PURPOSE: To prevent the generation of excessive force by comparing the radial forces generated on the rolls of a roll pair with each other and, in the case the forces are over the allowable deviation force, adjusting the force along the radial direction and simultaneously keeping a compared roll at a position corresponding to a reference value in the case the forces in the radial direction which are generated on the rolls of a pair of rolls are compared with each other and over the allowable deviation force.
CONSTITUTION: In the case the forces on the side of a controller are over the deviation force between the outer rolls 1/2, 2/2 which is set as the allowable value, the outer roll 172 of the 1st roll pair 1 is adjusted along the radial direction, that is, the depth of rolling is returned. In the case the outer roll 2/2 of the 2nd roll pair 2 is over the deviation force between the outer rolls 3/2, 4/2 which are kept at the reference value corresponding to the set depth of rolling, the outer roll 3/2 of the 3rd roll pair 3 is adjusted along the radial direction. In such a case, the outer roll 4/2 of the 4th roll pair 4 which is utilized as the compared roll is kept at the reference value which is initially set corresponding a desired outside diameter of a tube to be rolled.
MANFUREETO ETSUKERUTO