From material selection logic to component configuration: Deciphering the core essentials of refractory materials for glass furnaces.

Five Golden Rules for Selecting Refractories: It Is Not About Cost, But Suitability
The selection of refractory materials for glass melting furnaces must adhere to five core principles. Neglecting any one of them could create an "Achilles' heel" for the furnace.
1.1 Tailored to the Furnace: Furnace Type Dictates the Overall Approach
Different furnace types—such as end-fired (horseshoe-flame), cross-fired, all-electric, and electric-boosted—differ vastly in terms of temperature distribution, flame paths, and airflow patterns. In end-fired furnaces, the flame travels horizontally along the longitudinal axis in a horseshoe shape, and temperature fluctuations during the firing-reversal cycle can reach 50–100°C; consequently, the refractory materials used must possess exceptional thermal shock resistance. In contrast, all-electric furnaces lack direct flame impingement and experience relatively uniform corrosion, requiring a different logic for material selection.

1.2 Tailoring to the Material: Glass Composition as the Guiding Factor
Components within the molten glass—such as alkali metal oxides (Na₂O, K₂O) and boron oxides (B₂O₃)—exert vastly different corrosion mechanisms on refractory materials. Soda-lime glass, with its high R₂O content, causes severe corrosion to basic refractories; conversely, the dust from alkali-free borosilicate glass batches consists primarily of SiO₂ and B₂O₃—strongly acidic oxides—requiring a completely different approach to material selection.
1.3 Tailoring to the Location: Performance Priorities Dictated by Zone
Conditions—including temperature, corrosive agents, and mechanical loads—vary drastically across different sections of the furnace. Tank sidewalls must withstand both vertical immersion and horizontal scouring by the glass melt, necessitating a balance between corrosion resistance and thermal shock resistance. Meanwhile, regenerator checkerwork is subjected to dust condensation and thermal cycling, requiring resistance to creep and to alternating oxidizing-reducing atmospheres. A single furnace may require four or five distinct types of refractory materials across its various sections.
1.4 Preventing Contact Reactions: "Chemical Isolation" Between Adjacent Bricks
When refractory materials of different compositions come into contact, chemical reactions can easily occur, forming low-melting-point phases that lead to structural collapse. For instance, if silica bricks are in direct contact with zirconia-corundum bricks, high-concentration R₂O-rich liquid can seep into the joints and rapidly corrode the silica bricks, creating voids. Therefore, an isolation layer must be placed between dissimilar adjacent bricks—such as inserting several courses of zircon bricks between silica and zirconia-corundum bricks.
1.5 Economic Pragmatism: Batch Supply and Standardized Shapes
Prioritize the use of mass-produced, standardized refractory bricks; these offer consistent quality, reliable supply, and high masonry efficiency. Opting for non-standard custom designs or niche products often entails significant quality fluctuations, unpredictable delivery schedules, and difficulties with future maintenance.

The Refractory Material "Arsenal": Meet the Five Key Players
Before delving into the specific configuration of horseshoe-flame furnaces, it is essential to understand the "temperament" of the five core types of refractory materials.
2.1 Silica Bricks—The "Skeleton" of High-Temperature Zones
Silica bricks are acidic refractories with a refractoriness of 1690–1730°C and an initial load-softening temperature of 1640–1680°C. They undergo a total volumetric expansion of approximately 2% at 1450°C; paradoxically, this characteristic helps ensure the structural integrity and airtightness of the masonry. Silica bricks are widely used in components such as the main crown, breastwalls, and regenerator crowns.
However, they have a critical weakness: silica bricks undergo rapid volumetric expansion due to crystalline phase transformations at 200–300°C and 573°C. During heat-up, the temperature rise below 600°C must not be too rapid; during cooling, drastic temperature fluctuations must be avoided; and contact with alkaline substances is strictly prohibited.
2.2 Fused Zirconia-Corundum (AZS) Bricks—The "Ace" of Corrosion Resistance
Based on the Al₂O₃-ZrO₂-SiO₂ ternary system and manufactured via the fused-cast process, AZS bricks are categorized into three grades—AZS-33, AZS-36, and AZS-41—based on their ZrO₂ content.
AZS-33: Contains approximately 33% ZrO₂; exhibits minimal glass phase exudation and excellent resistance to contaminating the glass melt; suitable for areas in direct contact with the melt, such as tank sidewalls and working ends.
AZS-36: A standard oxidation-method product offering a balance between corrosion resistance and low contamination potential; suitable for direct-contact areas such as melting tank sidewalls and charging ports.
AZS-41: The premium-grade product offering unsurpassed corrosion resistance; specifically designed for the most severely eroded "death zones," such as throat channels, furnace dams, bubbler areas, and charging port corners. The core advantage of AZS bricks lies in the fact that ZrO₂ dissolves into the altered surface layer; the resulting layer possesses a viscosity far higher than that of the nepheline-rich altered layer found on pure corundum bricks, acting like a high-viscosity "shield" that adheres tightly to the brick surface and resists both diffusion and spalling.

2.3 Fused-cast Corundum Bricks—The Pure, "Gentle Guardian"
Fused-cast α-Al₂O₃ bricks consist primarily of α-corundum crystals, with an Al₂O₃ content exceeding 90% and a minor glass phase of approximately 2%. They do not contaminate the glass melt and exhibit excellent corrosion and wear resistance at temperatures below 1350°C, making them an ideal choice for the refining, cooling, and working sections of the furnace. However, their corrosion resistance drops sharply above 1600°C, marking the upper limit of their performance.
Fused-cast α-β-Al₂O₃ bricks are composed of 45% α-Al₂O₃, 53% β-Al₂O₃, and 2% glass phase. They perform equally well at 1350°C; furthermore, due to the unique structure of the β-phase (which effectively eliminates the glass phase), they do not release bubbles into the glass melt, making them particularly suitable for areas requiring high cleanliness.
2.4 Fireclay Bricks—The Economical "Foundation"
Fireclay bricks are classified as acidic refractory products; while they offer relatively poor resistance to alkaline corrosion, they possess high mechanical strength and are cost-effective. Large fireclay bricks (individual weight ≥50 kg) are the primary choice for paving furnace bottoms and constructing checker bricks in the lower sections of regenerators. They are especially well-suited for zones characterized by lower temperatures and heavy loads but mild corrosion.
2.5 Magnesia-based Refractories—The "Backbone" of the Regenerator
Magnesia-based materials—such as magnesia-chrome bricks and direct-bonded magnesia bricks—offer excellent resistance to alkaline corrosion, though their high-temperature strength is somewhat lower. They serve as core materials for regenerator side walls, partition walls, and checkerwork. High-grade magnesia bricks (MgO >97%) are specifically required for the upper sections of the checkerwork to withstand high-temperature fluctuations, dust carry-over, and repeated redox cycling.

Horseshoe-flame soda-lime glass furnace: A comprehensive configuration overview from the melting tank to the regenerator
The following section breaks down the components one by one, detailing specific temperature ranges, recommended materials, and selection criteria.
3.1 Melting Tank—The "Heart" of the Furnace
(1) Tank Walls
Main tank wall area: 1400–1600°C; AZS-33 bricks (TC)—offer excellent corrosion resistance and thermal shock resistance against molten glass.
Lower-temperature tank wall areas: <1400°C; Fused-cast zirconia-mullite—suitable for lower temperatures; offers superior cost-performance.
The tank walls endure the harshest operating conditions within the melting tank: vertical surfaces are subject to continuous immersion in molten glass, while the area near the glass line experiences the most severe erosion due to temperature gradients and airflow turbulence. Using large-format bricks to minimize joints is a key strategy for delaying erosion.
(2) Tank Bottom Paving Bricks
1300–1500°C; Fused-cast AZS-33 bricks (D.C.L)—corrosion and erosion resistant.
<1400°C; Large-format fireclay or high-alumina bricks—subject to high loads but minimal erosion; cost-effectiveness is the priority.
(3) Charging Port
1400–1500°C; Fused-cast AZS-36 bricks (R.V) or AZS-41# bricks (R.V)—exhibit extremely high resistance to glass corrosion.
The charging port is the entry point for the batch mixture; characterized by airborne dust and drastic temperature fluctuations, it is a zone highly susceptible to erosion. AZS-33 (Grade 30) zirconia-corundum bricks are recommended for the sides of the charging port, while silica bricks are used for the upper section near the crown; however, a separating layer of zircon bricks must be installed between the two materials.

(4) Bubbling zone
1400–1500°C | Fused-cast AZS-41# brick (D.C.L) | Area of ​​most severe corrosion; requires the highest grade.
Bubbling enhances fining by intermittently blowing gas into the hot spot at the furnace bottom; intense local turbulence leads to rapid corrosion rates. AZS-41 is the optimal choice here.
(5) Electrode zone
1400–1600°C | Fused-cast AZS-41# brick (R.D.C.L) | High temperatures and severe corrosion around the electrodes.
(6) Melting tank crown
1300–1650°C | High-density silica brick or fused-cast AZS brick.
3.2 Melting tank superstructure—the "front line" against flames and dust
(1) Area above the batch charger
1400–1500°C | Fused-cast AZS-36# brick (R.C) | Resistant to batch material corrosion, flame impingement, and thermal shock.
(2) Burner port
1500–1650°C | Fused-cast AZS-31# or 41# brick (R.C) | Highest temperature zone; requires extreme corrosion resistance.
(3) Port neck (crown and sidewalls)
1450–1600°C | Fused-cast β-Al₂O₃ or high-quality silica brick | Resists batch carryover adhesion and alkali vapor corrosion.

(4) Chequer wall
1400–1600°C: Fused-cast α-Al₂O₃ bricks or fused-cast AZS bricks
3.3 Working zone—the "transition zone" from melting to forming
(1) Tank sidewalls
1300–1450°C: Fused-cast α-Al₂O₃ bricks (T.C.) or fused-cast AZS (oxidation method) bricks. These exhibit minimal bubbling and good resistance to contamination when in contact with molten glass; at this temperature range, their corrosion resistance is comparable to that of AZS-33.
(2) Tank bottom paving bricks
1300–1400°C: Fused-cast AZS bricks (V.F.). These offer a balance of low bubbling, contamination resistance, and corrosion resistance.
(3) Forehearth (submerged section)
Fused-cast α-β-Al₂O₃ bricks (R.C.) or fused-cast AZS (oxidation method) bricks. AZS-41 has a high ZrO₂ content and offers excellent corrosion resistance.
(4) Throat (glass flow passage)
1400–1500°C: Fused-cast AZS-41 bricks (D.C.L.). The cover blocks and facing blocks have large downward-facing surface areas; corrosion must be uniform, and the material must be dense. The throat connects the melting section and the cooling section (dimensions: 200–350 mm high, 1000–2000 mm long) and serves as the critical passage for glass flow distribution. Corrosion products here tend to remain on the surface due to gravity, but if they fall into the molten glass, they create critical defects.

3.4 Working End Superstructure—A "Gradient Zone" of Stepwise Decreasing Temperatures
Working end main arch: 1300–1450°C; high-quality silica bricks
Working end sidewalls: 1300–1450°C; silica bricks, β-Al₂O₃ bricks
Area above working end inlet: 1300–1400°C; fused-cast β-Al₂O₃ bricks (R.C.), sintered mullite bricks, sillimanite bricks
Throat bridge bricks: 1400–1500°C; fused-cast AZS-33 (R.C.), fused-cast α-β-Al₂O₃ bricks
Sillimanite bricks are selected for the area above the working end inlet because they contain less glass phase than standard fireclay bricks, exhibit excellent mullite crystal growth, and offer superior corrosion resistance and thermal stability.
3.5 Regenerator—An "Energy Hub" for Waste Heat Recovery
The regenerator is a signature structure of the horseshoe-flame furnace; it recovers waste heat from flue gases and preheats combustion air using checker bricks, achieving a thermal efficiency of 45%–67%. The refractory configuration is highly complex, requiring stratification based on temperature:
**Location** | **Operating Temp.** | **Recommended Material** | **Selection Basis**
Crown & upper side walls | 1400–1550°C | Direct-bonded magnesia-chrome bricks or silica bricks (basic refractories) | Good resistance to alkali corrosion; poor high-temperature strength
Middle & lower side walls | — | Magnesia-chrome bricks, high-alumina bricks | —
Upper partition walls | 1200–1400°C | Direct-bonded magnesia-chrome bricks | Good creep resistance
Middle & lower partition walls | 600–1200°C | Low-porosity fireclay bricks | —
Upper checkerwork | 1300–1400°C | High-purity magnesia bricks, direct-bonded magnesia bricks, sintered AZS bricks | Withstand high-temp. fluctuations, dust carry-over, and redox cycling
Middle checkerwork | 1000–1200°C | Direct-bonded magnesia-chrome bricks | Alkali vapor condensation, sulfate condensation, redox cycling
Separation bricks | — | High-alumina bricks | —
Lower checkerwork | 600–1000°C | Low-porosity fireclay bricks | Low-temp. fluctuations
Checkerwork support arches | 400–600°C | Low-porosity fireclay bricks | Load-bearing at temperature, dust accumulation
The upper section of the checkerwork is the most demanding zone of the entire regenerator, subjected to severe high-temperature fluctuations, batch dust carry-over, and alternating oxidizing/reducing atmospheres; consequently, high-grade magnesia bricks (MgO > 97%) must be used here.

3.6 Forehearth—The "Passage" for Batch Material
Section | Operating Temp. | Recommended Materials | Selection Criteria
Upper Space | 1300–1400°C | Fused α-β Al₂O₃ bricks, sintered AZS bricks, sillimanite bricks, sintered mullite bricks | Sillimanite bricks have low glass phase content; mullite crystals exhibit good growth
Forehearth Channel | 1250–1350°C | Fused α-β Al₂O₃ bricks, sintered AZS bricks | Wear resistance, corrosion resistance, thermal shock resistance
Spout Bowl | 1250–1350°C | Fused α-β Al₂O₃ bricks, sintered AZS bricks | Good wear resistance
Plunger & Orifice Ring | 1050–1300°C | Fused α-β Al₂O₃ bricks, sintered AZS bricks, sillimanite bricks, sintered mullite bricks | —
Understanding the Core Logic of Refractory Configuration for Horseshoe-Flame Furnaces at a Glance
If the refractory configuration of the entire furnace were to be summarized in a single sentence, it would be:
AZS-41/36 anchors the high-temperature, high-corrosion zones; AZS-33 and α-β corundum provide a balanced setup for medium-temperature zones; clay bricks or silica bricks secure the low-temperature zones; and magnesia-based materials withstand cyclic fatigue in the regenerator.
The core logic is "gradient configuration and precise matching":
Above 1400°C: The AZS series is the primary choice, with ZrO₂ content increasing alongside temperature and corrosion intensity;
1300–1400°C: α-β corundum bricks, fused AZS-33, and silica bricks each serve their specific roles;
Below 1200°C: Clay bricks and low-porosity clay bricks offer an economical and practical solution;
Regenerator: Magnesia-based materials serve as the irreplaceable "cyclic warriors."

Three Common Pitfalls: Even the Right Material Can Be the Wrong Choice
Pitfall 1: Brick Joints Are the Weakest Link
Brick joints are the vulnerable points of a melting furnace, suffering from erosion rates far higher than the brick bodies themselves. In areas directly contacting the molten glass, large blocks (individual weight ≥50 kg) should be selected whenever possible to minimize the number of joints. Horizontal joints in multi-layer structures are susceptible to upward "drilling" erosion; the wider the joint, the faster the erosion occurs.
Pitfall 2: Overlooking Thermal Shock During Reversal
Temperature fluctuations of 50–100°C occur during the reversal cycle of horseshoe-flame furnaces, with rear sidewalls and areas near the port necks bearing the brunt of the impact. If material selection focuses solely on maximum temperature while ignoring thermal shock resistance, the bricks will rapidly crack due to repeated thermal cycling. AZS bricks with lower ZrO₂ content (e.g., AZS-30) actually offer superior thermal shock resistance compared to high-zirconia bricks and should be prioritized for areas subject to significant temperature fluctuations.
Pitfall 3: Direct Contact Between Dissimilar Brick Materials
Without an intervening isolation layer, high-concentration R₂O-rich liquid can seep from the joints into silica bricks; upon condensing into a liquid phase at approximately 1400°C, it rapidly erodes the silica bricks, creating voids. Installing several layers of zircon bricks between the silica bricks and zirconia-corundum bricks on either side of the charging port is a standard industry practice known as a "firewall."
Future Trends: Longer Lifespan, Greater Energy Efficiency, and Increased Intelligence
Refractory materials for glass furnaces are evolving in three directions:
High Purity and Homogeneity: The purity and uniformity of fused-cast AZS bricks continue to improve. Optimization of the fusion process reduces internal bubbles and impurities, steadily lowering the foaming index and further reducing the rate of glass defects.

Adoption of composite structures: Composite furnace wall designs—featuring highly corrosion-resistant refractories on the inner face, an intermediate transition layer, and a high-efficiency thermal insulation layer on the outer face—are rapidly gaining ground; these structures significantly reduce heat loss while ensuring a long service life.
Focus on sustainability and longevity: As furnaces scale up in size, the cost of a single cold repair rises sharply; consequently, the target design life for refractories is shifting from six years to eight–ten years, making total lifecycle cost a primary consideration.
Conclusion
Selecting refractories for glass furnaces is a multifaceted art that integrates materials science, thermal engineering, and operational experience. There is no "one-size-fits-all" solution; success lies in precise matching based on furnace type, glass variety, and operating conditions.
Keep three principles in mind:
Temperature dictates the material type; corrosion resistance determines the grade; thermal shock resistance defines the toughness.
Brick joints are the critical vulnerability; isolation layers serve as a safeguard; large-format bricks provide the foundation.
Don't choose the most expensive option—choose the most suitable one; total lifecycle cost is the true bottom line.
Extending a furnace's campaign by just one year saves far more than the cost of refractories—it avoids production losses amounting to tens of millions. Choosing the right refractory means securing the future of the entire furnace.