Continuous manufacturing method for a metal welded tube and a manufacturing apparatus therefor

A manufacturing method for making a metal welded tube, comprising the steps of:

• providing a metal band coil for supplying a metal band, a plurality of molding rollers for molding said metal band into a tubular member, abutting rollers abutting edge surfaces of the tubular member disposed downstream from said plurality of molding rollers, a high frequency preheating unit including an inductor disposed between said abutting rollers and said plurality of molding rollers, an impeder disposed within said tubular member corresponding to said inductor, a high density energy melting and welding unit, and an inert gas feed nozzle disposed within said tubular member corresponding to said energy melting and welding unit;
• sequentially passing said metal band through said plurality of molding rollers while uncoiling said metal band from said metal band coil, to form a tubular member from said metal band which surrounds said impeder, said tubular member having abutting edge surfaces;
• preheating said tubular member to a temperature lower than a welding temperature of said metal band using said inductor and impeder of said high frequency preheating unit;
• guiding said tubular member between said abutting rollers;
• using said welding torch of said high density energy melting and welding unit at an upstream side of a line connecting the centers of said abutting rollers, for melting and welding the preheated said abutting edge surfaces of said tubular member while using said abutting rollers to maintain said abutting edge surfaces together, to produce said welded tube.