摘要 |
PURPOSE:To obtain a blank pipe free from flaw and wall-thickness deviation by specifying the gap between guide rolls, the dimensions of the grooved-bottom corners of roll, and the speed ratio based on a prescribed definition, at each stage, in forming the corners of a blank material having square cross section by a four-roll guiding device. CONSTITUTION:In forming the corners of a blank material having square cross section by plural sets of four-roll type roll guides and restrictingly guiding the material at the inlet just before a piercer; the gap between guide rolls 9 at each stage is gradually decreased from a guide at the 1st stage so as to make the roll gap at the guide of final stage equal to the cross sectional dimension of blank material, and the corner R of grooved bottom of the guide roll 9 at each stage is gradually increased from the guide at the 1st stage to make the grooved bottom R of roll at the final guide equal to the prescribed corner R of grooved bottom, and further the speed ratio (alpha) defined by VR=alpha.lambda.VP(VR: roll peripheral speed, lambda: elongation, VP: speed of pusher) is fixed within a range of 0.9-1.3. In this way, a blank pipe free from rubbing-down and wall-thickness deviation is obtained. |