All-electric Melting Furnace for Basalt Rock Wool

1.1 The Reason of this Project

Basalt is a natural material that is found in volcanic rocks originated from frozen lava, and perhaps 80% of basalts are made up by two essential minerals; i.e. plagiocene and pyroxene. SiO₂ content varied from 45% ~ 52%, K₂O + Na₂O content slightly more than intrusive rocks, CaO, Fe₂O₃ + FeO , MgO content are slightly lower than the intrusive rocks. The bulk density of Basalt is 2.8-3.3 g/cm³, a great compact by compression strength of up to 300 MPa, and sometimes much higher, the strength decreased in the presence of vitreous and pores. The durability of basalt is very high, and sometimes changes from a joint plane pentagonal or hexagonal to columnar joints. It is brittle, and thus not easily mined large pieces of stone, as pores and almonds are common structure, although basalt is widespread on the surface, not so much can be used for facing stones.

Basalt is widely used, particularly as chopped fibers in the cement, is an irreplaceable material with excellent performance, because concrete is easy to crack, with low tensile strength, poor toughness. How to overcome these shortcomings so as to extend its use life, ensure the structural safety is an important issue. As natural ore, it is extensive fiber production source material. There is no emission, no pollution during the production and use of basalt, the construction sector has become a global response to energy saving to choice green material. Basalt fiber (BF) is made of pure natural basalt by 1450 ~ 1500 ℃ high temperature melting, drawing to cotton, with a high elastic modulus, high fracture strength, high temperature, low temperature, good corrosion resistance and processing performance, etc. It is so far the only pollution-free green healthy fiber products. Compared with carbon fiber, the tensile strength and elastic modulus of basalt fiber is lower, but the price is just one-tenth of the carbon fibers. The requirement of basalt fiber used in the concrete is “no crack under fatigue, no split when crack, and no separation when split”. Also Basalt fiber is non-metallic materials, electromagnetic induction and magnetic susceptibility is very low, it has good anti-electrochemical corrosion ability. Excellent heat and fire resistant, can work in a range of -269 ~ 650 ℃; not flash fire at high temperature of 250 ℃, and the tensile strength retention rate up to 85%. Good UV aging performance, low moisture absorption. Good insulation, high temperature filtration resistance, good anti-radiation and strong, and good performance through waves. Alkali resistance is acceptable alkali resistance depending on the chemical composition of basalts silica content may be, at present, when the silica content of 48% to 60%, that is neutral and weakly acidic basalt, the saturated Ca(OH)₂ solution cooking 4h tensile strength retention rate is more than 75%; After aging in 2 mol/L of NaOH at boiling water for 3h, the mass loss of the solution is no more than 6.0%. The standard silica content in basalt fiber is no less than 48%, which requires the development and production of alkali basalt fiber, a greater increase of alkali resistance in asphalt concrete and asphalt adhesion in cement concrete.

In summary, basalt fibers have pavement and concrete structure monofilament high tensile strength, high elastic modulus and moderate elongation, anti-corrosion ability, heat and fire resistant, good alkali resistance, also has excellent overall performance, the production process chain is short, low energy consumption, cost-effective, all-natural green and so on, especially in building an innovative country, innovative industries, resource-saving and environment-friendly green, save energy and reduce row, carbon reduction, harmony and long life of the construction of transportation facilities has drawn increasing attention and actively promote the use of highway engineering technology.

Tab. 1-1 The chemical compositions of basalt (wt.%)

1.2 The Importance of this Project

Basalt should firstly meltin the furnace at between 1500° and 1700 °C before drawing. Electric melting method is advanced technology of glass melting which is widely used in developed and developing countries. The batch was melted into glass melt by the Joule heat generated by its electric resistance.

Glass electric melting is a kind of advanced technology that using Joule heat coming out in glass melt on the basis of the ionic conductance characteristic of glass at high temperature. It is a kind of modern new technology used by our department and the developed countries. Advantages of all-electric melting technology are as following.

Advantages of all-electric melting technology:

• Improving thermal stability and uniformity coefficient of melt glass, it is perfect for the glass with higher quality and satisfied with product requirement.

• Higher heating efficiency, energy saving and consumption reducing, longer campaign life, it is good for diminishing the air bubble, stone and stripe.

• Shaping temperature of the glass can be adjusted neatly with higher sensitivity and accuracy.

• Lower investment，less area occupied，simpler operation，without noises and pollution，better work environment，higher labor-productivity.

• It accords with the industrial policy of developing country, and adapts to the transformation and adjusts of energy structure in and out of country. We can gain more opportunities in market competition and technology improvement.

  The all-electric melting furnace was applied to various disciplines, including thermaltechnical, electrical, chemical industry and automation etc. It is a kind of glass manufacturing craft with advanced technology. Once it was born, ithas beencommonly used. The fact proved that the benefits were appreciable.