Refractory castables include acidic, alkaline, and neutral castables; Divided by density into heavy castables and lightweight castables; According to the material, it can be divided into aluminum silicate, magnesium, magnesium chromium, corundum casting, silicon, etc. So how to choose refractory castables in different situations?

Firstly, we need to consider the kiln environment, usage location, usage temperature, erosion properties, construction precautions, etc., in order to select suitable refractory castables based on these basic requirements.

1、 Kiln environment

Firstly, we need to look at the overall kiln environment of the kiln we are constructing, including the medium in the kiln, the characteristics of the medium, the temperature at which the kiln operates, and a characteristic of the kiln during operation. Based on these environments, we can correctly choose refractory castables.

2、 Application location

If it is a working layer, high temperature resistant heavy refractory castables should be selected. If the erosion property is acidic, acid resistant castables should be selected. If the erosion is alkaline, alkaline resistant castables should be selected. If the part in contact with slag needs to use castables with strong resistance to slag erosion; High strength and wear-resistant castables should be selected for areas with severe material impact; If the temperature changes frequently, good thermal shock resistant castables should be selected.

The pouring material for the insulation layer should be lightweight refractory pouring material, mainly considering the load-bearing structure, reducing the temperature of the furnace shell, and minimizing heat loss. Then, insulation pouring materials with different bulk densities should be selected. Generally, insulation pouring materials with a bulk density of 1.2 should be used. If the user has weight requirements, insulation pouring materials with a bulk density of 0.6-1.0 should be selected.

3、 Usage temperature

The grade of castable used varies depending on the temperature, and the castable used for different temperatures is also different. Generally, clay castable is used below 1200 ℃, high alumina castable is used between 1300 ℃ and 1400 ℃, and corundum castable is used if it exceeds 1450 ℃;

4、 Construction thickness

The thickness of refractory castable construction varies. If it is less than 50mm thick, it should be coated or sprayed with paint. If it is used for repair or furnace top, plastic should be selected. If the thickness of the casting material is greater than 100mm, large particle aggregates are needed to improve the wear resistance of the casting material. Generally, the best casting thickness for the casting material is 200mm.

5、 Precautions for the construction of refractory castables

(1) Template: The template for pouring material construction can be made of steel plate or hardwood board (plywood). The template should have sufficient strength, good rigidity, no deformation, no displacement, and no leakage. The rigid template should be coated with release agent, and the wooden template should be coated with waterproof agent. The reused template should be cleaned first and then painted before use. Inspection holes and cleaning holes should be made of regular wooden molds. The metal tie bars supporting the wooden magic board should be more than 4 per square meter (to prevent strong heat transfer), and the tie bars should be welded based on the anchor (that is, the tie bars of the template should be welded to the anchor).

(2) Water cement ratio: The amount of water added when mixing the pouring material should be strictly controlled according to the instructions, and should not exceed the limit. On the premise of ensuring construction performance, the amount of water added should be less and not more.

(3) Mixing: The mixing time of the casting material should not be less than 5 minutes (according to the instructions), and a forced mixer should be used during operation. When stirring, it is advisable to first dry mix and stir, then add 80% of the required amount of water and stir. Depending on the dryness or wetness, slowly add the remaining water and continue stirring until the appropriate working level is achieved. When mixing different castables, the mixer should be cleaned thoroughly.

(4) The use of castable: The castable must be used in whole barrels and bags. The mixed castable must generally be used up within 30 minutes. In a high-temperature and dry working environment, this time should be appropriately shortened. The castable that has already set or even clumped should not be poured into the mold frame, nor should it be mixed with water before use.

(5) Vibration: The poured material into the mold frame should be immediately compacted layer by layer with a vibrating rod, and the height of each layer should not exceed 300mm. The vibration spacing should be around 250mm. During vibration, it is advisable to avoid touching the anchor components, do not damage the insulation layer, and do not vibrate or revive in the same position for a long time. When the surface of the casting material returns slurry, the vibrating rod should be slowly withdrawn to avoid segregation and voids in the casting material layer.

(6) Large scale construction: In the process of large-scale construction, it is necessary to divide the construction into blocks, and the area of each pouring area should be around 1.5m2. Expansion joints should be left according to the design requirements, without omission. Expansion joints should be left in the middle of the anchor spacing. Expansion joints can use 6-8mm thick wooden boards, and the distance between the cross-section of the wooden board and the formwork should be 40-60mm. The expansion wooden boards should be effectively fixed to prevent displacement during the pouring process.

(7) Regarding the welding of anchor components: Draw grid lines on the working surface (according to the requirements of the drawing), weld the anchor components at the junction of the grid lines, and ensure full welding at the root of the anchor components. After the completion of the pouring material construction, the poured body shall not be subjected to pressure or vibration again before solidification.

The above is how to choose refractory castables correctly. Only by choosing refractory castables correctly can our kiln work normally and stably. At the same time, strict construction can ensure that the kiln has a longer service life.