Key Points and Methods of Lining Maintenance of Electric Induction Furnace
The induction furnace needs to be lined when in use. Generally, nearly 400 furnaces can be used if the furnace lining is good. If it is not good, it may be used for dozens of furnaces, and the furnace lining may be broken. This also relates to the service life of the electric induction furnace lining. One reason for such a big difference in use may be the problem of the furnace lining material, and the other is the maintenance of the furnace lining. Therefore, in order to prolong the service life of the furnace lining, in addition to selecting suitable furnace lining materials, also need to know the key points and methods of induction melting furnace lining maintenance.
1. Key Points of Lining Maintenance of Electric Induction Furnace
1.1 Crack Repair
Before each startup of the cold furnace, observe whether there are cracks on the inner surface of the furnace lining. If the crack width is less than 2mm, it can still be used without repair. Otherwise, it must be repaired before reuse. When tapping, observe whether there are cracks at the junction of the side fireplace lining and the tap hole. If there are cracks, repair them. After tapping, visually observe whether the furnace lining at the furnace bottom and slag line is locally corroded. If there are cracks, repair them.
1.2 Empty molten iron
The molten iron should be emptied when the furnace is shut down for cooling. 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 cracking of the furnace lining when the molten iron condenses and damage the furnace lining; When the molten iron cannot be poured out, and the molten iron has been condensed, and it is impossible to judge whether the furnace lining is intact, the furnace should be dismantled for safety.
1.3 Uniform Cooling
Heating and cooling will destroy the structure of the metal. Therefore, when the medium frequency furnace needs to be shut down for cooling after the high-temperature operation, sudden cooling must be avoided and empty furnace cooling should be carried out. And in order to avoid cracks caused by excessive temperature differences between the upper, middle and lower parts during the cooling process of the furnace lining, it is necessary to cover the furnace cover to make the upper and lower parts of the furnace lining cool evenly, so as to prolong the service life.
1.4 Clean the Electric Induction Furnace Coil
If the induction furnace lining is maintained, such as purging the coil frequently, cleaning the sundries on the coil to prevent the coil from breakdown, so as to avoid furnace disassembly caused by equipment failure, the service life of the furnace lining can be effectively improved.
1.5 Cold Electric Induction Furnace Preheating
Preheating is required for cold furnace startup. Vertical cracks will inevitably appear in the medium frequency furnace when the furnace is cold. At this time, if the cold furnace is to be started, it must be preheated at low temperature first, and then gradually increase the temperature for melting operation. This can make the cracks that appeared in the previous cold furnace heal first, and avoid the penetration of molten iron into the cracks during melting, resulting in the continuous expansion of cracks.
1.6 Avoid Overheating of Electric Induction Furnace Lining
The Induction melting furnace should avoid overheating of the furnace lining. Because the heating rate of the medium frequency smelting furnace is quite fast, when the foreman is not careful, the furnace burden will appear “bridging” phenomenon, and the local high temperature of the furnace lining will even exceed the refractory degree of the furnace lining, which may cause the furnace lining to melt and erode; Or when the foreman is not careful, the melting temperature is too high, which may also cause the furnace lining to melt and erode; This will greatly reduce the service life of the furnace lining. Therefore, we must pay attention to it at any time during the melting process. For example, the melting chemical industry should poke the material frequently, and the foreman should master the temperature of the molten iron at any time according to the color of the molten iron, so as to ensure the safety of the furnace lining.
1.7 Low Temperature Oven
Because vertical cracks inevitably appear when the foundry melting furnace is cold, when the cold furnace is started, it should be dried at low temperature first, and then melted, so that the cracks can be bridged first, so as to avoid the penetration of molten iron into the cracks and further expansion of the cracks when molten iron melts.
1.8 Observation in Use
Pay attention to the furnace condition during the use of the crucible induction furnace. Observing the furnace condition is a kind of protection for the furnace. Measure the bottom of the furnace every 3 days and observe the furnace wall every day, so as to ensure the safety of the furnace lining.
2. Maintenance Method of Induction Electric Induction Furnace lining
2.1 For dry method furnace, the steel mold in the furnace is not taken out. When baking the oven, the principle of adding small materials and filling them up must be adopted to avoid local ignition and melting of the liner, so that the dry materials collapse. Therefore, it is required to try to accumulate some small materials in front of the oven. At the same time, the steel formwork shall be strictly observed during the heating process. When there is serious arcing, the current shall be reduced. If the current is too high, the steel formwork will be broken down by the arc and lead to the collapse of refractory materials.
2.2 When the Inductotherm induction furnace is shut down due to an emergency and the molten iron in the furnace solidifies, attention should be paid to:
(1) If the medium frequency furnace cannot be restarted in a short time, 3 ~ 5 steel pipes (with a diameter of about 20 mm) should be inserted into the furnace to facilitate the emission of gas during the remelting process.
(2) Before the top of the solidified molten iron in the furnace melts, the furnace body should be shaken up, inclined by 15 ° ~ 30 °, and powered on at a insulation power lower than that of the medium frequency furnace.
(3) The power shall not be increased before the solidified metal in the furnace is softened. If the temperature rises too fast, the expansion of the metal will exceed the expansion of the furnace lining, which can crack the furnace lining and lead to furnace penetration in serious cases; After softening the solidified metal, the power can be increased to about the insulation power until the metal hard shell above the condensed metal is melted through by the liquid metal below, then the furnace body can be leveled and heated and melted according to the normal power.
2.3 In order to reduce the cracking of furnace lining caused by repeated sudden heating and cooling, continuous blowing in is very important to prolong the service life of furnace lining, which has attracted enough attention of many users. If the medium frequency furnace cannot be used continuously, after the second use, add metal charge into the furnace and cover the furnace cover, which can not only preheat the metal charge, but also prevent cracks in the furnace lining caused by rapid cooling.
2.4 When the electric induction furnace is opened to about 20 heats, the furnace mouth shall be removed to check whether the furnace lining is drilled and whether the dry material of the furnace lining is loose and has a gap. When repairing the furnace mouth, try to use metal furnace mouth rings with different heights. Don’t pay attention to that the old and new interfaces should be cleaned up. When carrying out the next furnace repair operation, it should be removed to the bottom of the last furnace repair interface, and so on. The furnace mouth and mouth are places that are often slagged, corroded and impacted by furnace charge, which need regular maintenance and repair to ensure the normal maintenance and use of the medium frequency furnace.
2.5 Smelting personnel must pay attention to the erosion and cracks of the furnace lining. In the middle and late life of the furnace lining, the smelting condition should be observed from time to time, and the high melting power, current and turnover of the molten iron of the electric furnace should be observed. If necessary, the molten iron should be emptied and stopped for inspection.
2.6 The use of the furnace cover is very important for the electrotherm furnace. Some manufacturers do not pay attention to the use of the furnace cover, and even discard the furnace cover. This practice is wrong. When opening the furnace, cover the furnace cover well, which can not only prevent the loss of heat, speed up the melting of the furnace charge, but also avoid the splashing of molten iron when melting the material; When the furnace is shut down, covering the furnace cover can keep the furnace lining material cool slowly, so as to avoid cracks.