| 摘要 |
In a method of manufacturing seamless tubes according to the present invention, piercing from a solid billet can be accomplished through one pass by means of a piercing mill ao the present invention, piercing from a solid billet can be accomplished through one pass by means of a piercing mill at the piercing ratio above 4.0 or the expansion ratio above 1.15, or the wall thickness/outside diameter ratio below 6.5%, and the piercing mill having cone-shaped rolls is used with its feed angle beta and cross angle gamma satisfying the following relations, 8 DEG </= beta </=20 DEG 5 DEG </= gamma </=35 DEG 15 DEG </= beta + gamma </=50 DEG and the solid billet diameter do, outside diameter d and wall thickness t of a hollow shell after piercing satisfying a prescribed condition for realization, thereby manufacturing equipments can be largely simplified.
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