Quality of seamless hot-rolled pipe, taking account of mandrel oscillations

Abstract

In the piercing and rolling of pipe, dynamic loads of considerable magnitude arise in the rod that retains the mandrel. These loads, which vary over time, are associated with fluctuation in rod shape over the rolling axis. The considerable forces associated with rod oscillation impair pipe quality. To improve pipe quality with intensification of the technological process, the design of the piercing and rolling mills of the pipe-rolling system must be modified. It is important to establish the qualitative and quantitative influence of the technological parameters on the behavior of the rod system and the pipe quality. In order to provide a basis for modernization of the mills and improvement in the production technology, we need a reliable mathematical model. In the present work, we consider the rod system of the mandrel-retention mechanism in the piercing and rolling mills, taking account of the aspects of the technology and the dynamic parameters of the system that differ from those in [1] (Fig. 1). The oscillation of the rod system is transmitted to the mandrel, impairing pipe quality. The dynamic processes are considerably complicated by variation in the contact mass of the blank as it moves along the rod during piercing or rolling. Dynamic analysis calls for a mathematical model of the mill in the pipe-rolling system. By studying the dynamic behavior of the rod system, we may evaluate the dynamic state of the system together with the mandrel during piercing or rolling. The proposed dynamic model of the rod system takes the form of a rod of constant cross section with hinged supports at the ends and with elastic supports (centering units) between them. This model adequately reflects the processes in the initial system. The rod, rotating at speed ω around the rolling axis x , is subject to the action of longitudinal force ( t ). At constant rolling speed , the rod is subject to the distributed load of the rolled pipe, characterized by inten