New Products # 1995 Edinburgh
The die-drawing process was developed in this laboratory to produce thick uniaxially or biaxially oriented products.'" Earlier efforts to produce oriented polymer tubes at Leeds University were based on hydrostatic extrusion. Hope et a17 showed that, by using a stationary mandrel and converging die arrangement, round tubular products could be satisfactorily hydrostatically extruded although the extrusion speeds achieved at the higher extrusion ratios were disappointingly low, generally in the order of only few millimeters per minute. These very low production speeds together with the batch nature of the process have limited the development of the hydrostatic extrusion process for industrial purposes. To exploit the enhancement of mechanical and physical properties associated with oriented polymer tubes produced at an industrially acceptable rate the die-drawing technique was adopted for tube drawing. Die drawing is a technique which combines the best features of free tensile drawing and solid-state extrusion, allowing large-section products to be made at the high modulus levels obtainable by free drawing.