The ladle is an important equipment in the steelmaking industry. As the refractory material for the lining of the ladle, several major changes have taken place. High-quality magnesia-aluminum chrome bricks used traditional sintered clay bricks and third-class alumina bricks. This refractory material shows poor spalling resistance and erosion resistance during use, and has a low service life. Only 10 times, after treatment, it can only reach about 20 times. With the development of steelmaking technology, the requirements for refractory materials for the lining of ladle linings in the external refining of molten steel have increased. At the beginning of the 20th century, the use of integrally cast magnesium-aluminum ladle lining materials was once promoted. This kind of lining has good integrity and significantly improves the service life, but there is a long baking time for the ladle, and there is a serious phenomenon. It is difficult to unpack when most small and medium-sized steel plants do not have equipment. In order to make up for this shortcoming, aluminum-magnesium non-fired bricks were successfully applied. The lining brick is easy to build, short baking time and easy to unpack, but still has the problems of easy slagging and poor resistance to peeling. On this basis, in order to overcome the problem that the lining of the aluminum-magnesium non-burnable brick ladle is easy to cat slag, the aluminum-magnesium-carbon non-burnable brick was developed in the late period to replace the aluminum-magnesium non-burnable brick. This material combines the properties of aluminum-magnesium materials and carbon-containing materials. The main advantages of aluminum-magnesium-carbon non-fired bricks are: no brick joint melting loss, good slag resistance and thermal vibration resistance, overcoming the structural spalling phenomenon caused by the penetration of molten steel and slag, and significantly improving the service life. Because the product is not fired or fired at low temperature, it saves energy, reduces costs, and has obvious economic benefits, which has attracted people's attention. Converter magnesia carbon brick
As early as the 1960s, magnesia-aluminum spinel bricks had been developed but were not put on the market. In order to solve the problems in the production and use of chromium, Japan introduced spinel-containing magnesia bricks in the 1970s. That is, sintered spinel is added to magnesia, and magnesia spinel bricks are fired in a tunnel kiln at high temperature (1900°C). Spinel is used to replace chromium oxide and iron oxide.
Various magnesia-aluminum spinel bricks came out in those days, but their service life was not as good as that of chrome-magnesia bricks. After clarifying the cause of the damage, the performance of this type of brick has been fundamentally improved, which can rival the chrome-magnesium brick.
The excellent properties of magnesia products combined with spinel (magnesia-aluminum spinel), such as slag resistance, spalling resistance and creep resistance have long been known. There have been researches since 1942 and product development in 1964, but Europe did not show greater interest in this product until the end of the 1970s. Japan began to use magnesium-aluminum spinel in the cement industry in 1976. Stone bricks. In recent years, there has been an increasing international research on magnesium aluminum spinel and its products.
In the 20th century, my country began to use bauxite and magnesite (or light-burned MgO) to synthesize magnesia-aluminum spinel raw materials. In recent years, a series of researches on the process of preparing magnesia-aluminum spinel combined with magnesia products have been carried out, and many achievements have been made. However, high-purity products with excellent performance have been limited by the high firing temperature. Some people in China use activated spinel powder to reduce the foreign warm firing process (1850°C) to 1660°C. However, it is still possible for ordinary refractory kilns that generally use coal as fuel. For this reason, domestic refractory experts and scholars used self-made active magnesia-aluminum glue as a binder, and studied the performance of high-purity magnesia bricks and spinel bonded with magnesia-aluminum glue as a binder, using the activity of magnesia-aluminum glue. The two kinds of products with excellent performance are fired at 1550°C, which provides the possibility for firing such advanced products in the kilns of ordinary refractory plants.
High quality magnesia aluminum chrome brick
Refractory researchers and experts in some large domestic steel companies have recently developed and applied magnesia-aluminum spinel non-fired bricks. Through the actual production of active lime returning to the brick kiln, the magnesia-aluminum spinel non-burning brick was developed. The use shows that the developed magnesia-aluminum spinel non-burned brick has a burning service life of more than one year in the active lime rotary kiln. For a long time, direct-bonded magnesia-chrome bricks have excellent slag resistance and corrosion resistance, and have been widely used in large alkaline rotary kilns. However, as the problem becomes more and more serious, the hexavalent chromium produced after the use of magnesia-chromium products has become a world problem. For this reason, research has been conducted on magnesia-aluminum series with good exfoliation resistance, low thermal expansion rate, less structure degradation and corrosion resistance. Refractory materials are used in alkaline rotary kilns as substitutes for magnesium-chromium refractory materials. Since the emergence of monolithic refractories in the early 20th century, they have gradually been widely used in the metallurgical industry. Today, the output of monolithic refractories in some industrially developed countries accounts for almost half of the total refractory materials. At present, the steel industry has a wide range of applications. The refractories used are magnesium-aluminum unshaped refractories, accounting for about 85% of the total production of unshaped refractories. They are widely used in converters, ladles, iron ladles, heating furnaces and blast furnaces. Metallurgical thermal equipment.
Magnesium aluminum spinel (MgO·Al2O3) has a high melting point, small thermal expansion, low thermal stress, and good thermal vibration stability. At the same time, it has relatively stable chemical properties and strong resistance to alkaline slag. It is the point where the aluminum-magnesium non-burning brick can be used, and it is one of the key substances to improve the life. Due to the gradual maturity of synthetic magnesia-aluminum spinel technology in recent years, it is possible to directly produce ladle bricks using synthetic spinel materials, which can significantly improve its characteristics.
The quality of magnesia spinel is one of the key issues related to whether the magnesia spinel brick can achieve the appropriate effect. Through the test screening in the laboratory and the introduction of related materials, the corrosion resistance, structural spalling resistance and thermal vibration resistance of magnesium-rich spinel are relatively good at 20% to 30%. However, there are many factors in the production and operation of the ladle, and it is more reasonable to require the addition of magnesium-aluminum spinel to be between 30% and 40%. Therefore, in the process of making bricks, in addition to adding the produced artificial spinel, fused magnesia banknote powder and corundum powder are also added to make it regenerate secondary spinel during use, thereby improving the quality of the brick tomb. In order to control the content of harmful impurities in raw materials, Na20 and K2O, which are low melting point substances, the selection of raw materials needs attention.
The chemical formula of magnesium aluminum spinel (also called spinel) is MgO-Al2O3, containing 28.3% of Mg0 and 71.7% of Al2O3. Spinel is an intermediate compound in the phase diagram of the Mg0-Al2O3 binary system, and its melting point is 2135°C. Bartha pointed out that compared with magnesia-chromium spinel, the main advantages of magnesia-aluminum spinel are corrosion resistance to reducing atmospheres such as free CO2, free SO2/SO3 and free K2O/Na2O, as well as better thermal stability and sex. The Na2O content of most spinel refractories currently produced and used in industry is between 8% and 15%.
