Keywords: tundish; electromagnetic induction heating;
The tundish, as an important convergence point of steelmaking from intermittent operation to continuous operation, plays a very important role in process compliance, steel purification and improvement of billet quality. In recent years, the practice of continuous casting technology development also shows that the constant temperature casting with low superheat is conducive to improving the rate of equiaxial crystal and reducing the casting billet centre segregation, which plays an important role in improving the quality of casting billet and stabilizing the operation. In the whole continuous casting process, there are different degrees of heat loss in the tundish, especially at the beginning of pouring, ladle exchange and pouring at the end of the abnormal pouring period, which inevitably cause large temperature fluctuations. Steel mills mostly use external heat sources to compensate for the temperature drop of molten steel in the tundish.
Channel induction heating the tundish has high heating efficiency and large temperature rise. Its heater is mainly divided into single-coil type and double-coil type heater, the cooling type is air-cooled and water-cooled respectively, which can be applied to almost all types of continuous casting tundish (H, L and T type). It mainly consists of coils, refractory channels, cooling system, iron core and stainless steel sleeve: the coils are wrapped around a mouth-type removable core for easy disassembly and maintenance; the core and coils are encapsulated in a stainless steel sleeve, which is used externally to support alumina-graphite refractory and internally as a cooling and ventilation duct. In the above structure, the induction heater consists of a multi-turn coil and a muzzle-type core, while the muzzle-type core consists of a bar-shaped fixed yoke and a movable pi-type core; two concave stainless steel sleeves are connected to form a sleeve, which is used to encapsulate the core, support the refractory material, and control the heater's position; and the molten steel channel is made of alumina-graphite, buried at the bottom of the intermediate ladle partition wall, and serves as a secondary circuit for heating the molten steel. Domestic factories use this technology able to reduce the temperature fluctuation of molten steel significantly, and improve the quality of billet casting (average index of carbon segregation, proportion of billet casting equiaxial crystals, class B inclusions, class C inclusions, and indicators of the detection rate of picking out).
Channel centripetal electromagnetic force will compress the steel liquid, resulting in "hoop shrinkage" effect, so that the steel flow speed up, easy to cause the steel outflow when the formation of jets, which can lead to serious interruptions in the flow of steel, and there will be jets of steel exacerbated by the scouring of the packet wall, the fall of the refractory material and will affect the cleanliness of the steel. Some specific steel grades will increase hydrogen content after electromagnetic induction heating.
