Biaxially Oriented PE100 Pipes by Die-Drawing [PE]
# 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.
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The Leeds die-drawing process has been
used to produce biaxially oriented
polypropylene pipes with significant
enhancement of hoop mechanical properties
in terms of tensile modulus and tensile
strength due to a unique orientation of the
a-crystallites throughout their cross section.
Pendulum impact tests and...
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...
A novel die-drawing process has been developed at Leeds
University. By incorporating a mandrel, pipes may be expanded
hoopwise whilst being drawn axially. Such biaxially-oriented
pipes have properties better suited to the transmission of gases
and liquids than either isotropic or longitudinally-drawn pipes.
Existing test methods used for the characterisation of long term strength
properties of plastic materials for use in pressure pipe duties have been
A notched "C" ring type test has been developed to define the long term
crack resistance and strength properties of a CPE modified PVC. Since
materials of this...