Brakes work by two surfaces being pushed together by a force. Friction between these surfaces generates a force that will resist motion.  Brakes use this friction to convert the kinetic energy into heat. As heat is generated, kinetic energy is reduced, as is motion.  The heat generated causes elevated temperatures in the brake components. The temperature rise is determined by the quantity of heat as well as the mass and material of the brake components.

The temperature of the brake is reduced as it rejects heat to the surrounding air. This rejection of heat is determined by the surface area of the brake components and the movement of air across them. The greater the surface area or the faster the air flow, the greater the heat rejection.  The operation of the brake determines the resulting temperatures. Light operation may allow heat to be rejected from the brake at the same rate that it is generated and low temperatures result. In continuous operation, the heat generation is large and temperatures in the region of 400C can result. Temperatures are often even higher and this causes brake components to glow red.

One of the most important aspects of a brake is the wear rate of the braking material. This determines the useful life of the components, the maintenance intervals and most importantly the likelihood of brake failure due to over-worn parts. This last point impacts severely on the safe operation of the brakes.

Two main factors determine brake wear:

• component material selection; and
• temperature of brake components

Brake materials vary greatly; their selection is critical to wear, especially in dry brakes, where force is transmitted directly between these components. In SIBS, the cooling fluid becomes part of the force transmission, reducing wear.

The temperature of the brake components is the second important factor in determining brake wear. Elevated temperatures during braking operation increase wear rates.

The graph shows the exponential rise in wear due to temperature. The rise in wear is always increasing with temperature; becoming highly undesirable around 400C. This is due to the softening effect of heat upon the brake material. As the material softens, its ability to resist the friction force falls and larger wear results.