Requirements for safe melting of medium frequency furnace

May 21, 2022

1、 What should be paid attention to in order to ensure safety in the smelting process of medium frequency furnace

1. Routine

(1) The on-site personnel shall wear labor protection articles in strict accordance with the regulations and requirements of the company, and use special filter when observing high-temperature metal.

(2) The furnace lining shall be checked frequently at certain intervals to prevent "depletion". Check the furnace lining after cooling: when the thickness of the furnace lining (excluding asbestos board) is less than 65mm ~ 80mm after burning, the furnace must be repaired. If there is no abnormality, about 250 furnaces shall be forcibly removed. The feeding shall be careful to avoid "bridge crossing" and "capping" of materials. The ultra-high temperature of the metal under the "bridge and cover" will accelerate the corrosion of the furnace lining.

(3) The furnace charge shall be dry, free of combustibles, closed containers and excessive rust. The violent boiling of liquid or inflammables in the charge will lead to liquid metal overflow and even explosion.

(4) There shall be no ponding in the pit in front of the furnace to avoid explosion after molten iron splashes and tilts in.

2. Charging method of medium frequency furnace

(1) Regardless of the charge, the next melt shall be put into operation slowly before the previous charge is melted. "Bridging" is easy to occur if the furnace charge with much rust and sand is wrongly used, and the furnace charge is of poor lumpiness and shape, resulting in loose charging and serious overlapping, or too much cold charge is added at one time. The liquid level must be checked frequently. In case of bridging, it shall be handled immediately, and the "bridging" shall be poked off to avoid the formation of "bridging". Otherwise, the molten iron in the lower part will overheat, causing erosion of the lower furnace lining, or even leakage of molten iron or explosion.

(2) Bridging treatment method: reduce the melting current to below 500A; Poke and pierce with an iron rod; If it is not disposed of, the electric furnace shall be properly tilted to maintain low-power melting until the molten iron breaks through the bridging or capping layer;

(3) After the furnace charge is completely melted, the slag shall be removed immediately to prevent the formation of "slag cover". If the "slag cover" is formed, the power shall be cut off immediately, and the "slag cover" shall be broken and pulled out of the furnace, otherwise the molten iron in the lower part will overheat, causing erosion of the lower furnace lining, and even molten iron leakage or explosion

2、 Emergency treatment of medium frequency furnace smelting

1. There's a power failure

(1) Emergency treatment of cooling water

1) The dual power switch in the main power distribution cabinet in the electric furnace control room shall be kept in the self switching gear. When the main power supply is cut off, the security power supply will cut in automatically, and then start the boiler body water pump again immediately;

2) When the main power supply and the security power supply are cut off at the same time, inform the electrician on duty immediately and prepare to start the emergency generator to ensure that the small water pump of the furnace body runs the cooling water of the furnace body after it is powered on. Therefore, the diesel generator must ensure that it has a certain reserve of diesel oil and run once a month together with the equipment;

3) When the diesel generator cannot be started, tap water shall be cut into the furnace body immediately;

4) Due to the power failure, the water supply of the coil is stopped, and the heat transmitted from the molten iron is very large. If there is no water for a long time, the water in the coil may turn into steam, destroy the coil cooling, and burn out the rubber hose connected with the coil and the insulation of the coil.

(2) Emergency treatment of molten iron in furnace

1) Power failure occurs during the start of melting of cold furnace material, and the furnace material has not been completely melted. It is not necessary to dump the furnace, keep it in its original state, only continue to supply water, and wait for melting again when the next power is on;

2) Due to the failure of medium frequency power supply, the molten iron has melted, but the amount of molten iron is small and cannot be poured (the temperature is not reached, the composition is unqualified, etc.), it can be considered to tilt the furnace to a certain angle and then solidify naturally. If the quantity is large, consider pouring out the molten iron;

3) Due to the sudden power failure, the molten iron has melted. Try to insert a pipe into the molten iron before the molten iron solidifies, so as to eliminate the gas when melting again and prevent the explosion accident caused by gas expansion;

4) When the solidified charge is electrified and melted for the second time, it is best to tilt the furnace forward at an angle so that a part of the molten iron below flows out first at the lower part of the tilt to prevent explosion.

2. Molten iron leakage of medium frequency furnace

Molten iron leakage accident is easy to cause equipment damage and even endanger people. Therefore, it is necessary to do a good job in the maintenance of the furnace at ordinary times to avoid molten iron leakage accident.

(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 the molten iron leaks. In case of leakage, dump the furnace immediately and pour out the molten iron.

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

(3) Molten iron leakage is caused by the damage of furnace lining. The smaller the thickness of the furnace lining, the higher the electrical efficiency and the faster the melting speed. However, when the lining thickness is less than 65mm after wear, the whole lining thickness is almost a hard sintering layer and a very thin transition layer. There is no loose layer. If the lining is slightly cooled and heated, it will produce small cracks. The crack can crack through the interior of the whole furnace lining, which is easy to make molten iron leak out.

(4) In case of furnace leakage, personnel safety shall be ensured first. In consideration of equipment safety, the equipment mainly considers the protection of induction coil. Therefore, in case of furnace leakage, the power supply shall be turned off immediately to keep the cooling water unblocked;

3. Cooling water temperature too high

(1) The cooling water pipe of the inductor is blocked by foreign matters, resulting in reduced water flow and excessive cooling water temperature. At this time, it is necessary to cut off the power first, and then purge the water pipe with compressed air to remove foreign matters. The shutdown time of the water pump should not exceed 8min.

(2) The coil cooling water channel has scale, resulting in reduced water flow and excessive cooling water temperature. According to the quality of cooling water, the obvious scale on the coil water channel must be pickled in advance every one to two years.

(3) The sensor water pipe leaks suddenly. This leakage is mostly caused by the insulation breakdown between the inductor and the water-cooled yoke or the surrounding fixed support. When this accident is found, the power shall be cut off immediately, the insulation treatment at the breakdown shall be strengthened, and the surface of the water leakage shall be sealed with epoxy resin or other insulating glue to reduce the voltage. The furnace can be repaired after the molten iron is melted and poured. If the coil water channel is broken down in a large area and the gap cannot be temporarily sealed with epoxy resin, the furnace must be shut down, the molten iron must be poured out and repaired.