Method of anodically deburring articles of copper or copper allo

Details Method of anodically deburring articles of copper or copper allo Method of anodically deburring articles of copper or copper allo

1982-09-14

1983-09-20

Tufariello, T. M.

Chemistry: electrical and wave energy

Processes and products

Electrostatic field or electrical discharge

20412995, C25F 302

Patent

active

044054220

DESCRIPTION:

BRIEF SUMMARY
The present invention has for its object to provide an improved method for anodically deburring articles of copper or copper alloys, for instance brass, aluminium bronze or beryllium bronze.
The new method according to the invention is characterized thereby that the treatment is carried out in an acid solution having a pH not exceeding 6.5 and containing


______________________________________ grams per liter ______________________________________ water 100 to 300 alkali sulphamate 50 to 100 polyhydric alcohol 400 to 800 alkali nitrate 50 to 150 ______________________________________ 2 to 50 amperes per square decimeter.
The method according to the invention results in a swift and effective removal of burrs and sharp edges from the article treated and imparts a smooth, attractive surface to the same.
In a preferred form of the method according to the invention, the alkali salts of the bath consist of ammonium salts. This has proved to result in the advantage that an unimportant volume only of gaseous hydrogen is developed during the treatment. In contradistinction thereto, the use of sodium or potassium salts will result in the development of considerable quantities of gaseous hydrogen, which, if the supply of fresh air is inadequate, may cause an explosive mixture of air and hydrogen to form above the surface of the bath. The property of reducing the development of hydrogen exhibited by the ammonium salts was quite unexpected and has as yet found no satisfactory explanation.
The method according to the invention is preferably carried out at bath voltages in the range of 15 to 20 volts and current densities (at the anode surface) of the order of 10 to 20 amperes per square decimeter. The bath temperature should not exceed 25.degree. C. Preferably the temperature is maintained within the range of 15.degree. to 20.degree. C.
The deburring action is known to be due to the fact that the current density and, consequently, the removal of material is considerably more intense at sharp edges and protruding burrs on the article than at the even portions of its surface. This property (usually referred to as "selectivity") depends on several factors, for instance the shape and size of the article treated, the shape of the cathode, the distance between the anode and the cathode, and the conductivity of the bath solution. Too large a conductivity will cause deterioration of the selectively as well as of the smoothness of the surfaces treated. Moreover, it has been found that in the method according to the invention a substantial improvement of the selectivity can be obtained by supplying the bath current during active intervals separated by idle intervals during which no current flows. Preferably the length of the active interval should amount to 1/2 to 2 minutes. For the idle interval, a length of a few seconds only, for instance 5 to 10 seconds, is sufficient and suitable.
In the method according to the invention, the conductivity of the bath can be adjusted in a simple way by adjustment of the content of polyhydric alcohol. In the preferred form of the invention in which the alkali salts are ammonium salts, the polyhydric alcohol preferably is ethylene glycol.
The composition specified below is an example of a bath for the method according to the invention.


______________________________________ Ethylene glycol 650 parts by weight Ammonium sulphamate 100 parts by weight Ammonium nitrate 100 parts by weight Water 150 parts by weight ______________________________________
The following conditions are suitable for the anodic deburring of articles of steel or aluminium alloy in the bath above specified:


______________________________________ Bath temperature 15 to 20.degree. C. Bath voltage 15 to 25 volts Anodic current density 10-20 amperes per square decimeter pH 5.0 to 6.5 ______________________________________
Adjustment of the pH of the bath is carried out by the addition of a small quantity of nitric acid. Fresh additions have to be made from tim

REFERENCES:
patent: 3556957 (1971-01-01), Toledo
patent: 4269677 (1981-05-01), Blomsterberg

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