Solutions for the Corrosion of Refractory Materials at the Bottom of Glass Melting Furnaces

With the rapid development of the furnace industry, leakage incidents at the bottoms of melting tanks have frequently occurred in some glass plants in recent years. Expert analysis indicates that the primary cause is the inability of the tank bottom structure to effectively prevent "upward drilling" by molten glass and "downward drilling" erosion by metal particles; consequently, the bottom structure requires properties that resist these specific types of erosion.

Both the upward drilling of molten glass from beneath the refractory bricks and the downward drilling of metal particles are driven by convection within the free interface layer formed at the junction of three materials. Typically, these three materials are refractory brick, molten glass, and gas bubbles, or refractory brick, molten glass, and metal. This interfacial convection intensifies material exchange and accelerates the erosion of the refractory material. A well-known example of this phenomenon is the severe erosion observed in refractory bricks located at the glass melt line.

Bubbles form when molten glass flows beneath the fused-cast bottom paving blocks or penetrates the vertical joints between them to react with the underlying refractory materials; these bubbles rapidly erode the fused-cast zirconia-corundum blocks above. The tendency of the refractory bricks beneath the paving blocks to generate bubbles is a critical factor; a higher tendency to generate bubbles results in greater upward erosion.
Initial erosion caused by bubbles occurs within the horizontal interlayer joints—or, in the case of a single-layer paving system, at the horizontal interface between the paving blocks and the sealing layer. While erosion is less severe in vertical joints than in horizontal ones, molten glass can flow through vertical joints into the horizontal joints; therefore, the paving blocks, joints, and sealing layer must form a tight, inseparable unit to effectively prevent glass seepage into the horizontal joints.
Three types of fused-cast AZS ramming mixes—featuring a crystalline phase composition essentially identical to that of the paving blocks—are used to form the sealing layer beneath the blocks and to fill the gaps between them; this allows the fused-cast blocks, joints, and sealing layer to sinter at 1,250°C into a monolithic composite structure highly resistant to glass corrosion.

(1) The behavior of the composite layer—utilizing glass-melt-resistant AZS ramming mix—at high temperatures is described below:
(2) Below 800°C, the AZS ramming mix expands at a regular rate lower than the thermal expansion coefficient of fused-cast AZS material; there is essentially no difference in behavior whether the load is zero, 2 kg/cm², or 4 kg/cm². Between 800°C and 1100°C, the AZS ramming mix undergoes sintering driven by the glassy phase of the fused-cast particles. The glassy phase content increases progressively, peaking at 1200°C. This yields two key results: ① The plasticity of the AZS ramming mix is ​​most pronounced in this temperature range; ② "33#" fused-cast zirconia-corundum contains approximately 20% glassy phase—similar to the AZS ramming mix—enabling excellent adhesion between the two materials.
(3) Above 1200°C, the AZS ramming mix undergoes devitrification, with the glassy phase transforming into mullite; effectively, the mix undergoes ceramization and its plasticity decreases—a process offering several advantages: ① The expansion of the raw AZS ramming mix is ​​significantly lower than that of the furnace bottom paving bricks; furthermore, this expansion is limited to temperatures below 800°C, beyond which the mix behaves as a strain-accommodating material;
② Between 800°C and 1300°C, the plasticity and adhesion of the AZS ramming mix help maintain a tight seal at the joints even when slight displacement occurs—such as during the charging of cullet;
③ In actual operation, once the temperature stabilizes, the AZS ramming mix undergoes ceramization and gradually fuses into a unified mass, creating a sealed, monolithic furnace bottom structure. The glassy adhesive layer formed between the ramming mix and the bottom bricks serves as a reliable intermediate interface. This chemical and mineralogical structure ensures the uniformity and structural integrity of the entire furnace bottom.

It is particularly important to note that using ramming mixes with a different crystalline phase than the paving bricks—and which contain high levels of Fe₂O₃ and other impurities—results in poor resistance to upward "drilling" corrosion by the molten glass. This is because such mixes exhibit high foaming rates and fail to sinter with the paving bricks to form a monolithic composite layer. When this type of ramming mix was used in glass melting furnaces at glass plants in Zhejiang and Anhui, leakage occurred at the furnace bottom in less than a year, forcing a shutdown.

Downward "Drilling" Corrosion by Metal Particles

Metal particles typically enter the furnace mixed with raw materials, batch materials, and cullet. In specific instances, metal may also fall to the furnace bottom during hot repairs to the superstructure and main crown using metal tools. Therefore, the key to preventing downward "drilling" corrosion caused by metal particles lies in using powerful magnets to remove metal impurities from the batch materials and cullet. Additionally, installing zircon bricks beneath the AZS bottom sealing layer serves a protective function: they react with the glass to form a viscous substance that penetrates open brick joints and encapsulates the metal, thereby preventing the molten glass from penetrating to lower levels and stopping the metal from "drilling" downwards.