According to the temperature at the top of the electric furnace, they can be divided into hot-top electric furnaces, semi-cold-top electric furnaces, and cold-top electric furnaces. According to the types of glass being melted, they can be divided into electric furnaces for glasses with high volatile components (such as borosilicate glass, fluoride glass, lead glass, phosphate glass, etc.) and electric furnaces for dark-colored glass. According to daily output, they can be divided into small, medium, and large furnaces. According to the flow direction of the molten glass, they can be horizontal or vertical. According to the cross-sectional shape, they can be rectangular, square, triangular, hexagonal, or circular.
01 Hot-Top Electric Furnace
The hot-top furnace is equipped with a flat flame burner at the top, and the output can fluctuate significantly. It does not require a fully covering charge layer. Generally, in fuel-heated furnaces, electrical heating measures are used. This not only reduces the furnace size but also lowers the furnace top temperature, producing glass products with fewer defects. The necessary heat for the furnace comes from both fuel and electrical energy (with about half from each), which makes it a mixed melter. Electrical heating is used from the bottom of the charge to complete about half of the melting process, while fuel heating is used from above to complete the other half. This allows for high-quality glass similar to that produced in all-electric melting furnaces. Since the cost of fuel heating is generally lower than that of electric heating, the primary benefit of this type of furnace over all-electric melting is the reduction of energy costs per ton of glass. A new concept in furnace design has emerged: maintaining a moderate temperature (around 1430°C) in the flame space above the charge. The standard melting rate for a mixed heating furnace design is 4 tons/(m²·d).
02 Semi-Cold-Top Electric Furnace
This type of electric furnace operates entirely on electrical energy, with a fixed-position charging machine. Changes in the discharge volume cause variations in the coverage of the charge layer within the melting pool. This type of melting pool can be designed symmetrically or asymmetrically.
03 Cold-Top Electric Furnace
The electric furnaces typically referred to are cold-top electric furnaces. The cold-top electric glass furnace runs entirely on electrical energy, with a continuous and uniform charge layer distributed across the surface of the entire melting pool. The all-electric furnace uses a "cold-top" vertical melting process. The entire surface of the molten glass is covered by the charge layer, which blocks heat radiation from the furnace top, reducing the temperature in the upper space of the furnace to below 150°C. At the same time, most of the volatile components in the charge condense and flow back into the glass, while gases such as CO2 released during the melting process can easily pass through the charge layer into the space. Below the charge layer, the glass slowly flows down into the electrode area. After the glass is fully melted in this area, it begins to clarify, and then flows to the lower part of the melting pool, completing the clarification and homogenization process. The melted glass flows through the liquid outlet holes, the rising passage, and the feeding passage into the working pool.
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