Carbon ceramic brakes have a far higher operating temperature and are 50% lower mass compared to classic iron discs.
What are carbon ceramic brakes and how are they made?
Ceramic discs are more frequently optioned on high-performance sports and hyper cars. British engineers demonstrated the first application for TGV in 1988. The objective was to reduce weight and provide stable friction from high speeds. Carbon-fibre-reinforced ceramic brakes are also used in aircraft brake applications.
The carbon fibre is mixed with an epoxy binder and silicon and pressed into a mould. This is baked at high temperatures. The furnace removes the oxygen and the silicon amalgamates with the carbon resulting in silicon carbide. Additional coatings are often applied to prevent oxidation and corrosion.
Advantages of carbon ceramic brakes (Porsche and BMW)
Porsche’s Composite Ceramic Brakes (PCCB) are siliconised carbon fiber, with high temperature capability, a 50% weight reduction over iron discs. This reduces the vehicle’s unsprung weight and a significant reduction in dust generation. Found on some of their more expensive GT models, it is also an optional brake for all base Porsches. They are distinguished by bright yellow calipers. The discs are internally vented much like cast-iron ones, and cross-drilled.
The Brembo/BMW Carbon Ceramic Brake offers even greater efficiency in comparison to the OEM BMW kit.
Features & benefits ceramic brakes
- Greater wear-resistant and therefore replacement intervals are less frequent
- Braking performance under extremely high stress and a relatively high coefficient of friction
- Higher, extreme temperatures are possible due to the heat resistance
- Greater than 55% lighter than conventional brake discs. Reduced unsprung mass assists the dynamics
- Improved resistance against a decreasing braking effect (fade) due to a high thermal load
- High corrosion resistance
Brembo – leading manufacturer of carbon based brakes
Brembo has been leading the production and manufacture since 2002, pioneering the concept for Ferrari on their flagship, Enzo.
A unique blend of powders, resins and fibres all part of a very sophisticated manufacturing process, used since the 1970s for aerospace. At the turn of the century, a diversification into high end sports cars and motorsport opened up new markets. In 2004, Brembo were awarded The Golden Compass prize by the Italian Industrial Design Association.
In June 2009, Brembo agreed a JV with SGL, aiming to further the developments for the passenger car and commercial vehicle OEM markets. Brembo SGL Carbon Ceramic Brakes supplies components to all of the major marques in automotive including; Ferrari, Maserati, Alfa Romeo, Aston Martin, Bugatti and AMG.
How much do carbon ceramic brakes cost?
Organic brake pads
Asbestos, a heat-absorbing material was an original brake pad structural component but the later discovery of links to cancer has made this obsolete. Asbestos-based brake pads would wear down over time, releasing asbestos into the air.
Organic brake pads are a mixture of fibers, rubber, carbon compounds, fiberglass and Kevlar and are bound by resin. They tend to produce less dust than metallic ones and are often cheaper to manufacture. These pads generate a moderate amount of friction without much heat being present and are quiet. They are cheaper to repair. They also tend to function best within a smaller range of temperatures, meaning they don’t work as well in extreme weather or when they are being pushed too hard and overheat.
Ceramic brake pads
Ceramic brake pads are denser and more durable. Ceramic brake pads also have fine copper fibers embedded within them, to help increase their friction and heat conductivity. Ceramic brake pads are quiet and produce less dust and other particles over time as they wear down. These are much more reliable in a wider range of temperatures and driving conditions.
As ceramic and copper can’t absorb as much heat, the heat generated by braking will pass into the rest of the braking system. This can cause more wear and tear on other braking components.
Metallic brake pads
Metallic brake pads are comprised of anywhere between 30% and 70% metals including copper, iron, steel, or other composite alloys. These various metals are combined with graphite lubricant.
Racing applications prefer the metallic brake pads because they offer improved braking performance in a much wider range of temperatures. Metals conduct heat and are able to withstand more heat while simultaneously helping braking systems cool back down more quickly. They tend to produce more brake dust than the other two varieties as well. Metallic brake pads are at the mid price point compared to organic and ceramic pads.
Brake disc disadvantages and common problems (all materials)
Damage and wear occurs from scarring, cracking, warping or excessive rusting. Most leading vehicle manufacturers recommend brake disc skimming as a solution for lateral run-out, vibration issues and brake noises. The machining process is performed in a brake lathe, which removes a very thin layer off the disc surface to clean off minor damage and restore uniform thickness.
Brake disc run-out
Run-out is measured using a dial indicator on a fixed rigid base, with the tip perpendicular to the brake disc’s face. The difference between minimum and maximum value is lateral run-out. Discs can be machined to eliminate thickness variation and lateral run-out.
The majority of brake discs diagnosed as warped are actually the result of uneven transfer of pad material, leading to thickness variation of the disc. When the thicker section of the disc passes between the pads, the pads will move apart and the brake pedal will raise slightly, often termed pedal pulsation.
This can result in changes to the crystal structure of the metal that composes the disc. As the brakes are applied, the pads slide over the varying disc surface. As the pads pass by the thicker section of the disc they see higher levels of stress. This causes uneven heating of the surface of the disc. As the brake disc heats unevenly it also expands unevenly. The uneven distribution of heat results in further uneven transfer of pad material. The result is that the thicker-hotter sections receive even more pad material than the thinner-cooler sections, contributing to a further increase in the variation in the disc’s thickness. When the hotter sections of the discs reach extreme temperatures, the metal can undergo a phase transformation and the carbon which is dissolved in the steel can precipitate out as cementite. It is extremely hard, brittle, and leads to the integrity of the disc being compromised.
Brake pad scarring
Once enough of the friction material has worn away, the pad’s steel backing plate or the pad retainer rivets (for riveted pads) will bear upon the disc’s wear surface, reducing braking power and making scratches on the disc. If the scarring is deeper but not excessive, it can be repaired by machining a layer of the disc’s surface. This can only be done a limited number of times as the disc has a minimum rated safe thickness.
Cracking is limited mostly to drilled discs, which may develop small cracks around edges of holes drilled near the edge of the disc due to the disc’s uneven rate of expansion. A brake disc is a heat sink, but the loss of heat sink mass may be balanced by increased surface area to radiate away heat. Small hairline cracks may appear in any cross drilled metal disc, but in the severe case the disc will fail. These cracks occur due to the phenomenon of low cycle fatigue as a result of repeated hard braking.
Most discs are commonly made from cast iron and a certain amount of surface rust is normal. Rusting can lead to disc warping. Vented brake discs may develop severe rust corrosion inside the ventilation slots, compromising the strength of the structure and needing replacement.
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