How to buy or use refractory brick products?
The high-temperature properties of refractory materials are properties measured at high temperatures, such as: fire resistance, reburning line change, thermal shock resistance, slag resistance, load softening temperature and creep. The state of the refractory material during use. Therefore, Shenyang refractory brick cutting machine manufacturer Pengcheng Nonmetals believes that understanding these properties is of great significance for the selection and use of refractory materials.
1.Fire resistance
Fire resistance is a characteristic that indicates the high temperature resistance of a material. Raw materials such as mullite, kyanite, andalusite and sillimanite need to be tested for fire resistance in order to understand the purity of the raw materials. Such as impurities, especially those with strong flux effect, will reduce the fire resistance.
Method for measuring refractory: Triangular cone made of refractory raw materials or materials. The upper and lower sides of the triangular cone are 2mm long, the lower and lower sides are 8mm long and 30mm high. Then place it on the same cone disk as the high-temperature standard cone, and heat it at the specified temperature increasing rate. Compare the sample cone with the standard cone. The sample cone gradually softened due to the appearance of the high-temperature liquid phase, and was bent to the bottom by its own gravity. The temperature at which the apex of the cone bends down and contacts the cone is the fire resistance. The fire resistance is indicated by the number of the standard cone that is bent at the same time as the sample.
(1) Fire resistance and melting point have different meanings. Melting point is the equilibrium temperature for a crystalline single substance, melting from a solid to a liquid. The fire resistance is the melting range of various minerals. It is true that the melting point of crystalline minerals is high, and the temperature of the eutectic formed by the interaction is correspondingly high.
(2) Refractory cannot be misunderstood as the temperature at which refractory can be used under high temperature. Because it has completely softened to a loss of mechanical strength. For example, the basic refractory material melts first at a lower temperature, and its damage is based on the softening of the bonding agent. This temperature is much lower than the refractory degree of the material. The service temperature of general clay bricks is about 200 ~ 250 ℃ lower than the fire resistance.
2.Reburning line change
Reburning linear change refers to the residual expansion or contraction that occurs after the sample is heated to a specified temperature, held for a certain period of time, and cooled to room temperature.
Reburning line change is one of the important indicators for evaluating the quality of refractory products. The volume of the refractory products expands or contracts after re-burning, which means that during the firing process of the refractory products, the firing is insufficient due to insufficient temperature, holding time or uneven temperature. If the refractory product's reheating line change index exceeds the national specified value, when it is used in industrial kiln, due to the high temperature, some physical and chemical changes will continue, which will cause the volume of the product to expand or shrink and the size to be larger. The change will cause the brick gap of the furnace body to change, thereby affecting the integrity of the furnace lining, and in severe cases, the structure of the furnace body will be damaged. Therefore, it is necessary to standardize the firing system so that the reburning line of the product changes within the specified value.
3. Thermal shock resistance
Refractory is the basic material of industrial kiln. It must be affected by temperature in use, sometimes it is affected by sudden temperature changes. Thermal shock resistance refers to the ability of refractory materials to resist thermal stress due to rapid temperature changes without breaking.
There are many reasons that affect the thermal shock resistance index of refractories, so there are many expressions. The following relations are briefly used:
From the above-mentioned imperfect relationships (the above formula does not take into account the shape and size of the material, heating (cooling) conditions, local stress caused by sudden temperature changes, etc.), it can be seen that there are several main factors that affect the thermal shock resistance of materials:
(1) low elastic modulus;
(2) The coefficient of linear expansion is small;
(3) The thermal conductivity of the main body of the refractory material is high;
(4) The conjugate composition and main structure are appropriate.
In the production process of refractory materials, the basic ways to improve the thermal shock resistance of refractory products are:
(1) Change the phase composition of products to obtain low-expansion minerals, or superposition of low-expansion minerals, etc .;
(2) Properly select and control the production conditions to make the composition of the conjugate and the main structure appropriate, such as the formation of microcracks and the increase of the material particles of certain products. Table 1 lists the properties such as the expansion coefficient of several refractory materials.
4.Corrosion resistance
There are many types of industrial kiln. Refractory materials will be subject to various types of corrosion in industrial kiln, such as molten steel and molten iron, slag (acid or alkaline slag), temperature changes, thermal stress, and The effect of changes (especially reducing atmosphere) on the refractory damage. Therefore, refractories need to have corresponding characteristics according to the working environment of industrial kiln.
CO erosion resistance refers to the ability of refractory materials to resist cracking or disintegration in a CO atmosphere. When refractory products encounter a strong CO atmosphere at about 500 ° C (in the range of 300 ~ 600 ° C), a chemical reaction occurs 2CO = CO2 + C, and the separated free carbon will be deposited around the iron point of the product, causing the product to crack or damage . During the blast furnace smelting process, the cracking of the refractory products and the loose structure of the parts of the furnace body at 400 to 600 ° C are one of the important reasons for the damage of the lining of the blast furnace. Reducing the iron oxide content and porosity of refractory products can enhance their resistance to CO erosion.
5.Load softening temperature
The load deformation index of refractories under high temperature is expressed by the load softening temperature. It is the resistance of the product to the combined action of high temperature and load, and also indicates the softening range of the refractory product showing obvious plastic deformation. This index is also often used as a basis for determining the maximum use temperature of the refractory material.
According to the load softening temperature index of the refractory product, it can be judged under what conditions the refractory material loses the pressure bearing capacity during use, and the microstructure inside the refractory material can also be inferred.
6.High temperature creep
High temperature creep refers to the relationship between the deformation and time of a refractory material under constant high temperature and a certain load. The high temperature creep index includes the strength, temperature and time of the refractory at high temperature, indicating the deformation rate of the refractory product at a certain temperature and time period.
The above several indicators of commonly used refractory brick products need to be considered. In different high-temperature industrial kiln, due to the different use environment and working conditions, the main index factors considered in different parts of refractory bricks depend on the situation. For example, in addition to the material content of refractory brick products used in hot blast stoves, the most important thing is to look at the thermal shock resistance index.
