EX­PLAINED: TUNG­STEN-COATED BRAKE DISCS

New cast-iron/car­bon­ce­ramic mid­dle ground

Wheels (Australia) - - Contents - DANIEL GARD­NER R

What is it?

A reg­u­lar cast-iron brake disc that has un­der­gone a com­plex plat­ing process to coat the sur­face with an ul­tra-hard layer of tung­sten-carbide. The tech­nol­ogy has de­buted on Porsche’s third­gen­er­a­tion Cayenne SUV but will soon ap­pear on other mod­els and is likely to spread to other brands as well.

How does it work?

A layer of tung­sten-carbide, 100-mi­crons thick, is ap­plied to the fric­tion sur­faces of a reg­u­lar cast-iron brake ro­tor in a pow­der form through a ther­mal spray process. On con­tact, the very high tem­per­a­ture and ve­loc­ity forces the ul­tra-hard com­pound to bond to the disc, creat­ing a coat­ing many times harder than the sur­face of a reg­u­lar ro­tor. A spe­cial brake pad has been for­mu­lated to in­ter­act op­ti­mally with the tung­sten sur­face and is sim­i­lar in com­po­si­tion to the pads used for car­bon-ce­ramic discs, which are also ex­tremely hard. Other than the ex­otic ma­te­ri­als, the brake sys­tem func­tions as any other disc-brake set-up does, al­though in the Cayenne’s case, it em­ploys mas­sive 10-pis­ton calipers for max­i­mum clamp­ing force.

Why does it mat­ter?

Tung­sten ro­tors re­sist wear longer than con­ven­tional iron ver­sions and can last up to 40 per­cent longer, says Porsche. That of­fers a cost ben­e­fit that can off­set the higher price of pro­duc­tion. Im­por­tantly, the highly heat re­sis­tant coat­ing main­tains a more con­stant tem­per­a­ture and has a higher fric­tion co­ef­fi­cient for more pre­dictable brak­ing per­for­mance un­der hard and fre­quent use.

Fur­ther, the re­duced ro­tor wear also keeps wheels free from dust for longer. Not only are cleaner wheels more at­trac­tive but af­ter a few kilo­me­tres of use, the discs pol­ish to a mir­ror fin­ish to fur­ther im­prove aes­thet­ics. And if left for ex­tended pe­ri­ods will not rust like con­ven­tional un­coated iron.

White 10-pot calipers dif­fer­en­ti­ate this set-up from the yel­low units used for Porsche’s car­bon­ce­ram­ics Discs mea­sure 415mm15mm on the Cayenne’senne’s front axle but can the­o­ret­i­cally bee sized for any ap­pli­ca­tion

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