. Transactions. Fig. 8.—Four-blade, 18-ft. pitch, bthlt-up wheel of steamer Mystic. stand developed no variation in balance. It is one wheel of a twin-screwinstallation on the steamer Herman Frasche. Metal Used in Propellers In propellers used in the Navy, manganese bronze, having an ultimatestrength of 70,000 to 80,000 lb. per sq. in. and an elongation of 20 to 35per cent, is specified. For commercial use many wheels have been made of semi steel. In thecase of thirty such wheels, the lowest ultimate strength was 32,555 lb. ENRIQUE TOUCEDA 543 per sq. in., the highest 42,175 lb. per sq. in.; w
. Transactions. Fig. 8.—Four-blade, 18-ft. pitch, bthlt-up wheel of steamer Mystic. stand developed no variation in balance. It is one wheel of a twin-screwinstallation on the steamer Herman Frasche. Metal Used in Propellers In propellers used in the Navy, manganese bronze, having an ultimatestrength of 70,000 to 80,000 lb. per sq. in. and an elongation of 20 to 35per cent, is specified. For commercial use many wheels have been made of semi steel. In thecase of thirty such wheels, the lowest ultimate strength was 32,555 lb. ENRIQUE TOUCEDA 543 per sq. in., the highest 42,175 lb. per sq. in.; while the average was 36,658lb. The breaking of propeller blades has not been uncommon; in mostcases this has been attributed to lack of perfect balance. It is notunusual for an 18-ft. wheel to have a tip speed of over 5500 ft. per the use of this method, the following features can be guaranteed:The diameter will be a true circle; blade angle wall be accurately estab-. FiG. 9.—Three-blade, built-up, maxganesebkonze propeller. lished; pitch will be absolutely uniform; blade thickness will be correctto design; balance will be true in any position of wheel; more promptdelivery can be assured. From the foregoing there must result greaterspeed for same power, lower repair cost, fewer replacements, and moreship-service days. 544 THE ELECTRIC FURNACE IN THE IRON FOUNDRY The Electric Furnace in the Iron Foundry By Richard Moldenke, E. M., Ph. D., Watchung, N. J. (New York Meeting, February, 1921) One of the gravest problems of the iron foundry today is the accumu-lation of suKur in commercial scrap and its effect on the castings madetherewith. The ordinary jobbing castings today show a sulfur contentof per cent., and occasionally as high as per cent. The productof the foundry during the war is undoubtedly to blame for this rapidincrease and conditions will become worse as the millions of tons of gray-iron castings of the war period return to the
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