Problems that need attention in the construction of refractory castables

Problems that need attention in the construction of refractory castables

Refractory castable construction is a complex and critical process that requires attention to multiple aspects to ensure construction quality and the effectiveness of refractory castables. The following are some of the main issues that need to be paid attention to in refractory castable construction:

Preparation before construction

Equipment and site cleaning: Check and ensure that all construction equipment and tools are in good condition, and clean the construction site to ensure that there are no debris interfering with the construction.

Anchor inspection and welding: Check the material, type, size, layout and welding quality of the anchor to ensure that they meet the design requirements. Perform expansion compensation treatment on metal anchors and take wet water prevention measures to prevent adverse reactions with surrounding refractory bricks and other castables.

Water quality requirements: Construction water should meet drinking water standards to ensure the quality and performance of the castable.

Construction requirements

Formwork:

Use steel plate or hardwood board to make formwork. Steel plate needs to be coated with release agent, and wood board needs to be painted with waterproof paint to ensure no leakage.

The formwork should have sufficient strength and rigidity to prevent displacement during construction.

Mixing:

Use a forced mixer to mix to ensure uniform mixing.

Proportioning should be carried out strictly in accordance with the design or manufacturer’s technical instructions, and various materials should be accurately measured.

Control the amount of water added, which is usually between 7.0%-7.5%, and wet mix for 35 minutes after adding water.

The mixed castable should be used up within the specified time to avoid the use of primary setting material.

Vibration:

The castable poured into the mold should be immediately vibrated in layers with a vibrating rod to ensure no leakage and long-term vibration or heavy vibration in the same position.

The formwork and support should be observed during the vibration process, and measures should be taken in time if deformation is found.

Curation and drying:

The mold can be removed only after the surface of the castable is dry and reaches 70% strength. The demolding time is usually not less than 24 hours.

The curing time should be no less than 24 hours, and the curing temperature should be between 5 and 30°C.

According to different grades and thickness of castable lining and on-site climatic conditions, sufficient baking time should be provided to ensure that moisture is removed without bursting. The cumulative baking time is usually no less than 72 hours.

Precautions

Construction environment:

The construction temperature should be 10℃~30℃. When the temperature is too low, conditions should be created to meet the construction requirements.

When the relative humidity of the air exceeds 85%, it is not suitable for construction.

When the surface temperature of the steel plate is 3℃ lower than the atmospheric dew point or higher than 60℃, it is not suitable for construction.

It is not suitable for construction on windy and sandy days or rainy and foggy days.

Expansion joints:

The castable should be provided with expansion joints according to the design. When there is no design regulation, a well-shaped expansion joint can be provided at a spacing of 800~1200mm.

The width of the expansion joint is usually 23mm, and it can also be cut into seams after forming. The seam depth is 20%30% of the thickness.

Furnace bottom lining construction:

The furnace bottom lining should be carried out after all the work in the furnace is completed and the scaffolding is completely removed.

The lining should be dense, and it should be checked by tapping lightly every 200mm with a 0.5kg hand hammer. The sound should be sonorous and crisp, and no serious “hoarseness” or hollow drum sound is allowed.

Defect repair:

After the furnace is baked, if the castable has cracks with a width greater than 5mm or through-net cracks, it must be repaired.

Before repairing, all defects should be chiseled out to expose the solid surface or steel plate surface, and the chiseled area should form a pit that is larger inside and smaller outside.

When repairing, the lining material of the same ratio should be used to carefully tamp and smooth it.

Other precautions:

Refractory castables should be well sealed to retain moisture. Before construction, they should be constructed according to the current industry standard performance.

When ramming the furnace wall and furnace roof, the ramming direction should be parallel to the heating surface; when ramming the furnace bottom, the ramming direction can be perpendicular to the heating surface.

The expansion joints of the castable lining should be reserved according to the design requirements. The expansion joints of the inner wall of the roasting furnace and the longitudinal expansion joints on the top should be rammed evenly on both sides to make the expansion joints in a straight line.

The trimming of the castable lining should be carried out in time after demoulding. Before trimming, use a wooden hammer to gently knock the castable around the anchor end face to make it bite tightly.

In summary, the issues that need to be paid attention to in the construction of refractory castables involve many aspects, including pre-construction preparation, construction requirements, precautions, etc. Only by strictly following the construction specifications and design requirements can the construction quality and the use effect of refractory castables be ensured.