Raw material for manufacture of basalt fiber.

Basalt corresponds to magmatic undersurface rock of main composition (originated from deep aluminum silicate melt) solidified in top layers of Earth crust or on its surface. Basalt content in the Earth crust exceeds 30%. 

Unlike raw materials for manufacture of glass, basalt is already a ready to use natural raw materials for fabrication of fibers. Basalts contain (by weight): 45% 55% of SiO2; 10%-20% of Al2O3 and up to 20% of FeO+Fe2O3 as well as MgO. Besides the major oxides, basalts contain, in general (in form of mineral compounds) almost all elements of periodic table. Completely crystalline rocks of such composition are called dolerites; destroyed and modified by secondary processes basalts are known as diabases and basalt porphyries. Deep-earth analog of basalt has the name of gabbro.

History of Continuous Basalt Fiber.

Basalt fibers are divided into two big groups: continuous fiber and discrete fiber (rock wool, staple fiber) also known as basalt fine fiber (BFF).

Method of production of staple fibers was invented over five decades ago and it has been well perfected, while CBF production technology is young enough and being improved further.

Interest to continuous fibers emerged in the middle of XX century when rocket, nuclear and electronic sectors were in demand for materials with special properties like strength of alloyed steel while significantly lighter and heatproof.

Properties of fiberglass, which industrial production had been already adopted in 1940th, failed to meet requirements of special applications. Carbon fibers are the best in terms of strength, durability and temperature range of application, but they are the most expensive also. Basalt continuous fibers were considered to be a material that excels fiberglass in most of technical characteristics, and at the same time is comparable in terms of production cost and price. 

Ukraine has been developing CBF technology for as long as several decades. Under some assessments, this business consumed nearly 70-60 million rubles; the sum being large enough during the Soviet era. According to experts, the success in CBF technology was achieved due to adequate research and development funding during the extended period giving the chance to pick necessary technological parameters of the method by experienced judgment. 

First specimens of CBF were obtained in 1961 by a branch research institution. These specimens were rough, hardly elastic and only few meters long. 

By 1971, certain experience was accumulated in research of basalts, their chemical compositions and melt characteristics; in study of CBF characteristics in terms of strength, chemical and heat resistance; in areas of their application. They invented certain methods as well as pilot electric and gas-electric CBF production plants; they obtained specimens of materials made from CBF. 

In 1974, “Laboratory of basalt fibers” was created to deal with theoretical and practical aspects of fine and super-fine basalt fibers and materials made of it. One of its main goals was to develop method and equipment for manufacturing CBF. 

The first industrial-scale CBF plant was constructed by team of Victor Kibol in Ukraine at Belichsky "TeploZvukoizoliatsiya” factory (Kiev Region). The plant appeared to be a stone-melting furnace equipped with two feeders (feeder units). The feeders were equipped with platinum-rhodium bushings including heated feeding tube and a bushing itself. Feeder units provided production of high-quality fibers of 8 to 13 microns in diameter suitable for the textile process. The equipment suffered certain drawbacks – high energy consumption per unit of production, big mass of bushings and their relatively low efficiency. 

In 1990-1992, feeder plant was built at fiberglass factory in Sudogda under the lead of Victor Kibol. Existing enterprises and research institutions were engaged in development of CBF materials: like various types of fabrics, reinforcement meshes, road construction meshes, composite materials, section-shaped plastics, rebars, pipes, cylinders, vessels, and electrical insulators. These efforts resulted in accumulation of experience in manufacturing and application of CBF materials in various industrial fields, construction, energy, power in fabrication of composite materials for special purposes. 

In late 1980th – early 1990th Ukrainian specialists built plants in Georgia and Kazakhstan. In 1997 development of CBF new generation technology and equipment – modular units, was started. In 2003 plant of “Kamenny Vek” company in Dubna city was built. The necessity of the new units design came from rising energy cost and also from high cost of equipment manufacturing; furnaces, feeders and excessive mass of bushings (the most expensive part of the equipment). Average weight of the bushing was about 3,400 grams, and then it was possible to decrease it to 3,200 grams. In November 1999, first operating modular unit NBV-1 was producing continuous fiber with 1,780 grams slot type bushing; later they developed and started industrial modular units NBV-2 with two bushings. 

Since 2002, China started development of CBF manufacture. Research and production companies such as Basalt Fiber and Composite Materials Technology Development (BF&CM TD) (Hong Kong) and “Basalt fibers and Composite materials” (Ukraine, Kiev) that were engaged in invention and adoption of new technologies, in manufacturing of production equipment and in organization of industrial-scale production. Experts headed by S.P. Osnos had developed a modular unit - BCF-1 - with smaller energy consumption as cost of energy in China is higher than in European countries. In 2004, a factory in Chengdu successfully started BCF-1 unit. CBF and fabric manufacturing enterprise Sichuan Aerospace Tuoxim Science & Technology Co., LTD operates on the basis of these units. Shanghai continued development of CBF under the program of the Ministry of science and technology of the People’s Republic of China – “Basalt continuous fibers and composite materials”. In December 2005, Hengdian Group Shanghai Russia Gold Basalt Fiber company started modular unit of BCF-1 series (liquefied oil gas operated) that generates near 2,000 tons per year of BCF. Currently, Chinese enterprises have been aggressively expanding and increasing CBF output. On the basis of modular units of BCF-1GM and BCF-2GM series engineers designed production lines of TE BCF 1000, TE BCF 1500 and TE BCF 2000 with production capacity of 1,000; 1,500 and 2,000 tons per year accordingly. In 2008 SPE "Vulcan" (Perm) delivered 2,000 tons/year TE BCF 2000 production line.

Continuous basalt fiber production process .

At present, there are several methods for fabrication of continuous basalt fiber that differ from each other in furnace and feeder designs, cooling and winding mechanisms, etc. But in principle manufacturing process of all producers includes following key operations:  

  • raw material preparation; 
  • rocks melting; 
  • melt homogenization and delivery to bushings; 
  • melt drawing through bushing units;
  • drawing of elementary filaments, application of sizing agent and spooling.

Basalt rocks for CBF manufacture are prepared in peculiar way – crushing to fractions of 5 mm - 12 mm, separation of metal and magnetic impurities by method of magnetic separation, screening and washing out small inclusions (dust, etc.) then drying either at natural air circulation, or in a special dryer. Prepared raw material is periodically loaded into the hopper of the loader mounted above the smelting furnace. 

The smelting furnace represents a recuperative bath-type furnace of continuous operation with direct gas heating of the smelting zone. Basalt rock melts at temperature of 1500± 50°С as a result of burning the air-natural gas mixture. After homogenization melt flows to feeder by means of gravity forces. At bottom, this feeder is equipped with electrically heated feeding tubes. Through these tubes, melt is delivered to electrically heated platinum-rhodium bushing. From the bushing melt is drawn in forms of a filament yarn.

In the process of drawing of continuous fiber, their surface is covered with sizing agent – a special coating to promote association of fibers into a yarn (cohesion) and to reduce friction between fibers. This coating prevents formation of micro-cracks on its surface to avoid the reduction of fibers strength. In addition to that sizing agent improves adhesive properties of fibers.

The filament yarn passes through gathering shoe and is wound on the spool. After spooling, the spool with fiber is removed from spool holder of the winder and replaced with the empty reel.

Manufacturing of high quality continuous fiber requires selection of the proper raw material and determine melting and drawing technological parameters and properties.

The complexity of CBF manufacture comparing to fiberglass is that:

Basalts as natural raw materials are different in chemical composition and characteristics;
Melting and drawing of basalt fiber has to be carried at higher temperatures;
Physical and chemical properties of basalt melts at extraction through bushings significantly differ from those of glass melts.

One of the key parameters of a continuous fiber is a diameter of the monofilament, reduction of which increases elasticity and, hence, allows its use in textile processing. In turn, diameter of the monofilament depends on the temperature in the feeder and speed of the fiber drawing. For example, increase of the melt temperature in the bushing from 1350°С to 1400°С, allows reducing diameter of the monofilament from 13.5 microns to 10.5 microns. Acceleration of extraction speed from 1,580 to 2,570 m/min, will reduce diameter of the fiber from 17 microns to 10 microns.

Manufacture of continuous fibers require materials with low rate of crystallization; basalt glass should have wide enough drawing interval (temperature range within which technological properties of glass, and viscosity first of all, are in appropriate range and aren't subject to sharp deviations).

High viscosity molten liquid glass possesses extra resistance to stretching that leads to increase in pulling effort and could cause a fiber breakage. With melt temperature increase its viscosity goes down and can reach low values, at which surface tension forces promote formation of glass drops instead of continuous fiber.

In the interval between these extreme states of fluid glass there is an area of operational viscosity for fiber formation. Different basalt rocks have different ranges of operational viscosity.

An important challenge for manufacturers of continuous fiber lies in increase in number of bushing tips since their amount defines quantity of multifilament yarns in fabrication of folded roving or twisted yarn of certain tex. The higher quantity of multifilament yarns in folded roving, the higher will be its mechanical properties. Given problems of breakage rate in continuous fiber manufacture, the increase in number of bushing tips looks an extreme challenge.

Potential of CBF production technology is in expansion of machinery effectiveness and first of all in throughput of bushings. Fiber glass manufacturing development has also passed stages of bushing design from 200, 400, 800, 1200, 2000, 4000 and more tips bushings. The majority of CBF manufacturers have been actively improving their equipment and, according to experts, perfection of CBF manufacturing process happens faster than development of fiber glass production technology.