The manufacturing process consists of 12 carefully controlled stages, from raw material preparation to final packaging. Each stage is described below.

1. Raw material selection & pre‑treatment

• Composition: high‑plasticity clay (50–70%), shale, grog (pre‑fired crushed clay, 20–30%), feldspar, quartz, and other fluxes.

• Crushing: jaw crusher for coarse crushing, followed by a hammer crusher to reduce particle size to ≤2 mm.

• Screening: vibratory screens remove iron impurities and oversize particles to ensure uniform fineness.

2. Batching & mixing

• Automated weighing of each component with an accuracy of ±0.5%.

• Twin‑shaft mixer adds water (moisture content 18–22%) and intensively blends the materials into a homogeneous mass.

3. Aging (tempering)

• The mixed clay is placed in a sealed aging silo for 24–48 hours (up to 72 hours for premium products).

• Purpose: allow water to penetrate from particle surfaces to the interior, promote clay hydration and organic decomposition, and improve plasticity.

4. Vacuum extrusion

• Two‑stage vacuum extruder: the upper stage mixes, the lower stage houses the vacuum chamber and extrusion screw.

• Vacuum level: –0.092 to –0.096 MPa to completely remove entrapped air and prevent bubbles or lamination.

• Die design: custom‑built for each panel size (e.g., 300×600 mm, 400×1200 mm) with multiple parallel cavities – creating a hollow, ribbed structure that reduces weight by 30–50% and accommodates dry‑cladding anchors.

• Extrusion speed: 0.5–2 m/min, ensuring the green body has sufficient strength to support its own weight without deformation.

5. Cutting to length

• A synchronized flying saw cuts the continuous extruded strip to required lengths (typically 300–1200 mm) with a tolerance of ±1.5 mm.

• Chamfering or beveling can be performed simultaneously.

6. Secondary machining (back grooves / holes)

• Automatic drilling or grooving machines create dovetail slots, trapezoidal grooves, or cylindrical holes on the back side.

• Position tolerance: ±2 mm, ensuring secure engagement with the dry‑cladding anchors.

7. Drying (removal of free water)

• Green panels go through a multi‑layer roller drying kiln with a controlled temperature profile:

  • Inlet zone: 40–60 °C (prevents rapid shrinkage and cracking)

  • Middle zone: 100–120 °C (rapid water removal)

  • Outlet zone: 60–80 °C (slow cooling to relieve stresses)

• Drying cycle: 6–12 hours; residual moisture after drying <0.5% (strictly <0.3% for some products).

• 100% visual inspection for cracks, warping, edge defects, etc.

8. Surface treatment (optional)

• Engobe application: a fine clay slurry is sprayed to cover coarse particles and produce a smoother surface.

• Glazing: metallic glaze, matte glaze, or stone‑effect glaze is applied by spraying or roller coating, thickness about 0.1–0.3 mm.

• Texture printing: wood grain, fabric texture, or cement‑look patterns can be added via rollers or silk screens.

9. High‑temperature firing

• A wide‑body roller kiln (150–300 m long) with three zones: preheating, firing, and cooling.

• Firing temperature: 1120–1180 °C (typically 1120–1150 °C for terracotta‑body panels).

• Heating rate: 10–15 °C/min in the preheating zone, 5–8 °C/min in the firing zone.

• Soaking time: 30–60 minutes at peak temperature – ensures complete sintering, full mineral transformation, and stable colour development.

• Cooling: forced air or natural cooling to below 70 °C before exiting the kiln to avoid thermal shock cracking.

10. Calibrating & edge grinding

• A double‑end edge grinder precisely grinds the length and width dimensions to achieve tolerances of ±1.0 mm (length/width) and ±0.5 mm (thickness).

• Edges are chamfered or rounded for neat joint alignment during installation.

11. Quality inspection

• Physical properties:

  • Modulus of rupture ≥13 MPa (some export grades require ≥18 MPa).

  • Water absorption ≤6% (terracotta standard; low‑absorption grades reach 3–5%).

  • Freeze‑thaw resistance: no cracks after 25 cycles.

• Appearance:

  • Colour difference: ΔE ≤1.5 measured by colorimeter.

  • Dimensional accuracy: 5% batch sampling using callipers and straightedges; flatness deviation ≤0.5%.

• Non‑destructive testing: tap‑sound test to detect internal cracks.

12. Packing & warehousing

• Each panel is separated by soft padding (PE foam or cardboard) and packed in reinforced cartons or wooden pallets.

• Labels clearly show batch number, size, colour code, and production date.

• Store in a well‑ventilated, dry warehouse; stacking height ≤1.5 m to prevent moisture damage or pressure cracking.

Step 1: Investigate the market and confirm the demand

To determine new plant production scale should refer to the local market conditions.First of all, we shall thoroughly investigate local brick and tile market conditions and grasp following situation:current market demand,actual production volume of existing companies, how big the market gap is,current selling price of brick and tile products and the demand and price trend.Besides,is there the same new brick factory to be built?What is the production scale?After mastering above conditions, the new plant can be determined.

Step 2: Confirm brick type

Formulate product production plan according to the condition of raw materials.When you build a new factory, you must have a clear understanding of the local production materials.After determining the dosing plan and selecting raw materials, we must determine the production plan and scale according to local market conditions. It is suitable for hollow brick or hole brick?Whether annual production scale should be 50 million or 80 million?

Step 3: Confirm the production process and equipment

Selected production process and equipment according to raw materials.Clarify your raw material properties before starting new plant.Please have experienced technical staff to plan the production route and conduct selection or design production equipment.Not all equipment can adapt to your raw materials.

Step 4: Infrastructure construction

After determining production scale, it is possible to determine area, process direction, equipment layout of production plant and the location of living area according to the size of production volume.Plan plant elevation based on local geological, hydrological and meteorological conditions.]Arrange various production workshops according to the wind direction.To determine the mode of production, shall it be labor-intensive companies or technology-intensive enterprises,requires whole careful plan and design by technicians based on the results of technical and economic analysis.

1. Civil work: including Chenhuachi, workshops, doors, windows, and roofs of aging workshop.Meet installation requirements of reversible spreaders, multi-bucket excavators and conveyor belts.At the same time, water supply and drainage and heating are completed.

2. Aging workshop:The crushing workshop completes all civil construction tasks inside and outside the crushing room and feeding room.Complete the plant closure work.Meet installation requirements of feeder boxes, belts, crushers, vibrating screens, back-feed belts, and aging conveyor belts etc.

3. Molding workshop:including the feeding box, mixer, clay machine, extruder, cutting and transportation construction, as well as the kiln base after pouring belt,top car machine, tractor, kiln channel pavement, cushion and other construction.

4. The civil construction scope for air compressor stations, plumbing, substations, fire pump rooms, etc. includes drying kiln, roasting kiln, ferry car,hydraulic pusher,return tractor,traction machine, winch, tidal fan, blower, kiln cooling fan,pipeline , heat exchanger,kiln car production, track and so on.

Step 5:Preparation before production

1. organization construction

2. Make plans and regulations

3. Maintain and add equipment

4. Clean up the existing dry site and drying supplies

5. Maintain kiln

6. Maintain electrical equipment

7. Prepare sufficient fuel

8. Preparation of auxiliary items for production

9. Construct road and drainage

10. Prepare raw materials in advance

11. Ensure safety precautions

12. Run a test

13. Prepare spare parts

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.

Burning bricks requires coal or other fuels. How to maximize the thermal efficiency is the technical key of brick kiln design. The sintering temperature of brick is between 850 ° C and 1050 ° C. In order to save coal, the heat insulation effect of the kiln must be improved. The rotary tunnel kiln is stacked with refractory fiber cotton, which not only reduces the weight of the kiln body, reduces the thermal expansion and contraction stress of the kiln body, but also improves the thermal insulation performance of the kiln body. The kiln temperature is maintained for a long time, and the bricks consumed at one time increase in large area. The internal combustion heat energy can more effectively improve the kiln temperature and save fuel.

In ordinary tunnel kilns, in order to prevent high-temperature flue gas from flowing into the kiln car and burning out the wheels and bearings, it is also necessary to set up a gas source under the kiln car. In the whole heating system, the air supply pressure at the bottom and surface of the vehicle must be kept balanced, and the high temperature flue gas and cold air at the bottom of the vehicle must not rise to reduce the kiln temperature.

 The bricks of the rotary tunnel kiln are directly stacked on the ground, without air supply under the vehicle, and the ground temperature is directly fully utilized. It is found that the aluminum silicate fiber blanket can still be calcined normally after 48 hours of coal and air shutdown in actual production, which is impossible for ordinary tunnel kilns. In the annular rotary tunnel kiln, when the firing temperature of bricks is reduced to room temperature, the heat released is enough to dry wet bricks of the same volume, so there is no need to build a hot air furnace, nor need to use the superheat roasting process to consume more coal to dry the heat.

In the heating system of the annular rotary tunnel kiln, dry air enters from the kiln tail and cools the sintered bricks through the cooling section to reduce the temperature of the sintered bricks at the outlet of the kiln tail to room temperature, that is, all the heat emitted by the sintered bricks is carried to the roasting section and drying section through the air entering the kiln for combustion support and drying. The energy saving of circular rotary tunnel kiln is its remarkable feature. Its reasonable process design, layout and simple logistics route also greatly reduce the energy consumption of the whole brick factory.

The circular rotary tunnel kiln fully adopts mechanized operation and automatic digital control system. The temperature in the kiln is directly displayed on the display screen of the control system. There is no need to hire high-paying fire-watching teachers, which fundamentally eliminates brick-making and greatly increases production.

Compared with the traditional tunnel kiln, the new energy-saving and environment-friendly mobile rotary tunnel kiln has great advantages. It can be predicted that the production mode of the new energy-saving and environment-friendly mobile rotary tunnel kiln will be widely used in the field of sintered bricks by comparing the Helu aluminum silicate fiber blanket.

1, Malformed adobe, appears large cracks. In more serious cases, the whole adobe will split.

Reasons: the plasticity index of pug is too low, almost no plasticity.

Solution: to increase the plasticity index of raw materials, such as clay, coal slime or clay agent, etc.

For raw materials of low plasticity index, it can also be improved after aging, watering, stirring, rolling, extruding and other methods.

2, The body of adobe is not smooth, the obvious particles, more sand pits, and horns or flutes are missing.

Reasons: The shatter of raw materials does not meet the requirements of making bricks because there is much large particles.

Solutions: Install fine grinding equipment, as required for crushing the raw materials to make particles 3 mm or less.

Some kiln owners are not willing to spend money in equipping the machinery of raw material pre-treatment, such as roller crusher,double shaftmixers. Some kilns are only equipped with a pair of rollers, some only with mixers, some even neither of them. How can we get good bricks if there are bricks, tile, stone and other debris in the mud raw materials? Even if it is hard to send someone to pick them out clean. The fundamental way to solve the problem is equipped with auxiliary equipment.

3, The quality of adobe is unstable, sometimes good and sometimes poor.

Reasons: uneven mixing of raw materials

Solutions: Increase the mixer and feeder

Some brick factories are not equipped with rollers and mixers, even without the feeders, all by artificially feeding into the brick machine with shovel, which inevitably occurs two major drawbacks.①, raw material soil cannot be stirred and mixed well. The plasticity of raw soil is not exactly the same, and sometimes the disparity is very great, the Yellow River sludge is like that.②, the inside fuels such as coal, coal gangue, slime and others cannot be stirred evenly. The two heterogeneous, will inevitably lead to the instability of adobes’ quality.

4, malformed adobe and mud column, will spread immediately after cutting.

Reasons: Failure of the vacuum chamber

Solutions: a, improve the maintenance, service, repair technology of brick machine to ensure the normal function of brick machines’ properties. b, make the necessary technical transformation

    b, Another reason for resulting in failure of the vacuum chamber, is the sand-based raw material, so the closed mud layer of the upper auger is too thin, easy to be drawn through, causing the vacuum failure, so the adobe could not be molded. The best way to solve this problem is to change the ratio of raw materials, to increase the plasticity index of raw materials. The other way is to cut the front end of the superiors auger to 2-10 centimeters according to the material properties of soil (must be conducted under the guidance of skilled technical personnel, don’t do it by yourself).

5, Many brick cracks on adobes or broke into two sections, more wastes after sintering.

Reasons: There are too many viscous ingredients in raw materials, so the plasticity index is too high.

Solutions: change the ratio of raw materials, reduce the plasticity index. The plasticity index of clay can be up to 25, can be properly incorporated into the coal ash, slag, fly ash or waste of brick powder to make it thin.

6, Soft adobe, easy to form, or crack after cutting.

Reason: the improper control of moisture in the mud.

Solution: soft adobe, easy to be deformed, showing that the water of sludge is too much, should reduce water. If the mud column quickly occurs crack or split of mud column after molding, which is caused by too little water in mud, it can be solved by increasing appropriate water.

7. Brick production capacity not stable

Reason: Not equip with box feeder

Solution : Some brick factory owners in order to save money, they refuse to use box feeder but some labors to feed soil manually .Therefore, soil feeding amount is not stable,sometimes more than what the extruder need, some times, less what extruder need, thus greatly influencing production capacity.

All in all, there are all kinds of raw materials to make bricks, in addition to the different climate, some abnormal situations inevitably occur in the production and it is really hard to avoid. If there are problems, knowing the following two points will be easy. One isto havea team with a strong sense of responsibility and a technical team ofprofessional mechanics. Two is to timely communicate high and difficult technical problems with industry colleagues.

In summer, with the change of climate, the moisture content in raw materials fluctuates, so pay close attention to the change of moisture content in production. When the moisture content is low, it is necessary to add water to the raw material in time to make it reach the moisture required for molding. When the moisture content in the raw material is too high, it is necessary to properly reduce the moisture content in the raw material. It can be reduced by adding some dry materials to the raw material, such as dry fly ash, coal gangue, slag, tailings of other mines and other industrial waste slag. When adding these components into the raw material, it is necessary to select the right time and specify the adding position. It must be added at the crushing position of the raw material. In this way, the added components can form a good mixture with the main components of the raw material to make the performance of the raw material uniform. If the adding time is too late, and then add after the raw material is broken, then the performance of the raw material is not uniform because several materials cannot be fully mixed, The molding work cannot be carried out smoothly. That is, the forming can be carried out, but the quality of the formed green body is also extremely unstable. When adding water to raw materials, it is also necessary to pay attention to the time of adding water. It is necessary to add 98%~100% of the water required for raw material molding when raw materials are broken and crushed, so that the water content of raw materials can meet the requirements of molding water. Don't wait until the raw material enters the extruder to add water, which is too late to ensure that the added water is evenly dispersed in the raw material, and the water content on the surface and inside of the particles will also be greatly different, which is not conducive to the consistency of the raw material performance, and will cause certain harm to the molding and green body performance.

In terms of lubricating water at the machine mouth, attention should also be paid to the amount of water added. Under the condition of ensuring normal molding, water should be added as little as possible. Although molding can also be carried out with more water, this will make the surface of the green body absorb too much water, which will have a certain impact on the drying process of the green body and the uniformity of the green body performance. It is inevitable to form delamination phenomenon in the forming body by using the screw extruder, which is generally called spiral striation. This texture (layering) is formed by the uneven extrusion of mud from the machine mouth section through the spiral blade. When raw materials are formed into mud strips, we hope to increase the density of the green body by the close combination of particles, rather than by the effect of lubricants. According to the principle of the densest packing of raw materials, when the proportion of each component in the coarse, medium and fine particles of raw materials is distributed according to "big at both ends and small in the middle", the density of the green body is the largest, that is, the particles can reach the densest packing. All particles with one particle size can not achieve good forming effect, and when the proportion of each component is out of balance, it can not achieve good forming effect, and it is easy to produce delamination during forming.