Yingfeng Machinery-More Than 30 Years Experience In Clay Brick Making Machine ,Tunnel Kiln, Rotary Tunnel Kiln.
The production of fired bricks is a tightly integrated process combining raw material proportioning, forming, drying, and high-temperature firing. Its core principle is to trigger physical and chemical reactions at high temperatures to sinter the brick body, thereby endowing it with high strength and durability. The full standard production process for fired bricks is as follows:
Main raw materials (clay, shale, coal gangue) are crushed and ground by crushers and pulverizers,then blended with water in a mixer, with impurities sieved out.
The mixed clay material is piled up for ageing. It is then fed into a vacuum extruder to extrude clay strips, which are cut into standard green bricks by an automatic brick cutter. The wet green bricks are neatly stacked on kiln cars manually or by automatic stacking machines before being sent to the drying kiln.
Freshly formed green bricks have a high moisture content (approximately 15%–25%). Direct firing would cause rapid water evaporation and crack the bricks. Low-temperature drying is therefore essential. Stacked wet green bricks are conveyed into a tunnel drying kiln and dried at a low temperature using waste heat from the firing process to control moisture and prevent cracking.
Dried green bricks are transported on kiln cars into a tunnel kiln or annular kiln for gradient heating and sintering at 900–1100°C. The high temperature fuses and shapes the raw materials, hardening and strengthening the bricks.
Bricks are slowly cooled in the dedicated cooling zone inside the kiln. After exiting the kiln, qualified products are sorted manually or mechanically, then stacked for delivery from the factory.
Collapse often begins before the bricks even enter the kiln if the green body lacks physical integrity.
Moisture Threshold: The residual moisture content must be kept below 6%. High moisture levels drastically reduce the compressive strength of the bricks, causing the bottom layers to buckle under the weight of the stack.
Material Aging: Clay requires at least 3 days of aging to ensure uniform plasticity and water distribution. Insufficient aging leads to internal stresses and a fragile structure.
Mechanical Density: Ensure an extrusion pressure of ≥40kg/cm² to increase the density of the green body, making it more resistant to deformation at high temperatures.
Stacking is not just about volume; it is about managing gravity and thermodynamics.
The "Four-Point" Standard: Stacks must be level, stable, vertical, and straight. Any minor deviation in the center of gravity will be amplified as the bricks soften in the heat.
Airflow Optimization: Follow the principle of "Dense Edges, Sparse Centers" and "Dense Tops, Sparse Bottoms." This balances the temperature across the kiln cross-section, preventing the edges from over-firing while the center remains under-fired.
Load Management: Due to the high sensitivity of clay, limit the stacking height to 12 layers or fewer. This minimizes the static pressure on the base bricks.
This is the most common zone for collapses. If moisture is not evacuated efficiently, the bricks effectively "steam" and lose their rigidity.
Inlet Temperature Control: Keep the initial drying air below 116°C. Temperatures above this threshold cause the surface to harden too quickly, trapping steam inside and creating internal pressure.
Heating Rate: Maintain a steady rise of 6–8°C/h. Sudden temperature spikes, especially in winter, can cause thermal shock and structural failure.
Ventilation and Pressure: Ensure the exhaust fan provides sufficient negative pressure. Poor ventilation causes moisture to linger and re-condense on the bricks, leading to "soggy" bricks that collapse instantly.
Once the bricks reach high temperatures, preventing them from entering a pyroplastic state (melting) is vital.
Anti-Overfiring Measures: Strictly monitor the sintering peak. Exceeding the clay's softening point leads to viscous flow, where the bricks begin to behave like liquid and slump.
Internal Fuel Ratio: Control the amount of internal additives (coal powder or gangue). Excessive internal fuel generates uncontrollable heat within the stack, causing the bricks to "melt from the inside out."
Visual Monitoring: Use inspection holes to watch for "white-out" conditions or "shimmering/swaying" stacks, which are immediate warning signs of imminent collapse.
The physical environment of the kiln must remain consistent to prevent mechanical triggers.
Track Leveling: Regularly inspect kiln car tracks. Uneven rails cause vibration and jolting, which can topple a stack that is already weakened by heat.
Kiln Structure Maintenance: Check for sagging roof bricks or protruding exhaust ports. Mechanical obstructions are a frequent cause of "domino-effect" collapses during car movement.
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