Cold roll forming method for reducing a diameter of a metal pipe, and a metal pipe product having its diameter reduced by such method

摘要

A cold roll forming method for reducing a diameter of a metal pipe and a metal pipe product having a diameter reduced by such a method are disclosed, wherein the method includes: passing a raw metal pipe through a set of pre-forming rolls so that it can be pre-formed into an intermediate metal pipe having an elliptical, elongated circular or rectangular cross-sectional shape; and then passing the intermediate metal pipe through a set of diameter-reducing rolls disposed on a downstream side of the set of pre-forming rolls so that it can have its outer circumferential length reduced to be smaller than an outer peripheral length of the raw metal pipe, while at the same time being re-formed into a circular cross-sectional shape or any other cross-sectional shape different from the cross-sectional shape of the intermediate metal pipe.