MLS Head Gaskets

The cylinder head gasket is arguably the most important seal in the automotive engine. Since the birth of the internal combustion engine, gasket designers have specified many materials to meet this critical sealing challenge.

Traditional copper and brass gave way to metal and asbestos in the 1950s, superseded in turn by composite metal and impregnated fibre or graphite composites by the 1980s. However, those systems were largely overtaken by the development of the Multi-Layer Steel (MLS) gasket in Japan during the early 1990s.

MLS gaskets remain the automotive industry's preferred method of sealing between cylinder head and engine block, as yet unmatched by any other sealing system. Today an estimated 80 percent of new engines are designed with MLS gaskets as standard equipment, and further growth is projected.

In the MLS system, multiple thin layers of cold-rolled spring grade stainless steel are coated with 7-25 microns of elastomeric material. The resilient elastomer is essential to the structure by providing micro-sealing of metal surface imperfections while resisting aggressive combustion gases, oils and coolants at temperatures up to 250°C.

The Leading FKM

Fluoroelastomer (FKM) has been adopted by the industry in Europe as the most successful coating material for long-term functionality in this critical sealing environment. Although nitrile rubber (NBR) has been widely used for MLS coating in the US and Japan, rapidly increasing use of FKM is now expected in these regions over the next five years.

The predominant FKM chosen by compounders and MLS gasket manufacturers is Viton® fluoroelastomer. Viton® is applied to MLS gaskets fitted as original equipment to most automobile models assembled in Europe by BMW, Daimler, Fiat, Ford, General Motors, PSA, Renault and Volkswagen.

"Over 80 percent of all MLS gaskets specified for new engine designs in Europe are now coated with Viton®," reports Lucio Corrado, European automotive business development manager for DuPont Performance Elastomers. "Viton® meets stringent industry requirement for a high temperature and aggressive fluids resistant elastomer that can be applied as a very thin coating on a stainless steel substrate to seal micro-asperities between automotive engine heads and blocks."

Viton® offers static sealing at service temperatures ranging from -40°C to as high as 250°C and are highly resistant to fuels and fuel mixtures, oils, coolants and combustion gases. Combined with its excellent long-term compression set resistance, the FKM retains sealing functionality for the lifetime of the vehicle.