DESIGN OF STRAIN-RATE-CONTROLLED DIES FOR THE DIE DRAWING OF POLYMER SHEET

The die-drawing process may be used to achieve orientation of the mole cular structure of a polymer and thereby considerably enhance its stre ngth and stiffness. The effect of controlling the strain rate within a die by suitable design of the die profile has been investigated and s train-rate control is seen as a means of reducing product fracture dur ing processing. A method of designing a die profile is given in detail and manufactured dies having profiles where the strain rate either in creases, decreases or remains constant throughout the die have been te sted experimentally. Conventional taper dies are found to produce prod uct fractures at relatively low billet velocities, but the products ha ve a high draw ratio. The draw ratios achieved in constant-strain-rate dies are lower, with considerably higher billet speeds being achieved , particularly when using dies having a draw ratio of six. (C) 1997 El sevier Science S.A.