| 摘要 |
PURPOSE:To provide a double-pipe having excellent strength and heat conductivity, by radially expanding a inner pipe in a prescribed expanding rate of inner diameter after radially contracting a gap between an outer pipe and the inner pipe inserted to the outer one to be smaller than a prescribed dimension. CONSTITUTION:A gap between an outer pipe and an inner pipe is radially contracted to be <=0.02mm. after inserting the inner pipe into the outer one. Next, the inner diameter of the inner pipe is expanded by 1.3-2% by radially expanding it with a internally expanding plug. Then, the adhesive force between both the pipes is improved, and a generation of residual stress in the axial direction of the inner pipe is restricted, and a double-pipe having excellent strength and heat conductivity is obtained. |
