| 摘要 |
PURPOSE:To improve the wall thickness accuracy of an increased thickness part by calculating in advance a standard increased thickness volume, also estimating an average wall thickness of a pipe end part, deriving an upsetting length of the tube end part, based on its standard volume and average wall thickness, and upsetting it. CONSTITUTION:A temperature measuring instrument 19 of a tube end part is provided in the vicinity of the delivery, against a heating furnace 11. A heating condition of the heating furnace 11 is constant, therefore, the final heating temperature of the tube end part is varied high and low in accordance with an average wall thickness. A standard increased thickness volume of a tube body 10 is derived in advance by a measuring instrument 20, also the final heating temperature of the tube body 10 is measured by the temperature measuring instrument 19, and its average wall thickness is estimated. Based on this standard volume and average wall thickness, a control part 20 calculates an upsetting length L of the pipe end part. In accordance with this upsetting length L, the tube end part is upsetted by a die 14 and a mandrel bar 15. Accordingly the tube end part of the standard increased thickness volume portion is upsetted, and the wall thickness accuracy of the increased thickness part of a prescribed wall thickness shape is improved.
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