| 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 type 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 side just before a piercer; every gap between guide rolls 9 at each stand is made equal to the dimension of blank material, and the corner R of grooved bottom of guide roll 9 at each stage is made equal to the R corresponding to every corner R of the prescribed cross section of blank material, and further the speed ratio (alpha) defined by VP=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 flaw and wall-thickness deviation is obtained. |
