3/12/2015 Brakefrictionmaterials
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Brakes:BrakingSystems:Discbrakes&components
Brakefrictionmaterials
SummaryBrakepadsandliningsaremadefrommaterialswhichhaveahighcoefficientoffriction.Thechoiceofmaterialdependsonthebrakingapplication,butitneedstobeabletoabsorbanddisperselargeamountsofheatwithoutbrakingperformancebeingadverselyaffected.
Frictionistheforcethatactstopreventtwosurfacesincontactfromslidingagainsteachother.Whenfrictionoccurs,thekineticenergy(motion)oftheslidingsurfacesisconvertedintothermalenergy(heat).
Somecombinationsofmaterials,suchasiceonglass,haveaverylowcoefficientoffriction.Thatmeansthatthereisverylittlefrictionbetweenthem,andthereforealmostnoslidingresistance.Rubbertiresagainstahardroadsurfacehaveahighcoefficientoffriction,whichmeanstheytendtogripandresistslidingagainsteachother.
Discbrakepadsanddrumbrakeliningsaremadefrommaterialswhichhaveahighcoefficientoffriction.Theyalsoneedtohaveanabilitytoabsorbanddisperselargeamountsofheatwithouttheirbrakingperformancebeingadverselyaffected.
Astheheatinbrakepadsandliningsbuildsup,thefrictioncapabilityofthematerialandconsequentlyitsstoppingpowerreduces.Thisiscalledbrakefade,andminimizingorovercomingfadeisamajorfactorinthedesignofbrakesandthedevelopmentofbrakefrictionmaterials.
Brakefrictionmaterialswerecommonlymadefromasbestoscompounds,becauseoftheexcellentheatresistanceofthatmaterial,butasthathasnowbeenproventobehighlytoxic,asbestosisgenerallybannedandnolongerused.
Brakesarenowmanufacturedfromavarietyofdifferentmaterialsthatmaybe:
nonasbestosorganiclowmetallicsemimetallicceramic
Thechoiceofcompounddependsontheapplication.Lighterpassengervehiclesgeneratelessheatinthebrakesthanheavyorhighperformancevehicles.Theoptimumbrakecompositionforanygivenvehicleorusewillthereforebeacombinationofweightedattributeswhichinclude:
stoppingpowerheatabsorptionanddispersionresistancetofaderecoveryspeedfromfade
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