The photovoltaic (PV) glass industry is expanding at a remarkable pace. As the heart of the entire production line, the furnace's service life directly determines an enterprise's profitability cycle. Among all the refractory materials used in the furnace, sidewall blocks are the critical "lifeline"—immersed day and night in molten glass at temperatures exceeding 1,000°C, they endure the dual onslaught of chemical corrosion and mechanical erosion.
The reality is harsh: an incorrect choice of sidewall block material can lead to accelerated corrosion and a service life cut in half—or, in severe cases, force a cold repair and result in losses amounting to tens of millions. Currently, there is no unified standard for selecting sidewall block materials for PV rolling furnaces; practices range from using exclusively fused α-β alumina bricks to employing a combination of fused AZS bricks and fused α-β alumina bricks. How, then, should the selection and configuration be made? This is not a simple matter of "the more expensive, the better," but rather a complex equation involving temperature fields, molten glass composition, and furnace structure.
01 Two Key Players: Fused α-β Alumina Bricks and Fused AZS Bricks
1.1 Fused α-β Alumina Bricks: The Pure, "Gentle Guardian"
Fused α-β alumina bricks are produced from high-purity alumina (typically >90% Al₂O₃) by melting at temperatures between 2000°C and 2200°C. Their crystalline structure consists of an interlocking matrix of 45–55% α-Al₂O₃ and 45–60% β-Al₂O₃; the extensive interpenetration of the β-phase transforms the original tubular microstructure into a flaky one, resulting in finer crystals and significantly improved resistance to thermal deformation.
Their core advantage lies in their "purity": the nepheline-based alteration layer formed on the surface has low viscosity and dissolves easily into the molten glass. This means that even if trace amounts of material detach, they do not cause persistent contamination of the glass melt. They are the undisputed ideal choice for zones operating below 1350°C.
However, "gentle" also implies "vulnerable"—the alteration layer washes away too easily, meaning protective capability is insufficient at higher temperatures.
1.2 Fused AZS Bricks: The Tough, "High-Temperature Shield"
Fused AZS bricks belong to the Al₂O₃-ZrO₂-SiO₂ system, exemplified by the "33#" oxidation-method fused AZS brick (void-free type). Their primary crystalline phases consist of a dense, coexisting matrix of fused α-β alumina and baddeleyite (ZrO₂). With a ZrO₂ melting point of approximately 2700°C, these bricks possess exceptional corrosion resistance.
The key factor is that the surface alteration layer incorporates ZrO₂; this results in a viscosity significantly higher than that of the nepheline layer found on pure fused α-β alumina bricks. It adheres tightly to the brick surface like a "high-viscosity shield," resisting both diffusion and spalling. In high-temperature zones, this shield acts as a vital safeguard for the tank wall bricks.
However, there is a downside: if this protective layer does spall, the resulting impurities—which differ greatly in viscosity from the surrounding glass melt—are much harder to eliminate, posing a contamination risk that cannot be ignored.
1.3 Price-Performance Discrepancy
Interestingly, in terms of market price, standard cast Fused α-β Alumina brick is actually more expensive than the "33" grade—due to the greater manufacturing complexity and technical investment involved. This implies that selecting Fused AZS brick offers not only superior performance in high-temperature zones but potentially a cost advantage as well. The balance of cost-effectiveness is far more complex than the raw figures suggest.
02 The Unique Nature of PV Furnaces: Why Float Glass Practices Don't Apply
If you are transitioning from the float glass industry to PV rolled glass production, do not assume that the configuration of sidewall blocks can simply be "copy-pasted." PV rolled glass furnaces exhibit three significant structural and process differences that fundamentally alter the logic behind selecting sidewall blocks.
2.1 The "Waist" (Throat) is Becoming Shorter and Narrower
While traditional float glass furnaces feature relatively wide and spacious throats, the trend for PV rolled glass furnaces is toward shorter and narrower throats. For furnaces of comparable scale, it has become common practice to reduce the throat length from 7,500 mm to 5,000 mm and the width from 4,000 mm to 2,200 mm. A shorter, narrower throat reduces the surface area for heat dissipation as the molten glass passes through and increases flow velocity; consequently, the temperature drop is significantly reduced—plummeting from the 110°C seen in float furnaces to around 90°C.
What does this imply? The temperature of the molten glass near the throat exit is much higher than you might expect.
2.2 Elimination of Stirrers and Dilution Air
Float glass furnaces are typically equipped with horizontal or vertical stirrers, as well as temperature-control mechanisms in the cooling section such as dilution air and space-cooling water jackets. In contrast, many PV rolled glass furnaces have eliminated stirrers and dilution air while enhancing insulation in the working channel. This further restricts the scope for temperature reduction, causing the high-temperature zone to extend further downstream.
2.3 The "Low-Iron, High-Transmittance" Characteristics of PV Glass
PV glass has an extremely low iron content, resulting in high light transmittance and high thermal permeability, which drives strong horizontal convection currents. This leads to more intense scouring of the sidewalls by the molten glass, placing higher demands on the corrosion resistance of the refractory materials.
The combination of these three factors makes the selection of sidewall blocks near the throat exit of PV rolled glass furnaces the most challenging aspect of the entire refractory configuration process.
03 1350°C: An Uncrossable Watershed
At the heart of every discussion regarding configuration lies a critical temperature figure: 1,350°C. Empirical data reveal a clear pattern: taking two structurally identical 700 t/d furnaces as examples—producing the same glass specifications and maintaining the same pull rate—a difference of 20°C in the throat exit temperature arose solely from different fining temperature settings. One furnace’s throat exit temperature approached 1370°C, while the other was around 1350°C. The former, utilizing fused α-β alumina bricks, experienced a markedly accelerated rate of corrosion.
The reason lies in the fact that the nepheline alteration layer formed on fused α-β alumina bricks offers insufficient protection at high temperatures, whereas the high-viscosity alteration layer on fused AZS bricks truly acts as a "shield" within this temperature range.
Consequently, a "golden rule" has emerged in the industry:
Above 1350°C—fused AZS bricks are essential;
Below 1350°C—fused α-β alumina bricks are more economical and safer.
This is not merely anecdotal; it is a consensus distilled from extensive empirical data and engineering practice.
04 The 9000mm Rule: A Proven "Gold Standard" for Configuration
Based on temperature distribution patterns and engineering experience, the industry has established a simple yet highly effective configuration guideline: the "9000mm Rule."
4.1 The Rule Defined
Using the two corner bricks at the throat exit as centers, draw a circle with a radius of 9000mm. For the area inside the circle, select 33# oxidation-method (void-free) fused AZS bricks; for the area outside the circle, select fused α-β alumina bricks.
4.2 Why 9000mm?
Taking a 700 t/d melting furnace as an example, the average temperature drop of the molten glass from the hot spot to the throat is approximately 7.5°C/m. Adopting a conservative safety approach, the temperature drop near the throat exit is estimated at 6°C/m. Meanwhile, the initial glass-phase precipitation temperature for 33# fused AZS bricks is no lower than 1400°C. Taking 1400°C as the upper-bound throat exit temperature and applying the 6°C/m drop rate, the temperature is considered safe once it falls below 1350°C—and the distance required for this drop is precisely around 9000mm.
4.3 Schematic of Typical Furnace Configurations
One-furnace, four-line configuration: Circles are drawn with a radius of 9,000 mm, centered on the two corner bricks at the throat exit; Fused AZS bricks are used throughout the area within these circles (including the two main channels). By the time the molten glass reaches the nearest branch channel, its temperature has dropped below 1,350°C, so Fused α-β Alumina bricks are selected for the entire sidewall of the branch channels.
One-furnace, five-line configuration: Circles are similarly drawn centered on the two corner bricks, with Fused AZS bricks used inside them. Due to the increased number of channels, the coverage area of Fused AZS bricks is larger, yet the total cost remains manageable.
4.4 Economic Analysis: Where are the savings?
Taking the one-furnace, four-line configuration as an example, Fused AZS bricks account for approximately 30%–40% of the total sidewall brick volume. Compared to a design using exclusively Fused α-β Alumina bricks, the total cost is reduced by about 8%–10%, while the service life of critical sections is extended by over 30%. The savings go beyond material costs; they also include avoiding the massive losses—often running into the tens of millions—associated with furnace shutdowns for cold repairs.
05 Three Hidden Variables: Look Beyond Just Temperature
When configuring sidewall bricks, temperature is the primary factor, but the following three variables also significantly influence the overall outcome.
5.1 Furnace Tonnage and Cooling Rate
The larger the melting furnace's tonnage, the slower the cooling rate of the molten glass. A 700 t/d furnace experiences a temperature drop of approximately 7.5°C per meter, whereas large-tonnage furnaces (1000–1200 t/d) exhibit a more gradual temperature decline, meaning the high-temperature zone extends further downstream. Consequently, the "9000mm rule" should be adjusted—the coverage area of fused AZS bricks needs to be extended further downstream.
5.2 Refining Temperature Setting
Measurements indicate that for every 20°C increase in refining temperature, the temperature at the throat exit rises by approximately 20°C. If the refining temperature is set above 1455°C, pushing the exit temperature close to 1370°C, then even when applying the 9000mm rule, additional protective measures are essential—such as air-cooling the sidewall bricks to slow the rate of corrosion.
5.3 Balancing Energy Conservation and Thermal Insulation
Better insulation in the forehearth channels results in a slower temperature drop for the molten glass and an extended high-temperature zone. While this benefits the stability of glass flow and the absorption of micro-bubbles, it also necessitates covering a larger area with fused AZS bricks. Finding the right balance between energy conservation and refractory protection is a challenge every furnace manager must address.
06 Operational Advice: Temperature Control is More Effective Than Replacing Bricks
If the temperature at your furnace's throat exit remains consistently high, rather than rushing to replace bricks, consider these three steps first:
First, appropriately lower the refining temperature. A 20°C reduction is more effective than replacing any brick and simultaneously saves energy.
Second, optimize heat dissipation in the transverse and branch channels. Minimize unnecessary heat loss to prevent the glass from cooling excessively before reaching a safe temperature, while also avoiding localized overheating.
Third, implement air-cooling protection for sidewall bricks in the high-temperature zone. This is a cost-effective, high-impact auxiliary measure that can significantly delay brick corrosion.
Remember: A single cold repair of a furnace costs tens of millions. Getting the temperature regime and material configuration right represents the most cost-effective investment.
07 A Broader Perspective: A Systems Approach to Furnace Refractories
Sidewall bricks are merely one component of the furnace's refractory system. A properly functioning photovoltaic glass furnace relies on the synergistic coordination of materials across its various sections:
Furnace Bottom: A multi-layer composite structure; the main layer utilizes large clay blocks, topped with protective and wear-resistant layers—the latter typically employing fused AZS bricks that come into direct contact with the molten glass.
Charging Bay: Subjected to the most severe abrasion from batch materials and erosion from glass flow; typically utilizes void-free fused AZS bricks (41% ZrO₂) combined with enhanced air cooling.
Throat: Characterized by the highest flow velocity and strongest convection currents; cover blocks should be made of void-free AZS-41 bricks.
Cooling and Forming Sections: Require oxidation-method AZS-33 bricks; these feature a high glass-phase exudation temperature, ensuring no bubbles are introduced into the molten glass.
Crown and Breastwall: High-purity silica bricks are used in high-temperature zones, while fused AZS-33 bricks may be used in secondary high-temperature zones.
A weakness in any single section can become the furnace's "Achilles' heel."
08 Choosing the right source ensures the right protection; selecting bricks is not about choosing the most expensive option, but the right one.
The material and configuration of sidewall bricks ultimately determine product quality. While the market is crowded with refractory manufacturers, only those capable of controlling the entire process—from raw materials to finished products—can deliver stable, reliable performance under high-temperature conditions.
Selecting materials for photovoltaic glass furnace sidewalls is never a simple "either-or" choice. It is a dialogue between temperature and material, a balancing act between cost and service life, and a harmony of process and structure.
Remember these three golden rules:
1350°C is the watershed: Fused AZS bricks for high-temperature zones; fused α-β alumina bricks for lower-temperature zones.
9000mm is the safety radius: Centered on the corner brick, specific requirements apply to areas inside and outside this circle.
Temperature control beats brick replacement: Lowering the temperature by 20°C is worth more than a fortune.
Extending the furnace's service life by just two years saves more than just the cost of bricks—it preserves time, production capacity, and market opportunities. Choosing the right sidewall bricks means securing the future of the furnace.
Wechat Us 
