Common Fired Brick Block Quality Defects, Root Causes and Practical Solutions
Fired Bricks and blocks are essential building materials for industrial and civil construction projects worldwide. Their quality directly determines engineering stability, construction safety, and people’s life and property security. Even with modern advanced tunnel kiln production technology, most fired brick quality issues stem from improper raw material treatment, unreasonable molding parameters, and unscientific sintering and drying management. Based on years of wall material reform and production line operation experience, this article systematically analyzes six typical quality defects in fired porous brick, hollow brick and block production, and provides targeted, operable solutions for brick factory quality control.
1. Size Deviation
Size inconsistency is one of the most frequent defects in fired brick production. The core causes are unreasonable raw material particle gradation and insufficient raw material aging time, which lead to unstable clay plasticity and irregular mud strip extrusion.
Solutions: First, conduct professional sieve analysis to adjust and optimize raw material particle gradation. Second, extend raw material aging time; configure aging warehouses with a minimum capacity for 7-day raw material supply to improve clay plasticity index steadily. Third, optimize the outlet size of the brick extruder according to the actual plasticity data of local raw materials, to ensure the extruded mud strip size matches the raw material shrinkage deviation range.
2. Edge and Corner Cracks
Edge and corner cracks mainly occur due to excessive coarse particles in raw materials and low molding moisture, which increase mud strip extrusion resistance and cause uneven stress during molding.
Solutions: Reduce sieve aperture to improve raw material crushing fineness and optimize particle gradation. Adjust the gap of high-speed roller press to a standard 3mm to ensure uniform raw material crushing. Appropriately increase raw material moisture content to reduce extrusion resistance and eliminate edge corner cracks.
3. Horizontal Cracks on Ribs and Walls
Horizontal cracks on the ribs and walls of porous and hollow bricks are typical drying and shrinkage defects. Excessive coarse raw material particles cause inconsistent shrinkage of coarse and fine particles. Meanwhile, ultra-high drying temperature and over-fast drying speed will crack the wet brick blank surface before internal moisture evaporates completely.
Solutions: Optimize raw material particle gradation to balance shrinkage difference. Standardize drying kiln temperature control: keep the inlet temperature of wet blanks at about 40℃ and the outlet temperature of dried bricks at about 110℃. Adjust drying time and fan speed dynamically according to the internal temperature and humidity of the drying kiln to realize uniform and slow drying.
4. Underfired Bricks
Underfired bricks with pale color and low compressive strength often appear at the bottom and two sides of tunnel kiln cars, resulting in high finished product breakage rate. The primary cause is cold air leakage from the bottom of kiln cars, which reduces local firing temperature.
Solutions: Inspect and repair the sand seal and sealing groove of kiln cars and kiln walls regularly, keep sufficient sand in the sand seal groove to block cold air infiltration. Balance the positive pressure, zero pressure and negative pressure inside the tunnel kiln to reduce the upper and lower temperature difference of brick blanks. Supplement raw material internal heat properly and raise firing temperature if the heat value is insufficient. Strictly implement fixed zone, fixed temperature and fixed time firing standards, never shorten firing and heat preservation time for higher output.
5. Overfired & Blistered Bricks (Burst Bricks)
Burst bricks with bending deformation and surface bubbles usually appear in the middle and upper parts of brick stacks, caused by excessive raw material heat value, unreasonable stacking mode, and prolonged firing and heat preservation time.
Solutions: Recalculate and adjust the proportion of internal heat additives to control raw material heat value scientifically. Optimize brick blank stacking method to reserve reasonable gaps between blanks for uniform heat circulation. Control the position of the firing zone and shorten excessive firing and heat preservation time to avoid overfiring deformation.
6. Poor Weathering Resistance
Many fired brick products fail weathering resistance tests due to inadequate raw material aging and homogenization treatment. Direct molding of unaged and unhomogenized raw materials leads to unbalanced firing, forming a "half-cooked" sintering state that reduces durability.
Solutions: Mandate full homogenization and 7-day aging treatment for all raw materials. Properly increase tunnel kiln firing temperature to promote complete solid-liquid phase reaction of raw material particles. Improve crushing fineness for low-quality raw materials to ensure uniform sintering of brick blanks.
Core Conclusion: Fired Brick quality follows the industry principle of "70% raw material, 30% process; 70% firing, 30% craftsmanship". Stable product quality relies on standardized raw material treatment, precise equipment parameter adjustment and standardized production management.
