JEC COMPOSITES MAGAZINE - Issue #95 - Special JEC Europe - March 2015 - 21

crushing the liner. Filament
winding was the logical choice,
although researchers knew
winding heads would require
modifications to handle thermoplastic tapes.

Work to date

Fig. 2: Acetal vessel liner fully filament wound with acetal/carbon fibre
composite tapes

team members and the polymer's
long history of use for automotive fuel-handling components
and low-pressure fuel storage.
The liner was left unreinforced
(to improve permeation resistance) but the overwrap (which
provides the vessel's high hoop
strength and burst/puncture resistance) needed reinforcement.
Both E-glass and carbon fibre
were considered; and carbon
fibre was selected for its much
higher strength/unit weight and
industry familiarity. The easiest
form to provide acetal/carbon
composites in was as unidirectional thermoplastic tapes, which
are preimpregnated and have a
very low void content and no dry

spots - important for permeation
resistance.
To reduce leakage, it was important to produce the hollow liner
in one piece. The process for
liners needed to be inexpensive
at research volumes but scalable
for commercial production with
low-cost tooling, good surface
finish and wall thickness control,
capable of using inserts and
moulding threads, and with low
forming stresses (for low warpage). Blow moulding, casting,
and rotomoulding (rotational
moulding) were all considered;
but rotomoulding was judged
the best option. Fewer process
choices were available to apply
the composite overwrap without

Once materials and processes
were chosen, some members
conducted mechanical and
permeation tests, first on samples
cut from test plaques (liner materials were injection moulded,
composite materials were
autoclave cured) and later from
full-size parts. Other team members worked in parallel to design
the liner and coupling hardware,
and then to build a rotomoulding
tool to form the liners. A number
of moulding trials were conducted over a two-year period to
evaluate various liner designs as
well as the influence of process
variables on final performance
(Figure 1).
To carry out the high-pressure
permeation tests, the development of a custom fixture was
needed. Liner samples worked
well in the setup, but the
composite tapes proved too thin
for accurate testing. Therefore,

No95 March 2015 /

further along in the programme,
once winding paths are finalized
for the composite overwrap (Figure 2) and a method to join liner
and overwrap into a monolithic
structure is developed, completed tanks will be tested and
results compared back to baseline
liner-alone samples to see if the
composite reinforcement adds
to permeation resistance. To
date, good correlation has been
achieved between initial and
more recent tests. Permeation
results indicate that the acetal/
carbon composite tanks should
pass industry specs as long as the
liner is at least 5 mm thick.
A recycling study is now complete (with good results), and
other planned work over the
next few years includes completion of the modified filament
winding head and development
of a turnkey robotic manufacturing cell for drop-in replacement of current systems at tank
manufacturers. Last, a real-world
demonstration is planned on a
hydrogen-powered FCV to prove
out the technology. n
More information:
www.celanese.com

jec composites magazine 21

http://www.celanese.com http://www.porcher-ind.com

JEC COMPOSITES MAGAZINE - Issue #95 - Special JEC Europe - March 2015

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