Biaxially oriented hollow moulding with even wall-thickness - heating parison in two stages, axially drawing and expanding in mould

摘要

Mfr. of biaxially orientated hollow moulding having an irregular shape w.r.t. to one of its axes, comprises (a) introducing a thermoplastics tubular preform (parison) into a heating zone to heat it to a 1st orienting temp.; (b) additionally heating the entire circumference of an axial section of the parison in order to heat that section to a 2nd temp. higher than the temp. of the remainder of the parison; (c) axialy drawint the heated parison; (d) introducing this into a moulding zone that has a circumferential shape which is irregular w.r.t. the longitudinal axis of the parison, so that the axis section is axially aligned in that part of the moulding zone which has a circumference smaller than the greatest circumference of that zone; and (e) generating a pressure differential so as to cause the parison to expand to, and assume the shape of, the moulding zone. Used in mfr. of plastics containers. The prods. have closely controlled, uniform, wall thickness.