Engineering of CMC Tubular Components

Kurzfassung

Tubes of different sizes and shapes are used as a transportation devices for gases and liquids or as structural components for the design with high complexity. At normal conditions mate-rials like metals or CFRP meet the requirements, but their application is restricted at high temperature or in severe chemical surroundings. In contrast to these materials tubular compo-nents made of ceramics, especially CMC, can be used in the environment of high-temperature (> 1000 °C) combined with corrosive gas atmosphere. The CMC composites offer a new ap-proach for the development of a new generation of heat exchangers (HE) [1-3]. This material is currently investigated as an alternative to conventional material. Steel has a high heat re-sistance but shows a loss in strength at elevated temperatures. Monolithic SSiC ceramics are too brittle so that failure by critical crack growth can occur [4]. In contrast to this behaviour C/C-SiC shows an improved strength at elevated temperatures and a high damage tolerance [5]. HE are developed for power production and for the recovery of process heat. Industrial process heat is mainly formed in iron or steel manufacturing or in coal fired plants but also during the waste treatment. Due to the applications and conditions the design varies and com-prises open and closed tubes or tube-in-tube arrangements. The ceramic tubes are always used as the core element of the HE which must often be ceramically bonded together. Tube-to-tube joinings have been already realized in the carbonized or in the ceramic state [6]. For the manufacturing of C/C-SiC tubular components with different size, shape and ge-ometry and the construction of a HE thereof the LSI-processing can be used. The processing steps comprise CFRP manufacturing, pyrolysis and final siliconization. Joining experiments with components were conducted in order to obtain closed structures. Two different process-ing routes for making CFRPs have been investigated: the compression moulding (CM) as well as the resin transfer moulding (RTM) technique. The material properties of tubes made from both routes as well as the influence of different wall thicknesses versus the strength are re-ported.