US 2348517 A
Description (OCR text may contain errors)
Patented May 9, 1944 STAINLESS STEEL ANODIC POLISHING Glenwood J. Beckwith, Brecksville, Ohio, assignor to The American Steel and Wire Company of New Jersey, a corporation of New Jersey No Drawing. Application July 8, 1942, Serial No. 450,195
This invention relates to the anodic polishing of stainless steels, it being understood that'this polishing method is characterized by immersing the steel in an electrolyte and making the steel an anode in an externally powered electrolytic circuit, the current density per unit area of anode surface being adjusted sufficiently high to effect polishing.
It is known that most effective polishing is obtained when the electrolyte consists of mixtures of perchloric acid and acetic acid, but such an electrolyte is commercially undesirable because of the incidental obnoxious fumes and explosion hazards. Furthermore, such an electrolyte requires refrigeration in most instances, while high operating voltages are necessary requiring special electrical equipment for powering the electrolytic circuit. In the case of the present invention, the object is to obtain an equally high luster or p'olish without involving the various disadvantages connected with electrolytes including perchloric acid.
According to the present invention, an electrolyte is used containing an effective amount of glycine to function as a brightener when added to ordinary polishing electrolytes which do not involve the disadvantages above discussedilcient glycine to eifect this end.
More specifically, it is preferable to dissolve about '1 pounds of glycine in a gallon of hot water, and to form an electrolyte consisting volumetrically of one part of this glycine solution, five parts ortho-phosphoric acid, and four parts 96% sulphuric acid. This provides an extremely efiective polishing electrolyte, the optimum operating conditions for 18-8 including a current density of from 3-4 amperes per square inch of anode surface and an electrolyte temperature of around F. The time of polishing will range from 2-3 minutes depending on the surface of the steel being polished. The voltage will be in the neighborhood of 9 volts in the case of a circuit of average length.
The glycine will not crystallize out of this electrolyte it operated under these conditions, although a few crystals may form around still portions of the tank containing the electrolyte, when polishing is not proceeding. but due to the great solubility of glycine, slight heating of the electrolyte above room temperature will cause immediate and complete resolution.
A method of anodically polishing stainless steel, characterized by immersing said steel in an electrolyte by volume consisting of one part of a solution of 7 pounds of glycine to a gallon of water, five parts 85% ortho-phosphoric acid and four parts 96% sulphuric acid, and making said steel the anode in an electrolytic circuit including said electrolyte with the electrolyte current at a sufflcient density per unit area of said steel to effect polishing.