Study On The Performance Of C/C Composites Used As Rolling Seal

Carbon/Carbon (C/C) composites possess a series of excellent performances of low density, high strength, high heat conductive, proper friction coefficient and little bulk wear loss, well-processed and designed, et al., and much progress has made as aircraft brake material. Currently C/C composites are mostly opened up as seal device of airplane engine. Because the graphite materials have low strength and high open hole ratio, they must be infiltrated with pitch, resin or low melting point metal before using. Though the graphite materials can be used for a long time, it will not satisfy requirement with the development of hydraulic pressure technique and dynamical mechanism which require seal materials more and more highly, especially used in high velocity, high temperature or erosion condition. Because of possess of excellent performances, C/C composites become the preferred seal materials at this environment. However, the researches of C/C composites are concentrated in airplane brake, little for rolling axis seal at present. Because the process of seal and brake is greatly different, either is the require to materials, the author prepared several types of C/C composites of different performances with the process of chemical vapor infiltration (CVI), resin Infiltration/Carbonization and CVI+Infiltration/Carbonization, discussed the feasibility that C/C composites are used as rolling seal and studied the performances and influence factors of slip friction and abrasion, seal performances and erosion performances.The effect of densified process, density, rigidity(HRF) and the structure of basic coal and load and time on the behavior of slip friction and abrasion of C/C composites had been investigated. The results show that the composites, which had been densified to over 1.75 g/cm~3 by CVI +I/C, hold excellent friction and wear behavior. The samples of high density form the whole scrape film, its friction coefficient is low and stable and bulk wear loss is little. With rigidity(HRF) increasing, its bulk wear loss decreases. The C/C composites of the structure of RL/SL+resin coal have low and stable friction coefficient and little bulk wear loss. The friction coefficient decreases a little and bulk wear loss increases with load increasing, and the friction coefficient become stable and bulk wear loss increases gradually with time increasing. In contrast to STM900graphite, the friction coefficient and bulk wear loss of the self-prepared samples are all low. The observation of SEM shows that there is more velvet and integrated scrape film on the surface of the samples which have low and stable friction coefficient, however, there is uneven thick, half-baked and cumulate scrape film and surface of basic coal and fiber separated and fiber warped on the surface of the samples which have bad friction performances.The tests of rest pressure leakage in room temperature and rolling seal operation show that no leakage in rest pressure can be realized by infiltrating resin to C/C composites; C/C composites can be expected to realized no leakage By CVI in longer time. After operation test, the samples keep intrinsic figure and size, there is no desquamation, crack, laceration and impress on the interface and the friction samples are no damaged holisticly. The trace of grinding grain abrasion is observed on the surface of graphite and the bulk wear loss of the samples of graphite is greater, and the bulk wear loss of the C/C composites of high density is smallest. The SEM of samples after rolling seal operation shows that the friction section of C/C composites of high density is lubricous and integrated, and scrape is of piece, and good boundary lubrication state is formed with scrape and liquid medium.The same C/C composites have the most weight loss at aqua regia (room temperature). In the same erosion medium, the resin coal is eroded earlier than pyrogenation coal, moreover, the rate of erosion of the former is faster. After the erosion of aqua regia (room temperature) or 30% HNO3 solution (100°C), the resin coal is no longer continuous and becomes many bits, and pyrogenation coal is separated with fiber, and the holes of erosion appear among pyrogenation coal; After the erosion of 30% HNO3 solution(room temperature), the continuity of resin coal is destroyed, and pyrogenation coal is partially separated with fiber; After the erosion of 15% HNO3 solution(room temperature), resin coal is eroded clearly, but it is continuous yet, phenomenon of separating between pyrogenation coal and fiber are observed rarely; After the erosion of 40% NaOH solution(100°C), the erosion of the resin coal and pyrogenation coal is observed rarely.