Measurement of contact pressures in tube rolling

Abstract An attempt is made to explain some of the phenomena occurring in the longitudinal rolling of tube through two grooved rolls by the use of specially developed pin load-cells, which measured the pressure distribution on one roll surface. Observations were made also of the shape of the free and contact zones enabling the length of the arc of contact to be measured. These are compared with values calculated for a variety of rolling parameters. Solutions to some problems associated with pin load-cells are given. The principal conclusions are that (1) a free deformation zone occurs which results in a reduction in the length of the arc of contact by about 30%, (2) there are regions in contact with the roll surface where the neutral point lies outside the deformation zone. The industrial significance of these results is that uncontrolled deformation is now known to exist upstream of a stand. Also, the control of the shape of the tube is less than would be imagined from a geometrial reconstruction of the press. Consequently mill designers cannot estimate the performance of the pass soley from the geometrical deformation zone. To assist them it is shown that the actual arc of contact is about 1/√2 time the value expected from the geometry of the pass. It was found also that (3) the most reliable results are obtained when the pins are arranged to protrude above the surface of the roll by a small specified distance, and (4) the performance of the pin load-cells, of the design which was finally adopted, was not affected significantly by the presence of small amounts of extruded metal in the annular clearance between the roll and the pin. Thus, the findings of this investigation provide a contribution to the understanding of the mechanics of longitudinal tube-rolling for both industrial and research engineers.