In today‘s world, developed countries possess more advanced and mature technological expertise in glass furnaces, both in terms of service life and structural rationality. To conserve energy, these countries have widely adopted efficient and systematic insulation technologies, which not only significantly reduce energy consumption but also greatly enhance the operational stability of glass furnaces and the quality of glass products. Currently, the majority of domestic glass manufacturers have also recognized the importance of insulation and have implemented varying degrees of insulation measures for their glass furnaces. However, there remains a noticeable gap between our insulation technologies, the insulation refractory materials used, and the final insulation outcomes compared to those in developed countries. This gap is reflected not only in energy consumption indicators but also in aspects such as glass furnace lifespan, operational safety, and maintenance costs. To bridge this gap, technical personnel from numerous domestic research institutions, design institutes, and production enterprises have conducted extensive research and engineering practices, accumulating valuable experience. In this context, this paper focuses on the insulation technology for key parts of glass furnaces, such as the crown and regenerator crown, and highlights a more advantageous hot and cold combined insulation construction method, aiming to provide a reference for technological advancement in the industry.

 

According to information, most domestic glass factories currently employ the hot-state insulation method for the crown of their glass furnaces. The primary construction phase of this method occurs after the glass furnace has been heated to its operating temperature. This is done to prevent structural damage to the insulation layer caused by the thermal expansion of the crown during the glass furnace heating process. From the perspective of avoiding premature damage to the insulation layer due to expansion, this approach held a certain degree of rationality during the earlier stages when insulation technology was not fully mature. However, the hot-state insulation method has revealed numerous shortcomings in practical application, which are mainly reflected in the following aspects:


First, the working conditions are harsh, and the construction intensity is high. During normal operation of a glass furnace, the surface temperature of the crown is extremely high, typically exceeding 1300°C. Workers must operate in an environment with intense radiant heat, and the commonly used insulation mortar often contains components such as phosphoric acid. These components release irritating gases at high temperatures, causing harm to the workers‘ respiratory systems and eyes, and can easily lead to health issues such as dizziness, nausea, and even fainting. Working in such an environment for extended periods is not only inefficient but also poses significant safety risks.

 

Second, the construction period is long. Taking a glass furnace with a daily melting capacity of 400 to 500 tons as an example, completing the hot-state insulation of the crown typically requires over 40 days. Prolonged high-temperature operations not only increase labor costs but also disrupt the normal production rhythm of the glass furnace, indirectly leading to economic losses.

 

Third, and most critically, the overall quality of hot-state insulation is often difficult to guarantee, resulting in a series of issues in the later stages of glass furnace operation. For example, localized "reddening" or even "burn-through" often occurs on the crown. Reddening refers to a section of the crown appearing as a semi-transparent, orange-red glow due to thinning from erosion, while burn-through refers to complete perforation at that spot, allowing flames from inside the glass furnace to escape. These phenomena not only accelerate the damage to the glass furnace structure, shortening its lifespan, but also lead to significant heat loss and fluctuations in glass furnace pressure, severely affecting the melting quality and homogeneity of the glass melt. The reasons for this can be attributed to three main aspects: First, hot-state insulation often overlooks quality control during the cold-state masonry phase, particularly the tightness of brick joints. Second, during the glass furnace heating process, the significant temperature difference between the inside and outside of the crown causes uneven thermal expansion, easily leading to deformation and increased cracking of the crown. Third, the difficulty of construction in a hot-state environment makes precise operation challenging, often resulting in suboptimal density and bonding strength of the insulation layer.

 

To address the aforementioned issues, this article proposes a combined cold-state and hot-state insulation construction technique. This method involves completing the majority of the insulation layer construction during the cold state, with only localized finishing work performed during the hot state. This significantly improves working conditions and enhances both the insulation quality and the overall performance of the glass furnace. Below, the technique is systematically elaborated upon in terms of material selection, construction processes, glass furnace heating control, and practical applications.

I. Selection and Performance Requirements of Insulation Materials
II. Cold-State Masonry and Quality Control
III. Precise Control of the Glass furnace Heating Process
IV. Hot-State Finishing Construction
V. Practical Application Cases and Effect Analysis
VI. Conclusion

I. Selection and Performance Requirements of Insulation Materials

The quality of insulation work depends first and foremost on the performance of the materials. In the combined cold-state and hot-state insulation technique, material selection is particularly critical and must balance high-temperature stability, thermal expansion compatibility, and construction workability.

 

1. Bricks for the Main Crown Structure

High-quality silica bricks should be selected, typically with an SiO₂ content of not less than 95%. These bricks must possess high refractoriness and strong erosion resistance, especially against alkali vapor (R₂O). The thermal expansion characteristics of the silica bricks must align with those of the insulation layer materials to prevent cracking or detachment of the insulation layer due to differences in expansion coefficients.

 

2. Masonry and Sealing Materials

Silica mortar used for masonry should exhibit excellent bonding strength and high-temperature volume stability. Additionally, functional materials such as silica-based sealants, silica-based plastics, and silica-based ramming mixes should be used in conjunction. These materials must not only offer good sealing and erosion resistance but also have thermal expansion coefficients that match those of silica bricks. This ensures that the insulation layer and the crown structure deform synergistically during temperature changes, preventing delamination or cracking.

 

3. Insulation Bricks and Fillers

Insulation bricks should be selected for their low thermal conductivity and good thermal stability, such as lightweight diatomite bricks or ceramic fiber products. For joint and expansion gap treatments, silica-based fillers or refractory fiber blankets can be used to absorb stresses generated by thermal expansion.

 

II. Cold-State Masonry and Quality Control

The quality of the crown masonry is the foundation for successful insulation. During the cold state, each construction step must be strictly controlled to ensure a uniform crown structure and tightly sealed brick joints.

 

1. Masonry Process Requirements

Silica bricks should be inspected individually, and bricks with defects such as inversion, chipped corners, or cracks are strictly prohibited. During masonry, a staggered joint method should be adopted, with joint widths controlled between 1–2 mm. Specialized tools should be used to ensure the joints are fully filled with mortar, leaving no voids. Throughout the masonry process, laser positioning or traditional chord line verification should be employed to ensure accurate crown curvature and symmetrical structure.

 

2. Importance of Brick Joint Treatment

Brick joints are the primary channels for the penetration of glass furnace gases and erosive media. If voids or uneven widths exist in the joints, they can easily lead to "rodent hole erosion" under high temperatures. This occurs because alkali metal oxides (R₂O) in the glass furnace gases condense into a liquid phase at the relatively cooler joint areas, eroding the bonding phase in the silica bricks and gradually causing the bricks to pulverize and fall off, ultimately forming holes. Therefore, during cold-state masonry, it is essential to achieve uniform joints, fully filled mortar, and a level surface, eliminating any potential gas pathways.

 

3. Cold-State Insulation Layer Construction

After masonry is completed, a layer of silica-based sealing material, approximately 3–5 mm thick, should be evenly applied to the cleaned crown surface to ensure full adhesion to the silica bricks. Subsequently, the insulation brick layer should be laid immediately. Specialized mortar should also be used for the joints between insulation bricks, and expansion joints should be reserved according to the design. The width of the expansion joints should be calculated based on the thermal expansion coefficient of the materials and the temperature rise range, typically 3–5 mm per meter of length.

 

III. Precise Control of the Glass furnace Heating Process

Since the insulation layer is largely completed during the cold state, the glass furnace heating process must ensure uniform heating and gradual expansion of the crown to avoid cracking of the crown or insulation layer due to excessive temperature gradients.

 

1. Development of the Glass Furnace Heating Curve

A scientific heating curve should be developed based on the characteristics of the crown bricks and insulation materials. The heating rate should be slow rather than fast, especially during critical temperature ranges below 600°C and above 1200°C. Adequate holding times should be implemented to allow the internal and external temperatures of the crown to equalize, thereby reducing thermal stress.

 

2. Temperature Monitoring and Adjustment

Thermocouples should be installed at various locations on the crown to monitor temperature distribution in real time. If localized temperatures are found to be too high or too low, timely interventions—such as adjusting burners or modifying flue dampers—should be made to ensure uniformity in the temperature field.

 

3. Tracking and Observation of Expansion Joints

During the glass furnace heating process, the condition of the expansion joints should be regularly inspected to confirm that they are opening normally, without signs of excessive compression or over-expansion. If abnormalities are detected, heating should be paused to analyze the causes and implement appropriate corrective measures.

 

IV. Hot-State Finishing Construction

After the glass furnace has been fired and reached its major operating temperature, the glass furnace enters a stable production temperature phase. At this point, the final hot-state finishing work is carried out, primarily focusing on handling expansion joints and surface sealing.

 

1. Filling of Expansion Joints

Preheated silica brick pieces or specialized refractory fiber modules are used to secure the reserved expansion joints. The filling material must possess good compressibility, resilience, and high-temperature resistance to ensure sealing is maintained even during glass furnace temperature fluctuations. After filling, the surface is leveled with silica-based sealing material to align with the surrounding insulation layer.

 

2. Construction of the Surface Protective Layer

To enhance the integrity and surface hardness of the insulation layer and facilitate daily cleaning and maintenance, a final layer of silica-based plastic, approximately 10–15 mm thick, is applied over the insulation layer. The plastic material should be compacted and smoothed to form a complete and seamless protective shell, further improving the glass furnace‘s airtightness and durability.

 

V. Practical Application Cases and Effect Analysis

This combined cold-state and hot-state insulation technology has been successfully applied in multiple glass enterprises, demonstrating excellent performance. The following is a typical engineering case:

 

A float glass production line in Indonesia, with a daily melting capacity of 300 tons, adopted the combined cold-state and hot-state insulation technology described in this paper for the construction of its crown and regenerator crown. Operational data after commissioning showed that the glass furnace’s daily fuel oil consumption stabilized at 45–46 tons, representing a daily savings of over 15 tons compared to uninsulated glass furnaces. This significant energy-saving effect was highly recognized by the owner.

 

More importantly, in 1996, this glass furnace experienced a sudden power outage, leading to a complete loss of control. glass furnace pressure surged, causing smoke to spill out and blacken multiple areas in the workshop. However, the insulation layers of the crown and regenerator crown remained intact, with no signs of reddening, burn-through, or smoke leakage, fully demonstrating the reliability and sealing performance of this insulation technology under extreme conditions. To date, this glass furnace has operated safely and stably for many years, with no structural damage to the crown and the insulation layer still in excellent condition, achieving long service life, low maintenance, and high operational efficiency.

 

VI. Conclusion

The insulation technology for the crown of glass furnaces is not only related to energy consumption and production costs but also directly impacts the safe operation of the glass furnace and the quality of glass products. While traditional hot-state insulation methods have their merits, they exhibit obvious shortcomings in terms of construction conditions, duration, and quality. The combined cold-state and hot-state insulation construction technology optimizes material selection, enhances the quality of cold-state masonry, meticulously controls the glass furnace heating process, and completes localized finishing during the hot state. This ensures a high degree of synergy between the insulation layer and the crown structure, effectively avoiding common issues such as rodent hole erosion, reddening, and burn-through.

 

This technology combines safety, economy, and durability, making it particularly suitable for promotion in high-end production lines such as float glass and electronic glass, where glass furnace lifespan and operational stability are critical. With advancements in refractory material technology and continuous optimization of construction processes, the combined cold-state and hot-state insulation technology is expected to become the mainstream direction for glass furnace insulation, providing robust support for promoting green, efficient, and sustainable development in China‘s glass industry.

 

In the future, further research can be conducted in areas such as nano-modification of insulation materials, intelligent temperature-controlled glass furnace heating systems, and online monitoring and maintenance technologies. These efforts will continue to elevate the overall standard of glass furnace insulation technology, narrow the gap with international advanced benchmarks, and contribute to the advancement of China‘s glass industry toward higher-end, more energy-efficient, and smarter development.

 

Henan SNR Refractory Co., Ltd. is dedicated to the manufacture, research and development of fused cast AZS refractory blocks and bonded refractory materials for the glass industry. Meanwhile, SNR can provide total solutions and services for glass furnace design, glass furnace construction, renovation, and upgrading. Please contact me if you have any requirements.

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