Materials of Brake Pads. By Phillip Holifield and Nick Weil SRJC, Engr 45, Fall 2009 Semester. How do disk brakes work?. Disk brakes convert kinetic energy from the car into thermal energy by friction. Brake Caliper.
Materials of Brake Pads By Phillip Holifield and Nick Weil SRJC, Engr 45, Fall 2009 Semester
How do disk brakes work? • Disk brakes convert kinetic energy from the car into thermal energy by friction
Brake Caliper • The brake fluid compresses the piston inside the brake caliper applying pressure to the brake pads
Brake Rotors • Connected to the axel – rotating at the same speed as the wheel • Generally made out of steel • Commonly slotted or drilled for extra heat dissipation
Brake Pads • Fixed in the brake caliper • Various compounds of materials are used • Wear over time and must be replaced
Design Challenges • Increase pad and rotor life • Reduce brake noise • Cooling to prevent heat fade • Maximize braking force • Federal Safety Requirements • Environmental Impact
Design Challenges • Passenger Cars: • Low noise and wear • Trucks and SUV’s: • Heavier weight requires better braking • High Performance Cars: • Need maximum braking and cooling
Brake Pad Materials • Asbestos • Semi-Metallic • Non-Asbestos Organics • Low Steel • Carbon • Exact composition of each manufacturer’s pads is a closely guarded secret
Asbestos Pads • Widely used in early disk brake applications • Good for absorbing and dissipating heat • Average stopping power • Asbestos is legally regulate due to it’s carcinogenic properties • No longer used due to health risks
Semi-Metallic Pads • Range from 30% to 65% metal and filler • Different pads use Steel, Iron, and Copper • Harder material is very durable and has excellent heat resistance • Creates more noise and dust • Used in most cars and SUV’s
Semi-Metallic Pads • Low to medium coefficient of friction~ 0.28 –0.38 • Relatively high mu variation (temperature, duty cycle) • Good fade characteristics • Poor wear at low temps., <100C • Excellent wear at temps. over 200C • Good wear under heavy loads • Poor wear at high speeds • Generally inferior Noise, Vibration & Harshness compared to NAOs • Contains no copper • Low initial cost • High fluid temperatures can be an issue
Non-Abestos Organic Pads • Typically contain nonferrous metals, inorganic and organic fibers, abrasives, lubricants and property modifiers such as glass, rubber, kevlar and carbon • Typically used in high performance cars • Also referred to as “ceramics”
Non-Abestos Organic Pads • Low to medium-high coefficient of friction ~ 0.33 –0.40. • Excellent wear at lower temps. < 200C. • Good for wheel dust. • Relatively poor wear under heavy duty conditions and at higher friction levels. • Good noise & roughness characteristics • Can have morning effectiveness noise – squealing noise on first couple of brake applies in the morning • More expensive.
Low Steel Pads • Typically contain ferrous and nonferrous metals, inorganic and organic fibers, aggressive abrasives, lots of carbonaceous and sulfide lubricants • Replacing semi-metallic as the standard for passenger cars
Low Steel Pads • Higher coefficient of friction levels ~ 0.38 –0.50 • Good pedal feel and braking confidence • Good fade and high speed performance • High pad/rotor wear • Good for high speed wear • Lots of wheel dust • Inferior noise and life.
Carbon Pads • Composite materials reinforced with carbon fibers • Used for both pads and rotors • Used in Formula 1 and other race cars • Major manufacturers include Hitco, Brembo and Carbon Industries
Carbon Pads • Light weight – rotors weigh less than 1kg • High coefficient of friction - can decelerate an F1 car at over 5G • Operating temperature is around 800-1000°C • Extremely expensive to produce
References • Text: • http://en.wikipedia.org/wiki/Brake_pads • http://en.wikipedia.org/wiki/Disk_brake • http://auto.howstuffworks.com/auto-parts/brakes/brake-types/disc-brake.htm • www.suscon.org/bpp/pdfs/OEBrakePads.pdf • http://www.performancefriction.com/pages/pad_type.htm • http://www.f1technical.net/articles/2 • Images: • http://stmarysjin.org.uk/hsw/gif/disc-brake3.jpg • http://www.akebonobrakes.com/oem/brake_products/images/3d_exploded_caliper.gif • https://www.nzad.co.nz/store/images/standard%20brake%20rotor%20(Small).jpg • http://www.good-win-racing.com/miata/images/items/GWR-078.jpg