US 4,190,887 AGranted

Press roll piercing method

AssigneeNippon Steel Corporation

InventorsSeishiro Yoshiwara, Minoru Kawaharada, Samon Yanagimoto

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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.

Claims11

Dependent claims

In a press roll piercing method for manufacturing a hollow shell wherein a polygonal metal billet is pushed in the axial direction thereof between a pair of rolling rolls mounted one above the other and having opposed semicircular grooves therein so as to be rolled into a circular or almost circular shape, and the piercing is effected in the core portion of the billet by means of a piercing plug supported between the rolling rolls, the improvement comprising;

setting the pushing force to a predetermined value sufficient to cause a compressive stress above the yielding stress of the polygonal metal billet which is being pushed when the reacting force acts upon the billet;
setting the peripheral speed of the rolling rolls and the pushing speed of the pusher in relation to each other so that the volume per unit time of the hollow shell being discharged from the rolling rolls after the press roll piercing has reached a stable condition after the biting and the volume per unit time of the polygonal metal billet being pushed into the rolling rolls become substantially equal;
and
causing the billet pushed by the pusher at the pushing speed to be gripped between the rolling rolls rotating at the peripheral speed.

1 more element

setting the pushing force to a predetermined value sufficient to cause a compressive stress above the yielding stress of the polygonal metal billet which is being pushed when the reacting force acts upon the billet;
setting the peripheral speed of the rolling rolls and the pushing speed of the pusher in relation to each other so that the volume per unit time of the hollow shell being discharged from the rolling rolls after the press roll piercing has reached a stable condition after the biting and the volume per unit time of the polygonal metal billet being pushed into the rolling rolls become substantially equal;
causing the billet pushed by the pusher at the pushing speed to be gripped between the rolling rolls rotating at the peripheral speed;
pushing the billet between the rolls at the start of the rolling at a pushing speed V.sub.p,
V.sub.p =K.sub.1 K.sub.2 (L.sub.1 /L.sub.2)V.sub.R ;
and
carrying out the rolling and piercing of the billet while controlling at least one of the parameters from among the pushing speed and the peripheral speed of the rolling rolls beginning from a minute period of time after the billet is gripped between the rolling rolls so that at least one of the parameters from among the rolling load, the torque of the rolling rolls and the electric current for the roll driving motor approaches a target value.

4 more elements

Dependencies are inferred from the claim text.