The function of the air brick base is to protect the air brick core. If the base brick cracks during use, it will not only fail to effectively protect the brick core and affect its service life, but also cause steel leakage in severe cases. In addition to the quality problems of the base brick itself, external factors also have a crucial impact on the cracking of the air brick base brick.
The refractory design of the base brick itself is unreasonable
Phenomenon: The thermal shock resistance of the seat brick is poor, cracks and fractures occur during use, resulting in steel leakage.
Reason: The refractory material design is unreasonable and the thermal shock resistance is poor.
Solution:
1) Adjust the material ratio of the breathable seat brick to improve the thermal shock resistance;
2) Appropriately increase the amount of steel fiber added, especially for the ladle with slow turnover, the improvement effect is obvious.
External factors lead to cracking and steel leakage of air-permeable bricks
The opening at the bottom of the integral air-permeable brick installation package is too large
Phenomenon:
Due to historical reasons, operating habits, etc., the diameter of the hole at the bottom of the ladle is large, reaching 100mm or even larger, causing the seat bricks of the integral air-permeable bricks to crack and leak steel during use.
Reason:
The seat bricks of the integral air-permeable bricks are installed inside the ladle shell, and the tail pipe of the air-permeable bricks must extend through the bottom shell of the ladle and connect to the external gas source. There is a mounting hole at the bottom of the shell, and the diameter of the mounting hole can generally hold the tail pipe 30 to 50mm.
During use, the air-permeable bricks are in contact with molten steel inside, and the temperature reaches about 1600℃. The bottom is in contact with the outside air and stabilizes at about 150℃. The larger the opening, the faster the bottom of the seat brick cools down, the greater the temperature difference between the top and the bottom, and the easier it is for the seat brick to produce microcracks under the influence of the temperature gradient. As the number of uses increases, the crack width becomes larger and larger, which may eventually lead to steel leakage accidents.
In addition, the depth of the bottom of the air-permeable brick core embedded in the seat brick is between 0 and 40mm. When the ladle is connected to the steel, the static pressure of the molten steel acts on the brick core and then transmits to the bottom of the seat brick.
If the base brick is not supported by a steel shell or the supporting area is small, the 0-40mm castable material is likely to swell and crack under the dual effects of pressure and thermal shock, causing the brick core to move downward, which will also cause the air-permeable brick to leak steel.
Solution:
In this case, the steel mill can be required to plug the hole or open the hole normally as required to ensure the safe use of the air-permeable brick.
The bottom of the package is uneven or the steel shell is deformed
Phenomenon:
The bottom of the ladle is uneven, causing the bottom of the air brick seat brick to crack and steel leakage. The air brick installed on this severely deformed pad is likely to cause the bottom to crack and steel leakage.
Reason:
Most steel mills install the air brick directly on the steel shell. Some steel mills lay some leveling materials on the steel shell. Some steel mills used to have too large openings, and used a 10mm thick steel plate to pad the opening before placing the air brick. Some steel mills have overused steel shells, and the bottom plate or bottom steel pad has been deformed and uneven due to high temperature, impact of the unpacking machine, etc. After the air brick is installed, the bottom of the air brick and the steel shell at the bottom of the ladle are in point contact, and there is a phenomenon of shaking back and forth.
The bottom of the seat brick is uneven, which is equivalent to adding a fulcrum at the bottom of the seat brick. Under the action of thermal shock and static pressure of molten steel, the seat brick is prone to cracks.
Solution:
When placing the air-permeable brick base, you can use chrome corundum fire clay to level the bottom of the air-permeable brick base, and replace the severely deformed pads in time.
Improper replacement method
Phenomenon:
There are cracks inside the split air brick, and the brick core falls off and leaks steel during use.
Cause:
When some steel mills replace air bricks, they use steel rods to extend from the bag mouth to the surface of the brick core and manually pound the brick core down. This operation will inevitably hit the surface of the seat brick during implementation. The strength of the seat brick is very low in the hot state. When hit, it may cause damage to the surface seat brick or crack the seat brick. As the cracks expand in the later stage of use, it will cause steel leakage.
Solution:
Change the operation method of replacing air bricks. It is recommended to use a pulling mechanism to pull out the remaining bricks, which can avoid the above situation and reduce the labor intensity of workers. At present, more and more customers at home and abroad use pulling mechanisms to replace air bricks.
The expansion joint self-flowing material is not resistant to erosion
Phenomenon:
The caulking material filled in the reserved seams around the air-permeable brick base brick erodes too quickly, causing the air-permeable brick base brick to be exposed and cracked.
Reason:
In order to facilitate the replacement of the air-permeable brick base brick, the general design reserves a 40-100mm gap between the base brick and the bottom brick, and the castable (or ramming material) is used to seal the seam. If the quality of the material used for caulking is poor, it will also affect the use of the air-permeable brick, and in severe cases, it will also cause steel leakage.
Solution:
Use high-grade self-flowing material. At present, the main caulking material used at home and abroad is corundum self-flowing material. Corundum self-flowing material has been adopted by most manufacturers due to its good fluidity, easy construction, and corrosion resistance.
With the rapid development of steel smelting technology, the refining process outside the furnace has become an important part of the steel smelting process. The correct use of air bricks can ensure production safety. When using air bricks, it is necessary to promptly check for various hidden dangers, and choose reasonable improvement measures according to different damage conditions to avoid the occurrence of air brick leakage accidents.
