Retained mandrel rolling mill for seamless tubes

Abstract

A rolling mill ( 10 ) for processing seamless tubes comprises a plurality of rolling units (U) that are sequentially arranged along a rolling axis (L), each of which is provided with at least three removable working rolls ( 12 ), which are each equipped with a groove ( 12 a ) for accommodating the tube to be worked; the rolling mill comprises a mandrel suitable to be fitted in the tube cavity during the process; the tube is worked by being sequentially passed, with the mandrel ( 22 ) fitted in the tube cavity, within the grooves ( 12 a ) of the rolls ( 12 ) of the rolling units (U) such that the outer diameter of the tube (T) is reduced; in order to have low capital and production costs, each rolling unit (U) has an unchanged nominal diameter

1 . A rolling mill ( 10 ) for processing seamless tubes (T),
 said rolling mill ( 10 ) defining a rolling axis (L) along which the seamless tubes (T) are moved in a rolling direction (A) during processing by said rolling mill ( 10 ),   said rolling mill ( 10 ) comprising a plurality of rolling units (U) that are arranged one after another along said rolling axis (L),   wherein each of said rolling units (U) is provided with at least three removable working rolls ( 12 ) which can be driven to rotate about axes of rotation (X),   wherein said axes of rotation (X) of the working rolls ( 12 ) of respectively one rolling unit (U) are co-planar to each other and are laying in a plane orthogonal to said rolling axis ( 12 ),   wherein each working roll ( 12 ) has a groove ( 12   a ) for accommodating the tube (T) to be worked while it moves along said rolling axis (L),   wherein said grooves ( 12   a ) of the working rolls ( 12 ) have a profile similar to an arc of a circle with a groove radius (R 1 ; R 2 ; R 3 ; R 4 ; R 5 ),   wherein said groove radius (R 1 ; R 2 ; R 3 ; R 4 ; R 5 ) of said working rolls ( 12 ) decreases in said rolling direction (A) from a first rolling unit (U 1 ) to a last rolling unit (U 5 ) of said rolling units (U),   so that the tube (T) can be worked by being passed in said rolling direction (A), within the grooves ( 12   a ) of the rolls ( 12 ) of the successively arranged rolling units (U), such that the outer diameter of the tube (T) is reduced,   wherein each rolling unit (U) comprises a nominal diameter (D) defined as twice the distance between said rolling axis (L) and said axes of rotation (X) of the working rolls ( 12 ) of said rolling unit (U),   wherein said nominal diameter (D) is substantially unchanged from one rolling unit (U 1 ) to the next one (U 2 ) and said rolling mill ( 10 ) is configured that the working rolls ( 12 ) belonging to one of said rolling units (U 5 ) can be placed, after turning of their grooves ( 12   a ), in the preceding rolling unit (U 4 ) with respect to the rolling direction (A).   
     
     
         2 . The rolling mill according to  claim 1 , wherein said rolling mill ( 10 ) further comprises a mandrel ( 22 ) suitable to be fitted in the cavity of the tube (T) during the process, so that the tube (T) can be worked by being passed, with the mandrel ( 22 ) fitted in the tube (T) cavity, within the grooves ( 12   a ) of the rolls ( 12 ) of the successively arranged rolling units (U), such that the outer diameter of the tube (T) is reduced. 
     
     
         3 . The rolling mill according to  claim 1 , wherein the roll ( 12 ) consists of two parts ( 12 . 1 , 12 . 2 ), a first part ( 12 . 1 ) being integral with a drive shaft ( 21 ) for the roll ( 12 ) and a second part ( 12 . 2 ) being rigidly fastened to the first part ( 12 . 1 ) of the roll ( 12 ) in a removable manner. 
     
     
         4 . The rolling mill according to  claim 3 , wherein the second part ( 12 . 2 ) of the roll ( 12 ) has a substantially annular configuration. 
     
     
         5 . The rolling mill according to  claim 3 , wherein the second part ( 12 . 2 ) of the roll ( 12 ) is connected to the first part ( 12 . 1 ) by means of bonding. 
     
     
         6 . Method for operating a rolling mill ( 10 ) for processing seamless tubes (T),
 said rolling mill ( 10 ) defining a rolling axis (L) along which the seamless tubes (T) are moved in a rolling direction (A) during processing by said rolling mill ( 10 ),   said rolling mill ( 10 ) comprising a plurality of rolling units (U) that are arranged one after another along said rolling axis (L),   wherein each of said rolling units (U) is provided with at least three removable working rolls ( 12 ) which can be driven to rotate about axes of rotation (X),   wherein said axes of rotation (X) of the working rolls ( 12 ) of respectively one rolling unit (U) are co-planar to each other and are laying in a plane orthogonal to said rolling axis ( 12 ),   wherein each working roll ( 12 ) has a groove ( 12   a ) for accommodating the tube (T) to be worked while it moves along said rolling axis (L),   wherein said grooves ( 12   a ) of the working rolls ( 12 ) have a profile similar to an arc of a circle with a groove radius (R 1 ; R 2 ; R 3 ; R 4 ; R 5 ),   wherein said groove radius (R 1 ; R 2 ; R 3 ; R 4 ; R 5 ) of said working rolls ( 12 ) decreases in said rolling direction (A) from a first rolling unit (U 1 ) to a last rolling unit (U 5 ) of said rolling units (U),   so that the tube (T) can be worked by being passed in said rolling direction (A), within the grooves ( 12   a ) of the rolls ( 12 ) of the successively arranged rolling units (U), such that the outer diameter of the tube (T) is reduced,   wherein each rolling unit (U) comprises a nominal diameter (D) defined as twice the distance between said rolling axis (L) and said axes of rotation (X) of the working rolls ( 12 ) of said rolling unit (U),   comprising the steps of:
 providing said working rolls ( 12 ) so that said nominal diameter (D) is substantially unchanged from one rolling unit (U 1 ) to the next one (U 2 ), 
 turning said grooves ( 12   a ) of said working rolls ( 12 ) when they are worn, thereby increasing its groove radius, 
 placing the working rolls ( 12 ) belonging to one of said rolling units (U 5 ), after turning of their grooves ( 12   a ), in the preceding rolling unit (U 4 ) with respect to said rolling direction (A).