Sintered Brick Drying Mechanism: Four Key Stages That Dominate Brick Quality and Production Efficiency
Sintered brick drying is a combined process of heat transfer and mass transfer, which runs through the whole post-molding production process. Cracking, deformation and low structural strength of finished bricks are mostly caused by improper control of the drying process, which breaks the balance of heat and moisture migration inside brick green bodies.
Inside the drying chamber, waste heat and hot flue gas act as drying media. The media transfers heat to the surface of wet green bodies via heat exchange, and heat is further conducted to the interior of the bricks — this is the complete heat transfer process. Meanwhile, the heated surface moisture evaporates into the air, forming external diffusion. Driven by moisture gradient, internal moisture continuously moves toward the surface, which is defined as internal diffusion. In the whole sintered brick drying process, heat transfer, internal diffusion and external diffusion proceed simultaneously and interact with each other.
When the drying media stays stable and green bodies have no chemical changes, standard sintered brick drying can be divided into four continuous stages, each with unique characteristics in drying speed and physical state.
1. Acceleration Stage
New green bodies keep entering the drying chamber. The surface temperature of bricks quickly rises to the wet-bulb temperature of drying media, and moisture evaporation speed increases rapidly. This stage lasts for a short time with limited water removal. At this moment, the drying media features the lowest temperature and the highest humidity.
2. Constant Speed Drying Stage
This is the core period of water removal in sintered brick drying. Internal moisture continuously supplements the evaporated surface moisture, keeping the green body surface wet all the time. The drying speed and surface temperature remain stable, and free water evaporates efficiently. As more water vapor is produced, the humidity of drying media rises gradually.
3. Deceleration Drying Stage
After surface free water is fully removed, green bodies stop shrinking. The subsequent drying only removes deep residual moisture and forms more internal pores. In this stage, drying speed and heat consumption drop obviously, while the surface temperature of brick green bodies keeps rising.
4. Equilibrium Stage
When the moisture inside and outside green bodies reaches balance with the temperature and humidity of drying media, the drying speed drops to zero, and the whole drying process ends. The final residual moisture of bricks is totally determined by the parameters of drying media.
It is important to note that the four stages of sintered brick drying are not fixed. According to raw material properties, equipment conditions and production environment, the duration and transition points of each stage will change accordingly. Manufacturers need to test and summarize customized drying curves to match their own production lines.
