Basalt is a common volcanic rock formed from the rapid cooling of basaltic lava. The percentage content of minerals in basalt stone is dependent of deposit location and affects the properties of basalt fibers such as tensile strength or resistance to chemical environment. The single minerals included in basalt stone are silicon dioxide, aluminum oxide, magnesium oxide, calcium oxide, phosphorus oxide, magnesium oxide, potassium oxide, titanium oxide, manganese oxide, chromic oxide. Especially content of silicon dioxide affects melting temperature of raw basalt stone, whereby with lower silicon dioxide content increases the melting point of basalt stone.
The percentage share of minerals in basalt stone
Basalt Fiber Production
1. Preparation of crushed stone
- Chemical control of crushed stone;
- Water flushing of crushed stone;
- Visual control of crushed stone to separate stone of non-standard color and size;
- Charging of crushes stone onto furnace’s conveyer;
- Fiber production
- Charging of crushes stone into a furnace;
- Fusion of crushed stone in the furnace and getting of basalt melt;
- Melt’s homogenization and it’s preparation to drawing;
- Melt’s drawing through bushing;
- Sizing application;
- Winding of fiber on the cakes
Technological process of continuous basalt fiber production is similar to the process of glass fiber production. Crushed rock is charged into the melting furnace by dozing charger. The melting furnace is bath-typ. Furnace heating is carried-out by air-gas mixture, which comes from common mixer through burner. Air-gas water supply consists of pipes, air output set, stop and control valves, burners crushed rock comes into melt under temperature 1460-1500°C in a furnace bath. Molten basalt flows from furnace through feeder channels and platinum bushing with 200 up to 1000 holes. The fibers are drawn from the melt under hydrostatic pressure. The melt is cooled by cooler and get harden to fiber. The process of getting fiber is pretty difficult due to high crystallization ability of basalt melt and narrow temperature range of production process. One of the most important indicators of technological process stability is reducing of monofilament breakage during the production. There gives two key factors affecting the monofilament breakage:
- working temperature at the bushing
- steadiness of temperature distribution at the bushing.
In the next step after getting fibers a sizing is applied to the fibers surface, whereby the sizing components impart standard integrity, lubricity and resin compatibility. After sizing is applied, the roving are gathered into a bundles so-called strands by means of a gathering shoe before approaching the take-up device. The attenuation rate and therefore the final diameter, is controlled by the take-up device (forming winder). The strand passes from the gathering shoe to a winder where it is wound onto a forming tube also called “forming cake”. The dried cakes are ready for further processing such as assembling or twisting.
One of the crucial parameters of continuous fiber is its monofilament diameter. It’s reducing leads to increasing of the level of fiber elasticity and facilitates its textile processing in the future. Diameter of monofilament depends on working temperature at the bushing and pulling speed. All basalt fiber manufactures try to increase the hole’s number at their bushings this means appropriate increasing of monofilaments number in one-end roving, which is used to production of assembled roving’s and twisted yarns.