PURPOSE: To improve the quality of product by displacing the axial center line of a plug bar by a prescribed quantity from the pass line of a mill to the direction of one side of guide shoes located oppositely to each other and setting the face angles at the inlet and outlet sides of respective main rolls to respectively different angles.
CONSTITUTION: The upper and lower main rolls 21, 22 of a skew rolling mill are crossed with each other at a prescribed crossing angle (γ) with respect to the horizontal plane of a pass line PL along which a blank pipe passes, and the axial center of a plug bar 26 for holding a rolling plug 27 is made to coincide with the pass line PL. At that time, the relation between the face angles α1, α1' at the inlet side of respective main rolls 21, 22 is made to α1<α1', and the relation between the face angles α2, α2' at the outlet side is made to α2>α2'. Further, the axial center of plug bar 26 is previously set by displacing it by a prescribed quantity to the left side with respect to the center line in its longitudinal direction at the pass line PL, at need. In this way, a seamless steel pipe free from thickness deviation, inner and outer surface flaws, and cracks, etc. can be manufactured.
FUNIYUU YUTAKA
ARATAMA MIKIO
Next Patent: SKEW ROLLING MILL FOR MANUFACTURING SEAMLESS STEEL PIPE