Safe operation of medium frequency induction melting furnace

The induction melting furnace itself is a unified body of electricity, water and oil. Unreasonable operation often leads to serious accidents.

The main points of the induction melting furnace use prohibition operation are as follows:

   (1) adding moist charge and flux to the furnace;

    (2) connecting the molten iron with a ladle that is lined 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 with cooling water;

    (6) The iron liquid or furnace structure is operated without being grounded;

    (7) Operation without normal electrical safety interlock protection;

    (8) In the case of energization of the furnace, charging, beating the solid charge, sampling, adding a large number of alloys, measuring temperature, slag and the like. If it is necessary to carry out some of the above operations under power-on conditions, appropriate safety broadcasts should be taken, such as wearing Insulated shoes and asbestos gloves. 

    The repair work of the furnace and its supporting electrical equipment should be carried out under the condition of power failure. The reliability of the power failure is confirmed by the instrument on the control panel.

   When the induction melting furnace is working, the metal temperature, accident signal, cooling water temperature and flow rate during the induction melting furnace smelting process must be carefully monitored. The furnace power factor is adjusted to be close to 1, and the three-phase current remains substantially balanced. The outlet water temperature such as the sensor should not exceed the maximum specified by the design. The lower limit of the cooling water temperature is determined by 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. When this condition is not met, the surface of the sensor is dew condensation, and the probability of breakdown of the sensor is greatly increased. 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. When the furnace is continuously melted, a part of the molten iron should be retained as the molten liquid of the next furnace. When the amount of the molten liquid reaches 60% of the rated capacity of the furnace, the economic effect of the furnace operation is the best. Due to production conditions, it is impossible to retain so much molten iron, but at least 20 to 25% of the furnace's rated capacity is retained.

    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 sluice cover; the daily heat insulation bricks for the tapping and the molding sand are blocked; The gap between the lid and the mouth of the furnace is sealed with refractory clay or molding sand.

For the larger-sized  induction melting furnace, after the smelting operation is finished, try to avoid the lining to complete the cooling. The following methods can be used:

(1) Retaining part of the molten iron in the furnace, and energizing at low voltage, keeping the temperature of the molten iron at about 1300 tC;

(2) Install an electric heater or a gas burner in the crucible to keep the temperature of the crucible lining at 900 °C;

(3) After the furnace is shut down, the furnace cover is sealed, and the flow of the cooling water of the inductor is appropriately reduced, so that the furnace lining is slowly cooled to about 10000 C, and then the cast iron block with a slightly smaller shape and a smaller size is placed. Heat it in the furnace and keep it at a temperature of about 1000. When the next furnace starts the smelting operation, the cast iron block is used as a frit.

    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 complete cooling, after the shovel is exhausted, the slinger will take a frit and raise the temperature to 800-1000C, then close the lid and power off, let The furnace temperature is slowly cooled. In the long-term shutdown of the furnace village, cracks will inevitably occur.

When re-melting, be sure to check and repair it carefully. 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 often results in a shortened life of the lining, so the following common erroneous operations must be avoided:

The lining is not knotted, baked and sintered according to the prescribed process;

(2) The composition and crystal form of the lining material do not meet the requirements and contain more impurities;

(3) The superheat temperature of the molten iron in the later stage of smelting is outside the allowable range;

(4) When the solid material is loaded or the furnace material is bridged, the incorrect operation method and violent mechanical impact are used to cause serious damage to the furnace lining;

(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 sensor can be appropriately reduced, but it is not allowed to turn off the cooling forever, or the heat of the lining of the lining can burn the insulation of the inductor. Only when the surface temperature of the lining falls below 1000G can the cooling water of the sensor be turned off.

    For the groove type induction melting furnace, power failure is not allowed during normal operation. Even in the non-melting operation time, a certain amount of molten iron must be retained in the furnace, and the molten ditch must be filled, and the lower insulation power is passed to make the lining insulation. . At this time, the freezing ditch should be prevented, that is, the molten iron solidifies in the molten ditch. Even if power is cut off in order to replace the inductor, you should try to keep the lining warm. Only when the furnace lining is overhauled can the shovel and power outage be removed, and the lining should be repaired after cooling.