Rod dynamics in a press-roller piercing mill

Abstract

The production of hotrolled seamless pipe from continuouscast rectangular blanks may be based on press-roller piercing, which includes elements of press piercing and longitudinal rolling in round grooves. At present, the piperolling line at many foreign plants includes more than ten press-roller piercing mills, capable of producing pipe in the diameter range 150-410 mm. As a rule, the press-roller piercing mills produced in Ukraine and elsewhere consist of a tworoller longi� tudinalrolling mill with round grooves. In such mills, the rod with the mandrel is positioned on the rolling axis and is held there by means of special mechanisms in subsequent piercing operations. The blank is sup� plied to the working rollers by means of a hydraulic pushod unit, which steadily braces the blank by means of the necessary force, throughout the piercing cycle. The stress-strain state in the deformation source is such as to ensure favorable compressive stress and slight extension in the pierced metal (1). To ensure the required dynamic stability of the mandrel rod in the deformation source, we need to eliminate piercing conditions associated with high� amplitude parametric oscillation in the system. In the present work, we study rod vibration in the mechanism holding the mandrel at the axis of the press-roller piercing mill. The dynamic processes at the output side of the mill were studied theoretically and experimentally in (4, 5). The forces on the mandrel rod were analyzed, and possible conditions associated with transverse vibration in the mechanism holding the mandrel at the rolling axis were identified. This research focused on simplified dynamic models of the mandrel rod in pipe� rolling mills and did not adequately address techno� logical and operational aspects of press-roller pierc� ing, such as rod vibration in the mechanism holding the mandrel at the axis. In the present work, we investigate the appearance of transverse parametric vibration in the mandrel rod of the press-roller piercing mill. We take account of the nonsteady action of the deformation source and