Method and device for cutting metal sheets

Abstract

A metal sheet is cut along a cutting line of given shape by coating the sheet with a layer of insulating material to define an exposed portion of the same shape as the required cutting line; positioning the sheet inside an electrolytic cell having an anode and a cathode; connecting the sheet to the anode; and operating a direct-current generator to generate, between the anode and cathode, a potential difference such as to oxidize the metal of the sheet at the exposed portion.

1 ) A method of cutting a sheet ( 2 ) of metal material along at least one given cutting line ( 9 ) to obtain a given finished sheet ( 3 ), the method comprising the steps of partly coating the sheet ( 2 ) with a layer ( 6 ) of electrically insulating material, so as to define, on the sheet ( 2 ), an exposed portion ( 8 ) defining said cutting line ( 9 ); positioning said sheet ( 2 ) in an electrolytic cell ( 10 ) comprising a direct-current generator ( 25 ), and an anode and a cathode connected electrically to said generator ( 25 ); connecting the anode to the cathode by means of an electrolytic conductor ( 12 ); connecting said sheet ( 2 ) electrically to said generator ( 25 ), so that said sheet ( 2 ) is part of the anode; activating the generator ( 25 ) so as to maintain, between the anode and the cathode, a potential difference such as to oxidize the metal material of said exposed portion ( 8 ); and removing said sheet ( 2 ) from said electrolytic cell ( 10 ) once the metal material of said exposed portion ( 8 ) is oxidized.  
     
     
         2 ) A method as claimed in  claim 1 , wherein said electrolytic cell ( 10 ) comprises a saline solution ( 12 ), in which said cathode and said anode are immersed; said saline solution ( 12 ) comprising said electrolytic conductor ( 12 ).  
     
     
         3 ) A method as claimed in  claim 2 , wherein said saline solution ( 12 ) comprises chloride.  
     
     
         4 ) A method as claimed in  claim 3 , and comprising the further steps of aspirating, inside an absorption chamber ( 36 ), the molecular chlorine produced when said generator ( 25 ) is operating; and reducing, inside said absorption chamber ( 36 ), said molecular chlorine substantially to chloride by means of an absorption solution ( 38 ).  
     
     
         5 ) A method as claimed in  claim 4 , and comprising the further step of maintaining a substantially constant pH of said saline solution ( 12 ) by feeding part of said absorption solution ( 38 ) into the saline solution ( 12 ) in said electrolytic cell ( 10 ).  
     
     
         6 ) A method as claimed in  claim 2 , wherein said saline solution ( 12 ) selectively comprises one of the following: 
 sulfate,    nitrate,    a combination of these.    
     
     
         7 ) A method as claimed in  claim 1 , wherein said cathode comprises a grid ( 23 ) made of electrically conducting material.  
     
     
         8 ) A method as claimed in  claim 7 , wherein said electrically conducting material comprises iron.  
     
     
         9 ) A method as claimed in  claim 7 , wherein said sheet ( 2 ) is placed inside said electrolytic cell ( 10 ) in a position substantially parallel to said grid ( 23 ).  
     
     
         10 ) A method as claimed in  claim 9 , wherein said sheet ( 2 ) has two opposite surfaces ( 4 ,  5 ), only one ( 4 ) of which is coated with said layer ( 6 ) of electrically insulating material; said sheet ( 2 ) being positioned inside said electrolytic cell ( 10 ) with said coated surface ( 4 ) facing said grid ( 23 ).  
     
     
         11 ) A method as claimed in  claim 1 , wherein said sheet ( 2 ) has two opposite surfaces ( 4 ,  5 ), both of which are coated with said layer ( 6 ) of electrically insulating material.  
     
     
         12 ) A method as claimed in  claim 9 , wherein said grid ( 23 ) is larger than said sheet ( 2 ).  
     
     
         13 ) A method as claimed in  claim 1 , wherein said sheet ( 2 ) is a single sheet.  
     
     
         14 ) A method as claimed in  claim 1 , wherein said sheet ( 2 ) forms part of a strip ( 44 ), which is fed through said electrolytic cell ( 10 ).  
     
     
         15 ) A method as claimed in  claim 13 , wherein said cutting line ( 9 ) has at least one break defining a respective microjoint ( 52 ) between the relative finished sheet ( 3 ) and said strip ( 44 ).  
     
     
         16 ) A method as claimed in  claim 14 , and comprising the step of mechanically severing said microjoint ( 52 ) to detach each said finished sheet ( 3 ) from said strip ( 44 ).  
     
     
         17 ) A method as claimed in  claim 1 , and comprising the step of washing said sheet ( 2 ) before coating it with said layer ( 6 ) of electrically insulating material.  
     
     
         18 ) A method as claimed in  claim 1 , and comprising the step of removing said layer ( 6 ) of insulating material from said finished sheet ( 3 ).  
     
     
         19 ) A method as claimed in  claim 18 , wherein said removing step comprises washing said finished sheet ( 3 ) with a substantially basic wash solution.  
     
     
         20 ) A method as claimed in  claim 19 , and comprising the step of feeding part of said saline solution ( 12 ) into said wash solution.  
     
     
         21 ) A device for cutting a sheet ( 2 ) of metal material along at least one given cutting line ( 9 ); the sheet ( 2 ) being partly coated with a layer ( 6 ) of electrically insulating material defining, on the sheet ( 2 ), an exposed portion ( 8 ) defining said cutting line ( 9 ); and the device ( 1 ) comprising an electrolytic cell ( 10 ), in turn, comprising a cathode, an anode, an electrolytic conductor ( 12 ) connecting said cathode and said anode, and supporting means ( 26 ) for receiving said sheet ( 2 ) so that the sheet ( 2 ) is part of the anode; and a direct-current generator ( 25 ) for generating a potential difference between said anode and said cathode to induce oxidation of said metal material constituting said exposed portion ( 8 ).  
     
     
         22 ) A device as claimed in  claim 21 , wherein said electrolytic cell ( 10 ) comprises a saline solution ( 12 ), in which said cathode and said anode are immersed; said saline solution ( 12 ) comprising said electrolytic conductor ( 12 ).  
     
     
         23 ) A device as claimed in  claim 21 , wherein said saline solution ( 12 ) comprises chloride.  
     
     
         24 ) A device as claimed in  claim 25 , and comprising an absorption chamber ( 36 ) containing an absorption solution ( 38 ), and suction means ( 32 ) for aspirating gaseous molecular chlorine from said electrolytic cell ( 10 ) to said absorption chamber ( 36 ); said absorption solution ( 38 ) reducing said molecular chlorine to chloride.  
     
     
         25 ) A device as claimed in  claim 24 , and comprising first transfer means ( 39 ) for transferring part of the absorption solution ( 38 ) from said absorption chamber ( 36 ) to said electrolytic cell ( 10 ).  
     
     
         26 ) A device as claimed in  claim 25 , and comprising a control device ( 31 ), and at least one measuring means ( 42 ) for measuring the pH of said saline solution ( 12 ) and connected to said control device ( 31 ); said control device ( 31 ) controlling said first transfer means ( 39 ) to maintain a substantially constant pH of said saline solution ( 12 ).  
     
     
         27 ) A device as claimed in  claim 22 , wherein said saline solution ( 12 ) comprises sulfate.  
     
     
         28 ) A device as claimed in  claim 21 , wherein said cathode comprises a grid ( 23 ) made of conducting material.  
     
     
         29 ) A device as claimed in  claim 28 , wherein said conducting material comprises iron.  
     
     
         30 ) A device as claimed in  claim 21 , and comprising a stripping unit ( 53 ) for removing said insulating material from said finished sheet ( 3 ).  
     
     
         31 ) A device as claimed in  claim 30 , wherein said stripping unit ( 53 ) comprises a substantially basic wash solution.  
     
     
         32 ) A device as claimed in  claim 21 , wherein said sheet ( 2 ) forms part of a strip ( 44 ); the device ( 1 ) comprising feed means ( 47 ) for feeding said strip through said electrolytic cell ( 10 ).  
     
     
         33 ) A device as claimed in  claim 32 , wherein said feed means ( 47 ) are connected electrically to said control device ( 31 ); said control device ( 31 ) operating said feed means in steps.  
     
     
         34 ) A device as claimed in  claim 32 , and comprising a parting unit ( 55 ) for detaching said finished sheet ( 3 ) from said strip ( 44 ).  
     
     
         35 ) A device as claimed in  claim 21 , wherein said electrolytic cell ( 10 ) comprises an open-topped tank ( 11 ) containing the saline solution ( 12 ), and having two parallel vertical walls ( 16 ) having respective substantially horizontal openings ( 17 ) facing and coplanar with each other for the passage of the sheet ( 2 ).  
     
     
         36 ) A device as claimed in  claim 35 , wherein, adjacent to each opening ( 17 ), the electrolytic cell ( 10 ) comprises sealing means ( 18 ) for said saline solution ( 12 ).  
     
     
         37 ) A device as claimed in  claim 36 , wherein said sealing means ( 18 ) comprise two horizontal rollers ( 19 ,  20 ) located respectively below and above a plane defined by said openings ( 17 ); each said roller ( 19 ,  20 ) resiliently contacting in fluidtight manner the other roller ( 20 ,  19 ) and said vertical wall ( 16 ) of the relative said opening ( 17 ).  
     
     
         38 ) A device as claimed in  claim 24 , and comprising movable supports ( 24 ) on which said grid ( 23 ) rests; the movement of said movable supports ( 24 ) being controlled by said control device ( 31 ).