| 摘要 |
PURPOSE:To improve the service life of a piercing plug by supplying a coolant through a mandrel bar into the region of a billet in a hot state where the billet is under piercing by the piercing plug. CONSTITUTION:Plural injection holes 6 for injecting the coolant in the direction of the piercing part at the top end side of the plug 2 are provided to the rear end side of the plug 2 and the coolant introduced through the mandrel bar 1 is supplied from the holes 6 to the piercing part. The piercing part and the plug itself are thereby cooled and the service life of the piercing plug is improved.
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