How It’s Made: Carbon Ceramic Brake Rotors

You know the Brembo brand, which peeks out from between the wheel spokes on the world’s most potent automobiles, as a boutique maker of exemplary braking components. But while you weren’t paying attention, Brembo grew from a 1961 Italian upstart into the world’s largest independent manufacturer of cast iron brake rotors, aluminum calipers, and carbon-ceramic-material (CCM) discs. Brembo supplies braking equipment for cars, motorcycles, and commercial vehicles worldwide with 35 manufacturing and business operations in 14 countries on three continents. This $1-billion enterprise has over 5000 employees, more than 500 engineers and technical specialists, and its fingers in more than brake rotors, calipers, and friction materials. Brembo affiliates manufacture seat belts, child safety equipment, helmets, and motorcyclist air bag jackets. This firm also assembles corner modules — consisting of suspension linkages, wheel hubs, brake components, and ABS sensors — for Aston Martin, Ferrari, Maserati, and Porsche.

But what you really want to know is how the heck Brembo makes those big black rotors that stop the fastest Ferraris, Lamborghinis, Porsches, and Corvettes like a wall of jello? (The world’s top nine performance brands all use Brembo CCM braking systems.) Pay attention to what follows because there may be a quiz.

1. It all begins with the right materials. The mix of initial ingredients is two components long: carbon fibers and phenolic resin. The fibers are carefully chosen for length and thickness (diameter). The resin is in solid granular form. The Brembo experts we interviewed-business development director Roberto Vavassori, North American vice president Adrian Smith, and engineering manager Emanuele Bruletti-wouldn’t be more specific because they don’t want you cooking up brake rotors at home.

2. The ingredients are mixed together in a proprietary formulation and then loaded into a steel mold. Removable cores are fitted to provide the radial vents necessary to expedite heat rejection during brake applications. The mold halves are closed, pressure and heat are applied. When the molding dies are opened and the cores are extracted, a near-net-shape brake rotor emerges. The amount of excess material is minimized because removing it with subsequent operations is difficult due to the extreme hardness of a finished CCM rotor. While what emerges looks like a finished part, it’s not yet ready for use.

3. The serious business begins when the molded rotors are placed with other like parts in an oven with the ability to maintain an oxygen-free environment at high temperature. In addition to numerous rotors, a quantity of solid silicon is placed in the oven. Nitrogen is pumped in to displace the air and the temperature dial is set for 1000-degrees Celsius (1850-degrees Fahrenheit). That temperature is maintained for many hours (Brembo won’t divulge exactly how long) during which the silicon becomes a liquid and pyrolysis (essentially burning in the absence of oxygen) occurs. The silicon gradually migrates into the pores of the parent material by capillary action and the original carbon and phenolic materials are transformed into silicon carbide, a hard and highly heat resistant ceramic substance.

4. After the oven cools to room temperature at a controlled rate, the rotors are removed and machining operations begun. The inner and outer diameters, mounting locations, and braking faces must be finished with utmost accuracy to assure excellent braking performance with minimal noise and vibration. Grinding operations with diamond tools achieve the desired dimensions. The small lateral vent holes in the rotor faces are produced with an ultrasonic drilling process.

5. A coating is applied to all surfaces of the CCM brake rotor to provide oxidation protection.

6. The center or ‘hat’ section is attached to the CCM rotor with stainless-steel screw, nut, and anti-rattle hardware. Some axial and radial movement (float) between the metal hat and CCM rotor must be provided because the two components have drastically different temperature-expansion rates. Anti-rattle springs allow this movement while preventing noise and vibration. After the retention nuts are properly torqued, each fastener is marked with paint to indicate that that step has been completed. No retorquing is necessary during the life of the rotor.

7. During a quality-control inspection, the finished brake rotor’s lateral run out and other pertinent dimensions are verified. Various pieces of information-such as batch number to provide a means of tracking the rotor in the future, minimum acceptable mass, and minimum rotor thickness-are printed on the metal hat. Anodized aluminum is generally used unless a drum-type parking brake is integral with the mounting hat, in which case that component is made of stainless steel.

8. Upon completion of all manufacturing and inspection steps, each rotor is wrapped and packed for shipment to the end user. Start to finish, the CCM manufacturing process takes a full week.

A few other CCM-related details that may enhance your appreciation of these ultra-high-performance brake components:

  • During an aggressive application of the brakes, the rotor temperature may rise to 1000-degrees C (1800-degrees F) before stabilizing in the 500-750-degrees C (900-1400-degrees F) range. The host vehicle must be carefully developed to route vast amounts of heat away from the spinning CCM rotors.
  • CCM has 85 percent higher thermal capacity than iron and more than twice the thermal radiance. But since it has less than one-third of iron’s density and only 40-percent of iron’s conductivity, the heat accumulation in a CCM rotor is far lower, a boon to braking efficiency. In essence, CCM heats up and cools off much faster than iron. Thermal and fluid mechanical analyses are used to configure a CCM rotor’s radial and lateral vent channels.
  • Brembo supplied the first ever CCM brakes for the Ferrari Enzo in 2002. Several thousand CCM rotors are currently manufactured per year.
  • Brembo has a monopoly in the CCM business. In 2009, it joined forces with SGL, the German-based manufacturer that supplies Porsche and others with CCM brake rotors made using processes similar to Brembo’s.
  • The brakes currently used by Formula One competitors are similar but different. F1 rotors are instead a carbon-carbon design using carbon-fibers bound together in a carbon matrix without the silicon material found in CCM brakes.
  • CCM rotors provide higher heat (fade) resistance, greater stopping torques, and significantly longer life than cast iron brake rotors. Their friction coefficient doesn’t change much with temperature. They are also about half the weight of iron rotors, a characteristic with three-fold benefits: Acceleration is enhanced because of CCM’s lower rotating inertia and because the car’s total mass is reduced. The lighter unsprung weight with CCM rotors yields handling gains.
  • CCM rotors do not corrode and their normal service life is nearly 100,000 miles according to Brembo. In racing use-such as Ferrari Challenge-their useful life is shorter but still more than a 1000 miles of flat-out running.
  • Roughly 60-percent of the technology used to develop Brembo’s CCM brakes during the past 15 years came from the highest levels of motorsports.
  • Brembo builds monobloc (one piece) brake calipers in aluminum to provide the desired stiffness with minimum weight. These aluminum castings are anodized for corrosion protection then coated with epoxy paint resistant to brake fluid and friction-material dust.
  • Because their brake rotors are smaller but still prominently visible and because they generally dissipate heat more rapidly, motorcycle brake rotors are made of stainless steel versus the cast iron preferred for non-CCM car applications.
  • CCM is obviously one of the most remarkable materials ever developed for automotive use. Manufacturing advancements should lower the cost of these highly effective braking systems to bring them within the reach of more high-performance models in the future.

Take one step forward to accept your (virtual) diploma because you are now a Brembo CCM brake rotor expert.