Since the part is rectangular, the parison undergoes a
greater expansion in one direction than in the other, and if a
cylindrical parison is employed, the greater expansion in one
direction causes highly non-uniform thickness. To minimise
the highly non-uniform thickness distribution in the part, the
parison is pinched and a pre-blow pressure is applied in order
to increase the surface area that contacts the mould cavity.
The final part thickness distribution and weight, manufactured
with the initial operating conditions, were measured.
The experimental thicknesses were measured on the sides
where the parison had been stretched significantly, i.e., areas
with greater blowratio. The average thickness and partweight
obtained are presented in Table 1. The part weight of 273 g is
far from the goal of 175 g.