Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1991-06-28
1994-03-15
Valentine, Donald R.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
20412946, C25F 316
Patent
active
052943097
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
In semiconductor and other industries, the need is increasing to pass very clean and pure pressurized fluid through passages. To provide such passages, demand for stainless steel pipes of relatively small diameter with extra-smoothly mirror finished inner surface is increasing steadily.
This inveniton relates to the electro-abrasive polishing process of the inner surface of pipes to such an extra-smooth mirror finish as is suited for the above described applicaiton.
DESCRIPTION OF THE PRIOR ART
Conventionally, pipes whose inner surface is finished by means of electro polishing process with a thin electrode positioned along their central axis have been favored as best-suited for the passing of very clean and/or pure pressurized fluids. But the roughness of their surface finish varies so greatly that the practically guarnateed surface roughness is approximately 0.7 .mu.m Rmax at most. They involve other problems as well; such as reduction of wall thickness owing to much metal removal, costliness, and great susceptibility of finished surfaces to the aging of electrolyte and changes in the quality of pipe materials.
Meanwhile, the inventors proposed as electroabrasive polishing process of the inner surface of cylinders as per the Japanese Provisional Patent Publication No. 34227 of 1985.
This method uses a tool consisting of a rotating shaft of conductive material that is wrapped with a non-woven nylon sheet or other liquid-permeable elastic material which softly supports abrasive grains therearound. The tool is inserted in a cylinderical workpiece whose inner surface is electrolytically decomposed by a small amount of current passed through the electrolyte between the workpiece and the tool. Simultaneusly, the tool and workpiece are moved relative to each other, whereby the abrasive grains supported by the elastic material mechanically polish the inner surface of the workpiece. As the elastic material deforms in accordance with the internal contour of the cylinder, the abrasive grains are pressed against the inner surface without applying excessive pressure. Therefore, the inner surface of the cylinder is polished without deteriorating the accuracy of its profile, with the surface roughness reduced to below 0.2 .mu.m Rmax usually and to approximately 0.1 .mu.m under the most favorable conditions.
It has been desired to further improve the roughness of the inner surface of small-diamter pipe for passing pressurized fluids and other similar applications. But no methos have been proposed that can provide better surface roughness than the one just described.
SUMMARY OF THE INVENTION
An object of this invention is to provide an electro-abrasive polishing process of the inner surface of a pipe whose original roughness is approximately 3 .mu.m Rmax to an extra-smooth mirror finish of the order of tens of nm.
Another object of this invention is to provide a method of achieving the above extra-smooth mirror finish with the use of a simple tool and equipment.
Yet another object of this invention is to provide a method of achieving the above extra-smooth mirror finish in an extremely short time by applying a quick pre-polishing and a subsequent mirror polishing process.
In order to achieve the above objects, an electroabrasive polishing process of the inner surface of pipes to an extra-smooth mirror finish according to this invention comprises two processes.
One is a preliminary-polishing process in which a tool electrode, which comprises a core electrode shaft and a non-woven nylon sheet to support abrasive grains and to wrap around the core electrode, is inserted in a small-diameter pipe that is to be worked, the small-diameter pipe serving as the anode and the tool electrode as the cathode. By passing a small amount of current between the anode and cathode in the electrolyte, the inner surface of the pipe is polished by the action of electrolytic decomposition. At the same time, the tool electrode is rotated and it or the pipe is axially moved back and forth relative to each other to per
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Patent Abstracts of Japan, vol. 9, No. 209 (N-407)(1932), Aug. 27, 1985 & JP-A-60 071 122, Apr. 23, 1985.
Patent Abstracts of Japan, vol. 12, No. 120 (M-685)(2967), Apr. 14, 1988, & JP-A62 246 419, Oct. 27, 1987.
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Asagawa Keiichirou
Seimiya Kouichi
Agency of Industrial Science and Technology
Miracle Company Limited
Valentine Donald R.
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