I. What Safety Precautions Should Be Taken During Melting in a Medium Frequency Furnace

1. General Rules

(1) On-site personnel shall strictly comply with the company's regulations, wear correct personal protective equipment, and use special filter goggles when observing high-temperature metal.

(2) The furnace liner shall be inspected regularly at fixed intervals to prevent burnout. Inspect the furnace liner after cooling: when the thickness of the furnace liner (excluding asbestos board) is eroded to less than 65mm ~ 80mm, furnace repair must be carried out. If there is no abnormality, forced replacement is required after about 250 heating cycles. Charge feeding shall be done carefully to avoid material "bridging" and "crusting". The overheating of metal under the bridge/crust will accelerate the corrosion of the furnace liner.

(3) Furnace charge shall be dry, free of combustibles and closed containers, and not excessively rusted. Violent boiling of liquid or combustibles in the charge will cause molten metal overflow or even explosion.

(4) No accumulated water is allowed in the pit in front of the furnace to avoid explosion when molten iron splashes or pours into it.

2. Charging Method for Medium Frequency Furnace

(1) No matter what the property of furnace charge is, the next batch of charge shall be added slowly before the previous batch of charge is completely melted. Improper conditions such as charge with too much rust and adhered sand, improper size and shape of charge pieces leading to loose packing and serious bridging, or too much cold charge added at one time, will easily cause bridging. The liquid level must be checked frequently. Once bridging occurs, handle it immediately and break down the bridge to avoid formation of solid bridging. Otherwise, the molten iron in the lower part will overheat, causing erosion of the lower furnace liner, and even leakage of molten iron or explosion.

(2) Handling method for bridging: Reduce the melting current to below 500A; Pierce and break down the bridge with an iron rod; If the bridge still remains, tilt the electric furnace appropriately and keep melting at low power until molten iron breaks through the bridging or crust layer;

(3) After all the charge is completely melted, skimming shall be carried out immediately to prevent formation of "slag crust". If a slag crust is formed, cut off the power immediately, break the slag crust and remove it out of the furnace. Otherwise, the molten iron in the lower part will overheat, causing erosion of the lower furnace liner, and even leakage of molten iron or explosion

II. Emergency Treatment for Medium Frequency Furnace Melting

1. Power Outage

(1) Emergency Treatment for Cooling Water

1) The dual-power switch in the main distribution cabinet of the electric furnace control room shall be kept at the automatic switching position. When the main power supply fails, the safety power supply will be connected automatically, and then restart the water pump for the furnace body immediately;

2) If both the main power supply and the safety power supply fail, notify the on-duty electrician immediately, and prepare to start the emergency generator to ensure the small water pump of the furnace body is powered to supply cooling water for the furnace body. Therefore, the diesel generator must be guaranteed to have a sufficient diesel reserve, and it shall be tested run together with the equipment once a month;

3) If the diesel generator also fails to start, connect tap water to the furnace body immediately;

4) Due to power outage, water supply to the coil stops, and a large amount of heat is conducted from molten iron. If there is no water supply for a long time, the water in the coil may vaporize, which will damage the cooling effect of the coil, and burn out the rubber hose connected to the coil and the insulation of the coil.

(2) Emergency Treatment for Molten Iron in the Furnace

1) If power outage occurs during the initial melting period of cold charge and the charge is not completely melted, it is not necessary to tilt the furnace, keep the original state, only continue water supply, and restart melting when power is restored;

2) If molten iron is already melted due to medium frequency power supply failure, but the amount of molten iron is small and pouring cannot be carried out (due to unqualified temperature, unqualified composition, etc.), you can tilt the furnace to a certain angle and let the molten iron solidify naturally. If the amount is large, the molten iron shall be poured out;

3) In case of sudden power outage when molten iron has already been melted, insert pipes into the molten iron before it solidifies, so as to facilitate gas discharge during re-melting and prevent explosion accidents caused by gas expansion;

4) When re-energizing to melt the solidified furnace charge for the second time, it is better to tilt the furnace forward at a certain angle, so that part of the molten iron that has melted at the bottom can flow out first from the lower tilted part to prevent explosion.

2. Molten Iron Leakage of Medium Frequency Furnace

Molten iron leakage accidents are likely to cause equipment damage and even endanger personal safety. Therefore, regular furnace maintenance and care shall be done well to avoid molten iron leakage accidents.

(1) When the alarm bell of the furnace lining thickness measuring device rings, immediately cut off the power supply, patrol around the furnace body, and check whether molten iron leaks out. If there is any leakage, tilt the furnace immediately and pour out all molten iron.

(2) If molten iron leakage is already found, evacuate personnel immediately and pour all molten iron directly into the pit in front of the furnace;

(3) Molten iron leakage is caused by damage to the furnace lining. The thinner the furnace lining is, the higher the electrical efficiency and the faster the melting speed. However, when the worn thickness of the furnace lining is less than 65mm, almost the entire furnace lining is a hard sintered layer with an extremely thin transition layer, and there is no loose layer. Small cracks will form on the furnace lining once it is subjected to sudden cold and heat. These cracks can penetrate the entire interior of the furnace lining, easily causing molten iron leakage.

(4) When a furnace leakage accident occurs, personal safety must be guaranteed first, and then equipment safety should be considered. For equipment, the main consideration is to protect the induction coil. Therefore, when furnace leakage occurs, immediately turn off the power supply and keep the cooling water unobstructed;

3. Excessively High Cooling Water Temperature

(1) Foreign bodies block the cooling water pipe of the inductor, resulting in reduced water flow and excessively high cooling water temperature. In this case, cut off the power first, then purge the water pipe with compressed air to remove foreign bodies. The downtime of the water pump should preferably not exceed 8 minutes.

(2) Scale accumulates in the cooling water channel of the coil, reducing water flow and leading to excessively high cooling water temperature. According to the quality of cooling water, pickling shall be carried out in advance to remove obvious scale in the coil water channel every 1 to 2 years.

(3) Sudden water leakage from the inductor pipe. Most of such leakage is caused by insulation breakdown between the inductor and the water-cooled yoke or surrounding fixed supports. When this accident is found, cut off the power immediately, strengthen the insulation treatment at the breakdown position, seal the surface of the leaking part with epoxy resin or other insulating glue, and operate at reduced voltage. After the molten iron in this furnace is completely melted and poured out, repair the furnace. If the coil water channel is broken down in a large area and the gap cannot be temporarily sealed and repaired with epoxy resin and other materials, the furnace has to be shut down, all molten iron poured out, and then repaired.