There are many types of refractory castables (also known as refractory concrete) depending on their aggregate materials, binders and admixtures. The construction methods of several commonly used refractory castables - Portland cement refractory castable, aluminate refractory castable, water glass, and phosphoric acid (or phosphate) refractory castable are listed as follows.

 

Preparation work before construction of refractory castable

(1) Preparation of raw materials: The finished refractory castable should be subject to necessary technical inspection before construction, and it can be put into use after confirming that it meets the design requirements.

(2) Determination of mix ratio: The finished refractory castable is usually constructed according to the mix ratio and requirements specified in the construction instructions provided by the manufacturer.

(3) Configuration of formwork: The formwork used in the construction of refractory castables should be selected according to the characteristics of the project structure and the size of the project. The types of templates are fixed type, hanging type, and tool type. The formwork material is usually steel formwork and wooden formwork.

When the formwork is supported, the following requirements shall be met:

1) Accurate and in line with design regulations.

2) The support is firm, the combined installation of the formwork is convenient for construction, the lap joints are tight, and there is no leakage of slurry.

3) For refractory castables with strong corrosiveness or adhesion, an isolation layer should be provided in the formwork.

4) The wooden slats used for the reserved expansion joints should be fixed firmly to avoid displacement when subjected to vibration.

5) The formwork should be painted with a protective oil before construction to prevent sticking.

(4) The production and installation of anchors: The anchors are generally divided into two types: metal and non-metal. One end of the anchor is welded to the iron shell of the furnace or the supporting steel frame and is embedded in the refractory castable to support. connection effect.

The setting of refractory castable anchors should be in accordance with the design regulations. Usually, metal anchors are used in low-temperature parts, and ceramic anchor bricks are used in high-temperature parts.

Metal anchors take different forms according to different parts of the furnace structure. The metal anchors for furnace walls and vaults are V-shaped, L-shaped, and Y-shaped.

Generally, the front end of the metal anchor is buried to 2/3 of the thickness of the furnace wall; the anchor brick is generally exposed on the heating surface.

The installation spacing of metal anchors depends on the thickness and height of the furnace wall. Generally, the horizontal spacing is about 550~600mm, and the vertical spacing is about 450~500mm.

When using anchor bricks, the spacing of the sidewall parts is mostly 300-500mm, and the furnace top part is about 200-300mm.

Construction conditions of refractory castables

The main construction conditions are

 

(1) According to the construction amount required by the project, select and install one or several forced mixers. The inside of the machine should be kept clean, and the machinery installed in place should be used only after passing the test run.

(2) The construction site should be cleaned in advance, and if necessary, washed with water or blown with compressed air.

(3) For castable linings with anchoring devices, the position and welding of metal anchors or metal anchoring blocks of anchor bricks should be checked.

(4) Check the size, firmness, and joint condition of the template installation.

Stirring of refractory castables

When stirring, follow the manufacturer's instruction manual for materials. 

Pouring and Vibration

The pouring of refractory castables should be vibrated in layers by vibrating equipment. The vibrating machine should adopt a vibrating rod or plate vibrator. Manual vibrating can be used only in special cases.

When using an inserted vibrating rod, the thickness of the casting layer should not exceed 1.25 times the length of the action part of the vibrating rod, and when using a plate vibrator, the thickness should not exceed 200mm.

The castable should generally be poured continuously, and the next layer of castable should be poured before the initial setting of the previous layer of castable. If the construction gap exceeds its initial setting period, it should be carried out according to the requirements of construction joints.

 

Maintenance precautions

The maintenance precautions of silicate-based refractory castables are:

1) Silicate refractory casting is suitable for watering and curing so that the cement in the product forms dehydration and hardening during the hydration process. The maintenance of high alumina cement castable is particularly important, because the cement hydration in the high alumina cement castable product increases rapidly, and produces a large exothermic reaction, which is easy to causes cracks on the surface.

2) Wet curing should be covered and watered after the hardening of the castable begins.

3) The heating rate of Portland cement refractory castable for steam curing should be 10~15℃/h, the maximum should not exceed 20℃/h; the cooling rate should not exceed 40℃/h,

The maintenance precautions for water glass castables are:

The strong growth of water glass castables is produced during the dehydration of silica gel. Therefore, it should be kept in a dry environment for maintenance, and should not be watered for maintenance.

 

The maintenance precautions of phosphoric acid refractory castables are:

1) Phosphoric acid refractory castables should not be cured with water or steam but should be cured in a dry environment.

2) If the ambient temperature is low, low-temperature drying is required after pouring.

U) Precautions for demolding. The precautions for demolding are:

1) The non-load-bearing formwork should be removed when the strength of the castable can ensure that the surface and edges and corners are not damaged due to demoulding.

2) The load-bearing formwork should be removed when the castable reaches 70% of its strength.