Tom Shelley discovers breakthroughs with composites in
the Czech Republic, especially one that allows the commercial
manufacture of plastic gas cylinders
Commercially produced plastic cylinders for compressed propane
and butane are both lighter and much safer than their steel
equivalents while costing about the same.
The breakthrough comes from using thin glass reinforced epoxy
shells to contain the compressed gas, with an impervious liner
and a protective outer shell.
The idea has been around before, but to our knowledge, new Czech
cylinders developed for the Russian market are the first to be
commercially manufactured on any scale, and could soon be in use
in the UK too, pointing the way to other low cost, high
performance composite developments.
The cylinders are the brainchild of Kompozit-Praha, kompozit@cbox.cz based in
Prague. Its essential skill is in fabricating continuous glass
filament wound composite products for the military and aerospace
markets. We must mention at this point that Advanced Lightweight
Engineering, a firm in The Netherlands, also has an expertise in
this type of construction. The company has for some time been
promoting composite LPG tanks for cars (More information at www.lightweight.nl ) but
these still seem to be at the promotion and testing phase.
One of the skills which was crucial to the Czech development was
an ability to be able to produce very thin composite
constructions in order to keep down weight and cost. In the case
of smallest sized gas bottle, the glass-epoxy is only 1.2mm
thick, ranging up to 3.5mm for the thickest section of the
largest size bottle. The gas is actually contained within a PET
(Polyethyleneterephthalate) liner with the glass-epoxy over-wrap
providing the strength. One of the features of this combination
of materials is that they are transparent, allowing users to see
how much liquefied gas remains within the bottle. The outer
casing is HDPE (High Density Polyethylene) which provides
additional protection and allows the cylinders to be styled in an
individualistic way.
The biggest advantage of the new method of construction, however,
is neither its style, nor its low weight - half that of steel -
but its fire resistance. One might be tempted to imagine that
steel is the ultimate fire-proof material, and so it is until it
gets very hot, or internal pressure rises to a degree sufficient
to rupture it. The most powerful non-nuclear bombs made so far
are those that produce a sudden mixture of fuel of air that
subsequently ignites. Conventional steel gas cylinders can
sometimes perform in just such a manner.
The new cylinders, on the other hand, have a failure mode that is
non-explosive. If a 5 litre cylinder, 85% full, is subjected to a
'bonfire test', failure begins four minutes from the start of the
test when the inner liner melts. The gas then evenly leaks
through the composite over-wrap. All gas will have leaked out of
the cylinder in 25 minutes.
The cylinders fulfil all current and announced European Norms and
the company is now looking for additional customers in the
European Union, which the Czech Republic is expected to join in
2004. One of the companies they are actively talking to is BP.
Note: This story was brought to our attention by another company,
Zálesí, based in Luhačovice also in the Czech Republic, at the
44th International Engineering Fair in Brno, Czech Republic.
Zálesí supplied both tools and resin for the project. www.zalesi.cz
Pointers
* Composite gas cylinders now in commercial production are
explosion proof and half the weight of steel cylinders
* Ceramic powder in epoxy coatings use nano sized particles to
achieve flexibility on metal subsrates
* Natural ceramic-ceramic composites can be made by melting and
recrystallising natural basalt to produce a material with
exceptional hardness and abrasion resistance.
For more technical
developments see www.eurekamagazine.co.uk