Combined apparatus for rolling seamless tubes

Abstract

The present invention relates to a plant 10 for rolling a seamless tube. The plant comprises a rotary piercer 20 which is designed to pierce a billet 11 pressed against a plug 22 mounted on a rod so as to obtain a pierced blank 12 . The rod is connected to a thrust block 26 designed to oppose the axial thrust which is produced on the rod during piercing. The plant also comprises a longitudinal mill 30 which is designed to roll the pierced blank 12 on a mandrel 32 so as to obtain a semi-finished tube 13 . The mandrel is connected to a retaining block 34 designed to impart to the mandrel a predetermined speed during rolling. In the plant according to the invention the thrust block 26 and the retaining block 34 are formed by a single thrust/retaining block 36. The invention also relates to a method for rolling a seamless tube.

1 . Compact plant ( 10 ) for rolling a seamless tube, comprising:
 a rotary piercer ( 20 ) comprising two skew-axis rolling rolls and a plug ( 22 ) mounted on a rod ( 24 ), the rotary piercer defining a rolling axis X PR  and a rolling sense and being designed to:
 receive at its input a solid billet ( 11 ), 
 pierce completely the billet ( 11 ) against the plug ( 22 ), and 
 release a pierced blank ( 12 ) engaged on the rod ( 24 ) of the plug ( 22 ); 
   a longitudinal mill ( 30 ) comprising a plurality of rolling stations with adjustable motor-driven rolls, the longitudinal mill defining a rolling axis X LL  and a rolling sense and being designed to:
 receive at its input the pierced blank ( 12 ) released by the rotary piercer; 
 roll the pierced blank ( 12 ) on a mandrel ( 32 ), and 
 release a semi-finished tube ( 13 ); 
   wherein:   the rod ( 24 ) of the plug ( 22 ) of the rotary piercer ( 20 ) is connected to a thrust block ( 26 ) designed to oppose the axial thrust which is produced on the rod ( 24 ) during piercing and designed to impart to the rod ( 24 ) and to the plug ( 22 ) the movements necessary before and after piercing; and   the mandrel ( 32 ) of the longitudinal mill ( 30 ) is connected to a retaining block ( 34 ) designed to impart to the mandrel ( 32 ) a predetermined speed during rolling and designed to impart to the mandrel ( 32 ) the movements necessary before and after rolling;   and wherein the rotary piercer ( 20 ) and the longitudinal mill ( 30 ) have the same rolling sense;   and the thrust block ( 26 ) and the retaining block ( 34 ) are formed by a single thrust/retaining block ( 36 ).   
     
     
         2 . The plant ( 10 ) according to  claim 1 , wherein the thrust/retaining block ( 36 ) comprises a first gripping unit ( 260 ) designed to grip the rod ( 24 ) 5  and a second gripping unit ( 340 ) designed to grip the mandrel ( 32 ), both the gripping units being mounted on a single thrust bearing unit ( 362 ). 
     
     
         3 . The plant ( 10 ) according to  claim 2 , wherein the first gripping unit ( 260 ) and the second gripping unit ( 340 ) of the thrust/retaining block ( 36 ) form a single gripping unit ( 360 ). 
     
     
         4 . The plant ( 10 ) according to  claim 1 , wherein the rolling axes X PR  and X LL  coincide. 
     
     
         5 . The plant ( 10 ) according to  claim 1 , wherein the rod ( 24 ) of the plug ( 22 ) of the rotary piercer ( 20 ) is structurally connected to the mandrel ( 32 ) of the longitudinal mill ( 30 ). 
     
     
         6 . The plant ( 10 ) according to  claim 5 , wherein the rod ( 24 ) of the plug ( 22 ) of the rotary piercer ( 20 ) and the mandrel ( 32 ) of the longitudinal mill ( 30 ) are formed as one piece. 
     
     
         7 . The plant ( 10 ) according to  claim 5 , wherein the rod ( 24 ) of the plug ( 22 ) of the rotary piercer ( 20 ) and the mandrel ( 32 ) of the longitudinal mill ( 30 ) are releasably connected together. 
     
     
         8 . The plant ( 10 ) according to  claim 1 , wherein the rotary piercer ( 20 ) is chosen from the group comprising piercers with barrel rolls and piercers with conical rolls. 
     
     
         9 . The plant ( 10 ) according to  claim 1 , wherein the longitudinal mill ( 30 ) is chosen from the group comprising rolling mills with two-roll rolling stations and rolling mills with three-roll rolling stations. 
     
     
         10 . The plant ( 10 ) according to  claim 1 , further comprising an operating fork ( 40 ) for extracting the mandrel ( 32 ) from the semi-finished tube ( 13 ). 
     
     
         11 . Method A method for rolling a seamless tube, comprising the steps of:
 providing a solid billet ( 11 );
 providing a rotary piercer ( 20 ) which defines a rolling axis X PR  and a rolling sense and comprises two skew-axis rolling rolls and a plug ( 22 ) mounted on a rod ( 24 ); 
 providing a longitudinal mill ( 30 ) which defines a rolling axis X LL  and a rolling sense and comprises a plurality of rolling stations with adjustable motor-driven rolls, the longitudinal mill ( 30 ) being designed to roll a pierced blank ( 12 ) on a mandrel ( 32 ); 
 feeding the solid billet ( 11 ) to the rotary piercer ( 20 ); 
 piercing completely the billet ( 11 ) against the plug ( 22 ) so as to obtain a pierced blank  12 , and 
 opposing the axial thrust which is produced on the rod ( 24 ) during piercing; 
 releasing the pierced blank ( 12 ) engaged on the rod ( 24 ) of the plug ( 22 ); 
 displacing the pierced blank ( 12 ) from the rod ( 24 ) of the plug ( 22 ) to the mandrel ( 32 ) of the longitudinal mill ( 30 ); 
 feeding the pierced blank ( 12 ) engaged on the mandrel ( 32 ) to the longitudinal mill ( 30 ); 
 rolling the pierced blank ( 12 ) on the mandrel ( 32 ) so as to obtain a semi-finished tube ( 13 ); 
 retaining the mandrel ( 32 ) so as to impart to it a predetermined speed during rolling; and 
 releasing the semi-finished tube ( 13 ). 
   wherein the rotary piercer ( 20 ) and the longitudinal mill ( 30 ) have the same rolling sense and the steps of opposing the axial thrust on the rod ( 24 ) and retaining the mandrel ( 32 ) are performed by means of a single thrust/retaining block ( 36 ).