An Investigation into the Longitudinal Rolling of Tubes Through Two Grooved Rolls

Abstract

This work is an investigation of the process of the longitudinal rolling of tubes through two grooved rolls with the aim of contributing to the full understanding of the mechanics of the process in order to increase its efficiency. The tubes which were unsupported internally, were rolled through an oval groove. Two types of operation were examined, viz, sinking, where no external tensions were applied to the tube, and stretch-reducing where front and back tensions were applied in different proportions. Lead tubes were rolled under dry rolling conditions to simulate the hot rolling of steel. Two types of passes were used, viz., rolling round tubes through the oval groove( R-O pass), and rolling the resulting oval tubes through the oval groove (0-0 pass) with the major axes of the two ovals at right angles to each other. Recordings were made of all the loads, velocities, dimensions and pressure distribution. To achieve this, tests were carried out on a fully equipped 2-high roll stand based on an old milling machine. Devices were also designed for the application of the front and back tensions. A novel design of the pressure measuring pin loadcells was developed incorporating new features which simplified its use and increased its reliability. The four loadcells in the shape of cantilevers were fixed to one block, thus making the removal and refitting of the assembly for inspection relatively simple. A new theoretical approach to the problem based on the strain energy principle has been presented and compared with existing equilibrium approaches and the test results. The question of presence and shape of a neutral zone on the surface of contact has been studied in some detail and anew idea put forward. Also the extent and effect of the pre-contact plastic zone, i.e, free zone, on other process parameters, e.g., arc of contact and pressure peak has been examined and verified with specially devised tests. The variation of the wall thickness of the tube has been studied in the light of the experimental test results and the available theoretical treatments .A general survey of recently available literature, together with surveys covering specific aspects of the problem have also been carried out.