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Few points to be paid attention to when choosing a tunnel kiln ?

2026-03-16

1. Select mature technical solutions to ensure that the production line reaches the standard and reaches the production capacity.

When using tunnel kiln to burn bricks, various parameters used in production should be determined according to the basic properties of raw materials.

The firing output of the kiln is that the performance indicators of the fired product meet the requirements of the national standard, not just how much is fired, and the output of the kiln is how much. Some kiln-fired products are only 3mm~4mm on the surface, but the inside is not completely fired. Such products that do not meet the requirements of the national standard cannot be used as the basis for calculating the output of the tunnel kiln.

The length, width and height of the kiln are calculated according to the output of the kiln. When calculating the length, width and height of the kiln, the heating and cooling rates of the raw materials, the firing time of the raw materials, the highest firing temperature and the firing temperature range should be considered. And other factors.

The tunnel kiln should also have a complete working system, and various parameters of the working system must be calculated in detail, so as to ensure the normal operation of the tunnel kiln, so as to achieve the purpose of correct construction and correct use of the tunnel kiln, and to ensure that the tunnel kiln burns In the process of reaching the target and reaching the production.

2. Reasonable layout of the tunnel kiln system to make the firing stable.

According to the definition of tunnel kiln, tunnel kiln should be equipped with ventilation system, fuel combustion system, vehicle entry system, and sealing system. These subsystems constitute the working system of tunnel kiln. The close cooperation of each system can make the tunnel kiln work normally.

According to the requirements of the firing atmosphere in the kiln, the number and position of the fans used on the kiln are equipped, the air pressure of the fans is determined according to the shape of the fired products and the density of the kiln, and the ventilation volume of the fans is determined according to the output.

According to what kind of fuel is used, the method of fuel combustion system, what kind of combustion equipment to use, and the arrangement position and quantity of combustion equipment should make the temperature in the kiln as uniform as possible. The main contents included in the entry system are entry mode and entry time interval.

The sealing system includes the sealing between the kiln car and the kiln body, the sealing between the kiln door and the kiln body, the sealing between the pipeline and the kiln body, and the sealing between the kiln cars. It is isolated to form a good firing space inside the tunnel kiln, so that the semi-finished product can be fired into the finished product inside the kiln.

The division of the three zones in the firing process of the tunnel kiln should be carried out according to the basic properties of the raw materials, and should not be arbitrarily divided, so as to ensure the normal production and stable operation of the tunnel kiln.

3. Recognize the importance of kiln car and ensure the stable quality of fired products.

The kiln car is an indispensable equipment in the production process of the tunnel kiln, and it is also the key equipment related to the performance of the tunnel kiln and whether it can be used normally.

In order to make the kiln car play the role of key equipment, the first thing is to maintain a good seal between the kiln car and the tunnel kiln body, so as to completely isolate the inside of the kiln from the outside of the kiln, so that the cold air outside the kiln cannot enter at will In the kiln, the hot air in the kiln will not leak into the kiln, so that the firing process in the kiln can be carried out smoothly.

Secondly, the seal between the kiln cars should also be reliable, the reason is as mentioned above. Third, the operation of the kiln car should be stable, so as to avoid the occurrence of such phenomena as kiln collapse, uneven firing, and difficulty in entering the car. Fourth, the thermal insulation layer on the kiln car is very important. If the thermal insulation layer of the kiln car has a good thermal insulation effect, the temperature in the kiln will be consistent, the quality of the fired products will be uniform, and the color will be the same. If the thermal insulation effect of the kiln car is not good, Then, the temperature difference between the upper and lower sides of the kiln will be large, and the fired products will be cooked on the top and cooked on the bottom, or cooked on the top and under the coke. In short, the product quality is uneven and the color difference is large.

Some factories have been in operation for less than a year, and the kiln car often has problems and needs to be replaced, which not only increases production costs, but also changes the understanding of tunnel kilns, and feels that tunnel kilns are inferior to other kilns. In fact, the root cause is the insulation layer of the kiln car, and the seemingly simple insulation layer problem has not been properly handled.

Some kiln cars did not reduce the thickness and material of the thermal insulation layer, but the thermal insulation effect was still very poor. Why is the temperature under some tunnel kiln cars only 40℃~50℃, people can check it smoothly under the car, while the temperature under some cars is so high that people can't get into the car at all. In fact, the reason is very simple, it is caused by the gap in the insulation layer of the kiln car.

Problems that should be paid attention to in the construction of tunnel kiln

The performance of the tunnel kiln depends not only on the integrity of the design, but also closely related to the construction. The quality of each construction step affects the quality and performance of the tunnel kiln.

1. Construction materials must be guaranteed.

In the design process of the kiln, the material properties and usage requirements of various materials are considered, and the usage position and thickness of the materials are calculated. In order to ensure the construction quality, the use position and amount of materials shall not be arbitrarily changed during the construction process, nor the variety and quality grade of the materials used.

If it is to be replaced, the strength grade of the structural material must be higher than that of the original design material, and the thermal conductivity of the insulation material to be replaced must be lower than that of the original material.

2. Construction according to design requirements.

In the process of using the tunnel kiln, the technical requirements that should be met in the construction process, the construction difficulty and the solutions are fully considered. Many norms and standards are used in the design, including national standards and norms, provincial and ministerial-level standards and norms, local-level standards and norms, and industry standards and norms.

In the construction requirements, specific requirements are put forward for each part. These requirements are in line with the requirements of the construction specifications and standards. If you want to change them, you must refer to the corresponding items of the specifications and standards, and make changes according to the requirements of the specifications and standards. Change.

The materials used in construction are generally those published in national standards. If the specifications and models of the materials are to be changed, the original design materials should be replaced by materials with higher performance in accordance with the national standards.

Problems and lessons in tunnel kiln construction

As we all know, there are three principles to produce good fired bricks: raw materials are the foundation, kiln equipment is the key, and management is the foundation. If it is not designed, the materials used are inferior, and the construction is arbitrarily commissioned, the kiln will become the biggest obstacle to the sustainable development of the production enterprise. There are the following fatal problems in the reconstruction and new construction of tunnel kilns, which should be paid great attention by colleagues in the whole industry:

1. The furnace design is unreasonable

Some enterprises do not pay attention to the process design of sintering kilns. There are generally simple kiln structures, unscientific drying kiln structures, and unreasonable air duct design, so that various tunnel kilns of different lengths appear in front of us. In order to meet the owner's blind request to reduce the cost, many tunnel kilns are overweight and weak.

Whether the tunnel kiln design is reasonable and perfect directly restricts the quality of the kiln. Some investors pay too much attention to investment control and ignore the design and construction of the kiln, resulting in high coal consumption, high cost, high maintenance frequency, A vicious cycle of low reliability and difficult operation.

2. Most construction teams are unqualified, and the construction quality is worrying

It is one of the most prominent problems at present to arbitrarily entrust the construction of units without kiln construction qualifications. They lack necessary job training and qualification certification of construction personnel. The construction quality of most tunnel kilns cannot be guaranteed, the foundation is not strong, and the kiln The body is cracked, the drying effect of the bricks is not good, and the phenomenon of serious collapse and falling of the bricks occurs frequently during the drying process, and the product energy consumption is high and the quality is poor. Quality accidents and quality lawsuits are not uncommon.

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Related questions
1
How to Eliminate Spiral & S-Cracks in Clay Bricks？
Spiral cracks and S-cracks are the most frequent structural defects in clay brick manufacturing. These undesirable imperfections lead to high scrap rates, raw material waste, and poor finished brick appearance. This practical guide summarizes mature industrial solutions covering raw material treatment, extrusion optimization, moisture adjustment, equipment maintenance, and kiln processing, helping global brick manufacturers reduce defect rates and maximize production profits.
1. Optimize Raw Material Gradation & Reduce Clay Plasticity
Reasonable particle gradation is the foundation of crack prevention. Manufacturers should mix 20% to 30% coarse aggregates such as grog, shale, and coal gangue into raw clay. Coarse particles enhance interlayer friction and restrain clay internal sliding. Meanwhile, reduce high-plastic clay proportion and add limestone powder or quartz sand to lower drying sensitivity.
2. Balance Extrusion Speed & Optimize Clay Flow
To solve uneven flow velocity, install adjustable resistance bars at the extruder head to slow down the central clay flow and balance overall extrusion speed. Replace ordinary blades with variable-pitch spiral blades to reduce shear difference. Keep the gap between spiral blades and machine cylinder within 2mm for stable extrusion molding.
3. Precise Moisture Control for Raw Clay & Green Bricks
Control the raw clay moisture steadily between 18% and 22% according to local clay properties. Adopt staged slow drying technology for green bricks; keep the initial heating rate below 20°C/h to avoid surface crusting. Uniform moisture removal effectively prevents shrinkage cracks and layered cracks.
4. Standardize Daily Extruder Maintenance & Parts Replacement
Establish regular equipment inspection cycles. Timely replace worn spiral blades and damaged cylinder liners to guarantee stable pushing force. Check extruder head sealing and gaps weekly to avoid disordered clay flow caused by mechanical aging. Scientific maintenance reduces artificial brick defects greatly.
5. Upgrade Drying & Sintering Kiln Curves
Adopt gradient heating mode in drying chambers and tunnel kilns. Control the heating rate between 20°C/h and 30°C/h with sufficient constant-temperature holding time. During quartz crystal transformation (600℃-900℃), slow down heating speed below 40°C/h to relieve internal thermal stress.
Eliminating spiral and S-cracks requires systematic production management from raw materials to finished bricks. Scientific formula proportion, optimized extrusion equipment, precise moisture monitoring, standardized maintenance, and improved kiln technology can reduce brick scrap rates by 5%-10%. Stable product quality helps brick factories occupy more shares in the global construction material market.
2
How to Boost Brick Factory Output?
For modern brick factories pursuing stable production and high profits
low output and high defective rates have always been troublesome problems. Many brick plant owners blindly upgrade brick making machinery and increase production frequency, but ignore the core bottleneck restricting production efficiency—the drying process. In the actual brick production workflow, the drying section is the key link that determines the qualified rate of green bricks and the daily output of the entire brick factory. Relevant industry data shows that reducing the moisture content of bricks before entering the kiln can directly bring obvious output growth; every 1% reduction in kiln entry moisture can increase brick production by 3% to 5%.
Many brick factories have unreasonable drying settings, resulting in long drying cycles, damp green bricks, and mildewed blanks, which not only reduces the drying qualification rate but also causes adverse effects on the subsequent kiln firing process. To break the drying bottleneck of brick factories, enterprises need to optimize two core indicators: drying temperature and moisture exhaust efficiency.
  • First, reasonably increase the drying temperature according to the raw material characteristics, and ensure uniform temperature distribution in the drying chamber to avoid uneven drying of green bricks.
  • Second, strengthen the moisture exhaust system of the drying workshop, timely discharge water vapor generated in the drying process, and prevent water vapor from condensing on the surface of green bricks to cause secondary moisture regain.
In addition to temperature and moisture exhaust optimization, raw material management is also an auxiliary measure to improve drying efficiency. Brick factories need to maintain stable raw material ratio and uniform internal combustion blending. Frequent replacement and proportion adjustment of raw materials will lead to inconsistent moisture characteristics of raw mud, which increases the difficulty of drying control. Uniform internal combustion mixing can avoid local underfiring and reburning of bricks, reduce defective products caused by unreasonable combustion, and further cooperate with the drying process to improve the overall qualified rate of bricks.
For brick making equipment
the operating state of the molding end also indirectly affects the drying effect. The extruder needs to maintain a reasonable running speed while ensuring the compactness of the green bricks. The stable vacuum degree above 0.085 is an essential standard for high-quality brick blanks. Worn reamer blades should be replaced in a timely manner to prevent loose green bricks from being difficult to dry thoroughly. Only when the quality of molded bricks is up to standard can the drying link exert the maximum efficiency advantage.
In the production logic of brick factories, the optimization priority must be clear:
prioritize solving drying problems, then stabilize the firing process, and finally carry out equipment speed increase transformation.
It is necessary to clarify a core principle: the real output of a brick factory refers to the number of qualified bricks. Excessive defective products and reburning bricks will completely offset the production growth brought by equipment acceleration. Optimizing the drying system is the lowest-cost and highest-return way for most brick plants to increase production, which is suitable for small and medium-sized brick factories with limited transformation budgets.
3
How to Prevent Clay Bricks from Collapsing in Tunnel Kilns？

1. Pre-firing Material Constraints (The "Foundation" Stage)

Collapse often begins before the bricks even enter the kiln if the green body lacks physical integrity.

  • Moisture Threshold: The residual moisture content must be kept below 6%. High moisture levels drastically reduce the compressive strength of the bricks, causing the bottom layers to buckle under the weight of the stack.

  • Material Aging: Clay requires at least 3 days of aging to ensure uniform plasticity and water distribution. Insufficient aging leads to internal stresses and a fragile structure.

  • Mechanical Density: Ensure an extrusion pressure of ≥40kg/cm² to increase the density of the green body, making it more resistant to deformation at high temperatures.

2. Strategic Stacking Techniques (Mechanical Stability)

Stacking is not just about volume; it is about managing gravity and thermodynamics.

  • The "Four-Point" Standard: Stacks must be level, stable, vertical, and straight. Any minor deviation in the center of gravity will be amplified as the bricks soften in the heat.

  • Airflow Optimization: Follow the principle of "Dense Edges, Sparse Centers" and "Dense Tops, Sparse Bottoms." This balances the temperature across the kiln cross-section, preventing the edges from over-firing while the center remains under-fired.

  • Load Management: Due to the high sensitivity of clay, limit the stacking height to 12 layers or fewer. This minimizes the static pressure on the base bricks.

3. Dehumidification in the Preheating Zone (The "Critical" Stage)

This is the most common zone for collapses. If moisture is not evacuated efficiently, the bricks effectively "steam" and lose their rigidity.

  • Inlet Temperature Control: Keep the initial drying air below 116°C. Temperatures above this threshold cause the surface to harden too quickly, trapping steam inside and creating internal pressure.

  • Heating Rate: Maintain a steady rise of 6–8°C/h. Sudden temperature spikes, especially in winter, can cause thermal shock and structural failure.

  • Ventilation and Pressure: Ensure the exhaust fan provides sufficient negative pressure. Poor ventilation causes moisture to linger and re-condense on the bricks, leading to "soggy" bricks that collapse instantly.

4. Firing Zone Temperature Management (Thermodynamic Control)

Once the bricks reach high temperatures, preventing them from entering a pyroplastic state (melting) is vital.

  • Anti-Overfiring Measures: Strictly monitor the sintering peak. Exceeding the clay's softening point leads to viscous flow, where the bricks begin to behave like liquid and slump.

  • Internal Fuel Ratio: Control the amount of internal additives (coal powder or gangue). Excessive internal fuel generates uncontrollable heat within the stack, causing the bricks to "melt from the inside out."

  • Visual Monitoring: Use inspection holes to watch for "white-out" conditions or "shimmering/swaying" stacks, which are immediate warning signs of imminent collapse.

5. Infrastructure and Mechanical Integrity (Environmental Factors)

The physical environment of the kiln must remain consistent to prevent mechanical triggers.

  • Track Leveling: Regularly inspect kiln car tracks. Uneven rails cause vibration and jolting, which can topple a stack that is already weakened by heat.

  • Kiln Structure Maintenance: Check for sagging roof bricks or protruding exhaust ports. Mechanical obstructions are a frequent cause of "domino-effect" collapses during car movement.

4
How to Crusher Output in Sintered Brick Plants Efficiently？
In sintered brick production lines, the output and quality are often restricted by four key pieces of equipment: crushing equipment, belt conveyor equipment, vacuum extruders, and kiln thermal equipment. Among them, jaw crushers and hammer crushers, as common primary and secondary crushing equipment, directly determine the overall production efficiency of the entire line. Many brick plant operators are eager to maximize crusher output while ensuring the particle size of crushed materials—here are practical and actionable tips to achieve this goal.
First, ensure proper feeding. To make the jaw plates wear evenly and reduce operating costs, gangue or hard shale should be evenly distributed along the feeder inlet and fill the crushing chamber completely. Uneven feeding will not only accelerate jaw plate wear but also reduce crushing efficiency, leading to unnecessary energy waste.
Second, adjust the feeder amplitude reasonably. During normal use of the feeder, you can adjust the amplitude through the knob on the control box within the rated amplitude range according to the required productivity, so as to achieve stepless adjustment of the feeder. Sufficient amplitude ensures that materials enter the crushing chamber continuously and stably, avoiding gaps that affect output.
Third, pay attention to feeding precautions. It is crucial to prevent iron blocks from entering the crushing chamber, as iron blocks can damage jaw plates and other key components. The height of the materials to be crushed should not exceed the fixed jaw plate, and the maximum feed particle size should be smaller than the feed inlet—large blocks are likely to block the crushing chamber and reduce crushing efficiency.
Fourth, set a reasonable discharge port size. The discharge port is the distance between the two jaw plates at the lower end of the crushing chamber. Too small a discharge port will cause blockages and excessive energy consumption, leading to serious damage to the crusher; too large a discharge port will increase the load of the second crushing. Finding the optimal size according to the production needs is the key to improving output.
In addition, regular inspection and replacement of jaw plates, proper lubrication of bearings, and scientific adjustment of the discharge port opening are also essential links to ensure stable and high output of the crusher. By following these tips, sintered brick plants can effectively improve crusher production capacity while ensuring product quality.
5
Why Poor Drying & Dehumidification Causes Cracked Clay Bricks?
As a professional engaged in the brick-making industry for years, we often receive questions like: “Why do my clay bricks crack after sintering?” “How to make clay bricks stronger and more durable?” Today, we will popularize the critical role of drying and dehumidification technology in clay sintered brick production, and tell you how to avoid common quality problems completely.
First, let’s understand the basic principle: clay raw materials contain a lot of moisture, and if this moisture is not fully removed before sintering, it will expand rapidly when heated in the kiln, generating huge internal pressure. This pressure will directly cause the bricks to crack, burst, or even break into pieces—just like the “tofu bricks” that have been exposed in some quality incidents, which are mostly related to insufficient drying and dehumidification before sintering. In addition, uneven drying will lead to inconsistent moisture content in different parts of the brick blank. During sintering, the shrinkage degree of each part is different, resulting in uneven surface, low compressive strength, and poor weather resistance of the finished bricks.
Many small and medium-sized brick factories still use traditional natural drying or simple hot air drying methods. These methods have obvious defects: natural drying is greatly affected by the weather, and it is easy to cause the brick blanks to get damp again or dry unevenly; simple hot air drying often leads to too fast surface drying and too slow internal moisture diffusion, forming a “dry shell” on the surface, which traps the internal moisture and eventually causes cracks during sintering. These problems not only reduce the qualified rate of bricks but also increase production costs and affect project progress.
The good news is that these quality problems can be completely solved with advanced drying and dehumidification technology. Our company’s clay sintered brick making machine is equipped with a high-efficiency intelligent drying and dehumidification system, which perfectly solves the pain points of traditional drying methods. The system can accurately control the temperature, humidity, and air flow during the drying process, realizing uniform drying of the brick blanks from the inside out. It can quickly and thoroughly remove the moisture in the clay, ensuring that the moisture content of the brick blanks before sintering is controlled at the optimal range of 2% or less—which is the key to ensuring the quality of sintered bricks.
With our machine, you don’t have to worry about cracked, crumbly, or uneven clay bricks anymore. The sintered bricks produced by our equipment have uniform texture, high compressive strength, strong weather resistance, and no cracks or defects. They fully meet the international construction quality standards and are widely used in residential buildings, industrial workshops, and municipal engineering. Whether you are a brick manufacturer or a construction enterprise, our machine can help you improve production efficiency, reduce waste, and create higher economic benefits.
6
Which Ceramic Clay Split Face Brick Making Machine Adapts to Various Overseas Regions and Raw Materials?
Overseas brick factories are distributed in different regions, with great differences in raw material types, voltage standards and transportation conditions. Many buyers buy brick making machines that are not suitable for local conditions—either they cannot adapt to local ceramic clay and other raw materials, or they cannot be used normally due to voltage mismatch, or they are difficult to transport due to large volume. So, which ceramic clay split face brick making machine can adapt to various overseas regions and raw materials?
Our Ceramic Clay Split Face Brick Red Brick Making Machine is designed with "global adaptability" as the core, perfectly solving the problem of regional mismatch. In terms of raw material adaptation, it has strong compatibility, and can process not only pure ceramic clay, ordinary clay, but also mixed raw materials such as clay mixed with sand, tailings and coal gangue. It can automatically adjust the mixing ratio according to the characteristics of local raw materials, ensuring stable product quality without additional raw material processing equipment.
In terms of voltage adaptation, we can customize the motor voltage according to the local voltage standards of different countries and regions—whether it is 220V (North America, Southeast Asia), 380V (Europe, Africa), or other special voltages, we can meet the requirements, avoiding equipment failure caused by voltage mismatch and ensuring normal production.
In terms of transportation, the machine adopts a detachable design, which can be disassembled into small parts for transportation, greatly reducing the volume and transportation cost. For regions with inconvenient transportation (such as remote areas in Africa and Southeast Asia), it can be easily transported to the factory and assembled quickly—only 1-2 days are needed to complete the installation and commissioning, and it can be put into production immediately.
In addition, the machine is designed with a dust-proof and moisture-proof structure, which can adapt to different climate conditions—whether it is the high temperature and dryness in Africa, the humid and rainy in Southeast Asia, or the low temperature in Europe, it can operate stably without being affected by the climate. Up to now, our machine has been used in more than 60 countries and regions around the world, adapting to various complex working conditions and winning unanimous recognition from local customers.
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