Refractories are an important component in the design of industrial furnace linings. Its refractoriness is usually specified above 1580°C. When designing, it is necessary to understand its characteristics and the use requirements of the furnace lining, and make quantitative calculations, in order to design finished products that are technologically advanced and economically reasonable.
1. Material classification There are many kinds of refractory materials, which can be divided into shaped refractory products and unshaped refractory products according to the manufacturing process. Now help you analyze the concepts and differences between these two materials:
1. Shaped refractory products Shaped refractory products with a certain shape, among which the thermal conductivity at 350 ° C is less than 0.70W/(m?K) are called heat-insulating refractory products. Shaped refractory products are divided into fired bricks, unfired bricks and fused cast bricks according to the molding process. According to chemical characteristics and mineral composition, it is divided into: (1) Acid bricks. Refers to silica bricks and lightweight silica bricks with a SiO2 content of more than 93% and clay refractory bricks with a SiO2 content of more than 50% (the rest are minerals such as Al2O3). The last type is also known as semi-acid brick. (2) Neutral brick. Generally refers to high alumina bricks (slightly acidic) and chrome bricks (slightly alkaline); (3) alkaline bricks. Magnesia bricks, magnesia-alumina bricks, magnesia-chrome bricks and dolomite bricks with MgO and CaO as the main components. (4) Special bricks. Materials with special properties such as high melting point, good chemical stability and thermal shock resistance, and high temperature strength. It usually includes pure oxides, non-oxides and cermets, such as zircon bricks, silicon carbide bricks, brown corundum-silicon carbide bricks, etc. High temperature refractory fibers also belong to this category.
2. Unshaped refractory material It is made by mixing refractory aggregate, binder and additives. Some are directly constructed in the delivery state, and some are constructed after being mixed with some liquids. There are two kinds of unshaped refractories: dense and heat-insulating. According to the hardening process and the properties of the binder, they are divided into ceramic bonding (hardening due to sintering during the calcination process), hydraulic bonding (condensation at room temperature and through hydration reaction) And hardening), chemical bonding (hardening by chemical reaction rather than hydration reaction at room temperature or below the temperature of ceramic bonding), organic bonding (bonding or hardening at room temperature or slightly higher temperature) four types.
It can also be divided into three categories according to the type of use: overall construction materials and repair materials, masonry and joint materials, and refractory coating materials.
l Overall construction materials and repair materials include: (1) Refractory ramming materials. It can be applied directly or mixed with some liquids. It is applied by ramming, and most of them harden under the action of heating above normal temperature. (2) Refractory plastic. It is delivered as a plastic soft billet or irregularly shaped dough, which can be used directly, constructed by ramming, vibrating, pressing or extruding, and hardened during the calcination process. (3) Refractory castables. It is delivered as dry material, used after adding water or mixed with other liquids. It is constructed by pouring, vibrating, and tamping. If necessary, it is constructed by tamping. It can be condensed and hardened without heating. (4) Refractory spray coating. It is a specially prepared mixture for construction by wind power tools or mechanical spraying, and its hardening characteristics can be classified into one of the first three types.
l Masonry and joint materials are refractory mortar. Construction with a spatula or similar tools can also be used for filling joints or dipping blocks, divided into three types: hydraulic bonding, ceramic bonding and chemical bonding.
l Refractory smear is a mixture composed of fine aggregate and binder. All kinds of binders can be used, and the water (or other liquid) content is generally higher than that of refractory mud, and it can be constructed by manual, pneumatic or mechanical spraying.
On the basis of the above classification method, it is further classified and named according to the properties of the main components of the mixture and (or) the aggregate that determines the characteristics of the mixture, such as high-alumina refractory plastics, clay-based low-cement refractory castables and corundum Quality ultra-low cement refractory castables, etc.
Compared with shaped refractory products, its advantages are: (1) The factory occupies a small area, does not require molding and firing processes, consumes little energy, and has low investment and operating costs. (2) The variety and quantity of special-shaped bricks can be significantly reduced, which is convenient for material preparation and construction. (3) The integrity of the furnace lining is good, which improves the strength and air tightness and reduces heat loss. (4) Equipped with metal or ceramic anchors, or reinforced with stainless steel fibers, it can improve the resistance to mechanical vibration and thermal shock, and can also partially repair the damaged part. (5) It is convenient for storage and transportation, and is conducive to the mechanization of furnace construction. Only the construction management must be strict, otherwise it will affect the physical and chemical properties and life of the furnace lining. Sometimes monolithic refractories are used as prefabricated components.
2. Material selection Refractory products and dense amorphous refractory materials are mainly used for the refractory layer of high-temperature furnace lining. In addition to being used for the refractory layer of medium-temperature furnace lining, heat-insulating refractory products and lightweight castables are generally used in high-temperature furnace lining. Between the refractory layer and the heat insulation layer, or directly as the heat insulation layer of the middle and low temperature furnace lining. There are not many cases where a single material is used as a furnace lining. The common one is a composite furnace lining: the innermost layer is mainly fire-resistant, and the remaining layers are mainly heat-insulating. Sometimes diatomite refractory bricks are also included in thermal insulation refractory products. The heat insulation layer not only reduces the loss of heat dissipation and heat storage, but also improves the heating rate and cooling rate of the furnace, as well as the efficiency, operating rate and output of the furnace. In addition, the structure of the furnace is simplified and the weight of the furnace is reduced.
The performance of refractories has three aspects: (1) mechanical properties. Such as compressive strength, flexural strength. (2) Chemical properties. Such as slag resistance, reaction with controlled atmosphere. (3) Physical properties. Such as bulk density, refractoriness, softening temperature under load, thermal expansion rate, re-firing line change rate, thermal shock stability, thermal conductivity and specific heat capacity, etc. (Table 1-3). According to the purpose, start from the comprehensive comparison of various performances required, select several types, and finally confirm according to investment and economic benefits. In view of the fact that some important indicators (such as service life) are not easy to be quantitatively calculated, they can only be arranged and compared according to the degree of priority when selecting materials, so design experience and use experience still play a considerable role in material selection. According to the design conditions of the furnace and the factors to be considered. According to different parts of use. The development trend of furnace refractories is diversification of varieties, high quality of materials and energy saving. With the development of production technology, in addition to the refractory fiber that has been used in the refractory insulation layer of the furnace lining, high temperature resistant refractory fiber products are gradually being used in the refractory layer of the furnace lining. The goal of material selection is to select the appropriate refractory material according to the type of furnace and different parts of use, and at the same time improve the furnace structure design and build a multi-layer composite furnace lining, so that the materials of each layer in different temperature regions will fail at the same time, thereby prolonging the overall use of the furnace lining number of years. When different materials are available for application under the same conditions of use, materials with good economic benefits should be used first.
