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|Title: ||Material and process problems in the manufacture of coolant reservoir tanks|
|Authors: ||Yeh, Po-Len|
|Issue Date: ||1984|
|Publisher: ||© Po-Len Yeh|
|Abstract: ||The programme was concerned with the effects of processing
variables on the structure and properties of coolant reservoir tanks. The
work was concentrated on the extrusion blow moulding process and on
propylene polymers, following an earlier similar research in the Institute on
high density polyethylene. We have worked with a company which
specialises in technical blow mouldings; the work has dealt with coolant
tanks which are required for high temperature, high pressure service in the
presence of antifreeze.
It soon became apparent that the application made severe
demands on polypropylene in that failure was possible by a variety of
mechanisms, including environmental stress cracking and ductile blow-out
failure. Additionally, the shaping process by extrusion blow moulding was
not being carried out in the optimum way, either with respect to process
economics or to product properties.
Investigation of the surface texture of corn mercial tanks revealed
that shrinkage from the mould occurred frequently due to inadequate holdon
pressure; this loss of contact gives poor surface finish and retarded
cooling. This phase of the research was supported by a programme carried
out on the Bradford University equipment and by providing appropriate
thermal data for the Bradford mathematical model for cooling. To reduce
the cooling cycle time, the efficacy of internal cooling techniques,
including forced air cooling and liquid carbon dioxide, was studied.
Further, the possibility of shaping polypropylene in the supercooled region
was investigated and a double extruder system was developed to examine
the shear viscosity of supercooled polymers.
The main concern has been failure caused by stress cracking and
environmental stress cracking, especially of development grades of
propylene polymers. The structures of various ethylene-modified
polypropylenes have been elucidated, as have the relationship of structure'
to processing history and its relevance to the severe stress cracking
encountered. A new method for determining ethylene content of ethylene-
propylene systems has been developed, as this is one of the important
characteristics of ethylene modified polypropylene.
The available processes of manufacturing the coolant reservoir
tanks have been considered; in particular, competing methods of
manufacture of extrusion blow moulding and injection moulding/welding
have been compared. The design of coolant tanks, in particular the wall
thickness required, has been examined. Stress analysis, supported by
tensile failure and relaxation data, has been carried out to provide
background to the failures encountered in practice.
Finally, possible new candidate material for the coolant tank
application, polypropylene-linear low density polyethylene (ethylene-octene
copolymer) blends have been investigated.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University|
|Appears in Collections:||PhD Theses (Materials)|
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