Patent ID: 8151612

Claim:
An elongation rolling control method characterized by comprising: a first step of measuring a groove bottom wall thickness of a hollow shell in a stand immediately before an installation position of an ultrasonic wall thickness gauge installed between predetermined stands of a mandrel mill, a second step of calculating an outer diameter of a mandrel bar based on a set value of a roll gap in the immediately preceding stand and the groove bottom wall thickness of the hollow shell measured in the first step, a third step of determining a location in a lengthwise direction of the mandrel bar for which the outer diameter was calculated in the second step based on positional information on a bar retainer, a fourth step of calculating a distribution in the lengthwise direction of the outer diameter of the mandrel bar by repeating the first step through the third step, a fifth step of determining a location in the lengthwise direction of the mandrel bar which contacts the hollow shell in a stand subsequent to the immediately preceding stand based on positional information on the bar retainer, a sixth step of calculating the outer diameter of the location in the lengthwise direction of the mandrel bar determined in the fifth step based on the distribution in the lengthwise direction of the outer diameter of the mandrel bar calculated in the fourth step, and a seventh step of setting the roll gap in the subsequent stand based on the outer diameter of the location in the lengthwise direction of the mandrel bar calculated in the sixth step.