Sounds like alchemy
What would happen if there were a brake that functioned nearly as well as a ceramic brake and had the same thermal stability but cost only about one-third as much, didn’t need racing pads, showed much less wear than a conventional gray-iron brake, produced hardly any brake dust, and didn’t rust? That sounds like alchemy—yet it’s serious technology from Porsche. “But believe me, it was a long road getting here. Otherwise we would have offered it ages ago,” says Leber. Amazing developments don’t just fall from the sky. They’re the product of dedicated development work.
New technology developed for racing is often transferred to road vehicles. One example would be the Porsche Ceramic Composite Brake (PCCB), which is a master at deceleration and the absolute benchmark in its field. Modern gray-iron brakes are no slouch either. But there was a need for a hybrid of these two types—for those especially powerful Porsches that don’t necessarily hit the racetrack every day. The solution was obvious to Leber and his team: a carbide coating. For why shouldn’t tool steel with a century-long track record work just as well for a brake disc?
PSCB—a global first
Simply put, a brake disc made entirely of tungsten carbide would cost as much as several sets of ceramic brakes. Moreover, the technology wasn’t sufficiently advanced to bind tungsten carbide to a substrate—such as gray iron. But following a lengthy series of tests in close collaboration with Bosch/Buderus, Porsche made a breakthrough. A gray-iron disc was laser-processed to offer structure, then galvanized with an interlayer. The interlayer acts like a flexible bond to relieve the differential thermal extension of gray iron and tungsten carbide, which is then applied in a spectacular manner: a high-velocity oxy-fuel spraying process shoots tungsten carbide particles at the disc at supersonic speeds. For a moment, it looks like a Star Wars lightsaber is firing around the disc. The result is a coating around one hundred micrometers thick—but it still doesn’t do the trick on its own. Now what it needs are very special brake pads.
Searching for the right composite
“The pads required at least as much development effort,” says Leber. Laser technology and high-precision, automated production processes for a new type of disc are one thing. Pads with the right composite are another. A surface as smooth as a mirror needs a special pad that’s adhesive. Imagine running your finger with light pressure over a mirror; it doesn’t slide uniformly but instead keeps sticking for an instant. However, an overly soft pad on a very hard surface would wear down too quickly at high disc speeds. So the engineers added some very hard materials to the pad: microscopic particles that penetrate the tungsten carbide coating. These pads positively cling to the disc.
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