Firing Hollow Bricks with High Plasticity Clay: Overcoming Core Under-Firing via Continuous Tunnel Kiln Technology

Firing Hollow Bricks with High Plasticity Clay: Overcoming Core Under-Firing via Continuous Tunnel Kiln Technology

Industry Pain Points: Causes of Core Under-Firing and Black-Heart in Central Asian Hollow Bricks

During the modernization of the Central Asian construction market, fired hollow bricks and porous bricks with high hole-opening rates have progressively replaced traditional solid red bricks. However, local clay in Central Asia typically features high plasticity and interleaved carbonate minerals, presenting severe challenges to the firing process.

When firing hollow bricks with high hole-opening rates, any non-uniformity in the kiln's internal thermal field across its cross-section causes thermal energy to only vitrify and densify the outer walls. Concurrently, the complex geometric structure of the hollow brick's inner walls restricts internal airflow penetration, leaving the core of the internal holes in a chronic negative temperature variance state (below the target firing temperature). If physical moisture and organic matter cannot fully oxidize and escape before the outer walls seal, it directly leads to core under-firing (black-heart defects) and substandard compressive strength, severely impacting the plant's product yield.

Technical Solution: Three-Zone Thermal Balancing via Continuous Tunnel Kilns

Relying on outdated intermittent kilns or manual operations makes it difficult to resolve the thermal sensitivity of thin-walled, high-porosity green bodies. Implementing a continuous tunnel kiln with digital zoning allows for precision control over the thermotechnical parameters across the preheating, firing, and cooling zones, fundamentally eradicating core under-firing defects.

Preheating Zone: Extending Time Windows for Synchronous Inner Wall Dehydration

Inside the preheating zone of the continuous tunnel kiln, the system manages the overall charging and firing cycle to approximately 20 hours. Compared to traditional large kilns requiring 3-5 days of unmanaged slow-firing, this continuous system forces exhaust gases into a penetrative convection through the hollow brick cavities using top-blowing recirculation fans.

This directional airflow organization ensures that the inner rib walls and outer shell of the hollow bricks heat up uniformly and synchronously. This allows crystalline chemical water and volatile matter to exhaust fully before reaching the high-temperature zone, preventing the outer layers from sintering and closing prematurely, which would otherwise trap gases inside the core.

Firing Zone: Automated Burner Group Adjustment to Eliminate Thermal Dead Zones

The primary cause of core under-firing in hollow bricks is the presence of "insufficient bottom temperatures" or "central cold spots" across the kiln cross-section. The firing zone of the continuous tunnel kiln utilizes proportional adjustment technology for automated gas or oil burner groups.

The burners are arranged in staggered, multi-level configurations on both sides of the kiln wall, adjusting the combustion gas injection velocity and air-fuel ratio in real-time via digital systems. Consequently, even the hollow bricks located at the lowest deck of the kiln car receive thermal energy identical to those on the top deck. Because temperatures in the preheating, firing, and cooling zones are consistently maintained within stable, preset parameters, thermal dead zones are eliminated, resulting in uniform vitrification and consistent compressive strength.

Equipment Selection Guide: System Specifications for Central Asian Conditions

To address the Central Asian inland environment and the stringent processing demands of hollow bricks, the following parametric indicators are highly recommended during equipment selection and technical evaluation:

• Energy Metrics (Energy Efficiency): Because hollow bricks suffer from slow thermal penetration, traditional kilns incur extreme energy overheads. This modern tunnel kiln utilizes the counterflow principle for waste heat recovery, channeling hot air from the cooling zone back to the front end, achieving approximately 50-60% fuel savings.

• Kiln Lifespan and Integrity (Structural Lifespan): Cold Central Asian climates are highly suited for prefabricated steel structure (steel-assembled) kiln bodies. Because they are immune to sudden thermal shocks, both the kiln shell and interior furniture remain exceptionally durable, pushing the overhaul maintenance cycle to 5-7 years and drastically cutting down international component logistics downtime.