Plastics fuel tanks have been used successfully abroad ;
metal counterparts are still predominant in this country
plastics tanks have to satisfy stringent performance
regulations : low temperature impact tests ; permeability ;
and fire resistance.
Blow moulded high density polyethylene (HDPE) fuel tanks
have superior strength to mass ratio compared with metal
equivalents (the density of steel is about 8000 kg/m3
compared with HDPE, which has a density of under 1000
kg/m3 ). HDPE will tend to drip in a fire situation, thus
reducing explosion risk. HDPE is the chosen material
because it possesses inherent properties suitable for the
blow moulding process : it has a high viscosity at low
stresses ; and is highly inert.
Rotational moulded HDPE fuel tanks can also be considered.
However, these are shown to have inferior properties when
compared with blow moulded tanks ; attraction of rotational
moulding is the cheapness of equipment.
Petrol immersion was found to enhance impact properties of
HDPE, although yield stresses were lowered slightly.
The thickness distributions of blow moulded fuel tanks were
found to vary ; this is because of the present difficulty of
predicting parison behaviour with respect to time.
Thickness is important because of impact strength and
Impact properties of fuel tanks were assessed ; peak force
of impact was found to be heavily dependent on thickness
(raised to the power 1.1) and temperature of mould in the
blow moulding process (a low mould temperature led to
inferior properties). Pinch-offs were found to be
particularly detrimental to impact properties.
Cooling behaviour was investigated. With the aid of a
cooling model for blow mouldings, it was found that a warm
mould (40·C) could be used with internal air circulation to
obtain a cooling time the same as that with a cold mould and
no air circulation. Thus optimising mechanical strength and
maintaining economic viability.
Welding of injection moulded fittings to the main blow
moulded body of the fuel tank was found to be faulty, in all
of the tanks examined ; many weld failures have been
reported in use. This work determines optimum welding
conditions for HDPE grades, these are Rigidex H060-45P and
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.