Abstract: Analyzed here in the paper are the causes for development of defects like porosity，sand inclusion，and sink of the coned drum asmade with conventional vertical centrifugal casting process.Accordingly，the casting mould of the conventional vertical casting process ismodified by means of adding the sand core.Result of the actual operation shows that thanks to addition of the sand core to the castingmould，the machining allowance of the coned drum is properly controlled，and thus the process yield is enhanced.Moreover，the coned drum it self as castwith the modified mould is free of weld seam，and defects like porosity，sand inclusion and sink.This modified vertical centrifugal casting process is capable ofmeeting the requirement for making seamless coned drum to be used under special service conditions.