Friction Materials Information
Image Credit: WC Branham, Inc.
Friction materials are used to generate controlled friction for braking or power transfer applications while minimizing wear. Products include brake pads and brake shoes, clutch plates, bonded assemblies, and friction bands, liners and rolls. When selecting friction materials, industrial buyers need to consider the form and material type as well as product and performance specifications.
Friction Material Forms
The GlobalSpec SpecSearch database classifies friction materials by form.
- Friction bands are used in automotive transmissions and in friction-sawing, a metal-cutting technique where blades run at very high speeds. Because longer saw blades can better dissipate heat, friction bands are used mainly with very large saws.
- Friction blocks are used in overhead cranes, hoists and winches; crane and shovel bands; and mining and oilfield equipment. Some products are rigid.
- Friction pads and shoes are used in automotive brakes and braking systems. Brake pads use friction to convert the kinetic energy of the car to thermal energy. The friction of the pad against the rotor provides most of the stopping power.
- Friction plates or discs are used in clutches, torque limiters, disc drivesand power transmission devices. The disc may consist of friction material or the plate may be lined with friction material.
Friction rolls, sheets and lining systems are also available.
Types of Friction Materials
In addition to form, buyers need to select the material type.
- Ceramic materials are extremely durable and well-suited for applications with heavy loads. They can withstand higher heat than other friction materials, but have a high rate of wear because of their hardness.
- Aramid fibers such as Kevlar (DuPont) combine the pulling capabilities of ceramics with the smooth engagement of organic materials. When used properly, Kevlar can outlast other friction materials by two to five times. It is lighter and tougher than steel, and provides exceptional thermal stability.
- Organic materials were once made mainly of asbestos, but are now largely made from other materials.
- Metallic friction materials include bronze or copper alloys, cast iron, and steel. Often, organic facings are made of brass and fiberglass.
Rubber, molded thermoset resins, carbon and graphite, and cork are also used as friction materials.
Applications for Friction Materials
Friction materials are used in automotive, military, manufacturing, and mining applications. When selecting products, buyers should specify the coefficient of friction under both normal and hot conditions. The coefficient of friction (μ) of a material determines the retarding force (Ffriction) produced when two sliding surfaces are held against each other by an applied normal force (N). The equation concerning the process is Ffriction = μN.