Tar Dolomite Refractory Bricks

Tar dolomite refractory brick products are various shaped refractory brick products made from high-quality sintered dolomite as raw material and adding tar or asphalt as binding agent.

Tar Dolomite Refractory Bricks

(1) Characteristics of raw materials.

Sintered dolomite is the main raw material for tar dolomite refractory brick products, and its chemical composition, sintering degree and freshness must be qualified.

Tar and asphalt act as binding agents in tar dolomite refractory brick products. It is distributed between the sintered dolomite particles and partially penetrates into the interior of the dolomite. During the heating process, fine volatiles are softened, leaving fixed carbon, which is further graphitized to form a carbon network skeleton. Thereby enhancing and improving the high-temperature structural strength (load softening temperature), slag resistance and hydration resistance of the product. At the same time, the carbon mesh skeleton improves the thermal conductivity of the product and enhances thermal shock stability. Tar pitch is required to have high carbon content, moisture content less than 0.5%, low softening temperature and strong bonding ability. Using tar or asphalt each has its own advantages. Tar has low carbon content and strong binding ability and does not require a lot of molding pressure. Asphalt has high carbon content and high fluidity, requiring greater molding pressure. According to practical experience, it is more appropriate to mix tar and asphalt in half or slightly more than asphalt as a binder.

(2) Manufacturing characteristics of refractory bricks.

Before the advent of magnesia carbon refractory bricks, many oxygen steelmaking converter linings at home and abroad generally used tar dolomite bricks or directly pounded the linings with tar dolomite. A lot of valuable experience has been accumulated in making bricks, building furnaces, baking ovens and formulating reasonable smelting operating systems.

In the process of making refractory bricks, the ingredients, mixing and molding of tar dolomite products have certain characteristics. At present, there is no unified standard for the particle ratio of tar dolomite products. The ratio of coarse particles (8-20mm), medium particles (0.5-8mm), and fine particles (<0.5mm) is used to increase the volume density and improve the product's ability to withstand erosion and chemical erosion. The principle of ingredients is "big in the middle and small in the middle". If the proportion of coarse particles can be appropriately increased and the critical diameter of coarse particles can be ensured as much as possible, it will be very useful to improve the overall performance of the product.

The ingredients sequence of tar dolomite products is divided into two steps. The first step is to heat the sintered dolomite material to a high enough temperature to ensure uniform mixing when adding tar asphalt. The second step is to add the tar pitch heated to about 120°C to the sintered dolomite ingredients and stir thoroughly to mix evenly. Generally, it is more appropriate to add 5 to 10% tar asphalt. Too much will lead to refractory brick deformation and increased porosity, thus affecting the bulk density of the product and reducing slag resistance. The amount of tar asphalt is too small, making it difficult to mix evenly, producing white material, making it difficult to form, and reducing the performance of refractory bricks.

The forming methods of tar dolomite refractory brick products include machine pressing, vibration and pounding. No matter which molding method is used, it is important to control the temperature of the mixture. If the material temperature is too high, it is prone to distortion, peeling, cracking and other defects. The material temperature is too low, the deformation ability is poor, and molding is difficult. In severe cases, the particles may be damaged due to pressure molding, thereby destroying the particle ratio and reducing product performance.

In order to improve the quality of sintered dolomite refractory brick products, the products can be impregnated. The impregnation method is to first roast the product at low or high temperature, and then soak it in tar or asphalt for a certain period of time. It can also be steamed at normal pressure and low temperature or impregnated in vacuum. Practice has proven that impregnation is effective in improving the performance of tar dolomite products.

(3) The reliability of tar dolomite refractory brick products.

• 1) Porosity, density and bulk density. Since tar dolomite products contain almost no moisture, the molding pressure is generally relatively high, so the porosity is low, and the apparent porosity is about 21%. Because the composition is free calcium oxide and magnesium oxide, it has a high density.
• 2) Refractoriness and load softening temperature. Because tar dolomite refractory brick products contain less main crystals and matrix low-melting point compounds, the residual carbon in the products has a high refractory degree. Therefore, the refractory resistance of the product is as high as over 1900°C, and the load softening temperature is also over 1500°C.
• 3) Thermal expansion and thermal glow stability. Thermal expansion of tar dolomite refractory brick products is small, and the linear expansion coefficient is only 10×10-6/℃. At the same time, there is carbon in the refractory bricks, which makes it have better thermal and thermal conductivity, and the content of solid-soluble magnesium ferrite is also low, so the thermal shock stability of the product is also better. Generally, the number of water cooling is more than 20 times.
• 4) Slag resistance. Tar dolomite refractory brick products are alkaline and contain a certain amount of carbon to reduce the wetting of slag, and have strong resistance to alkaline slag erosion. However, if there is a large amount of iron oxide in the slag, the slag resistance of the product will be weakened due to the oxidation of carbon.
• 5) Hydration. Tar dolomite refractory brick products contain more free calcium oxide and are prone to hydration reactions when exposed to water at normal or high temperatures. Therefore, tar dolomite products should not be stored for a long time, and they are not allowed to be used under artificial conditions in contact with water.

(4) Application of tar dolomite refractory brick products.

Because tar dolomite refractory brick products have a series of advantages such as high refractoriness and strong resistance to alkaline slag erosion, they also have a long history of manufacturing and use experience. Therefore, so far, some countries still use tar dolomite bricks as steelmaking converter linings and some small and medium-sized furnaces in my country are still using them. my country's dolomite mineral resources are widely distributed and have large reserves. It is of practical significance to further study how to improve the quality of tar dolomite refractory brick products and further expand its application in other high-temperature kilns.