An Overview Of Process Principles And Equipment For Fiberglass Melting
The production of fiberglass starts with its core procedure: glass melting. This process refers to heating batch materials with specific proportions in a high-temperature furnace to undergo a series of complex physical and chemical reactions, ultimately forming molten glass with uniform chemical composition that meets forming requirements. Based on the core reactions, the whole process can be distinctly divided into five consecutive and interrelated stages:
Five Stages of Glass Melting
1. Silicate Formation Stage
The batch materials (mainly silica sand, limestone, dolomite, soda ash, borax, etc.) are heated to 800~900°C. Decomposition, chemical combination and solid-phase reactions take place in this stage, releasing large volumes of gases such as CO₂ and H₂O. The mechanical mixture of raw batches turns into sinter containing various silicates and residual silica.
2. Glass Formation Stage
The temperature rises further to 1200~1250°C. The sinter begins to melt, and residual silica particles gradually dissolve into the silicate melt formed. At the end of this stage, the batch materials are mostly converted into glassy substances, yet the molten glass contains abundant bubbles with extremely uneven chemical composition and temperature distribution.
3. Glass Refining Stage
The temperature climbs to the peak melting temperature (normally 1400~1600°C). The viscosity of molten glass drops sharply, enabling dissolved gas, reaction-generated gas and residual bubbles to expand, rise and escape from the liquid surface. This stage is critical for eliminating visible bubbles and obtaining clear molten glass.
4. Homogenization Stage of Molten Glass
This stage proceeds at refining temperature or a slightly lower temperature. Thermal convection, bubbling agitation and mechanical stirring of molten glass eliminate chemical inhomogeneities (striae, knots) and thermal inhomogeneities, achieving highly consistent chemical composition and temperature throughout the molten glass. Homogenization is vital to the stability of final fiber properties.
5. Molten Glass Cooling Stage
High-temperature homogenized molten glass is cooled down to a viscosity range suitable for fiber forming (direct drawing or blowing), approximately 1000~1300°C. The temperature gradient and cooling rate must be precisely controlled during cooling to avoid damaging thermal uniformity and reach the exact viscosity required for forming.
Core Melting Equipment
The above high-temperature melting process relies on a specialized melting equipment system:
1. Melting Furnace
The core thermal equipment for glass melting, generally a continuously operated tank furnace (such as unit furnace, electric boost furnace or all-electric melting furnace). Its refractory-lined tank holds the batch materials, and high-temperature environments are supplied by combustion flames or electrodes to complete all melting stages. Strict zoning control of temperature, atmosphere and pressure is required inside the furnace.
2. Auxiliary Equipment
(1) Batch Charger: Feeds batch materials continuously, evenly and steadily into the furnace feeding port to guarantee stable furnace operation and consistent molten glass quality.
(2) Bubbler: Installed at the bottom of the melting tank, it injects gases (air, oxygen, nitrogen, etc.) into molten glass to generate upward bubble streams, enhancing convection and stirring, and greatly accelerating refining and homogenization. (3) Combustion System: Supplies thermal energy for melting, consisting of two parts:
Furnace combustion system: Provides primary heat for the main furnace (natural gas/fuel oil burners and control systems).
Forehearth combustion system: Supplies heat for heat preservation or temperature adjustment of forehearths, the molten glass channels connecting the melting furnace and forming equipment. (4) Metallic Heat Exchanger: Recovers waste heat from high-temperature flue gas discharged by the furnace to preheat combustion air (and sometimes fuel gas), greatly improving furnace thermal efficiency and reducing fuel consumption.
Conclusion
In summary, fiberglass melting is a precisely controlled high-temperature physical and chemical reaction process with five interlinked stages. The melting furnace and its sophisticated auxiliary equipment system jointly form the fundamental platform for executing this complex process and producing high-quality molten glass, laying an essential material foundation for subsequent fiber forming.
