The Investigation Of Suitability Of Abradable Seal Materials For Application In Centrifugal Compressors And Steam Turbines.

Abstract

Clearances between sealing devices of rotating and stationary components of turbomachinery have always been important to engineers in controlling gas leakages. One way of accomplishing this is by the use of abradable seals which reduces clearances and limits the risk of damage to the rotating/stationary member if a rub occurs. The program presented evaluates various candidate abradable materials through performance in a test rig and the development of the final process parameters. The results of the tests indicated that for centrifugal compressor applications, the mica filled tetrafluoroethylene (TFE), silicone rubber, aluminum polyester and nickel graphite are all acceptable materials for abradable seals. Temperature limits were specified for each of these materials. For steam turbines, nickel chromium and nickel graphite are suitable and, again, temperature limits were specified. Application of abradable seals to centrifugal compressors has shown efficiency improvements of up to 0.5 percent per stage for high flow machines, and up to 2.5 percent per stage for low flow machines. Performance improvements in excess of two percent have been calculated for noncondensing steam turbines utilizing abradable materials in shaft end packing, blade tip and stage diaphragm seals.