Manufacture of cast iron

Claim 1

IN THE ART OF MANUFACTURING GRAY CAST IRON IN WHICH THE UNCOMBINED CARBON APPEARS PREDOMINANTLY IN FLAKE GRAPHITE FORM, THE IMPROVEMENT WHICH COMPRISES INJECTING FINELY DIVIDED CALCIUM CARBIDE INTO A MOLTEN HYPOEUTECTIC CAST IRON COMPOSITION, CONTINUING SAID INJECTION UNTIL THE CHILL OF THE RESULTING TREATED IRON, AS MEASURED BY THE DEPTH OF THICKNESS OF THE WHITE IRON IN A CHILL TEST PIECE, IS SUBSTANTIALLY REDUCED OR SUPPRESSED, AND CASTING THE RESULTING TREATED IRON TO PROVIDE A CAST PRODUCT CONTAINING UNCOMBINDED CARBON PREDOMINANTLY IN FLAKE GRAPHITE FORM AND WHICH IS SUBSTANTIALLY FREE OF NODULAR GRAPHITE AND ELEMENTAL CALCIUM, SAID PRODUCT BEING CHARACTERIZED BY IMPROVED MACHINEABILITY WITHOUT REDUCTION IN TENSILE STRENGTH.