Refectory materials are essential for industrial furnaces, kilns and other high-temperature processes where temperatures can exceed 1000 °C. Refractory castables are a form of unshaped refractory that is installed as a “cast” lining using a wet or dry mix. Among various types, gunning refractory castables provide an economical solution for lining industrial furnaces and kilns.

What are Gunning Refractory Castables?

Gunning refractory castable comprises a mixture of refractory aggregates, bond materials and additives that are applied in a plastic state using air pressure. The castable mix is prepared with sufficient water to make it pumpable and sprayable using a gunning machine. Once sprayed onto the surface and exposed to heat, the water evaporates leaving behind a dense, high-strength refractory lining.

Key Components Of Gunning Castables

The main components of gunning refractory castables include:

• Refractory aggregates: Mainly comprised of alumina, silica, chromite and zirconia particles that provide heat and corrosion resistance.
• Bonding agents: Typically calcium aluminate cement or colloidal silica solutions that bond the castable together upon drying and firing.
• Additives: Include fillers, fibers and other additives to control plasticity, drying shrinkage andfinal properties.

Based on the aggregate type, gunning castable can be alumina-based, silica-based, zirconia-based or chromia-based. The optimum composition and properties of the castable mix are designed based on the specific furnace requirements.

Widely Range Of Applications From Gunning Castables

Thanks to their sprayability, versatility and economical price point, gunning refractory castables are widely used in industrial furnaces and kilns to provide:

• Lining for main furnace chambers

Gunning castable is ideal for lining large furnace chambers where high abrasion and thermal shock resistance are required. The spray application method allows rapid and economical lining of irregular chamber walls.

• Lining for burner zones

Gunning castables with high refractory content and strength are used to withstand harsh conditions in burner zones of gas or oil fired furnaces.

• Lining for flue gas ducts

Gunningcastable having good thermal shock resistance and low pickup of dust and ash are used for lining flue gas ducts and stacks in waste heat recovery boilers.

• Lining for transition and inspection openings

Gunning castables ensure a smooth transition and seal between different furnace components like transition ducts and inspection holes.

• Repair mortar

Gunning castables can be used as a repair mortar for patching small voids and cracks that develop in existing refractory linings over time.

Properties And Advantages

The key properties and advantages of gunning refractory castables include:

• High refractoriness: Gunning castables can withstand temperatures up to 1700 °C, depending on aggregate type.
• Good thermal shock resistance: Optimized composition and porosity result in high thermal shock resistance.
• Ease of application: The pumpable and sprayable nature of gunning mix allows for fast and convenient application in any furnace geometry.
• Good adherence: Gunning castables adhere well to the substrate surface upon drying, producing a monolithic lining.
• Versatility: A wide range of compositions are available to suit varying furnace requirements.
• Cost effectiveness: Compared to shaped refractories, gunning castables offer a lower total installed cost due to fast application and less wastage.