Refractory basic knowledge

A variety of types of refractory materials, usually divided according to the degree of fire resistance of ordinary refractory materials (1580 ~ 1770 °C), advanced refractory materials (1770 ~ 2000 °C) and special grade refractory (above 2000 °C); according to the chemical properties are divided into acidic Refractory materials, neutral refractories and basic refractories. In addition, there are refractory materials for special occasions.

The definition of refractories now depends not only on whether the refractoriness is above 1580°C. At present, refractories refer to inorganic non-metallic materials used in metallurgy, petrochemical, cement, ceramics and other production equipment linings.

Second, the variety In the ordinary and special refractories, the commonly used varieties are the following: 1. A large number of acidic refractory materials are silica bricks and clay bricks. Silica bricks are siliceous products containing more than 93% of SiO2. The raw materials used are silica, waste silica bricks and so on. Silica bricks have strong resistance to acidic slag, but they are vulnerable to alkaline slag. Its softening temperature is very high and it is close to its refractoriness. After re-calcination, the volume does not shrink, and even slightly expands, but the thermal shock resistance is poor. Silicon bricks are mainly used in coke ovens, glass melting furnaces, acid steelmaking furnaces and other thermal equipment. Clay brick contains 30%～46% alumina. It is mainly made of fire-resistant clay, and its refractoriness is 1580～1770°C. It has good thermal shock resistance and belongs to weak acid refractory material. It has corrosion resistance to acid slag and is widely used. Is the largest production of a type of refractories.

2. The main crystal phases in the neutral refractories high-alumina products are mullite and corundum, and the content of corundum increases with the increase of alumina content. Corundum products containing more than 95% aluminum oxide are widely used. High quality refractories. The chrome brick is mainly made of chrome ore, and the main crystal phase is chromite. Its corrosion resistance to steel slag is good, but its thermal shock resistance is poor, and its high temperature load deformation temperature is low. Chromium-magnesia bricks made with different proportions of chrome ore and magnesia have good thermal shock resistance and are mainly used as alkaline open hearth top bricks.

Carbonaceous products are another type of neutral refractories. According to the composition of carbonaceous raw materials and the mineral composition of products, they are divided into three categories: carbon bricks, graphite products, and silicon carbide products. Carbon bricks are made from high-quality petroleum coke, tar, and bitumen as binders, and fired at 1300°C in air-isolated conditions. Graphite products (except natural graphite) are obtained by graphitizing carbonaceous materials in an electric furnace at 2500 to 2800°C. Silicon carbide products are based on silicon carbide as raw materials, and clay, silica and other binders are fired at 1350-1400°C. Silicon carbide-silicon carbide products can also be produced by adding silicon carbide and silicon powder in an electric furnace under a nitrogen atmosphere.

Carbonaceous products have a low coefficient of thermal expansion, high thermal conductivity, good thermal shock resistance, and high high temperature strength. It does not soften under long-term use at high temperatures, is free of any acid-base attack, has good salt resistance, is also free of metal and molten slag, light weight, and is a high-quality, high-temperature material. The disadvantage is that it is easily oxidized at high temperatures and should not be used in an oxidizing atmosphere. Carbonaceous products are widely used in high-temperature furnace linings (bottoms, hearths, lower parts of the furnace body, etc.), linings for smelting non-ferrous metal furnaces. Graphite products can be used as reaction tanks and petrochemical autoclave linings. Silicon carbide and graphite products can also be made from smelting copper with gold and light alloys.

3. Basic refractories are represented by magnesium products. It contains more than 80% to 85% of magnesium oxide, with periclase as the main crystalline phase. The main raw materials for the production of magnesia bricks are magnesite, seawater magnesia, magnesium hydroxide extracted from seawater, calcined at high temperature, etc.). Good resistance to alkaline slag and iron slag. The melting point of pure magnesium oxide is as high as 2800°C. Therefore, the refractoriness of magnesium brick is higher than that of clay brick and silicon brick. Since the mid-50s of the 20th century, due to the adoption of oxygen-blown converters and the use of alkaline hearth furnace tops, the production of basic refractories has gradually increased, and the production of clay bricks and silica bricks has decreased. Basic refractories are mainly used for open hearth furnaces, oxygen furnaces, electric furnaces, non-ferrous metal smelting, and some high-temperature thermal equipment.

4. Oxide materials such as aluminum oxide, yttrium oxide, cerium oxide, calcium oxide, zirconium oxide, uranium oxide, magnesium oxide, cerium oxide, and yttrium oxide have melting points in the range of 2050 to 3050C.

5. Refractory compounds such as carbides (silicon carbide, titanium carbide, tantalum carbide, etc.), nitrides (boron nitride, silicon nitride, etc.), borides (zirconium boride, titanium boride, tantalum boride, etc.) Silicides (molybdenum disilicide, etc.) and sulfides (antimony sulfide, antimony sulfide, etc.). Their melting point is 2000 to 3887 °C, of ​​which the most infusible are carbides.

6. High-temperature composite materials such as cermets, high-temperature inorganic coatings and fiber-reinforced ceramics.

Third, the performance Physical properties of refractories, including structural properties, thermal properties, mechanical properties, performance and job performance.

The structural properties of refractory materials include porosity, bulk density, water absorption, air permeability, porosity pore size distribution, and the like.

The thermal properties of refractories include thermal conductivity, thermal expansion coefficient, specific heat, heat capacity, thermal conductivity, and thermal emissivity.

The mechanical properties of refractory materials include compressive strength, tensile strength, flexural strength, torsional strength, shear strength, impact strength, abrasion resistance, creep, bond strength, elastic modulus, and the like.

Refractory materials use properties include refractoriness, load softening temperature, reheat line change, thermal shock resistance, slag resistance, acid resistance, alkali resistance, hydration resistance, corrosion resistance to CO, conductivity, oxidation resistance Wait.

Fourth, the production process According to the degree of compactness of products and different shapes, there are sintering, melting and melt blowing method. Sintering method is to pre-burn some of the raw materials into clinker, crushing and sieving, then mixing with the raw materials according to a certain ratio, and forming, drying and firing. The purpose of the raw material burn-in is to burn out the moisture, organic impurities, and sulphate-decomposed gas, so as to reduce the firing shrinkage of the product and ensure the accuracy of the product's external dimensions. The raw materials need to be sifted after crushing and grinding, because the blanks are graded with powders of different sizes, which can ensure the closest packing and obtain compact bodies.

In order to homogenize the ingredients and granules of various raw materials and clinker, kneading is performed and a binder is added at the same time to enhance the binding strength of the blank. For example, the aluminum silicate raw material is added with the binding clay, the magnesium slate is added with the sulfite pulp waste liquid, and the silicon material is added with lime milk. Depending on the moisture content of the blank, semi-dry molding (about 5% moisture), plastic molding (about 15% moisture) and grouting (about 40% moisture) can be used. It is then dried and fired. The smelting method is the process of mixing raw materials and fine grinding and other processes, melting at high temperature, direct casting, cooling and crystallization, annealing into products. Such as casting mullite brick, corundum brick and magnesium brick. Their green compact, high mechanical strength, high temperature structure strength, good slag resistance, the scope of use is constantly expanding. Melt-blowing is a method in which the ingredients are melted and blown with high-pressure air or superheated steam to disperse them into fibers or hollow balls. The products are mainly used as lightweight fire-resistant and heat-insulating materials. In addition, it can also be made into powdery or granular monolithic refractories. When it is used, it can be cemented with binders such as tar, asphalt, cement, phosphate, sulfate, or chloride, and used directly without molding and sintering.