According to the material of refractory aggregate, refractory plastics are divided into: clay, high aluminum, corundum, silicon, magnesium, chromium, zircon and silicon carbide refractory plastics. According to the type of binder, they are divided into: water glass, phosphate, sulfate and organic binder refractory plastics. According to the hardening method, they are divided into: gas-hardening and heat-hardening refractory plastics. This article introduces three types of refractory plastics needed in the iron and steel metallurgical process.
1. Pyrope-based plastics
Pyrope-based plastics have good anti-stripping and slag erosion resistance, suitable for high-temperature section furnace linings, and can be used in soaking furnaces, heating furnaces and burners. Compared with alumina-based plastics, it has the advantage of relatively low cost.
Zhang Wei et al. studied the effect of heat treatment temperature on the performance of pyrope-based plastics, and developed and prepared pyrope-based plastics with slightly lower performance than alumina-based plastics, and used them in the low-temperature section of the heating furnace roof and flue of a domestic steel plant. The results show that the developed pyrope-based plastics have good use effect and no damage occurs. Therefore, this pyrope-based plastic can partially replace alumina-based plastic in the low-temperature section and flue of the heating furnace, achieving the purpose of saving costs and reducing the unit consumption of refractory materials. However, this plastic is prone to freezing during winter construction. If the plastic freezes, it will lose its plasticity, causing a series of problems such as loose lining and reduced strength. Therefore, ordinary plastic has great limitations in construction in cold northern regions.
In response to this problem, Dai Wenyong and others used pyrope and clay as the main raw materials, aluminum sulfate solution as a binder, and antifreeze to develop an antifreeze plastic that can be used in winter construction. The research results show that after the antifreeze plastic and ordinary plastic are frozen for the same time, the ordinary plastic freezes, and the flexural strength and compressive strength of the antifreeze plastic are greater than those of the frozen ordinary plastic. Moreover, the flexural strength and compressive strength of the antifreeze plastic have not changed significantly compared with normal plastic. Therefore, this antifreeze plastic can ensure the safety of the construction body in terms of strength at low temperatures.
2. Mullite-based plastics
Mullite has high mechanical strength, low thermal expansion coefficient, good chemical stability, excellent creep resistance and high temperature performance, so the amorphous refractory material with mullite as the matrix has excellent performance.
Wang Hongfang et al. used fused mullite as the matrix, mixed silica fume, andalusite, Guangxi white mud, SiC, α-Al2O3 micropowder, brown corundum, and then added sodium hexametaphosphate and oxalic acid to prepare a hot repair plastic with mullite as the matrix. In order to ensure that the repair plastic is closely combined with the refractory knotting material in the repair crack and play the purpose of preventing the infiltration of molten steel, the repair material is required to have a certain micro-expansion, but not too large, otherwise it will produce negative effects. To offset the shrinkage of plastics, three stones can be introduced into the plastics, namely kyanite, andalusite, and sillimanite. It can be seen from the literature and the research of Zhang Wei et al. that at high temperatures, the expansion of kyanite is large, the expansion of sillimanite is small, and the expansion of andalusite is relatively moderate. In the hot repair plastic prepared by Wang Hongfang and others, the amount of garnet added was determined to be 6-9%. In addition, the dosage of the binder sodium hexametaphosphate is best at 3%. When it is higher or lower than this value, the medium and high temperature compressive strength of the hot repair plastic varies greatly. The developed plastic was used to repair the cracks of the desulfurization gun. After the repair, the plastic did not burst or crack, indicating that the anti-burst performance is good. After a desulfurization with the desulfurization gun, it was found that the repair material did not fall off from the repaired part, proving that the repair material has fast sintering and good adhesion.
3. Magnesium-chromium plastic
Magnesium-chromium plastic has excellent properties such as stability in vacuum, erosion resistance, and erosion resistance, so it is particularly suitable for use in RH furnaces in steel plants. Liu Baoliang and others used sintered magnesia sand, high-iron magnesia sand, chromite, and pre-synthesized magnesia-chromium sand as raw materials, and sodium hexametaphosphate and phosphate as composite binders to develop and prepare a new type of magnesium-chromium ramming material.
The results show that the plastic has good bonding, is easy to tamp, has good moisture retention, long hardening time and is easy to construct. After adding composite metal Al powder and Fe powder to the plastic, the medium-temperature strength of the material is improved; after adding Cr2O3, the high-temperature strength of the material is significantly improved. The developed plastic was applied to the riser and downcomer around the RH furnace of a steel plant. The results show that the plastic has the advantages of good corrosion resistance, erosion resistance, and thermal shock resistance, and its performance is comparable to that of imported materials.
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