Core Restricting Factors of Fired Brick Output and Quality
In the modern production of clay fired bricks, the drying process stands out as the most critical procedure that restricts the production capacity and finished product quality of fired bricks, directly determining the economic benefits of brick manufacturing enterprises. Many brick factories overly focus on the firing process and ignore the importance of green brick drying, which becomes the main bottleneck restricting long-term production growth.
Whether it is small-scale brick plants adopting natural drying and annular kiln firing, medium-sized production lines with secondary stacking and tunnel kilns, or modern large-scale one-time stacking tunnel kiln production systems, the drying of wet brick bodies is always the core link affecting final yield and quality. The raw material mixing, molding and high-temperature firing processes indeed affect production efficiency, but the drying procedure has become the primary factor restricting enterprise benefits in current brick production practices.
The moisture inside green bricks is the key object of the drying process. Brick body moisture is divided into three types: free moisture, adsorbed moisture, and chemically bound moisture. Free moisture, also known as mechanical moisture, exists between raw material particles and capillaries with weak binding force, which is easy to remove and will cause volume shrinkage during drying. Adsorbed moisture adheres to the surface of material particles, changing reversibly with ambient temperature and humidity without causing brick body deformation. Chemically bound moisture is tightly combined in mineral molecular structures, requiring a high temperature of 430℃ to 750℃ in the kiln preheating section for removal, with a low overall content.
In actual brick manufacturing production, green brick moisture mainly comes from raw material inherent moisture and artificial water addition during primary mixing, secondary mixing and extrusion molding. To pursue short-term output, many manufacturers reduce extrusion pressure, resulting in decreased green brick strength and excessive moisture content. Unreasonable high stacking operation also exceeds the bearing capacity of bottom bricks, greatly reducing the finished product rate of fired bricks. Therefore, enterprises should adopt low-moisture molding technology to ensure non-deformation and non-cracking of green bricks on kiln cars.
The brick drying process is a simultaneous heat transfer and mass transfer reaction completed by drying media (waste heat and hot flue gas). The hot medium transfers heat to the brick surface first, then heat conducts inward, while internal moisture diffuses outward to the surface and evaporates into the air. This process includes external diffusion (surface moisture evaporation) and internal diffusion (internal moisture migration).
Under stable drying conditions and without chemical changes of brick bodies, drying is divided into four stages: accelerated drying stage, constant-rate drying stage, falling-rate drying stage, and equilibrium stage. The drying speed is ultimately determined by the heat transfer and moisture diffusion efficiency, which are affected by the temperature, humidity and airflow velocity of drying media. Sufficient air volume is more important than high temperature alone for efficient drying; high-temperature and low-air-volume drying leads to poor effect, while moderate temperature with sufficient airflow can achieve ideal drying results.
FAQ
Q1: What is the biggest factor affecting fired brick production efficiency?
A1: The green brick drying process is the core restricting factor for fired brick production efficiency and quality, far more critical than the firing link in modern brick production lines.
Q2: What are the three types of moisture in fired green bricks?
A2: Green brick moisture includes free moisture, adsorbed moisture and chemically bound moisture, with different removal conditions and effects on brick quality.
Q3: How to improve the finished product rate of fired bricks?
A3: Adopt low-moisture extrusion molding technology, control reasonable green brick stacking height, and optimize drying medium temperature and airflow parameters.
