Kiln Car: Structure, Materials, and Sealing in Tunnel Kiln

The kiln car is an important component of the tunnel kiln, forming a moving kiln bottom.

1. Form of kiln car

Kiln cars come in two types: steel kiln cars and iron kiln cars. Steel kiln cars are lighter and easier to maintain. Cast iron kiln cars have advantages such as high rigidity, small thermal deformation, resistance to oxidation and corrosion, and robustness. Moreover, they use iron instead of steel, saving materials. However, due to the heavy weight of the frame, a better casting process is required to ensure quality. The wheels can use standard bearings or custom-made non-standard bearings, but these have higher frictional resistance and a shorter service life.The structure of the kiln car is shown in Figure 6-8.

Figure 6-8 Simplified diagram of a kiln car

 2. Selection of Lining Brick Materials

Because the kiln car lining bricks are in an unstable heat transfer state within the kiln, the heat accumulated in the lining bricks and the heat dissipated downwards through them change over time. To reduce the heat transferred to the lower part of the kiln car through them and to minimize the impact of accumulated heat on the temperature distribution within the kiln, lightweight insulation materials with low thermal conductivity and low heat capacity should be selected. This not only helps to reduce the temperature difference between the upper and lower parts of the kiln and promotes uniform firing of the products, but also reduces heat dissipation downwards, lowering the temperature of the metal parts of the kiln car and the area beneath it. On the other hand, the surface and surrounding areas of the kiln car lining bricks, due to their contact with high temperatures and the bearing of loads, and their exposure to periodic temperature changes, should be made of refractory materials that can withstand high-temperature loads and have good thermal stability.
When selecting lining materials, brick and tile factories can consider using irregularly shaped refractory bricks or irregularly shaped heat-resistant concrete blocks for the perimeter lining, and standard-shaped refractory bricks or ordinary red bricks for the roof lining. Each material has its advantages and disadvantages. In terms of thermal conductivity, refractory bricks have lower thermal conductivity than red bricks; in terms of heat capacity, red bricks have lower thermal capacity than refractory bricks; refractory bricks have higher strength than red bricks, but their cost is also higher. Each factory can choose one based on its own conditions.
The materials for the middle and lower lining bricks can be lightweight clay bricks, vermiculite, expanded perlite, ceramic fiber, and slag, etc.

3. Kiln car sealing

In tunnel kilns, the quality of the kiln car seal directly affects their thermal performance. Severe air leakage can lead to increased temperature differences within the kiln, prolonged firing time, and increased fuel consumption.
The kiln car seal consists of two parts: the two sides rely on the sand sealing plates on the car frame to be inserted into the sand sealing groove inside the kiln to achieve the seal between the kiln car and the kiln wall, and the two ends of the kiln car rely on the overlapping of the adjacent kiln car lining bricks and the contact seal at the ends of the kiln car to achieve the seal between the kiln car and the kiln workshop.
To ensure good sealing during production, in addition to appropriately filling the kiln sand sealing trough, the sand sealing plate must be rigid and free from deformation. Therefore, for kiln cars longer than 1.5m, 8-12mm thick steel plates can be used for the sand sealing plate; for cars shorter than 1.5m, 5-6mm thick steel plates can be used. Furthermore, the connection of the sand sealing plate should have the freedom to expand at both ends to prevent warping and deformation due to thermal expansion. Additionally, the front and rear ends of the kiln car have raised and recessed grooves filled with refractory materials such as asbestos rope; when the flanges are pressed into the grooves, a contact seal is formed.