Materials
Brake pad materials range from asbestos to organic or semi-metallic formulations. Each of these materials has proven to have advantages and disadvantages regarding environmental friendliness, wear, noise, and stopping capability. Semi-metallic pads provide strength and conduct heat away from rotors but also generate noise and are abrasive enough to increase rotor wear.
Ceramic compounds and copper fibers in place of the semi-metallic pad's steel fibers accommodate higher temperatures with less heat fade and generate less dust and wear on both the pads and rotors. They also provide much quieter operation due to the ceramic compound that helps dampen noise by shifting its resonant frequency beyond the human hearing range and reduced metal use (approximately 15% metal content by weight).
There are environmental factors that govern the selection of brake pad materials. For example, recent legislation in Washington State (SSB 6557) and other states will limit the amount of copper that is allowed to be used in friction materials, to be eventually phased out to trace amounts. Other materials like antimony compounds will be monitored as well.
Asbestos was widely used in pads for its heat resistance but, due to health risks, has been replaced with alternative materials, such as mineral fibers, cellulose, aramid, PAN, chopped glass, steel, and copper fibers. Depending on material properties, disc wear rates vary. The properties that determine material wear involve trade-offs between performance and longevity. Newer pads can be made of exotic materials like ceramics, aramid fibres, and other plastics.
Vehicles have different braking requirements. Friction materials offer application-specific formulas and designs. Brake pads with a higher coefficient of friction provide good braking with less brake pedal pressure requirement, but tend to lose efficiency at higher temperatures, increasing stopping distance. Brake pads with a smaller and constant coefficient of friction don’t lose efficiency at higher temperatures and are stable, but require higher brake pedal pressure.
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Famous quotes containing the word materials:
“Realism to be effective must be a matter of selection. ... genius chooses its materials with a view to their beauty and effectiveness; mere talent copies what it thinks is nature, only to find it has been deceived by the external grossness of things.”
—Julia Marlowe (1866–1950)
“If our entertainment culture seems debased and unsatisfying, the hope is that our children will create something of greater worth. But it is as if we expect them to create out of nothing, like God, for the encouragement of creativity is in the popular mind, opposed to instruction. There is little sense that creativity must grow out of tradition, even when it is critical of that tradition, and children are scarcely being given the materials on which their creativity could work”
—C. John Sommerville (20th century)
“Young children learn in a different manner from that of older children and adults, yet we can teach them many things if we adapt our materials and mode of instruction to their level of ability. But we miseducate young children when we assume that their learning abilities are comparable to those of older children and that they can be taught with materials and with the same instructional procedures appropriate to school-age children.”
—David Elkind (20th century)