Cracks in Sintered Brick Causes and Professional Fixes
Tensile and compressive cracks are typical green brick defects, mainly appearing on the strip surfaces of lower-layer and horizontal bricks in the green brick stack, manifesting as large-scale fracture cracks. This type of crack is closely related to green brick strength, drying environment, stacking mode and equipment operation, and is a key quality problem that needs to be controlled in the drying and pre-sintering stage of sintered bricks.
Excessive molding moisture is the most common cause of tensile and compressive cracks. High moisture content will significantly reduce the structural strength of green bricks, making them prone to compression fracture under the pressure of upper brick layers during stacking. The most direct solution is to reasonably reduce the molding moisture content and enhance the compactness and structural strength of green bricks.
Low molding temperature also leads to tensile cracks. Low-temperature green bricks will absorb moisture and soften after entering the drying chamber, and then crack due to rapid shrinkage under sudden high-temperature heating. Production personnel need to real-time monitor the temperature of mud strips extruded from the machine mouth and adjust the thermal parameters of the drying chamber according to seasonal and environmental changes to avoid sharp temperature fluctuations.
Poor plasticity of raw materials will reduce green brick strength, resulting in compression cracks during stacking and transportation. For raw materials with insufficient plasticity, manufacturers can add high-plasticity auxiliary materials and strength-enhancing admixtures, or appropriately reduce the number of brick stacking layers to lower the bearing pressure of lower green bricks.
Uneven mixing of plastic and non-plastic raw materials will cause inconsistent shrinkage of green bricks. Different raw materials have different shrinkage coefficients during drying, and ununiform batching will produce internal tensile stress and crack the brick body. Strengthening raw material pre-mixing and ensuring consistent mixing uniformity are the fundamental solutions to this problem.
Excessively high plasticity of mixed materials is also a major risk factor. High-plasticity mud has a large linear shrinkage rate, and rapid drying in the drying chamber will directly cause tensile cracks. Adding inert materials such as gangue, slag and hard shale can effectively reduce the overall plasticity of the mixture, stabilize shrinkage parameters and avoid cracking.
Unreasonable kiln car configuration and high residual temperature are important external causes. Insufficient kiln cars lead to green bricks being stacked on high-temperature kiln cars, and rapid water loss under high temperature causes crack damage. Manufacturers can increase the number of kiln cars, optimize sintering operation to reduce discharging temperature, or install large-hole heat-dissipating cushion bricks on kiln cars to accelerate heat dissipation.
Uneven kiln car surfaces and unsmooth tunnel kiln tracks will cause vibration and shaking of kiln cars during operation, leading to compression and fracture of green brick stacks. Regular trimming of kiln car table surfaces and calibration of tunnel kiln and circulating track flatness can ensure stable kiln car operation.
In addition, irregular top car operation will cause collision between kiln cars, resulting in severe vibration, green brick fracture or stack collapse. Standardizing operation specifications and improving the professional skills of operators can effectively avoid man-made crack defects.
