| 摘要 |
PURPOSE:To suppress the thickness increase in an unnecessary part and to improve yield by maintaining the part to be thick-walled at the temp. lower than the part to be thin-walled and loading compressing force to a pipe material in the axial direction thereof. CONSTITUTION:High-frequency current is supplied from a high-frequency heater 25 to a heating coil 13B having a track shape and a pipe material 1 is heated. A cooling medium injector 24 is operated by the command from a control device 26 when the max. set temp. attained to the temp. in the part 1a and part 1b is detected by temp. sensors 23a, 23b. A cooling medium 20 is injected from the injection port 19a of a cooling nozzle 19 to the neighborhood of the part 1a of the material 1; at the same time, the output of the heater 25 is regulated to control the temp. in the part 1a and the temp. in the part 1b so as to attain respective set working temp. A working device for increasing the thickness is turned on upon lapse of prescribed time. The material 1 is then upset by said device. The uneven-thickness pipe having the thick-walled part 1a and the thin-walled part 1b and having the peripherally changing wall thickness is formed.
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