| 摘要 |
PROBLEM TO BE SOLVED: To prevent mill scale from being left in a complete screw part at an end part. SOLUTION: When screw-cutting the end part of an oil well pipe 1, the screw-cutting is performed by holding the oil well pipe 1 at a position having a ratio L/D of a projecting length L from chuck devices 2 and 3 up to an end face of the oil well pipe 1 and an outer diameter D of the oil well pipe 1 of≥3.0 and≤4.5 when the outer diameter D is less than 88.9 mm and a ratio t/D of thickness t and the outer diameter D is≤0.07, the L/D of≥2.5 and≤3.5 when the t/D exceeds 0.07, the L/D is≥2.0 and≤3.5 when the outer diameter D is≥88.9 mm and≤139.7 mm and the t/D is≤0.07, the L/D is≥1.5 and≤3.5 when the t/D exceeds 0.07, the L/D of≥1.5 and≤2.5 when the outer diameter D exceeds 139.7 mm and the t/D is≤0.07, and the L/D of≥1.0 and≤2.5 when t/D exceeds 0.7. As a result, machining accuracy at the end part becomes good and mill scale is not left in the complete screw part, even when a distal end is bent and the end part becomes an elliptical shape by being held by large pressure. COPYRIGHT: (C)2009,JPO&INPIT
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