Continous electrolytic pickling method for metallic products using alternate current supplied cells

Abstract

Continuous electrolytic pickling method for steels, Nickel, superalloys, Titanium and alloys thereof, characterised in that the material to be treated , for a time comprised between 3 sec and 60 sec, is immersed into or passes through at least one electrolytic cell with an electrolytic solution consisting of a neutral or acid aqueous solution, at a temperature comprised between 20 DEG C. and 95 DEG C., with at least one pair of electrodes connected to an alternate current power supply having a frequency ranging from 1 Hz to 1000 Hz, the electrolysis being carried out at a current density having an effective amplitude ranging from 10 A/dm2 to 250 A/dm2. The Figure depicts the progress of the weight loss of an AISI 409 (X6CrTil2) steel as a function of the application time of an embodiment of the pickling method according to the present invention.

1 . A continuous electrolytic pickling method for steels, Nickel super alloys, Titanium and alloys thereof, characterised in that the material to be treated, for a time comprised between 3 sec and 60 sec, is immersed or travels through at least one electrolytic cell with an electrolytic solution, free from nitric acid, consisting of a neutral or acid aqueous solution, comprising sulphuric acid from 20 to 300 g/l at a temperature comprised between 20° C. and 95° C., with at least one pair of electrodes connected to an alternate current power supply having a frequency ranging from 40 Hz to 70 Hz, the electrolysis being carried out at a current density having an effective amplitude ranging from 10 A/dm2 to 250 A/dm2.  
     
     
         2 . The electrolytic pickling method according to  claim 1 , wherein the electrolytic solution is an aqueous solution, at a temperature comprised between 20° C. and 95° C., containing the following components having concentrations expressed in g/l: 
 sulphuric acid (H2SO4) from 20 to 300, and at least one among  
 hydrofluoric acid (HF) from 5 to 50  
 orthophosphoric acid (H 3 PO 4 ) from 5 to 200  
 ferric ion (Fe +3 ) from 5 to 40.  
 
     
     
         3 . The electrolytic pickling method for stainless steels according to any one of the  claims 1  to  2 , wherein the electrolytic solution is maintained at a temperature between 70° C. and 90° C. and comprises sulphuric acid at a concentration comprised between 150 g/l and 250 g/l, and ferric ions (Fe +3 ) at a concentration of from 5 g/l to 40 g/l.  
     
     
         4 . The electrolytic pickling method for Nickel-base super alloys and for Titanium and alloys thereof according to  claims 1  to  2 , wherein the electrolytic solution is maintained at a temperature between 70 and 90° C. and comprises sulphuric acid at a concentration between 150 g/l and 250 g/l and at least one between hydrofluoric acid at a concentration between 5 g/l and 50 g/l and hydrochloric acid at a concentration between 5 g/l and 50 g/l.  
     
     
         5 . The electrolytic pickling method for carbon steel according to any one of the  claims 1  to  2 , wherein the electrolytic solution is maintained at 70° C.-90° C. and comprises sulphuric acid at a concentration between 150 g/l and 250 g/l.  
     
     
         6 . The electrolytic pickling method according to  claim 1 , wherein the electrolytic solution is a sodium sulphate (Na 2 SO 4 ) aqueous solution having a concentration ranging from 25 g/l to 300 g/l at a temperature between 50° C. and 95° C.  
     
     
         7 . The electrolytic pickling method according to any one of the  claims 1  to  6 , wherein pairs of adjacent electrodes are connected to two separate power supplies, so that the current lines, outputted from a first electrode pair facing one side of the material to be treated, cross said material and close again on a second electrode pair, opposed to the first pair and facing the other side of the material to be treated, defining a substantially X-shaped course.  
     
     
         8 . The electrolytic pickling method according to any one of the  claims 1  to  6 , wherein electrodes facing one side of the material to be treated are connected to a power supply, so that the current lines, which are outputted from said electrodes and cross the material, close again on other electrodes opposed to the first ones and facing the opposite side of the material to be treated, defining a course which is substantially orthogonal to said sides of the material to be treated.  
     
     
         9 . A use of the electrolytic pickling method according to  claims 1  to  8 , for inducing a physical-chemical modification of the scale of the metallic oxides present onto the surface of the material to be pickled.  
     
     
         10 . The use of the electrolytic pickling method according to  claim 9 , for stainless steels, with a treatment time between 1 and 1.0 sec.  
     
     
         11 . The use of the electrolytic pickling method according to  claims 1  to  8 , in a step subsequent to that of the physical-chemical modification of the scale of metallic oxides present onto the surface of the material to be pickled.  
     
     
         12 . The use of the electrolytic pickling method according to  claim 11 —in a step subsequent to that of the physical-chemical modification of the scale of metallic oxides present onto the surface of the material to be pickled—for stainless steels, with a treatment time comprised between 2 sec and 15 sec.  
     
     
         13 . The use of the pickling method according to  claims 1  to  12 , combined to other conventional pickling systems.  
     
     
         14 . Electrolytic cells, characterised in that they have an electrode connection as indicated in  claim 7  or  8 .