Композитные изделия не взрываются

Tom Shelley discovers a composite breakthrough from the Czech Republic which allows the commercial manufacture of safe plastic gas cylinders

Commercially produced plastic 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 in combination with an impervious liner and a protective outer shell.

This is not a particularly new idea but, to our knowledge, the cylinders, developed for the Russian market, are the first to be commercially manufactured on any scale, and could soon see use in the UK and they may act as a precursor to other low-cost, high-performance composite developments.

The cylinders, their materials and the methods behind their manufacture are the brainchild of Prague-based Kompozit-Praha. Its essential skill lies in its ability to fabricate continuous glass filament-wound composite products for the military and aerospace markets. One of the skills, crucial to the Czech development, was its ability to produce very thin composite constructions which were able to keep weight and cost to a minimum. In the case of smallest sized gas bottle the glass-epoxy is only 1.2mm thick (even the largest bottle have a wall thickness of just 3.5mm). The gas is contained within a PET (Polyethyleneterephthalate) liner with a glass-epoxy over wrap providing the strength. One of the features of this combination of materials is transparency, allowing users to see how much liquefied gas remains within the bottle. The outer HDPE (High Density Polyethylene) casing provides additional protection and allows the cylinders to be styled to supplier's needs or coloured to indicate hazards or content.

The biggest advantage of the new method of construction, however, is neither its style nor its low weight – being half that of steel – but its fire resistance. One might imagine that steel is the ultimate fire-proof material. It is, until it gets very hot or internal pressure rises to a degree sufficient to rupture it. Bear in mind, the most powerful non-nuclear bombs are those that produce a sudden mixture of fuel of air that subsequently ignites. Conventional steel gas cylinders have the potential perform in just such a manner.

The new cylinders, on the other hand, have a failure mode that is non-explosive. If an 85% full, 5litre cylinder is subjected to a 'bonfire test', failure begins four minutes from the start of the test when the inner liner melts. The gas then leaks evenly through the composite over-wrap, with all gas having leaked out in 25 minutes.

The cylinders fulfil all current European legislation and the company is looking for additional customers in the European Union – which the Czech Republic is expected to join in 2004. One of the companies it is actively talking to is BP.

This story was brought to our attention by another company, Zбlesн, based in Luhacovice also in the Czech Republic, at the 44th International Engineering Fair in Brno, Czech Republic. Zбlesн supplied both tools and resin for the project.

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, but these still seem to be at the promotion and testing phase.