The performance of refractories should have. Next, let’s learn what kind of refractories should be used in various parts of aluminum melting furnace~
- Refractory for induction melting furnace
Although the working temperature of cored induction furnace is similar to that of coreless induction furnace, due to the differences in structure and operation mode, the applicable refractory materials are different. Since the early 1980s, our institute has done a lot of research work in the development of refractory materials for aluminum melting furnace, and has successfully developed high-strength castables especially suitable for cored furnace and dry forming materials for coreless furnace.
1.1 high strength refractory castable for cored induction furnace
The lining materials of cored induction melting furnace are divided into four parts: furnace cover, furnace, throat and refractory materials of inductor melting ditch. The throat, especially the refractory of the melting ditch, is the most critical material, which directly affects the service life and operation cost of the furnace.
(1) Furnace cover refractory
The main function of the furnace cover is to reduce the heat loss of the furnace and prevent the splashing of liquid metal during feeding and melting. This requires that the furnace cover material has good thermal insulation performance, light weight and strong corrosion resistance. Based on this, at present, aluminum silicate refractory fiber with light weight and low thermal conductivity is mostly used as the lining. Because the working temperature is usually lower than 800 ℃, it is mostly fixed on the furnace cover shell with heat-resistant steel rivets and heat-resistant steel mesh. The furnace cover is not only heat preservation and insulation, but also lightweight, so it is very convenient to close and open.
(2) Furnace refractory
Although the physical and chemical effects of furnace refractories in use are not as severe as those of trench refractories, their chemical properties are also inert to liquid aluminum and have high strength and density. Therefore, low porosity, high density and high alumina bricks with excellent performance should be used for masonry. During bricklaying, special attention shall be paid to reducing the width of brick joints and filling them with mud.
(3) Throat and trench refractory
The throat and melting ditch are of complex structure and should not be built with bricks. Amorphous refractory materials are mainly used. After carefully analyzing the stress state of the refractory material in the melting ditch, according to the actual situation in China, we have done a lot of laboratory research on the particle gradation, the amount of binder and the amount of cement dispersion accelerator, and developed a high-performance castable which is especially suitable for the inductor of the cored induction furnace. The castable adopts high alumina refractory, with corundum and mullite as the main crystalline phase.
It can be seen that the strength of this castable at room temperature and high temperature is very high, especially the strength after burning at 850 ℃ has a small reduction compared with the drying strength at 110 ℃. Therefore, this castable is resistant to erosion and wear during use.
The erosion test shows that this material is not easy to be infiltrated by molten aluminum and has no sign of reaction.
1.2 refractory for coreless induction melting furnace
Coreless induction furnace has developed rapidly due to its flexible operation mode, especially the development and progress of static frequency conversion technology. However, with the increase of furnace power and capacity and the improvement of molten aluminum quality, the requirements for refractory materials are more stringent.
As a refractory for coreless induction furnace, it should have very excellent thermal shock stability and the ability to resist crack propagation. Obviously, the castable used in cored induction furnace is not suitable for coreless furnace lining. According to the actual use of coreless furnace lining at home and abroad, we set our main direction on dry formed refractory.
Dry formed refractory is a new type of amorphous refractory which contains almost no water and any liquid additives, and can be heated and baked quickly after short-time vibration or tamping. It is a special kind of heat setting refractory. When heated, the sintering agent acts to make the working layer have high strength, but the non working layer still maintains the unsintered bulk structure. In the process of use, when the hot surface working layer cracks, the unfired liner layer can absorb the local concentrated thermal stress, prevent the extension of the crack and ensure the safe use of the furnace.
Since 1989, on the basis of investigation and research, we have done a lot of experimental work on the selection of raw materials, particle gradation and binder. A new type of neutral dry forming furnace lining material containing special low-temperature sintering agent was finally developed through the comprehensive comparative test of multiple groups of formulas.
- Actual use
The refractory material for the melting ditch of cored induction furnace has been put into use since 1984. It has been used in the 5-ton furnace of Kunming National Aluminum products factory, Lanzhou Aluminum products factory and Qinghai Aluminum products factory. The longest service life is up to 8 months, and the normal service cycle is maintained at more than half a year. Practice has proved that the wet castable has simple construction process, excellent properties and long service life. It is a reliable lining material for large-scale cored induction aluminum melting furnace.
Dry formed refractories for coreless induction melting furnace have been put into practical use since 1992. The material shall be vibrated by hand-held vibrator or air pick equipped with special tamping head in layers. The whole construction period is much shorter than that of wet castable. Since 1992, many manufacturers have used the refractory to build furnaces.
Whether it is power frequency coreless induction furnace or medium frequency coreless induction furnace, after using high-performance dry forming materials to build the furnace, the longest service life of the furnace lining has reached eight months.
- Summary
Based on domestic resources, the refractories for cored induction melting furnace and coreless induction melting furnace developed by our institute are trusted and adopted by many users with low price (only 1 / 4 ~ 1 / 5 of imported materials) and excellent performance (the normal service life of refractories can reach 5-6 months, note: except smelting special alloys). We are still making continuous efforts to further improve the performance of formula materials and strive to achieve better use results.
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