| 摘要 |
<p>An inner tube (2) is inserted into an outer tube (1), and an annular high-frequency induction heater (4) or a burner, and a cooler (5) adapted to sprinkle cooling water, which are combined unitarily with each other, are inserted into the inner tube (2) so that this combination of the heater and the cooler can be moved in the lengthwise direction of the inner tube (2). In accordance with a movement of the heater (4), the inner tube (2) is heated with lines of magnetic flux (6) or a gas flame and annularly expanded. The portion (9) of the inner tube (2) which is thus expanded with the heat from the heater (4) is cooled annularly with the cooler (5) moving after the heater (4) toward a position immediately behind the expanded portion (9). The expanded portion (9) of the inner tube (2) exhibits an effect of expanding a cooled portion behind the portion (9), so that this cooled portion yields, whereby the expansive deformation of the inner tube (2) occurs. When the heater (4) and cooler (5) have been moved along the entire length of the inner tube (2), the inner tube (2) comes to be combined firmly with the outer tube (1) owing to the expansion of the inner tube (2). The above-described procedure of expanding an inner tube is also applied to expand an outer tube (1) of a combined double tube. The outer tube (1) is separated form the inner tube (2) by expansion.</p> |
