Tunnel Dryer for Bricks: How to Reduce Cracks and Improve Drying Consistency

Drying is a critical stage between forming and firing. A tunnel dryer must remove moisture from green bricks at a controlled rate while maintaining consistent conditions across the dryer and through the full production cycle.

When cracks or deformation appear, the cause is often a combination of factors: raw material behavior, initial moisture, brick setting, airflow and the drying curve. Adjusting only the air temperature may not solve the problem.

Why green bricks crack during drying

As water leaves a green brick, the material shrinks. If the surface dries much faster than the core, internal stress can develop. The brick may crack, warp or lose its shape.

Common contributing factors include:

•   -A drying rate that is too aggressive for the clay
•   -Uneven airflow around the brick stacks
•   -High or inconsistent moisture in the green bricks
•   -Dense setting that blocks air movement
•   -Sudden changes in temperature or humidity
•   -Different drying behavior among clay batches

The first diagnostic step is to identify where the defects occur: at the dryer entrance, in a particular zone, on specific stack positions or across a certain product type. The location often points to the process variable that needs attention.

Understand the three controls: temperature, humidity and airflow

Tunnel dryer performance depends on the interaction of temperature, relative humidity and air velocity.

Temperature

Higher temperature increases the potential rate of evaporation, but a rapid temperature rise can dry the surface before moisture inside the brick has moved outward. Temperature should follow a controlled profile suited to the brick and clay.

Humidity

Air that is already moisture-laden has less capacity to accept water from the bricks. Managing exhaust and recirculation helps maintain appropriate humidity in each dryer zone.

Airflow

Air must reach the brick surfaces evenly. Poor distribution can leave some parts of a stack wet while others dry too quickly. Fan operation, duct design, baffles, stack spacing and the quantity of bricks loaded on each car all affect airflow.

These controls should be reviewed together. For example, raising temperature without increasing moisture removal may increase humidity and leave the dryer unable to achieve uniform drying.

Set bricks to support even air circulation

The stacking pattern influences both airflow and drying uniformity. Bricks placed too close together can restrict circulation. Excessively open spacing may reduce the effective dryer loading and change the flow pattern.

When reviewing a setting pattern, check:

•   -Whether gaps between bricks are consistent
•   -Whether airflow paths remain open through the stack
•   -Whether the stack height and width match the dryer design
•   -Whether bricks are set in the same orientation
•   -Whether different product sizes need separate setting patterns

Any change should be tested with a consistent sample and recorded. This makes it easier to see whether an improvement came from the setting pattern or from a change in raw material or dryer operation.

Use a staged drying profile

A typical drying process starts with conditions that limit rapid surface drying, then gradually moves toward higher drying potential as moisture content falls. The actual profile must be established for the product and factory; fixed temperature values should not be copied without checking the clay and equipment.

Useful monitoring points include:

•   -Green brick moisture before entering the dryer
•   -Temperature and relative humidity by zone
•   -Supply and exhaust air conditions
•   -Brick moisture at dryer exit
•   -Defect type and location
•   -Dryer cycle time and production rate

A profile that works for one brick size or clay body may not work for another. A change in raw material, extrusion moisture, wall thickness or stacking arrangement can require a new drying assessment.

Check dryer balance before changing the cycle

If the dryer produces inconsistent results, inspect the system as a whole:

1.  1. Confirm that fans and dampers are operating as intended.
2.  2. Compare temperature and humidity at several locations across the dryer.
3.  3. Check whether the exhaust removes moisture at the required rate.
4.  4. Inspect for air leakage or short-circuiting between supply and return paths.
5.  5. Confirm that dryer cars move at a consistent interval.
6.  6. Compare the moisture and condition of green bricks entering the dryer.

These checks can reveal whether the issue is a process setting, a loading problem or an equipment balance problem.

Coordinate the dryer with the kiln

The dryer and kiln are connected through production flow and heat management. If dryer output is inconsistent, kiln loading can become irregular. If dryer and kiln schedules are not aligned, production may experience bottlenecks or unnecessary waiting.

Where the plant design allows, heat from kiln cooling or exhaust may be considered for dryer use. The heat source should be controlled to match the dryer’s temperature and moisture-removal needs. Heat recovery is a process integration decision, not simply a matter of connecting a duct.

Conclusion

A tunnel dryer produces consistent green bricks when the drying profile, airflow, humidity, brick setting and production rhythm are considered together. When defects occur, map their location and pattern, then check the operating conditions at the relevant dryer zones.

Systematic monitoring helps distinguish between raw material variation, loading issues and dryer control problems. This gives plant operators a clearer basis for improving drying quality and coordinating the dryer with the tunnel kiln.