Lightweight Clay Insulation Brick

Clay heat-insulating refractory bricks refer to lightweight refractory products containing 30% to 46% Al2O3. Clay heat-insulating refractory bricks use clay clinker or lightweight clinker and plastic clay as the main raw materials. They use refractory clay, floating beads, refractory clay clinker, and add binders and sawdust. After batching, mixing, molding, drying and firing, they can produce products with a volume density of 0.3 to 1.5 g/cm'. Usually, the combustible method is used for production, and the chemical method or foam method can also be used to form a porous structure. The ingredients are mixed with water to form a plastic mud or mud, which is extruded or cast into a mold. After drying, it is fired in an oxidizing atmosphere at 1250 to 1350C. The volume density of commonly used lightweight clay bricks is 0.75 to 1.50 g/cm3, and the compressive strength is 2.0-5.9 MPa. Clay heat-insulating refractory bricks are widely used, mainly used as heat-insulating materials in various industrial furnaces that do not contact molten materials and have no corrosive gas effects, and the use temperature is 1200~1400C. According to the Chinese standard (GB3994--1983), clay heat-insulating refractory bricks are divided into NG-1.5, NG-1.3a, NG-1.3b, NG-1.0, NG-0.9, NG-0.8NG-0.7, NG-0.6 and ten other grades according to volume density.

 

The commonly used production process for clay insulating refractory bricks is the burnout addition method with floating beads, and the foam method can also be used.

Raw materials, binders and sawdust for clay-based heat-insulating refractory bricks (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 raw materials for clay-based heat-insulating refractory bricks with an AlO: content greater than 30%, a Fez0: content less than 3%, and a refractoriness greater than 1610°C. Most of the floating beads are closed hollow spheres with thin walls and high strength. Their volume density is 0.38~0.44gcm', their color is grayish white, and their particle size is 20~250pm, of which 50~150μm is more common. 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) Clinker fines and floating beads are both 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 phosphate, dextrin resin, etc. Refractory clay has high binding, dispersibility, plastic refractoriness and sintering properties. It is also cheap and has abundant resources. Therefore, most mixtures are based on refractory clay. 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 for clay heat-insulating refractory bricks The volume density of the product is different, and the amount of floating beads added is also different. 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 after firing, add an appropriate amount of sawdust.

Mixing of clay-based heat-insulating refractory bricks makes the material moisture mix evenly and improves the molding performance of the clay. 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 minutes to obtain a clay material 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 powder, binding clay and sawdust into the machine, 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 12 to 24 hours. The moisture content of the clay depends on factors such as product volume density, ingredient ratio, and molding method. Generally, the moisture content of the clay is 20% to 30%.

The forming of clay heat-insulating refractory bricks is mostly done by hand and machine pressing. Machine pressing should use a 150~300kN brick press. The strength of the bricks after forming is very low, so they should be handled with care; semi-finished products with complex shapes, large single weight or low volume density can be held with pallets or plywood to prevent the bricks from deformation and damage.

The packing and firing of clay heat-insulating refractory bricks are side-loaded, requiring flatness, stability and straightness, and rice husks are sprinkled layer by layer. Hand gaps should be left between bricks. The kiln loading height is generally 1.5~1.8m, and products with a volume density of less than 0.6g/cm* should not exceed 1.2m: and should be loaded in the low-temperature part of the kiln. When the products are fired 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, clay and the volume density of the products. Usually, the products with bulk density of 0.4~0.6g/cm° have a fire-stop temperature of 1220~1250℃; the products with bulk density of 0.8~1.0g/cm° have a fire-stop temperature of 1250~1280℃, and the heat preservation 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. Therefore, according to the temperature distribution in the kiln, products of different brands are installed in different parts to improve the firing quality.

Clay heat-insulating refractory bricks are widely used, mostly in the heat insulation layer of thermal equipment and industrial furnaces. They can be used in areas without strong erosion and scouring of high-temperature molten materials. Some surfaces in direct contact with flames are coated with a refractory coating to reduce erosion by slag and scouring by furnace gas and dust, and reduce damage. The working temperature of the product does not exceed the test temperature of the reburning line change.

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