pipe fittings Hough section,Pipeline components Hough portion,Pipe joint Hough section,FRP big-diameter tubing,GRP Sewage Pipe Zhejiang Huafeng new material Co., Ltd. , https://www.cnhfpipe.com
Analysis and Discussion on Optimizing Characteristics of Firebrick
Some high-temperature kilns in China use imported refractory materials for their masonry linings, capable of withstanding temperatures up to 1760°C and delivering excellent performance. However, these imported refractory bricks come at a high cost. To address this issue, we developed domestically produced corundum-mullite lightweight firebricks that match the properties of the imported ones. We conducted extensive research on the factors influencing their performance, focusing particularly on the impact of raw material composition.
The selection of raw materials is crucial, as impurities significantly affect the high-temperature performance of corundum-mullite lightweight bricks. Therefore, we aimed to use materials with a high content of (Al₂O₃ + SiO₂) and minimal other impurities. The initial determination of the three types of Al₂O₃ additions was based on ensuring that the C-alumina added would react with most of the clay below 1600°C to form mullite. The A-alumina addition needed to be sufficient to react with the SiO₂ from the raw materials, forming mullite with an Al₂O₃ content of approximately 72.8%. This reaction should be completed during firing at 1700°C. The amount of corundum added was adjusted based on the proportion of ultrafine powder (10 µm) during the first firing. After reacting with other materials to form mullite, any remaining corundum should continue to react with Al₂O₃ during long-term use in a furnace operating at 1750°C, producing a mullite solid solution with about 78% Al₂O₃, with a slight excess.
Based on this approach and the minimum clay content required for shaping the brick, seven experimental formulations were designed. In all seven, the four raw materials were used in equal amounts: 13% Suzhou soil, 4% montmorillonite clay, 15% sillimanite, and 13% C-alumina. The only difference was the ratio of A-alumina and fused corundum. Sample No. 1 contained 10% A-alumina and 45% fused corundum. From No. 1 to No. 7, the A-alumina increased by 5% each time, while the fused corundum decreased by 5%. Sillimanite had a particle size of 74 µm and was used to decompose and generate mullite around 1600°C, helping to offset firing shrinkage through volume expansion. C-alumina and A-alumina had a particle size of 10 µm, while fused corundum had a particle size of 43 µm. Sawdust was added, followed by extrusion molding and drying in an experimental kiln at 1700°C for 20 hours. The fired samples had a controlled volume density of 1.42 g/cm³. Key performance metrics such as linear shrinkage, deformation softening temperature under 0.1 MPa pressure, and line change after reburning at 1700°C for 12 hours were measured.
As the amount of corundum increased, both the firing line shrinkage and the reburning line shrinkage decreased. However, the load softening temperature did not show a linear relationship with the amount of corundum added. Instead, it reached its highest value when the ratio of A-alumina to corundum was 20:35. This is due to the poor reactivity of corundum; when too much is added, both the liquid phase and residual corundum increase, which reduces the load softening temperature.
We also studied the effects of firing temperature and holding time on the performance of the bricks, as these are key factors affecting production costs. Under the condition that product performance meets usage requirements, the firing temperature should be as low as possible, and the holding time should be minimized. For example, recipe No. 3 was fired at various temperatures (1600°C, 1620°C, 1640°C, 1660°C, 1680°C, 1700°C, 1720°C, 1740°C, 1760°C, and 1780°C) for 20 hours, then re-fired at 1700°C for 12 hours. The test included measurements of heavy burn line change and 0.1 MPa load softening temperature.
Additionally, the effect of holding time on high-temperature performance was evaluated. Sample No. 3 was sintered at 1700°C for different durations (4h, 8h, 12h, 16h, 20h, 24h, 28h, and 32h). After firing, the samples were tested for load softening temperature at 0.1 MPa and for line change after reburning at 1700°C for 12 hours. As the holding time increased, the reburn line shrinkage rapidly decreased, and the load softening temperature significantly increased. However, after 20 hours of holding, the changes leveled off, indicating that further increases in holding time had minimal additional benefit.