| 摘要 |
PURPOSE:To shorten the time for maintaining a uniform temp. and to permit maintaining of a wire rod precisely at a uniform temp. by subjecting the wire rod which is quickly heated to a prescribed temp. to direct resistance heating at the time of hardening the wire rod inline then subjecting the same to tempering including isothermal holding. CONSTITUTION:The wire rod W is run in an arrow direction on a passage L through a hardening device 10 consisting of a heating means 11 and a quick cooling means 12 and a tempering device 20 consisting of a quick heater 21 and a direct resistance heater 22 provided with paired electrode rings 22a, 22b for pinching the wire rod W on the line L. The entire section of the wire rod W is uniformly hardened from the circumferential direction over the entire length in the hardening device 10. The successively hardened wire rod W is then heated over the entire section up to the prescribed temp. or the temp. slightly higher than said temp. (but below the A1 transformation point) in the heater 21. The voltage by the direct resistance heating is impressed on the wire rod W between the paired electrode rings 22a and 22b for the prescribed time. The impressed voltage is so set as to generate the Joule heat corresponding to the quantity of the heat radiated at the time when the heated wire rod is allowed to cool. The entire section of the wire rod is then annealed by maintaining the same at the uniform temp. for the prescribed time and thereafter, the wire rod is cooled.
|
