WORKING METHOD FOR INCREASING WALL THICKNESS OF CYLINDRICAL BODY

PURPOSE:To work a cylindrical body to increase the wall thickness thereof while suppressing the increase in the hardness of a working member and assuring the ductility thereof by attaching a heater for heat treatment to the rear part of a device for spraying a coolant and subjecting the material to the wall thickness increase and heat treatment at the same time. CONSTITUTION:A cylindrical body 1 consisting of a carbon steel or the like is fixed by a chucking device 3 and a fixing device 7 for said body. A local heater 6 and a heater 8 for heat treatment are operated and at the same time a coolant is sprayed from the ejection ports 5 of a device 4 for the coolant. The device 6 and the device 4 as well as the device 8 are run at the same speed V. When the temp. of the body 1 attains an equil. state, a pressurizing device 2 for increasing wall thickness is operated to extrude the body 1 at a specified swaging speed V. The equil. temp. of the part to be heated by the device 6 is kept at the temp. at which the strength of the material decreases as much as necessary for increasing the wall thickness. The equil. temp. of the part to be heated by the device 8 is kept lower than the temp. of the increased thickness part and higher than the temp. at which strength is high and martensite transformation is initiated.