Compressive strength of refractory materials

The compressive strength of refractory materials is one of the important indicators to measure their quality and performance. It is related to the service life of refractory materials and directly affects the safety and stability of industrial furnaces and related equipment. The following is a detailed analysis of the compressive strength of refractory materials:

1. Definition and classification

 Crushing strength, also known as compressive strength, refers to the ultimate load that refractory materials can withstand per unit area at a certain temperature. It is one of the important performance indicators to measure the quality of refractory materials, and indirectly reflects the organizational structure of the product, such as density, uniformity, sintering, etc. It is usually divided into normal temperature compressive strength and high temperature compressive strength.

Normal temperature compressive strength: refers to the value measured at room temperature.

High-temperature compressive strength: The sample is heated to a specified temperature for a pressure test, and the result obtained is called high-temperature compressive strength at that temperature.

2. Influencing factors

 Chemical composition: Different chemical compositions and mineral phases can significantly affect the compressive properties of the material. By optimizing the chemical composition and selecting appropriate refractory raw materials and additives, the compressive strength of the material can be effectively improved.

 Microstructure: The size, shape, distribution and porosity of grains all affect the compressive strength of the material. Materials with fine and evenly distributed grains usually have higher compressive strength because fine grains can reduce defects within the material and improve the density and uniformity of the material. Materials with higher porosity will have lower compressive strength because the pores reduce the effective load-bearing area of the material.

 Production process: including the mixing, molding, drying and sintering of raw materials, all of which will have an important impact on the compressive properties of the material. For example, during the sintering process, precise control of the sintering temperature and holding time can obtain fine and uniform grains and low porosity, thus improving the compressive strength of the material.

 Temperature: Generally at high temperatures, the compressive strength of materials decreases. This is because high temperatures will cause changes in the microstructure inside the material, such as grain growth and pore increase, thereby reducing the material's compressive resistance. However, some special types of refractory materials, such as refractory steel, can maintain high compressive strength at high temperatures.

3. Test method

 Normal temperature compressive strength test: According to the Chinese national standard "Test Method for Normal Temperature Compressive Strength of Dense Shaped Refractory Products" (GB5072), cut a cube or cylinder sample from the refractory product, and press it on the pressure testing machine at the specified pressurization rate , pressurize the sample until it is destroyed, record the maximum pressure value, and calculate the pressure per unit area, in MPa.

 High-temperature compressive strength test: During the test, the pressure testing machine should be equipped with a high-temperature heating furnace. The sample is heated in the furnace at a specified heating rate until it reaches the specified temperature, and after being kept warm for a certain period of time, the sample is pressurized until it is destroyed. The rest is the same as the method for measuring the normal temperature compressive strength.

4. Compressive strength values of common refractory materials

The following are the normal temperature compressive strength values (MPa) of some common refractory materials:

Clay bricks for blast furnace: greater than 49.0

Clay bricks for hot blast stoves: greater than 19.6

Large clay bricks for glass melting furnaces: greater than 34.3

General purpose high alumina bricks: greater than 49.0

Hot blast stove high alumina brick: greater than 39.2

High alumina bricks for electric furnace cover: greater than 58.8

Coke oven silica brick: greater than 19.6

Silica bricks for glass melting furnace: greater than 24.5

Ordinary magnesia brick: greater than 39.2

Magnesia-alumina bricks for open hearth furnaces: greater than 29.4

Magnesia chrome brick: greater than 24.5

5. Measures to improve compressive strength

In order to improve the compressive strength of refractory materials, the following measures can be taken:

 1. Optimize the chemical composition of the material and select appropriate refractory raw materials and additives to enhance the material’s compression resistance.

 2. Precisely control the production process to obtain fine and uniform grains and low porosity, and improve the density and uniformity of the material.

 3. Appropriate heat treatment can also enhance the compressive strength of the material.

 4. In some applications, the compressive strength of refractory materials can also be improved through external reinforcement measures, such as the use of metal anchors.

 To sum up, the compressive strength of refractory materials is an important indicator of their quality and performance. By optimizing chemical composition, controlling microstructure, improving production processes, and taking appropriate heat treatment measures, the compressive strength of refractory materials can be effectively improved, thereby extending their service life and improving the safety and stability of industrial furnaces and related equipment.