Extreme environments demand extreme solutions

Hostile environments – oil exploration, sub-sea cabling, high-performance engines – demand seals and mouldings capable of surviving temperature extremes and aggressive fluids. However, suitable raw rubber compounds for these applications are extremely costly, making components very expensive; even a simple O-ring can cost upwards of £35 (€50/$60). 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 combined with fair resistance to heat and ageing. The introduction of smaller, higher revving, engines in the 80s raised running temperatures, driving the switch to hydrogenated nitrile (HNBR) compounds with a 25°C higher top temperature range.

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. These have united to highlight 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 – and opening up new opportunities.

These new compounds maintain HNBR’s high temperature performance while extending low temperature performance to –40°C, expanding opportunities in extreme weather applications; Arctic temperatures frequently drop to this level. Additionally, HNBR’s excellent resistance to abrasion is extended, offering engineers a choice between optimised HNBR and FFKM for applications such as down-hole exploration and monitoring equipment.

This fully-fluorinated perfluoroelastomer provides 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 makes 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 are coming down, enabling increased application across the oil, gas, petrochemical, pharmaceutical and semiconductor industries.

Below FFKM is FKM - commonly called Viton. Originally formulated for aerospace applications, FKM’s high temperature performance, exceptional resistance to chemicals and mineral oils, resistance to climatic factors such as ozone and sunlight, and low gas permeability soon extended its application into automotive engineering, domestic appliances, fluid power and chemical processing. However, FKM exhibits long-term problems in high pH chemicals, triggering premature failure.

Chemicals 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, making it ideal for use in oil and gas exploration, chemical processing, utilities, automotive and heavy duty/off-highway markets.

This new fluoroelastomer also offers the moulder significant advantages: better mould flow, faster cure rates, improved mould release and reduce mould fouling. This should lead to more efficient manufacturing with reduced reject rates - and manufacturing costs.

At DP Seals, we specialise in providing customised solutions to customers seeking extreme performance without an extreme price tag. As a result we have mastered the production parameters surrounding these exciting new materials, putting us at the forefront of custom rubber moulding.

A version of this article was published in DPA Design Products and Applications, December 2004.