The rolling mill has at least three inclined rollers at 120 degrees to each other. Each roller has an approach part in front of the shoulder, a trailing part behind it. The continuous transitional section from approach to trailing part is determined by three tangential radii, which merge into the sections. The central transitional radius (R2) is larger than the approach radius (R1), and smaller than the trailing radius (R3). Transitional and trailing radii have the same direction of curvature, and all radii are described by the shoulder height (Hs) of the Assel roller. Shoulder height is calculated from blank diameter and the ratio of hollow block diameter and hollow block wall.
