Lightweight fire brick is a kind of thermal insulation refractory material, which refers to the fire brick with high porosity, low bulk density and low thermal conductivity. Lightweight fire bricks are characterized by a porous structure (the porosity is generally 40-85%) and high thermal insulation.
1. Lightweight fire bricks have a variety of classification methods:
(1) Classified by bulk density. Lightweight fire bricks with a bulk density of 0.4 to 1.3g/cms; ultra-lightweight fire bricks with a bulk density below 0.4g/cm3.
(2) Classified by operating temperature. The use temperature of 600-900 ℃ is a low-temperature thermal insulation material; 900-1200 ℃ is a medium-temperature thermal insulating material; a temperature exceeding 1200 ℃ is a high-temperature thermal insulating material.
(3) Classification by product shape. One is shaped light fire bricks, including clay heat insulating fire bricks, high alumina heat insulating fire bricks, siliceous fire bricks and some pure oxide light weight fire bricks; the other is unshaped light weight fire bricks , such as lightweight refractory concrete.
The heat storage loss of industrial furnace masonry and the heat dissipation loss of furnace body surface generally account for about 24-45% of fuel consumption. Using lightweight fire bricks with low thermal conductivity and small heat capacity as furnace body structural materials can save fuel consumption; at the same time, because the kiln can heat up and cool rapidly, it can improve equipment production efficiency; it can also reduce the weight of the furnace body and simplify the kiln Furnace structure, improve the quality of fire bricks, reduce ambient temperature and improve working conditions.
The disadvantage of lightweight fire bricks is that the porosity is large, the organization is loose, and the slag resistance is poor. The slag quickly penetrates into the pores of the fire brick body, causing it to shatter, and cannot be used for direct contact with slag and liquid metal parts; It has low mechanical strength, poor wear resistance and poor thermal stability, so it cannot be used in load-bearing structures, nor should it be used in parts that are in contact with the charge and are severely worn.
Due to the above shortcomings of lightweight fire bricks, in industrial kilns, lightweight fire bricks are generally not used in furnace parts that are in contact with the charge, slag, and hot air with high flow velocity and large mechanical vibration parts. Lightweight fire bricks are mostly used as insulation, lining or insulation for kilns.
Second, the manufacturing methods of lightweight fire bricks usually have the following four:
(1) Burn out the addition method. Also known as the addition of combustibles. Combustibles that are easy to burn out, such as charcoal powder, sawdust, etc., are added to the mud for making fire bricks, so that the fire bricks have certain pores after firing.
(2) Foam method. A foaming agent, such as rosin soap, is added to the mud for making fire bricks, and it is foamed by a mechanical method, and a porous fire brick product is obtained after firing.
(3) Chemical method. Using a chemical reaction that can properly generate gas, a porous fire brick product is obtained in the process of making fire bricks, usually dolomite or periclase plus gypsum, and sulfuric acid as a foaming agent.
(4) Porous material method. Lightweight fire bricks are prepared from porous raw materials such as natural diatomite or artificial kerosene foam clinker, alumina or zirconia hollow spheres.
The commonly used lightweight fire bricks are mainly lightweight clay fire bricks, lightweight high-alumina fire bricks and lightweight siliceous fire bricks.
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