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-alumina spinel linings, the resistance to rapid cooling and rapid heating of magnesia and quartz linings is very poor. 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 mangesia bricks 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.
- The influence of smelting temperature on the service life of the furnace lining If the temperature of the molten steel is too high during the melting process, the temperature of the slag will rise, the erosion of the furnace lining will be intensified, and the furnace lining will 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. Under the action of high temperature, the SiO2 in the furnace lining material will undergo a reduction reaction with C in the steel (iron) liquid, rapidly eroding the furnace lining. High temperature holding is the main cause of furnace lining corrosion under normal circumstances, and the high temperature holding time should be minimized. High temperature tapping and low temperature casting have always been the operating criteria. However, each casting has its melting process requirements. When reaching a suitable temperature, do not pursue excessive over-temperature, but observe and measure the temperature frequently. It is enough to meet the process requirements, achieve low temperature melting and rapid heating. The longer the high temperature molten steel stays in the lining, the greater the erosion of the lining.
When a foundry uses quartz sand as the furnace lining material to produce cast iron castings, the molten iron inspection is qualified and the pouring is normal, but when inspecting the quality of the castings, it is found that the carbon element is low and the silicon element is high, resulting in unqualified castings. The reason is actually caused by the blind pursuit of high temperature tapping. After the molten iron sample was sent for inspection, the ultra-high temperature on the furnace caused the carbon element to form carbon monoxide gas to evaporate under the action of high temperature, and the furnace lining material was melted under the action of high temperature - the silica element in the quartz sand infiltrated into the molten iron in large quantities. - The effect of smelting steel grades on the service life of the furnace lining When smelting high carbon and high manganese steels 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 steel 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, when smelting steel grades, high carbon steel and high manganese steel should be smelted in the later stage of the furnace lining.
In addition, when smelting different materials, attention should be paid to the properties of the 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. - The effect of slag on the service life of the lining The pH of the slag should be compatible with the material of the 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.