Method and Device for Picking Metals

Abstract

A method and a device ( 13 ) are disclosed for the electrolytic pickling of flat metal products ( 2 ), in particular special steel and/or carbon steel strips. At least one diamond electrode and/or at least one lead/tin electrode, for example a lead 93/tin7 electrode ( 15 ) is used. The special characteristic of the diamond electrodes and/or lead/tin electrodes is the form of water replacement. Whereas in electrolysis water is usually split into hydrogen and oxygen, the diamond electrode and/or lead tin electrode provides a working range in which ozone or highly reactive hydroxyl radicals are formed instead of oxygen. As a result the pickling times are significantly reduced in comparison to the conventional chemical descaling, and also in comparison to the conventional electrolytic pickling.

1 . Method for the electrolytic pickling of flat metal products ( 2 ), in particular special steel and/or carbon steel strips, characterized in that at least one diamond electrode and/or at least one lead/tin electrode, for example a lead 93/tin7 electrode ( 15 ) is used.  
     
     
         2 . Method according to  claim 1 , characterized in that the current is delivered on the one hand directly to the flat product ( 2 ) and on the other to at least one pair of electrodes.  
     
     
         3 . Method according to  claim 2 , characterized in that one electrode ( 15 ) of the pair of electrodes and where necessary the flat product ( 2 ) is connected as anode and the other electrode ( 15 ) as cathode.  
     
     
         4 . Method according to any one of  claims 1  to  3 , characterized in that the current is delivered intermittently.  
     
     
         5 . Method according to any one of  claims 1  to  4 , characterized in that the current is delivered constantly.  
     
     
         6 . Method according to any one of  claims 1  to  5 , characterized in that direct current is impressed alternately (reverse pulse plating) on the flat product ( 2 ) to be pickled and the electrodes ( 15 ).  
     
     
         7 . Method according to any one of  claims 1  to  6 , characterized in that a mixture of mineral acids and water in a concentration of 10 g/l to 250 g/l mineral acid, in particular between 50 to 200 g/l, preferably 150 g/l, is used.  
     
     
         8 . Method according to any one of  claims 1  to  7 , characterized in that a mixture of water and Na 2 SO 4  (sodium sulphate) is used, the concentration of Na 2 SO 4  being set between 100 and 350 g/l, preferably 150 g/l Na 2 SO 4 , as a function of the flat product to be pickled.  
     
     
         9 . Method according to any one of  claims 1  to  8 , characterized in that mixed acid is used, the concentration being set between 20 and 100 g/l HF and 50 and 300 g/l HNO 3 , preferably to 50 g/l HF and 150 g/l HNO 3  as a function of the flat product ( 2 ) to be pickled.  
     
     
         10 . Method according to any one of  claims 1  to  9 , characterized in that the current densities on the electrodes are set between 0.5 and 150 A/dm 2  as a function of the flat product ( 2 ) to be pickled.  
     
     
         11 . Method according to any one of  claims 1  to  10 , characterized in that the electrolyte temperature is set between 20 and 90° C., preferably to 75° C., as a function of the flat product ( 2 ) to be pickled.  
     
     
         12 . Method according to any one of  claims 1  to  11 , characterized in that the electrical voltage is variably adjusted.  
     
     
         13 . Method according to any one of  claims 1  to  12 , characterized in that the distance between the flat product and the electrode is adjusted with the quantity of electrolyte fluid fed between the flat product ( 2 ) and the electrode ( 15 ).  
     
     
         14 . Method according to any one of  claims 2  to  13 , characterized in that the distance between the electrodes ( 15 ) of a pair of electrodes or between the electrode ( 15 ) and the flat product ( 2 ) is adjusted to the undulation of the flat product.  
     
     
         15 . Device for performing a method according to any one of  claims 1  to  14  for the electrolytic pickling of flat metal products ( 2 ), in particular special steel and/or carbon steel strips, characterized in that at least one diamond electrode and/or at least one lead/tin electrode, for example a lead 93/tin7 electrode ( 15 ) is used.  
     
     
         16 . Device according to  claim 15 , characterized in that at least one pair of opposing electrodes ( 15 ) is provided, between which a flat product ( 2 ) can be fed.  
     
     
         17 . Device according to either of claims  15  or  16 , characterized in that a device ( 19 ) is provided for delivering current on the one hand directly to the flat product ( 2 ) and on the other to the electrodes ( 15 ), in particular so that one electrode of a pair of electrodes is connected as cathode and the other electrode as anode, and the flat product can if necessary be connected as anode.  
     
     
         18 . Device according to any one of  claims 15  to  17 , characterized in that guide devices ( 14 ,  14 ′) are provided, by means of which a strip ( 2 ) can be guided at an angle to the horizontal, that electrodes ( 15 ) are arranged at the same angle, and that devices ( 21 ,  21 ′,  21 ″,  21 ′″,  22 ,  22 ′,  22 ″,  22 ′″) are provided, by means of which electrolyte fluid can be introduced between the strip ( 2 ) and the electrodes ( 15 ).  
     
     
         19 . Device according to  claim 18 , characterized in that a strip can be led obliquely downwards at an angle, in particular an angle of 30 to 45°, and then following at least one deflection roller ( 14 ′) obliquely upwards at an angle, in particular an angle of 30 to 45°.  
     
     
         20 . Device according to any one of  claims 16  to  19 , characterized in that the position of at least one electrode ( 15 ) of a pair of electrodes and the deflection roller ( 14 ′) can be adjusted perpendicular to the direction of movement of the flat product.  
     
     
         21 . Device according to any one of  claims 16  to  20 , characterized in that the gap between the electrodes of a pair of electrodes is adjustable.  
     
     
         22 . Device according to any one of  claims 15  to  21 , characterized in that a control device is provided for regulating the delivery quantity of the electrolyte fluid.  
     
     
         23 . Device according to any one of  claims 15  to  22 , characterized in that at least one separator is fitted on at last one electrode.  
     
     
         24 . Device according to any one of  claims 15  to  23 , characterized in that a control device is provided for controlling the current flow to the electrodes ( 15 ).