The advantages of magnesia carbon brick are: slag erosion resistance and good thermal shock resistance. The disadvantage of previous MgO-Cr2O3 bricks and dolomite bricks is that they absorb slag components and produce structural spalling, resulting in advanced damage to magnesia-carbon bricks. By adding graphite, this disadvantage is eliminated. Its characteristic is that slag only penetrates into the working surface, so the reaction layer is limited on the working surface., Less structural spalling and long service life.
Now, in addition to traditional asphalt and resin-bonded magnesia carbon bricks (including fired oil-impregnated magnesia bricks), magnesia carbon bricks sold on the market are:
(1) Magnesia-carbon bricks made of magnesia containing 96% ~ 97% MgO and 94% ~ 95% C graphite;
(2) Magnesia carbon brick made of magnesia containing 97.5~98.5 MgO and 96 ~ 97% C graphite;
(3) Magnesia carbon brick made of magnesia containing 98.5 ~ 99% MgO and 98% ~ C graphite.
According to the carbon content, magnesia carbon brick is divided:
(I) fired oil-impregnated magnesia bricks (carbon content less than 2%);
(2) carbon bonded magnesia brick (carbon content less than 7%);
(3) Synthetic resin combined with magnesia carbon brick (carbon content is 8% ~ 20%, a few cases up to 25%). Antioxidants are often added to pitch/resin bonded magnesia carbon bricks (with a carbon content of 8% to 20%).
Magnesia carbon brick is produced by matching high-purity MgO sand, flake graphite, carbon black, etc. Its manufacture has the following processes: raw material crushing, sieving, grading, mixing according to material formula design and product setting performance, heating up to nearly 100~200 ℃ according to binder type, and mixing with binder to obtain so-called MgO-C clay (green body mixture). The MgO-C mud using synthetic resin (mainly phenolic resin) is formed in cold state; the MgO-C mud combined with asphalt (heated into fluid state) is formed in hot state (under the condition of about 100 ℃). According to the batch and performance requirements of MgO-C products, the MgO-C clay material can be processed into an ideal shape by vacuum vibration equipment, press molding equipment, extruder, isostatic press, hot press, heating equipment and ramming equipment. The formed MgO-C body is placed in a kiln at 700 to 1200 ° C for heat treatment to convert the binder into carbon (this process is called carbonization). In order to improve the density of magnesia carbon brick, strengthen the combination, can also be used with the binder similar to the filler to impregnate the brick.
Nowadays, synthetic resins (especially phenolic resins) are used as binders for magnesia-carbon bricks. The use of synthetic resin combined with magnesia carbon brick has the following basic advantages:
(1) The environment can allow the production of these products;
(2) The process of producing products under the condition of cold mixing saves energy;
(3) The product can be processed under non-curing conditions;
(4) Compared with tar pitch binder, there is no plastic phase;
(5) increased carbon content (more graphite or bituminous coal) can improve wear resistance and slag resistance.