| 摘要 |
A piercing method for manufacturing a seamless pipe capable of suppressing the rotary forging effects and suppressing the redundant shear strain without excessive narrowing of the roll diameter is provided. This method is characterized by holding a feed angle ² and a cross angle ³ of main rolls in a range satisfying the following expressions (1) to (3), setting the relationship between outer diameter "do" of the solid billet and the outer diameter "d" and thickness "t" of a hollow piece after piercing so as to satisfy the following expression (4), and further setting the relationship between inlet diameter D 1 and outlet diameter D 2 of the main roll with the above-mentioned "do", "d" and ³ so as to satisfy the following expression (5). 8 ° ‰¤ ² ‰¤ 20 ° 5 ° ‰¤ ³ ‰¤ 35 ° 15 ° ‰¤ ² + ³ ‰¤ 50 ° 1.5 ‰¤ ˆ’ ¨ r / ¨ ¸ ‰¤ 4.5 ( d / d 0 ) / ( 0.75 + 0.025 ³ ) ‰¤ D 2 / D 1 In the expression (4), ¨ r = ln ( 2 t / d 0 ) €‰ and €‰ ¨ ¸ = ln { 2 ( d ˆ’ t ) / d 0 }
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