Method to produce a metal strip, and production plant implementing said method

Abstract

Method to produce metal strip that comprises the casting of a cast product through a casting machine provided with a crystallizer to obtain a slab, and the hot rolling of the slab in a rolling station to obtain metal strip. The casting machine, during casting, exerts an action of reducing the thickness of the cast product exiting the crystallizer.

1 . A method to produce metal strips, in particular steel, in a production plant configured to work in coil to coil and/or semi-endless rolling mode and/or in endless rolling mode, in which through a casting machine provided with a crystallizer is cast a slab, with a defined casting speed Vc, and said slab is hot rolled in a rolling station, comprising a number of rolling stands, to obtain metal strip having different strip thicknesses, wherein said casting machine, during casting, exerts a first action of liquid core reduction of the thickness of the slab exiting from the crystallizer, through a pre-rolling device with rollers, and a second action of solid core reduction of the thickness of the slab, through a drawing unit located downstream of said pre-rolling device, wherein said casting machine is selectively set, as said strip thicknesses vary, in order to exert a different action of reducing the thickness of the slab, in which said first action of liquid core reduction of the thickness is comprised between 5 and 25 mm, said second action of solid core reduction of the thickness is maximum 7 mm and is applied for strip thicknesses comprised between 0.6 mm and 3.5 mm, with an overall reduction thickness of the slab exiting from the casting machine comprised between 2% and 75%, and wherein the rolling mode of the slab is chosen in relation to said strip thicknesses and to the various types of produced steel, in order to optimize the productivity of the strip production plant with the lowest number of stands possible, while maintaining the maximum casting speed Vc in relation to the various types of produced steel. 
     
     
         2 . The method as in  claim 1 , wherein said casting machine comprises a pre-rolling device with rollers which exerts an action of reducing the thickness of the cast product exiting from the crystallizer by means of pre-rolling with liquid core. 
     
     
         3 . The method as in  claim 1 , wherein said pre-rolling device with rollers is provided with a plurality of opposite rollers between which said cast product passes and said rollers are selectively moved toward/away from each other to exert a selective action of liquid core reduction of the thickness of said cast product. 
     
     
         4 . The method as in  claim 2 , wherein said pre-rolling device with rollers is provided with a plurality of opposite rollers between which said cast product passes and said rollers are selectively moved toward/away from each other to exert a selective action of liquid core reduction of the thickness of said cast product. 
     
     
         5 . The method as in  claim 1 , wherein said casting machine comprises a drawing unit which exerts an action of reducing the thickness of the cast product exiting from said pre-rolling device with rollers, by means of solid core rolling of the cast product. 
     
     
         6 . The method as in  claim 2 , wherein said casting machine comprises a drawing unit which exerts an action of reducing the thickness of the cast product exiting from said pre-rolling device with rollers, by means of solid core rolling of the cast product. 
     
     
         7 . The method as in  claim 3 , wherein said casting machine comprises a drawing unit which exerts an action of reducing the thickness of the cast product exiting from said pre-rolling device with rollers, by means of solid core rolling of the cast product. 
     
     
         8 . The method as in  claim 4 , wherein said casting machine comprises a drawing unit which exerts an action of reducing the thickness of the cast product exiting from said pre-rolling device with rollers, by means of solid core rolling of the cast product. 
     
     
         9 . The method as in  claim 1 , further comprising determining the thickness of said cast product exiting from the crystallizer which is a number comprised between 10 mm and 15 mm more than a nominal slab thickness (SBN) defined by the formula SBN = PR/OPERATING HOURS/(VC*LN*PS), where PR is the productivity of the plant, VC is a casting speed chosen between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific weight of the steel. 
     
     
         10 . The method as in  claim 2 , further comprising determining the thickness of said cast product exiting from the crystallizer which is a number comprised between 10 mm and 15 mm more than a nominal slab thickness (SBN) defined by the formula SBN = PR/OPERATING HOURS/(VC*LN*PS), where PR is the productivity of the plant, VC is a casting speed chosen between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific weight of the steel. 
     
     
         11 . The method as in  claim 3 , further comprising determining the thickness of said cast product exiting from the crystallizer which is a number comprised between 10 mm and 15 mm more than a nominal slab thickness (SBN) defined by the formula SBN = PR/OPERATING HOURS/(VC*LN*PS), where PR is the productivity of the plant, VC is a casting speed chosen between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific weight of the steel. 
     
     
         12 . The method as in  claim 4 , further comprising determining the thickness of said cast product exiting from the crystallizer which is a number comprised between 10 mm and 15 mm more than a nominal slab thickness (SBN) defined by the formula SBN = PR/OPERATING HOURS/(VC*LN*PS), where PR is the productivity of the plant, VC is a casting speed chosen between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific weight of the steel. 
     
     
         13 . The method as in  claim 5 , further comprising determining the thickness of said cast product exiting from the crystallizer which is a number comprised between 10 mm and 15 mm more than a nominal slab thickness (SBN) defined by the formula SBN = PR/OPERATING HOURS/(VC*LN*PS), where PR is the productivity of the plant, VC is a casting speed chosen between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific weight of the steel. 
     
     
         14 . The method as in  claim 6 , further comprising determining the thickness of said cast product exiting from the crystallizer which is a number comprised between 10 mm and 15 mm more than a nominal slab thickness (SBN) defined by the formula SBN = PR/OPERATING HOURS/(VC*LN*PS), where PR is the productivity of the plant, VC is a casting speed chosen between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific weight of the steel. 
     
     
         15 . The method as in  claim 7 , further comprising determining the thickness of said cast product exiting from the crystallizer which is a number comprised between 10 mm and 15 mm more than a nominal slab thickness (SBN) defined by the formula SBN = PR/OPERATING HOURS/(VC*LN*PS), where PR is the productivity of the plant, VC is a casting speed chosen between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific weight of the steel. 
     
     
         16 . The method as in  claim 8 , further comprising determining the thickness of said cast product exiting from the crystallizer which is a number comprised between 10 mm and 15 mm more than a nominal slab thickness (SBN) defined by the formula SBN = PR/OPERATING HOURS/(VC*LN*PS), where PR is the productivity of the plant, VC is a casting speed chosen between 4.5 m/min and 6 m/min, LN is the average width of the strip, and PS is the specific weight of the steel. 
     
     
         17 . The method as in  claim 1 , further comprising determining a thickness ratio (RSP) applied by the rolling station calculated as the ratio between the value of the slab thickness (SB2) entering said rolling station, when the strip of minimum thickness (SMIN) is processed, and the value of said minimum thickness (SMIN) of the strip. 
     
     
         18 . The method as in  claim 2 , further comprising determining a thickness ratio (RSP) applied by the rolling station calculated as the ratio between the value of the slab thickness (SB2) entering said rolling station, when the strip of minimum thickness (SMIN) is processed, and the value of said minimum thickness (SMIN) of the strip. 
     
     
         19 . The method as in  claim 17 , further comprising determining the number of rolling stands of the rolling station, where:
 for a ratio of thicknesses comprised between 4 and 12, four rolling stands are provided;   for a ratio of thicknesses comprised between 12 and 21, five rolling stands are provided;   for a ratio of thicknesses comprised between 21 and 52, six rolling stands are provided;   for a ratio of thicknesses comprised between 52 and 110, seven rolling stands are provided.   
     
     
         20 . A plant for producing metal strip, configured to work in coil to coil and/or semi-endless rolling mode and/or in endless rolling mode, comprising a casting machine provided with a crystallizer for casting a slab, with a defined casting speed Vc, and a rolling station for hot rolling of said slab, the rolling station comprising a number of rolling stands, to obtain metal strip having different strip thicknesses, wherein said casting machine, during casting, exerts a first action of liquid core reduction of the thickness of the slab exiting from the crystallizer, through a pre-rolling device with rollers, and a second action of solid core reduction of the thickness of the slab, through a drawing unit located downstream of said pre-rolling device, wherein said casting machine can be selectively configured, as said strip thicknesses vary, in order to exert a different action of reducing the thickness of the slab, in which said first action of liquid core reduction of the thickness is comprised between 5 and 25 mm, said second action of solid core reduction of the thickness is maximum 7 mm and is applied for strip thicknesses comprised between 0.6 mm and 3.5 mm, with an overall reduction thickness of the slab exiting from the casting machine comprised between 2% and 75%, and wherein the rolling mode of the slab is chosen in relation to said strip thicknesses and to the various types of produced steel, in order to optimize the productivity of the strip production plant with the lowest number of stands possible, while maintaining the maximum casting speed Vc in relation to the various types of produced steel.