How to Avoid Thermal and Structural Failures in Fused Alumina-Zirconia-Silica (AZS) Bricks During Use
I. Prevention at the Root: Kiln Baking and Temperature Control (Most Critical)
70% of fused Alumina-Zirconia-Silica (AZS) brick failures stem from improper kiln baking/cooling.
The 900–1150℃ phase transformation danger zone must be avoided.
In this range, ZrO₂ undergoes a crystal transformation, resulting in drastic volume changes.
Slow heating at ≤15℃/h is required; rapid temperature increases and quick firing are strictly prohibited.
If necessary, maintain the temperature in this range for 4–8 hours to release stress.
Gradual temperature control throughout the process:
Ambient temperature → 600℃: ≤20℃/h
600 → 900℃: ≤15℃/h
900 → 1150℃: ≤10℃/h
Above 1150℃: The rate can be appropriately increased, but not exceeding 30℃/h. Strict cooling during furnace shutdown is also required:
Above 1200℃: ≤20℃/h
1150 → 900℃: ≤10℃/h
Avoid forced air cooling and rapid cooling by opening doors.
II. Masonry Design: Eliminate stress structurally.
Sufficient expansion joints must be provided.
Longitudinal/transverse joints should be reserved for 1.0–1.5% linear expansion.
Corners, T-joints… Densify expansion joints in stress concentration areas such as letter walls and flow channels.
Control brick joints to the extreme.
For critical areas such as working pools and flow channels: ≤0.3mm.
Prohibit the use of high SiO₂ and high-alkali clay materials to avoid eutectic melting.
Strictly prohibit the use of incorrect brick types.
AZS bricks should not directly contact clay bricks or high-alumina bricks.
A transition layer/isolation layer must be added in between to prevent low-temperature eutectic melting, cracking, and leakage.
Ensure uniform stress distribution.
Avoid localized hardening or jamming at the arch, corners, and upper part of the pool walls.
Strictly prohibit single-point stress and corner chipping during the hoisting and construction of large bricks.
III. Usage Process:
Avoid thermal shock and localized overheating.
Prevent drastic temperature fluctuations.
The areas near the liquid level line, feeding port, and burner nozzle are most prone to thermal shock spalling.
Control the flame to prevent it from directly hitting the brick surface.
Avoid frequent feeding and discharging, which can cause sudden temperature changes.
Maintain an oxidizing atmosphere.
A reducing atmosphere will cause glass phase precipitation, loose structure, and a sharp drop in strength.
Control the kiln pressure to a slightly positive pressure to prevent air leakage and localized reduction.
Maintain a stable liquid level.
Significant liquid level fluctuations → Repeated wetting and drying, and alternating hot and cold temperatures on the brick surface can easily cause peeling, cracking, and groove corrosion.
IV. Material Selection and Quality: Reduce Failures at the Source
Select non-shrinkage, dense cast bricks. Shrinkage cavities, air holes, and internal looseness are the starting points for cracking. Prioritize 33#/36#/41# non-shrinkage, dense AZS bricks. Use specialized bricks for critical areas.
Pool walls and flow holes: High density, no air bubbles, no segregation.
Electric annealing furnace: High zirconium, high insulation type to avoid leakage and thermal stress accumulation. Mandatory inspection upon arrival.
Appearance: No cracks, no chipped corners, no through-holes.
Internal: Ultrasonic/tapping inspection; remove bricks with internal hidden cracks.
V. Online Monitoring and Maintenance: Early Detection and Early Treatment
Monitor pool wall temperature. Localized abnormal high temperatures → internal loosening/cracking.
Observe glass defects. Sudden increase in stones and streaks → brick peeling. Prohibit hot repairs and forced cold repairs. High-temperature rapid repairs, rapid patching, and water cooling will cause instant cracking.
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