Main mechanical properties of refractory materials

Mechanical properties of refractory materials

Refractory materials are structural materials used to construct the lining of industrial furnaces. During long-term use, the material is subjected to the dual effects of temperature and external forces, and various stresses and changes will occur in response. The ability of refractory materials to resist these stresses and strains is called the mechanical properties of refractory materials. In engineering, the main technical indicators for evaluating the mechanical properties of refractory materials are: mechanical strength at room temperature, mechanical strength at high temperature, load softening temperature, high temperature creep, elastic modulus and wear resistance.

Mechanical strength of refractory materials at room temperature

The critical stress of refractory materials that can resist external forces without damage at room temperature. It is usually expressed by three technical indicators: room temperature compressive strength, room temperature flexural strength and room temperature shear strength.

Shear strength at room temperature

The critical shear stress of refractory materials against shearing at room temperature. Except for some refractory clays, this indicator is generally not measured.

High temperature mechanical strength of refractory materials

1. High temperature compressive strength, the critical compressive stress of refractory materials at high temperature (in MPa), the calculation formula is the same as the compressive strength at room temperature.

2. High temperature flexural strength, the critical bending stress of refractory materials resisting bending moment at high temperature (in MPa), the calculation formula is the same as the flexural strength at room temperature.

3. High temperature shear strength, the critical shear stress of refractory materials resisting shear force at high temperature (in MPa), except for some refractory slurries, this indicator is generally not measured.

Refractory material softening temperature under load

The corresponding temperature at which refractory materials produce different degrees of deformation under high temperature and constant load is called the load softening temperature of refractory materials, also known as load change temperature or simply load softening point. It reflects the degree of strain of refractory materials under constant load at a certain temperature, and is one of the important quality indicators that characterize the high-temperature structural strength of refractory materials. The load softening temperature of refractory materials can be measured by two experimental methods: heating method and insulation method. The main factors affecting the load softening temperature of refractory materials are: chemical mineral composition and organizational structure; the number and interaction of crystal phase and liquid phase and the viscosity of liquid phase; macroscopic organizational structure, such as density, porosity, etc. Generally speaking, the load softening temperature of refractory materials with network-like crystal structure is higher, and the load softening temperature of refractory materials with island-like structure distributed in the liquid phase is lower; when the amount of liquid phase in the material is large or the viscosity of the liquid phase is low, its load softening temperature is low; the higher the porosity, the lower the load softening temperature.

High temperature creep

When refractory materials are subjected to long-term action of a constant force exceeding their critical strength at high temperature, they deform, and the amount of deformation increases with time. This phenomenon is called high-temperature creep. Material damage due to creep is called creep fracture. The relationship between the amount of deformation and time of refractory materials under the long-term action of constant temperature and force characterizes the high-temperature creep of the material. According to the type of application, it can be divided into high-temperature compression creep, high-temperature tensile creep, high-temperature bending creep and high-temperature torsion creep. At present, my country mainly uses high-temperature compression creep to represent the high-temperature creep of refractory materials, that is, the relationship curve between the amount of deformation of the material and time under the long-term action of a specified constant temperature and pressure. It can also be expressed as a creep rate, or the time required to achieve a certain specified deformation to represent its high-temperature creep.

Elastic modulus

The elastic modulus of refractory materials is an important reference for characterizing the structural characteristics and mechanical properties of refractory materials. Generally, refractory materials with higher compressive strength and flexural strength also have larger elastic modulus, and the elastic modulus of refractory materials is roughly proportional to their wear resistance. The main methods for determining the elastic modulus of refractory materials are the audio frequency method and the static load method.

Wear resistance of refractory materials

The ability of refractory materials to resist mechanical erosion and membrane action of solid materials, gases and melts is called refractory wear resistance, also known as wear resistance. The wear resistance of refractory materials depends on the hardness of particles in the material, the bonding strength between particles and the existence of voids. Therefore, refractory materials with dense and uniform structure, low porosity, high hardness and high strength usually have good wear resistance. In practical applications, these properties can also be used to judge and evaluate the wear resistance of refractory materials. If it is necessary to directly measure the wear resistance of refractory materials, grinding and sandblasting methods can be used.