Basalt Rock Fibre

Basalt fibre, extracted from basalt rock and endowed with superior properties, can be used effectively in various fields including technical textiles. An analysis.

Today everybody in textile field is talking about technical textiles. Meeting end product specification is a big challenge especially for industrial goods. Many textile fibres have been invented by researches for meeting customer demand. Basalt fibre, a fibre extracted from basalt rock can be used effectively in various fields owing to its superior properties. Not only do they boast good mechanical and chemical resistance, but also exhibit excellent thermal, electric and acoustic insulation properties. Due to its favourable properties, basalt fibre can be used in several applications in technical textiles. In this paper, properties and applications of basalt fibre has been discussed.

Basalt fibre or basalt rock fibre is manufactured from extremely fine fibres of basalt, which is composed of pyroxene, minerals plagioclase and olivine. Basalt rock is abundantly found everywhere all around the world. Basalt is a generic name for solidified lava which pours out of the volcanoes. It is 1/3 of earth crust. Basaltic rocks are melted approximately in the range 1500-17000C. When the rocks melt, they solidify into glass like nearly amorphous solid. So cooling leads to more or less complete crystallisation to an assembly of minerals. They are usually grey to black and fine-grained due to rapid cooling of lava on the surface of the planet.

The chemical composition of basalt rock

Paul from Paris, France, was the first with the idea to extrude fibres from basalt. He was granted a US patent in this regard in 1923. Professor RV Subramanian of Washington State University (Pullman Wash) conducted research that correlated the chemical composition of basalt with the conditions for extrudability and physio-chemical characteristics of the resulting fibre.

Fibre forming characteristics

For fibre drawing, the viscosity of molten basalt should be in range of 500 to 1000 poise. At a lower viscosity, the basalt is too fluid and droplets form at nozzle, and at a higher viscosity, the flow rate is too low and the tension in the fibre drawing is too high. The crystallysed characteristics of the melt are equally important in fibre formation. The liquid’s temperature is important because formation of fibre is difficult or impossible when crystallisation is taking place, while a fibre is being drawn. Crystals may form in the bushing or orifice, and may occur outside the orifice. They will be contained in solid fibre. This leads to weak spot or discontinuity which causes the fibre to fail during processing. If the viscosity of the basalt is 100 to 200 poise, formation of crystals occurs rapidly and mechanical drawing of the fibre becomes difficult. If the melt viscosity of basalt fibre is 1000 poise, crystal formation is impeded and favourable drawing conditions exist.

The surface tension is also one of the important fibre forming parameter. If tile surface tension is very high, a spherical bead forms at the nozzle of bushing and it becomes impossible to draw the fibre. If the surface tension is very low, the material will not have sufficient strength to form a molten fibre while it is being drawn.

The liquid’s temperature has to be below 12500C. Useful staple fibres are produced with materials of lower viscosity.

Fibre formation

In many ways, basalt fibre production technology is similar to glass fibre production, but it requires less energy.

Basalt fibre is produced by melting basalt stone at about 14500C in furnace. The molten material flows into a fore hearth. It is then gravity fed into a platinum alloy bushing.Electricity is passed through the bushing to provide a final stage of resistance heating and precise adjustment of the viscosity of the molten mixture. Depending upon the end use, number of orifice and diameter of spinnerets are decided. Hundreds of filament from each orifice is gathered to form a continuous filament basalt fibre. These filaments are then quenched with a water based sizing to solidify strands and to deposit lubricant. Then winding of those strands is done on bobbins.

Applications

Taking into view above facts and figures, basalt fibre can be used widely for number of applications in various industries viz construction, road construction, engineering networks, agriculture, underground construction, machine construction, environmental safety. Basalt fibre can replace almost all applications of asbestos. It has potential to replace glass fibre, steel fibre, polypropylene, polyethylene, polyester, aramid and carbon fibre cost effectively in many applications.

About the Authors:

PD Anade is an M.Text student at the department of textile technology of the DKTE Society’s textile & engineering institute, Ichalkaranji.

PM Katkar & AA Raybagi are assistant professors at the department of textile technology of the DKTE Society’s textile & engineering institute, Ichalkaranji.

This article was originally published in the Textile Review magazine, November, 2012, published by Saket Projects Limited, Ahmedabad.