When selecting magnesia-alumina bricks, focus on the three key factors: ingredient ratio, key performance indicators, and compatibility with the intended use scenario. Ensure their high-temperature resistance, thermal shock resistance, and corrosion resistance meet actual requirements.
Ⅰ. Screening Key Ingredients and Performance Indicators
The composition and performance directly determine the quality of magnesia-alumina bricks.
Product test reports should specifically verify the following:
MgO and Al₂O₃ content: This is the foundation of brick performance, and the ratio must be tailored to the intended use scenario.
The higher the MgO content, the greater the brick’s resistance to high temperatures and alkaline slag corrosion. Generally, high-quality magnesia-alumina bricks have an MgO content of ≥75%.
Al₂O₃ primarily enhances thermal shock resistance, and its content is typically between 5% and 15%. A higher content reduces high-temperature strength, while a lower content results in insufficient thermal shock resistance.
Bulk density: This reflects the density of the brick; a higher value indicates greater corrosion resistance.The bulk density of ordinary magnesia-alumina bricks must be ≥2.9g/cm³, while bricks used in high-temperature critical areas (such as the firing zone of a cement kiln) must be ≥3.0g/cm³.
Compressive strength at room temperature: This ensures the structural stability of the brick during transportation, masonry, and initial use. A strength of ≥35MPa is generally required. Lower strength can easily lead to breakage.
Thermal shock resistance: This assesses the brick’s ability to withstand sudden temperature changes and should be selected based on the operating method.
Batch kilns prioritize bricks with good thermal shock resistance. Typically, a strength loss of ≤20% after 3-5 cycles of 1100°C water cooling is required.
Ⅱ. Appearance and Physical Condition Inspection
Visual inspection and simple manual testing can be used to initially eliminate products with obvious defects and reduce operational risks.
Surface Quality: The brick surface must be flat and uniform in color, free of cracks, holes, impurities, or spots. Edges must be free of chipped corners or broken edges, as these increase the risk of spalling during use.
Dimensional Accuracy: Use a tape measure to measure length, width, and height. Deviations must comply with industry standards. Inaccurate dimensions can result in excessive gaps in the masonry, affecting the kiln’s airtightness.
Structural Solidity: Tap the brick and it should make a crisp sound. If it sounds dull, it may be loose or hollow inside and should be avoided.
Ⅲ. Precise Matching Based on Application Scenario
The performance requirements of magnesia-alumina bricks vary significantly across different industrial scenarios, requiring targeted selection to avoid wasted or insufficient performance.
Cement rotary kiln firing zones require refractory bricks that are resistant to high temperatures, alkali corrosion, and wear. Magnesia-alumina bricks with a high MgO content (≥80%), high bulk density, and high wear resistance are recommended.
Glass furnace regenerators require resistance to thermal shock and alkaline gas corrosion. Therefore, bricks with a moderate Al₂O₃ content (8%-12%) and good thermal shock resistance are recommended.
Non-ferrous metal smelting furnaces require resistance to slag corrosion and high temperatures. Therefore, bricks with high density and low impurities (Fe₂O₃ ≤ 1.5%) are recommended.