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The ignition of metals and alloys have been investigated by rotating the end of a hollow cylinder against an identical stationery cylinder on a common axis (frictional heating) in gaseous oxygen. A ranking criterion that measures the resistance of metals and alloys to ignition is discussed. It consists of the power per unit area required for ignition, conveniently expressed as the product of contact pressure P and average linear velocity ¯v. Data are presented that demonstrate that materials that are high in nickel and copper require greater Pv products for ignition (more resistant to ignition) than materials that are high in iron. Aluminum and titanium alloys are shown to require the lowest Pv products for ignition. The effects of varying surface velocity, contact pressure, coefficient of friction, and oxygen pressure on P¯v products required for ignition are discussed. The results indicate that P¯v product required for ignition increases as surface velocity increases, as contact pressure decreases, and as the coefficient of friction decreases. Increasing oxygen pressure will cause the P¯v product required for ignition to decrease at low pressures and increase at high pressures. In some cases, the relative ranking of materials based on P¯v products will also change as conditions are varied.
The data presented in this paper are from a development program to determine the merits of using such a dynamic test method for ranking materials for oxygen service. The results to date have indicated that more testing is required before this method can be made into a standard test. The data presented do show some of the major parameters affecting the ignition of materials when exposed to frictional heating. The repeatability of the data at any set of conditions have not been throughly investigated.
ranking, carbon steels, stainless steels, copper alloys, nickel alloys, brasses, aluminum alloys, titanium alloys, friction ignition, oxygen compatibility, ignition criteria
Materials engineer, NASA/JSC White Sands Test Facility, Las Cruces, NM
Engineer, Lockheed-EMSCO, White Sands Test Facility, Las Cruces, NM