| 摘要 |
PURPOSE:To obtain a plurally-layered heat-insulating pipe, which has a heat- insulating material hard to powder and, has high durability and is suitable for bending, by inserting an inner pipe covered with a heat insulating material into an outer pipe, and then, passing the pipe through rolls having projections and recesses and successively through sizing rolls. CONSTITUTION:A plurally-layered pipe formed by inserting an inner pipe 1 covered with a heat insulating material 2 into an outer pipe 3 is passed through a space between an upper roll 51, a lower roll 52 and side rolls 61, 62 having projections respectively in a group of radially contracting rolls. A part of the outer pipe 3 is rolled to have recesses as shown by 41 by the projections of respective rolls. Next, ordinary sizing rolls are arranged at the rear side of said rolls having projections, and the recesses 41 formed at the preceding stage are bent while radially contracting the pipe. The recesses are further bent as shown by 43 by the following sizing rolls 83, 84, 93, 94 arranged after said sizing rolls to have a strong spacing function. |
