METHOD OF MAKING STRAIGHT-SEAM ELECTRICALLY WELDED LARGE DIAMETER TUBES FOR TRANSPORTING ABRASIVE LOOSE MATERIALS AND PULPS AND APPARATUS FOR PERFORMING THE SAME Russian patent published in 1997 - IPC

FIELD: tube production, namely manufacture of large-diameter electrically welded tubes with oriented single-side wall thickness difference for transporting abrasive loose materials and pulps. SUBSTANCE: skelp sheet with thickness variable along its width is used as tube blank; thickened portion oriented along generatrix of tube is arranged in mean part of said sheet or near its edges. Thickness of sheet in zone of said thickened portion exceeds at least by 1.5 times nominal sheet thickness. Width of said thickened portion is determined according to given relations. As edge planed tube blank is guided to edge bending mill or press for bending up its edges in accordance with tube radius. Diameter of cylindrical portion of upper bending discs is selected in dependance upon shape of said blank and size of thickened portion of sheet. Sheet with bent up edges is fed to preshaping hydraulic press for bending central portion of sheet by means of punch. Radius of cylindrical portion of said punch is selected in dependance upon type of used blank. Then in finally shaping press semifinished product is shaped to tube to be fed to outer welding mill. Distance between centers of rollers of inner mandrel of said mill and distance between centers of rolls of vertical non-driven and horizontal driven stands are selected while taking into account size of said thickened portion of sheet. Welded tube is subjected to expanding in hydraulic press in which tube end portions are calibrated by means of calibrating cones and then tube is hydraulically expanded by diameter. Said calibrating cones have variable profile. At placing tube in hydraulic press it is oriented in such a way that profiles of said cones and profiles of tube end portions are coincided. EFFECT: enhanced efficiency, improved arrangement of units. 4 cl, 13 dwg