Nippon Steel Corporation

Wataru Midzutani

Koe Nakajima

Toshio Kikuma

Seiichi Sasahira

Keitaku Ondo

A method and apparatus for manufacturing metal pipe. The edges of a metal plate are bent up slightly, and the thus bent plate is then bent into a U-shape cross-section blank. The U-shape blank is finish-formed into an O-shaped blank with the longitudinal edges opposed to each other in a position for welding by placing one end of the U-shaped blank into at least one two-part die the parts of which are movable toward and away from each other. The die has at least one portion with the shape of the opposed die recesses defining a reforming area on one end of the die portion which has an O-shaped cross-section, a finish forming area in the middle of the length of the die portion having an O-shaped cross-section, these O-shaped cross-sections being the shape of the O-shaped blank, and a transitional area at the other end of the die portion having a cross-sectional shape which changes gradually from an O-shape adjacent the finish forming area to an oval shape elongated in the direction of movement of the die parts at the other end of the die portion. The transitional area is relatively short as compared to the remainder of the die parts. This one die portion is shorter than the length of the blank. The U-shaped blank is placed in the die with the elongated dimension of the cross-section corresponding to the elongated dimension of the oval shape and with one end of the blank at the one end of the die portion, and the two part die is closed for shaping the U-shaped blank into a blank having an O-shaped cross-section reformed portion on said one end of the blank, a finished O-shaped cross-section and a transitional section. The two part die is opened and the thus formed blank along the die until the edge of the transitional section of the blank is at the end of the finished forming area of the die portion adjacent the reforming area. The steps of positioning the blank and opening and closing the die are repeated until the blank is completely formed into an O-shaped cross-section, and the opposed edges of the plate are then welded to produce the O-shaped cross-section blank.

Method and apparatus for manufacturing metal pipe

In a method and an apparatus for manufacturing a metal pipe wherein a flat strip or skelp is formed into a cylindrical pipe while being fed in its longitudinal direction by a forming mill having a prefinishing stand, a train of forming stands for forming the skelp with a U-shaped cross section, and a train of finishing stands, the improvement wherein both edge surfaces of the skelp are caused to contact in substantially point contact recess-defining surfaces of concave V-shaped recess in pairs of forming rolls, the respective rolls which are disposed symmetrically in a plane normal to the pass line as the skelp moves through the train of forming stands along the line, and the skelp has a bending load applied by the forming rolls so as to form the skelp into a U-shaped skelp. According to this method and apparatus, there is no need to change the forming rolls even if the diameter or wall thickness of the pipe to be manufactured are changed, and also since the skelp edge is held, during the forming process, at positions in a plane normal to the pass direction by the surfaces of the concave recesses, the skelp is not twisted around the pass line so that threading of the forming mill can be carried out accurately and easily.

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Kitakyshu, Japan

Wataru Midzutani