Blow-Moulding of Cavity-Walled Containers
April 5th, 1993
Paper to the Polymer Processing Society 9th Annual Meeting, UMIST, 5th-8th April 1993.
S F Bush with K R Large
Introduction
Cavity walled containers are of major interest because of their high flexural strength to weight ratios, insulation properties and protection of the contents against penetration. The use of a suitably designed I-beam type cross-section in a container wall has been shown to yield weight savings of up to 50% over an equivalent solid cross-section[1]. At the same time the insulation characteristics of these structures with air filled cavities have been calculated to extend the insulation times by about 75% over the equivalent solid walled containers. The inclusion of a double skin also lends protection to the container contents if the outside skin is accidentally pierced in use or transit, provided the inside skin remains intact.
A number of techniques already exist for the manufacture of such containers, but all depend on making the inner and outer walls separately and then assembling the container. A requirement was therefore envisaged for a process to manufacture these articles in a single operation. A design approach was adopted which broke the polymer process up into unit operations and this showed the economic advantage of blow-moulding a cavity-walled container. A novel prototype blow-moulding process was therefore designed incorporating an innovative die-head and parison inflation circuitry. The new process has been given the name Cavity Wall Blow Moulding (CWBM).
References
[1] K R Large, Design of a Novel Cavity Wall Blow Moulding Process, MSc Thesis, UMIST (1990).
[2] FIDAP Fluid Dynamics Package, Fluid Dynamics International, Illinois (USA).