Electropolishing method

Abstract

The present invention describes a cost-saving and environmentally conserving process for the electrochemical polishing of steel, in particular of low-alloy steels. The workpieces are rinsed after electropolishing in an arid phosphoric acid-sulfuric acid-bath in a first rinsing step with a phosphoric acid-containing solution, whereby a chemical attack on the freshly polished surfaces is avoided without the use of environmentally harmful and unhealthy inhibitors such as chromates. By recycling of the acids and the rinsing solution, these acids and solutions can be regenerated, whereby the process can be designed effluent-free.

1 . A method of electrochemical polishing of low-alloy steels using an electrolyte containing 100 to 30 wt. % phosphoric acid and 0 to 70 wt. % sulfuric acid and in which the electrolyte is rinsed off, characterized in that a solution containing phosphoric acid is used for the rinsing, where the phosphoric acid content of the rinsing solution is at least 50 wt. %. 
   
   
       2 . The method as claimed in  claim 1 , characterized in that concentrated phosphoric acid is used for the rinsing. 
   
   
       3 . The method as claimed in  claim 1  or  2 , characterized in that the electrolyte is substantially chromium-free. 
   
   
       4 . The method as claimed in  claim 1  or  2  characterized in that the electrolyte has a water content of max. 20 wt. %. 
   
   
       5 . The method as claimed in  claim 1  or  2 , characterized in that the electrolyte contains 80-50 wt. % phosphoric acid and 20-50 wt. % sulfuric acid. 
   
   
       6 . The method as claimed in  claim 1  or  2 , characterized in that the electrolyte contains iron ions in an amount that inhibits chemical attack on the surface of the steel. 
   
   
       7 . The method as claimed in  claim 6 , characterized in that the electrolyte contains iron ions in an amount of at least 1 wt. %. 
   
   
       8 . The method as claimed in  claim 6 , characterized in that the electrolyte has more than 2.0 wt. %, though at most approx. 8% iron ions. 
   
   
       9 . The method as claimed in  claim 1  or  2 , characterized in that the electrochemically polished steel is rinsed with water following the rinsing with solution containing phosphoric acid. 
   
   
       10 . The method as claimed in  claim 9 , characterized in that the inorganic acids contained in the rinsing water are recovered. 
   
   
       11 . The method as claimed in  claim 1  or  2 , characterized in that the electrolyte is supplemented at least partially with the electrolyte-enriched phosphoric acid from the first rinsing stage and optionally with phosphoric acid recovered from at least one other water-based rinsing stage. 
   
   
       12 . The method as claimed in  claim 1  or  2 , characterized in that the electrolyte is supplemented at least partially with the electrolyte-enriched phosphoric acid from the first rinsing stage and optionally with phosphoric acid recovered from at least one other water-based rinsing stage.