Method for marking sheet metal blanks and for welding can bodies from marked sheet metal blanks

Abstract

A method for marking tin coated sheet metal blanks is provided in which the marking is indicative whether the blank comprises an edge region that includes a tin coating thicker than the rest of the blank. This marking is preferably brought on the blanks when a plurality of blanks is cut from a sheet metal plate. In the alternative the marking may have been applied to the sheet metal plate already. The sheet metal blanks thus marked are provided in form of a stack comprising marked and unmarked blanks, depending on whether there is a thicker edge region coating present on the individual blank or not. When making container bodies of these blanks by de-stacking and rounding the sheet metal blanks and welding the longitudinal seam of the rounded container body blanks, the marking is read in the container making apparatus and at least one welding parameter is changed for welding container body blanks with a marking in comparison with container body blanks without marking.

1 . A method for providing sheet metal blanks with a coating on one side or on both sides thereof, comprising the steps of: cutting a plurality of blanks from a one-sided or double-sided coated sheet metal plate that has two opposite edge regions of the sheet metal plate with a greater coating thickness than in the region between the edge regions, the cutting providing sheet metal blanks including such edge regions of the plate and sheet metal blanks devoid of such edge regions of the plate, applying a machine-readable marking to the sheet metal that indicates the regions of greater thickness, and collecting the cut sheet metal blanks to form a stack which includes blanks with such marking and blanks without such marking. 
   
   
       2 . A method according to  claim 1  wherein the coating is a tin coating. 
   
   
       3 . A method according to  claim 1  wherein the stack is collected from blanks cut from several sheet metal plates. 
   
   
       4 . A method according to  claim 1  wherein the marking is applied during the step of providing the sheet metal plates by cutting such plates from a sheet metal band. 
   
   
       5 . A method according to  claim 1  wherein the marking is applied to the sheet metal during the step of coiling a sheet metal band to form a coil or during the step of uncoiling a sheet metal band from a coil and wherein the sheet metal plates are provided by cutting sections from the sheet metal band. 
   
   
       6 . A method according to  claim 1  wherein the marking is applied in a double slitter in which the metal plates are cut by cutters arranged at a right angle to each other to form the plurality of blanks from each sheet metal plate. 
   
   
       7 . A method according to  claim 1  wherein the marking is provided by a marking substance invisible to the human eye. 
   
   
       8 . A method according to  claim 1  including the steps of performing coating thickness measurements in the regions of coating with greater coating thickness and applying different markings dependent on the measurement results providing the sheet metal blanks with different markings indicative of different thickness values. 
   
   
       9 . A stack of tin coated sheet metal blanks of the same size provided for making container body blanks contains sheet metal blanks including an edge region of the blank with a tin coating thicker than outside of the edge region of said blank, and wherein the stack contains sheet metal blanks without a tin coating in the edge region of the blank thicker than outside of the edge region of said blank and wherein the blanks with the thicker edge region coating are provided with a machine readable marking indicative of the thicker coating. 
   
   
       10 . A method for making container bodies from single sheet metal blanks made by the method of  claim 1  and provided on a stack according to  claim 9 , comprising the steps of consecutively de-stacking sheet metal blanks, rounding the sheet metal blanks, providing a succession of rounded container body blanks, and feeding the container body blanks in a welding apparatus for welding the longitudinal seam of the body blanks by welding rollers and wire electrodes and with welding parameters controlled by a control device, wherein marking provided on said sheet metal blanks is machine-read and at least one of said welding parameters is controlled for each consecutive blank dependent on the machine-reading of the marking. 
   
   
       11 . A method according to  claim 10  wherein the parameter is selected from the group of welding force, amount of welding current, welding current shape, welding current frequency. 
   
   
       12 . A method according to  claim 10  wherein the markings are machine-read before rounding of the sheet metal blanks. 
   
   
       13 . A double slitter for cutting sheet metal plates into a plurality of sheet metal blanks of the same size, comprising a stack receiving section for taking up a stack of sheet metal plate, a first cutting device for cutting the sheet metal plates into a first number of sheet metal strips and a second cutting device arranged at a right angle to the first cutting device for cutting the sheet metal strips into a second number of sheet metal blanks, wherein the double slitter comprises at least one marking device for applying a machine readable marking onto two opposing edge regions of the sheet metal plate before or during cutting thereof or on cut strips or blanks. 
   
   
       14 . A double slitter according to  claim 13  wherein the marking devices are arranged on both sides of the stack receiving section. 
   
   
       15 . A container body making apparatus comprising a receiving section for receiving a stack of metal sheet blanks, a de-stacker for de-stacking from the stack, a rounding apparatus arranged for taking up the de-stacked blanks and outputting rounded container body blanks and a welding machine for welding the longitudinal seam of the container body blanks fed from the rounding apparatus to the welding machine, said welding machine comprising an upper and a lower welding roller and wire electrodes running on the welding rollers and a welding current generator controlled by a controller, wherein the container body making apparatus comprises at least one detection device for detecting the presence of machine-readable markings being present or not being present on consecutive sheet metal blanks and on a predefined area on the sheet metal blanks, and wherein the at least one detection device is connected to said controller, the controller being adapted to control the welding current generator dependent on a signal from the detection device. 
   
   
       16 . A container body making apparatus according to  claim 15  wherein the controller is arranged to control the welding force applied by the welding rollers dependent on the signal from the detection device. 
   
   
       17 . A method according to  claim 2  wherein the stack is collected from blanks cut from several sheet metal plates. 
   
   
       18 . A method according to  claim 11  wherein the markings are machine-read before rounding of the sheet metal blanks.