Stiffness and Leakage Characterization of Ceramic-Metallic Rope Seals

Ceramic-metallic rope seals are suitable for use in high-temperature and low-cycle displacement applications. This paper discusses performance aspects that need to be considered during seal selection such as the maximum load generated at assembly and during operation, seal resiliency and leakage performance for a given application. Extensive load-displacement and leakage tests are conducted on several candidate seals. Selected rope seals are of hybrid seal type consisting of ceramic fiber core along with an outer sheath of fine metallic wires. Test parameters include rope manufacturers, rope diameters, and combination of core/sheath materials. Testing is performed on as-received ropes as well as ropes that are heat-treated at temperatures over 1000°F. The load-displacement behavior is non-linear, hysteretic and varies with the number of loading cycles. The force generated by the rope at a given displacement decreases with increasing number of loading cycles for a given displacement. The ropes do not recover to their original size after the first cycle of compression, and the residual height decreases with increasing cycles. The seal behavior tends to saturate after about 5 loading cycles. The rope selection for a particular application needs to consider the saturating residual deflection and maximum force generated. Leakage testing was also performed for rope seals placed in a rectangular race-track type geometry. The seals demonstrate good leakage resistance under desired pressure conditions. The ropes with smaller diameters show the best leakage performance, but exhibit low spring-back.