Open arc melting (electrode is higher than the melt level) and closed arc melting (electrode is inside the batch) are different. Resistance system melting is that the electrode falls into the melt and the current heats the melt along the melt. In some cases, the fused zirconium corundum bricks begin to melt under the open arc, and the batch charging is finished and melted in the resistance system.
The key equipment for producing fused zirconium corundum bricks is the arc furnace. Whether its structure is reasonable and the level of automation directly affects the quality of fused zirconium corundum bricks and the cost of products. Most of the melting equipment used in my country's fused zirconium corundum brick industry uses the steelmaking arc furnace in the metallurgical industry. In recent years, China Building Materials Research Institute has developed an externally cooled arc furnace for fused zirconium corundum bricks.
The size of the arc furnace is expressed in terms of transformer capacity, in units of KV•A. The transformer power of the arc furnace used in my country's fused zirconium corundum bricks is mostly 600KV•A~2000KV•A. Although the equipment for melting fused zirconium corundum bricks is different, the arc furnaces used are similar. Each electric furnace has a special substation, which is equipped with transformers and switches to directly supply power to the electric furnace, and pass the electric energy to the graphite electrode through the secondary circuit. The lower end of the electrode is inserted into the furnace pool charge, the electric energy is converted into heat energy, the temperature in the furnace rises, the charge melts, and various chemical reactions are carried out at the same time. After the melting is completed, the furnace body is tilted to pour the molten liquid into the mold, and the casting is annealed to obtain fused zirconium corundum bricks.
When the electric furnace is molded, the electric furnace capacity is usually calculated according to the annual output and unit power consumption of the product, the rated voltage is calculated according to the working voltage, and then the electrode diameter is calculated according to the allowable current density of the electrode; the electrode distribution circle diameter is calculated according to the electrode circular power; the furnace pool diameter is calculated according to the furnace pool power; the furnace pool depth is calculated according to the melting cycle and the furnace pool liquid capacity; finally, these calculated parameters are corrected according to practical experience or reference values.
One of the main disadvantages of the electric arc furnace is that the graphitized electrode contacts the fused zirconium corundum brick melt, causing the melt to be saturated with carbon and gas. Operational technical measures should be used to reduce the carbon content in the melt. For example, the electrode is soaked in soluble salts, dust is covered with high-temperature materials at the edge of the plasma, and hollow electrodes are used.
The melting temperature should be higher than the liquidus temperature, but it should not reach the boiling temperature of the basic components.
The ultimate goal of melting the fused zirconium corundum brick batch is to obtain a uniform melt with a specified chemical composition with the lowest carbon content. The operation of the entire electric arc furnace obviously shows that the system is not fixed, the temperature of the working space fluctuates greatly, and when the imbalance is quite large, the gas is separated along the surface of the fused brick melt. The imbalance of the current distribution by phase usually causes a large power consumption of one electrode (the so-called wild phase, skew phase), and also causes the imbalance of the melting of the zirconium corundum brick raw material and the wild phase. The furnace lining is damaged greatly. Therefore, the melting conditions in the electric arc furnace cannot be guaranteed to be the same according to all melt parameters. In fact, in most cases, only the heat convection method is used to homogenize the melt, that is, the intensity is not high. In order to improve the uniformity of composition, induction stirring is used in some cases to limit the volume of the molten pool (the maximum capacity of fused zirconium corundum bricks is 10t). Based on many years of practice, it is recognized that the chemical uniformity of the melt should first be achieved with the help of the selection of raw materials and their pre-equivalent uniformity.
Wechat Us 
