In the anode assembly production process for electrolytic aluminum, the intermediate frequency furnace is called the "heart" of the system, responsible for the output of hot metal, and the recovery and melting output of phosphorus and iron after the completion of a process. Therefore, the working performance of the intermediate frequency furnace directly affects the production efficiency, energy consumption and casting quality of the anode assembly process. The operation performance of intermediate frequency furnace is mainly divided into melting efficiency and furnace age, in which melting efficiency is determined by its own electrical system and is subject to more congenital uncontrollable factors. The age of the furnace is closely related to the human management of the day after tomorrow, such as the use of furnace lining materials, furnace building methods, oven technology, daily maintenance and the melting of the furnace charge composition. The longer cycle of the furnace life, not only can maximize the continuous supply of hot metal production, is conducive to the improvement of production efficiency, but also through the planned arrangement of furnace shutdown ** intermediate frequency furnace safe operation.

1. Furnace lining structure

The lining of an intermediate frequency furnace sintered according to the standard has a typical three-layer structure: sintered layer, semi-sintered layer and loose layer. The initial thickness of each layer is about one-third of the thickness of the lining, and the boundary is clear, as shown in FIG. 1 and FIG. 2.

1) sintered layer. The surface is smooth and glazed, there is no obvious coarse cracks in the section, is the furnace wall material under the action of high temperature hot metal, so that quartz sand from β-quartz, α-quartz, α-scale quartz, with the temperature step by step to increase the crystal form into the working surface crucible of α-cristobalite sintering, forming a uniform and complete sintering network, with impact resistance, high temperature resistance, corrosion resistance, hot stability characteristics.

2) Semi-sintered layer. It is a transition zone between the sintered layer and the loose layer, and its function is to stress the sintered layer and prevent the cracks generated in the sintered layer from extending outward.

3) Loose layer. It is almost unsintered sand, and its role is to buffer the damage caused by volume expansion and contraction. The cracks in the sintered layer cause the loose layer to act as a barrier to prevent the occurrence of furnace leakage failure and heat insulation.

2, lining life

The anode assembly process of a company once fell into a passive situation due to the short life of the intermediate frequency furnace lining and the tight supply of hot metal, and the abnormally short furnace life made the operator's slight carelessness would cause furnace leakage accident, and there was a great safety risk. The statistical situation of the furnace age of a certain company in July 2014 is shown in Table 1. The average normal operation age of the furnace is 50 times, about 13 days. Long not more than 60 furnace times, short only 30 furnace times, about 7 days, far lower than the normal furnace age in the same industry.

3, the influence of lining life on anode assembly production

3.1 Influence on oven time

Due to the short age of the furnace, the replacement of the new and old need to frequently build the furnace, start the furnace and bake the furnace, especially the oven occupies a long period (more than 30h), resulting in the lack of hot metal supply directly affects the output of the anode casting line. The casting yield is low, and the production task can only be completed by adding additional shifts, which puts pressure on the normal oven process. Under normal conditions, the oven process is arranged on the scheduled maintenance and shutdown day of the casting line, so that the oven process time is sufficient and the furnace lining sintering quality is up to standard.

3.2 Influence on furnace building quality

Due to the frequent construction of the furnace, the average frequency of building 1 furnace per day is basically reached. 5 people are assigned to work in two groups, including digging old furnace linings and building new furnace linings on the same day. The labor intensity of the furnace building personnel is very large, and the fatigue operation leads to the deterioration of the furnace building quality, especially the knotting time and knotting density are difficult to beat.

3.3 Influence on the quality of hot metal

Although the process requires that the hot metal oven temperature is controlled at 1400±50℃, the casting temperature is controlled at 1350±50℃. However, due to the large viscosity and poor fluidity of the hot metal implemented according to this standard, the second half of the hot metal in the pouring ladle can hardly be cast with the decrease of the temperature during the casting operation, and it can not be returned to the furnace in time, and it is dumped nearby to make a melting block, which indirectly contributes to the hot metal gap in the casting line.

In order to meet the needs of casting production, the fluidity of hot metal can only be enhanced by increasing the hot metal temperature in actual operation. According to field measurements, the hot metal that can meet the needs of casting fluidity has a temperature of at least 1520 ° C and a casting temperature of 1450 ° C, and the hot metal is shiny and white when it is released.

3.4 Influence on casting quality

The phosphorus and iron cast in the carbon bowl is not solid and uneven. Due to the poor fluidity and fast solidification of the molten iron, the designed injection space of the phosphorus and iron ring is not filled, and the molten iron is solidified, resulting in defects in the interior and appearance of the phosphorus and iron casting, thus affecting the overall quality of the casting.

In short, the short furnace age, the insufficient supply of hot metal, the large output pressure, the poor fluidity of hot metal, and the high temperature of the furnace restrict each other, forming a vicious circle, resulting in the passive situation of production. Therefore, it is necessary to improve the service life of intermediate frequency furnace lining and reduce its influence on anode assembly production.