Forming process and its apparatus in the pipe mill

To promote the forming performance of band material into pipes and to decrease the number of forming stages and changes of the forming rolls in the steel pipe mill, considering that it is superior when forming the band material into pipes of required diameters if the sectional shape of the band material is provided with a curved surface which changes its curvature continuously into the required diameter, we provide a curved roll surface of tube mill machine changing continuously. In a continuous roll forming in accordance with the present invention, a forming roll having an approximate involute curve based upon a polygon comprising a plurality of sides is used. By using the conventional rolls in various combinations therewith in each stage of forming as a horizontal roll, side roll and upper intermediate roll or a cage roll, the number of stages of the forming roll can be reduced. Moreover, the production of steel pipes having various diameters and thicknesses in a broader range from small diameter to large diameter pipes can be formed by a single set of forming rolls. Also the edge bending of the band material is corrected and the influence due to its spring back is reduced to increase the form ability in the initial and intermediate forming stages in the pipe making machine.
Forming roll apparatus for a pipe milling machine characterized in that, in forming each portion of the band material in the forming region in the production of pipes by continuous roll forming, in order to form with a part or the whole roll surface by changing the contacting direction of a forming roll responsive to the width of the material being formed and the required forming stage, a part or the whole sectional curve of the roll surface includes a sectional curve comprising an involute curve based upon a polygon having a plurality of sides previously set, so as to agree with the curve of the required portion of the band material of each roll flower of the steel pipes having various diameters in said forming region, wherein said roll apparatus includes a pair of upper and lower forming rolls for bending the edge portion of the band material, and wherein the contacting direction of at least one of said rolls is changeable.