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A survey of experience in a large fleet of ships and a literature survey suggested that a cause of thrust pad wear in service, which could also contribute to wire-wooling when other necessary conditions were present, was low oil pressure in thrust housings. The effect of low oil pressure, which is intensified by aeration of the oil, is to allow intermittent failure of the oil film. Laboratory tests showed that such intermittent failure could initiate wire-wooling. Experience indicated a complicated interaction between steel quality and oil quality. It had been suggested that this variation might be a result of differences in carburizing susceptibility, but special tests indicated no significant effect. Failures were simulated in a full-scale turbine thrust bearing rig by partly embedding ferrous particles in the white metal. Tests indicated that particles had to be greater than 0.020 in. to initiate failure. Investigations on the rig with different oils and different steels indicated that steels with greater than 1 per cent chromium required an EP oil to prevent wire-wooling. Detailed examination of an EP oil which prevented wire-wooling of a low chrome steel when unused but allowed failure after it had been used, showed that the difference in behavior was caused by depletion of a highly polar sulfur-containing compound.
turbine, thrust bearing, ship, steel, lubrication, chromium, wear, evaluation
Evans, E. M.
Scientist, Thornton Research Centre,
Fowle, T. I.
Senior technologist, Shell International Petroleum Co. Ltd., London