Causes of Inward Tilting of Glass Melting Furnace Breastwalls and Solutions

Theories Related to Glass Melting
1.1 Fuel Combustion Mechanism in Glass Melting Furnaces
Fuel combustion in glass melting furnaces takes place within individual port assemblies. Upon entering the furnace, fuel and combustion air mix to form a flame that heats the batch materials, melting them into molten glass; the resulting flue gases then exit the furnace through the opposing port. Throughout the combustion process, the flame temperature profile is characterized by higher temperatures in the center and lower temperatures at the ends—meaning temperatures at the inlet and outlet ports are lower than those in the central zone.
1.2 Furnace Pressure
Furnace pressure control in float glass melting furnaces is based on the pressure at the molten glass surface. Automated computer control regulates the system using the pressure at a specific sensing point—located on the breastwall of the refining section—as the standard reference for the entire furnace. Additionally, manual control is applied to the pressure in the flame zone to ensure it remains slightly above atmospheric pressure; this prevents the ingress of cold ambient air, which would lower internal temperatures and increase energy consumption. Conversely, it also prevents excessive pressure from causing hot internal gases to escape, which would accelerate erosion of the furnace structure.
1.3 Glass Melting Furnace Breastwall Structure
The breastwall of a glass melting furnace consists of breastwall bricks, hanger bricks, and supporting brackets (shelf angles), with the entire weight of the breastwall borne by these brackets. Cooling air is directed at the exterior of the furnace sidewalls to lower their temperature; as this air is blown at an upward angle, it cools the breastwall supporting brackets simultaneously with the sidewalls.

Analysis of Causes for Inward Tilting of the Melting Furnace Breastwall
The breastwall is supported by breastwall support brackets; therefore, the inward tilting is caused by the softening and deformation of these brackets. Since the brackets are connected to the furnace buckstays, the deformation manifests as a downward sagging of the front section, causing the breastwall bricks to slide inward along with this tilt. The causes of high-temperature deformation in the breastwall support brackets include:
(1) Insufficient volume of sidewall cooling air
After blowing across the sidewall, the cooling air rises to strike the surface of the breastwall support brackets, lowering their temperature and protecting them from high-temperature deformation. However, if the airflow volume is insufficient, the cooling effect is diminished and the bracket temperature rises; in severe cases, this leads to high-temperature deformation of the brackets, subsequently causing the breastwall bricks to tilt inward.
(2) Impact of the seal in the gap between the breastwall and the sidewall
The gap between the breastwall and the sidewall is typically sealed with polycrystalline mullite fiber felt. During production, if the batch pile severely scrapes against the sidewall and the sealing material, the polycrystalline mullite fiber is rapidly eroded. This allows flames to penetrate the gap; the escaping flames directly heat the breastwall support brackets, exacerbating bracket deformation and increasing the likelihood of the breastwall bricks tilting inward.

(3) Impact of the flame on the inward tilting of breastwall bricks
Fuel combustion in glass melting furnaces takes place at the port level. When the air-to-fuel ratio at the port is unbalanced—specifically when the airflow is insufficient—the flame becomes turbulent and elongated. Flames may then escape the furnace through the burner blocks and the gaps between the breastwall and the sidewall, directly heating the breastwall support brackets; this accelerates bracket deformation and, in severe cases, causes the breastwall bricks to tilt inward.
(4) Impact of furnace pressure on the inward tilting of breastwall bricks
Furnace pressure is primarily controlled based on the pressure at the breastwall in the refining section, whereas pressure in the combustion zone can only be adjusted manually by regulating the opening of the dampers at each port. The appropriateness of these settings is typically judged by visually inspecting the length and rigidity of the flames through the observation ports on the rear walls of the regenerators. During the initial phase of operation, the combustion zone pressure is sometimes set higher than normal to conserve energy. While high furnace pressure may not cause immediate signs of furnace deterioration, prolonged exposure leads to large volumes of high-temperature exhaust gas escaping through burner blocks and gaps between the breastwall and sidewall. This raises the temperature of the breastwall support brackets, exacerbates their deformation, and ultimately results in the inward tilting of the breastwall bricks.

(5) Impact of factory skylights on breastwall support brackets and breastwall bricks
Adjustable skylights are located in the center of the melting furnace building roof to exhaust smoke, dust, and waste gases. They also serve another purpose: by exhausting waste gases, they induce airflow from the furnace base up to the skylights, drawing out hot air from the gaps near the furnace ports. This lowers the ambient temperature in those gaps, thereby reducing the temperature of the breastwall support brackets and protecting them.
To save energy, some enterprises close a large number of skylights, causing the ambient temperature around the furnace to rise. With no air circulation, the high-temperature airflow in the port gaps cannot be exhausted promptly; this raises the temperature of the breastwall support brackets, creating a risk of high-temperature deformation.
(6) Impact of the design of the gap between the breastwall and the sidewall on breastwall bricks
There are two design options for the gap between the breastwall and the sidewall: a 30 mm gap and a 100 mm gap. Each has its advantages and disadvantages; however, in the later stages of the furnace's service life—specifically when sidewall brick thickness has eroded to less than 50 mm—the 100 mm gap design offers clear advantages. The reason is that a wider gap allows for the installation of "knife-handle" bricks (L-shaped bricks) above the sidewall when the sidewall bricks have worn down to approximately 50 mm. These bricks shield the sidewall, mitigating erosion caused by the batch pile. Simultaneously, they provide a better seal for the gap between the sidewall and the breastwall, reducing heat loss, lowering the ambient temperature in the port area, and decreasing the operating temperature of the breastwall support brackets, thereby extending their service life.

Routine Inspection and Maintenance
(1) Routine inspection for inward tilting of breastwall bricks: Inward tilting of breastwall bricks does not happen overnight; therefore, it is essential to monitor and inspect changes in the bricks on a regular basis.
Inspection method: Periodically measure and record the distance between the breastwall bricks and the furnace buckstays at various locations. Compare these measurements over time, specifically tracking changes in the distance at two points—the lower and middle sections—of each breastwall brick.
(2) Maintenance methods for inward-tilting breastwall bricks: Once inward tilting is detected, prompt action is required. On one hand, investigate and rectify the underlying cause. On the other, insert a water-cooled bar (water bar) through the furnace crown to brace against the breastwall bricks, thereby preventing further deformation or displacement.
Installation method: Create an opening in the furnace crown and insert the water bar. Use jacking screws fixed to the furnace buckstays to adjust the distance between the bar and the buckstays. Applying the principle of leverage—using the crown as a fulcrum—press the water bar firmly against the breastwall bricks to halt any further inward movement.
Precautions: During operation, monitor the water temperature of the bar during every shift and replace the bar immediately if any leakage is detected.
Conclusion
The inward tilting of breastwall bricks is a complex issue involving process management. Furnaces exhibiting this phenomenon typically present a combination of the causes listed above; however, the primary cause is usually insufficient cooling airflow to the sidewalls, with other factors playing a secondary role. Therefore, close attention must be paid to the sidewall cooling airflow volume during production.