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Methods to reduce anode iron-carbon voltage drop Anode, pressure drop, molten iron, aluminum powder, resistance In the production of electrolytic aluminum plants, the anode is known as the "heart of electrolysis", and as the main indicator of anode assembly quality, the level of iron-carbon pressure drop determines the power consumption per ton of aluminum to a certain extent. Especially in the production practice of large-scale prebaked aluminum electrolytic cells, the current intensity is generally large, and the voltage drop at each location (even if it is small) accumulates to a large number over a long period of time. How to reduce the iron-carbon pressure drop can be said to be one of the major issues directly related to the cost of aluminum electrolysis production. Our workshop adopts various specific measures to reduce the iron-carbon pressure drop, and the results are very good. Generally speaking, the main reasons for the increase in anode iron-carbon pressure drop are as follows:: 1. The steel claws are not sand-washed and rust-free, the height is not high enough, and they are unclean. Rust, impurities, etc. are attached to them, forming an isolation layer, affecting conductivity, thereby increasing the voltage drop. 2. The treatment of dust and carbon particles in phosphorus pig iron is not up to standard. Impurity bubbles are generated during the pouring process, which increases the resistance of phosphorus pig iron and increases the pressure drop. The content of gases and non-metallic inclusions in molten iron not only affects the strength and density, but is also related to the formation of pores, cracks and other defects in phosphorus iron, and directly reduces the electrical conductivity. 3. Failure to absorb dust and clean the carbon bowl before pouring will affect the flow of molten iron, or may be mixed into the molten iron, resulting in loose contact between the molten iron and the carbon bowl, and the molten iron itself being mixed. If the dust is not sucked cleanly, it may also cause an obvious gap between the phosphorus iron ring and the carbon bowl after pouring, and the guide rod may shake slightly. During the pouring process, alumina powder or shell blocks bonded to the steel claws will fall into the carbon bowl, affecting the pouring quality. 4. The lead powder and graphite paint applied on the claw heads are not in place and are uneven, which cannot play a good conductive role, but increases the voltage drop. The water in the lead powder and graphite cannot evaporate, which will cause the molten iron to bubble or tumble during pouring. In severe cases, blasting will occur, affecting the pouring quality. 5. Due to the moisture of the carbon block during the pouring, a second pouring had to be performed (first pour a small amount of molten iron into the carbon bowl to preheat the carbon block, and then pour it. From the residual phosphorus iron bowl recovered to the workshop, you can clearly see a clear boundary between the two). Uneven or too fast flow rates of the pouring molten iron will cause the molten iron to shrink unreasonably and form cracks in the phosphorus iron ring, that is, explosion cracks (some have more than two fracture lines). The second pouring will cause the molten iron to roll up and down, mixed with bubbles, and faults will appear between the two pourings of phosphorus iron, which will increase the resistance and generate heat during electrolysis production. In severe cases, the entire anode carbon block will fall off. 6. The steel claws and anode carbon blocks themselves have quality problems and have too many impurities. There are pores and slag inclusions in the steel claws, which will affect the conductive properties of the steel claws. The main component of the carbon anode is carbon, and the content of other impurities should be as low as possible, especially oxides such as iron, silicon, vitriol, titanium, nickel, and sulfur, which not only affect the physical and chemical indicators of the carbon anode, but also enter the aluminum liquid during the electrolysis process, affecting the purity of the aluminum or affecting the current efficiency, which is detrimental to production. The carbon block has large ash content and high porosity, which increases the resistivity. The result is an increase in the iron-carbon pressure drop. Cupola furnaces generally use coke and residual anode blocks. If the sulfur content is high and the ash content is large, it will affect the quality of the molten iron. 7. Molten iron pouring temperature. Temperature has always been the focus of iron phosphorus pouring. According to general operating requirements, the exit temperature of molten iron is at least 50°C higher than the pouring temperature, and the exit temperature of molten iron is at least not lower than 1350°C (the minimum operating requirement is 1300°C). If the temperature of the molten iron is too high, the shrinkage ratio will be large (the shrinkage of the molten iron is divided into three steps: Liquid iron shrinkage, liquid-solid shrinkage, solid-state shrinkage) and cracks, the guide rod is prone to loosening ； If the temperature is too low, the fluidity of the molten iron will become poor, the carburizing ability will be reduced, and the electrical conductivity will be poor, making pouring difficult. The molten iron cannot be used and must be dumped, which is a waste of manpower and material resources. 8. The desulfurization and slag removal effects are not good, which affects the pressure drop. During the cast iron smelting process, harmful elemental components (sulfur and other trace elements that interfere with the normal crystallization and structure control of cast iron, etc.) must be controlled below limits. Improper proportions of raw material components and feeding order of phosphorus pig iron will affect the desulfurization and slag removal effects. During the cupola melting process, frequent desulfurization and slag removal are required. The sources of sulfur in the molten iron in cupola furnace smelting are, firstly, the inherent sulfur in the charge, and secondly, the sulfur absorbed from the coke. Acidic cupolas do not have desulfurization capabilities, and alkaline cupolas can desulfurize to a certain extent. However, we use a straight cold-air acidic cupola, so we can only use external desulfurization. When the alkalinity of the slag is increased within a certain range, it will help reduce the sulfur content of the molten iron. ； When the temperature increases, the amount of sulfur added to the molten iron during the smelting process decreases. ； When the furnace gas is highly oxidizing, the FeO content in the slag increases, which is not conducive to the desulfurization reaction. Appropriately increasing the coke-to-iron ratio and reducing the air supply intensity are beneficial to desulfurization. The raw material contains high sulfur content. The sulfur converts iron into ferrous sulfide with a low melting point. The fluidity of the molten iron becomes poor, the carburizing performance of the molten iron is poor, the conductivity is reduced, the resistance is increased, and the iron-carbon pressure drop is high. We generally use desulfurization outside the furnace (using soda ash, calcium carbide desulfurizer, etc. to desulfurize). Sulfur mainly exists in the form of iron sulfide in molten iron. Soda ash can decompose in high-temperature molten iron. The decomposition product sodium oxide can react with iron sulfide in molten iron to form stable sodium sulfide that is insoluble in molten iron. The specific gravity of sodium sulfide is relatively small, so it floats to the slag and is eliminated, thus playing a desulfurization effect. If the slag removal after desulfurization is not good, impurities and sulfides will still remain in the molten iron, increasing the resistance and affecting the conductive properties. Therefore, during the use of the desulfurizer, a slag remover must be used (generally using perlite chips as a slag remover or a special slag remover), otherwise the effect will not be good. 9. The ratio of phosphorus pig iron and the influence of the five elements in phosphorus pig iron. The composition range of general cast iron is roughly: C2.4-4.0%, Si0.6-3.0%, Mn0.2-1.2%, P 0.1-1.2%, S 0.08-0.15%. The ingredients we require are: C2.5-3.5%, Si2.5-3.5%, Mn0.3-0.9%, P 0.6-0.9%, S