Prodn. of large dia. pipes comprises use of U and O presses. In the O press, the free ends of the U sides are brought together before the rounding process takes place. The bottom region between three o'clock and nine o'clock orientations in the U form is preformed in such a way that at the moment of closure of the edges, the pipe cross-section has a form of an equilateral triangle with grossly rounded corners. The max. width (a) of the triangle corresponds to the final pipe dia.. The radius of the frontal region of the punch contour of the U press exceeds the nominal pipe radius.
