Ladle Furnace Technology

Ladle furnace technology is a method in which the crude molten steel produced by the steelmaking furnace is poured into the ladle for further refining. It is used to remove impurities such as hydrogen, nitrogen, carbon and sulfur in the molten steel, adjust the temperature and composition of the molten steel, and reduce non-metallic inclusions. The multifunctional ladle refining device can have the functions of vacuum degassing, argon blowing stirring, electromagnetic stirring, arc heating, vacuum decarbonization, etc. The productivity and quality of steel can be greatly improved.

Ladle metallurgy is a smelting technology, also called secondary metallurgy, which transfers the traditional steel-making process to the ladle after the initial smelting in the steel-making furnace (such as open hearth furnace, electric furnace and converter), and its refining tasks, such as removing gas and impurities, temperature control, fine adjustment and homogenization of components.

The problem of white spots or crack defects in forged steel parts caused by hydrogen has been identified as a hydrogen hazard. Therefore, dehydrogenation has been carried out in the machinery manufacturing industry for a long time.

However, this problem was solved in one fell swoop after the development of the vacuum casting method by Bochum and Leuven in 1952. The vacuum pouring method is the beginning of the vacuum suction degassing method (DH method) and circulation vacuum degassing method (RH method). Now vacuum treatment has become indispensable main equipment in the steel-making industry. The development of the real chamber degassing method makes it possible to treat molten steel in large quantities.

The ladle furnace technology can increase the oxygen blowing intensity in the smelting process, shorten the smelting cycle, and thus increase the steel output. Putting the deoxidation requirements in the steel into the later vacuum treatment process can reduce the consumption of deoxidizers and thus reduce the cost of smelting alloy. In addition, the billet can be raised to a new level. The oxygen blowing intensity in the smelting process will be increased, the smelting cycle will be shortened, and the steel output will be increased.

Technical Installation

Since all the produced molten steel is degassed by one set of VaD, the degassing capacity needs to be expanded. The focus of the internal discussion is to install the second treatment station to increase the capacity of the existing VAD, or to replace the existing VAD unit with more common process technology and more modern equipment. It is understood that most steel mills use VTD and LF to produce special bar steel. Even though VAD is still a feasible technology, the combination of VTD and LF is more conducive to maintaining production costs. In addition, the double tank degassing tank is required to ensure sufficient treatment time to meet the requirements of the continuous casting process.

For VAD and VTD design, a lot of planning and research work is required to determine the total installation cost, including all auxiliary equipment such as water supply systems and the like. It is finally determined that if VAD is installed, the foundation of existing buildings will be affected and the cost will be high. Later, it was decided to install a set of VTD. To help make decisions, many of the plant's personnel visited many steel plants in the United States, Mexico and Europe to obtain ideal designs and identify suitable suppliers. During these visits, the design requirements of all equipment were clear. The degassing station must be built in the attached span on the top of a single slope, and it is required that VTD use the tank installed on a transport vehicle.

From the technical point of view, the ladle furnace needs to be incorporated into this set of equipment, with observation windows, so that casting does not need to be tested. Therefore, the final design is how to integrate arc heating into the equipment cost-effectively. The final arrangement includes that two vacuum treatment stations are built in one auxiliary span, two tank cars for transporting ladle are set between the two stations, and the arc heating position is set in the channel of the ladle. This new type of heating equipment is called a ladle heating station (LRS). The ladle heating station includes a rotary furnace top and an electrode configuration using an existing VAD transformer.

Structure of Ladle

The ladle is an important piece of equipment for continuous casting. It is a container for carrying and holding molten steel from tapping to pouring. There are also customary names such as large tank, steel tank and ladle.

The utility model is composed of a barrel body, an inner lining, a nozzle opening and closing device and a permeable brick. From the outside to the inside, the inner lining is composed of three layers: thermal insulation layer, permanent layer and working layer; From top to bottom, the working layer is composed of several parts, such as ladle rim, slag line, ladle wall and ladle bottom, and the ladle bottom includes refractory materials for ladle bottom, nozzle device, seat brick and permeable brick.

The function of the ladle is mainly to receive the molten steel and some slag flowing out of the tapping door of the primary molten steel furnace (converter or electric furnace) for partial deoxidation and alloying, which can make the molten steel calm for a period of time to adjust the temperature of the molten steel, uniform the composition and float the non-metallic inclusions in the molten steel. At the same time, the molten steel flow is opened and closed during the pouring process to control the flow of the molten steel and make the pouring smoothly. In recent years, in order to further improve the quality of steel, ladle furnace technology such as argon blowing in ladles and vacuum treatment in ladles have been adopted. It is gradually evolving into important equipment for secondary refining devices and plays an important role in secondary refining and continuous casting.

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