| 摘要 |
PURPOSE:To reduce occurrence of wall thickness deviations of products by pausing a mandrel at an intermediate position toward the extruding position, performing the 1st piercing, moving a billet forward by a preliminary pressing, performing the 2nd piercing, and extruding a tube. CONSTITUTION:The 1st piercing, in which a mandrel 2 is moved forward to the position retracted by prescribed distance from a proper position after extruding action and is paused, is performed. A retracting distance L1 of the mandrel 2 is preferred to be 50-100mm. Then, a billet A is subjected to a preliminary pressing in the extruding direction and a centering condition of the mandrel 2 is corrected. The correction in a state of a stem 4 moved forward by 20-40mm is preferable. Then, the mandrel 2 is moved forward to the final position to perform the 2nd piercing before the stem 4 is moved forward so as to press the billet A, to perform a productive extrusion to obtain a tube. In that method, wall thickness deviations are reduced.
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