ANALYSIS OF THE MECHANICS FOR DRAWING POLYVINYL-CHLORIDE TUBES OVER AN EXPANDING MANDREL

An analysis is presented of the mandrel drawing process in which a tub ular polyvinyl chloride (PVC) billet is drawn over an expanding mandre l so as to achieve a tubular product having a high degree of molecular orientation in the hoop and axial directions and enhanced mechanical properties. The stress and deformation behaviour of material moving ov er the mandrel are determined from equilibrium considerations and mode lling of the material using the Ogden representation. Experimental res ults from drawing tests carried out on a large-scale test facility are presented and the effects of mandrel semi-angle, mandrel exit diamete r and processing temperature on drawing behaviour are evaluated. Good agreement is shown between the experimental results and theoretical pr edictions of final product thickness, die exit stress and drawing load .