Magnesia-carbon bricks have two brick-making methods: burned oil-impregnated magnesia-carbon bricks and unburned magnesia-carbon bricks. The former brick-making process is more complicated and rarely used. Here, only the brick-making process characteristics of unburned magnesia-carbon bricks are briefly described.
Preparation of sludge. The selection of the critical size of particles during breeding is important. Refinement of aggregate particles can reduce open porosity and enhance oxidation resistance. However, the small aggregate particles will increase the closed pores and decrease the volume density. In addition, the fine-grained MgO aggregate easily reacts with graphite, and it is generally considered that the particle size of 1 mm is appropriate. Under the condition of high-pressure forming equipment, the particles of magnesia tend to be miniaturized. The pressure of molding equipment in my country is relatively low. In order to increase the density of refractory bricks, many manufacturers use particle diameters above 5mm.
The quality and quantity of graphite added to the ingredients are critical. Generally speaking, by increasing the graphite content in refractory bricks, the slag resistance and thermal shock stability of refractory bricks will be improved, but the strength and oxidation resistance will be reduced. If the carbon content in the magnesia carbon brick is too small (<10%), If the network skeleton cannot be formed in the refractory bricks, the advantages of carbon cannot be effectively utilized. Therefore, the carbon content is more suitable in the range of 10-20%.
During the mixing process, in order to evenly surround the graphite around the magnesia particles, the feeding sequence should be: magnesia particles → binder → graphite → magnesia fine powder and additive powder. Because the graphite content is large, the density is small, and the amount of additives is very small, it takes a long time to mix uniformly. However, if the mixing time is too long, it will easily cause the graphite and fine powder around the magnesia particles to fall off, so the mixing time should be appropriate.
The forming of magnesia-carbon bricks is an important factor in the densification of the structure of refractory bricks: due to the large amount of graphite in the mud and the small critical particles of the aggregate, it is advisable to adopt high-pressure forming and strictly follow the operation of light and heavy, and repeated pressure The procedures are suppressed to avoid forming cracks. The operating procedures of vacuuming and exhausting pressure are adopted. In addition, the surface of the high-pressure molded bricks is very smooth and easy to slide during transportation and construction. Therefore, the molded bricks should be impregnated or coated with a thermosetting resin of 0.1 to 2mm to form a resin film to prevent sliding. This kind of treatment is generally called anti-slip treatment.
The formed magnesia-carbon bricks must be hardened before they can be used. The hardening treatment has a great influence on the performance of refractory bricks. Studies have proved that hardening treatment at 200-250°C is more suitable, and it is suitable for ensuring the bulk density of bricks and reducing porosity. When the temperature is higher than 250°C and lower than 200°C, the hardening treatment will bring adverse effects. It is necessary to strictly promote and control the air. Generally, when the temperature is 50-60℃, because the resin is softened, it should be kept warm; when the temperature is 100-110℃, because a large amount of solvent is discharged, it should be kept warm; if the temperature is 200-250℃, in order to complete the reaction, it should be kept properly.