FM 1-506 Fundamentals of Aircraft Power Plants ... - Survival Books

WWW.SURVIVALEBOOKS.COMFM 1-506holding the metals at that temperature longenough to produce a solid solution of the hardeningcomponents in the alloy. This is followedby rapid quenching to retain theproduced condition.Hardening– involves heating the metal to atemperature above the critical range and thenquenching The cooling rate will determinehardness.Tempering– steel is usually too brittle for useafter quenching. Tempering restores some ofthe ductility and toughness of steel at thesacrifice of hardness or strength. The process isaccomplished by heating the hardened steel to aspecific point below the critical temperature,holding it at that temperature for a specifictime, and then cooling material in a controlledarea.Nonmetallic MaterialsTeflon, nylon, carbon, rubber, Bakelite, and a host ofplastic materials are used in the gas turbine engine mainlyas sealing and insulation materials. For example, nylonand Teflon are used to insulate and protect the shieldedelectrical wiring located on the outside of the engine.Teflon is also used on the J-79 F4 Phantom engine for thesealing the variable- stator-vane actuators. Carbon isused largely inside the engine in the form of carbonrubbing seals. Some of these “face” carbon rubbing sealsmust be flat to within two helium light bands, or approximately23 millionths of an inch Rubber and rubberizedfabric materials makeup the sealing edge of thefire seal which divides the hot and cold sections of theengine when mounted in the nacelle. Synthetic rubber isused extensively throughout the engine in the form ofO-rings or other shaped seals.3-31