B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
B21B—ROLLING OF METAL
B21B19/00—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work
B21B19/02—Tube-rolling by rollers arranged outside the work and having their axes not perpendicular to the axis of the work the axes of the rollers being arranged essentially diagonally to the axis of the work, e.g. "cross" tube-rolling ; Diescher mills, Stiefel disc piercers or Stiefel rotary piercers
B21B19/06—Rolling hollow basic material, e.g. Assel mills
B21B19/10—Finishing, e.g. smoothing, sizing, reeling