Magnesium-carbon bricks are made by firing oil-immersed magnesia-carbon bricks and non-firing magnesia-carbon bricks. The former brick-making process is relatively complex and seldom used. Here, the characteristics of the brick-making process of unburned magnesia-zirconium brick are briefly described.
Preparation of mud. For magnesia-carbon brick manufacturers, it is important to select the critical size of particles when mating. Fine aggregate particles can reduce the opening porosity and enhance the antioxidant capacity. However, small aggregate particles will increase the closed stomata and decrease the volume density. In addition, fine-grained MgO aggregate is easy to react with graphite, and the particle size of 1 mm is usually considered appropriate. Under the condition of high pressure forming equipment, magnesia particles tend to be fine. In order to improve the density of refractory bricks, many manufacturers adopt particle diameters of more than 5mm.
The quality and quantity of graphite added to the batching are very important. Generally speaking, with the increase of 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 magnesia-carbon bricks is too small (< 10%), the network skeleton can not be formed in refractory bricks, then the advantages of carbon can not be effectively brought into play. Therefore, carbon content in the range of 10 - 20% is more appropriate.
In the mixing process, in order to make graphite surround magnesia particles evenly, the order of feeding should be magnesia particles binder graphite magnesia fine powder and additive powder. Because the graphite content is large, the density is small, the amount of additives is very small, it takes a long time to mix evenly, but if the mixing time is too long, the graphite and fine powder around magnesia grains will fall off easily, so the mixing time should be appropriate.
The formation of magnesia-carbon bricks is an important factor to densify the structure of refractory bricks: because of the large amount of graphite in the mud and the small critical particle size of aggregate, it is appropriate to adopt high-pressure forming and press it strictly according to the operation rules of first weight, then weight, multiple pressure, so as to avoid forming cracks. It is better to adopt the operating rules of vacuum pumping and exhaust pressure. In addition, the surface of high-pressure forming brick is very smooth, easy to slide when handling and building, so the brick after forming should be impregnated or coated with 0.1-2 mm thick thermosetting resin to form resin film to prevent sliding. This treatment is generally called anti-skid treatment.
Formed magnesia-carbon brick billet must be hardened before it can be used. Temperature epidemic of hardening treatment has a great influence on the performance of refractory brick. It has been proved that the hardening treatment at 2001 250 is suitable for guaranteeing the volume density and reducing the porosity of bricks. When the temperature is higher than 250 and lower than 200 the hardening treatment will bring adverse effects. Strictly raise and control the air. Usually at 50-60 C, due to resin softening, it should be properly insulated; at 100-110 C, due to a large amount of solvent discharged, it should be insulated; at 200-250 C, in order to make the reaction complete, it should also be properly insulated.