New carbon-carbon composite breaks through the cost barrier

Tom Shelley reports on the development of technology that revolutionises the manufacture of high-performance friction materials

Although widely used for aircraft and F1 brakes because of their lightness and energy absorption, carbon-carbon composites are currently extremely expensive due to the time spent making them. However, a new wet processing method developed by Freno Huntercombe allows them to be produced in a fraction of the time.

The current method of making carbon-carbon composites is to react a carbon fibre pre-form with a mixture of gases in a furnace, thus depositing carbon in the interstices. Since this normally takes between 500 and 800 hours, the resulting material is very expensive.

While F1 cars usually use a new set of brake linings for each race, aircraft brakes have to endure 2000 to 4000 landings. An Airbus A380 has 16 sets of brakes at a cost of approximately £20,000 to £30,000 per brake, making them a major cost item. According to Boeing, use of carbon-carbon composite brakes enables weight savings relative to steel brakes that range from 250kg on a Boeing 737-600 or 700 to 443 kg on a MD-10 freighter. Naturally, this allows more passengers and/or freight to be carried or fuel consumption to be reduced.

The breakthrough achieved by Freno Huntercombe is the development of a process in which the carbon fibre pre-form is infiltrated by carbon nanoparticles in a water-based suspension. These are followed by ceramic particles that are then reacted to produce a phosphate ceramic. This takes 20 to 30 minutes, meaning composite brakes can be produced at a similar cost to cast iron and steel equivalents.

The compressive strength of the material, according to research director Dr John White, is 100 to 120MPa, which is about the same as that of carbon-carbon fibre composite brakes made by the chemical vapour deposition route. However, as managing director Martin Murphy points out: "Unlike F1 brakes, because ours is a ceramic, wear is low and cold and wet performance is excellent."

The company is currently in pilot production, manufacturing and supplying sample parts to customers. Patents have recently been granted and, says Dr White: "We have already had loads of enquiries." Because the new material can incorporate ceramics, structural strength is greatly improved, opening up entirely new applications that take advantage of its light weight and thermal insulation properties. A dynamometer brake has been made and tested and one of the potential applications identified has been in lightweight heat shields. There is even a possibility that the material could find use as the soft part of lightweight sandwich armour.

As production increases, it is possible that an application could be found in rear wheel brakes for volume production front wheel drive cars. For the time being, though, the company is focusing on high-end applications, where sales should yield a better margin.

Tom Shelley

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