Diatomaceous Earth Insulation Products

Diatomite insulation bricks are insulation refractory products made of diatomite as the main raw material. Silica insulation bricks have fine closed pores, high porosity, good thermal insulation performance, but low mechanical strength, especially after being damp, the strength decreases significantly. Its main chemical composition is SiO:, followed by Al, O:, and impurities such as iron, potassium, sodium calcium, and magnesium oxides.

Diatomite insulation brick process includes five parts: raw materials and their processing, batching and mixing, molding and firing.

Raw materials and processing The main raw materials for manufacturing diatomite insulation bricks are diatomite, fly ash, sawdust and waste insulation brick return materials. Diatomite has a certain plasticity. The finer the particles, the better the plasticity. Diatomite used for brick making should meet the following requirements: SiO2 content is greater than 65%; A10, content is less than 18%; Fe2O3 content is less than 7%; ignition reduction is less than 14%. In order to improve the plasticity of diatomite and remove some soluble salts (impurities) to improve its physical and chemical properties, there should be a certain weathering period before use. For raw material processing, different methods are used according to the quality and process requirements of diatomite. Some should be crushed to less than 1.5mm, some should be weathered fragments, some newly mined diatomite should be stirred into small mud blocks by mud knives, and some should be moistened with water. The moisture content of fly ash in thermal power plants should be less than 26%. The moisture content of sawdust should be less than 50%, and the particle size should be less than 1mm. Waste and recycled materials should be sieved after crushing (waste through 1.5mm sieve, recycled materials through 1mm sieve), and added to brick materials according to proportion. In order to make brick materials have better molding and sintering properties, some manufacturers add binders and mineralizers to brick materials, such as iron scale, lime milk, sulfite pulp waste liquid and molasses.

 

Ingredients and mixing of diatomite insulation bricks In order to reduce the shrinkage of the blank during drying and firing and the generation of cracks and waste products, a certain proportion of fly ash and clinker are added to the ingredients; when producing low-density products, a certain proportion of sawdust is also added to the ingredients. The proportion of various materials is determined according to the product brand, quality requirements, molding method and firing conditions and other process conditions. Mixing is carried out in a double-shaft mixer or mixer. When the temperature is low, hot water and hot steam should be introduced. The moisture content of the mud varies depending on the molding method and brand, generally 35% to 50%.

Diatomite insulation brick molding Diatomite bricks are generally formed by extrusion molding, machine pressing molding and manual molding.

(1) Extrusion molding. The mud is fed into the extruder to extrude mud strips of specified size, and then cut into the required thickness or length by a cutting machine.

(2) Machine pressing molding. Press in a brick press with a nominal force of 150 to 300 kN, but during the pressing operation, the layer cracking and cracking due to elastic aftereffect should be prevented.

(3) Manual molding. Small quantities, complex shapes and large products are formed manually with wooden molds. Drying is carried out in a heated kang or tunnel dryer. Since the moisture content of the bricks is high, low temperature and slow drying should be used to avoid cracks. When drying in a tunnel dryer, the inlet temperature of the bricks should be controlled at 40-50°C and the outlet temperature should be around 150°C; and sufficient air volume should be supplied. The residual moisture of the bricks after drying should be controlled below 3%, and large or complex-shaped products should be controlled below 1%.

The "well" code method is mostly used for kiln loading, and the stacking height does not exceed 1.5m. During firing, at the low temperature stage (below 200C), the main purpose is to remove physical water, and the temperature should not rise too fast. During operation, adjust the fire gate, increase the suction force in the kiln, and thus increase the ventilation volume. After 200C, crystal water and compound decomposition begin to be removed. Organic matter such as sawdust in 500-600℃ bricks burns, and an oxidizing atmosphere should be maintained in the kiln to facilitate the full combustion of organic matter. The final firing temperature can be controlled at around 900℃. Some of the fired products need to be shaped into finished products.

Application of diatomite insulation bricks The heat resistance of the products is only about 1280℃, so the use temperature can only be used in the insulation layer below 900℃.

Diatomite insulation bricks are insulation products made of porous diatomite, and can also be directly cut from natural diatomite. But usually diatomite is used as the raw material, with a small amount of clay combined, lightly wetted, mixed, molded and fired. It is a commonly used insulation product in industrial kilns and thermal pipelines, with a safe use temperature of 900℃.

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