PURPOSE: To enable a high expansion rolling with a high roundness by making the radius of curvature a single value around the pass line on the shoe face of a guide shoe at each position in the direction along the pass line of the guide shoe.
CONSTITUTION: A plug 12 is arranged on a pass line between a pair of cone shaped rolling rolls 11, and a pair of guide shoes 13 are arranged on both sides of a rolling zone held by the pair of rolling rolls 11. At each position in the direction along the pass line of the guide shoes 13, a single value is set for the radius of curvature Rs around the pass line of the shoe face, in the width area of 2/3 or more of the entire width Wi in the half part of the entrance side where a tube stock 1A enters against the center point in the width direction of the shoe face of the guide shoe (Wix≥2/3W1), and in the width area of 1/2 or more of the entire width W. in the half part of the exit side where the tube stock 1A exits against the center point in the width direction of the shoe face (Wox≥1/2Wo). Consequently, a high expansion rolling is possible with a high roundness by avoiding the lowering of the roundness caused by the flaring of the rolling stock.
SHIMIZU TETSUO
TOYOOKA TAKAAKI
