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When an accident occurs suddenly, remain calm and handle it correctly to prevent the accident from escalating and to minimize its impact.

 

1. Power outage

 

Medium-frequency furnace Power outages are caused by overcurrent in the power supply network, ground faults, or accidents involving the induction furnace itself. When the control circuit and the main circuit share the same power source, the pump in the control circuit will also stop working. If the water supply to the induction coil is interrupted for more than 3 to 5 minutes, the coil’s insulation could be damaged, leading to an accident. Therefore, several preventive measures should be taken in advance during the design phase:

 

1) Urban (tap water) supply;

 

2) Water in the high-level tank;

 

3) Water powered by a DC motor driven by a gasoline engine pump or a battery-powered pump;

 

4) The power supply for the water pump should have two separate circuits (one of which should be relatively stable). In open-loop cooling water systems, the first two backup water sources are commonly used; in closed-loop cooling systems, the third backup water source is typically employed. However, regardless of the type of circulation system, a fourth backup source is always essential.

 

5) Due to the power outage, the induction coil’s power supply is also cut off. Therefore, during normal power supply, the water flow in the induction coil requires only 20% to 30% of the usual water supply. During a power outage, the capacity of the elevated water tank should be determined based on the water consumption of the electric furnace over a period of more than 10 hours.

 

6) Within 1 hour of a power outage, you can cover the metal surface with charcoal to prevent heat loss and wait for the power to be restored. Generally speaking, no other measures are necessary, as the temperature drop of the molten metal is limited—and the drop itself is relatively small.

 

7) When the power outage lasts longer than 1 hour, the molten metal in small-capacity electric furnaces may solidify. The solidification of molten metal inside the crucible can restrict the shrinkage of the furnace lining, leading to cracking of the lining. Therefore, it is essential to avoid the solidification of molten metal in the crucible as much as possible. Ideally, when the molten metal is still liquid, you should switch the oil pump’s power supply to the backup power source or use a manual backup pump to pour out the molten metal. → In the design, consideration should be given to providing pits for storing molten iron. For blast furnaces, the pits are directly constructed in a grid pattern; for cupola furnaces, slag-storage pits should be built on the ground. However, since there is no need to retransport the molten iron, the existing pits can be utilized.

 

8) If a power outage occurs during the melting of cold charge, and the charge has not yet completely melted, there is no need to dump the charge from the furnace. You can leave it as it is, but continue to circulate water through it. Once power is restored, the charge will continue to melt.

 

 

 

2. Leakage

 

 

 

Liquid leakage accidents can easily cause equipment damage and even endanger personal safety. Therefore, in daily operations, we should do our utmost to maintain and care for electric furnaces, thereby preventing furnace leaks from occurring.

 

 

 

1) When the alarm bell of the alarm device sounds, immediately cut off the power supply, conduct a patrol around the furnace body, and check whether any molten metal has leaked. If a leak is detected, promptly tilt the furnace to empty it of the molten metal. If no leakage is found, follow the inspection and handling procedures for furnace chamber leakage alarms. If it is confirmed that molten metal has leaked through the furnace lining and come into contact with the electrodes, triggering the alarm, then empty the furnace of the molten metal, repair the furnace lining, or rebuild the furnace lining.

 

 

 

2) Furnace leakage is caused by damage to the furnace lining. The thinner the lining thickness, the higher the electrical efficiency and the faster the melting rate. However, once the lining wears down to less than one-third of its original thickness, nearly the entire lining thickness will consist of a hard sintered layer and a transition layer, with no loose layer remaining. As a result, even slight quenching and heating of the lining can cause fine cracks to form. These cracks can lead to complete cracking of the entire lining, making it easy for molten metal to leak out.

 

3) Improper furnace construction, drying, and sintering methods—or the inappropriate selection of furnace lining materials—can all lead to furnace leaks during the initial few melting cycles.

 

3. Cooling Water Accident

 

1) Cooling High water temperature is generally caused by the following reasons:

 

a. The cooling water pipe of the sensor is blocked by foreign objects, causing the water flow rate to decrease. In this situation, it is necessary to shut down the power and use compressed air to blow through the pipe and remove the foreign objects (the pump should be stopped for no more than 3 minutes).

 

b. The cooling water passages in the coil are fouled with scale. Depending on the quality of the cooling water, the coil water passages must be descaled with hydrochloric acid every 1 to 2 years. Additionally, the hoses should be removed and inspected for scale buildup every 6 months. If significant scale blockage is observed in the water passages, descaling should be performed ahead of schedule.

 

A sudden leak occurred in the sensor piping. The cause of the leak was mostly due to dielectric breakdown between the inductor and the magnetic yoke or the mounting bracket. Once this incident is detected, immediately cut off the power supply and reinforce the insulation at the affected area. The TSC-L ultra-high-temperature insulating varnish currently in use can withstand temperatures as high as 750°C, ensuring that even under the harsh operating conditions of the medium-frequency furnace, the insulating varnish will not lose its insulating properties due to high-temperature carbonization, thereby effectively preventing arcing and breakdown. After a copper pipe is punctured, the leakage area should be sealed using the FCAR rapid copper crack repair agent, and the voltage should be reduced during the repair process. Before repairing the furnace, empty the charge and the molten iron completely. If the coil’s water passages suffer extensive cracks and cannot be temporarily sealed with the FCAR rapid copper crack repair agent, the furnace must be shut down, the molten metal drained, and the damage repaired accordingly. Appendix: The fixing bolts on the furnace’s rotating base and furnace frame supports need to be inspected (and tightened) weekly. Since these bolts are subjected to periodic tensile and shear stresses during tilting and dropping, they are prone to fatigue failure, loosening, and accelerated fracture. In addition to regular tightening and maintenance, the bolts should be made of high-strength materials and replaced annually.