Many factories do not opt for the manufacturer’s integrated construction services when purchasing refractory castables. Instead, they typically handle the installation themselves or hire separate construction crews after purchasing the castables. This often leads to issues upon receiving the materials: when requesting application and construction methods from the manufacturer, water-mixed materials frequently become too thin or too thick during mixing, resulting in failed casting. Phosphate-based or adhesive-based mixtures often suffer from improper ratio control, causing casting failures, cracks, and other defects.
Today, we will focus on detailing the water addition, mixing, pouring, curing, and baking processes for water-mixed and phosphate (adhesive)-mixed refractory castables.
Water-mixed castable construction
1. Anchors and Formwork
Anchors must be fabricated from heat-resistant steel (1Cr18Ni9Ti). All anchors delivered to the site must pass inspection before use. For cast thicknesses below 10cm, use V-shaped anchors made of heat-resistant steel with a diameter of 10mm, with anchor welding intervals not exceeding 10cm. For poured thicknesses exceeding 10cm, use Y-shaped anchors made of heat-resistant steel with a diameter of 12mm. The welding spacing of anchors shall not exceed 20cm. For poured thicknesses exceeding 25cm, use specially manufactured double-Y anchors made of heat-resistant steel with a diameter of 16mm. The welding spacing of anchors shall not exceed 25cm. Anchors must be positioned no more than 5 cm from the edge wall. Double-sided welding is required for anchors, ensuring no missed or incomplete welds for secure attachment. Welds should be staggered. Coat anchor surfaces with a 1–2 mm layer of asphalt paint or wrap with adhesive tape to counteract thermal expansion effects.
Formwork templates shall be constructed from high-quality timber such as pine or cypress, or steel forms. Template dimensions must comply with design drawings or construction requirements. Templates must withstand the weight of the castable material and the vibration from the vibrator. Measures shall be taken to seal gaps in the formwork to prevent mortar leakage. The distance between the formwork and anchorage components shall be 1-2 cm.
2. Measures to Prevent Water Loss
Surfaces of formwork, insulation materials, refractory bricks, and other components in contact with the castable must be coated with asphalt paint or machine oil to prevent them from absorbing moisture from the castable body. Alternatively, a layer of oil paper can be applied to the formwork. This not only prevents moisture absorption but also facilitates easier form removal.
3. Mixing and Water Addition
(1) Before construction, carefully inspect the quality of the castable material to confirm it is within the warranty period and free from clumping or hardening. Proceed only after verification. Specialized castables must be used for high-temperature areas such as kiln mouths and pulverized coal injection pipes; other areas require manufacturer-specified castables.
(2) Before switching to a different type of refractory castable, thoroughly clean all debris and residue from the mixer before proceeding. Do not mix in foreign materials such as lime, sand particles, or Portland cement. During construction, do not mix with other types of castables or products. When the mixer is temporarily idle, clean its interior immediately.
(3) Each bag of castable contains a setting accelerator powder. Pre-mix for 1-2 minutes until uniform before adding water for mixing. Note: Use entire bags to ensure consistency.
(4) Strictly control water addition. Mix with 5%-8% water for application. Water content varies by castable type, as it significantly impacts refractory quality. Strictly adhere to specified water ratios during construction. Use potable-grade water for mixing.
(5) Mixing must be performed in a forced-action mixer. Dry mix for 2 minutes, then add water and mix for 3-6 minutes before pouring. The weight of each batch of mixed refractory castable should be controlled between 200–300 kg.
(6) During summer construction, avoid prolonged exposure of materials and water to direct sunlight. The temperature of construction water and materials should generally remain below 30°C.
During winter construction, store materials and water in a warm indoor environment. Use warm water for mixing and casting, and appropriately extend the mold-curing time. Additionally, ensure the ambient temperature during pouring and curing does not fall below 5°C. The unauthorized use of setting accelerators is strictly prohibited.
(7) Once water is added to the castable and mixed, it must be used within 30 minutes (counting from the time water is added). Castable that remains unused after the specified time or has already hardened must not be re-mixed with water or reused.
4. Pouring
(1) Thoroughly clean the interior of the equipment prior to pouring.
(2) Expansion joints must be installed strictly according to design specifications. Where no design requirements exist,
1.5-2.0 m²; expansion joints may be formed using 3 mm plywood or cardboard. The refractory castable within each section divided by expansion joints must be poured continuously in a single operation. Pouring must not be interrupted until the entire pouring area is completed. Pouring and vibration must be completed before any part of the castable within the section begins to set.
(3) Immediately after pouring the material into the formwork, compact it using a vibrator. Ensure thorough compaction without overdoing it, as excessive vibration may cause segregation and compromise quality. Generally, once surface bleeding occurs, slowly withdraw the vibrator while continuing vibration.
(4) Avoid sudden power interruptions during vibration. Do not reinsert the vibrator into already compacted material.
(5) The poured surface should be level, but do not use a trowel to smooth it. Sprinkling cement powder on the surface for smoothing is strictly prohibited.
(6) For dead corners created by obstacles where formwork installation is impractical, manually compact the material in layers. Alternatively, slightly increase the water-to-refractory ratio, ensuring no uncompacted dead corners remain.
5. Curing
(1) After pouring is complete, the cast structure generally requires curing in the mold for 24 hours before demolding. In areas with lower temperatures or where high-strength castables are used, the curing and demolding times should be appropriately extended.
(2) Inspect the casting quality after demolding. Promptly decide on repairs or rework if honeycombing, pitting, or voids are detected. Non-structurally required irregularities should also be promptly smoothed.
(3) Cover the cast surface with plastic film after demolding to prevent moisture evaporation. Regularly spray water onto the cast surface using a sprayer to prevent surface drying.
6. Site Cleanup
After construction is completed, the site should be promptly cleaned. Residual debris and fragments inside the equipment must be thoroughly swept away.
7. Baking Regimen
After undergoing the above curing process, refractory castables must also undergo a specific baking regimen prior to use. For newly constructed kilns, the pre-decomposition system, kiln head system, and grate cooler system shall each be baked for one day using firewood. Subsequently, the following temperature ramp-up baking regimen shall be followed (for reference):
For kilns undergoing maintenance—such as replacement of kiln mouth castables, kiln tail castables, or grate cooler castables—follow the aforementioned heating schedule. The cooler is dried by adjusting the airflow of the kiln head exhaust fan during kiln heating. The kiln tail is controlled by raising the flap valves and regulating the kiln tail exhaust airflow. However, the heating rate must be strictly controlled to prevent excessive temperature rise that could cause the castable refractory to crack.
Phosphate (Bonding Agent) Castable Construction
1. Anchors and Formwork
The requirements and methods for anchors and formwork are the same as above (for water-mixed castable materials). They will not be repeated here.
2. Mixing and Water Addition
(1) Before construction, carefully inspect the quality of the castable material to confirm it is within the warranty period and free of clumping or hardening. Proceed only after verification. Specialized castables must be used for high-temperature areas such as kiln mouths and pulverized coal injection pipes; other areas require manufacturer-specified castables.
(2) Before switching to a different type of castable, thoroughly clean all debris and residue from the mixer. Rinse the mixer interior with adhesive and allow it to soak before proceeding. Do not mix different castable types or products during application.
(3) Each bag of castable contains a small pouch of powder. Pre-mix the main powder with the small powder for 1-2 minutes until uniform. Then add approximately 10% binder and stir thoroughly. Note: Use entire bags to ensure consistency.
(4) Strictly control binder dosage. The adhesive ratio varies by castable type. The amount of adhesive added significantly impacts the quality of the refractory castable and must be strictly controlled according to specifications. For phosphate-based castables, the typical adhesive ratio is approximately 10-12%.
(5) Mixing must be performed in a forced-action mixer. Dry mix for 2 minutes, then add adhesive and mix for 3-6 minutes before pouring. The weight of refractory castable mixed per batch should be controlled at approximately 200–300 kilograms.
(6) Castable material mixed with binder must be used within 30 minutes (counting from the time binder is added). Castable material not used within the specified time or that has already hardened cannot be remixed with binder or reused.
3. Casting
(1) Thoroughly clean the interior of the equipment prior to casting. Surfaces of refractory bricks or existing castable material in contact with the new castable must be pre-cleaned with adhesive to ensure stronger bonding at high temperatures.
(2) Expansion joints must be installed strictly according to design specifications. Where no design exists, joints should be spaced at 1.5-2.0m². Use 3mm plywood or cardboard to form the expansion joints. Refractory castables within each expansion joint compartment must be poured continuously in a single operation. Do not interrupt pouring before the entire area is completed. Pouring and vibrating must be completed before any portion of the castable within an expansion joint compartment begins to set.
(3) Immediately vibrate the castable material with a vibrator after pouring it into the formwork. Ensure thorough compaction without over-vibration, as excessive vibration may cause segregation and compromise quality. Generally, once surface bleeding occurs, slowly withdraw the vibrator while continuing vibration.
(4) Avoid sudden power interruptions during vibration. Never reinsert the vibrator into already compacted material.
(5) For hard-to-reach corners caused by obstructions where formwork installation is impractical, manually tamp the material in layers. Alternatively, slightly increase the binder content in the castable material. Ensure no uncompacted dead corners remain.
4. Curing
(1) After pouring is complete, the cast structure generally requires curing in the mold for 24 hours before demolding. In areas with lower temperatures or where high-strength castables are used, the curing and demolding times should be appropriately extended.
(2) Inspect the casting quality after demolding. Promptly decide on repairs or rework if honeycombing, pitting, or voids are detected. Non-structurally required protrusions or depressions should also be promptly smoothed.
(3) Avoid water exposure during the static curing period of the castable material and prevent impact from heavy objects.
5. Site Cleanup
Promptly clean the site after construction completion. Thoroughly sweep away residual debris and fragments from the equipment.