# 1998 Gothenburg
Over the last decade Leeds University has developed a continuous die-drawing process to produce thick uniaxially and biaxially oriented polymeric products. Die-drawing offers a simple and effective route to stronger and stiffer polymer products. Biaxially oriented pipes with their improved hoop strength offer particular benefit to the pipe industry, allowing a much higher pressure to be used for any given wall thickness. In previous papersl-10 we have described the die-drawing process to produce biaxially oriented tubes of polyethylene, polypropylene, PVC and PET using a very simple batch process.
Recent work has shown that the mechanical properties of isotropic PElOO can also be improved by die-drawing. Hoop strengths of 32 MPa and even greater can be obtained for material with initial hoop strength in isotropic pipe of 21.5 MPa. Impact strengths also show significant improvement.
The production of biaxially oriented pipe of commercial quality depends on carefully controlling a number of parameters in the drawing process. The most important influences on the pipe quality are these of dimensional accuracy of the feed stock and uniformity of temperature during the drawing operation. Post-mandrel cooling of the drawn pipe allows it to be drawn at higher speeds.