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The Secret Of LF Refining Furnace Lining Longevity Is Here!
Dec 17, 2018

The LF ladle furnace is a refining equipment that uses arc heating technology. It is a device that refines the molten steel that is initially refined in a general steelmaking furnace into a special ladle. The LF furnace is characterized by three electrodes for submerged arc heating; on the one hand, the electrode is heated to make a high alkalinity reducing slag; on the other hand, deoxidation, desulfurization, and molten steel composition adjustment are performed. In order to make the molten steel fully contact with the slag, the refining reaction is promoted to make the temperature of the molten steel uniform, and an inert gas (argon gas) is blown into the bottom of the ladle to stir the molten steel, so that the alloy of the ladle is homogenized in the molten steel.


1. Characteristics of LF refining furnace


LF furnace has a series of advantages such as low investment, simple equipment, reasonable combination of refining technology, flexible smelting process, low gas content in molten steel after refining, less harmful impurities, large inclusions, stable composition and uniform temperature. Power electric furnace and continuous casting are an optimized metallurgical process. Because LF furnace smelting has the following advantages: the molten steel temperature can meet the requirements of continuous casting process; the processing time can meet the requirements of multi-furnace continuous casting; the fine-tuning of components can ensure the qualified components of the products and achieve the lowest cost control; the purity of molten steel can Meet product quality requirements.


2. Structure of LF refining furnace


The LF refining furnace consists of an electrode heating system, an alloy and slag feeding system, a bottom ventilating brick blowing argon stirring system, a temperature measuring sampling system, a feeding system, a furnace cover cooling system, a dust removal system and a control system. The parts used in these structures for refractory materials are: LF refining furnace top (furnace cover), refined ladle, bottom blowing gas permeable brick, and tundish skateboard. Figure 1 is a schematic diagram of the LF furnace equipment.


 


3, LF furnace working conditions


LF is working at a high temperature (1700 ° C), the temperature in the hot spot is as high as 2000 ° C or more; due to the long smelting time, the slag is severely eroded, and the slag is mainly alkaline slag, the alkalinity fluctuation The range is large (2~3.5), sometimes up to 5; when LF is working, due to the argon agitation of the bottom permeable brick, the flow of molten steel is severe, and the molten steel is seriously eroded by the lining; in the refining, due to the addition of reducing agent, the furnace The atmosphere is in a reducing atmosphere, which may cause the reducing agent to reduce the lining material and erode the lining; LF smelting in vacuum for a long time, the average is more than 30min per furnace; under the ultimate vacuum (66.67~200Pa) It needs to be kept for 15 minutes. The LF furnace operates intermittently and has frequent thermal shocks.


4, the cause of damage to the LF furnace lining


(1) Chemical reactions and ablation.


At high temperatures, molten steel and slag diffuse into the refractory material, and at the same time, corrosion occurs. The slag is sometimes in contact with the brick surface for up to 90 minutes. The chemical reaction of CaO, SiO2 and CaF2 in the slag with the brick causes the slag permeable layer to form on the surface of the brick, while the matrix is filled with silicate, and the low melting silicate formed at the edge of the granule has C2S (melting point 2130 ° C) and decomposition ), CMS (melting point 1450 ° C) and yellow feldspar solid solution (2CaO•MgO•2SiO2-2CaO•A12O3•2SiO2), etc., causing discontinuous damage to the liner.


(2) Volatilization of refractory materials under high temperature vacuum.


Experiments show that the magnesia-calcium dolomite has the lowest volatilization rate under vacuum conditions.


(3) Erosion of slag and molten steel.


Due to the high permeability of CaO and CaF2 in the refining, CaO and SiO2 in the slag migrate to the freezing point along the liquid channel formed by the pores, cracks and impurities of the brick matrix at high temperature, forming a low silicate-based The melting point of the mineral phase changes the structure of the brick and produces a metamorphic layer, which will form a structural flaking when the temperature changes. For refining slag with high CaO content, the slag can be made of magnesia-calcium refractory material compatible with the slag composition to enhance slag resistance and durability.


(4) Thermal shock and mechanical scouring.


At the bottom of the LF (V) furnace, argon is blown for strong agitation. The average argon blowing time per furnace is longer than argon gas. The flow rate of argon gas is Q=50L/min. The unit stirring ability is strong. The distance from the electrode to the wall is close when the three-phase arc is heated. Therefore, the refractory material is subjected to strong scouring and thermal shock at high temperatures.


(5) Thermal shock shock caused by intermittent operation will cause structural flaking on the surface of the slab to cause structural flaking, which will intensify the damage of the material.


Knowing the working principle of the LF furnace and the causes of damage to the lining refractory, the refractory material required for the long-life lining is easy to configure. For example, the slag line is the most severely damaged and has the shortest life. Magnesia carbon bricks, magnesia-calcium carbon bricks, and electrofusion combined with magnesia-chrome bricks. The repair materials for the wall, the furnace cover, the bottom and the lining also have different materials. If you have more questions about refractory materials for ladle, you can submit it to the technician for a response.


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