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Brake pad
Brake pads are a component of disk brakes used in automotive and other applications. Brake pads are steel backing plates with friction material bound to the surface that faces the disk brake rotor.
Function
Brake pads convert the kinetic energy of the car to thermal energy by friction. Two brake pads are contained in the brake caliper with their friction surfaces facing the rotor.<ref name="Haynes, Brake manual" >Template:Citation/core{{#if:|}}</ref> When the brakes are hydraulically applied, the caliper clamps or squeezes the two pads together into the spinning rotor to slow/stop the vehicle. When a brake pad is heated by contact with a rotor, it transfers small amounts of friction material to the disc, turning it dull gray. The brake pad and disc (both now with friction material), then "stick" to each other, providing the friction that stops the vehicle.
In disc brake applications, there are usually two brake pads per disc rotor, held in place and actuated by a caliper affixed to a wheel hub or suspension upright. Although almost all road-going vehicles have only two brake pads per caliper, racing calipers utilize up to six pads, with varying frictional properties in a staggered pattern for optimum performance.
Depending on the properties of the material, disc wear rates may vary. The brake pads must usually be replaced regularly (depending on pad material), and most are equipped with a method of alerting the driver when this needs to take place. Some have a thin piece of soft metal that causes the brakes to squeal when the pads are too thin, while others have a soft metal tab embedded in the pad material that closes an electric circuit and lights a warning light when the brake pad gets thin. More expensive cars may use an electronic sensor.
Technology
Advantages of disc brakes
These brakes offer better stopping performance than comparable drum brakes, including resistance to "brake fade" caused by the overheating of brake components, and are able to recover quickly from immersion (wet brakes are less effective). Unlike a drum brake, the disc brake has no self-servo effect—the braking force is always proportional to the pressure placed on the braking pedal or lever—but many disc brake systems have servo assistance ("Brake Booster") to lessen the driver's pedal effort.
Laser shaping
Ordinary brake pads inherit vibration characteristics since the shape of the pad and contact of the caliper piston causes vibration that distorts the contact or the transfer of force to the rotor upon contact. The new laser cutting technology of the pad decreases the contact area and focuses on more force being distributed over a smaller amount of an area for more positive contact of the pad and rotor creating more efficient quality stopping.
Laser burnishing process
A precisely controlled laser beam is used to heat and condition the pad surface, eliminating the need for a traditional break-in period on the vehicle following installation.
IMI-sound insulator
Spreads out and absorbs heat and energy over a greater surface area for longer brake pad life and quieter performance.
Types
There are numerous types of brake pads, depending on the intended use of the vehicle, from very soft and aggressive (such as racing applications) and harder, more durable and less aggressive compounds. Most vehicle manufacturers recommend a specific compound of brake pad for their vehicle, but compounds can be changed (by either buying a different make of pad or upgrading to a performance pad in a manufacturer's range) according to personal tastes and driving styles. Care must always be taken when fitting non standard brake pads, as operating temperature ranges may vary, such as performance pads not braking efficiently when cold or standard pads fading under hard driving. In cars that suffer from excessive brake fade, the problem can be minimized by installing better quality and more aggressive brake pads.
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 provide high brake temperatures with less heat fade, generate less dust and wear on both the pads and rotors. They also provide much quieter braking because the ceramic compound helps dampen noise by generating a frequency beyond the human hearing range and use less metal (approximately 15% metal content by weight). Ceramic brake pads typically are suited for light-duty applications and not severe duty applications, medium duty trucks, etc.
There are environmental factors that govern the selection of brake pad materials. For example, recent legislation in Washington State 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. The legislation can be found in Washington State SSB 6557. 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.
Cataloguing
There are different systems for the cataloguing of brake pads. The most frequently used system in Europe is the WVA numbering system.<ref>WVA numbering system</ref>
