Causes and Prevention of Refractory Spray Coating Detachment in Glass Furnaces

Glass furnaces operate continuously at high temperatures. The furnace lining is exposed not only to constant thermal loads but also to temperature fluctuations, flame impact, hot gases, and other harsh operating conditions. When refractory spray coatings are used for furnace lining repair or protection, local detachment, cracking, or powdering after installation can affect the integrity of the lining and increase the frequency of maintenance.

The detachment of refractory spray coatings is usually not caused by the material alone. Inadequate substrate preparation, dust or loose particles on the surface, improper coating thickness, incorrect water addition, and insufficient curing or improper heating procedures can all affect the bonding between the spray coating and the existing furnace lining.

1. Inadequate Substrate Preparation

Before applying refractory spray material, the surface of the existing furnace lining should be properly cleaned.

Dust, loose particles, powdery refractory layers, or oil contamination can reduce the bonding strength between the spray coating and the existing lining.

Severely damaged areas should be thoroughly removed and cleaned before spraying. Applying new material directly onto an unstable or loose refractory surface may result in premature detachment.

2. Improper Material Selection

Different areas of a glass furnace are exposed to different temperatures, thermal shocks, flame conditions, and corrosive environments.

Therefore, the refractory spray material should be selected according to the specific operating conditions.

If the refractory temperature, thermal shock resistance, corrosion resistance, or bonding performance of the material does not meet the requirements of the application, cracking, powdering, and detachment may occur during long-term operation.

3. Improper Spray Coating Thickness

A thicker refractory spray coating does not necessarily provide better performance.

If the coating is applied too thickly in a single operation, moisture inside the material may be difficult to remove during drying and heating. This can generate internal stress and increase the risk of cracking or spalling.

On the other hand, a coating that is too thin may not provide sufficient protection or repair the damaged area effectively.

Therefore, the coating thickness should be controlled according to the material specifications and construction requirements. For thicker repairs, multi-layer application may be more appropriate.

4. Improper Water Addition and Construction Control

Some refractory spray materials require water addition or specific mixing procedures before application.

Excessive water can reduce the strength and bonding performance of the material, while insufficient water may affect workability and material distribution.

Therefore, water addition, mixing time, spraying equipment, and other construction parameters should be controlled according to the technical requirements of the refractory material.

5. Improper Curing and Heating

After spraying, refractory materials may still contain a certain amount of moisture.

If the repaired area is heated too quickly without sufficient curing and drying, the rapid evaporation of water can generate internal vapor pressure. This may result in cracking, blistering, or local detachment of the spray coating.

Therefore, an appropriate curing period and controlled heating schedule should be applied according to the material type and actual furnace conditions.

6. Thermal Shock and Mechanical Erosion During Operation

During long-term furnace operation, refractory spray coatings are exposed to repeated thermal cycles.

Certain areas may also experience continuous flame impact, hot gas flow, and dust erosion.

If the bonding strength of the spray coating is insufficient, repeated thermal cycling may gradually enlarge existing microcracks and eventually cause local spalling or detachment.

How to Prevent Refractory Spray Coating Detachment

To improve the service life of refractory spray coatings in glass furnaces, the following measures should be considered:

• Thoroughly remove dust and loose materials from the substrate before spraying.

• Select refractory spray materials according to the specific furnace area and operating conditions.

• Strictly control water addition and mixing parameters.

• Maintain an appropriate spray thickness.

• Use multi-layer application for thicker repair areas when required.

• Allow sufficient curing and drying after installation.

• Follow a controlled heating schedule during furnace start-up.

• Regularly inspect the coating for cracks, powdering, blistering, and local detachment.

Conclusion

The detachment of refractory spray coatings in glass furnaces is often caused by a combination of material selection, substrate condition, construction quality, curing, heating procedures, and operating conditions.

Therefore, simply changing the refractory material may not completely solve the problem.

For glass furnace maintenance and repair, the damaged area, existing lining structure, operating temperature, thermal conditions, and service environment should be evaluated together. Selecting the appropriate refractory spray material and applying the correct construction procedure can help improve bonding strength, extend lining service life, and reduce furnace maintenance frequency.