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SOME FACTORS AFFECTING SPHERICAL TYPE MACRO-GAS POROSITY IN 85-5-5-5 BRONZE

2343
Journal: Transactions of the American Foundrymen's Society V 61 P 327-346, 1953 (20 p)
Author: Fischer, R B

The effect of mold materials, binders and coatings on the liberation of gas in S5-5-5-5 bronze when poured into dry sand mold cavities was investigated. Melting methods, degassifying and deoxidizing practices were also studied. The observations were made on a specially designed casting and the results recorded by photograph. More than 250 test castings have been examined. Spherical type macro-gas porosity has been observed on 85-5-5-5 bronze poured into oil bonded silica sand molds. Gassing is the result of a metal-mold reaction or direct absorption of gas which is liberated upon solidification of the metal. Many commercial sand binders were tested. Ounce metal poured in pitch-bonded molds showed no spherical type macroporosity. Cement bonded and natural sand molds produced castings practically free of the macro-gas porosity. Molds made with phenolic, urea, wood resins, etc., gassed ounce metal to various degrees of intensity. Graphite coatings containing pitch and a special coating containing zircon filler in a resin-volatile solvent vehicle inhibited or reduced the gas porosity. These coatings gave poorer casting surfaces. Lithium was found to be an effective degassifier but was characterized by higher metal shrinkage. Deoxidizers were tested and their relation to shrinkage is shown on a special test cast ing. Metal composition also influences macro gas-porosity.



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