Graphite is an indispensable part of magnesia carbon brick. The production of magnesia carbon brick mainly uses flake graphite, which is a natural crystalline graphite, belonging to the hexagonal crystal system, with layered structure, insoluble in water, dilute acid, alkali and organic solvent, high temperature resistance, good conductivity and thermal conductivity, good lubrication. The graphite used to produce magnesia carbon brick is generally in the following range: fixed carbon 85% ~ 98%, ash 13% ~ 2% (main components SiO2, Al2O3, etc.), relative density 2.09 ~ 2.23, melting point 3640k (volatilization). But graphite is very easy to be oxidized, which is a fatal defect of graphite.
(scale graphite)
Causes of graphite oxidation
During the field application of MgO-C brick, the main reasons for graphite oxidation are as follows:
(1) Free oxygen in atmosphere;
(2) Various oxides in slag;
(3) The impurities and oxides contained in graphite and magnesia in magnesia carbon brick.
Classification of graphite types
According to the national standard, flake graphite can be divided into four types according to the fixed carbon content: high purity graphite, high carbon graphite, medium carbon graphite and low carbon graphite. The common graphite used in refractories is high carbon graphite and medium carbon graphite. However, due to the complexity of the division of graphite in national standards and the difficulty in remembering the names, the common standards between enterprises have been used.
(scale graphite)
The scale of positive graphite is larger than that of negative graphite. After the symbol, the fixed carbon content of graphite is added to classify and name the graphite. This classification and naming method is intuitionistic and clear. Even in enterprises, many people who are not skilled in technology can easily distinguish the taste of graphite, which is convenient for workers to identify the taste of graphite when purchasing and producing.
Common graphite for magnesia carbon brick
The graphite used to produce magnesia carbon brick 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 brick is oxidized, which makes the structure of the product loose, the pores increase and the strength decrease. The impurities in the graphite will accelerate the oxidation of the graphite. Therefore, in order to obtain high-performance magnesia carbon brick, the graphite with high purity and large scale is preferred in the production. But the price of large scale and high-purity graphite is not cheap. For industrial production, we can not blindly pursue the high index of raw materials, and the price index can not be ignored. After several years of exploration and investigation, we found that the demand for high-grade graphite is not large. The largest demand for graphite is - 194, - 195, - 196, which are three types of graphite. Of course, they are also useful in low-grade magnesia carbon brick - 190, - 192 stone Ink. The main purpose of the factory is to create profits. The cost of graphite accounts for a large proportion of the production cost of magnesia carbon brick, so it is very important to select graphite reasonably.
Selection of graphite for different kinds of MgO-C brick
What kind of graphite should be selected for several magnesia carbon bricks
(1) Magnesia carbon brick for converter: in the smelting process of converter, magnesia carbon brick at the furnace cap is subject to relatively large mechanical wear and relatively weak slag erosion. We choose - 194 graphite, and magnesia carbon brick at the furnace body is subject to relatively strong slag erosion. We choose - 195 or - 196 graphite. Magnesia carbon brick at the furnace bottom is mainly subject to the abrasion caused by the agitation of steel water, and the slag is basically not eroded, so we choose - 192 graphite, the graphite above The selection can basically meet the needs of various steel mills at present in China.
(2) Ladle slag line brick: there are many kinds of ladle slag line bricks. Ordinary non refining ladle slag line brick has a fast turnover time. It is OK to choose - 193 graphite. The refining ladle slag line brick basically uses graphite above - 195. The wall and bottom of ladle are less eroded by steel slag, and graphite of - 192, - 193 and - 194 can be selected.
(3) MgO-C brick for electric furnace: in the smelting process of electric furnace, MgO-C brick in the molten pool is very little eroded by steel slag, and some of them are buried in the bottom ramming material, so the graphite of - 192 can be selected. The slag line is not only eroded by steel slag, but also burned by electric arc. In this case, we choose graphite of - 195 or - 196. The upper furnace wall is not eroded very much, so we choose graphite of - 195 or - 196 Use - 190 graphite.