The processing methods of lightweight thermal insulation refractory bricks usually include the following:
①Cut the natural porous light raw rock to get bricks:
②Use natural lightweight porous materials as raw materials to process bricks;
③ Add easily burned combustibles to form a porous structure, such as adding rice husks, sawdust, etc.; or add substances that are easy to sublime, such as burning naphthalene and volatilizing to obtain a porous structure;
④ Add a foaming agent to form a porous structure, such as adding rosin soap and firing to obtain a porous structure;
⑤ Through the action of inorganic foaming agent, gas is released through chemical reaction to obtain porous structure.
Generally speaking, the two processing methods ③ and ④ are more commonly used.
At present, the more common preparation methods of thermal insulation materials are as follows:
(1) Hollow sphere bonding molding method:
The method mainly uses a binder to bond the pre-prepared porous lightweight aggregate to form, and then dry and sintered at an appropriate temperature to obtain a product. The products produced by this method have low cost and simple process, but are prone to delamination during the molding process, and are prone to cracking or even collapse during repeated cooling and heating processes due to the difference in thermal expansion between the binder and the aggregate. .
(2) Burnout method of pre-buried filling:
This method is simple in process and low in cost, and is the main production method. Commonly used combustible additives are sawdust, cork powder, charcoal, anthracite ash, coke powder, rice husk, polystyrene particles, naphthalene particles, etc.
(3) Chemical reaction foaming method:
This method uses the chemical reaction between the pore-forming agent powder mixed in the slurry and the liquid phase components to release gas, so that the slurry becomes a porous flowing slurry, which is cast, molded and dried to obtain a porous body. High temperature calcination is done. This method is suitable for the manufacture of pure oxide heat-insulating refractory products, and its porosity can reach 55% to 75%. From the literature (1), the commonly used chemical reactions are sodium carbonate and acid to produce CO2, caustic soda and aluminum or acid and aluminum to produce hydrogen. The reaction rate of these reactions is slow at low temperature, and the foaming time is long. At the same time, the residual amount of these additions after sintering is large and belongs to low-melting substances, thus reducing the refractoriness of the product. In addition, due to the high price of aluminum, it also increases the cost of brick making.
(4) Pre-embedded volatile material driving method:
This method is to mix volatile substances into the slurry and then sublime the volatile substances to form pores under certain conditions.
(5) Foam premixed casting method:
This method is to add foam (obtained by physical foaming agents such as protein, rosin soap, saponin fat, etc.) into the slurry and mix to obtain a foam slurry, which is then cast and molded, dried and fired to obtain porous lightweight materials. Thermal insulation refractory. The performance of the heat-insulating refractory products produced by this method is largely related to the performance of the foaming agent. At present, the main types of foaming agents are rosin foaming agent, waste animal hair foaming agent, resin soap foaming agent, hydrolyzed blood glue foaming agent, aluminum petroleum sulfonate foaming agent, lignosulfonate, protein hydrolysis This method has the advantages of simple process, easy to master, low equipment cost, strong adaptability, and wide source of raw materials, etc., and is especially suitable for the preparation of high porosity, low density, lightweight thermal insulation refractory materials. Therefore, more and more attention is paid to the production industry of lightweight thermal insulation materials.
At present, the most commonly used methods in actual production are the embedded filler burnout method and the foam premixed casting method. The strength and thermal conductivity of lightweight insulating materials produced by different production methods vary widely. When using the combustible method to produce lightweight thermal insulation materials, when the combustibles are fired, the air diffuses into the brick through the pore channels to provide oxygen and the combustible products are discharged inward along the pore channels, thus forming continuous pores inside the material. The main structure is an open structure with continuous gas phase and discontinuous solid phase, but its microstructure is loose and its strength is far less than that of foamed materials.
