(Department of Material Engineering, XXXXXXX, Baotou City, Inner Mongolia 0 14030)
XX XXX XXX
Abstract: The high refractory, good thermal stability, good slag resistance, good corrosion resistance and compact sintering of high bauxite lining are expounded. Suitable for melting all kinds of nonferrous metals, ordinary cast iron, nodular cast iron and all kinds of alloy cast iron, carbon steel, alloy steel, stainless steel and heat-resistant steel. When smelting, the burning loss of metal alloy elements is low, and the metal burden can be overloaded twice. The furnace lining adopts the technical measures of low temperature baking, rapid heating and short time high temperature dense sintering. The service life of furnace lining is mostly around 150 heats, and the highest can reach 200 heats.
Keywords: dense sintering of high bauxite lining induction furnace
I. Introduction
The bauxite lining studied in this paper is not only suitable for smelting all kinds of nonferrous metals, ordinary cast iron, nodular cast iron and alloy cast iron, but also suitable for smelting all kinds of carbon steel, alloy steel, stainless steel and heat-resistant steel. The burning loss of metal alloy elements smelted with high bauxite lining is lower than that of quartz sand and magnesia lining, which not only improves the utilization rate of alloy, but also greatly enhances the ability to resist the corrosion of alloy and slag on furnace lining. Another advantage of high-alumina furnace lining is its high heat resistance, long service life and small linear expansion coefficient, which is only 1/2 ~ 1/3 of that of acidic and alkaline furnace lining, which greatly improves the service life of furnace lining under intermittent production conditions. The lining has good thermal stability, strong quenching and heating resistance, heavy high-temperature load, strong metal corrosion resistance and less alloy element burning loss, which is incomparable to quartz sand and magnesia lining. The wall thickness of bauxite lining can be made thinner, which can almost double the metal burden in production. In addition, the lining sintering process adopts low temperature baking, rapid heating and short time high temperature sintering. The time of adopting this new process is only 2/3 ~ 1/2 of that of the old process. Time-saving and electricity-saving furnace lining is sintered well. The service life of high-alumina lining is mostly around 150 heats, and the maximum is 200 heats.
Second, the performance of high alumina lining
1, physical properties
(1) High fire resistance.
Chemical composition of high bauxite
al2o 3 80 ~ 90%； 7 ~15% of silica; fe2o 3 0.8 ~ 1.7%； ca0 0.2 ~ 0.5%； MgO 0. 15 ~ 0.5%； k20 0. 180% ~ 5%； na20 0. 1 ~ 0.3%； Titanium dioxide 1.5~4.3%.
The fire resistance limit is 1750℃ ~ 1800℃, and it can work stably at 1650℃ 1 ~ 750℃. It can reduce the erosion loss of molten steel to the furnace lining and prolong the service life of the furnace lining. The refractoriness of pure quartz sand is 17 10℃.
(2) Excellent thermal stability
Using bauxite as furnace lining, the mineral phase after sintering is mullite, followed by corundum and a small amount of Shi Ying and glass phase. The linear expansion coefficient of mullite (4.5-5.3 × 10-6mm/mm? ℃) is only about 1/3 of magnesia and quartz sand, and the linear expansion coefficient of corundum is (8. O× 10-6mm/mm？ C) It is also lower than magnesia and quartz sand. When it is composed of sillimanite (containing 62.9% Al2O3), its linear expansion coefficient can be as low as 3.2× 10-6mm/mm? Therefore, the thermal shock resistance of high bauxite lining is much better than that of magnesia and quartz sand lining, which is helpful to reduce thermal stress and make it better resistant to rapid cooling and rapid heating. Even if cracks appear in use, they are very small. If the ingredients are properly mixed and knotted, cracks will not occur even if intermittent melting is used. The expansion coefficient of quartz sand magnesia furnace lining is large, and the temperature difference between inside and outside is large when working, so the furnace lining is easy to crack and crack. Generally, the service life of quartz sand lining is only a few dozen times, while the service life of magnesia lining is even lower.
When the furnace heats up, the volume of magnesia and quartz sand lining expands greatly, so we must take the operation of slowly heating up and prolonging the furnace time to minimize cracks and prevent the furnace from collapsing. However, the high bauxite lining does not have the above problems, which can greatly shorten the baking time without cracks, thus ensuring the quality of the lining and reducing energy consumption.
(3) The compressive strength of 30-40N/mm2 (calcined at1000℃ for 5 hours) is 3-4 times that of ordinary clay bricks. The lining has good mechanical strength, the wall thickness can be reduced, and it can bear twice the metal load overload. When the sensor is fixed, if the wall thickness is thin, the exposure will be larger; At the same time, the non-magnetic space inside the inductor is reduced, and the magnetic leakage is reduced, so that higher electrical efficiency can be obtained. This has high productivity and low power consumption.
(4) The thermal conductivity is1.7-2w/MK.
(5) The bulk density is 1600kg/m3.
(6) The microporosity is 18-22%.
(7) The bulk density after sintering is 1750- 1770kg/m3.
2. Good slag resistance
The alkaline slag resistance of bauxite lining is better than that of quartz sand lining. In bauxite lining, al2o 3 is more stable than MgO. The weak reaction between al2o 3 and MgO can produce alumina-magnesia spinel with melting point of 2 135℃, manganese spinel with melting point of 1560℃ and iron spinel with melting point of 1780℃. Al _ 203 reacts with MnO and Fe2O3 to form * * crystal with melting point of 1520℃, and forms solid solution with Cr _ 203, which can strengthen furnace lining. It should be noted that it is best not to smelt chromium-free or low-chromium alloy after smelting high-chromium alloy, otherwise it will cause Cr203 to dissolve, make the lining surface loose and reduce the strength. Bauxite lining basically does not react with C, Fe203 and SiO2, but reacts with ZnO to generate spinel, and reacts with B203, P205 and CaO to generate insoluble aluminate. The combined action of CaO, Al-203 and Fe-203 has stronger erosion effect on furnace lining than the single action. React with Na20 and K2O to generate soluble crystals and compounds. Therefore, Na2O, K2O and CaO in slag corrode bauxite lining greatly, while quartz sand lining reacts strongly with MgO, Zn0, PbO, CaO, Na2O and K20 in slag, which is more likely to cause lining erosion. The complex action of CaO, Si02 _ 2 and FeO forms soluble compounds, especially ZnO and PbO, which corrode the furnace lining greatly. The fe2o 3 content in the quartz sand lining should be strictly controlled and mechanically crushed. The ground quartz sand (magnesium oxide in alkaline lining) should be strictly magnetically separated, otherwise the lining will be burned through by electric leakage.
3, good corrosion resistance
The high bauxite lining is mainly mullite, followed by corundum, with a small amount of cristobalite and glass phase. It has high chemical stability and is weakly alkaline at high temperature, and basically does not react with al, Mn, Fe, Si, Sn, Go, Cr and Ni. It reacts weakly with zinc, lead, magnesium and titanium. The reaction with Cu is obvious (when smelting copper alloy). However, quartz sand lining has obvious reaction with aluminum, magnesium, lead, zinc and manganese. Zn, Pb (brass) will seriously erode the lining, and even often burn through the lining in a short time, while Al, Mg and Ca will seriously erode the lining. When smelting low silicon cast iron, carbon also has a great influence on the corrosion and crack propagation of furnace lining. Generally speaking, the output of high bauxite lining is higher than that of quartz sand lining by 1.4%, and the total irretrievable loss of burning loss is 1. 4% lower. The reason is that the bauxite lining has little slagging effect, the liquid is not easy to oxidize, and the reaction of metal in the reduced slag is strong. When the high-alumina furnace lining is kept above 1500℃ for a long time, there is almost no burning loss to chromium, nickel, aluminum and copper, while carbon and silicon do not change below 1350℃, and the burning loss of carbon and silicon ranges from 1400℃ to 1500℃. Si burns 0.013-0.017% per hour; The relative loss on ignition of Mn at 1500℃ for 3 hours is only 2.7%. When smelting corrosion-resistant cast iron with quartz sand lining, the loss of elements is: C 2.9%, Si 5. 18%, Mn 1 1.5%, Cr 1. 16%, Ni0./kloc-. The burning loss of elements in high strength cast iron is: C 2%, Si 5.25%, Mn 5.09%, P 2.8%, Fe0.24% and S9.2%. Because bauxite is more stable than magnesium oxide at high temperature, and its interaction with Cr, C and Mn elements is generally weak, the lining erosion is slight. It can be seen that the high bauxite lining is not only suitable for melting all kinds of nonferrous metals, ordinary cast iron, nodular cast iron and alloy cast iron, but also suitable for melting all kinds of carbon steel, alloy steel, stainless steel and heat-resistant steel.
3. Densification and sintering of high bauxite lining
The purpose of lining sintering of induction furnace is to transform knotted refractories with a certain thickness near molten metal into dense bodies. Only the dense sintered crucible can withstand the erosion of high temperature molten steel (iron) and slag. The densification degree of crucible sintering is related to the chemical composition, particle size ratio, sintering process and sintering temperature of refractories.
1, particle size ratio
Reasonable particle size ratio can obtain the minimum porosity before sintering. If the particle size ratio is unreasonable, the porosity of the lining after knotting is high. The sintering process includes particle rearrangement, pore filling and grain growth. If the porosity is high, it is difficult to fill most of the pores during sintering, which affects its densification. In addition, reasonable particle size ratio can also obtain the maximum thermal shock resistance. In order to give consideration to low porosity and high thermal shock resistance, the particle size ratio is: coarse (3 ~ 5 mm): medium (0.5 ~ 1 mm): fine (-0.5 ~1mm) = 60:10: 30.
2. Adhesives
At high temperature, a small amount of additives can form a small amount of liquid phase with the main crystal phase, which accelerates the sintering process and plays a certain bonding role. Bauxite clinker contains trace impurities such as fe2o 3, CaO, MgO and TiO2, which are evenly distributed. At high temperature, they form a small amount of liquid phase with the main crystal phase, which can meet the needs of diffusion and mass transfer during sintering. Fe2o 3, CaO and MgO are also promoters of mullite during sintering. Therefore, there is usually no need to add any adhesive. However, for the small-capacity induction furnace, because the tire clamp should be taken out after knotting, in order to prevent the aggregate particles from scattering during baking, it is necessary to add 1 ~ 1.5% industrial boric acid (H3B03).
3. Sintering temperature
According to the sintering mechanism, only volume diffusion can lead to the densification of the green body. Surface diffusion can only change the shape of pores, but not make the center distance of particles close, so there is no densification process. In the high temperature sintering stage, volume diffusion is the main factor, while in the low temperature stage, surface diffusion is the main factor. If the crucible stays at low temperature for a long time in the sintering process, it is not only not dense, but also the pores are closed due to surface diffusion, so the internal gas is difficult to be discharged and remains in the sintering layer. This will reduce the service performance of the crucible. Generally, TS = 0.8 ~ 0.9tm (TS is the sintering temperature and tm is the melting temperature). Theoretically, the sintering process should be raised from low temperature to high temperature as soon as possible to create conditions for volume diffusion. Therefore, high temperature and short time sintering is an effective means to obtain dense crucible.
It is reasonable to control the sintering temperature at 1450℃ ~ 1500℃. Excessive sintering temperature will lead to the rapid movement of grain boundaries, so that the pores on the grain boundaries will be surrounded by large grains before they can be spread out, which will inevitably lead to crystal defects. Therefore, it is necessary to control the sintering temperature, make the grain boundary move slowly, and eliminate the pores to the maximum extent to obtain a compact crucible sintered body.
4. Sintering process
In the process of sintering crucible, the specific method is: after the lining is knotted, it is naturally air-dried for 24 hours and baked at 5 ~ 30% power. Intermittent power supply, keep the lining red at the initial stage (≤500℃) until it is dry (4 ~ 5 hours). Subsequently, 1/3 charge is added, and the charge is operated at high power and full load, so that the charge is melted quickly and kept at the melting temperature for one hour. And then enters the later smelting process. This is the so-called low-temperature baking, rapid heating and short-time high-temperature sintering. The time of adopting this new process is only 2/3 ~ 1/2 of that of the old process. Time and electricity saving, convenient operation and good sintering. No bad phenomena such as cracks were found in use. The lining life can exceed 150 heats. Up to 200 heats.
Four. conclusion
1, suitable for all kinds of nonferrous metals, ordinary cast iron, nodular cast iron and all kinds of alloy cast iron, and also suitable for melting all kinds of carbon steel, alloy steel, stainless steel and heat-resistant steel.
2. The burning loss of metal alloy of high bauxite lining is lower than that of acid-base lining, which not only improves the utilization rate of alloy, but also greatly enhances the ability to resist the corrosion of alloy and slag on lining.
3. High heat resistance, long service life and small linear expansion coefficient, which is only 1/2- 1/3 of acid and alkaline furnace lining, greatly improving the service life of furnace lining under intermittent production conditions.
4. The wall thickness of bauxite lining can be made thinner, which can almost double the metal burden in production.
5. The lining is baked at low temperature and sintered at high temperature for a short time, the time is only 2/3 ~ 1/2 of the original process, and the densification rate is more than 2 times of the original process. Not only saves the time of drying and sintering, but also saves electricity.
6. The furnace lining is well sintered and dense, and no bad phenomena such as cracks are found in use. The service life of high-alumina furnace lining is mostly around 150 heats, and the highest can reach 200 heats.
refer to
1 Li. Densification sintering of crucible in high bauxite induction furnace. Casting 199 1. three
2 Zhan Guoxiang. The lining of induction furnace for melting complex cast iron. Casting 1995. five
3 "Investment Precision Casting" writing group. Precision Casting National Defense Industry Press 1984
four
Research and application of high bauxite induction furnace lining
(Baotou Vocational and Technical College, Department of Materials Engineering, Baotou, Inner Mongolia 0 14030)
Sun Min Wang Shutian Shi Jidong
Abstract: High bauxite lining has the characteristics of high fire resistance, good heat resistance, good slag resistance and strong corrosion resistance. Through compact sintering, it is used to smelt various nonferrous metals, ordinary cast iron, graphite cast iron, cast alloy cast iron, carbon steel and alloy steel, stainless steel and heat-resistant steel. The burning loss of alloy elements is low during melting; The charge can be loaded by a multiple. Technical measures such as low-temperature baking, rapid heating and short-time high-temperature dense sintering are adopted for the furnace lining. The life of furnace lining is usually 65438 050 times, and the highest life can reach 200 times.
Key words: high bauxite; Furnace lining; Induction furnace; Tight agglutination