Correct Usage and Operating Procedures for Medium-Frequency Furnaces

1. Cold Startup of Medium-Frequency Furnaces

1. During cold startup, sufficient time must be given for the furnace lining material to undergo reversible expansion. The material should seal before the molten metal comes into contact with the furnace lining, preventing cracks caused by thermal shock (sudden temperature changes between cold and hot).
2. For medium-frequency furnaces, the temperature of the thermocouple in the middle of the effective coil serves as the control temperature. Additionally, gas combustion can be added at the furnace bottom to help reduce the temperature difference between the upper part of the furnace and the entire furnace lining. During cold startup, 3 to 4 K-type thermocouples should be used for temperature detection, and the thermocouples must be placed tightly against the furnace wall or furnace bottom.
3. Start by supplying power at low power, then gradually increase the power. After maintaining 20% to 30% of the full power for 15 minutes (to seal the small cracks formed in the furnace lining during cooling), switch to full power. After the heat preservation process is completed, melt the furnace charge quickly before putting the furnace into normal use.

2. Startup Operation of Medium-Frequency Furnaces

1. Close the switch of the incoming low-voltage switch cabinet, check whether the indicators of the three-phase incoming voltage meter and ammeter are normal, and turn the power adjustment potentiometer to the minimum value.
2. Press the "Control Power On" button. After 2 to 3 seconds, press the "Main Circuit On" button, then press the "Inverter Start" button. The medium-frequency power supply will start working, and at this point, the DC voltmeter, ammeter, medium-frequency frequency meter, and power meter should all show readings.
3. After successful startup, slowly adjust the power knob to the required power level to input power.
4. If the medium frequency is not established, it indicates a startup failure. Press the "Inverter Stop" button to reset the system, then press the "Inverter Start" button again to establish the medium frequency.

3. Shutdown Operation of Medium-Frequency Furnaces

1. When shutting down, first turn the power adjustment knob to the minimum position, then press the "Inverter Stop" button.
2. If a long-term shutdown is required: first press "Inverter Stop", then press "Main Circuit Off", and finally press "Control Power Off". These steps must be followed strictly in the above order—do not reverse the operation sequence!
3. Turn off the internal circulating cooling water for the medium-frequency power supply and electric heating capacitors, and stop the operation of the circulating water pump in this system. However, for the internal and external circulating systems of the furnace body, the water pump and water supply can only be stopped after the surface temperature of the furnace lining drops below 100°C (this process usually takes 72 hours).
4. When stopping the cooling water supply in winter, precautions must be taken to prevent water pipes from cracking due to freezing of residual water inside. Measures such as thermal insulation, draining all water, or adding ethylene glycol to the water can be adopted.