| 摘要 |
A pierced billet is fed through a plug rolling mill, equipped with a plurality of grooves. Initial rolling is effected in conventional manner, i.e. the shell is (i) rammed over a forming plug mounted on the front end of a mandrel, (ii) drawn over the plug by the work rolls, (iii) removed from the mandrel and (iv) returned to the entering side of the mill. Rather than effecting a second pass on the shell in the same roll groove, the shell is transferred to an adjacent receiving trough, aligned with a second groove of the same work roll. A second shell is then placed on the trough aligned with the first roll groove, thereafter the first shell is given a second pass in conjunction with the first pass of the next shell. Because of the use of more than one groove for subsequent passes, each roll pass can be contoured to suit the reduction desired. Thus, use of a second groove for the second pass permits a reduction in the roll flare employed, such that a significantly rounder tube can be delivered in the finish pass. |
