Wellrohr sowie Verfahren und Gerät zu seiner Herstellung.

摘要

A flat strip-like metallic material (1) having both surfaces coated with a first synthetic resin layer is passed between plural pairs of upper and lower rollers (31-36) so that a U-shaped recess (12) is formed at the central portion in the longitudinal direction of the strip material and ring-like projection (13) at both edges of the strip material. Then, the strip material is bent into a spiral form. The spirally wound strip material is passed to a transferring means (5) and first, second and third extruders (6-8) to extrude molten resin and first, second and third pressing rollers operating in association with the respective extruders, whereby a second synthetic resin layer is formed at the outer circumferential portion of the adjoining edges of the spirally wound strip material, a third synthetic resin layer is formed on the back side of the recess portion of the same, and a fourth synthetic resin layer is formed on the outer circumferential surface of the recess portion and the adjoining edges of the spirally wound strip material.