Yingfeng Machinery－More Than 30 Years Experience In Clay Brick Making Machine ,Tunnel Kiln, Rotary Tunnel Kiln.
How to Manufacture Premium Grade Fired Bricks from Inferior Coal Gangue？
Recycling inferior coal gangue for fired brick manufacturing is a profitable circular‑economy solution for mining areas. Nevertheless, many new‑built brick plant project suffer massive quality failures because operators skip raw‑material assessment and adopt improper equipment or firing workflows. To convert low‑grade coal gangue into qualified solid bricks, hollow bricks and hollow blocks, systematic technical controls must be implemented across raw‑material testing, internal‑combustion firing, extrusion forming, drying‑firing configuration and defect elimination.
Raw‑material characterization is the very first step before you invest in a fully‑automatic fired brick production line. Complete chemical and physical tests plus sintering thermal experiments must be carried out for coal gangue samples. Test scope covers chemical composition, heat value, plasticity index, drying sensitivity coefficient, particle gradation, hardness, drying linear shrinkage, firing linear shrinkage, sintering temperature window, post‑firing water absorption, lime bursting test and efflorescence test. Mineral composition analysis shall be performed when needed.
Only test data can validate whether coal gangue is suitable for brick‑making, determine target brick categories, and guide the selection of raw material preparation system, forming machinery and tunnel kiln. Never launch brick‑plant construction based on empirical judgment only.
Special notes for plasticity‑index testing: crush all test samples down to below 1 mm and apply liquid‑plastic limit combined tester. Particle dimension greatly changes plasticity performance. For instance, shale sample crushed <1 mm shows plasticity index 7.2; the same shale crushed below 0.5 mm reaches plasticity index 11.2. Lab‑test particle size 1 mm simulates real‑world production target 2 mm. Larger particles will obstruct the test cone and produce misleading test outcomes.
There exists no dedicated national standard for coal‑gangue calorific‑value measurement. The industry uniformly applies GB/T 213‑2003 Test Method for Calorific Value of Coal. Do not use empirical industrial calculation formulas, which are not fit for coal gangue feedstock.
Coal gangue fired bricks run on internal‑combustion firing technology. Calorific value of coal gangue largely defines the whole production scheme. When calorific‑value hits approximately 450 × 4.17 kJ/kg, pure coal‑gangue raw material can support full internal‑combustion brick‑making without extra fuel additions. The maximum allowable calorific‑value for 100 % coal‑gangue feedstock is 600 × 4.17 kJ/kg.
Under over‑internal‑combustion circumstances, you have to modify process parameters and extend firing duration. A lengthened customized tunnel kiln is required, fitted with double‑layer kiln gates at inlet and outlet. Supporting subsystems including waste‑heat recovery, flue‑gas re‑ignition, flue‑gas damper adjustment, circulating‑air circuit, rapid‑cooling combustion‑aid, external forced air supply, kiln‑bottom balanced cooling and surplus‑heat releasing shall be installed. These systems enable slow burnout of redundant combustibles inside green brick green body, delivering end‑products with compressive strength above MU20.
If coal gangue calorific‑value is insufficient, mix appropriate raw coal or middling coal. Adding fuel outside kiln is discouraged due to higher particulate emissions. If heat value is excessively high, blend non‑combustible brick‑making materials such as shale, clay or burnt coal gangue. Without available blending materials, adopt screening, air separation, flotation or low‑temperature decarbonization treatment, and tune comprehensive calorific‑value close to 450 × 4.17 kJ/kg.
Most inferior coal gangue appears as massive rock with low plasticity index (except montmorillonite‑rich ore), creating obstacles for wet plastic extrusion forming. Five proven technical solutions can resolve low‑plasticity challenges:
- Optimize crushing fineness: crush feedstock below 2 mm for standard solid & hollow bricks; crush below 1 mm for thin‑wall high‑void‑ratio products. Re‑crush over‑size particles to 0.5 mm and remix them to optimize particle distribution and improve overall plasticity.
- Adopt heavy‑duty hard‑extrusion vacuum extruder. Modern brick‑making vacuum extruder offers extrusion pressure over 4.0 MPa, forming moisture as low as 13 %. It can produce sound green bodies even for raw materials whose plasticity index drops to 5.
- Incorporate high‑plasticity additives like silt, shale or clay. Ensure precise metering and homogeneous blending. For materials with big density gaps, deploy wheel roller mill and disc kneader for intensive mixing besides conventional mixers.
- Equip steam‑heating system for mud mixer before vacuum extrusion. Steam can be supplied by waste‑heat boiler connected to tunnel kiln. Steam‑treated mud gains better plasticity, reduces extruder load and shortens green‑body drying cycle.
- Implement dual vacuum mud refining. Mud receives primary vacuum kneading in vacuum pug mill before entering main brick extruder. Multi‑stage degassing enhances mud plasticity, increases green‑body density and improves wet‑brick mechanical strength and surface quality.
One‑time stacking‑firing requires multi‑layer stacking of green brick green body on kiln cars, which tends to produce black spot pressing marks on contact surfaces. Apart from low‑temperature slow‑firing process, spread a thin sand layer atop each wet brick to boost inter‑layer air circulation. Alternatively change stacking pattern from upright‑setting to flat‑laying, so pressing marks appear on cutting surfaces and will not affect visible brick faces.
Inferior coal gangue contains harmful mineral components that trigger lime bursting and efflorescence.
- Lime bursting originates from calcite and limestone impurities. During firing they convert into quicklime CaO. After being discharged from kiln, quicklime absorbs ambient moisture and turns into slaked lime with sharp volume expansion, destroying brick structure. Crushing raw‑material particle size below 2 mm and saturating hot fresh‑out‑of‑kiln bricks with water can efficiently avoid lime bursting damage.
- Efflorescence comes from soluble salts such as magnesium sulfate and sodium sulfate generated during firing. These salts migrate with water inside bricks and precipitate white crystalline powder on brick exterior after water evaporation. Improve raw‑material fineness and prolong firing & heat‑preservation time, transforming soluble salts into water‑insoluble silicates to suppress efflorescence.
Black‑core cross‑section is typical for internal‑combustion coal‑gangue bricks. Two root causes: insufficient firing temperature & holding time leading to incomplete internal combustion; rapid temperature rise causing early surface sintering and oxygen‑deficient reduction inside bricks. Regulate heating‑up gradient and extend low‑temperature firing period, securing sufficient oxygen penetration inside green bodies, reducing over‑fired black‑core bricks and eliminating under‑fired black‑core defects.
For special low‑grade coal gangue with unique chemical, physical and mineral characteristics, customized process solutions can be deployed to manufacture high‑quality fired brick products.
Although this stage may appear straightforward, improper handling can create production problems.
Unstable stacking, excessive gripping force, inconsistent positioning, and poor coordination between equipment can lead to green brick damage, handling interruptions, and uneven loading conditions.
An automatic brick stacking machine helps organize these operations through programmed movement and controlled positioning.
However, not every brick factory needs the same stacking solution. Machine selection should consider brick dimensions, green brick strength, required handling capacity, stacking patterns, dryer configuration, and the overall production line.
This article explains the main factors to evaluate before choosing an automatic brick stacking system.
1. What Does an Automatic Brick Stacking Machine Do?
An automatic brick stacking machine is designed to arrange freshly cut green bricks into predetermined patterns for subsequent drying, transfer, or kiln loading.
Depending on the system configuration, its functions may include:
-Receiving green bricks from the cutting line
-Grouping individual bricks
-Picking up and transferring brick groups
-Positioning bricks according to a programmed pattern
-Adjusting brick orientation and spacing
-Stacking bricks onto pallets, kiln cars, or designated supports
-Coordinating with conveyors and transfer equipment
Some systems use robotic arms, while others use gantry-type or specialized mechanical stacking structures.
The correct configuration depends on the brick type, production route, required cycle time, and stacking arrangement.
2. Why Is Green Brick Handling Important?
Freshly extruded clay bricks have not yet undergone drying and firing. Their mechanical strength is therefore different from that of finished fired bricks.
They must be handled carefully to maintain their shape and dimensions.
Common problems in manual or poorly controlled stacking
Uneven stacking: Differences in brick positioning can create inconsistent stack geometry.
Edge damage: Repeated manual handling or excessive contact force may damage corners and edges.
Production interruptions: Manual operations may become a bottleneck when the cutting line operates faster than the stacking team can handle.
Inconsistent spacing: Different spacing arrangements can affect airflow through the stack during drying.
Unstable loading: Poorly arranged bricks may move or deform during transfer.
Automatic handling can improve positioning consistency and reduce repetitive manual operations, provided the machine is correctly matched to the bricks.
3. Key Factors When Selecting an Automatic Brick Stacking Machine
Factor 1: Brick Type and Dimensions
The first step is to identify the products the machine will handle.
Different brick types may require different gripping methods and stacking patterns.
Examples include:
-Solid clay bricks
-Perforated clay bricks
-Hollow bricks
-Facing bricks
-Other compatible green building units
The machine should be evaluated against actual brick length, width, height, weight, hole arrangement, and green body condition.
If the factory produces multiple brick sizes, determine whether the system can accommodate product changes through programmable adjustments, replaceable grippers, or other configuration changes.
Factor 2: Green Brick Strength and Gripping Method
Green bricks can be vulnerable to deformation and surface damage.
The stacking machine must apply sufficient force to hold the bricks securely without creating excessive pressure.
When evaluating a gripper or robotic system, check:
-Contact surface design
-Grip force adjustment
-Brick positioning accuracy
-Transfer acceleration and deceleration
-Compatibility with different brick geometries
-Protection against slipping or dropping
A suitable gripping solution should be tested using representative green bricks under actual production conditions.
Factor 3: Required Handling Capacity
The stacking system must match the output of the cutting line.
If the extruder and cutting machine produce bricks faster than the stacking equipment can handle, green bricks may accumulate and force the production line to slow down.
Capacity evaluation should include:
-Green brick quantity per cutting cycle
-Cutting cycles per minute
-Number of bricks per gripping operation
-Transfer time
-Stacking pattern
-Planned operating hours
-Expected downtime
Do not compare machines using hourly capacity figures without checking the brick dimensions, gripping arrangement, and operating assumptions.
Factor 4: Stacking Pattern and Dryer Requirements
Stacking patterns influence more than the appearance of a brick stack.
They affect airflow channels, load stability, and the arrangement of bricks during drying.
A suitable pattern should consider:
-Required spacing between bricks
-Stack height
-Load distribution
-Airflow access
-Brick support
-Transfer stability
For tunnel dryer applications, the stacking arrangement should be coordinated with the dryer airflow design.
A high stacking density is not automatically beneficial if it restricts the circulation of drying air or increases the risk of deformation.
Factor 5: Production Line Integration
An automatic brick stacking machine should be selected as part of the complete production route.
A typical automated clay brick line may include:
1. Raw material processing
2. Mixing and aging
3. Vacuum extrusion
4. Brick strip cutting
5. Individual brick cutting
6. Automatic grouping and stacking
7. Drying
8. Firing
9. Finished brick unloading and packing
The stacking system should communicate and operate in coordination with upstream and downstream equipment.
Engineers should review conveyor speeds, transfer positions, control signals, emergency stops, and recovery procedures.
Factor 6: Maintenance and Operating Conditions
A stacking machine is a mechanical and control system that requires regular inspection.
Before purchasing, evaluate:
-Drive and transmission components
-Servo motors and control equipment, where applicable
-Gripper wear parts
-Sensors and positioning devices
-Lubrication requirements
-Access for cleaning and maintenance
-Availability of replacement parts
-Operator training requirements
The design should allow maintenance work without creating unnecessary disruption to the entire production line.
4. Robotic Stacking vs. Mechanical Stacking: Which Is More Suitable?
Different stacking technologies can be used in brick factories.
The appropriate solution depends on production capacity, brick type, factory layout, and investment requirements.
| Comparison factor | Robotic stacking | Gantry or mechanical stacking |
| Movement structure | Robotic arm with programmed movement | Linear or guided mechanical movement |
| Layout | Depends on robot reach and cell arrangement | Depends on gantry dimensions and travel range |
| Pattern flexibility | Depends on programming and gripper design | Depends on mechanical axes and control configuration |
| Product changeover | May require program or gripper adjustments | May require parameter or mechanical adjustments |
| Maintenance | Robot, drive, gripper, and control maintenance | Rails, drives, lifting mechanisms, and gripper maintenance |
| Selection priority | Flexible movement and suitable working envelope | Defined movement route and stacking arrangement |
The decision should be based on the required movement sequence and actual factory layout.
5. How Does Automatic Stacking Affect Drying Quality?
Stacking is directly connected to the drying process.
The arrangement of green bricks determines how drying air can pass through and around the stack.
If the spacing is too narrow, some areas may receive insufficient airflow. If the arrangement is unstable, the lower layers may be exposed to excessive load.
Key points to control
Airflow channels: The stacking pattern should follow the dryer design requirements.
Stack stability: Brick weight should be distributed without exceeding the green brick's load-bearing capability.
Consistent orientation: Similar bricks should be positioned consistently to reduce variations between stacks.
Loading accuracy: Stacks should be transferred to the dryer or kiln system without excessive impact.
Process compatibility: The stacking pattern must be suitable for the selected drying and firing route.
Automatic stacking improves repeatability, but it cannot replace correct dryer design and process control.
6. What Is a Twice-Stacking System?
Some brick production lines use a twice-stacking arrangement to separate the initial drying arrangement from the final firing arrangement.
Depending on the equipment configuration, green bricks are first arranged for drying. After drying, they are unloaded, regrouped, and stacked again into a pattern suitable for firing.
This approach may be considered when the factory needs different stacking arrangements for the drying and firing stages.
What should buyers evaluate?
-The reason for using two stacking stages
-Whether pallets or trays are required
-The unloading and regrouping mechanism
-The final firing arrangement
-The transfer equipment between stages
-Additional floor space and control requirements
-Compatibility with the selected dryer and kiln
A twice-stacking system should be evaluated as a complete handling process rather than as an isolated machine.
7. Practical Checklist Before Purchasing
Use this checklist when evaluating an automatic brick stacking machine.
1. Confirm all brick dimensions and product types.
2. Measure green brick weight and handling strength.
3. Define the required hourly handling capacity.
4. Confirm the cutting machine's output and cycle time.
5. Select a suitable gripping method.
6. Define the stacking pattern and spacing requirements.
7. Check compatibility with the dryer and kiln loading system.
8. Review the complete equipment layout.
9. Confirm control system and communication requirements.
10. Evaluate maintenance access and spare parts.
11. Request a handling test using representative green bricks.
The best machine is the one that matches the actual production route, not necessarily the machine with the highest advertised speed.
8. Yingfeng Machinery's Automatic Brick Handling Solutions
Zhengzhou Yingfeng Machinery provides brick production equipment and automated handling systems for clay brick factories.
Its equipment range includes automatic brick stacking machines, robotic stacking systems, cutting equipment, and integrated brick production line solutions.
For equipment selection, the following information should be prepared:
-Brick dimensions and product types
-Green brick weight and condition
-Extruder and cutting machine model
-Required hourly production output
-Dryer and kiln configuration
-Factory layout
-Expected level of automation
These details help determine the appropriate stacking method and its connection with the rest of the production line.
Related resources:
Fully Automatic Brick Plant Solution: https://www.zzyfmc.com/fully-automatic-brick-plant-solution.html
Automatic Brick Stacking Equipment: https://www.zzyfmc.com/products_list6.html
Automatic Loading and Unloading System: https://www.zzyfmc.com/faq.html
Existing Project References: https://www.zzyfmc.com/cases.html
Conclusion
An automatic brick stacking machine is an important part of an integrated clay brick production line.
Its role extends beyond transferring bricks. It also affects handling accuracy, stack stability, drying airflow, and the coordination between forming and subsequent production stages.
Before selecting equipment, manufacturers should evaluate brick geometry, green body strength, handling capacity, stacking patterns, and the entire production layout.
A properly matched stacking system can help improve process consistency and reduce repetitive manual operations while supporting more coordinated brick factory automation.
When planning a new brick factory, choosing a kiln is not only a question of firing technology. The kiln configuration also determines how green bricks move through the plant, how drying and firing are coordinated, and how much space is needed for material handling and supporting equipment.
A straight tunnel kiln typically uses a linear kiln structure, with bricks transported through the thermal zones in a defined direction. A rotary tunnel kiln, as used in certain brick production systems, employs a circular or rotary material-handling arrangement designed around its specific kiln configuration.
The term "rotary tunnel kiln" can describe different equipment arrangements across manufacturers. Therefore, buyers should confirm the actual kiln structure, movement mechanism, drying and firing zones, and loading method rather than relying on the product name alone.
This article explains the main selection factors for both configurations.
1. How Does a Straight Tunnel Kiln Work?
A straight tunnel kiln uses an elongated firing chamber. In a conventional kiln-car system, green bricks are stacked on kiln cars and transported through preheating, firing, and cooling zones.
The kiln itself is generally integrated with a production route that may include:
1.Raw material crushing and preparation
2.Mixing and aging
3.Vacuum extrusion
4.Brick cutting and stacking
5.Green brick drying
6.Kiln-car loading and transfer
7.Firing and cooling
8.Finished brick unloading and inspection
Key engineering considerations
Kiln length and thermal zones: The kiln length, zone arrangement, and residence time must suit the intended product and firing curve.
Kiln-car design: Car dimensions, refractory layers, sealing arrangements, and loading patterns influence effective capacity and heat transfer.
Plant footprint: The layout must accommodate the kiln, dryer, kiln-car circulation, loading and unloading stations, maintenance access, and service areas.
Handling synchronization: The forming and drying systems must supply prepared bricks at a rate compatible with kiln loading and unloading.
A straight tunnel kiln is often considered where the factory can accommodate a linear production route and where the project requires a clearly organized continuous process.
2. How Does a Rotary Tunnel Kiln Work?
In rotary or circular tunnel kiln systems, the kiln arrangement and material movement are designed around a rotary path or a moving kiln configuration. The exact mechanism varies by equipment design.
Depending on the system, rotary movement may change how bricks are transferred between operating zones and how the overall production route is arranged.
Before selecting this type of kiln, request a layout drawing and confirm the following:
-Whether the kiln structure itself rotates or kiln cars move along a circular track
-How green bricks are loaded and unloaded
-How preheating, firing, and cooling zones are arranged
-How the drying system connects to the firing system
-How kiln movement is driven, guided, and controlled
-How maintenance access is provided around the kiln
-How the design handles the required brick sizes and stacking patterns
These details are important because two products described as rotary tunnel kilns may have different mechanical structures and operating arrangements.
Potential planning considerations
A rotary arrangement may offer layout advantages in projects where a circular material-handling route is appropriate. It may also require specialized transfer mechanisms, drive systems, structural supports, or maintenance procedures.
The suitability of the design should be established through the actual engineering drawings, site dimensions, and production requirements.
3. Rotary vs. Straight Tunnel Kiln: Comparison Table
| Factor | Straight tunnel kiln | Rotary tunnel kiln |
| General arrangement | Linear kiln structure | Rotary, circular, or moving-kiln arrangement, depending on design |
| Material movement | Commonly uses kiln cars moving along a straight route | Uses the movement mechanism specified by the particular system |
| Site planning | Requires a suitable linear production corridor | Requires sufficient space for the rotary arrangement and its service areas |
| Thermal process | Preheating, firing, and cooling zones are coordinated along the route | Thermal zones must be coordinated with the specific rotary configuration |
| Loading and unloading | Commonly arranged at opposite ends of the production route | Depends on the rotary path and transfer design |
| Mechanical maintenance | Includes kiln cars, rails, drives, seals, and related equipment as applicable | May include rotary drives, guides, transfer devices, and related mechanisms |
| Automation integration | Can integrate with automatic stacking, kiln-car transfer, and unloading | Can integrate with automation when the handling system is designed accordingly |
| Best selection basis | Site geometry, required output, product range, and process design | The same factors, plus rotary movement and maintenance requirements |
4. Which Layout Is Better for a Limited-Space Factory?
Limited land does not automatically mean that a rotary tunnel kiln is the better option.
The total factory footprint includes more than the firing chamber. It also includes the raw material workshop, extrusion area, green brick storage, drying system, kiln loading and unloading zones, finished product storage, maintenance access, and vehicle routes.
A rotary arrangement may be useful when a circular process layout fits the site. A straight tunnel kiln may be suitable where a long, linear production route is available.
To compare both options, engineers should prepare scaled site layouts showing:
-Building dimensions and column positions
-Raw material storage and delivery routes
-Main production equipment
-Dryer and kiln dimensions
-Kiln-car or rotary transfer paths
-Maintenance and replacement access
-Finished brick storage and dispatch areas
-Utility connections and environmental facilities
The relevant measurement is the total usable factory area required for the complete production system, not simply the kiln body's length or diameter.
5. How Should You Compare Production Capacity?
Kiln capacity must be evaluated alongside the rest of the production line.
A kiln with a high theoretical firing capacity cannot achieve its intended output if the extruder, dryer, loading system, or unloading station becomes a bottleneck.
Before comparing quotations, establish a common set of assumptions:
Product specifications
-Brick dimensions and mass
-Solid, perforated, or hollow brick type
-Required fired appearance and performance
Production conditions
-Planned operating hours per day
-Green brick supply rate
-Drying cycle and residual moisture
-Stacking pattern and kiln loading density
-Firing cycle and cooling time
-Expected rejection rate
Handling conditions
-Loading and unloading speed
-Transfer equipment availability
-Kiln-car or rotary mechanism operating schedule
-Planned maintenance and downtime
The output comparison should use the same product specifications and operating assumptions for both systems.
6. Fuel Consumption and Heat Recovery: What Should Be Measured?
It is not technically sound to assume that rotary movement automatically reduces fuel consumption or that a straight tunnel kiln is inherently more energy-efficient.
Fuel use depends on multiple variables, including:
-Moisture entering the dryer and kiln
-Kiln insulation and structural heat losses
-Fuel type, calorific value, and combustion control
-Brick stacking pattern and airflow resistance
-Firing curve and production rate
-Heat recovery and air circulation
-Product dimensions and required firing temperature
For a fair comparison, calculate or measure fuel consumption per 1,000 saleable bricks under comparable conditions.
Also record electricity consumption, maintenance costs, and the effect of production interruptions. A system with lower fuel consumption may not have the lowest total operating cost if it requires more maintenance or has lower usable output.
7. Automation and Maintenance Requirements
Both kiln configurations can incorporate automation, but the required equipment differs according to the mechanical arrangement.
A complete evaluation should consider:
Loading and unloading
Determine whether green brick stacking, kiln loading, fired brick unloading, and transfer operations are manual, semi-automatic, or fully automatic.
Drive and transfer systems
For a straight tunnel kiln, review kiln-car movement, rail alignment, drive equipment, and transfer stations where applicable.
For a rotary system, review the actual rotation or movement mechanism, guiding system, drive components, and transfer points.
Control systems
Check how temperature, fuel supply, airflow, kiln movement, and alarms are monitored and controlled.
Maintenance planning
Ask for the recommended inspection intervals, lubrication requirements, wear parts list, critical spare parts, and safe access arrangements.
Automation should be evaluated in terms of operating reliability and maintainability, not only the number of automated devices.
8. A Practical Checklist Before Choosing a Kiln
Use the following checklist when comparing rotary and straight tunnel kiln proposals.
-Confirm the required daily output and brick specifications.
-Test the raw material and verify forming and drying requirements.
-Obtain a complete production-line layout.
-Confirm the actual kiln structure and movement mechanism.
-Compare dryer and firing capacity as one system.
-Review fuel type, supply conditions, and heat recovery options.
-Confirm loading, unloading, and transfer automation.
-Review maintenance access and spare parts availability.
-Compare investment scope and lifecycle operating costs.
-Request technical references for a comparable application.
9. Explore Yingfeng Machinery's Kiln and Brick Production solutions
Zhengzhou Yingfeng Machinery provides tunnel kiln systems, rotary tunnel kiln configurations, brick-making machinery, and integrated production-line solutions.
For a project-specific comparison, provide the site dimensions, target daily output, brick type, raw material information, fuel source, and preferred automation level.
The engineering team can then evaluate which configuration is suitable for the actual site and production route.
Related resources:
Tunnel kiln systems: https://www.zzyfmc.com/p-products-tunnel-kiln-factory.html
Brick-making equipment: https://www.zzyfmc.com/products.html
Project case studies: https://www.zzyfmc.com/cases.html
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