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Induction furnace test and precautions during the process
1. Furnace lining sintering and baking
Sintering and baking of the lining should be based on the capacity, form (furnace or grooved furnace) of the furnace and the selected refractory materials to establish the corresponding furnace, baking and sintering processes.
For the crucible-type electric furnace, the first melting after sintering must be melted at the full furnace to allow the furnace portion to be fully sintered. In order to reduce the erosion of the furnace lining by electromagnetic stirring, the operating voltage should be reduced during melting and sintering, and the voltage should be 70-80% of the rated voltage (at this time, the power is 50-60% of the rated power). After the sintering is completed, several furnaces should be continuously melted, which is beneficial to obtain a perfect flaw and has a good effect on improving the life of the lining. When the first few furnaces are melted, use as clean and rust-free as possible, preferably low-carbon cast iron. In the smelting process, it is necessary to avoid the process of intensifying the erosion of the lining, such as carbonation and other processes.
For induction furnaces, because the structure of the furnace is relatively complicated, and the wet or dry method is used to build the furnace, the oven must be heated slowly for a long time to dry and sinter the lining. After the induction body of the furnace is energized, the heating of the tire mold makes the furnace lining dry, and the rest of the furnace is initially cooled by means of other heat sources. When the furnace is dried and reaches a certain sintering temperature, it is melted by the induction body. Iron or iron is injected to gradually reach high temperature sintering. The induction furnace starts from the first baking and sintering furnace lining. In the oven and sintering process, the heating specification should be strictly implemented, and attention should be paid to prevent the occurrence of the segmentation event. During normal operation, always pay attention to changes in the state of the groove.
2. Problems that should be paid attention to during the smelting operation
The induction electric furnace body itself is a unified body of three systems of electricity, water and oil, and the irregular operation often causes serious accidents. The following are strictly prohibited operations:
(1) Unqualified charge and flux are added to the furnace;
(2) connecting the molten iron with a ladle covered with defects or moisture;
(3) found that the furnace lining has serious damage and continues to smelt;
(4) violent mechanical impact on the lining;
(5) The furnace is operated without cooling water;
(6) The iron liquid or furnace structure is operated without being grounded;
(7) Operation under normal electrical safety interlock protection;
(8) In the case where no furnace is energized, charging, beating solid charge, sampling, adding large
Batch alloy, temperature measurement, slag and so on. Appropriate safety measures, such as wearing insulated shoes and wearing asbestos gloves, should be taken if some of the above operations must be performed under power.
The repair work of the furnace and its supporting electrical equipment must be carried out in the event of a power failure.
When the furnace is working, the metal temperature, accident signal, cooling water temperature and flow rate during the smelting process must be carefully monitored. The furnace power factor is adjusted to be close to 0.9 or higher, and the three-phase or six-phase current remains substantially balanced. The outlet water temperature such as the sensor does not exceed the maximum specified by the design. The lower limit of the cooling water temperature is generally determined on the condition that the outer wall of the inductor is not dew condensation, that is, the temperature of the cooling water is slightly higher than the ambient air temperature. If these conditions are not met, condensation will form on the surface of the sensor and the probability of breakdown of the sensor will increase.
After the chemical composition and temperature of the molten iron meet the requirements, the power should be cut off and the iron should be discharged in time.
At the end of the smelting operation, the molten iron is exhausted. In order to prevent the rapid cooling from causing large cracks in the lining, appropriate slow cooling measures must be taken, such as adding asbestos sheets on the tarmac; the tapholes are blocked with insulating bricks and molding sand; The gap between the furnace cover and the furnace opening is sealed with refractory clay or molding sand.
For large-sized induction furnaces with large capacity, after the smelting operation is finished, try to avoid complete cooling of the lining. The following methods can be used; (1) part of the molten iron is retained in the furnace, and low-voltage is energized to keep the temperature of the molten iron at about 1300 °C; (2) Install an electric heater or a gas burner in the crucible to keep the temperature of the crucible lining at 900~1100 °C; (3) After the furnace is shut down, seal the furnace cover and properly reduce the flow of the sensor cooling water. The lining of the crucible is slowly cooled to about 1000 °C, and then the cast iron block with the smaller size and the smaller size is hoisted into the furnace, and is heated by electricity to keep the temperature at about 1000 ° C. When the next furnace starts The ingot is used as a frit during the smelting operation.
If it is necessary to stop the furnace for a long time, it is not necessary to keep the crucible warm. In order to better store the lining in the case of completely cooling the water, after the molten iron in the crucible is exhausted, a piece of the frit is lifted and the temperature is raised to 800-1000 ° C, then the furnace lid is closed, the power is cut off, and the furnace is turned off. The temperature is slowly cooled. After long-term shutdown of the furnace lining, cracks will inevitably occur. When re-melting, it must be carefully inspected and repaired. The temperature must be slowly increased during melting to make the fine cracks formed in the lining self-heal.
During the operation of the furnace, the condition of the lining should be checked frequently to ensure safe production and improve lining life. Incorrect operation methods often lead to shortened lining life, so the following common erroneous operations must be avoided: (1) the lining is not knotted, baked and sintered according to the specified process; (2) lining material composition and crystal form Does not meet the requirements, contains more impurities; (3) the superheated temperature of the molten iron in the later stage of smelting is out of the allowable range; (4) when loading solid materials or by removing the charge of the furnace, using inaccurate operation and violent mechanical shock, so that The lining of the kiln is seriously damaged; (5) after the furnace is shut down, the lining is quenched and a large crack is generated.
When the furnace is interrupted, the amount of cooling water of the inductor can be appropriately reduced, but it is not allowed to close the water, otherwise the residual heat of the lining can burn the insulation of the inductor. The cooling water of the sensor can only be turned off when the surface temperature of the lining falls below 100 °C
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