Lightweight Clay Insulating Brick

Clay insulating refractory brick is a new type of thermal insulation material, which has a small bulk density (bulk density), extremely low thermal conductivity, and good thermal insulation performance. It is suitable for various boilers, kiln linings, pipeline insulation and other thermal equipment with hot surface temperatures below 1000℃.

 

The characteristics of clay insulating refractory bricks are high porosity, generally 40%-85%; low volume density below 1.5g/cm³; low thermal conductivity, generally below 1.0W (m.K). As an insulating material for industrial kilns, it can reduce the heat loss of the kiln, save energy, and reduce the weight of thermal equipment.

Clay insulated refractory bricks Insulating refractory products with Al2O3 content of 30% to 48% made of refractory clay as the main raw material. Refractory clay, floating beads, refractory clay clinker are used as raw materials, and binders and sawdust are added. After batching, mixing, molding, drying and firing, products with a volume density of 0.5 to 1.5 g/cm3 can be obtained, and the production volume accounts for more than half of the total production of insulating refractory bricks.

The commonly used production process is the burnout addition method with floating beads. The process flow is shown in the figure. The foam process can also be used. The burnout addition method is used to produce clay insulating refractory bricks with a larger volume density; the foam process gradually forms a series of products with a volume density of 0.4 to 1.5 g/cm3. The raw materials, binders and sawdust (1) The raw materials are refractory clay, clay clinker and floating beads. The chemical composition of floating beads fluctuates greatly. In order to obtain products that meet the quality standards, it is necessary to select clay-based insulating refractory bricks with an Al2O3 content greater than 30%, a Fe2O3 content less than 3%, and a refractoriness greater than 1610°C. Most of the floating beads are closed hollow balls with thin walls and high strength. Their volume density is 0.38-0.44 g/cm3, and their color is grayish white. The particle size is 20-250/μm, of which 50-150/μm is more common, and the whole bead rate is greater than 95%. Inclusions can be removed by screening or rinsing. If rinsed, they should be dried or spun. (2) Both clinker fines and floating beads are lean aggregates. The floating beads are round or nearly round, with a smooth surface, fine particles, and a large specific surface area, which requires the binder to have a strong binding property. The main binders are: refractory clay, sulfite pulp waste liquid, aluminum sulfate, water glass, phosphoric acid and phosphates, dextrin, resin, etc. Refractory clay has high binding, dispersibility, plasticity, refractoriness and sintering properties. It is also cheap and abundant in resources. Therefore, refractory clay is the main binder. According to the product type, bulk density and technical requirements, add an appropriate amount of organic or inorganic binder. (3) Sawdust should be screened and the particle size should be less than 1-2 mm.

Ingredients The amount of floating beads added varies with the volume density of the product. Generally, it fluctuates between 10% and 70%. The smaller the volume density of the product, the more it is added. Add some clay clinker powder to the ingredients to reduce the volume shrinkage caused by the deformation of the floating beads. In order to reduce the amount of floating beads, improve the strength of semi-finished products and reduce the shrinkage of burning, add an appropriate amount of sawdust.

Mixing makes the material water mix evenly and improves the molding performance of the mud. Commonly used mixing equipment includes sand mixers and forced countercurrent mixers. There are two operating methods: one is to add floating beads, sawdust, binder, water, clay and clinker powder in order. Mix for 5 to 6 rain to obtain a mud with floating beads or sawdust as the core, binder and clay as the outer layer, and dry powder as the outermost layer. The other is to add floating beads, clinker fine powder, binding clay and sawdust into the machine, dry mix for 2 to 3 minutes, add water and binder, and wet mix for 3 to 4 minutes. The mixed clay can be molded after being trapped for 12 to 24 hours. The moisture content of the clay depends on factors such as the product volume density, ingredient ratio, and molding method. Generally, the moisture content of the clay is 20% to 30%.

Molding Manual and machine pressing are mostly used. Machine pressing should use a 150-300kN brick press. The strength of the molded bricks is very low and should be handled with care; semi-finished products with complex shapes, large single weights or low volume density can be held with pallets or plywood to prevent the bricks from deformation and damage.

Drying The molded bricks can be dried in a tunnel dryer or in a fire pit. Due to the high water content of the bricks, the inlet temperature of the tunnel dryer shall not exceed 50uC, and the outlet temperature shall not exceed 150℃. The residual moisture of the bricks after drying should be controlled below 2%.

Loading and firing Use side loading, requiring flatness, stability and straightness, sprinkle rice husks layer by layer, and leave hand gaps between bricks. The loading height is generally 1.5-1.8m. Products with a bulk density less than 0.6g/cm3 should not exceed 1.2m and should be loaded in the low-temperature part of the kiln. When firing products in a downdraft kiln or tunnel kiln, the kiln temperature should be uniform. The maximum firing temperature varies depending on the quality of the floating beads and clay and the bulk density of the product. Usually, the products with a bulk density of 0.4-0.6g/cm3 have a fire-stop temperature of 1220-1250℃; the products with a bulk density of 0.8-1.0g/cm3 have a fire-stop temperature of 1250-1280℃, and the insulation time is 6-8h. The cooling kiln speed is similar to that of clay bricks. In actual production, products with different bulk densities are often fired in the same kiln. This means that different brands of products are loaded in different parts according to the temperature distribution in the kiln to improve the firing quality.

Due to the development of metallurgy, glass, coking, ceramics and other industries that consume a lot of fuel, clay insulating refractory bricks used at higher temperatures have appeared. Clay insulating refractory bricks have a wide range of applications. They are mostly used in the insulation layer of thermal equipment and industrial kilns. They can be used in areas without strong erosion and scouring of high-temperature molten materials. Some surfaces that are in direct contact with the flame are coated with a refractory coating to reduce erosion by slag and scouring by furnace gas and dust, reducing damage. The working temperature of the product does not exceed the test temperature of the reburning line change.

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