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Mg-Al refractories

Release Date:2012-05-09  Hits:824
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The ladle is an important and indispensable equipment in the steel industry, ladle lining refractories, has undergone several major changes. Is the use of traditional by sintering of clay brick-and third-alumina bricks, refractories in the process of using poor spalling resistance and corrosion resistance, low life, an average of only 10 times, by handle only about 20 times. With the development of steelmaking technology, refining the molten steel retaining ladle lining refractories requirements increase, in the early 20th century, who promote the use of the whole cast Mg-Al quality ladle lining material. The liner integrity, significantly increase the service life, but there are baked ladle long time, there are more serious dregs phenomenon for small and medium-sized steel mills there is no special equipment to the majority of circumstances, unpacking difficult. To compensate for this deficiency, then the successful application of aluminum-magnesium unfired brick. The lining brick building is easy to assemble, baking time is short and easy unpacking, but there are still easy to kill slag resistance and spalling resistance. On this basis, in order to overcome the aluminum-magnesium unfired brick steel package lined cat slag around the corner late. Developed aluminum-magnesium carbon brick, replacing the aluminum-magnesium unfired brick. The material combination of aluminum and magnesium materials and the performance of carbonaceous materials. The aluminum-magnesium carbon brick has the main advantages are: no cracks between the blocks melt loss, has good resistance to slag and thermal vibration, to overcome the structural spalling caused by the penetration of the molten steel and slag, significantly improved service life. Of the product does not burn or low-temperature firing, save energy and reduce costs, the economic benefits are obvious, has aroused people's attention.
Early as the 1960s, has been the development of spinel bricks, but not on the market. In order to solve the problem of chromium in the production and use in the 1970s, Japan launched a spinel magnesia brick. Added to the magnesia sintered spinel, and high temperature (900C) fired magnesia spinel brick in a tunnel kiln. Chromium oxide and iron oxide spinel alternative.
's A variety of spinel bricks have come out, but its life not as good as chrome magnesia brick. To ascertain the damage to the reasons, the performance of such a brick has been a fundamental improvement, which can match the chrome magnesia brick. Spinel (MgAl2O4) binding in
magnesia products, excellent performance, such as slag resistance, spalling resistance and creep resistance has long been known. Former Soviet Union has been since 1942 and has product development in 1964, but fishes such products in Europe until the late 1970s showed a greater interest in Japan in 1976 on the use of magnesium aluminate in the cement industry spinel brick. In recent years, the international study of MgAl2O4 and products is increasing.
In China in the 20th century advised's bauxite and magnesite (or light burned MgO) magnesium aluminate spinel raw materials. In recent years, carried out a series of preparation of magnesium aluminate spinel combined with the process of magnesia products have achieved a lot, but the performance of high-purity products has been suffering from high firing limited by the very degree. Domestic activity spinel powder. Foreign ultra-high temperature sintering process (1 850c) down to 1 660C. But for the ordinary refractory furnace of coal as fuel, is still difficult to achieve. To this end, the experts and scholars of the refractory-made activity of Mg-Al gum as a binding agent to study the activity of Mg-Al adhesive binder of high-purity magnesia brick and spinel performance combined with magnesia brick using the adhesive activity of Mg-Al Both performance products at 1 550 ° C firing, the firing of such advanced products in the ordinary fire-resistant plant kiln Shanghai.
Some large iron and steel enterprises refractory researchers and experts recently developed and applied alumina spinel brick. Active lime back to the actual production of the brick kilns, and research and development of magnesium aluminate spinel unfired brick. With the development of magnesium aluminate spinel brick in the active lime rotary kiln firing service life of more than 1 year. A long time, direct bonded magnesia-chrome brick with excellent slag resistance and resistance to erosion by the dry, left behind by the S & P for large alkaline rotary kiln. With the theme of environmental protection between increasingly severe magnesium chromium products after use of hexavalent chromium has become recognized the world, To this end, the research resistance to spalling, low thermal expansion, the organization off of less corrosion resistance of magnesium aluminum refractories, magnesia-chrome refractories best alternative materials used in alkaline rotary kiln. Since the early 20th century after the emergence of monolithic refractories, it has gradually been widely used in metallurgical industry. Today, some industrial countries unshaped refractory production to almost half of the total of the refractories. Steel industry, the scope of application is the most extensive use of the largest refractory Mg - Al unshaped refractory, account for about 85% of the unshaped refractories of total production, is widely used in BOF, ladle, iron package, furnace and blast furnaces, nearly all of the metallurgical thermal equipment.
Magnesium aluminate spinel (MgO · Al2O3) has a higher melting point, small thermal expansion, low thermal stress, thermal vibration stability, it has a more stable chemical properties, with a strong alkaline slag ability to resist the use of aluminum-magnesium unfired brick core is one of the key substances to improve life. Gradually mature in recent years, synthetic MgAl2O4-synthesized spinel materials directly to the production of ladle brick as possible, allows it to feature significantly improved. Quality of
magnesium aluminate spinel is one of the key problem related to the Mg-Al spinel brick can achieve the right effect. Laboratory test screening and the introduction of the relevant information, the magnesium-rich spinel in 20% to 30% of its corrosion resistance, resistance to structural spalling resistance and thermal vibration are better. Ladle a variety of conditions factors in the production process more requirements of magnesium aluminate spinel amount should be more reasonable 30% to 40%. In addition to join the production of a good artificial spinel in the brick-making process, but also must be added to the fused magnesium the banknote powder and corundum powder, generated in the course of the secondary spinel. To improve the brick tomb of quality part of the performance, particularly for the control of raw materials harmful impurities is low melting point material Na20 and K2O contents, selection of raw materials need to pay special attention to the exhausted. The
magnesium aluminate spinel (also known as spinel), chemical formula MgO-Al2O3-containing Mg0 28 World pipe network reported that the world's steel pipe network to provide the world's steel pipe network editor .3%, Al2O3, 71.7%. Spinel is only an intermediate compound in the Mg0-Al2O3 binary system phase diagram, the melting point of 2 135 C.Bartha pointed out that magnesium aluminate spinel and magnesia-chrome spinel, the main advantage is that the reducing atmosphere free of CO2, free of SO2/SO3 and free K2O/Na2O corrosion resistance, and good thermal stability and wear resistance. At present most of the industrial production and use of spinel refractories Na2O content of about 8% to 15%. The MgAl2O4 brick in
production process is as follows. Magnesia
(or fused town aluminum spinel sand) - crushing - screening (finely ground - powder) - raw materials - mixing - forming - dry - firing at high temperature - the products
Mg-Al tip spar production process is as follows. The
magnesia and fused magnesia alumina spinel sand according to the crushing process, aggregate particle composition and powder fineness process requirements. Preparation of a good aggregate and powder according to process requirements strictly weighing ingredients, by adding a certain binding agents; mixed in the mixing mill 15 to 20 min, forming on the friction brick press, semi-dry by 8 a 16 h; loaded dried brick tunnel kiln firing, the maximum firing temperature 1660-1680C.
alumina spinel brick raw material selection of mid-sintered magnesia, pre-synthesis of magnesium aluminate spinel, silica powder and alumina powder.
To be unfired brick does not pump high temperature firing, after baking can be directly masonry, fired brick temperature strength requirements more stringent, binding agents we need to meet: magnesia as main components not brick a good combination, to suppress the brick have sufficient mold strength after baking temperature strength of 40 MPa, to meet the transportation, masonry requirements; binders easy to use. complex production process: the binding properties of the binder, the addition amount is less, in order to avoid a significant reduction in the high temperature properties of unfired brick.
Usually choose between two binders: one is a sodium silicate solution, and sodium fluoride hardener; other polyphosphate as a binding agent, the dosage of 0.8% to 1.0% by 200T for 24 h after treatment at room temperature compressive strength has reached the power 80MPa; mixture of sodium silicate and sodium fluoride as a binder, adding a large amount. In theory, high temperature performance of the products will be affected due to the introduction of too much Na2O. Of magnesia refractory to
polyphosphate as a binder with magnesia generated Mg (of H2PO4) 2, Mg (PO3) 2, MgHPO4, and Mg2HP2O4 the melting point are high, but also in the heating process occur to help improve the strength of the material polymerization does not occur phase transitions leaving the combination of loose structure, making it a higher strength at room temperature to the temperature. From the production process, polyphosphate, solid-state to join, you can also dissolve in water by adding liquid, use a more convenient and simple to adapt to the needs of large-scale industrial production, but slightly higher production costs. Spinel
by adding the amount of the determination of: magnesium-rich spinel powder form of the introduction to the unfired brick in order to pre-where part of the spinel nucleation in the matrix of unfired brick World steel pipe network editing , so that the magnesia this nucleation and alumina-based spinel reaction occurs during use, easy to generate the MA-MA binding phase, so that the brick as soon as possible sintering, resulting in the firing products similar to the magnesium aluminate spinel crystal phase structure, in order to achieve the purpose of anti-alkaline erosion resistance, spalling. In theory, the bond strength of this MA-1/1 higher than the bond strength of MA-M-phase. And local reducing conditions, the sensitivity of the kiln atmosphere and may occur. Terms of the amount of the magnesium-rich spinel as a powder in the introduction where not too much, but otherwise affect the unfired brick in the course of sintering, the introduction of magnesium-rich spinel control in I% a 1.5 % is more appropriate.
The micropowder the role and the amount determined as follows.
Introduction of spinel bricks the sio2 part of the powder and the Al203 micronized. Sio2 the micropowder the role mainly is to increase the room temperature strength and promote sintering; main function of the Al203 powder alumina spinel, and magnesia powder reaction in the tomb of quality to improve the unfired brick thermal vibration stability and corrosion resistance . Of MgO-Al2O3-SiO2 phase diagram analysis, unfired brick, magnesia as main components, the introduction of sio2 powder is harmful, sio2 content a little while in the course of sio2 priority and Mg sand formation of forsterite within the unfired brick part of the ceramic phase, which is good for the promotion of non-fired brick as soon as possible sintering. With the increase in the amount of Al2O3 powder, not brick thermal vibration stability is an upward trend, which is unfired brick, magnesia alumina spinel formation will also increase with the increase of Al2O3, the heat have the vibration stability The sex will rise, but the amount of Al2O3 powder should not be too much.

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