Mechanics of rolling tube on a mandrel through two grooved rolls

Abstract

This project is an investigation into the process of tube rolling on a mandrel through two grooved rolls. The research was carried out to assist operating companies insetting-up multi-stand mills to operate efficiently,especially when rolling thin walled tubes. Lead, which was used as an analogue material for hot steel, was formed into tubes and rolled on a mandrel in-an experimental single-stand mill. Rolling trials were performed to establish the way in which roll separating force, rolling torque and pressure distribution round the groove, vary for different rolling conditions, e.g.reduction of area, tube diameter to thickness ratio,friction conditions on the mandrel surface and front and back tensions. The pressure distribution round the groove perimeter and along the arc of contact was measured by means of pin-load cells situated in the top roll. Results taken from pin-load cell readings during rolling showed that the pressures round the groove were not uniformly distributed. Also, by the use of pin-load cells, the existence of a free deformation zone, wherein deformation takes place prior to the contact zone was established. Rolling loads and torques were greatly affected by the change in tube thickness and friction conditions on the mandrel surface. While front and back tensions helped in reducing the rolling loads, increasing the mandrel speed reduced significantly the rolling torques. A new theoretical approach based on the principle of least work done was proposed and comparisons were made with other existing equilibrium approaches and the experimental results.A computer programme was developed for the assessment of the total work reauired in the process and for the calculation of tube and mandrel velocities in a production multi-stand mill. It is shown that there is good agreement between the theoretical predictions and the experimental results.