The Under-the-Bonnet battle between plastic and metal

November 5, 2013
The Under-the-Bonnet battle between plastic and metal

Metal is the accepted material for dealing with extremes. That’s just the way it’s always been. We fabricate and install graded metals with a mindless reflex, knowing the material has a dense enough molecular bond to withstand all kinds of hazardous environment. Let’s take our lead from the petroleum industry and chemical processing field for a time and aid our material engineers in re-evaluating the role of metal. Certainly, metal is an invaluable resource, but each alloy requires expensive heat treatment to make it malleable and easy to shape. Plastic is the key to the issue. The argument for plastic already overwhelms any metal when considering weight ratios and cost. The carbon polymers that form plastics are simply much lighter than metal and easier to mold. Unfortunately, although weight and cost are major factors in the automotive industry, this is still a complex puzzle to unravel.

Consider one area where steel and aluminium tend to enjoy dominion over plastic, the fuel system and any areas of the vehicle where caustic liquids are present. Road vehicles adopt engines to run on diesel, petrol, ethanol, and various mixes with potential catalysing properties. While plastics are available to match these fuels, the need to create a strategy to match the solvent characteristics of certain fuel grades creates an additional layer of logistics to deal with in the manufacturing stage. Steel doesn’t react to the caustic components within an ethanol blend, plus, steel deals with transient pressure and temperature variations more efficiently than typical plastic alternatives. Flip the coin once more, though, to see the acceleration of developments in the engineering plastics sector.

The coin flip shows a range of elastomers, thermoplastics, fluoropolymers, and much more arriving to compete with high-end metals. The fluorocarbon market, including Teflon, uses formulations of carbon-fluorine bonds to create near friction-free materials that are chemically inert. Imagine a future, perhaps ten or fifteen years from today, a future where engine performance has increased twenty-fold. The elimination of heavy metal must be a key part of this goal. The cars will run on a combination of biofuel and exotic chemical processes, passing through plastic fuel tanks that will never become permeable to the fuel source. The fossil fuel market will finally have the lightweight chassis and lighter engine required to squeeze the last ounce of energy from rapidly dwindling reserves, and this optimized mass-to-fuel performance ratio will usher in a new age of savings through science.

Expect to see more entries from the fluoropolymer family within fuel systems. This penetration of plastic is already being paved by PPA, Polyphthalamide, and nylon polymers. Set to replace engine manifold components with injection-molded plastic as of today, the polymer industry is destined for big things.