METAL FORMING DURING PIPES REDUCTION ON A THREE-HIGH ROLLING MILL

 Pipe rolling plants (PRP) with three-high screw rolling mills are  used to produce hot-rolled seamless pipes. In Russia, two such rolling  units are used: PRP 160 at Pervouralsk Novotrubny Plant and PRP  200  at Volzhsky Pipe Plant. Recently, the most acute issue is increasing their  technological capabilities. There is a need of expanding size and grade  mix, as well as non-traditional use of gauge and rolling mill for screw  rolling. The paper presents results of experimental study of the process  of reduction or un-adjusting rolling of pipes on three-high screw rolling  mills with an increase in reduction of diameter up to 25  %. The results  of computer finite element modeling in QFORM program are provided.  The aim of this work was to study effect of rolling process with increased  reduction in diameter on change of metal form in deformation zone and  changes in geometrical dimensions at reduction of cups with different  wall thickness on the pilot mill. Important role in process of metal forming during screw rolling (especially when rolling hollow products and  pipes) plays cupped blank ovality that is equal to the ratio of the roll  radius when the metal comes in contact with the roller to the radius under  the roller in the cross section of deformation zone. Ovality characterizes  stability of change in geometric dimensions of pipes and their resistance  to deformation in inter-roll space. The reduction of thin-wall cupped  blank is accompanied by large va lues of ovality, deformation process is  less stable, and as a result, form defects (faceting) and end defects occur  during plug rolling. Ovality at plug rolling increases more intensely in  comparison with plugless rolling. Presence of plug limits displacement  of metal in axial direction and contributes to displacement of metal in  gaps between rollers. At plugged rolling, it is necessary to use rolls with  collars allowing main reduction along the wall, thereby localizing reduction zone on the plug, and reducing ovality of cupped blanks.

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