Method for producing seamless tube with grooved inner surface

摘要

Disclosed is a producing method which allows low-cost and highly productive production of a seamless tube with a grooved inner surface having a smooth outer surface and an inner surface formed with plural types of grooves such that a protrusion is not formed at the produced seamless tube with a grooved inner surface. The tube is reduced in diameter by using a die and a plug. Then, the outer surface of the tube is pressed against a grooved plug by means of a pair of rolls such that a groove is formed in a portion of the inner surface of the tube. The process flattens the cross-sectional configuration of the tube in the direction in which the tube is pressed with the rolls. Subsequently, a sizing process using a die is performed with respect to the tube such that the tube has a generally circular configuration. Then, the outer surface of the tube is pressed against a grooved plug by means of another pair of rolls disposed such that the rotation axes thereof are orthogonal to the rotation axes of the rolls, whereby a groove is formed in a portion of the inner surface of the tube. Thereafter, the tube is subjected to a diameter reducing process using a die.