Apparatus and method for straightening a metal wire

Abstract

Apparatus (10) for straightening a metal wire (W) comprising a support structure (11) on which there are mounted in sequence at least a straightening unit (12), configured to reduce the tensions present in the metal wire (W), a main drawing unit (13), which is configured to exert a certain pull on the metal wire (W) for its advancement, and an outlet unit (14), which is configured to guide the metal wire (W) along an outlet axis (X). The present invention also concerns a process for straightening a metal wire (W).

1 . An apparatus ( 10 ) for straightening a metal wire (W) comprising a support structure ( 11 ) on which there are mounted in sequence at least a straightening unit ( 12 ), a main drawing unit ( 13 ) and an outlet unit ( 14 ) which is configured to guide the metal wire (W) along an outlet axis (X), wherein the apparatus ( 10 ) further comprises at least one calibration unit ( 15 ) disposed upstream of said straightening unit ( 12 ) and provided with at least two rollers ( 16 ,  17 ) which are configured to receive said metal wire (W) between them, along an inlet axis (Y). 
     
     
         2 . The apparatus ( 10 ) of  claim 1 , wherein said calibration unit ( 15 ) comprises at least one other roller ( 18 ), wherein said rollers ( 16 ,  17 ,  18 ) define a first group of rollers and are disposed angularly offset from each other by the same offsetting angle (α). 
     
     
         3 . The apparatus ( 10 ) of  claim 1 , wherein said calibration unit ( 15 ) comprises a second group of rollers disposed downstream of the first group of rollers and comprising other rollers ( 16 ′,  17 ′,  18 ′) disposed angularly offset from each other by said same offsetting angle (α), and wherein said second group of rollers is disposed in a rotated configuration with respect to the first group of rollers ( 16 ,  17 ,  18 ). 
     
     
         4 . The apparatus ( 10 ) of  claim 2 , wherein said rollers ( 16 ,  17 ,  18 ;  16 ′,  17 ′,  18 ′) have a cylindrical peripheral forming surface ( 16   a ,  17   a ,  18   a ;  16   a ′,  17   a ′,  18   a ′). 
     
     
         5 . Apparatus ( 10 ) as in  claims 2 and 3 , wherein said rollers ( 16 ,  17 ,  18 ;  16 ′,  17 ′,  18 ′) have a peripheral forming surface ( 16   a ,  17   a ,  18   a ;  16   a ′,  17   a ′,  18   a ′) that is circumferentially concave toward the center of the roller. 
     
     
         6 . The apparatus ( 10 ) of  claim 5 , wherein said circumferentially concave peripheral forming surface ( 16   a ,  17   a ,  18   a ;  16   a ′,  17   a ′,  18   a ′) has a radius of curvature greater than the nominal radius of said metal wire (W). 
     
     
         7 . The apparatus ( 10 ) of  claim 1 , wherein said drawing unit ( 13 ) comprises two rollers ( 13   a ,  13   b ) disposed at different heights and defining between them an S-shaped path for said metal wire (W). 
     
     
         8 . The apparatus ( 10 ) of  claim 7 , wherein said outlet axis (X) is parallel and vertically misaligned with respect to said inlet axis (Y) by an amount equal to the sum of the distance between the centers of said drawing rollers ( 13   a ,  13   b ) and the radiuses of said drawing rollers ( 13   a ,  13   b ). 
     
     
         9 . The apparatus ( 10 ) of  claim 7 , wherein each of said drawing rollers ( 13   a ,  13   b ) has a peripheral circumferential seat ( 19 ) shaped as “V” for said metal wire (W). 
     
     
         10 . The apparatus ( 10 ) of  claim 9 , wherein said seat ( 19 ) has a seat angle (γ) comprised between 50° and 100°, preferably between 60° and 90°. 
     
     
         11 . The apparatus ( 10 ) of  claim 9 , wherein said seat ( 19 ) is provided with recesses or ribs. 
     
     
         12 . The apparatus ( 10 ) of any of  claim 7 , wherein said drawing unit ( 13 ) comprises one or more presser rollers ( 13   c ) disposed peripherally to said drawing rollers ( 13   a ,  13   b ). 
     
     
         13 . The apparatus ( 10 ) of  claim 1 , wherein said outlet unit ( 14 ) comprises two distinct series of rollers ( 14   a ,  14   b ). 
     
     
         14 . The apparatus ( 10 ) of  claim 1 , wherein said outlet group ( 14 ) comprises a first series of outlet rollers ( 14   a ) with a horizontal axis and a second series of outlet rollers ( 14   b ) vertical to them. 
     
     
         15 . A method for straightening a metal wire (W) comprising at least one step of straightening said metal wire (W) performed by a straightening unit ( 12 ), a step of drawing said metal wire (W) performed by a drawing unit ( 13 ), and a step of guiding said metal wire (W) performed by a guiding unit ( 14 ) along an outlet axis (X), wherein the method further comprises a calibration step performed by a calibration unit ( 15 ) before said straightening step and in which at least two rollers ( 16 ,  17 ) receive said metal wire (W) along an inlet axis (Y) and exert a longitudinal flattening action on the lateral surface of the metal wire (W) in order to regularize its cross-section. 
     
     
         16 . The method of  claim 15 , wherein said calibration step occurs by means of at least a first group of three rollers ( 16 ,  17 ,  18 ) disposed around said metal wire (W), angularly offset from each other by a same offsetting angle (α). 
     
     
         17 . The method of  claim 15 , wherein after said calibration step, the cross-section of the metal wire (W) has a uniform profile having at least three calibrated sides interspersed with as many sides that have not been subjected to flattening. 
     
     
         18 . The method of  claim 15 , wherein after said calibration step, the area of the final cross-section of the metal wire (W) is smaller than a value comprised between 0.5% and 1.5% with respect to the area of the initial cross-section of the metal wire (W).