Basalt continuous filament could be the fiber of the future

July 1st, 2004 / By: / Fabric Basics

BCF has distinct advantages over mineral fibers like carbon, ceramic and glass fibers.

Spewed by erupting volcanoes millions of years ago, solidified lava—called basalt rock—turns out to be an excellent raw material for making effective fireproof fabrics and barriers, insulation materials, and reinforcement agents. Basalt continuous filament (BCF) is a fiber produced by melting the stone at temperatures above 1,400 degrees C and extruding it as a continuous strand of uniform diameter.

BCF manufacturers sell rovings, twisted yarns, and woven and nonwoven materials. Some of the many products made with the fiber include fire barriers and fireproof clothing; acoustic barriers; reinforcement rods for concrete; car interior panels, seats and dashboards; heat shields; and filler material for mufflers.

BCF is considered an environmentally safe and relatively inexpensive alternative to materials such as asbestos and glass filament products like fiberglass. Since large deposits of the igneous rock exist around the world, manufacturers say they are poised for global expansion into a number of different industries.

Considering its relatively cheap price, BCF has distinct advantages over other man-made mineral fibers like carbon, ceramic and the different types of glass fibers. Comparable properties include mechanical strength and stiffness, resistance to chemicals, and functionality in a broad temperature range. Because basalt melts at a higher temperature than glass, BCF outperforms glass fibers, yet it has the same reinforcing capabilities. Also, BCF is resistant to alkaline, and therefore is a less expensive alternative to glass fiber for reinforcing concrete. Also, because of its thermal stability, BCF is a non-carcinogenic and non-toxic insulation alternative to asbestos, which is hazardous if inhaled.

Given the large amount of basalt rock lying around, so many identified uses for it, and a relatively economical production process, one wonders why the world isn’t already inundated with BCF fiber products made by hundreds of manufacturers. Scientists and engineers in the Soviet Union first developed a processing method during the 1950s. During the early 1970s, it was predicted that basalt fibers would emerge as an important new industry.

“Why it never materialized is a question that long puzzled us,” says Jean-Marie Nolf, head of new business development for the Belgian company Groep Masureel Veredeling, which produces the Basaltex line of BCF fiber products. Nolf says one reason may be the glass fiber industry’s view that basalt can always be synthesized using chemicals. However, it is the lack of chemicals that makes BCF environmentally safe and recyclable, which are important advantages over glass fibers.

Another reason for the industry’s slow growth, Nolf says, is the sheer technical complexity of the production process. Several things make it difficult, such as a very high furnace temperature to melt the rock (about 1450 degrees C); the need to be extremely precise about the temperature (within two to three degrees); and controlling the temperature of the extrusion bushings, which are heated using electricity outside the furnace.

In addition, the bushings must be made of platinum to withstand the heat. They cost about $150,000 each, says Graham Miller, executive vice president of Houston-based Sudaglass Fiber Technology Inc. Sudaglass has a BCF manufacturing plant in Sudogda, Ukraine, and is planning to open one in the United States in the next year or two. Miller says Sudaglass’ furnace uses eight platinum bushings.

“Basically, what we do is crush the rock into chips about the size of your thumb, and then we put this into a furnace, which has already been heated up to a high temperature,” Miller explains. At a controlled rate, the rock melts into a liquid state. Then the liquid basalt is passed into a feeding trough called a “forehearth.” Gravity then sends the liquid through the extrusion bushings, each of which has 800 holes that form the fiber strands.

“What makes it difficult is these platinum extrusion bushings that are heated electrically,” Miller continues. “If you try to make them too big, you can’t get an even temperature across the template where the holes are. If there’s an uneven temperature, you’re going to get good fiber coming out of one side of it and bad fiber coming out the other, which would scrap the whole lot.”

Compared to the 800 holes in the BCF extrusion bushings, glass fiber production is capable of using bushings with 1,500 to 4,000 holes, Miller says. Therefore, glass fiber productivity is much greater, and that is another reason why BCF has lagged behind. Miller says Sudaglass is working to develop technology that will allow it to increase the size of the extrusion bushings and increase production.

Nolf says Masureel continues to research and develop technology for improving BCF production and creating new uses for the fiber. The company is developing tailored products for its customers, such as an anti-vandalism, fire-blocking interliner for railway seatings and a fire-blocking tape for electrical cable installation that would outperform glass fiber tape.

Eddie Grosfield is a freelance writer living in the Rochester, Minn., area.

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