Design and Manufacturing of Kiln Cars

The kiln car of the tunnel kiln is the most expensive component in the tunnel kiln system, and it has a significant impact on the safe operation and energy consumption of the tunnel kiln. The kiln car often encounters various technical issues, which are the main factors affecting the firing quality, operational reliability, and economic efficiency of the tunnel kiln.

The kiln car surface is the component with the most issues in the structure of the tunnel kiln. The two side walls, the top of the kiln, and the kiln car surface form the four sides of the kiln. The kiln car surface should consume the least amount of heat, as the temperatures of the other three sides remain constant after heating, and their heat consumption is limited to heat loss conducted outward.

During normal ignition production of the sintered brick tunnel kiln, the kiln is generally not stopped. However, sometimes issues with the kiln car's quality force the kiln to shut down, leading to an inability to produce normally. Therefore, the quality of kiln car manufacturing directly affects the normal operation of the kiln.

In the manufacturing process of the kiln car, in addition to reasonable design, the selection of materials for the kiln car is crucial. Currently, there are various sources of steel supply in the market, and different manufacturers exist, making it essential for manufacturers to ensure the quality of materials. How to control the material requirements? This is particularly relevant for profile steel kiln cars.

1. The selected materials must meet the physical and chemical indicators and physical performance requirements according to the design to satisfy the production needs of the kiln under thermal conditions.

Based on this issue, I sampled some indicator data from certain manufacturers, particularly noting that the geometric dimensions were all within the negative design deviation, but still within certain acceptable tolerances. However, during actual use, the kiln car experienced varying degrees of deformation under stress during operation. This directly affects the changes in the overall structural dimensions of the kiln car, leading to collisions with the kiln walls during operation.

2. The welding points of the kiln car. 

The technical requirements for the stress points of the main beam, secondary beam, and top car machine must be clearly defined. However, in many kiln car design processes, there are no clear specifications, and manufacturers often overlook the special treatment of key areas. In particular, the welding between the main beam and the stress beams should be done with groove welding and corner welding as per standard practices, and specific data should be provided during the design of the welds. However, some manufacturers neglect the special treatment of key areas to save labor, leading to the collapse of the kiln car during production.

3. Material selection for the kiln car base plate. 

One must never consider saving materials, especially for kiln cars with larger cross-sectional areas. The design should include reinforcement ribs, and the connection between plates should be fully welded with groove welds, avoiding indirect welding at all costs. Some manufacturers use indirect welding to save labor and materials, leading to heat transfer issues at the bottom of the kiln car, and in some cases, material loss occurs, causing debris to block the kiln tracks and preventing the kiln car from running smoothly. Some designs have the sand sealing plate welded to the main beam as a single unit, which, under high temperatures, can lead to uneven thermal stress, causing deformation of the sand sealing plate and collisions with the sand sealing groove, resulting in poor operation. Based on the experience of some manufacturers, the sand sealing plate should be connected to the main beam with oval hole bolts to allow for adjustments in case of uneven stress.

4. Selection of wheels and bearings for the kiln car. 

The kiln car wheels are the support points during operation, and the assembly and selection of the kiln car wheel bearings are key to smooth wheel operation. If the kiln car wheels lack strength, have shallow surface hardness, or are not quenched at all, they will wear out quickly, affecting wheel performance. Similarly, improper bearing selection increases wear resistance, leading to increased load on the top car machine, poor operation, and rapid wear of the kiln track surface, affecting the geometric dimensions within the kiln. When selecting bearings, the gap between the balls and the shaft ring must be reasonable, and bearings with small gaps should not be chosen. The optimal depth of surface quenching hardness for the wheels is 3-5mm.

5. Geometric dimensions of the wheels and the car body. 

This is a fundamental guarantee during assembly, requiring precision in both assembly and adjustment, especially for large cross-section tunnel kiln cars. When assembling the kiln car, the geometric dimensions of each part must be precisely controlled on the tooling platform, and random assembly on the kiln's external tracks should be avoided. For multi-wheel kiln cars, stability and alignment of the connecting axes should be organized during assembly, rather than assembled individually. After assembly, a comprehensive inspection of the dimensions between each wheel and the track contact points or surfaces is necessary, ensuring concentricity and alignment with the car body axis, with tolerances not exceeding design requirements. Additionally, after the kiln car has run continuously in the kiln for more than two cycles, corresponding dimensional inspections should be conducted to identify any other issues.

To ensure the overall quality of the kiln car, the masonry of the kiln car must not be overlooked. Many brick factories neglect the inspection and maintenance of the kiln car during its use, failing to identify and address quality hazards in a timely manner, leading to unnecessary accidents when the kiln car enters the kiln.

The quality of the kiln car's masonry should be taken seriously: the kiln car should meet the same quality requirements as the kiln body, with joints not being too large, and the assembly method should be reasonable. Certain geometric dimensions must adhere to the principles of allowable negative and positive tolerances. When constructing the kiln car, the flatness of the car platform's masonry must not be neglected, and shrinkage joints should be properly reserved.

After unloading bricks from the kiln, the residual bricks and dust on the car platform should be cleaned up at all times. For inexperienced manufacturers, a safety inspection gate should be set up at the return line outside the kiln and at the entrance of the kiln. The kiln car loaded with bricks should pass through the safety inspection gate before entering the drying room and firing kiln, which helps ensure that the brick stacks are not too wide or too high, preventing the car from colliding with the kiln walls and roof, allowing for smooth operation within the kiln.

Compared to cast-in-place kiln cars, masonry kiln cars are more difficult to repair after damage. However, cast-in-place kiln cars have better thermal insulation and sealing performance. It is essential to monitor for any broken pieces falling into the kiln passage during the operation of the kiln car. This issue can easily damage the kiln body, such as destroying the structure of the curved sealing bricks, causing derailment of the kiln car during top car operation, or leading to reverse movement within the kiln. Therefore, to reduce production costs, maintenance expenses, and sintering energy consumption, and to extend the lifespan of the kiln and kiln car, it is crucial to pay attention to the quality of the kiln car.