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Hazards to be noted when using medium-frequency induction furnaces (which may cause injury or death)

I. Furnace Leakage

Also known as a “furnace burn-through” failure, the phenomenon is as follows: During normal operation, an electric furnace suddenly experiences an abnormal trip, and the power supply repeatedly fails to restart. At this point, a furnace burn-through may have occurred. The cause is that molten iron has pierced through the furnace lining and reached the conductive coil, which contains circulating cooling water, resulting in a ground fault and trip of the coil. In such a situation, operators should immediately stop attempting to restart the furnace, disconnect the power supply, and call maintenance personnel to identify the root cause. In most cases of furnace burn-through, when the sharp, needle-like edges of the molten iron first come into contact with the furnace coil, the protective system swiftly activates and automatically cuts off the power supply to the coil. However, if the furnace leak is extremely severe and the alarm does not react in time, the molten iron can rapidly melt through large areas of the coil, causing massive amounts of water to vaporize instantly and potentially leading to an explosion. In the event of a serious furnace burn-through and explosion, operators must promptly evacuate the danger zone and take all necessary precautions to ensure their own safety. In daily production, it is crucial to pay close attention to the number of furnace cycles used and monitor the condition of the furnace lining for signs of erosion.

II. Metal “Bridging”

Also known as “hanging material,” this is an insulating body with air gaps between the molten metal and the bridging material. If operators unknowingly continue to increase the power and raise the temperature, the bottom of the furnace lining will quickly overheat under high power, exceeding— Lining of the furnace The material’s maximum temperature can cause excessive turbulence in the molten metal at the furnace bottom, leading to rapid corrosion of the furnace lining and ultimately resulting in a furnace-bottom leakage accident. If the furnace bottom is pierced, it could ignite a fire at the furnace base, damaging the hydraulic system, the water-cooling system, and the power supply. Moreover, if the electric furnace coil is melted through, water coming into contact with the molten metal will cause the water volume to expand instantaneously by a factor of 1,600, triggering an explosion that could injure or kill personnel and severely damage equipment.

If bridging occurs—meaning the bridging material completely seals off the upper part of the molten pool—the safest course of action is to shut down the furnace and allow the molten metal to solidify and cool. If the bridging material does not completely seal the molten pool and no significant pressure has built up inside the furnace, tilt the furnace body at a 45-degree angle. First, use low-power melting to create a small opening, allowing the molten iron that has been covered at the bottom to slowly overflow and come into contact with the bridging material, thereby gradually melting the bridging material. Alternatively, you can pour additional molten iron into the furnace to help accelerate the melting of the bridging material. Under no circumstances should you use an oxygen torch to blow holes at close range—such practices are extremely dangerous. Once the hole is opened, the high pressure inside the furnace could pose a serious threat to life safety.

III. Furnace Charge Safety

(1) It is essential to avoid accidentally introducing partially sealed containers (such as soft-drink or beer cans) into the furnace as furnace charge. Such containers can undergo explosive vaporization in an instant, causing molten metal to spatter violently. Additionally, care must be taken to prevent low-melting-point metals—such as aluminum or zinc—as well as their oxide slags—from being added to a high-temperature molten iron bath. Otherwise, if these low-melting-point materials sink to the bottom of the bath before melting and then melt there, they will rapidly vaporize and expand, leading to boiling or even explosion.

(2) If the raw materials are not clean, slag must be removed promptly. Failure to remove it in a timely manner can lead, on the one hand, to slag accumulating against the furnace lining, causing overheating and rapidly shortening the lining’s service life, as well as increasing the likelihood of metal bursts or boiling at the molten iron surface. On the other hand, accumulated slag on the liquid surface means that low-melting-point waste slag, once dropped into the furnace bottom along with the charge material by the charging car, will quickly vaporize, raising the pressure and causing the slag to overflow from the furnace surface. Therefore, during the charging process, operators must frequently monitor the condition inside the furnace and promptly address any abnormalities to prevent accidents.

(3) Improper charging can also lead to cracks in the furnace lining and even cause molten iron to penetrate through the furnace. For example, when large pieces of iron charge fall onto the furnace lining surface due to vibrations from the charging car, they can strike the lining with great force. Similarly, during the lifting and handling of large scrap metal pieces, the swinging of steel cables may impact the furnace mouth, most likely causing molten iron to penetrate through the furnace at the weak point near the lower end of the furnace mouth.

Four. Capacitor Explosion hazard

If a capacitor leaks electrolyte or its connections remain loose for an extended period, arcing and gas generation may occur. This gas accumulates and expands within the capacitor, causing the casing to deform and potentially leading to a severe capacitor explosion.

A pressure-sensing switch is installed on the capacitor to prevent deformation of the capacitor casing and excessive pressure buildup. If the main switch trips unexpectedly, you must first check whether the pressure switches on each capacitor panel and the door-mounted switches on each switchgear cabinet are functioning normally. (Kangda electric furnaces are equipped with such switches; however, the 8-ton electric furnace does not have capacitor-switch detection—instead, its condition is assessed solely by visually inspecting for any deformation of the casing or leakage of liquid.) V. Cold start-up of accident furnaces containing large amounts of solidified molten iron.

Do not increase the power before the solidified molten iron has begun to melt, because at this stage, rapid heating could cause the metal to expand far more than the furnace lining can accommodate, leading to cracks in the lining and potentially serious accidents such as furnace breakthrough. Once the lower portion of the solidified molten iron has gradually started melting, you may increase the power to around the holding-power level—maintaining this setting until the cooled metal shell at the top is completely melted through by the liquid metal below. At that point, you can slowly ramp up the power to facilitate further melting.

Remember: The melting time must be exactly as long as the time it takes for the molten iron from the accident to solidify.

6. Grounding Leakage Probe—A Key to Ensuring the Safe Operation of Induction Furnaces

(1) The grounding leakage detection probe at the bottom of the electric furnace is made of 304 stainless steel wire. The material must be accurate; otherwise, if it becomes magnetic, it will generate heat. This probe provides grounding detection protection for both the electric furnace operator and the coil. The welded joints of the stainless steel wire must be extremely secure, and the grounding connection cable at the bottom of the furnace must be reliably connected. Otherwise, all protective measures will be rendered ineffective.

(2) Working Principle: The stainless steel probe operates in conjunction with the ground detection module. If the molten metal in the melt pool approaches the energized water-cooled coil, the resistivity decreases. As a result, the stainless steel probe can divert the current from the conductive coil into the earth. Simultaneously, once the ground detection module detects a signal exceeding the rated leakage current, it immediately shuts down the inverter power supply. This further prevents operators from suffering severe—甚至是 fatal—electric shocks in an instant and also helps to prevent the furnace leakage fault from escalating further.

Remember: The inverter power supply must be turned off when removing slag, taking samples, and performing measurements on the electric furnace.

Yingda Company provides a simple portable grounding test device that helps operators determine whether the grounded stainless steel probe is functioning properly and whether the stainless steel wire has broken or been covered by furnace lining material, thereby interrupting its connection with the molten iron.

7. Any alarm faults that occur must be promptly recorded and resolved.

For example, when a temperature sensor triggers an action that causes the inverter power supply to trip, it’s essential to identify which particular water circuit has experienced excessively high temperature. It’s crucial not to simply and blindly manually reset all temperature sensors. Although this might allow the electric furnace to continue operating temporarily, the underlying fault will persist, posing a potential safety hazard. If the overheating is caused by a blockage in the water-cooling hose, repeatedly resetting the sensor could eventually lead to sensor failure. Once the sensor fails, the temperature will keep rising unchecked, potentially causing the hose to burst and significantly expanding the scope of the malfunction. Therefore, during shift handovers, it’s imperative to meticulously document any previous fault symptoms and promptly notify the next shift to investigate the root cause of the issue and eliminate the隐患before it escalates into a more serious problem.