| 摘要 |
PROBLEM TO BE SOLVED: To provide a mandrel mill, capable of raising the elongation ratio of a pipe and further suppressing generation of a hole defect. SOLUTION: The first means of the invention is a mandrel mill, which is provided with a plurality of rolling stands individually having two grooved rolls R11, R12 arranged, and in which each of the roll diameter ratios (D<SB>R</SB>/D<SB>C</SB>) of the first rolling stand and the second rolling stand is set to be≥4.6. The second means is a mandrel mill, which is provided with a plurality of rolling stands individually having three grooved rolls R21-R23 arranged, and in which each of the roll diameter ratios (D<SB>R</SB>/D<SB>C</SB>) of the first rolling stand and the second rolling stand is set to be≥2.8. COPYRIGHT: (C)2009,JPO&INPIT
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