The mechanical properties of refractories refer to the ability of refractories to resist deformation and damage under the action of external forces.
Refractory materials will be deformed or even damaged by various external forces during use and transportation, such as compression force, tensile force, bending force, shear force, friction force or impact force. Therefore, testing the mechanical properties of refractories under different conditions is of great significance for understanding its resistance to damage, exploring its damage mechanism, and seeking ways to improve the quality of products.
The mechanical properties of refractories include compressive strength, flexural strength, bond strength, elastic modulus, torsional strength, and wear resistance.
Compressive Strength
The compressive strength is the ultimate load that the refractory can bear without being damaged per unit area at a certain temperature. The compressive strength of refractories is divided into normal temperature compressive strength and high temperature compressive strength.
The normal temperature compressive strength can indicate the sintering condition of the material and the properties related to its structure. In addition, the normal temperature compressive strength can indirectly judge other properties, such as wear resistance and impact resistance.
Flexural Strength
Bending strength refers to the maximum bending stress that can be borne by the strip-shaped specimen of refractory material with a certain size on the three-point bending device, also known as bending strength. The bending strength of refractories is divided into normal temperature bending strength and high temperature (hot) bending strength.
The chemical composition, mineral composition, microstructure and production technology of the material have a decisive influence on the flexural strength of the material, especially the high-temperature flexural strength. The flexural strength of the material can be improved by selecting high-purity raw materials, controlling the reasonable particle size distribution of the brick, increasing the molding pressure, using high-quality binders and improving the sintering degree of the products.
Bonding Strength
Bonding strength refers to the bonding force between unit interfaces when two materials are bonded together.
The bonding strength of refractories is mainly the strength index of amorphous refractories under various temperatures and specific conditions, mainly under service conditions.
Wear Resistance
Wear resistance is the ability of refractory materials to resist the friction and wear (grinding, friction, impact, etc.) of hard materials or gases (including solid materials). It can be used to predict the adaptability of refractory materials in wear and scouring environment. It is usually expressed by the volume loss or mass loss of the material after a certain grinding condition and grinding time.
The wear resistance of refractories depends on their mineral composition, microstructure, firmness of particle bonding and their density and strength. Materials with high compressive strength at room temperature, low porosity, compact and uniform structure and good sintering always have good wear resistance at room temperature.
Load Softening Temperature
The load softening temperature of refractory refers to the temperature at which the material deforms under the condition of constant compressive load and heating at a certain heating rate. It shows the ability of refractory materials to resist high temperature and load at the same time, and to a certain extent indicates the structural strength of products under similar service conditions.
The technological factors affecting the load softening temperature of refractory materials are the purity of raw materials, the composition of ingredients and the sintering temperature of products. Therefore, by improving the purity of raw materials to reduce the content of low melting matter or flux, adding some components to optimize the bonding phase of products, adjusting the particle gradation and increasing the molding pressure to improve the density of brick, properly increasing the sintering temperature and prolonging the holding time to improve the sintering degree of materials and promote the growth and good combination of crystal phases, the load softening temperature of products can be significantly improved.
Thermal Shock Resistance
Thermal shock resistance refers to the ability of refractory materials to resist damage caused by rapid changes in temperature. It used to be called thermal shock stability, thermal shock resistance, temperature variability resistance, cold and heat resistance, etc.
The mechanical and thermal properties of materials, such as strength, fracture energy, elastic modulus, linear expansion coefficient and thermal conductivity, are the main factors that affect the thermal shock resistance. Generally speaking, the smaller the linear expansion coefficient of refractory, the better the thermal shock resistance; The higher the thermal conductivity (or thermal diffusion coefficient) of the material, the better the thermal shock resistance. In addition, the particle composition, density, pore size, pore distribution and product shape of the refractory have influence on its thermal shock resistance. There are a certain number of micro cracks and pores in the material, which is conducive to its thermal shock resistance; The large size and complex structure of the product will lead to the serious uneven temperature distribution and stress concentration in the product, and reduce the thermal shock resistance.
High Temperature Volume Stability
High temperature volume stability refers to the performance that the external volume or linear dimension of refractory material remains stable and does not change (shrink or expand) due to the effect of heating load during the use process. For fired refractory products, it is usually expressed by the heating volume change rate or the heating permanent line change rate of the products under no heavy load; For unburned refractories (mainly amorphous refractories), it is usually expressed by the change rate of heating line.
The permanent linear change rate of heating refers to the residual expansion and contraction after the fired refractory products are heated to the specified temperature again, kept for a certain time, and cooled to room temperature. The permanent linear change rate of heating is an important index to evaluate the quality of refractory products. It is of great significance to judge the high-temperature volume stability of products, so as to ensure the stability of masonry, reduce the gap of masonry, improve its sealing and corrosion resistance, and avoid the damage of the overall structure of masonry.
The heating line change rate of the amorphous refractory includes the drying line change rate and the post firing line change rate. The drying linear change rate refers to the ratio (%) of the irreversible change in length of the sample after drying at (110 ± 5) ° C for a certain time to the length of the sample before drying. The post baking linear change rate refers to the irreversible change in length of the sample after heating at the specified temperature and holding for a certain time, expressed in (%) by the change in length of the sample. The heating line change rate of amorphous refractories is a very important performance index. If the linear change rate is too large, it will cause great damage to the masonry lining, which will easily cause structural peeling or reduce the compactness of the lining, thus reducing other properties such as erosion resistance and reducing the service life of the lining.
High Temperature Creep
High temperature creep refers to the isothermal deformation of products under stress at high temperature. High temperature creep can be divided into high temperature compression creep, high temperature tensile creep, high temperature bending creep and high temperature torsional creep due to different external forces. High temperature compression creep is commonly used.
In addition to its chemical mineral composition and microstructure, the high-temperature creep property of refractories is also related to the external factors in the use process, such as the use temperature, pressure, atmosphere, the erosion of smoke, molten metal and slag on the refractories in the use process.
In order to improve the creep of refractory, it is important to improve its chemical mineral composition and fiber structure. Measures can be taken to improve the purity of raw materials, formulate a reasonable particle gradation, increase the molding pressure, properly increase the firing temperature and extend the holding time.
Erosion Resistance
Erosion resistance refers to the ability of refractory to resist the erosion and erosion of various erosion media at high temperature. Due to the diversity and complexity of erosion media, the test methods for studying the corrosion resistance of refractories are also different. The commonly used test methods are slag resistance, acid resistance, alkali resistance, liquid glass corrosion resistance and co corrosion resistance.
Corrosion resistance is a very important index to measure the resistance of refractory materials to chemical corrosion and mechanical wear, which is of great significance for the formulation of correct production process and the rational selection of refractory materials.
There are internal and external factors affecting the corrosion resistance of refractories. The internal factors mainly include: the chemical and mineral composition of the refractory, the structure and other properties of the refractory; The external factors include the nature of the erosion medium, the service conditions (temperature, pressure, etc.) and the interaction between the erosion medium and the refractory under the service conditions.
Slag Resistance
The ability of refractory materials to resist slag penetration, erosion and erosion at high temperature.
Acid Resistance
Acid resistance is the ability of refractory to resist acid medium. Sulfuric acid is generally used as an aggressive agent to determine the acid resistance of refractory products.
Alkali Resistance
Alkali resistance is the ability of refractory to resist alkali attack at high temperature. There are two methods to determine the alkali resistance of refractories, i.e. mixed erosion method and direct contact melting erosion method, usually using anhydrous K2CO3 as the erosion medium.
Resistance to Glass Melt Erosion
Corrosion resistance of glass melt is the ability of refractory materials used in glass furnace to resist the corrosion and erosion of glass melt.
Co Resistance
Co corrosion resistance refers to the ability of refractory materials to resist cracking or disintegration in CO atmosphere.
Oxidation Resistance
Oxidation resistance refers to the ability of carbon containing and other non oxide refractories (mainly materials containing carbides, borides, nitrides, Sialon, alon, etc.) to resist oxidation under high temperature oxidation atmosphere.
Hydration Resistance
Hydration resistance is the ability of alkaline refractories to resist hydration in the atmosphere. Cao and MgO in alkaline refractories, especially Cao, are very easy to absorb moisture and hydrate in the atmosphere, generate calcium hydroxide, and make the products loose and damaged.
Vacuum Resistance
The vacuum resistance of refractories refers to their durability when used under vacuum and high temperature.