ABSTRACT
One of the earliest uses of manufactured carbon in mechanical devices was as piston rings for nonlubricated compressors. For many years manufactured carbon was the only material used in this type of compressor. Since 1960 there has been growing use of carbon-filled PTFE rings for low-pressure, low-temperature applications. Carbon remains the preferred material in applications where the fluids or the surrounding environment are loaded with abrasive dust or grit. The seal ring on an aircraft hydraulic actuator where the extended rod is exposed to grit illustrates this type of application. The segmental piston ring with its steel expanders is a relatively expensive assembly of parts and requires painstaking care to properly match segments during installation. During compression when the piston with its installed ring is slid into the cylinder, the outermost fibers are placed in tension. Solid metal pistons are generally used with carbon-lined cylinders.
