METHOD OF HOLLOW BILLETS PRODUCTION Russian patent published in 1996 - IPC

FIELD: metallurgy, rolling, hollow blanks production. SUBSTANCE: aim is to improve quality of hollow billets due to decrease of inner surface oxidation of pierced hollow billets in production of hollow billets using method of cross-screw rolling by piercing in barrel-type roll piercing rolling mill. Method provides for piercing of heated solid billet in barrel-type roll piercing rolling mill on mandrel held by rod, on which after mandrel conical-cylindrical bush is mounted with capability of relative motion, and hollow billet release by removal of rod with mandrel and bush. Method is distinguished for the fact, that since the moment of mandrel nose coming out of billet rear butt rod with mandrel is being moved along rolling run at speed of rolling. After hollow billet coming out of rolls hollow billet and rod with mandrel and bush are stopped simultaneously, cooled and then hollow billet is released. Inner cavity of hollow billet during whole process of piercing and cooling remains plugged: from one side - by mandrel, that does not come out beyond limits of hollow billet rear butt, and from other side - by cone-cylindrical bush, so that air entrance in inner cavity of hollow billet is limited or fully prevented and intensity of hollow billet inner surface oxidation is decreased. EFFECT: improved quality of hollow billets, decreased their inner surface oxidation. 4 dwg