Influence of smelting process on service life of furnace lining

Continuous smelting and batch smelting have a great influence on the service life of the furnace lining. During continuous smelting, the furnace lining is always in a hot state and is less affected by temperature changes. During intermittent operation, the lining of the furnace will change from low temperature to high temperature to low temperature, which is periodically quenched and heated. The result of this rapid cooling and rapid heating changes will cause cracks in the furnace lining, thereby reducing the service life of the furnace lining.

Except for magnesia-aluminum spinel linings, magnesia and quartz linings have poor resistance to rapid cooling and rapid heating. Among them, the quartz lining is particularly significant. During the heating and cooling process of the lining, the linear expansion or contraction rate of the sintered layer of the lining is 0.9%. That is to say, for every batch of smelting furnace, the volume of the furnace lining will expand and contract once. This rate of change is the largest below 800 °C. If the furnace lining is continuously smelted, the temperature of the furnace lining wall will not be lower than 800 °C, so the rate of change of the volume of the furnace lining is very small, and the time of crack generation will be delayed. The life of the furnace lining is increased. Therefore, in order to prolong the life of the furnace lining, the temperature of the crucible must be kept above 800°C when the large industrial frequency furnace for smelting cast iron is shut down.

During the smelting process, the solution will penetrate into the interior of the refractory matrix through the capillary channels in the refractory matrix to erode the furnace lining. The components infiltrated into the refractory matrix include: CaO, SiO2, FeO in the slag; Fe, Si, Ai, Mn, C in the molten steel, and even metal vapor, CO gas, etc. These infiltrating components are deposited in the refractory capillary channels, resulting in the discontinuity between the physical and chemical properties of the refractory working surface and the original refractory matrix. Under the rapid change of operating temperature, cracks, spalling and structural looseness will appear. Strictly speaking, this damage process Much more serious than the dissolution damage process.

Taking the basic furnace lining as an example, increasing the content and viscosity of magnesium oxide is beneficial to reduce the erosion of the furnace lining and improve the slag collection effect.

1. The influence of melting temperature on the service life of furnace lining

During the smelting process, the temperature of the molten steel is too high, which will cause the temperature of the slag to rise, and the erosion of the furnace lining will intensify, causing the lining to be damaged prematurely along the slag line. In addition, high temperature will also accelerate the fluidity of molten steel and accelerate the penetration of cracks into the furnace lining, which intensifies the chemical erosion of the molten metal on the furnace lining. While controlling the smelting temperature as much as possible, there should be no long-term high temperature or heat preservation waiting for casting. Excessive temperature will not only easily burn the alloy, but also increase the energy consumption. In short, the higher the melting temperature, the lower the service life of the furnace lining.

2. The influence of smelting steel grade on the service life of furnace lining

When melting high carbon and high manganese steel with low melting point and good fluidity, the penetration effect of molten steel on the furnace lining is intensified, which will reduce the service life of the furnace lining.

When smelting low-carbon, high-nickel-chromium steels with poor fluidity, the furnace lining has a relatively long service life.

Materials with high melting point require higher temperature, and prolonged high temperature will also reduce the service life of the furnace lining.

Therefore, high carbon steel and high manganese steel should be smelted in the later stage of the furnace lining when smelting steel grades.

In addition, when smelting different materials, attention should be paid to the properties of metal materials. For example, when smelting metals with high sulfur content in the previous furnace, the furnace wall is easily eroded when smelting high-manganese steel in the next furnace. Therefore, when smelting steel grades, high carbon steel and high manganese steel should be smelted in the later stage of the furnace lining.

3. The influence of slag on the service life of furnace lining

The pH of the slag should be compatible with the material of the furnace lining. The appropriate slag should be selected according to the material of the furnace lining. Alkaline slag is suitable for magnesia lining, but can be corroded by high-CaO slag and SiO2 slag. Excessive CaF2 will also corrode basic lining and cause premature erosion in the slag line area. Acidic slag is suitable for quartz lining, and magnesia-aluminum lining is only suitable for weak alkaline or neutral slag. Alumina lining will show typical amphoteric in different pH at high temperature, and it can adapt to slag with different pH, which is slightly worse than acidic furnace lining and basic furnace lining.

4. Influence of smelting operation on the service life of furnace lining

Whether the metal charge can be smoothly melted during the melting period has a great influence. The tightness of the charge is directly related to the melting speed of the charge. In order to heat and melt quickly, the charging should be as tight as possible, but the bridging phenomenon should be avoided during the melting process, which will overheat the molten metal in the lower part, make the molten metal absorb and increase the burning loss of alloying elements, prolong the melting Time, high temperature and violent eddy current will seriously erode the furnace wall, resulting in great damage to the furnace wall by bridging and handling. When the metal liquid level is too low, special attention should be paid to feeding. If large blocks are added and high power is input to the electric furnace, the bottom will be severely overheated and the erosion will be exacerbated. serious. After the molten metal reaches the appropriate temperature and quality requirements, the power should be cut off, which is not only safe and reduces energy consumption, but also protects the lower half of the furnace lining from being damaged by the scouring of the superheated molten metal. The smelting time should be shortened as much as possible to reduce the power consumption of molten steel smelting.

The air burning and the lower part of the furnace body are under the condition of local electromagnetic stirring. Will severely and accelerate the erosion of the furnace lining.

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