To provide a tube with a grooved inner face capable of preventing a stock tube from being broken in its manufacturing process and excellent in grooving property, and to provide a method for manufacturing the tube.
A holding plug 2, a plug shaft 4, and grooved plugs 5a and 5b are disposed inside a stock tube 1. Work rolls 16a and 16b are disposed at the position corresponding to the grooved plugs 5a and 5b outside the stock tube 1, and back-up rolls 18a and 18b are disposed so as to be brought into contact with the work rolls 16a and 16b in a rolling manner. In a roll form rolling method for working the stock tube 1 by using a tandem type manufacturing device in which a sizing die 8a is disposed between the work roll 16a and the work roll 16b and a sizing die 8b is disposed on the downstream side of the work roll 16b in the tube drawing direction, the working ratio D1 at the holding die 3 is set to be ≤ 19%, the working ratio D2 in other diameter reducing works or diameter reducing and rolling works is set to be ≤ 10%, and the total working ratio DT is set to be ≤ 35%, respectively.
SAEKI CHIKARA
IWAMOTO HIDEKI
TATEYAMA TOMOYUKI
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