PURPOSE: To locally decarburize the centrifugally cast pipe by blowing oxygen for a prescribed period of time in the molten ductile cast iron cast into the inside surface of a rotating centrifugal casting mold before the molten metal solidifies.
CONSTITUTION: The melt 7 of the ductile cast iron is cast into the inside surface of the centrifugal casting mold 1 while the mold 1 is kept rotated. An oxygen supplying means (oxygen lance) 8 is inserted into the mold 1 before the molten metal 7 solidifies. The oxygen supplied from the oxygen supplying means 8 is then acted for a specified period of time to the molten metal at both ends of pipe to remove the C in the molten metal 7 near both ends of the pipe. The quantity of the C at both ends of the cast pipe is decreased in this way and job site welding work is facilitated. The usefulness of the piping operation of the ductile cast iron pipe is thus improved.
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