PURPOSE:To make the wall thickness of a finish pipe obtd. in reduction uniform by providing the clearance as much as the predicted amt. of the expansion in the outside diameter at the end of a hollow blank pipe with reduced thickness rolling of said pipe is offset between the inside diameter of the hollow blank material prior to the reduced thickness rolling and the outside diameter of a mandrel and suppressing the expansion in the outside diameter with the reduced thickness rolling. CONSTITUTION:The rear end of a hollow blank pipe 6 is fed 39 into the working center of a reduced thickness rolling device 12 for pipe end. A mandrel 13 and rolling rolls 14 are set respectively in rolling down positions. Driving devices 21, 28 for revolution and rotation are respectively operated to bring the rolls 14 into contact with the outside peripheral part at the end of the pipe 6 in the state of revolution and rotation. The amt. of expansion in the outside diameter at the end of the pipe 6 with the reduced thickness rolling by the mandrel 13 and the rolls 14 is predicted during this time, and a clearance as much as the predicted amt. of expansion is offset is provided between the inside diameter of the blank pipe 6 prior to the reduced thickness rolling and the outside diameter of the mandrel 13. The pipe 6 subjected to the rolling is thus negated of the amt. of expansion with the thickness reduction and the part which is not rolled by the rolls 14 is made approximately equal in the outside diameter to the part rolled by said rolls.
展开▼
