Magnesia carbon brick is a kind of magnesia refractory material. Magnesia refractory material has high refractoriness and strong ability to resist alkaline slag. The most widely used and most important type of refractory material is also the most commonly used refractory material in high temperature zones such as glass melting furnace regenerators and cement kilns. Graphite is used as the main raw material for the production of magnesia-carbon bricks because it has excellent physical properties: non-wetting to slag, high thermal conductivity, low thermal expansion, no eutectic with refractory materials at high temperatures, and high refractoriness. The following briefly introduces the factors that affect the test results of apparent porosity and compressive strength, as well as the accurate test results detected in accordance with national standards.
1. Factors affecting the test results of apparent porosity
Apparent porosity is an important index to evaluate the quality of refractory products. It can not only reflect the compactness of refractory materials, but also characterize whether its manufacturing process is reasonable. The inspection of apparent porosity is based on GB/T2997-2000 “Test method for bulk density, apparent porosity and true porosity of dense shaped refractory products”.
1) The influence of sample preparation
Sample preparation is based on GB/T7321-2004 “Preparation Method for Samples of Shaped Refractory Products”. This method stipulates that the principle of determining the sample preparation position is to take samples from the weak part of the refractory product or the key part of use. The preparation part of the apparent porosity sample is the corner of the sample. Because the pressure on the corners is smaller than that of the middle part during the molding process, it is the weak part of the sample, so samples are cut from the corners of the sample for inspection.
2) The influence of moisture
During the drying process, the temperature is well controlled, and the mass before and after drying is accurately weighed to make the sample reach a constant weight. The difference between the last two weighings is not more than 0.1%, and the water is drained to reduce the interference of water on the results.
3) The influence of immersion liquid
In the inspection project, kerosene was selected as the immersion liquid. The reason for choosing kerosene as the immersion liquid was that the wettability of water to graphite was poor. By selecting water and industrial pure kerosene as different immersion liquids, the study of magnesia carbon bricks with a carbon content of 14% to 18% shows that the apparent porosity measured with industrial kerosene as the immersion liquid is about 14% higher than that of water.
Through the above analysis, it can be seen that the real data of the apparent porosity of magnesia carbon bricks can be obtained by paying attention to the above influencing factors in the test.
2. Factors affecting the test results of compressive strength
Although refractory materials are rarely damaged by static load at room temperature during use, the compressive strength can indirectly evaluate the wear resistance and impact resistance of the product, and the bonding strength of the unfired product. Therefore, the normal temperature compressive strength of refractory materials is a common inspection item for judging the quality of products. The test basis for compressive strength is GB/T5072-2008 “Test method for compressive strength at room temperature”.
1) The influence of sample preparation
The samples for the compressive strength at room temperature and the apparent porosity are taken from the corners of the samples, and the weak parts of the samples are taken. The sample is drilled from the pressure-bearing surface of the product, because graphite is a scaly crystal, and there is a large difference between the parallel and vertical directions. During the pressing process of the green body, the scaly crystals of graphite are easily arranged perpendicular to the pressing direction, and the product has a higher compressive strength in the pressing direction.
2) Influence of flatness
The compression surfaces at both ends of the drilled cylindrical sample should be ground flat. If the surface flatness is poor, the force on the surface of the sample is uneven, and the local stress is concentrated, huge oblique cracks will be generated, which cannot reflect the true compressive strength of the sample.
3) The influence of moisture
During the drying process, the temperature is well controlled so that the sample reaches a constant weight, and the water is drained to prevent the sample from being damp.
4. Conclusion
In the inspection process, we strictly follow the national standards, pay attention to every detail in the test process, and obtain data that accurately reflect the samples. Provide accurate inspection data for enterprises and fulfill their supervisory responsibilities.