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What is converter lining


The converter lining refers to the refractory layer built in the metal shell of the converter. The main function of the converter lining is to provide a durable vessel for the high-temperature metallurgical melt to complete the steelmaking reaction. It is required that the lining material can withstand high temperature and severe temperature fluctuations, and resist the chemical attack of slag and the mechanical impact and abrasion of molten steel.

All the converter linings are made of alkaline refractory materials. There are a wide range of refractory materials. According to its shape, it can be divided into two categories: shaped products and unshaped products, or divided into fired products and unfired refractories. Shaped products include fired bricks and knotted shaped bricks. Unshaped materials are bulk refractory materials, which can be filled in special parts or knotted to form the entire furnace lining when building the furnace.

The basic refractory oxides are mainly MgO and CaO. According to the different proportions, there are categories such as dolomite, high-magnesium dolomite and periclase. The natural magnesite becomes periclase after being calcined. The periclase is a pure MgO crystal with a melting point of 2800°C. It is a high-quality alkaline refractory material. Dolomite is a crystal composed of equal CaO and MgO phases, with a melting point of about 2500°C, a wide distribution of resources, and a low price. The MgO content of high-magnesium dolomite is higher than that of dolomite, but lower than that of periclase. There are naturally occurring high-magnesium dolomites, and some are artificially formulated to increase the MgO content of dolomites. The refractoriness and slag erosion resistance of periclase are better than dolomite, but the appropriate CaO content can improve the quenching and rapid heat resistance of refractories. According to research, the MgO/CaO ratio of about 80/20 has the best effect, so magnesium Dolomite brick is an excellent material for converter lining.

Carbon has a high refractoriness (above 3000°C). Carbon bricks with carbon and graphite as the main body have good heat resistance, wear resistance and high-temperature strength. They are ideal masonry materials for blast furnace hearths. However, carbon bricks are not resistant to oxidation and cannot be used in steelmaking furnaces. However, adding 10% to 20% carbon to magnesia bricks and dolomite bricks has the advantages of both MgO and C, namely high refractoriness, high temperature strength, good thermal shock resistance, and strong slag erosion resistance. The carbon in refractory bricks is mixed with magnesia (or magnesia dolomite sand) with a certain particle size and carbon content of >90% flake graphite, and combined with phenolic resin and other binders, and some also add antioxidants such as aluminum powder . The periclase grains in the refractory material are completely surrounded by the carbon film, and the carbon film is connected with some large flaky carbon to form a solid carbon network structure. Since the 1970s, the slag line, tap hole, furnace mouth and other highly corroded parts of the converter and the refining ladle outside the furnace have been replaced with carbon composite refractory masonry, which significantly improves the service life and can maintain the designed geometric shape.

Dolomite refractories contain CaO, which is prone to deliquescence by absorbing water, which is a serious disadvantage. In order to prevent dolomite from absorbing water, anhydrous asphalt is used as a binder to make bricks, and the carbon content in the bricks can reach about 2%. In order to further increase its carbon content, the asphalt-bonded bricks can be buried in carbon powder for low-temperature roasting to gasify and remove the volatiles in the asphalt, and then the lightly burned bricks can be immersed in the asphalt again. This increases the carbon content in the brick to 5% to 6%. Although its performance is not as good as that of carbon composite refractories, it is better than ordinary dolomite bricks, and the cost is lower. It is called light-burning oil-impregnated brick.


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