Brick explosions in roller kilns are not only costly but also dangerous. If not resolved, production efficiency and product quality will suffer, and management pressure will rise. This article summarizes common roller kiln problems, causes, and solutions from a refractory and ceramic production perspective.
Unreasonable drying kiln pressure and temperature curve
– The solution is to adjust the pressure and temperature curve to a reasonable level.
Excessively high kiln-head temperature
– Lower the kiln-head temperature, appropriately reduce exhaust draft, or open one or two emergency ports in the front section to allow cold air in for cooling.
Excessive moisture content in brick blanks (powder materials) before entering the kiln
– Check and strictly control the moisture level of incoming green bodies.
Key kiln-related factors affecting product size:
Left–right temperature difference
Local over-firing
Overall temperature too high or too low
Judgment method:
If products on one side or in the middle are always larger or smaller, or if one edge is consistently bigger regardless of mold number → caused by left–right temperature difference.
If product size overall is too small with blistering → caused by over-firing or excessive temperature.
If product size overall is too large with high water absorption → caused by low firing temperature.
Cracks may include drying cracks, mechanical cracks, firing cracks, and cooling cracks.
Drying cracks
– Caused by unreasonable drying schedule or excessive local airflow.
– Features: fine, large internal gaps along thickness, smooth fracture surface, sharp edges. In glazed products, surface is still glazed after firing.
Mechanical cracks
– Caused by forming cracks, uneven conveyor line, vibration, or dirty/uneven rollers.
– Features: fixed position, blunt edges, rough fracture surface.
Firing cracks (small-fire cracks)
– Caused by high moisture in blanks and rapid heating in kiln-head.
– Features: rough fracture, blunt edges.
Large-fire cracks
– Occur around 900 °C when liquid phase forms and heating rate is too fast.
– Features: large cracks, rough fractures, sometimes thread-like, uneven edges, cracks develop deeper and not straight.
Cooling cracks (wind cracks)
– Caused by insufficient cooling time during crystalline phase transition or uneven cooling zone.
– Features: fine cracks, smooth arc-shaped fracture surface, sharp edges.
How to judge mechanical crack location:
Apply kerosene at different kiln sections or rotate product direction to check.
Forming cracks → mold number and crack position fixed, visible at drying kiln-head after kerosene wipe.
Drying kiln cracks → visible at drying kiln tail after kerosene wipe.
Conveyor cracks → may appear at kiln-head or drying kiln tail, revealed by rotating product direction.
Improper temperature curve setting
Excessively high firing temperature
Dirty or uneven rollers
Uneven product loading and misaligned movement in kiln
Unreasonable raw material formulation
Stirring air holes in the preheating zone of roller kilns inject low-temperature air to reduce kiln-head temperature.
Kiln wall refractory material structures: traditional, composite, and full fiber.
Cooling zone of ceramic kilns is divided into rapid cooling, slow cooling, and low-temperature cooling sections.
Pressure schedule is established to ensure proper temperature and atmosphere control.
Firing zone temperature control in tunnel kilns focuses on actual combustion temperature and peak temperature point.
Gaps between rollers in roller kilns facilitate airflow circulation.
Thermal expansion coefficient of materials affects thermal shock resistance.
Ceramic firing schedule includes temperature, pressure, and atmosphere systems.
Kiln roof refractory structures are arch type and flat type.
Roller materials include high alumina, heat-resistant alloys, and recrystallized SiC.
Gas curtain stirring: hot gases are injected at high velocity and angle from kiln roof to force downward flow, improving temperature uniformity.
Fire suction holes in flame-reversal kilns function as flue gas inlets.
Checkerwork structure in regenerative chambers affects service life and heat storage efficiency.
Kiln (thermal equipment): a structural space where raw materials are heated following firing schedule to undergo physical and chemical changes into final products.
Key refractory indicators for kiln life: permanent linear change and thermal shock resistance.
Roller kiln systems include combustion, exhaust, and cooling systems.
Advances in energy technology, refractory processes, and firing technology have rapidly improved kiln performance.
Sealed gas curtain: multiple jets from roof and walls form an air curtain; dynamic pressure converts to static, creating 1–2 Pa positive pressure at kiln-head to prevent cold air ingress.
Hot air from cooling zone can be reused for drying, combustion aid, and gas curtain.
Preheating zone dampers in tunnel kilns distribute flue gas to meet local temperature requirements.
Main kiln coating (kiln skin): molten material (25–30%) adheres to refractory surface, its proper thickness/length indicates stable calcination.
Double-center arch kiln roof: two half-arches with different centers for structural strength.
Refractory types: dense (heavy) and lightweight (insulating).
Roller materials for ceramics also include aluminum alloys, heat-resistant steels, and mullite.
Exhaust system of roller kilns is centralized; since no kiln doors, part of exhaust recirculates as sealed gas curtain. Preheating zone side holes also inject cool air to reduce kiln-head temperature.
Heat-curing schedule consists of preheating, heating, holding, and cooling stages.
Kiln wall hole bricks support rollers, ensure smooth operation; their thickness is slightly less than kiln wall thickness.
Under-firing and over-firing: caused by excessive positive pressure cooling (too much cold air) or insufficient positive pressure (negative pressure, too little cooling air). Manifestations: porous low-strength structure, flue gas backflow, product smoke staining.
Sealing sand troughs isolate kiln car top and bottom, prevent cold air ingress and heat leakage.
Atmosphere curtain in tunnel kilns ensures oxidation before reduction zone (950–1050 °C), creating proper firing conditions.
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