Application of tundish magnesia dry material and tundish gunning mass

1 Application of tundish gunniing mass
Our company's tundish gunniing mass was tested on four tundishes on a special-shaped continuous casting machine. During use, the mixed coating material was poured into a mixer, and water was added while stirring. The water content was 14-17%, and the stirring time was 5-10 minutes. After thorough mixing, the coating material with an appropriate amount of water was poured into the prepared tundish (the temperature inside the tundish was 60-100℃). Then, the coating was applied to the tundish wall from bottom to top using a trowel. The first coat was thin to facilitate rapid hardening and shorten the time interval between coats. If the first coat was too thick, the coating material would harden slowly and not harden thoroughly, making it prone to peeling off during the second coat. A total of three coats were applied to the tundish wall, with the final coat smoothed with a trowel. Finally, the coating material was poured onto the bottom of the tundish and smoothed with a trowel. The typical tundish wall thickness was approximately 30mm, and the slag line thickness in the impact zone was 50-60mm. After being coated and naturally dried, the tundishes were rapidly baked to over 1100℃ and held at this temperature until use. During the curing, drying, and baking processes, the coating on the four tundishes showed no cracking, collapse, spalling, or peeling. The tundish ages after trial use were 23, 22, 22, and 21 hours, respectively. This coating exhibited good erosion resistance; after use, the thinnest residual thickness of the slag line in the impact zone was 15-20 mm, and the maximum erosion rate of the slag line was 1.5 mm/h. The tundishes showed good disintegration properties upon unpacking. Through trial use, this coating basically met the production requirements of steel mills and has been widely adopted. Currently, to adapt to the different usage requirements of tundishes, our company's series of tundish coating products are widely used in Maanshan Iron & Steel's No. 2 and No. 3 Steel Rolling Mills. The required tundish life for one type of steel billet is >6 heats (actual average 10 heats). For plate steel tundishes, the lifespan requirements vary depending on the steel grade, with requirements of ≥8 heats (actual average 12 heats) and ≥16 heats (actual average 19.2 heats). For two types of steel, the tundish lifespan is ≥30 hours (actual average 31.6 hours). For three types of steel, the lifespan requirements are ≥10 hours for low-alloy steel (actual average 12 hours) and ≥24 hours for plain carbon steel (actual average 27 hours).

2. Application of  Tundish lining dry Material
With the widespread application of rapid nozzle replacement technology in tundishes, the service life of tundishes has been continuously improved. To adapt to the needs of new smelting conditions, our company, in cooperation with Wuhan University of Science and Technology, successfully developed a dry tundish material system. Because it involves waterless construction, it reduces the possibility of magnesia hydration, facilitates construction, and shortens the baking time, thereby improving labor productivity and saving significant energy and time.

This dry material was tested on five tundishes on a 3" continuous casting machine for irregular billets from July 21, 2003 to April 27, 2004. The process involved first spreading a layer of premixed dry material at the bottom of the tundish and smoothing it with a scraper. Then, the mold was placed, leaving a gap of approximately 40-60mm between it and the tundish wall. The dry material was then poured evenly into the tundish along the wall, filling it to the top. The vibration device on the mold was then activated until it was completely filled and compacted. The burner was then turned on, and the mold was baked at a temperature not exceeding 300℃ for approximately [time missing]. After 3 hours, turn off the burner and allow it to cool naturally before demolding. During demolding, apply force evenly to avoid damaging the dry-material construction body. The dry-material usage during construction is 3-3.5 tons, with a ladle bottom and wall thickness of approximately 30 mm and a slag line thickness of 50-60 mm in the impact zone. After installing the nozzle bricks and fixing three impact guard plates near the impact zone, allow it to bake online for 2-3 hours before putting the tundish into use.

The service lives of the five tundishes tested were 2065 min (65 heats), 1236 min (46 heats, which were shut down due to a problem with the quick-change nozzle), 2058 min (81 heats), 2119 min (87 heats), and 1865 min (61 heats). During use, except for the slag line erosion in the toxic zone (where the working environment is harsh and erosion is slightly greater), the erosion in other areas was minimal. Based on the erosion rate, the slag line lifespan in the impact zone of the working layer is estimated to be 30-35 hours. The dismantling performance of the five tundishes was good, achieving the expected goals.

Now, to meet the different requirements of tundishes, our company's dry tundish lining series products are also widely used in a certain main plant. For the 1" continuous casting machine, a service life >17 hours is required (actual average service life 21.3 hours), and for the 3" continuous casting machine, a service life ≥30 hours is required (actual average service life 33.8 hours). Both types of dry lining meet the requirements, and the residual lining remains relatively thick after use. Usage shows that this series of dry linings has strong integrity, a high relative service life and production efficiency, convenient construction, energy and time savings, and good resistance to slag penetration and erosion. In addition, it also has good dismantling performance.