Superior sealing and consistent maintenance of that seal throughout the entire service life of a float glass furnace are critical to glass manufacturing operations. A well-sealed furnace not only prolongs the service life of refractory materials but also minimizes glass production defects caused by poor sealing performance.
Effective glass furnace sealing is not merely dependent on refractory bricks and mortars—it starts with scientific furnace design. Defective sealing areas can almost always be corrected by adjusting furnace structures and modifying sealing requirements. Additionally, strict adherence to refractory material application guidelines is essential, as certain materials are chemically incompatible and cannot be used together.
This article provides professional guidance and recommendations for float glass furnace sealing practices and refractory material selection, based on practical industry experience and engineering expertise, to help glass manufacturers optimize furnace sealing, extend equipment life, and improve production efficiency.
Float Glass Furnace Sealing: Key to Extending Refractory Life & Optimizing Production
1. Sealing Methods for Float Glass Furnaces
1.1 Optimal Sealing Timing
Permanent sealing should not be applied until nearly all furnace expansion has occurred. For float glass furnaces, the following temperature-based sealing timeline is recommended:
Begin sealing silica expansion joints when the temperature exceeds 760℃ (at the end of furnace baking).
Start sealing fused AZS expansion joints and other potential gaps when the temperature rises above 1250℃.
Complete sealing of expansion joints for the furnace crown and upper structures before hot furnace commissioning.
1.2 Key Sealing Positions
Sealing work for float glass furnaces covers all critical structural joints and gaps, including:
Charging port: Wing wall and breast wall joints
Melting zone: Furnace crown expansion joints, breast wall and gable wall expansion joints
Port neck: Slope expansion joints, port neck side wall expansion joints
Regenerator: Expansion joints, regenerator wall gaps, regenerator partition end joints
Constriction: Crown expansion joints
Cooling zone: Crown expansion joints, breast wall and gable wall expansion joints
Tank wall: Upper gap sealing
Flow channel: Expansion joint sealing
Other: Sealing of random gaps formed during furnace baking
1.3 Standard Sealing Operations for Expansion Joints
There is no universal industry standard for sealing expansion joints at each position, but the following practical operation requirements are proven effective through field experience, with material selection tailored to joint width and structural characteristics:
Joint width ＞10mm: Seal with special-shaped (wedge/cylindrical) high-quality silica bricks + silica refractory patching material.
Joint width ＜10mm: Directly seal with silica refractory patching material after proper surface treatment.
Straight joints between bricks and gables, plus constriction expansion joints: Cover with high-quality silica bricks first, then seal with silica refractory patching material.Note: Wedge-shaped expansion joints perform better than straight “blade-shaped” ones—imprecise straight joint sizing often causes brick fracture from thermal expansion pressure.
Charging port wing wall joints: Seal with zircon self-leveling refractory grout.
Breast wall & gable wall expansion joints: Use silica thin bricks or high-quality high-silica grout (based on joint width).
Port neck side wall expansion joints:
Joint width ＞15mm: Seal with zircon thin bricks + zircon self-leveling refractory grout.
Joint width ＜15mm: Directly seal with zircon self-leveling refractory grout.
Port neck slope crown expansion joints:Two methods are available—covering and clamping. A field test on a 400t furnace at Fuyao Group demonstrated that the covering method is far superior:
Covering side: No refractory damage or brick slag falling, clean port neck pit, no re-sealing required after years of use.
Clamping side: Severe refractory damage, heavy slag accumulation in the pit, and one full re-sealing required.Optimal covering operation: Cover with fused AZS or zircon bricks, then cast zircon self-leveling refractory grout on the outer surface.
Joint width ＜15mm: Direct sealing with silica refractory patching material or zircon self-leveling refractory grout.
Tank wall upper gaps: Seal with zircon self-leveling refractory grout.
Furnace crown transparent gaps: Seal with high-quality high-silica grout.
Core Sealing Criterion: A well-sealed furnace should show no visible red heat emission on the outer surface—this is the primary visual check for sealing effectiveness.
2. Performance Requirements for Refractories in Furnace Sealing
The quality and service life of float glass furnace expansion joint sealing depend on three key factors: furnace design, construction technology, and refractory material quality and selection.
We have developed a full range of high-performance refractory patching and sealing materials for glass furnace applications, through in-depth engineering cooperation and field testing. These materials have been proven effective on multiple glass furnaces, with several varieties fully replacing expensive imported alternatives and delivering equivalent or superior performance.
Below is a detailed performance specification for our core glass furnace sealing refractories:
2.1 High-Quality High-Silica Grout
Multi-purpose material for sealing furnace crowns and various expansion joints; also used as a base coat (silica slurry) on furnace crown exteriors to ensure strong bonding with thermal insulation layers.
Performance Index
Requirement
SiO₂ Content (%)
≥95
Refractoriness (℃)
≥1710
Particle Size Distribution
+0.5mm ≤5%; -0.088mm ≥75%
Bond Strength (MPa) – 110℃ Dried
≥3
Bond Strength (MPa) – 1450℃×3h
≥4.5
2.2 Silica Refractory Patching Material
Widely used for sealing silica-based expansion joints in all glass furnace zones, with excellent high-temperature stability and bonding performance.
Performance Index
Requirement
Bulk Density (g/cm³)
≥1.75
Working Density (g/cm³)
≥2.1
Refractoriness (℃)
≥1730
Permanent Linear Change (1450℃×3h, %)
≤0.1
Compressive Strength (1450℃×3h, MPa)
≥35
2.3 Zircon Self-Leveling Refractory Grout
A high-performance sealing material widely adopted in international glass furnaces, now localized in our R&D. It is suitable for manual or mechanical (pump) application, and is the premium choice for high-wear, high-temperature furnace joints (e.g., charging ports, tank walls).
Performance Index
Requirement
ZrO₂ Content (%)
≥62
Refractoriness (℃)
≥1750
Bond Strength (MPa) – 110℃ Dried
≥8
Bond Strength (MPa) – 1450℃×3h
≥18
2.4 Special High-Quality Silica Mortar
Domestic standard silica mortars often fail to meet the construction and performance requirements of high-grade glass furnace masonry (e.g., premature drying, poor fluidity, uneven joint thickness), leading to crown brick displacement, red heat emission, alkali vapor erosion, and excessive heat loss.
Our specially developed SSQSIL-97 silica mortar addresses all these pain points, with construction performance and internal quality matching imported silica mortars. It is the ideal choice for furnace crown brick masonry, while our SQSIL-96 is suitable for general silica brick masonry.
Performance Index
Special High-Quality Silica Mortar (SSQSIL-97)
Standard High-Quality Silica Mortar (SQSIL-96)
SiO₂ Content (%)
≥97
≥96
Max Service Temperature (℃)
1650
1630
Bonding Time (min)
≥3
≥3
Bond Strength (MPa) – 110℃ Dried
≥1
≥1
Bond Strength (MPa) – 1450℃×3h
≥2.5
≥3
Max Particle Size (mm)
0.8
0.8
Application Scope
Furnace crown brick masonry
General silica brick masonry
Key Benefits of Our Silica Mortar:
Eliminates crown brick displacement during furnace baking.
Prevents red heat emission and “rat hole” erosion from alkali vapor through dense brick joints.
Reduces heat loss and energy consumption; lowers furnace crown surface temperature for easier thermal insulation construction.
3. Conclusion
This article provides practical, field-proven guidance for float glass furnace expansion joint sealing methods and refractory material selection, which will play a positive role in standardizing glass furnace sealing practices across the industry.
Effective furnace sealing is a systematic project that combines scientific design, precise construction, and high-quality refractory materials. Our independently developed range of glass furnace sealing refractories—including high-silica grout, zircon self-leveling grout, and special silica mortar—offers a cost-effective import-substitute solution for glass manufacturers. These materials not only optimize furnace sealing performance, extend refractory and furnace service life, and reduce production defects but also lower energy consumption and maintenance costs, creating tangible economic benefits for glass production enterprises.
For customized glass furnace sealing refractory solutions tailored to your specific furnace design, production capacity, and operating conditions, contact our professional engineering team today—we provide full-cycle technical support from material selection to on-site construction guidance.
