Sillimanite is a natural high-grade refractory mineral. It has the characteristics of low thermal expansion, resistance to metallurgical slag and various glass liquids, and good high temperature wear resistance. Refractories based on natural sillimanite also have these advantages. Therefore, sillimanite refractories are widely used in metallurgy, chemical and building materials industries. A glass refractory factory in China has fully understood the advantages of natural sillimanite refractories through foreign technical exchanges and inspections of relevant glass manufacturers. According to the needs of the daily glass industry, the natural sillimanite refractories for daily glass furnace forehearths and feeders were first developed and put into mass production and passed the provincial appraisal. Subsequently, the sillimanite brick for float glass tin baths of the "Seventh Five-Year Plan" of the National Building Materials Bureau were completed. Over the years, it has been praised by users for its high refractoriness, high thermal shock stability and high corrosion resistance, and has achieved huge social and economic benefits.
2 Raw material properties and formula selection of sillimanite bricks
2. 1 Performance of Jixi sillimanite
In the open-pit mining of Sandaogou Sillimanite Mine in Jixi, the linear sillimanite is distributed in crystalline granite, and the grade is generally 10% to 20%. The ore is crushed, ball milled, and then floated. The ore body mainly contains quartz and sillimanite, followed by potash feldspar, mica, ilmenite and graphite, etc., with a recoverable reserve of 30 million tons and an annual output of sillimanite concentrate of 4,000 tons. The technical indicators, chemical composition, physical properties and thermal expansion rate of Jixi sillimanite are shown in Tables 1, 2, 3 and 4.
Table 1 Main technical indicators of Jixi sillimanite
Table 2 The chemical composition of sillimanite I concentrate selected for trial production /%
Table 3 Jixi sillimanite physical properties
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Table 4 Thermal expansion rate of Jixi sillimanite before conversion
The conversion temperature of Jixi sillimanite is relatively high, and the linear expansion before conversion is small. When heated to 1 545 ℃, it is decomposed into quartz and mullite according to the following formula, accompanied by a certain volume expansion.
2.2 The choice of aggregate
It can be seen from the particle size composition of sillimanite that most of the coarse particles are below 0.2mm. The coarse particles are too fine and the fine powder is too coarse. This brings difficulties to the reasonable particle gradation. The production cost is greatly increased, so the appropriate coarse particles must be selected to meet the requirements of production and product performance. The mineral with similar properties to sillimanite is mullite. The thermal expansion rate of synthetic mullite is 0.53% at 1 200 ℃, which is very close to the thermal expansion rate of natural sillimanite. Therefore, it is more reasonable to introduce synthetic mullite coarse particles into sillimanite products. After comparison, Hunan Chenxi synthetic mullite is selected, and its performance indicators are shown in Table 5.
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Table 5 Main performance indexes of Hunan Chenxi synthetic mullite
2.3 The choice of binding agent
The physical and chemical properties of the bonding agent for sillimanite products should be close to that of natural sillimanite, especially the chemical composition and thermal expansion coefficient, which should be basically consistent with natural sillimanite. In comparison, high-alumina bonding agent can meet these requirements, so it is selected Fixed high aluminum bond.
Through experiments, the composition range of the bonding agent was determined, and the bonding agent samples were subjected to physical and chemical tests.
3 Production process and control
(1) The process of grouting products The production of grouting products first selects qualified raw materials (including natural sillimanite, synthetic mullite, high-alumina clinker, kaolin, etc.), and at the same time makes gypsum molds according to the shape of the product. And prepare the binder (electrolyte), and then prepare the slurry required for casting.
The next step is the pouring and forming of the mud: the qualified mud is slowly poured into the mold, and the mud is flattened when it is full, covered with gypsum board (upper template), and then demolded. The demolding time is determined by the thickness of the blank, and the rough blank is formed After that, the inside and outside should be trimmed, that is, the blank is trimmed.
The formed semi-finished products must be dried to a certain level of moisture, then loaded into the kiln and fired at high temperature to become finished products, processed at the back of the neck, product inspection, and packaged for delivery.
It is worth noting that during the flotation of sillimanite in the beneficiation field, it is more or less brought into the chemical active agent used in the flotation, which greatly interferes with the grouting performance when the product is formed. When grouting, the binder, that is, electrolyte, must be carefully selected to meet the molding requirements of special-shaped products.
(2)
Figure 1
(3) Process control index
① Raw materials
Sillimanite concentrate: Al2O3≥56 Fe2O3≤1.5
Synthetic mullite: A3S2＞90% Fe2O3＜0.6
Kaolin: Al2O3≥38%
Degumming agent: adsorbed water <1.0%
② Process index
Raw material adsorption water: ≯1%
Weighing error: raw material ±0.5%, degelling agent ±1g
Ball filling factor: ⊙=0.4±0.01%
Binder particle size: <10 mm
Binder moisture: specified index ±0.5%
Binder composition: Al2O3≮61% Fe2O3 ≯0.8%
Beating time: no less than 20 min
Mud aging time: not less than 24 h, not less than 20 ℃
Mud moisture: specified index ±0.5%
Molding room temperature: temperature ≮ 20 ℃, humidity ≮ 60%
Drying temperature of semi-finished products: 30 ℃
Moisture of semi-finished products entering the kiln: small pieces ≯ 1% large pieces ≯ 0.5%
Heating rate: specified standard ±5 ℃/h
Firing temperature: specified index ±5 ℃
Insulation temperature fluctuation: ±5 ℃
Product size requirements: according to the drawing standard requirements
4 Product performance and comparison with similar foreign products
Product performance and comparison with similar foreign companies are shown in Tables 6 and 7.
Table 6 Comparison of chemical composition
Table 7 Comparison of physical and chemical indicators
5 The use of sillimanite in the glass industry
Sillimanite bricks are currently mainly used in the tin bath top cover bricks of float glass production lines in the flat glass industry. They have been used in the floatation of Zhuzhou Glass Factory, Jiangsu Donghai Glass Factory, Qinhuangdao Yaohua Glass Group, Taiyuan Flat Glass Factory and other manufacturers. French glass production line. Over the years, users have reported that the use is good, especially Qinhuangdao Yaohua Glass Group, which has continuously increased orders during use, which further proves the broad application prospects of this product.
Because sillimanite refractories have good high-temperature thermal stability, are resistant to erosion and erosion by molten glass, and have little pollution to molten glass, they are mostly suitable for equipment such as forehearths, feeders, and pipe-drawing machines in the glass industry, which can significantly improve productivity. Products include channel bricks, flow troughs, rotating pipes, bowls, bowls, mixing slurry, punches, barrels, fire-stop slag bricks, gate bricks, front arch bricks, rear arch bricks, bowl covers, and ports Various varieties and specifications such as bricks, burning nozzle bricks, beams, and cover bricks.
6 Conclusion
(1) Using Jixi sillimanite as the main raw material, introducing some high-quality, high-purity refractory aggregates, sillimanite products made by grouting and firing at high temperature, its main performance indicators are close to similar foreign products The performance indicators of the product can better meet the use of light industry, building materials, and metallurgical industries.
(2) Sillimanite products have good physical and chemical properties, low cost, and can replace imports, with significant economic and social benefits, and their development prospects are very broad.
(3) Sillimanite products need to further improve their physical and chemical proper.
