| 摘要 |
PURPOSE:To improve the quality of a seamless steel pipe by providing a lubricating agent injection port to the top end of a mandrel bar and injecting the lubricating agent to the inside surface of a piercing pipe stock through the mandrel bar. CONSTITUTION:A lubricating material supply pipe 4 and a cooling water supply pipe 5 are disposed concentrically in the mandrel bar 2. A block 6 having at least one lubricating agent injection port 7 is attached to the top end of the bar 2. A heated round billet is supplied between a pair of upper and lower piercing rolls 3 and piercing is started by a piercing plug 1 at the top end of the bar 2. The lubricating agent is then supplied to a lubricating agent supplying pipe 4 at a set timing. The round billet is pierced under rotation and therefore the lubricating agent from the port 7 is uniformly coated on the inside peripheral surface of the pipe stock. The generation of a thickness deviation by the exfoliation of a film, etc. to the pipe stock is thus prevented and the quality of the seamless steel pipe is improved.
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