its length having an exterior diameter of 62 mm and a wall thickness of 0 225 mm the hoop draw ratio of the outer surface was 2 25 the axial draw ratio was 6 5 the 10 sec creep modulus at 0 1 strain of samples cut from the drawn tube was determined for the axial and hoop direction using the standard dead loading creep method described by gupta and ward v b gupta and i m ward j macromol sci b1 373 1967 the 10 sec creep modulus in the axial direction was 3 7 gpa and in the hoop direction 1 7 gpa a tubular billet having an external diameter of 25 mm and an internal diameter of 17 mm of a clear amorphous copolyester eastmann 9921 was first deformed so as to provide a belled nose the tube was placed in an oven at a temperature of 110 u00b0 c in such a way that a zone of a length of approximately 15 centimeters was heated after 5 minutes the tube was removed and quickly inflated with room temperature compressed air to a pressure of 620 kn m 2 whereupon a bubble is blown in the heated part after depressurising and cooling one end of the bubble is removed so as to produce a belled end on the tube the tube was then mounted in the apparatus illustrated in fig1 air heated to a temperature of 95 u00b0 c was passed through the slit 6.