Factors Affecting the Service Life of Kiln Furniture

The service life of Kiln Furniture is determined by its strength and thermal shock resistance. In addition, possible chemical reactions between the Kiln Furniture and the product it supports should be considered. So what are the factors that affect the service life of Kiln Furniture? Let's see together.

The following is a list of contents:

• Strength

• Thermal shock resistance

• Chemical pollution of Kiln Furniture

Strength

The compressive strength of inorganic materials is about 10 times the tensile strength. Therefore, the research is generally focused on its tensile strength, which is the weakest link of Kiln Furniture. There are more or less cracks in the actual material. The reasons for its formation are as follows:

1) Due to the existence of defects in the crystal microstructure, when subjected to external force, stress concentration will be caused by these defects, resulting in crack nucleation. For example, piling up, dislocation combination, intersection, etc. in dislocation motion can lead to crack nucleation.

2) Mechanical damage and chemical corrosion on the surface of Kiln Furniture materials form surface cracks. Such surface cracks are the most dangerous, and the propagation of cracks is often initiated by surface cracks.

3) Cracks are formed due to thermal stress. Most inorganic materials are polycrystalline and multiphase. The grains are oriented differently inside the material, and the thermal expansion coefficients of different phases are also different. This will cause stress concentration at the grain boundary or phase boundary due to the different expansion or contractions in each direction, resulting in cracks. generate. During the manufacturing and use process, when the high temperature is rapidly cooled, the thermal stress is caused by the temperature difference between the interior and the surface, resulting in the formation of cracks on the surface. In addition, Kiln Furniture materials, which undergo crystal transformations with temperature changes, can also cause cracks due to volume changes. Under the action of external force, stress concentration occurs near these cracks and defects. When the stress reaches a certain level, the crack begins to expand and leads to fracture. Therefore, the fracture is not the result of two parts of the crystal being pulled along the entire interface at the same time, but the result of crack propagation.

Thermal shock resistance

Thermal shock resistance, also known as thermal stability, refers to the ability of Kiln Furniture materials to withstand drastic changes in temperature without breaking. Since Kiln Furniture is subject to frequent thermal shocks during use, the thermal shock resistance of Kiln Furniture is the most critical parameter to determine its service life of Kiln Furniture. The thermal shock resistance of Kiln Furniture directly determines its service life.

At present, the theories describing the thermal shock resistance of materials mainly include thermal stress fracture theory and thermal shock damage theory. Thermal stresses in Kiln Furniture under thermal shock conditions are caused by temperature differences between the surface and interior of the material or between parts of the material. The theory of thermal stress fracture resistance starts from the point of view of thermoelasticity and takes the balance between thermal stress and the inherent strength of the material as the criterion for thermal shock failure. It is believed that after the thermal stress in the material reaches the limit of tensile strength, the material will produce cracking, once a crack nucleates can lead to the destruction of the material. According to the theory of thermal stress fracture, when the actual firing conditions of the Kiln Furniture and the geometric shape of the product are determined, the thermal shock resistance of Kiln Furniture is proportional to its flexural strength and thermal conductivity; it is proportional to its effective elastic modulus, the thermal expansion coefficient is inversely proportional. This theory is more suitable for fine-grained and dense ceramics, but not for refractory materials with larger particles and more pores. An obvious example is that some refractory bricks used for furnace construction often have the best thermal shock resistance when it contains 10% to 20% porosity. This is because the existence of pores causes the uneven structure of the refractory material, which reduces the strength and thermal conductivity of the material, thereby reducing the two thermal stress fracture factors, making thermal stress easy to cause cracks. Cracks are not easy to expand. Therefore, the material can still maintain considerable strength after the crack is cracked.

Chemical pollution of Kiln Furniture

Often, when Kiln Furniture is contaminated with glazes or metals from the products it carries, it reduces its useful life. Atmospheres in the kiln such as glaze steam, metal steam, or electro-magnetic ceramic steam can also seriously shorten the service life of Kiln Furniture. These effects become more pronounced when the corrosivity of the material increases during firing. The thermally activated diffusion process greatly enhances the interaction between the Kiln Furniture and the product and the consequent chemical reaction, which severely shortens the service life of the Kiln Furniture. For example, in the firing of lead titanate electronic ceramic materials, the destructive effect of lead vapor is a good example. At this point, the chemical contamination of the Kiln Furniture represents the parameters that determine the service life of Kiln Furniture. The use of zirconia Kiln Furniture, liners, or coatings is essential in this case. Another well-known phenomenon is the effect of silicon carbide refractories when used in an oxidizing atmosphere. In this case, it is best to use oxide-based Kiln Furniture materials such as cordierite and mullite.

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