Graphite is an indispensable part of magnesia carbon bricks. The main material used in the production of magnesia carbon bricks is flake graphite, which is natural crystalline graphite. It belongs to the hexagonal crystal system and has a layered structure. It is insoluble in water, dilute acids, dilute alkali and organic solvents. It is resistant to high temperatures and has good electrical and thermal conductivity. , good lubricity. The indicators of graphite used to produce magnesia carbon bricks are generally in the following range: fixed carbon 85% ~ 98%, ash content 13% ~ 2% (main components SiO2, Al2O3, etc.), relative density 2.09 ~ 2.23, melting point 3640K (volatile). But graphite is very easily oxidized, which is the fatal shortcoming of graphite.
During on-site use, graphite is oxidized mainly for the following reasons:
(1) Free oxygen in the atmosphere;
(2) Various oxides in slag;
(3) Impurity oxides contained in the graphite itself in magnesia carbon bricks and oxides contained in magnesia.
According to national standards, flake graphite is divided into four categories based on fixed carbon content: high-purity graphite, high-carbon graphite, medium-carbon graphite, and low-carbon graphite. The graphites commonly used in refractory materials are generally high carbon graphite and medium carbon graphite. However, because the national standards’ classification of graphite is relatively complicated and the naming is not easy to remember, companies have always used the standards that are common among companies.
Taking a 100-mesh sieve as the standard, what is below the sieve is negative, and what is above the sieve is positive. In short, the scales of positive graphite are larger than the scales of negative graphite. The fixed carbon content of graphite is added after the symbol to classify and name graphite. This classification and naming method is intuitive and clear. Even many non-technical personnel in the enterprise can easily distinguish the taste of graphite, which is convenient for workers to distinguish during procurement and production. Identification of graphite taste.
The graphite used to produce magnesia carbon bricks is commonly used as follows: (1)-190, -192, -193, -194, -195, -196, -197, -198
(2)﹢194,﹢195,﹢196,﹢197,﹢198
The graphite in the magnesia carbon bricks is oxidized, causing the product structure to become loose, the pores to increase, and the strength to decrease. The impurities contained in the graphite will accelerate the oxidation of the graphite. Therefore, in order to obtain high-performance magnesia carbon bricks, high-purity materials tend to be used during production. , graphite with large scales. However, both large flakes and high-purity graphite are expensive. For industrial production, we cannot blindly pursue high indicators of raw materials, and the price indicators cannot be ignored. After several years of exploration and investigation, we have found that the demand for high-grade graphite is not high. Not big. The graphite with the greatest demand is -194, -195, and -196 graphite. Of course, -190 and -192 graphite are also useful in low-end products. The main purpose of the factory is to create profits. The cost of graphite accounts for a large proportion of the total production cost, so the reasonable selection of graphite is crucial.
Below we introduce what grade of graphite should be used for several magnesia carbon bricks:
(1) For converter: During the smelting process of the converter, the furnace cap part is subject to greater mechanical wear and is weakly eroded by slag. We choose -194 graphite. The furnace body part is strongly eroded by slag. We choose -195 or -196 graphite. , the bottom part of the furnace is mainly worn by the agitation of molten steel, and the steel slag is basically not corroded, so we choose -192 graphite. The selection of the above graphite can basically meet the needs of various domestic steel plants at this stage.
(2) Ladle slag wire bricks: There are many types of ladle slag wire bricks. Ordinary non-refined ladle slag wire bricks have a fast turnover time, so just use -193 graphite. Refined ladle slag wire bricks basically use graphite above -195. The wall and bottom of the bag are less eroded by steel slag, so graphite of -192, -193 and -194 can be used.
(3) For electric furnace: During the smelting process of the electric furnace, the magnesia-carbon bricks in the molten pool are slightly eroded by steel slag, and some of them are buried in the ramming material at the bottom of the furnace, so -192 graphite can be used for this piece, and the slag In addition to being corroded by steel slag, the line parts are also burned by arcs. Here we choose -195 or -196 graphite. The upper furnace wall is basically not corroded, so we choose -190 graphite.