| 摘要 |
PROBLEM TO BE SOLVED: To make hot rolling into one process and to enable cost reduction by making a solid round billet having a diameter not more than a prescribed outside diameter into a hollow tube stock and executing cold diameter reducing/ elongating work with an inclined roll type piercing mill provided with main rolls and a guide for guiding a material. SOLUTION: The heated solid round billet B whose outside diameter is <=100mm is bitten in the inlet part of the conical main rolls 1, 1 which are oppositely arranged around the pass center X-X so as to form a crossed axes angleγand inclined angle. After that, the billet is matched with the pass center X-X with disk rolls, spirally moved by the rotation of the main rolls 1, 1 and pierced by receiving intermittent reduction once per a half rotation between the plug 2 which is interpenetrated in the position of the axial center and the main rolls 1, 1. The material to be rolled is swelled out to the outside in the radial direction by rotation, but suppressed by contacting with the disk rolls, rolled while presenting as elliptical shape and gradually made into the circular hollow tube stock H. In this way, the metallic tube is worked by hot rolling of one process and the cost reduction is enabled.
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