The tundish is named because it is located between the ladle and the continuous casting machine during operation. It is also called the middle ladle or the intermediate tank. There are many types of tundishes, and the common shapes are rectangular and T-shaped. The construction of the tundish is also varied. The permanent layer can be bricked or cast, and the working layer can be installed with insulation boards, sprayed, or painted. In recent years, there is also a working layer formed by dry castables as a whole. The lining materials used are acidic, alkaline, and neutral. However, the tundish has a simple structure and is generally divided into a ladle bottom and a ladle wall. There is a water inlet and an impact zone (plate) at the bottom, and an overflow trough on the upper edge of the ladle wall. Some tundishes also have slag retaining walls (plates). The tundish is the refractory lining that is most frequently overhauled in steel mills. Its construction characteristics and development trends are: applicable materials and quick construction.
Taking the tundish of a certain factory as an example, the construction of plate tundish and coating tundish is briefly introduced. The permanent layer of the tundish is made of high-aluminum castable material, and the working layer is installed with insulation plates or coatings according to the needs of the steel type.
Construction points
(1) Pouring of the permanent layer as a whole:
Clean the cladding shell, place the square brick mold of the tundish water inlet, and pour the bottom with high-aluminum casting material. The surface should be flat and compacted with a vibrating scoop. The machine should not be stopped unless there are special circumstances during the mixing process: After the bottom is dried naturally for 24 hours, place the cladding wall mold to pour the cladding wall. The gap between the mold and the cladding wall steel plate should be uniform. The material should be evenly distributed during pouring and compacted with vibration. The thickness of the pile should not exceed 300mm; after natural curing for 24 hours, demould and place on the baking table.
(2) Install the sprue and seat bricks:
Place the sprue at the center of the injection port. It should be stable and centered. Pour an appropriate amount of ramming material around it. Ram it tightly with special tools. Do not move the sprue. When it is slightly lower than the upper horizontal surface of the sprue, install the seat bricks. Use magnesium-chromium refractory mud to wet-lay the joints. The refractory mud must be applied evenly and fully. The contact seam should not be larger than 1mm and the surface should be clean. At the same time, the base brick should be concentric with the water outlet. After it is fixed, continue to tamp the surrounding layers until it is flush with the castable.
(3) Install insulation board and fill with sand:
1.The order of insulation board installation: bottom → end face → side face;
2.Before installing the bottom insulation board, first lay quartz sand according to the design, then install the bottom insulation board, and build from the middle impact area to both sides. The end face and side insulation boards are installed from left to right. Before installation, use paper sticks to separate the insulation board from the permanent layer casting material, so that quartz sand can be filled after the insulation board is installed. The insulation board is installed with homogeneous refractory mud wet masonry, the mud is full and uniform, and the male and female joints are well matched. The door is closed at the mouth, and the side symmetrical insulation board is firmly supported by paper sticks.
3.The gap between the insulation board and the top brick of the water inlet is filled and scraped with homogeneous refractory mud to avoid affecting the normal insertion of the plug rod, and the edge of the impact plate is sloped with fire mud.
4.After assembly, quartz sand is filled in the gap between the insulation board and the cast permanent layer, flush with the upper edge of the insulation board.
5.The insulation board at the overflow trough is processed and built according to the size of the overflow trough.
(4) Construction of coating material.
The construction of the tundish coating material is relatively simple. First, install the nozzle, seat brick, impact plate and slag retaining wall, and then evenly apply the mixed bulk material on the permanent layer in layers. After reaching the designed thickness, pierce the heat dissipation holes; the joints between the coating material and the seat brick, impact plate and slag retaining wall should be smeared into a slope, and the surface of the overflow trough should also be coated with the working layer of bulk material.
The materials used in the tundish are more complex and have a faster turnover. The working layer is generally baked on a low fire and can be used after being baked for more than 24 hours.
In recent years, the application and promotion of dry materials in tundishes have been rapid. Dry materials (using magnesium refractory materials) have the advantages of long service life, easy ladle turning, and low labor intensity. Although they have disadvantages such as high construction requirements and long construction time, they have been widely promoted and used in recent years.
The construction of dry materials is similar to the integral pouring of the permanent layer. The vibration force generated by the vibrator fixed on the mold is transmitted to the refractory material through the mold, thereby densifying the refractory material. After molding, the mold evenly supplies heat (or transports hot air) to bake the dry material. When it reaches a certain temperature, it is demoulded and hung on the baking table for use.
The specific construction method of dry material is as follows:
(1) Before construction, hoist the tundish into the tundish pit and remove the residual steel and slag in the tundish. Evenly apply butter mixed with a small amount of graphite on the outer surface of the tundish dry vibration mold, and paste horse manure paper according to the standard.
(2) When the temperature of the permanent layer reaches the condition, install the nozzle seat brick mold and impact brick.
(3) Spread a layer of dry vibration material with a thickness that meets the standard on the bottom of the ladle, scrape it flat with a wooden board, and then hoist it into the mold. The gap around the mold and the permanent layer should be uniform and meet the design requirements.
(4) After the mold is placed, pour the dry vibration material evenly from all sides of the mold, fill it up at one time and the height of the material is higher than the edge of the ladle, turn on the vibration motor on the mold, add material and vibrate at the same time, so that the dry vibration material is filled and filled until the material is flush with the edge of the ladle. The vibration time is 3~4min. Finally, spray a small amount of water on the vibrated surface.
(5) After the vibration is completed, it is hoisted to the baking platform and baked for 2 hours. After cooling for 1 hour, demoulding is carried out according to the separation between the working layer and the mold (demolding can only be carried out when there is separation around the junction of the dry material and the mold, otherwise the cooling time will be extended).
(6) When the demoulding tundish is cooled to below 100℃, the impact bricks and slag retaining walls are installed according to the relevant construction standards, and the joints are filled with dry vibration repair materials provided by the manufacturer; finally, the cover and plug rod are installed, and it is put into use after the platform is baked. The baking of dry refractory materials formed by vibration is divided into ground baking and casting platform baking. When baking on the ground, you must first light the fire and then turn on the gas, and finally turn on the compressed air. When turning off the fire, turn off the gas first and then the compressed air. Bake on the ground for 12 hours, and determine the cooling time according to the separation around the junction of the dry refractory materials and the mold.