The main factors that affect the service life of electric furnace crucibles include lining refractory materials, drying process, and usage process. Below, the manufacturers of furnace materials will introduce them separately.

1. Refractory materials for furnace lining

The quality and performance of refractory materials for furnace lining play a fundamental role in the service life of the furnace.

(1) Refractory materials for building furnaces should have a relatively high degree of fire resistance, resist the action of high temperature heat loads, do not soften, and do not melt. At the same time, it also needs to have high volume stability, resistance to high-temperature thermal load, non shrinkage of volume, and only uniform expansion.

(2) The composition of refractory materials. Impurities in refractory materials can form low melting point compounds at high temperatures, thereby reducing the refractoriness of refractory materials. Therefore, it is necessary to ensure the quartz content in the furnace lining sand, strictly control the impurity composition, and control the composition of the furnace lining sand as follows: ω (SiO2) ≥ 98.0%; ω (Al2O3) ≤ 0.5%; ω (Fe2O3) ≤ 0.5%; ω (TiO2) ≤ 0.05%; ω (H2O) ≤ 0.5%.

(3) The particle size ratio of refractory materials. A reasonable particle size ratio of refractory materials can easily form a high-density refractory layer during the furnace construction process, making it less prone to defects during use. The following is a reasonable set of ratios: 3.35mm to 5mm, 0.85mm to 1.70mm, 0.1mm to 0.85mm, and ratios below 0.1mm are 17%, 33%, 20%, and 30%, respectively.

2. Oven drying process

Oven drying is the process of obtaining a sintering layer, and the quality of the sintering layer directly affects the service life of the furnace. Oven drying is an important link.

After the furnace chamber is built, the oven should be dried immediately; Before baking, check whether the electrical equipment and cooling water system are normal; When drying the furnace, it is necessary to strictly follow the drying process. The drying process is a key factor in the drying process, and the specific points are as follows: ① Control the heating speed, especially in the early stages of drying. If the heating speed is too fast and the water in the furnace lining is discharged too quickly, it is easy to form cracks, greatly shortening the service life of the furnace. ② When the furnace lining is heated to 573 ℃, excessive expansion during the quartz phase transformation process can easily cause cracks or even peeling. Therefore, when heating from 400 ℃ to 600 ℃, the heating speed should be slowed down, and at 870 ℃, it should be kept for 1-2 hours to enable slow and complete phase transformation. ③ Oven drying. The later stage is sintering insulation, and the sintering temperature depends on the specific refractory material. Generally, it is desired to obtain a sintering layer with a thickness of 30% of the furnace lining thickness. Therefore, the sintering temperature is generally 50-100 ℃ higher than the tapping temperature.

3. Furnace process

The various processes involved in the use of the furnace are also crucial for its lifespan, and improper operation may reduce its lifespan. Therefore, the following points should be noted during use.

(1) Due to the thin sintering layer of the new furnace, the usage process of the new furnace is very important. The first furnace with new water outlet should be melted by adding 50% of the material, which can avoid defects such as cracks in the furnace lining caused by sudden cooling after all water outlet is added; The new furnace should be continuously melted as much as possible to avoid cracks caused by intermittent melting, cold and hot. Generally, it should be continuously melted for one week.

(2) Try to avoid high-temperature melting during the melting process. At high temperatures, the furnace lining will react with the molten iron in a crucible, as follows: SiO2+2C → Si+2CO. The higher the temperature, the higher the C, and the lower the Si, the more severe the corrosion of the furnace lining, especially in new furnaces. Therefore, during melting, try to avoid high temperatures while ensuring the outlet water temperature.

(3) Avoid overheating the furnace lining. Due to the rapid heating rate of the intermediate frequency furnace, when the smelter is not paying attention, the furnace material may experience "bridging" phenomenon, causing local high temperatures or even exceeding the refractory degree of the furnace lining. This may cause the furnace lining to melt and corrode.

(4) During use, if the furnace needs to be shut down for a long time due to faults or other reasons, the molten iron in the furnace should be emptied to avoid causing damage to the furnace lining due to the cracking of the furnace lining caused by the condensation of the molten iron.

(5) During use, especially when using a new furnace, try to use clean furnace materials as much as possible.

(6) When stopping the furnace for cooling, in order to avoid sudden cooling of the furnace lining, empty furnace cooling should be carried out. At the same time, to avoid cracks caused by excessive temperature difference between the upper and lower parts of the furnace lining during the cooling process, the furnace cover should be covered to ensure that the furnace lining is evenly cooled up and down, thereby ensuring the service life of the furnace.

(7) Due to the inevitable occurrence of vertical cracks during furnace cooling, when starting the cold furnace, it is necessary to first dry the furnace at a low temperature and then melt it, so that the cracks can be bridged first and avoid further expansion of the cracks due to the infiltration of molten iron during melting.

(8) During the use of the furnace, attention should be paid to observing the furnace condition. Observing the furnace condition is a form of protection for the furnace. The bottom of the furnace should be measured every 3 days, and the furnace wall should be observed every day, ensuring the safety of the furnace lining.

(9) Maintenance and upkeep of the electric furnace equipment, such as frequent blowing of the coil and cleaning of debris on the coil to prevent coil breakdown, thus avoiding furnace dismantling caused by equipment failures and effectively improving the service life of the crucible.