Basalt fiber (BF), known as “the green industrial material of the XXI-century”, combines ecological safety, natural longevity and many other properties. It is not a new material, but its applications are surely innovative in many industrial and economic fields, from building and construction to energy efficiency, from automotive to aeronautic, thanks to its good mechanical and chemical performances. Hence basalt fiber has gained increasing attention as a reinforcing material especially compared to traditional glass and carbon fibers. In this context, several studies dealing with glass and carbon fiber reinforced composites consider the significance of basalt fiber as a new reinforcing material.

Production process

In many ways, basalt fiber technology production is similar to glass fiber one, but it requires less energy. This aspect, together with an easy availability of raw material all over the world, justifies the lower cost of basalt fibers compared to glass fibers.

BF are extruded from basalt rocks through a melting process without the application of additives. The manufacturing process can be summarized as shown in figure 2.

Source: Composite market web portal

Figure 2 - Basalt fiber production: general scheme

Quarried basalt rock is first crushed, then washed and moved into melting baths in gas-heated furnaces. under temperature of 1.460-1.500 °C. Here, the process is simpler than glass fiber processing because the basalt fiber has a less complex composition.

Molten basalt flows from furnace through a platinum-rhodium bushing with 200, 400 ,800 or more holes and the fibers can be drawn from the melt under hydrostatic pressure. Then a sizing is applied to the surface of the fibers by a sizing applicator to impart strand integrity, lubricity, and resin compatibility. Finally, a winder allows to realize some large spools of continuous basalt filament.

The production process, particularly temperature levels in the furnace, is of considerable importance in relation to final mechanical properties of basalt fibrous materials (rovings, etc). Infact it has been reliably determined that low variations in chemical composition of basalt rocks have a minor effect on the level of mechanical of continuous basalt fibers while the greatest effect comes from direct molding conditions of the fibers (drawing temperature and the period of melt homogenization).

For example, for the same basalt chemical composition, a fiber drawing temperature increase of 160 °C (from 1.220 °C to 1.380 °C) increased their strength from 1.3 to 2.23 GPa and modulus of elasticity from 78 to 90GPa.

Great importance on final properties has also the fiber dimension: as the filament diameter increases of 3-4 μm, the strength value decreases from 2.8 to 1.8 GPa.

As a result of its characteristics and properties, basalt fiber can be really considered as the material of our future for a green and sustainable development. If we consider the environmental impact of the whole complex of technological processes on obtaining an exploitation of basalt fibers, it is much lower than that of glass, carbon or mineral fiber material in general...

1. Tank for sizing

2. Furnace

3. Bushing

4. Sizing applicator

5.Tray for used sizing collection

6. Winder

7. Spool

8. Tank for used sizing

Basalt fiber: from earth an ancient material for innovative and modern application

by Piero De Fazio

[1] ENEA, Unità Tecnica Tecnologie Trisaia, Laboratorio Tecnologia dei materiali e metrologia

Basalt fiber: from earth an ancient material for innovative and modern application

Piero De Fazio[1]