Improving the service life of the induction furnace body is the goal pursued by every foundry worker, and it will also be of great significance to the enterprise. The main factors affecting the service life of the electric furnace crucible are the furnace lining refractory material, the furnace process and the use process, which will be introduced separately below.
1. Furnace lining refractory
The quality and performance of furnace lining refractories play a fundamental role in the service life of the furnace.
1) The refractory material for building the furnace must have a relatively high refractoriness, resist the action of high temperature heat load, and do not soften or melt. At the same time, it must have high volume stability, resist high temperature thermal load, not shrink in volume and expand uniformly.
2) The composition of the refractory material. Impurities in refractory materials can form compounds with low melting point at high temperature, thereby reducing the refractoriness of refractory materials. Therefore, the quartz content in the lining sand should be guaranteed, and the impurity composition should be strictly controlled. The composition of the lining sand should be controlled as follows: ω(SiO2)≥98.0%; ω(Al2O3)≤0.5%; ω(Fe2O3)≤0.5%; ω(TiO2)≤ 0.05%; ω(H2O)≤0.5%.
3) Refractory particle size ratio. The reasonable particle size ratio of the refractory material can easily form a high-density refractory layer during the furnace construction process, and it is not easy to cause defects in the use process. The following is a set of more reasonable ratios: 3.35mm~5mm, 0.85mm~1.70mm, 0.1mm~0.85mm, and the ratios below 0.1mm are 17%, 33%, 20%, and 30%, respectively.
2. Oven process
The oven is the process of obtaining the sintered layer. The quality of the sintered layer directly affects the service life of the furnace. The oven is an important link. After the furnace cavity is built, the oven should be oven immediately; before the oven, check whether the electrical equipment and cooling water system are normal; the oven should be in strict accordance with the oven process. The oven process is the key factor in the oven process. Specific points: ① Control the heating speed, especially in the early stage of the oven. If the heating rate is too fast and the moisture in the furnace lining is discharged too quickly, cracks will easily form, which will shorten the life of the furnace. greatly shortened. ②When the furnace lining is heated to 573°C, the quartz will expand too fast during the phase transformation, which will easily cause cracks or even peeling off. Therefore, when the furnace lining is heated to 600°C from 400°C, the heating speed should be slowed down, and at 870°C, it should be kept for 1h to 2h. , enabling a slow and complete phase transition. ③The furnace stage is sintering and heat preservation. The sintering temperature depends on the specific refractory material. Generally, it is hoped to obtain a sintered layer with a thickness of 30% of the furnace lining thickness. Therefore, the sintering temperature is generally 50-100 °C higher than the tapping temperature.
3. Furnace process
Various processes in the use of the furnace are also very important to the service life of the furnace, and various improper operations may reduce the service life of the furnace. Therefore, the following points should be paid attention to during use.
1) Since the sintered layer of the new furnace is thin, the use process of the new furnace is very important. The first furnace of the new furnace should produce 50% of the water, that is, feeding and melting, so as to avoid defects such as cracks and other defects caused by the sudden cooling of the furnace lining after all the water is discharged; the new furnace should be continuously smelted as much as possible to avoid intermittent smelting. The cracks should generally be continuously melted for 1 week.
2) Try to avoid high temperature smelting during the smelting process. At high temperature, the furnace lining will react with molten iron in the crucible, as follows: SiO2+2C→Si+2CO, the higher the temperature, the higher the C, the lower the Si, the corrosion of the furnace lining will be aggravated, especially in the new furnace. Therefore, when melting, try to avoid high temperature while ensuring the water temperature.
3) Avoid overheating of the furnace lining. Since the heating rate of the intermediate frequency furnace is quite fast, when the smelter does not pay attention, the "bridging" phenomenon of the charge will appear and the furnace lining will have a local high temperature or even exceed the refractoriness of the furnace lining, which may cause the furnace lining to be melted and corroded.
4) During the use process, when the furnace needs to be shut down for a long time due to faults and other reasons, the molten iron in the furnace should be emptied to avoid the furnace lining being damaged due to the cracking of the furnace lining when the molten iron condenses.
5) In the process of use, especially when the furnace is new, try to use a clean charge.
6) When the furnace is stopped for cooling, in order to avoid the sudden cooling of the furnace lining, the furnace should be cooled in an empty furnace. At the same time, in order to avoid the cracks caused by the excessive temperature difference between the upper and lower sides of the furnace lining during the cooling process, the furnace cover should be covered to make the furnace lining even up and down during cooling. Guarantee the service life of the furnace.
7) Since vertical cracks inevitably appear when the furnace is cold, when the cold furnace is started, the furnace should be baked at a low temperature first, and then melted, so that the cracks can be bridged first, and the cracks can be prevented from infiltrating the cracks when the molten iron is melted.
8) During the use of the furnace, pay attention to observe the furnace condition. Observing the furnace condition is a kind of protection for the furnace. Measure the furnace bottom every 3 days, and observe the furnace wall for each furnace every day, so as to ensure the safety of the furnace lining.
9) Maintain and maintain the electric furnace equipment, such as frequently purging the coil, cleaning the sundries on the coil to prevent the coil from breaking down, thus avoiding the disassembly of the furnace due to equipment failure, and effectively improving the service life of the crucible. (Editor/Li Zijun)
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