EUREKA NOVEMBER 2002 COVER FEATURE STORY

Composite materials go without a bang

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


Nano particles give flexibility to ceramic composite coating

Also encountered in the Czech Republic is Ceram-Kote www.ceram-kote.com , a US developed, flexible ceramic composite coating. Unlike most ceramic coatings, a piece of metal coated with CeRam-Kote 54 can be bent back and forth in the fingers without cracking. According to Czech agent Zdenek Vyroubal of Ceramed ( ceramed@volny.cz) this behaviour arises because the ceramic particles are so close together they interact with each other directly by physical means. The matrix is epoxy resin, and the solids content is 80% with a gradation of particles sizes ranging from 40 microns down to nm.
The material was developed and patented some 20 years ago by Freecom in Texas, and is used there in the oil industry. In Europe, it was for a long time only used for coating cylinders for pulp and paper manufacture, but it is now manufactured by CeRam-Kote Europe in Germany ro@ceram-kote.de , which describes recent take-up as, "very promising." In the Czech Republic, it has been used to coat 280 tanks for the Libyan "Great Man-Made River" project in which underground water is extracted from beneath the desert and delivered to agricultural areas on the coast. Mr Vyroubal says the coating can be supplied in any of 10,000 colours and costs 10 euros/litre in large quantities or 30 euros/litre in small quantities. Application is best undertaken by spraying but it can also be rollered on.

Coated tanks for the Libyan Great man-made river project


A shine taken to natural composites


Polished tiles of re-crystallised basalt, a ceramic-ceramic composite material, are used to make skid pans for all the major automotive companies. The material is very hard and abrasion resistant, and can be given a high polish or made non-slip. Its abrasion resistance also makes it very suitable for lining pipes used for the pneumatic and hydraulic conveying of bulk materials.


Non slip platform

Lined chemical pipes

To our knowledge, one company stands above all others in its manufacture, the Czech company Eutit ( www.eutit.cz and kompozit@cbox.cz ). The firm started out as a glass works, but has spent the last 50 years perfecting the black art of selecting natural basalts, and then melting, casting and heat treating them to produce optimum mechanical properties. Although basalt is a natural volcanic rock, found all over the world in large quantities, turning it into useful engineering product requires considerable technical expertise. The present process is the result of much research undertaken in various institutes in the Czech Republic and in the Technical University in Prague. For tasks too arduous even for basalt, the firm also produces another ceramic, which they call 'Eucor', made by melting corundum (aluminium oxide) and baddeleyite (zirconium oxide). However, basalt is cheaper, and while Eutit has a regular customer base, it is eager to find new markets. Hardness on the Mohs scale is 8 (Diamond is 10), compression strength is 309 to 483MPa and bend strength, 48 to 64 MPa. UK agent is Greenbank www.greenbanktl.demon.co.uk and info@greenbank.tv

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

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