| 摘要 |
PURPOSE:To prevent air bubbles from occurring between a steel pipe and a vinyl chloride pipe and thus prevent the vinyl chloride pipe from overexpanding by, when a steel pipe inserted with a vinyl chloride pipe is heated in its outer surface through hot-air, changing the distribution of the hot-air flow rate in a direction of a pipe axis and controlling the temperature rising pattern of respective parts of the pipe. CONSTITUTION:In a nozzle box 6 in the latter half of a first heat-zone, a gate valve 10 is mounted. And, at an outlet side of the first heat-zone, a pipe central thermometer 11 and a pipe end thermometer 12 are disposed. Through the increasing and decreasing in the opening area, the hot-air flow rate in each nozzle box is regulated. From the index value T1 of the pipe central thermometer 11 and the index value T2 of the pipe end thermometer 12, a temperature difference T1-T2 is obtained and in the case that the value is negative, a gate valve control unit 13 gives an instruction to a driving unit 14 in accordance with its value for decreasing the opened area of the gate valve 10. On the contrary, in the case that the temperature difference T1-T2 is positive, the gate valve control unit 13 gives an instruction to the driving unit 14 in accordance with its value for increasing the opened area of the gate valve 10. |
