The basalt
has been used since ancient times for its hardness
for paving roads and as filling in the construction
industry. More recently it was also used in the production
of anti-abrasive coatings and tile
flooring through the melted rock moulding. Actually,
in recent decades, it was discovered that all the basalt
rocks are not chemically identical, and that those
with certain chemical compositions have definite physical
characteristics that make them suitable for the extrusion
of continuous filaments of various diameters
(9 ÷ 24 m) . The Parisian Paul Dhé in 1923 was the first who
obtained a patent for the production of basalt continuous
filaments. After World War II, researchers from France, Germany,
Great Britain, Italy and, mainly, the USA carried on the first
attempts at extrusion of basalt. The first
significant results were obtained only in the 50s/60s, in
Moscow and Prague and, in the following decade, interest started
again even in the north west of the United States, motivated
primarily by the existing large basalt deposit. During those
same years, the Soviet Ministry of Defence also showed interest
in the potential of this technology for military and aerospace
applications. The research based at the important centre in
Kiev, clearly with an unlimited budget: the development came
to fruition, but the technology was kept secret except for
few brief publications. Research institutes and production
facilities were obviously off limits. Only in 1990/92, after
the Perestroika, this technology was declassified and civilian
research begun. Currently, basalt fibers are industrially
produced in the countries of the former Soviet Union, Russia
and Ukraine and in China too: they are mainly used in the
automotive sector by Japanese companies,
for the manufacture of exhaust systems and
other details, for the production of special series of tripods
for photographers and snowboards.
Because of its infinite development potential and its many
fields of application, in recent years basalt fibers have
attracted increasing interest and curiosity in Europe too.
The technological process for the production of basalt
fiber is based on four basic steps:
â–ª first preliminary treatment of basalt rock
â–ª melting process in furnace in order to obtain continuous
fibers
â–ª in continuous "spinning"
â–ª "weaving" or other, more particular processing,
to obtain other forms for specific final applications
The main parameters to obtain the required
properties of viscosity and crystallization in "spinning"
area of the furnace, determine the stability of the fibers
formation process. The large content of iron oxide in basalt
rock gives the characteristic dark colour and increases
the time of homogenization, the temperature of crystallization
and makes the viscosity curve much more abrupt compared ,
for example, with the glass. These issues require a particular
design of the furnace to provide the necessary conditions
for the maintenance of the status of the homogeneous molten
mass during the different phases of the process. The typical
plant for the production of continuous mineral fibers makes
use of the vertical melting method. The final treatments,
after the important steps of extraction, vertical drop, initial
treatment and winding in rolls, use other technologies similar
to those used in the manufacture of yarns and fabrics.
The following table summarizes the main properties of basalt
fibers, compared with low-value fibrous materials
such as fibreglass or high-value, as the silicon fibers. |
