Improving the service life of induction crucible in induction melting furnace is the goal of every worker, and it will be of great significance to the enterprise. The main factors affecting the service life of electric furnace crucible are lining refractory, furnace laying process, furnace building process, furnace drying process and service process, which are introduced below.

1、 Lining refractory

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

1) Refractory materials for furnace construction should have good performance. Refractories are required to have high refractoriness, resistance to high temperature heat load, no softening and no melting; high volume stability, resistance to high temperature heat load, no volume shrinkage and only uniform expansion; high room temperature strength and high temperature thermal strength, high load softening temperature, no loss of strength under the combined action of high temperature heat load and heavy load It has good thermal shock resistance, rapid temperature change resistance, no cracking, no spalling, and good slag resistance.

2) Composition of refractories. Impurities in refractories can form compounds with low melting point at high temperature, thus reducing the refractoriness of refractories. With the increase of impurity content in refractory, the refractoriness decreases and the service life of crucible decreases. Therefore, it is necessary to ensure the quartz content in the furnace lining sand and strictly control the impurity composition. The workshop controls the composition of the furnace lining sand as follows: (SiO2) 98.0%; (Al2O3) 0.5%; (Fe2O3) 0.5%; (TiO2) 0.05%; (H2O) 0.5%.

3) The particle size ratio of refractories. Reasonable particle size ratio of refractory materials can easily form high density refractory layer in the process of furnace construction, and defects are not easy to appear in the process of use. Improper proportioning of coarse, medium and fine particles of refractories will reduce the service life of refractories. The refractories used in the workshop are provided by professional manufacturers. The proportioning of coarse and fine particles is as follows: 17%, 33%, 20% and 30% of refractories are 3.35mm-5mm, 0.85mm-1.70mm, 0.1mm-0.85mm and below 0.1mm respectively.

2、 Furnace laying process

The quality of laying furnace is of great significance to the life and safety of furnace. When laying the furnace, first check whether the coil is damaged, if so, brush insulating paint on the damaged part to repair it; then use glass mixed with fire-resistant mud to repair the furnace wall, and clean the furnace wall and bottom; successively lay mica plate, alarm stainless steel net and asbestos cloth cut according to the size in advance; connect the alarm stainless steel net with copper core wire to pass out of the furnace coil, and then lay three expansion rings The lower, middle and top of the furnace wall of asbestos cloth should be tightened; the paved furnace should be well covered to avoid sundries falling into it.

3、 Furnace building technology

1) Furnace building tools

① The proper selection of furnace building machine also affects the quality of furnace building. The workshop uses an electric vibrator. As far as the electric vibrator is concerned, the power, frequency and weight of the furnace building machine should meet the specific requirements of the workshop. It is necessary to avoid layering in the process of furnace building and ensure high density lining.

② There are tamping fork and flat hammer in the workshop. Tamping fork is used to pound the furnace bottom and furnace wall, and flat hammer is used to pound the furnace bottom after it is pounded.

③ There are several points for attention in the making of crucible mold: the exhaust hole should be designed reasonably to facilitate the discharge of water vapor during the drying process; the corner should be circular arc to avoid sharp angle; the weld must be polished smooth; the wall thickness of crucible mold should ensure its rigidity, and the reinforcing rib can be welded in the mold to prevent deformation during the process of the furnace.

2) Preparation before furnace construction

Before building the furnace, make good preparation. Check whether the coil is damaged, if any, take measures to deal with it; prepare all kinds of furnace building tools, check whether the furnace building machine has loose screws, whether the tamping fork is firm, etc. to prevent foreign matters from falling into the furnace lining; prepare furnace building materials, cut the bag, and require split flat shear, so as to avoid the wrapping paper falling into the furnace lining in the charging process; prepare lighting tools To observe the specific situation in the process of building the furnace; prepare the crucible mold, check its various sizes to see if it is deformed, if there is deformation, replace the crucible mold, polish the rust on the surface of the crucible mold with emery cloth, clean it with broom, and block the vent with small firewood, but the surface of the crucible mold should be smooth to prevent the lining sand from discharging from the vent when it is pounding the furnace, and it can be used after preparation.

3) Furnace building process

The quality of furnace bottom and wall directly affects the service life of furnace, so this link is very important. The bottom thickness of induction furnace is 300 mm and the wall thickness is 110 mm. When building the furnace bottom, 16 bags of 25kg furnace lining sand are added and tamped by three furnace building machines for about 50min to ensure a solid furnace bottom; after building the furnace bottom, put it into the crucible mould, correct the wall thickness with a positioning ruler, and require the error in each direction to be less than 5mm, then tighten it with a wooden wedge, and put in a pressing iron block to prevent the crucible from moving in the process of flushing, and then loosen the crucible with a flat shovel Quartz sand between the crucible and the stone cloth; as the inclined part of the crucible mold is not easy to tamp, the first layer of the furnace wall needs less charging to avoid local compactness or delamination, the first layer is 4 packs of furnace lining sand; the second layer to the sixth layer each layer is 6 packs, tamping time is about 30 minutes, and the charging amount should ensure that the furnace builder can tamp to the first layer to avoid delamination, The feeding amount shall be determined according to the specific situation; due to the inevitable floating phenomenon of coarse particles in the process of flushing, the floating coarse particles shall be separated after each layer is finished to avoid stratification; after the furnace is capped, the quartz sand mixed with water glass shall be laid on the top of the furnace and the water outlet tank, which shall be tamped and leveled; after the furnace is built, the asbestos plate shall be covered and the hot plate shall be inserted Electric couple and set a good position, ready to dry.

4、 Oven drying process

Oven drying is a process to obtain the sintering layer. The quality of the sintering layer directly affects the service life of the furnace. Oven drying is an important link. After the furnace cavity is built, the furnace should be dried immediately; before drying, check whether the electrical equipment and cooling water system are normal; the drying process should be strictly followed. Oven drying process is the key factor in oven drying process. The specific points are as follows: 1) the heating speed should be controlled well, especially in the early stage of oven drying. If the heating speed is too fast and the moisture in the furnace lining is discharged too fast, it is easy to form cracks and greatly shorten the service life of the furnace. ② When the furnace lining is heated to 573 ℃, the quartz in the furnace lining is rapidly transformed into quartz, and the volume expansion is 0.82%. As the temperature continues to rise, quartz transforms into lepidolite at 870 ℃, and its volume expands by 16%. In the process of phase transformation of quartz, too fast expansion will easily cause cracks or even spalling. Therefore, the heating rate should be slowed down when heating from 400 ℃ to 600 ℃, and it should be kept for 1-2 h at 870 ℃ to make the phase transformation complete and slow. ③ The final stage of furnace drying is sintering and heat preservation. The sintering temperature is determined according to the specific refractory materials. Generally, it is expected to get a sintering layer with a thickness of 30% of the furnace lining thickness. Therefore, the general sintering temperature is 50 ℃ ~ 100 ℃ higher than the tapping temperature.

5、 Furnace technology

Various processes in the process of furnace operation are also very important to the service life of the furnace. Improper operation may reduce the service life of the furnace. Therefore, we should pay attention to the following points in the use process.

1) As the sintering layer of the new furnace is thin, the application process of the new furnace is very important. The first furnace with water from new furnace should be melted by 50% charging, so as to avoid cracks and other defects caused by sudden cooling of furnace lining due to charging after all water comes out; the new furnace should be melted continuously as far as possible, so as to avoid cracks caused by intermittent melting, which should be melted continuously for one week in general; when the new furnace is used, the furnace bottom and furnace wall should not be impacted strongly, so as to avoid cracking under strong impact The existing lining spalling, cracks, etc. Therefore, in order to obtain a high furnace life, the early furnace using process should be done well.

2) High temperature melting should be avoided as far as possible. At high temperature, the furnace lining will react with molten iron in crucible, as follows: SiO2 + 2csi + 2CO. The higher the temperature, the higher the C and the lower the Si, the more serious the corrosion of the furnace lining will be, especially in the new furnace. Therefore, when melting, try to avoid high temperature under the condition of ensuring the water outlet temperature. The water outlet temperature is 1490 ℃ ~ 1540 ℃, but it is generally controlled at 1490 ℃ ~ 1520 ℃ in the melting process. It is worth mentioning The most important thing is that the power is cut off after the water is discharged to keep the temperature at a lower temperature. When the water is discharged, the temperature is raised according to the temperature of the last ladle. This can reduce the erosion of high temperature molten iron on the furnace lining, prolong the service life of the furnace lining, and reduce the power consumption. It is a good method to improve the furnace life and reduce the power consumption.

3) Avoid overheating the lining. Due to the rapid heating rate of induction melting furnace, when the smelter does not pay attention to it, the charge will appear "bridging"; This phenomenon will cause local high temperature of furnace lining or even exceed the fire resistance of furnace lining, which may cause furnace lining melting and corrosion; or when the foreman does not pay attention, when the melting temperature is too high, it may also cause furnace lining melting and corrosion; this will greatly reduce the service life of furnace lining. Therefore, attention must be paid at any time in the melting process, for example, the foreman should frequently poke materials, and the foreman should pay attention to molten iron The temperature of hot metal can be controlled at any time to ensure the safety of furnace lining.

4) In the process of use, if 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 damage of the furnace lining due to the cracking of the furnace lining when the molten iron condenses; when the molten iron cannot be emptied and the molten iron has been condensed, the furnace should be dismantled for the sake of safety when it is impossible to judge whether the furnace lining is in good condition.

5) In the process of use, especially when the new furnace, try to use clean charge.

6) When the furnace is shut down for cooling, in order to avoid the sudden cooling of the furnace lining, the empty furnace cooling should be carried out. At the same time, in order to avoid cracks caused by the excessive temperature difference between the upper and lower parts of the furnace lining during the cooling process, the furnace cover should be covered to make the furnace lining even up and down, so as to ensure the service life of the furnace.

7) Due to the inevitable occurrence of vertical cracks when the furnace is cold, it is necessary to dry the furnace at low temperature before melting, so that the cracks can be bridged first to avoid the penetration of molten iron into the cracks and the further expansion of the cracks.

8) In the process of using the furnace, we should pay attention to observe the furnace condition. Observing the furnace condition is a kind of protection for the furnace. Measure the furnace bottom every three days and observe the furnace wall every day, so as to ensure the safety of the furnace lining.

9) For the maintenance of electric furnace, such as purging the coil frequently, cleaning the impurities on the coil to prevent coil breakdown, so as to avoid furnace dismantling due to equipment failure, and effectively improve the service life of crucible.