Core Causes and Practical Solutions to Severe Overburning and Sticking in Tunnel Kilns
Severe overburning and brick sticking are common and troublesome defects in the brick and tile firing process of tunnel kilns, which seriously reduce finished brick yield and production efficiency. This article systematically analyzes the key causes of large-area overburning and severe adhesion of brick bodies in tunnel kilns, providing reliable references for kiln operation optimization and brick production quality control.
First, excessive internal combustion heat of green bricks is a primary inducement for overburning and sticking. When the combustible components inside the brick blanks are too high, the heat released during sintering exceeds the standard firing temperature required for bricks and tiles. Excess heat accumulates in the high-temperature zone of the tunnel kiln, causing the brick surface to produce liquid phases in advance, which leads to mutual adhesion between adjacent blanks and large-area overburning defects.
Second, unreasonable design of tunnel kiln air supply and exhaust system leads to poor overall kiln ventilation. The misalignment between the ventilation channels on the brick stack and the exhaust ducts on the kiln wall disrupts the normal hot air circulation and heat dissipation rhythm. The internal combustion heat cannot be discharged smoothly and erupts violently in the high-temperature firing zone, resulting in concentrated overburning and serious sticking of brick bodies.
Third, unreasonable gap setting between brick stacks, kiln walls and kiln roofs is a key structural cause. The standard gap is controlled within 80mm, while excessive gaps will cause more than 80% of the air volume to flow through the top and side gaps. The middle of the brick stack lacks effective air circulation, leading to insufficient preheating of green bricks. When under-preheated blanks enter the high-temperature zone, internal combustion burns rapidly in a short time, triggering large-area overburning and adhesion.
Fourth, irregular brick stacking methods affect internal ventilation of the stack. Excessively high stacking density and insufficient reserved ventilation channels between brick stacks block the internal air flow. The accumulated heat inside the stack cannot be dissipated, and the local temperature rises sharply, causing uneven firing and overburning sticking of bricks and tiles.
Fifth, improper manual operation exacerbates firing defects. Common wrong operations include using near gates to pursue higher output, refusing to lift far gates to control flame forward speed, and excessively high fan suction leading to low gate height. These operations cause the brick surface to form liquid phases and sinter prematurely, forming stable sticking structures and large-area overburning phenomena.
Sixth, unreasonable tunnel kiln length design restricts the preheating effect. If the overall length of the preheating zone and firing zone is insufficient, green bricks cannot complete gradual and full preheating. The blanks directly enter the high-temperature firing zone, and the sudden temperature surge causes instantaneous intense combustion of internal fuel, resulting in overburning and severe brick adhesion.
In addition, for rotary kilns, the main causes of similar overburning and sticking problems are summarized as excessive internal combustion of blanks, insufficient preheating zone length, frequent use of high near gates, and insufficient overall kiln suction.
FAQ
Q1: What is the most common cause of large-area sticking in tunnel kiln brick firing?
A: The most frequent cause is poor ventilation inside the brick stack caused by unreasonable stacking methods and unaligned ventilation systems, coupled with excessive blank internal combustion, which leads to concentrated high temperature and premature liquid phase firing.
Q2: How to judge whether tunnel kiln gap size causes overburning defects?
A: The standard gap between brick stacks and kiln walls/roofs is within 80mm. If the gap is too large, most air flows away from the gaps, resulting in no wind in the middle of the stack, insufficient preheating and subsequent overburning sticking.
Q3: What is the difference between overburning causes of tunnel kilns and rotary kilns?
A: Tunnel kiln defects are mainly caused by unreasonable ventilation design, gap size and stacking methods; rotary kiln overburning is mostly induced by excessive internal combustion, insufficient preheating length and insufficient kiln suction.
