldings capable of surviving aggressive fluids and temperature extremes. However, top-of-the-range rubber compounds suitable for these applications can cost several thousand pounds per kilo, making each component very expensive; even a simple O-ring can cost upwards of £35. Recent advances in rubber compounding have identified some lower cost alternatives. For many years, automotive seals were manufactured from nitrile rubber because of its excellent resistance to attack from mineral oils and petroleum solvents, and reasonable resistance to heat and ageing. However, the introduction of smaller, higher revving, engines in the 1980s raised running temperatures, driving the switch to hydrogenated nitrile (HNBR) compounds with a 25°C higher top temperature range. Optimised HNBR There is nothing simple about today's modern lubricants: up to 25% of content is detergents, surfactants and low-molecular polymer additives to improve viscosity. Synthetic oils are now widely accepted, while transmission and power steering fluids increasingly contain aliphatic amines, all of which highlights the gaps in HNBR's performance envelope. However, a new generation of optimised HNBR compounds is now available which addresses these problems, offering many applications a performance envelope similar to perfluoroelastomers such as FFKM at a significantly lower cost. These new compounds retain HNBR's high temperature performance with improved abrasion resistance and an extended low temperature operation down to -40°C. FFKM This fully-fluorinated perfluoroelastomer provides engineers an exceptional combination of temperature and chemical performance. As a result, it has long been the material of choice for the harshest down-hole well drilling conditions, whilst its low out-gassing characteristics made it ideal for the ultra-pure environments demanded by semiconductor manufacturing. As more rubber moulders learn how to master FFKM's production parameters - it is a difficult material to mould - product prices will come down and will develop wider applications appeal. Beneath the perfluoroelastomers are the fluoroelastomers. FKM, commonly called Viton, was originally formulated for aerospace applications. Its high temperature performance, exceptional resistance to chemicals and mineral oils, its low gas permeability and resistance to climatic factors such as ozone and sunlight soon extended its application into areas such as automotive engineering, domestic appliances, fluid power and chemical processing. However, fluoroelastomers exhibit long-term performance problems when exposed to high pH chemicals, triggering premature seal failure. Viton Extreme Chemical bases are often used to clean or purge industrial and food processing equipment, and corrosion inhibitors, designed to protect metal components, contain bases to counteract the long-term effects of acid build-up. Fortunately for designers, there is a new Viton (trade name Viton Extreme) that takes up this challenge and provides other advantages, including reduced manufacturing costs. In addition to its enhanced base resistance - and the fluid and chemical resistance inherent in FKM - Viton Extreme offers improved tensile strength, superior compression set resistance and lower volume swell for longer seal life and wear resistance. It is thus suitable for use in oil and gas exploration, chemical processing, the utilities, automotive applications and heavy duty/off-highway markets. This new fluoroelastomer also offers the moulder significant advantages, including better mould flow, faster cure rates, improved mould release and reduced mould fouling. This should lead to more efficient manufacturing with reduced reject rates and consequently lower manufacturing costs. Andrew Piper is technical director at DP Seals