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How Does The Roasting Temperature Determine The Finished Quality Of Sintered Bricks?

2026-05-28

The quality difference of finished sintered bricks is fundamentally caused by inaccurate firing temperature and atmosphere control, and the standard sintering temperature range for qualified bricks is fixed at 900℃ to 1100℃. All green bricks and mixed raw materials must complete sintering within this range to achieve partial melting and form stable physical properties. Any deviation from this temperature standard will cause typical quality defects, while matched atmosphere adjustment and internal combustion technology can further optimize brick performance.

The most common unqualified products in brick production are overfired bricks and underfired bricks, both caused by improper temperature control. Excess temperature and long sintering time lead to overfired bricks, which are dark-colored, crisp in sound and severely deformed, failing dimensional and flatness standards. Low temperature and insufficient sintering time result in underfired bricks, which have pale appearance, dull knocking sound, low strength, high water absorption and poor durability, greatly shortening the service life of building structures.

Even with standard 900–1100℃ temperature control, different kiln environments create different brick types. Oxidative atmosphere sintering produces red bricks. The iron oxide in raw materials is oxidized into ferric oxide (Fe₂O₃), forming a stable red finish with balanced cost and basic performance, making it the most widely used building brick. After oxidative sintering, closed kiln smoldering creates a reducing atmosphere, turning Fe₂O₃ into ferrous oxide (FeO), which forms high-density blue bricks. Blue bricks feature excellent alkali resistance and durability, superior to red bricks, yet their complex process and high cost limit large-scale use.

To solve the problems of high raw material consumption, high energy consumption and unstable partial sintering in traditional brick making, internal combustion brick technology is widely adopted. By mixing coal slag and high-carbon fly ash into brick raw materials, the carbon inside the green brick burns autonomously at 900–1100℃. This realizes uniform internal and external sintering, saves massive fuel and 5%–10% clay resources, improves brick strength by about 20%, and reduces bulk density and thermal conductivity, achieving energy-saving, environmental-friendly and high-quality production

Why do sintered bricks develop cracks?

How Can A Sintered Brick Factory Reduce Fuel Costs To Achieve Energy Saving And Consumption Reduction?

Related questions

What Practical Methods Can Accelerate Fired Clay Brick Sintering Speed in Tunnel Kiln Production?

1.Strictly control fuel moisture content to improve coal ignition efficiency

Excess water in coal consumes massive heat for water evaporation after entering kiln, delays ignition time; damp coal agglomerates and reduces contact area with air to slow down combustion. Build rainproof coal storage shed to avoid coal soaking in rainy days; coal with excessive moisture must be air-dried or artificially dried before feeding into kiln.

2. Screen and crush raw coal to expand fuel contact area with air

All kiln-used coal needs pre-screening; large lump coal shall be fully crushed. Fine granular coal increases oxygen contact area, speeds up burning, and effectively lowers coke accumulation and black brick defects.

3. Standardize stacking layout & coal feeding rules with fixed quantitative parameters

Follow the operation rule: feed frequently with small dosage, add coal according to real-time kiln fire condition.

For full external combustion bricks: feeding circulation interval = 1.5 minutes/time
Temperature section 800~900℃: single feeding weight 0.1~0.2Kg
Temperature above 900℃ up to peak firing zone: single feeding weight 0.2~0.3Kg Reduce external coal consumption properly when internal combustion proportion of green brick rises. Keep the proportion of coal falling onto kiln bottom at the optimal value: 10%. Replace manual feeding with automatic coal feeder: save around 20% fuel consumption for even feeding. Over-large one-time feeding causes oxygen shortage and unstable kiln temperature.

4. Unify operation specifications of three working shifts to stabilize fire advancing speed

Inconsistent operation among shifts leads to fluctuating kiln temperature and uneven fire travel, resulting in extra fuel waste, unstable brick quality and limited output. Uniform operating standard ensures steady sintering rhythm.

5. Properly increase excess air volume under qualified firing temperature

On the premise of meeting required sinter temperature, raise surplus air reasonably to lift oxygen concentration inside firing zone, accelerate oxidation reaction and shorten sinter cycle.

6. Adopt low-temperature long-time firing technology for internal combustion bricks (especially high-internal-combustion bricks).

Rapid early heating makes green brick surface vitrify prematurely, seals internal pores and blocks oxygen penetration, causing incomplete or even stopped combustion of inner fuel.

Keep slow temperature rise at front section of firing zone to reserve open pores for continuous oxygen infiltration;
Maintain high temperature at middle & rear firing zone to burn out internal fuel completely, reduce finished brick faults including black core and indentation. This craft is defined as low-temperature long firing compared with high-temperature short firing process.

7. Transform solid bricks into hollow bricks to optimize inner oxygen supply

Hollow structure reserves holes inside bricks, greatly boosts contact between internal fuel and infiltrated oxygen. Hollow design is highly recommended especially for high internal combustion bricks to speed up inner fuel burning obviously.

How to quickly solve the core faults of a brick factory strip cutting machine?

The brick strip cutting machine serves as core processing equipment in fully automatic brick making production lines, responsible for cutting raw mud strips, compressing blanks and feeding strips to the brick cutter. Unexpected breakdowns will halt whole production and raise factory maintenance costs. Most malfunctions originate from faulty proximity sensors, unstarted air compressors and worn brake pads. Below are six frequent faults with actionable fixing steps for on-site maintenance technicians.

1. Strip cutter cannot cut mud strips

Fault reason: X2 proximity sensor fails to trigger induction or is broken; air compressor remains shut down without air supply.

Solution: Two workers cooperate for inspection. One manually blocks the X2 sensor, another checks the corresponding indicator lamp on I/O monitoring page of the touchscreen. If the X2 lamp stays off, replace the defective X2 sensor; meanwhile confirm the air compressor is powered on.

2. Cutter unable to compress mud blanks

Fault reason: X4 or X5 sensor loses induction or gets damaged.

Solution: Dismount X4 and X5 sensors one by one, test with ferromagnetic metal parts. No lighting during testing means sensor damage and needs replacement.

3.Continuous strip feeding while brick cutter never cuts blanks

Fault reason: Damaged or non-inductive X7 sensor, missing feeding-in-place feedback signal.

Solution: Carry out paired detection via touchscreen I/O interface. Block X7 manually, check indicator status; replace X7 if no light is on.

4. No strip feeding but brick cutter keeps cutting nonstop

Fault reason: X7 sensor is permanently triggered by constant induction, sending wrong position signal to PLC control system.

Solution: Adjust X7 mounting position and sensing distance to eliminate false continuous induction.

5. Mud strip feeds into position but cutting mechanism refuses to cut

Fault reason: X6 sensor malfunction or damage, no in-place signal transmitted to control unit.

Solution: Remove X6 sensor and test with iron accessories; replace the component when indicator does not light up.

6.Cutting unit returns home but fails to stop instantly or stops extremely slowly

Fault reason: Excessive abrasion on cutting motor brake lining leads to insufficient braking force.

Solution: Fine-tune brake pad clearance; replace severely worn brake pads if adjustment cannot solve the issue.

Conclusion: Daily regular calibration of all cutting machine sensors and periodic inspection of brake wear can drastically reduce unplanned downtime and maximize continuous brick output.

Why Temperature Fails to Prevent Winter Brick Collapse?

Humidity Control Is the Hidden Key of Tunnel Kiln Drying Chamber

In recent years, large-section tunnel kilns have achieved continuous output breakthroughs in the brick and tile industry. Many production lines have even far exceeded the designed production capacity. However, the stubborn problem of green brick collapse in winter drying processes has plagued most manufacturers and cannot be completely solved for a long time. Most technicians have long regarded exhaust temperature as the core standard to judge drying quality, believing that increasing the exhaust temperature can effectively avoid brick collapse. In actual production, most enterprises control the exhaust temperature above 30°C, and some even set the standard at 40°C or 50°C.

However, a large number of field production practices have overturned this traditional cognition. Many drying chambers with exhaust temperature exceeding 45°C still face severe winter brick collapse failures. This fully proves that exhaust temperature is not the decisive factor for green brick collapse. The real core parameter that determines the drying effect and avoids blank collapse is exhaust humidity.

The optimal exhaust humidity range for tunnel kiln drying chambers is 90%-100% (excluding 100% saturation). Within this range, the hot air can maintain the highest heat utilization rate, realize uniform and gentle dehydration of green bricks, and avoid structural damage caused by rapid drying or secondary moisture absorption. The higher the exhaust humidity (within the standard range), the higher the thermal efficiency of the drying system, which means no waste of hot air heat.

The biggest flaw of current domestic drying chamber design and operation is the lack of effective humidity detection and adjustment devices. Most production lines are only equipped with temperature monitoring equipment, without humidity meters installed. A small number of factories that have installed humidity meters still fail to solve the collapse problem due to the absence of supporting adjustment systems, making humidity detection a mere formality. Unreasonable humidity control leads to unstable drying atmosphere in the chamber, which is the fundamental reason for frequent winter brick collapse, even if the temperature index meets the standard.

To completely eliminate winter blank collapse, tunnel kiln production lines must abandon the single temperature control logic, take exhaust humidity regulation as the core, and match scientific exhaust mode and air volume design to build a stable and efficient drying environment.

What Are The Key Factors Affecting The Drying Efficiency Of Sintered Bricks?

Low drying efficiency is a common trouble for most sintered brick production lines. Many factories install high-temperature hot air systems for the drying chamber, yet still face slow drying speed, frequent cracking and deformation of bricks. In fact, the efficiency of sintered brick drying depends not merely on temperature, but the combined coordination of three core factors: temperature, humidity and airflow velocity of drying media. All these factors jointly affect heat transfer and moisture diffusion inside green bodies.

All elements influencing sintered brick drying act on heat transfer and mass transfer. Heat transfer efficiency is decided by the total heat the drying chamber can obtain per unit time, while diffusion efficiency depends on the migration and evaporation speed of moisture inside and outside green bodies. A widespread mistake in production is only raising hot air temperature while ignoring airflow and humidity control. This wrong operation leads to poor drying efficiency and restricts the overall output growth of the factory.

Air volume and airflow velocity are the most easily overlooked factors in sintered brick drying. Some lines supply high-temperature hot air, but the fan has insufficient air output. Hot air circulates slowly in the drying chamber, so even if the displayed temperature is high, each green body cannot get enough heat. Unbalanced heat and mass transfer result in extremely slow drying. On the contrary, production lines with moderate temperature but sufficient air volume can realize fast hot air circulation. Heat covers all green bodies evenly to complete uniform drying, delivering better product quality and higher output.

Humidity of drying media also plays a vital role. Excessively high humidity in the drying chamber will slow down surface water evaporation, block internal moisture discharge and cause internal cracks. If the humidity is too low, the green body surface will dry too fast and form a hard shell, which hinders internal moisture migration and results in hollowing and surface cracking.

Optimizing the sintered brick drying process is the most cost-effective way to boost factory benefits, much more effective than simply upgrading the firing section.

Production teams must abandon the outdated idea of valuing firing over drying. On the basis of low-moisture molding and standard green body stacking, adjust hot air temperature, air volume and humidity according to raw material features, and optimize drying curves in real time.

Scientific optimization of sintered brick drying can eliminate common drying defects, shorten production cycles and improve the rate of qualified products. It will thoroughly break the output and quality bottlenecks of sintered brick production, and help enterprises operate stably and gain maximum economic returns.

How Can A Sintered Brick Factory Reduce Fuel Costs To Achieve Energy Saving And Consumption Reduction?

Fuel cost is the largest variable expenditure in the production process of sintered bricks and the core factor determining the profit margin of brick factories. Unlike fixed costs such as equipment depreciation, staff salaries and certification amortization, fuel expenses fluctuate greatly due to regional raw material prices, fuel quality differences and batching technologies, ranging from $70 to $150 per ten thousand standard bricks in different regions.

Most sintered brick enterprises adopt calorific solid fuels including coal, coal gangue and fly ash. To achieve precise fuel cost control, brick plant managers must abandon the simple price comparison of fuel tonnage and adopt aunit calorific value cost accounting method, which is the key to scientific fuel procurement. For example, if 3000-kcal fuel is priced at $42 per ton and 3500-kcal high-quality fuel is $45 per ton, the latter has a lower actual calorific value unit price and higher combustion efficiency, which is more cost-effective in long-term production.

In addition to standardized procurement accounting, fuel quality inspection is indispensable. Unscrupulous suppliers often cut corners by falsifying calorific value data, insufficient weighing and excessive moisture content, which directly leads to insufficient brick firing, increased secondary fuel supplementation and hidden cost losses. Brick factories need to arrange special purchasers to track local real-time fuel market prices, screen stable and high-quality suppliers, and strictly inspect fuel weight, moisture and calorific value before warehousing to eliminate unqualified fuel materials.

The internal combustion batching ratio is the top priority of fuel cost control and quality management for sintered brick plants. For the once-setting and once-firing wet brick production process, unreasonable internal combustion proportion will trigger a huge cost chain reaction. Practical production data shows that insufficient internal combustion fuel will force enterprises to invest 3 times more external combustion fuel to meet the brick firing qualification standard. Worse still, mismatched batching will cause quality defects such as underfiring and unstable brick hardness, damage corporate market reputation and cause long-term operational losses.

Therefore, brick factories must formulate fixed internal combustion batching management systems based on local raw material characteristics and production equipment conditions. After repeated debugging to determine the optimal batching standard that requires no external combustion and avoids underfiring, the standard shall be strictly implemented in daily production. This can not only stabilize product quality fundamentally, but also maximize fuel utilization and effectively reduce the core production cost of sintered bricks.

Why do sintered bricks develop cracks?

Structural cracks are one of the most common defects in sintered brick production, caused by improper raw material treatment and brick molding processes. Unlike regular molding cracks induced by fixed machine mouth equipment issues, structural cracks featureirregular distribution and random occurrence—a core distinguishing feature that often leads to misjudgment by production technicians. Accurate identification and targeted adjustments can effectively eliminate structural brick cracks and improve finished brick yield.

The first leading cause of structural cracks is uneven batching of raw materials. When two or more raw materials with inconsistent moisture content, plasticity, and particle gradation are mixed inadequately, the green bricks will produce uneven internal stress after extrusion and molding, resulting in irregular cracks. Many production lines rely solely on crushing, stirring and screening equipment for raw material mixing, which is a typical production mistake. Raw materials must be fully pre-mixed evenly before entering crushing equipment to lay a foundation for uniform mud performance.

Impurity contamination in raw materials also triggers structural cracks. Foreign matter such as tree roots, grass roots, plastic ropes, and large hard materials cannot be completely removed if the screen mesh is damaged or poorly maintained. These impurities disrupt the internal compactness of the mud strip, forming weak structural points and cracking during subsequent drying and molding. Manufacturers need to inspect screen meshes regularly, replace damaged parts in a timely manner, and thoroughly clean on-site sundries after equipment maintenance to avoid secondary impurity mixing.

Unstable moisture content of mud entering the brick machine is another critical factor. The leftover mud remaining in belts and equipment after shutdown will lose water naturally during downtime, forming dry-wet mixed mud. Temporary water addition via the brick machine agitator cannot solve the uneven moisture problem, leading to inconsistent shrinkage of green bricks and structural cracks. Standardized shutdown procedures are essential: all residual mud in conveying and molding equipment must be completely cleaned after daily production.

Worn mixer blades and unreasonable water addition parameters will cause inadequate mud stirring. Excessive gaps between agitator blades and the mixer box lead to uneven mud mixing, while inappropriate water addition timing and dosage disrupt mud plasticity stability. Regular detection of blade gaps and optimized water addition strategies are effective improvement measures.

In addition, severely worn spiral augers of brick machines cause unbalanced extrusion speed of mud strips, resulting in inconsistent density of green brick bodies. Different density parts produce different shrinkage rates during drying, eventually forming structural cracks. Timely inspection and replacement of worn augers are required to ensure uniform mud extrusion.

Unreasonable installation or unqualified production of core frames will also induce internal structural defects of bricks. Adjusting the core frame installation position and replacing substandard core frames can completely eliminate this type of crack source. Moreover, uneven connection between machine mouth and belts, belts and cutting machines will bend the extruded mud strips. Regular calibration of equipment levelness and cleaning of adhesive mud on belt rollers can avoid bending-induced structural cracks.

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