Abstract: A press roll piercing method wherein a polygonal billet is pushed in the axial direction thereof between a pair of driven rolling rolls mounted one above the other and a piercing plug is supported in the center of the pass by a mandrel, is improved by selecting a pushing force of a predetermined value which corresponds to a stress above the yield stress of the billet at the starting of the piercing although the actual stress occurring at the starting of the piercing may or may not exceed the yield stress by selecting the pushing speed and/or the peripheral speed of the rolls such that the volume of the billet pushed in per unit time and the volume of the hollow shell discharged from the rolling rolls become substantially equal, whereby the billet is positively gripped by the rolling rolls.

Abstract: In the rolling of metallic material by using a rolling mill having a working roll for each surface of the workpiece reduced and having the shafts fixed with respect to movement in the direction of travel of the workpiece, the workpiece is rolled at such a high reduction rate in cross-sectional area that the contact angle .theta. between the working roll and the workpiece can have a value of .gtoreq. tan.sup.-1 .mu. (.mu. being the coefficient of friction between the working roll and the workpiece), and the rolling operation is carried out by pushing the workpiece between the working rolls, so that a neutral point of relative movements between the rods and the workpiece wire remain within the surface along which the working roll and the workpiece contact each other.

Abstract: A metal extrusion process with high reduction wherein a metal blank is extruded from a container through an opening which is formed by a plurality of work rolls. The metal blank is guided to the opening from the outlet of the container by causing the metal blank to adapt to the shape of the opening by means of a forming die so that the metal blank does not overfill the opening. This extrusion process is capable of forming the metal blank into a product having the desired cross section with high elongation in one pass and also the radius of curvature of the corner portion of the product can be freely adjusted.

Abstract: A method of producing a cylindrical metallic tubular body in a press roll piercing mill. The method involves applying a pressing force to a polygonal metal billet in the axial direction thereof while guiding the billet by means of a guide during its advance, rolling corner portions of the billet to a certain degree with a pair of rolling rolls having semicircular grooves disposed above and below the billet prior to the contacting of a plug with the center of the front end surface of the billet, and successively piercing the billet by means of the plug while the billet is rolled, the tip portion the plug being retained on the pass center line by the rolling rolls.

Abstract: In a method of producing seamless steel tube from billet having a square or rectangular cross-section by the step of piercing a workpiece and rolling steps following the piercing step, each of such steps being conducted with a plug held by a mandrel toward the center of cross section of the workpiece while the workpiece is rolled by a pair of rolls with axes arranged horizontally.