Development of Dimensional Control Technology for Seamless Steel Pipe Rolling by Controlling Circumference Length in Sizing Mill

It is increasingly important to improve dimensional control techniques for pipe rolling to meet stringent requirement for dimensional accuracy. Sizing mill, which is the final process for seamless steel pipes, is an important mill that determines outer diameter accuracy and roundness. Outer diameter accuracy and roundness of seamless steel pipe is usually controlled by fill in seamless steel pipe into caliber roll, which’s shape is a perfect circle of the final stand. However, depending on size of product, caliber roll’s shape of the final stand became elliptical, making it difficult to achieve both high precision control of outer diameter accuracy and roundness. Therefore, in this study, we proposed to divide the role of stand for controlling outer diameter accuracy and roundness in order not to be affected by caliber roll’s shape of the final stand. Outer diameter was determined by controlling circumference length at the penultimate stand. And roundness was controlled at the final stand. As a result of the actual test, it was confirmed that the seamless steel pipe can be controlled by the new rolling control technology considering the roll wear aiming at the outside diameter accuracy and roundness. The newly proposed dimensional control technique enabled to obtain outer diameter and roundness of seamless steel pipe with high accuracy by means of several size of caliber rolls.