PURPOSE: To improve parts life and machining accuracy of the device by forming a groove on the inside surface of the part to be machined of a tube through the rotation of a grooving plug as the tube to be machined is moved in the axial direction and thereby suppressing the slippage of a machining roll and a backup roll.
CONSTITUTION: In case of increasing the pressing quantity of a machining roll 12, a backup roll is moved in the direction of the center of a tube 1 to be machined, by operating the adjusting mechanism of a shaft 13 by which the backup roll 20 is fixed. By this adjusting mechanism, the backup roll 20 is all simultaneously moved for the same quantity and the moving quantity is individually adjusted. Consequently, the pressing force of the machining roll 12 is increased, and the inside wall of the tube 1 is strongly pressed to a grooving plug 7. Thus, since the tube 1 is pressed linearly on its outer circumference, the protrusion 7a of the grooving plug 7 provided inside the tube is pressed with a prescribed width, and an internally grooved tube 11 is formed which is provided with a continuous groove 10 on the inside wall.
SUZUKI YOSHIO
KAGAWA MANABU
