C/C-SiC Composites For High Performance Emergency Brake Systems

Kurzfassung

In co-operation with an industrial manufacturer of brake systems (Mayr-Antriebstechnik) DLR has investigated new designs of Ceramic Matrix Composites (CMC) for their use in high performance emergency brake systems in fields of mechanical engineering and conveying. These electromagnetic spring applied brakes for braking or holding loads, operate as important safety elements in case of a power failure or an emergency "OFF" situation. The brake system consists of a rotating and two stationary brake disks similar to the heat pack of aircraft brakes. Increasing drive and higher circumferential velocities in modern power transmission necessitate new concepts for emergency brake systems. Conventional emergency brakes with metallic disks and organic friction linings are inapplicable for extreme power input due to the insufficient thermal stability of these braking materials. The use of Carbon/Carbon composites (C/C) for high performance and extremely weight sensitive brake systems is state-of-the-art for aircraft and racing cars. However, C/C composites show high wear rates and an instability of their coefficient of friction caused by humidity and temperature. Long manufacturing times, multiple reinfiltration steps and expensive raw materials lead to very high prices for the finished C/C brake disks. These disadvantages have prevented their application in commercial brake systems like vehicles or mechanical engineering components. By using CMC brake disks, these technical disadvantages of C/C can be avoided and the efficiency and the lifetime of emergency brake systems can be increased. These so called C/C-SiC composites offer high coefficients of friction and low wear rates even at temperatures above 1000 °C. Due to the high friction energy and the resulting high temperatures while braking, the conventional construction of the emergency brake system was modified and adapted to the new C/C-SiC braking material. In various screening tests, different C/C-SiC qualities were tested to get the best compromise of friction and wear behaviour. Presently, emergency brake systems equipped with these new materials are being tested in field trials. In summary, the paper presents the successful development of new C/C-SiC composite materials for a commercial application by substituting conventional materials and the adaption of the brake system to the new requirements, resulting in an advanced braking system of improved tribological characteristics for high performance applications.