11 FAQ About Refractories
NO. 1 What is the porosity of refractories?
There are three types of porosity in the production process of refractory materials, namely, open porosity, closed porosity and through porosity.
The sensible gas fraction is the ratio of the volume of the open gas fraction to the total volume of the refractories connected with the atmosphere, and the direct gas fraction is the ratio of the volume of all the subfractions of the refractories (including the volume of the open porosity, the volume of the closed porosity and the volume of the through porosity) to the total volume.
NO. 2 What is the permeability of refractories?
Air permeability is a characteristic value that characterizes the difficulty of a certain amount of gas passing through a refractory product under certain conditions. It is defined as: in a certain period of time, a certain pressure of gas through a certain section and thickness of the number of refractory samples.
In addition to the breathable brick of ladle, the smaller the permeability of the remaining refractory materials, the better, which can reduce the erosion rate of slag and reduce the thermal conductivity of refractory materials.
NO. 3 What is the thermal expansion of refractories?
During the use of refractory materials, with the increase of temperature, the atomic anharmonic vibration in the middle of the main crystal phase of refractory materials and the matrix increases the atomic distance in the object, resulting in volume expansion, which is called thermal expansion of refractory materials.
The thermal expansion of refractory materials is usually expressed by linear expansion rate and linear expansion coefficient. It is defined as:
(1) Linear expansion rate. The relative rate of change of the length of a refractory sample during heating from room temperature to the test temperature.
(2) linear expansion coefficient. The relative rate of change of the length of the refractory sample during the heating from room temperature to the experimental temperature, with each 1℃ increase in temperature. The thermal expansion of refractories is related to the crystal structure of refractories. The bond energy in the middle of the crystal structure determines the coefficient of thermal expansion. For example, in the middle of the crystal structure of Mg0 and A1203, oxygen ions are tightly packed, and after the refractory is heated, the mutual thermal vibration of oxygen ions causes a large thermal expansion rate of the refractory. The thermal expansion rate of refractories with high anisotropy in structure is low, and cordierite is typical. The thermal expansion of refractory materials is related to the safe performance in the process of steelmaking. For example, refractory materials with poor thermal expansion performance will expand and crack during the baking stage of use, causing damage to refractory materials; There are cracks in the process of use, which is also an important factor affecting the smooth implementation of steelmaking.
NO. 4 What is the thermal conductivity of refractories?
Thermal conductivity is the amount of heat passing through a unit vertical volume in a unit time at a unit temperature gradient. There is a close relationship between thermal conductivity and porosity and mineral composition of refractory products. Generally speaking, the thermal conductivity of the gas in the middle of the porosity of refractory materials is very low. Therefore, refractory materials with larger porosity have lower thermal conductivity.
In the mineral composition of refractory materials, the more complex the crystal structure, the lower the thermal conductivity: the more impurity components, the lower the thermal conductivity.
NO. 5 What is the heat capacity of refractories?
The heat required to heat 1kg of a certain substance under atmospheric pressure to warm it by 1 ° C is called the heat capacity of the substance, also known as the specific heat capacity. The specific heat capacity will affect the baking heating and cooling of refractories during the use of refractories. Refractory materials with large specific heat capacity have a relatively long baking time.
NO. 6 What is the refractoriness of refractories?
The resistance of refractories to high temperature without melting is called refractoriness. Refractories do not have a fixed melting point, so refractories actually refer to the temperature at which the refractories soften to a certain extent. Refractoriness is an important indicator of refractory materials, and the refractoriness of refractory materials should be higher than its maximum service temperature. The test of refractoriness is to make the refractory material to be tested into a cone sample in accordance with the regulations, and heat the standard sample together, the cone is softened by high temperature and bent, and the temperature when the tip of the cone contacts the chassis is the refractoriness of the refractory material.
NO. 7 What is the load softening temperature of refractories?
Load softening temperature is also called load softening point. Refractory products have high compressive strength at room temperature, but after bearing the load at high temperature, they will be deformed and reduce the compressive strength. The load softening temperature is the temperature at which a certain deformation occurs under the condition of constant load at high temperature.
NO. 8 What is the thermal stability of refractories?
The ability of refractories to change rapidly with temperature without cracking or damage, as well as the ability to resist fragmentation or rupture in use, is called the thermal stability of refractories. The thermal stability of refractory materials is expressed by the number of urgent cooling and urgent heating, also known as the resistance to urgent cooling and urgent heating.
NO. 9 What is the slag resistance of refractories?
The ability of refractory to resist slag attack at high temperature is called slag resistance.
The slag contacts with the refractory in liquid form, forms liquid phase with the refractory, and is stripped from the surface of the refractory. Or the porosity from the refractory into the refractory inside, in the process of temperature change, resulting in volume expansion changes, resulting in loose damage to the refractory, or into the refractory inside, forming a new high-melting point spinel phase, resulting in ladle and other refractory materials can not be used normally and damaged. Furnace gas and all kinds of substances in contact with electric furnace refractories may have the above forms of damage, so in addition to the surface dissolution of the slag erosion of refractory materials, slag can also invade or penetrate into the interior of refractory materials, expand the reaction area and depth of slag and refractory materials, resulting in near the surface of refractory materials. The composition and structure of the refractory material undergo qualitative changes, forming a metamorphic layer that can be easily dissolved into the slag, shortening the service life of the refractory material. The erosion mode of this refractory is mainly related to the porosity of the refractory. Different refractories, the same composition, if the organizational structure is different, the corrosion rate is not the same. The higher the porosity of the refractory, the weaker the slag resistance.
NO. 10 What is the burn index of refractories?
The burning index of refractories represents the burning effect of the arc on the dry furnace wall, which was proposed by W. Esschwabe of the United States in 1962. This index plays an important role in determining the smelting process route, such as the determination of the secondary side voltage of ladle refining furnace is determined according to the burning index of refractories.
NO. 11 What is the mineral composition and chemical composition of refractories?
Mineral composition is the structural component of mineral lithofacies contained in refractory products. For example, the main crystalline phase in magnesium carbon brick cubic magnesite crystalline phase is the main mineral composition of magnesium carbon brick. The same mineral composition of the refractory, the size of the mineral crystallization, shape and distribution of different, the nature of the refractory will be different. The mineral composition of refractories can be a single crystalline phase or a combination of polycrystalline phases. At present, the mineral phase is generally divided into two kinds of crystalline phase and glass phase, and the mineral composition that constitutes the main body of the refractory and has a high melting point is called the main crystalline phase, and the rest of the material that exists in the middle of the large crystal or aggregate gap of the refractory is called the matrix, such as the carbon in the magnesium carbon brick is the matrix. The nature, quantity and binding state of the main crystal phase directly determine the use of refractory properties.
