|Publication number||US3342711 A|
|Publication date||Sep 19, 1967|
|Filing date||Nov 13, 1964|
|Priority date||Nov 14, 1963|
|Publication number||US 3342711 A, US 3342711A, US-A-3342711, US3342711 A, US3342711A|
|Inventors||Akio Shiga, Hideyuki Furukawa|
|Original Assignee||Kyowa Hakko Kogyo Kk|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (8), Referenced by (7), Classifications (9)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent 3,342,711 ELECTROLYTIC PgLlsHIlNG 0F STAINLESS TEE Akio Shiga and Hideyuki Furukawa, Machida-shi, Japan, assignors to Kyowa Hakko Kogyo Co., Ltd., Tokyo, Japan, a corporation of Japan No Drawing. Filed Nov. 13, 1964, Ser. No. 411,100 Claims priority, application Japan, Nov. 14, 1963, 38/ 60,874 4 Claims. (Cl. 204-1405) This invention relates to a method for electrolytically polishing metals and to a solution for electrolytic polishing of metals. More particularly this invention relates to a method for polishing metals electrolytically by the use of a solution obtained by adding gluconic acid, alkali and alkali-earth metal (e.g. sodium and calcium) salts thereof, picoline or quinoline with or without ethylene glycol, to a mixture of phosphoric acid and sulfuric acid as an electrolyte solution, and constituting a metal to be polished as anode.
For the purpose of polishing metals electrolytically, there has been used an electrolyte consisting mainly of phosphoric acid and sulfuric acid together with, as additive, chromic acid anhydride or glycerine. In such cases, e.g. where chromic acid anhydride is used, it is possible to obtain electrolytic products in lustrous form as long as the electrolyte solution is fresh, but with the prolonged continuation of electrolysis, the luster of the products begins to lose uniformity, apparently due to change to chromic acid. When glycerine is used as additive, carrying out the electrolysis operation at a high voltage and/or at a high temperature causes a change of composition of the electrolyte solution, so that control of the composition of the electrolyte solution becomes diflicult and products having uniform l'uster can no longer be obtained.
An object of the present'invention is, accordingly, to provide a method for polishing metals electrolytically, which method is free from the above-mentioned drawbacks of the prior art methods. Another object of the present invention is to provide a method for yielding socalled 18, 16 and 13 stainless steels having perfect lustre by electrolytic polishing. This has been unsuccessful according to conventional methods. A further object of the present invention is to provide an electrolyte solution having no age deterioration and no change of composition, and which makes it possible to operate under a stabilized condition over a long period of time. A still further object of the present invention is to provide a method for electrolytically polishing metals with a small electric current at a low voltage and at a low temperature. These and other objects can be realized by the present invention.
According to the present invention, a solution obtained by incorporating, as additive(s), at least one of gluconic acid, alkali and alkali-earth metal (eg sodium and calcium) salts thereof, picoline, or quinoline, with or without ethylene glycol, into a mixture of phosphoric acid and sulfuric acid, is used as an electrolyte solution and the polishing of the metals is carried out while using the said metals as anodes.
The functions of the gluconic acid, salt thereof, picoline, salt thereof, and quinoline appears to be somewhat different from that of the ethylene glycol in that the latter seems to act predominantly as a stabilizer and secondarily as polishing activator, whereas the reverse is true for the other additives. It is therefore advantageous to have ethylene glycol present in all situations where a predominant stabilizing action is required. However, the results according to the invention can be achieved with the use of ethylene glycol alone or with any one or more of the other additives in the absence of ethylene glycol.
The phosphoric acid and sulfuric acid used in the present invention are preferably of a concentration greater than 85 percent and 95 percent, respectively. The proportion of mixing is advantageously 2 parts of phosphoric acid to 1 part of sulfuric acid (by volume) but a considerable variation is allowable, While still achieving the objects of the invention. Into this acid mixture, various additives are incorporated, i.e. at least one additive selected from the above-mentioned group is incorporated into the acid mixture. The amount of additive is variable in accordance with the composition thereof; see the illustrative examples hereinafter disclosed. Accordingly it is also to be understood that the amounts of additives are not restricted to those disclosed by way of illustration in the examples.
As regards metals to be polished, various kinds of metals can be objectives of the present method. The present method affords particularly excellent effect upon various kinds of stainless steel, aluminum, aluminum alloys and the like.
In the practice of the present electrolytic polishing method, the electrolysis is carried out by the use of the above-mentioned liquid as an electrolyte solution, with the article to be polished as anode, and lead, lead allay, carbon or the like as cathode. The voltage is preferably more than 7 volts, and the amperage is preferably more than 5 amperes/dm. There is no limit as to the elec trolysis temperature but a temperature about 40 C. is preferable. There is also no limit to the electrolysis time but the polishing will be finished usually in several minutes. These conditions are variable according to the composition of the electrolyte solution and the substance to be polished but those skilled in the art can readily select the most suitable conditions.
The following examples, wherein the procedure is as set forth in the preceding paragraph, are given to illustrate the present invention without limiting its scope:
EXAMPLES-COMPOSITION OF ELECTROLYTE SOLUTION FOR POLISHING Phosphoric Gluconic Acid Acid Acid Sodium Gluconate (a) (a) Potassium Calcium Gluconate Gluconate (a) (a) Ethylene Picoline Quinoline Glycol (g.) (g.)
NOTE 1.The abbreviations cc. and g. stand for cubic centimeters and grams, respectively.
NOTE 2.The concentration of the sulfuric acid is 95%.
The concentration of the phosphoric acid is CONDITIONS OF ELECTROLYTIC POLISHING Example Anode Cathode Voltage Current Tempera- Time State of polished No. (v.) (A/dmfl) ture 0.) (min.) substance I 18-8 stainless steel Carbon 7 5 6 Mirror surface.
.do d 7 12 15 3 Do. 10 8 3 Do. 20 20 70 1 Do. 10 12 2 D0. 7 20 60 3 Do. 7 20 40 3 Do. 18 or 16, 13 stainless steel 7 20 20 3 Do. 18-8 or 18, 16, 16, stainless steel 7 30 60 3 Do. Aluminum L 7 20 3 Do. 18-8 or 18, 16, 13, stainless steel 10 40 3 Do. 18-8 stainless steel L d 7 20 50 5 Do. do 7 30 5 Do. 7 30 7O 5 Do. 7 40 60 5 Do.
No'rE.v.=volts; A/dmfi =amperes per square decimeter; min.=minutes.
What is claimed is:
1. A method for polishing stainless steel which cornprises electrolyzing a solution consisting essentially of a minor proportion of (a) at least one member selected from the group consisting of gluconic acid, alkali and alkaline earth metal salts thereof and picoline, and (b) ethylene glycol, and a predominant proportion of concentrated aqueous phosphoric acid and concentrated aqueous sulfuric acid, with the metal to be polished constituting the anode.
2. A method for polishing stainless steel according to claim 1 in which the voltage is more than 7 volts, the amperage is more than 5 amperes/dm. and the temperature is above 40 C.
3. A method for polishing stainless steel according to claim 1 in which the initial concentration of the phosphoric acid is more than by weight and the initial concentration of the sulfuric acid is more than by weight.
4. A method in accordance with claim 1 wherein the 20 proportion of phosphoric acid to sulfuric acid is about 2:1
by volume, and the solution contains about 10 grams of sodium gluconate and about 50 grams of ethylene glycol for each 400 milliliters of concentrated sulfuric acid.
References Cited UNITED FOREIGN PATENTS Australia. Great Britain.
JOHN H. MACK, Primary Examiner.
40 R. K. MIHALEK, Assistant Examiner.
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|U.S. Classification||205/680, 252/79.4|
|International Classification||C25F3/24, C25F3/00, C25F3/20|
|Cooperative Classification||C25F3/24, C25F3/20|
|European Classification||C25F3/20, C25F3/24|