8 Core Processes to Produce High-Quality Fired Bricks from Low-Grade Coal Gangue | Defect Prevention Guide
Low-grade coal gangue features low plasticity, unstable calorific value and trace harmful impurities, making it difficult for traditional brick-making processes to produce qualified products. To convert inferior coal gangue into standard-compliant fired bricks, standardized process optimization and targeted quality defect prevention are essential in industrial production.
First, solving the low plasticity problem of coal gangue raw materials is the key to smooth molding. Most low-grade coal gangue is massive rock with a low plasticity index, which cannot be directly extruded and molded. Enterprises can adopt five mature improvement measures: crushing raw materials to 2mm or even 1mm ultra-fine particle size to optimize particle gradation; adopting 4.0MPa high-pressure vacuum extrusion equipment to adapt to low-plasticity raw materials; blending high-plasticity materials such as clay, shale and silt; heating mud with tunnel kiln waste heat steam to enhance mud activity; and implementing secondary vacuum mud refining to increase green body density and strength.
Second, the one-time stacking and firing process with separate tunnel drying chamber and tunnel kiln (smoke-heat separation technology) is the optimal production solution for full coal gangue fired bricks. This independent drying and firing system realizes separate regulation of green body drying and high-temperature firing, effectively avoiding cracking, deformation and other quality defects, and simplifies flue gas treatment to meet environmental protection emission standards.
In terms of appearance quality control, the multi-layer stacking of green bodies in one-time firing process is prone to black spot pressing flowers. The industry adopts two efficient solutions: low-temperature slow firing process to uniform heat conduction, and spreading thin sand on the green body surface or vertical-to-horizontal stacking adjustment to avoid surface pressing marks, ensuring the aesthetic appearance of finished bricks.
For common quality defects of low-grade coal gangue bricks, targeted technical solutions are available. Lime bursting caused by calcite and limestone impurities can be solved by ultra-fine crushing (particle size below 2mm) and rapid water saturation treatment of newly fired bricks. Efflorescence caused by soluble inorganic salts can be eliminated by extending high-temperature heat preservation time, converting soluble salts into insoluble silicates through full high-temperature reaction.
The black core fracture of internal combustion coal gangue bricks is another common problem, mainly caused by insufficient firing time, low temperature or premature surface firing leading to internal oxygen deficiency. By controlling the kiln heating rate and prolonging low-temperature pre-sintering time, the internal fuel of the green body can be fully burned with sufficient oxygen, completely solving the black core defect and improving the overall structural strength of finished bricks.
