METHOD OF PIERCING IN SCREW-ROLLING MILL Russian patent published in 2017 - IPC B21B19/04 

FIELD: metallurgical engineering.

SUBSTANCE: method includes the piercing of a round in a screw-rolling mill. Reduction of the difference and pipes and shells ovality are ensured by the fact that the piercing is produced in a mill having four rollers, all the rollers are driven, the two rollers are cup-shaped and of the same size, the other two rolls are mushroom-shaped and of the same size, the ratio of the diameter in the necking of the cup-shaped roll to the diameter in the necking of the mushroom-shaped roll is 1.1-1.4, the toe angle for the cup-shaped rolls is from 5 to 7°, for mushroom rolls is from 7 to 10°, the feed angle for all rolls is from 14 to 16°, the cobbing in front of the nozzle of a simple male punch is 6%, the cobbing in the necking is 8%.

EFFECT: production of seamless pipes and hollow pipe shells with a screw piercing.

4 dwg, 1 tbl