Jon BeVier, Chris Brazell, Sam Tipton, Wesley Holleman Engineering 45 Santa Rosa Junior College 12/5/2005 More than you ever wanted to know about brake pads!

The history of brake pad technology Wood Brake pads –Often splintered wood –Wood would not adhere to contact surface if burnt by heat –Used on wagons of the west –Would wear down tires on automobiles. –VERY EASY AND CHEAP ***Your new car with wooden brakes =….***

Brakes of the 20 th century Initial copper brake pads –Stopping distance better than wood –Harder to make –Lasted longer than wood Asbestos brake pads Developed not to long after copper pads Lasted longer than copper HARMFUL brake dust

Current brake pad technology Composed of a variety of materials –Copper, aluminum, ceramic compounds –Kevlar, polymers, resins, carbon fiber, other fillers Broad range of applications –Racing –High load –Daily Use Variety of shapes and sizes for vehicles Disk brakes Drum brakes: air powered, hydraulic powered.

Brake Pad Composition Ceramic brake composition Carbon fiber brake composition Ceramic brakes include trace amounts of copper and other metals to create a longer lasting brake pad. They use resin and other polymers for filler and to create a higher coefficient of friction at high temperatures. Carbon fiber brakes use the same fillers as ceramic brakes however carbon fiber brakes create more dust and last longer. In the case of carbon fiber brakes the filler is what determines the noise level and life of the brake pad. Felt fillers make less noise than epoxy fillers.

Brake pad compression analysis Heated organic ceramic 300C for 2,4,and 8 minutes with 1 control pad. Compressed pads with Tinius Olsen Materials testing machine.

Results of Compression What does this MEAN????

I’ll tell you what it could mean! The unheated pad showed its ability to give with the compression of the machine, no heat means the materials inside do not fuse together. The two minute pad BARELY compressed, perhaps due to the composition and heat reactivity of the materials inside. The four and eight minute pads could have exceeded the correct level of heat for this composition, thus the materials inside start to “carbonize”, or burn, and the pad starts breaking apart.

Before compression: After Compression: All of our pads looked the same after compression. The Non-recoverable compression in each is as follows: No heat – 14/1000” – 11/1000” – 10/1000” – 16/1000” Pictures of our different brake pads

Heat Cycles of brake pads Brakes are subject to heat cycles as cars apply pressure to the brake lever

Current brake pad limitations Everything has a limit, Brakes have some limits too. Manufacturers will post temperature ranges for operation. Anything above this temperature and the brake pad will carbonize. Metal on metal contact causes warping if not “broken in” correctly, all manufacturers give “breaking in” instructions. This allows the brakes to conform to the brake disc/drum and heat up and cool down a few times to “set” the materials inside the brake pad.

Manufacturer’s posted limits and maximum coefficients of friction

Brakes of the future New Compounds –Companies are always working on new compounds that will make brakes quieter, produce less dust, last longer, and stop faster. –The leading edge of brakes generally starts in racing and works its way into industrial applications. But compounds can only take us so far…

Electromagnetic Brake Consists of non-linear magnetic steel plate, a permanent magnet and a current coil. The coil generates a magnetic field which acts against the field of the permanent magnet. The brake is applied when the coil current is zero. Increasing the coil current will release the brake. The braking force can be calculated as a function of the coil current.

Electromagnetic brake (cont.) With no friction, heat would be minimized, there is nothing to burn up or be sheared off to make dust or shorten the life and no contact to make noise Current applications –Rollercoasters –Industrial machinery Brakes clutches

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