18 correct habits of operating medium frequency furnace

Jul 27, 2022


Observe the cooling water (temperature, water pressure, flow) on the internal and external circulating water system at any time

1. Observe the cooling water (temperature, water pressure, flow) on the internal and external circulating water system at any time. If the water flow of a branch is found to be small, leaking, blocked, or the temperature is too high, the power shall be reduced for operation, or the machine shall be shut down for treatment; If it is found that the furnace cooling system is powered off or the pump is stopped due to failure, so that the furnace cooling water is cut off, the melting shall be stopped immediately and:

1). Start the water pump with the help of standby power supply;

2). Or start the emergency diesel generator to supply power and start the emergency circulating cooling system;

3). Or open the tap water (or emergency water tank) and directly enter the cooling (at the same time, open the drain) to directly discharge the water cooled by the furnace body;

4). If it cannot be treated in a short time and the water circulation is difficult to recover for a while, the molten iron in the furnace should be emptied to avoid turning into iron blocks due to the long-term cooling of molten iron, which is difficult to take out of the furnace.

2. Observe various indicating instruments on the power cabinet door of the medium frequency furnace at any time, and adjust the input of the medium frequency power in time to obtain the best melting effect and avoid long-term low-power operation.

3. Pay close attention to the current indication value of the leakage current indicator to grasp the change of furnace lining thickness. When the indicator needle reaches the alarm value, the furnace shall be shut down and rebuilt.

4. In case of sudden protection indication during normal operation, first adjust the power knob to the minimum position, and immediately press "inverter stop", find out the cause, and then start it after troubleshooting.

5. In case of emergency or abnormal conditions, such as abnormal sound, smell, smoke, ignition or sharp drop in output voltage, sharp increase in output current, and the intermediate frequency frequency is higher than that in normal operation, and the leakage current (lining alarm) value fluctuates greatly, which may be the thinning of lining, leakage of molten iron, arc and short circuit of induction ring gate, it is necessary to immediately press the "inverter stop" button to stop the machine and deal with it in time to prevent the accident from expanding.

6. When feeding and slag raking, the power should be reduced first, and the variable-frequency power supply must be placed in the "inverter stop" position when dumping the furnace and tapping the molten iron.

7. When the cold material of the hot furnace lining melts, the starting loading can only be loaded to 50% of the crucible height. When the current drops to a level that can raise the voltage to the rated value, continue to add material to the crucible. (this is because the resistance coefficient of cold furnace material is small, the current is large, and the regulated voltage is limited by the current, which affects the power input).

8. During the production process, it is not allowed to overfill or even exceed the furnace mouth at one time, because the magnetic field of the furnace charge above the upper end face of the induction ring is weak, and it is mainly heated by the heat transferred by the molten iron below, so the melting speed is slow. At the same time, because the furnace cannot be covered, a large amount of heat energy is emitted through the furnace mouth, reducing productivity.

In addition, the crucible at the upper end of the induction ring and the furnace lining at the junction with the furnace nozzle are not easy to tamp, the oven is not perfect, and the sintering is not good, but it is subject to the maximum mechanical vibration stress, so this section is prone to furnace leakage. Therefore, the solution surface in the crucible should be controlled to be flush with the upper end face of the induction ring.

9. Although the molten iron of medium frequency furnace can be emptied, it is good for smelting different materials. However, if the material is not changed, it is better to leave residual liquid in the furnace. This is because there is molten iron in the furnace, which makes the added charge easy to be connected into many large blocks, and the single charge will be arc welded together to form a large block, thus improving the melting rate. The speed of arcing and bridging between single small charges depends on the frequency. The frequency is low and the lap welding speed is low (the reason why the power frequency furnace must leave residual liquid to melt).

If it is not emptied, a small part of molten iron is left at the bottom of the furnace, and the disadvantage of using a lower frequency can be easily overcome (the frequency of medium frequency furnace is relatively not very high). In addition, due to the small load change at the initial stage of power on, high power can be input at the beginning, which can at least shorten the melting time of metal charge.

10. During charging, the highest surface of molten iron shall not exceed the limit of 80% capacity, so as not to cause accidents when molten iron overflows the furnace mouth during charging.

11. Add small charge first and then large charge.

12. Frequently observe the melting condition in the furnace. Before the furnace charge is completely melted, it should be added in time. If it is found that the shed is built, it should be handled in time to avoid penetrating the furnace due to the sharp rise of the temperature of molten iron under the shed, which exceeds the melting point of the furnace charge (quartz sand 1704 ℃).

13. After molten iron is melted, slag removal and temperature measurement shall be carried out in time, and it shall be discharged in time when the tapping temperature is reached.

14. Under normal circumstances, when the crucible wall is 1/3 of the thickness of the original furnace lining, the furnace should be dismantled and rebuilt.

15. Empty the molten iron once a week, measure the lining size and observe its surface condition, grasp the actual situation of the lining in time, and deal with problems in time.

16. It is better to add c-increasing agent little by little during the process of adding metal charge. If it is added too early, it will adhere to the bottom of the furnace and will not easily dissolve into the molten iron. Adding too late will prolong the melting and heating time, which will not only delay the adjustment of composition, but also cause excessive high temperature. The addition of ferrosilicon (increase of Si) is bad for the medium frequency furnace with weak stirring force, because the high content of Si in the molten iron will make the increase of C poor, so it is better to add ferrosilicon later, but it will cause delay in the composition analysis and adjustment of molten iron in the furnace.

17. The retention of liquid metal in the furnace during the initiation helps to improve the electrical efficiency of some electric furnaces and improve the power factor in the initiation stage. However, these molten iron may be overheated in the furnace for a long time and endanger the metal quality, so the residual liquid metal should account for 15% of the furnace capacity. Too little molten iron will aggravate the overheating state, and too much will reduce the effective use of molten iron and increase the unit energy consumption.

18. The thickness of furnace charge should be 200 ~ 300mm. The greater the thickness, the slower the melting.