Tube rolling plant

Abstract

The present invention teaches rolling a seamless tube, typically with a large diameter. The system comprises a furnace for heating billets produced by continuous casting. The system comprises a piercing mill for longitudinally piercing the heated billets to obtain a pierced blank. The system comprises an expanding-elongating mill for expanding the pierced blank diameter and for elongating the pierced blank to obtain a semi-finished tube. The system comprises a continuous main rolling mill with adjustable rolls for mandrel-rolling a semi-finished tube. The system comprises a fixed-roll extracting-reducing mill positioned downstream of the main rolling mill. The extracting-reducing mill extracts the semi-finished tube from the mandrel, reducing the diameter to a predetermined value close to that desired for the finished tube. The system comprises an adjustable-roll sizing mill to adjust the radial position of the rolls and define the diameter of the outgoing tube.

What is claimed is: 
     
         1 . A system for rolling a seamless tube, the system comprising:
 a furnace for heating a billet, the billet produced by continuous casting;   a piercing mill for longitudinally piercing the billet to produce a pierced blank;   an expanding-elongating mill for expanding the diameter of the pierced blank;   the expanding-elongating mill for elongating the pierced blank to produce a semi-finished tube;   a continuous main rolling mill for rolling the semi-finished tube with a retained mandrel, wherein the continuous main rolling mill includes a first plurality of rolls, each of the first plurality of rolls having adjustable radial positions;   a extracting-reducing mill positioned downstream to the continuous main rolling mill, wherein the extracting-reducing mill includes a second plurality of rolls, each of the second plurality of rolls having a fixed radial position, further wherein the extracting-reducing mill is configured to extract the semi-finished tube from the mandrel and reduce the diameter of the semi-finished tube to a value that is proximate to a first desired final diameter of a completed version of the semi-finished tube;   a sizing mill positioned downstream to the extracting-reducing mill, the sizing mill including a third plurality of rolls, each of the third plurality of rolls having adjustable radial positions, the sizing mill configured to calibrate the diameter of the semi-finished tube to a value that is proximate to a second desired final diameter of the completed version of the semi-finished tube; and   a cooling bed;   wherein the system includes a by-pass line for directing the pierced blank produced in the piercing mill to the continuous main rolling mill, whereby the expanding-elongating mill is not utilized for rolling the seamless tube.   
     
     
         2 . The system according to  claim 1 , wherein the piercing mill includes an ogive-shaped plug and a fourth plurality of rolls, each of the fourth plurality of rolls rotating about their respective axes in a radial position relative to a rest of the fourth plurality of rolls. 
     
     
         3 . The system according to  claim 1 , wherein the expanding-elongating mill includes an ogive-shaped plug and a plurality of variable-conicity rolls, each of the plurality of variable-conicity rolls rotating about their respective axes in a radial position relative to a rest of the plurality of variable-conicity rolls. 
     
     
         4 . The system according to  claim 1 , wherein a function of the piercing mill and a function of the expanding-elongating mill can both be performed in a general mill, the general mill including an ogive-shaped plug and a fifth plurality of rolls, each of the fifth plurality of rolls having adjustable radial positions, the ogive-shaped plug having an adjustable form, wherein the general mill has a plurality of configurations based on the radial positions of the fifth plurality of rolls and the form of the ogive-shaped plug, wherein a first particular configuration of the general mill can be utilized to perform the function associated with the piercing mill, further wherein a second particular configuration of the general mill can be utilized to perform the function associated with the expanding-elongating mill. 
     
     
         5 . The system according to  claim 1 , wherein the continuous main rolling mill includes a plurality of rolling stands, each rolling stand including a sixth plurality of rolls. 
     
     
         6 . The system according to  claim 1 , wherein the continuous main rolling mill includes a plurality of rolling stands arranged in succession to each other. 
     
     
         7 . The system according to  claim 1 , further comprising, positioned downstream to the extracting-reducing mill, a means for measuring the wall thickness of a given tube; and a means for adjusting the radial position of each of the first plurality of rolls in the continuous main rolling mill according to a measured wall thickness of the semi-finished tube produced by the extracting-reducing mill. 
     
     
         8 . The system according to  claim 1 , wherein the mandrel is held in the main rolling mill such that none of the mandrel's sections are subjected to a action of two successive rolling stations. 
     
     
         9 . The system according to  claim 1 , wherein the mandrel in the main rolling mill includes at least two sections and wherein a joint connecting two sections of the mandrel is not subjected to any rolling in the first plurality of rolls. 
     
     
         10 . The system according to  claim 1 , the sizing mill further comprised of means for measuring a temperature of a given tube; means for measuring a diameter of the given tube; and means for adjusting the radial position of each of the second plurality of rolls according to the temperature and diameter of the given tube. 
     
     
         11 . A method for rolling a seamless tube, the method comprising:
 heating a billet, the billet produced by a continuous casting;   longitudinally piercing the heated billet to produce a pierced blank;   expanding the pierced blank;   elongating the pierced blank, the expansion and elongation of the pierced blank resulting in a semi-finished tube, the semi-finished tube having a larger diameter than the pierced blank, the semi-finished tube having a longer length than the pierced blank, the semi-finished tube having a lesser thickness thank the pierced blank;   rolling the semi-finished tube with a mandrel in a main rolling mill, wherein the main rolling mill includes a first plurality of rolls, each of the first plurality of rolls having adjustable radial positions, wherein the mandrel is held in the main rolling mill such that none of a sections of the mandrel are subjected to the action of two successive rolling stations;   extracting the semi-finished tube from the mandrel;   reducing the diameter of the semi-finished tube to a predetermined value in a sizing mill, the predetermined value being proximate to a desired final diameter of a finished tube, wherein the sizing mill includes a second plurality of rolls, each of the second plurality of rolls having adjustable radial positions; and   cooling the finished tube,   wherein the steps of piercing the billet and expanding and elongating the pierced billet can be performed by a general mill, the general mill having a plurality of configurations, wherein a first particular configuration of the general mill can perform the step of piercing the billet, wherein a second particular configuration of the general mill can perform the steps of expanding and elongating the pierced billet.   
     
     
         12 . The method according to  claim 11 , the method further comprising:
 measuring a wall thickness of the semi-finished tube extracted from the mandrel; and adjusting the radial position of the first plurality of rolls according to the measured wall thickness.   
     
     
         13 . The method according to  claim 1 , the method further comprising:
 measuring a temperature of the semi-finished tube entering the sizing mill;   measuring a diameter of the completed version of the semi-finished tube leaving the sizing mill; and   adjusting the radial position of the second plurality of rolls according to the temperature of the semi-finished tube entering the sizing mill and according to the diameter of the completed version of the semi-finished tube leaving the sizing mill.