Application of 3 Kinds of Magnesium Monolithic Refractories
Magnesium refractory materials are alkaline refractory materials, which are widely used in kilns in high-temperature industries such as steel and cement. Magnesium amorphous refractory materials include magnesium castables, magnesium dry vibrating materials (ramming materials), magnesium gunning materials, magnesium refractory mud, etc. Rongsheng Refractory Material Manufacturer, environmentally friendly fully automatic amorphous refractory production line, specializes in providing refractory lining materials for high-temperature industrial furnaces. Contact Rongsheng for free samples and quotes.
Since calcium aluminate cement can form high melting point CaO·6Al2O3 (CA6) with Al2O3. Therefore, aluminum-magnesium castables combined with calcium aluminate cement are widely used in steel ladle.
If MgO-MA alkaline castable combined with hydrated alumina can be used instead, due to the absence of CaO impurities, hydrated alumina and MgO form magnesium-aluminum spinel self-combination during use, its load softening temperature and slag resistance will be better than Al2O3-MA castable combined with calcium aluminate cement, and it is also beneficial to improve the quality of steel.
Another direction of the development of magnesium castable is to form a cohesive bond between SiO2 fine powder, MgO fine powder and water. The advantages of this combined magnesium castable are: due to the addition of SiO2 fine powder, the castable has good fluidity. The gel contains less structural water, and dehydration is gradual during heating, which will not cause damage to the structure. During use, a magnesium castable combined with forsterite is formed. Adding a small amount of ZrO2 or zircon to this castable can also improve the thermal shock resistance of the castable. In addition, magnesium castables that are combined with TiO2 micropowder, Al2O3 micropowder and magnesia fine powder to form M2T-MA solid solution are also being studied and developed. In order to improve the slag resistance of magnesium castables, the method of adding AlN, AION or MgAlON is also used.
Magnesium carbon-containing castables have been affected by the inability of water to wet graphite and the low density of graphite. Using surfactants to change the hydrophobic surface of graphite to hydrophilic may be an important way to solve the problem of carbon-containing refractory castables. In addition, carbon-containing refractory materials used in steel plants are also good raw materials for making magnesium carbon-containing castables, because the particles or powders made from this kind of residual bricks have a high carbon content, uniform C distribution, and are dense.
Alkaline magnesium dry ramming material is widely used in various induction furnace linings and ultra-high power electric furnace bottoms. In recent years, it has been used on the intermediate ladle of continuous steel casting with good results.
Dry ramming material is an amorphous refractory material without liquid binder and water. It does not need to undergo strict maintenance after construction. It mainly relies on baking or heating of high-temperature melt during use to sinter the hot surface of the dry ramming material into a whole, forming a dense working layer with a certain strength. In use, except for the working layer, the rest of the dry material is still an unsintered dense stacking structure. Therefore, it has good thermal insulation performance, and at the same time avoids cracking and perforation caused by stress caused by expansion and contraction of refractory materials during use. In addition, it is also convenient to dismantle. However, dry ramming material is not suitable for kilns with rotation and high furnace height.
The commonly used sintering agent for magnesium and MgO-CaO dry ramming materials is iron oxide. FeO and calcium ferrite have low melting points and will gradually be absorbed by periclase to form a solid solution, namely magnesium fustenite [(Mg·Fe)O]. The impurities of magnesium and magnesium calcium dry ramming materials are SiO2 and Al2O3 respectively, and their content should be as low as possible and should not exceed 1%.
If MgO-CaO dry ramming materials use low-melting calcium silicate or magnesium silicate as a sintering agent. At this time, iron oxide becomes a harmful impurity and should be limited.
For MgO-MgO·Al2O3 dry materials, iron oxide or magnesium silicate can be used as a sintering agent. For Al2O3-MgO·Al2O3 dry materials, iron oxide or low-melting calcium aluminate can be used as a sintering agent.
Magnesium Coating or Gunning Material
Magnesium and magnesium-calcium materials are good for purifying molten steel, so they are widely used in intermediate ladle for continuous steel casting. However, when this kind of coating or gunning material is used for casting low-phosphorus steel, phosphate binders should be avoided. Secondly, since a lot of water is added to the coating, it is necessary to bake at high temperature to remove the water as much as possible to avoid hydrogenation in the first few barrels of molten steel.
For magnesium-calcium coating, the source of CaO can be lime milk [Ca(OH)2], light calcium carbonate, etc. according to the method of segmented decomposition, and high-calcium magnesium sand can be used less.
Drying and Curing of Magnesite Ramming Mass Before Use
During the drying process of amorphous refractory materials before use, the surface moisture is first evaporated by heat, and the heat is conducted from the surface to the inside, causing the temperature of adjacent parts to gradually increase. Due to the evaporation of surface moisture, the moisture (steam) inside the refractory gradually diffuses to the surface to replenish. If the heat supply is too large and the temperature rises too fast, the amount of steam generated per unit time is too much. Due to the poor air permeability of amorphous refractory materials, the internal moisture (steam) is blocked from diffusing outward. At the same time, due to the vaporization of moisture, the volume increases sharply, and a large tension will be generated inside the refractory. If the tension exceeds the compressive strength of the refractory, it will cause the refractory to expand and crack. When the difference between the two is large, it will peel off or explode. Therefore, conventional heating and drying requirements are high, and the performance of the refractory cannot be guaranteed. The magnesite ramming mass used can be dried naturally at room temperature, avoiding the damage of high temperature to the refractory, and effectively guaranteeing the performance of the refractory.
Unshaped refractory is a kind of refractory that can be used directly without firing. It has the advantages of fast construction, simplified process, energy saving, good integrity, easy replacement, etc. It is widely used in the metallurgical field. Among them, ramming material is an unshaped refractory material that is constructed by ramming (manual or mechanical), made of a high proportion of granular material and a low proportion of binder and other components, and hardened under heating above normal temperature. The use of magnesite ramming mass on the top of the electric furnace and the copper water jacket at the flue gas outlet of the oxygen-enriched side-blown furnace not only meets the process requirements, but also reduces production costs.
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