METHOD OF PLUGLESS CONTINUOUS LONGITUDINAL ROLLING IN MULTIPLE-STAND ROLLING MILL

The method of plugless continuous longitudinal rolling of tubes in the multiple-stand rolling mill relates to the field of production of seamless and welded pipes on the reducing and sizing mills. Successive deformation of billet in each i stand of the mill by shafts with calibers, at which the oval shape (?i) of the caliber of each i stand of mill is selected depending on the set values of partial relative reduction of billet along the diameter (mZi) in each i stand of the mill. Accordingly to invention one additionally sets width (Bi) of the caliber of each i stand of mill, and the oval shape (?i) of the caliber of each i stand of mill is selected depending on the radius of the bodies of rolls (Rui) of each i stand of mill in accordance with the ratio: , where - set partial relative reduction of billet along diameter in the stand with ordinal number i; Rui - assigned radius of body of roll in the stand with ordinal number i, mm; ? - current value of angle, which characterizes the positions of longitudinal section of the cell of deformation; - oval shape of caliber, which forms the rolls of stand with ordinal number i; Bi - set width of caliber in the stand with ordinal number i, mm; Hi - height of caliber with ordinal number i, mm; Di - mean diameter of caliber formed by rolls in the stand with ordinal number i (mean diameter of billet after rolling in the cage with the ordinal number i), mm; - mean diameter of caliber, which is formed by rolls in the stand with ordinal number i (mean diameter of billet after rolling in the stand with ordinal number i - 1), mm; w = 1,2,à,i-1 - ordinal number of cofactor (number of stand) in the multiplication ; N - ordinal number of stand, taking for i = 1 the first stand in the direction of the motion of rolling; N - total quantity of stands in the multiple-stand rolling mill of plugless continuous rolling of tubes; D0 - diameter of billet at the beginning of deformation in the multiple-stand rolling mill, mm; ; ; ; ; k - total quantity of rolls, which form caliber. The invention allows to reduce the middle relative transverse wall thickness variation of tubes for 1.03... 1.12 times and to reduce the longitudinal wall thickness variation of tubes for 4...15 %.