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　　 Medium-frequency electric furnace It consists of a spiral induction coil made of a single-layer rectangular copper tube, and in the water-cooled spiral induction coil, a refractory-lined crucible with a knot is used to hold the metal being heated. Medium-frequency furnaces typically comprise four main components: the power supply, the furnace body (primarily consisting of the induction coil and a crucible made of refractory materials housed within the induction coil), a capacitor bank (used to improve the power factor), and a control and operating system.

　　1. The furnace body of the medium-frequency induction furnace: (1) Induction coil of the induction furnace: The induction coil is the heart of the induction furnace. Electromagnetic energy is converted into thermal energy through the induction coil, melting the metal charge inside the crucible. The rectangular copper tubes are wound into a multi-turn spiral coil, with the outer surface coated with high-strength insulating paint and wrapped with insulating tape. Refractory cement is also applied at the bends of the medium-frequency furnace. Water-cooling rings are installed above and below the induction coil. (2) Magnetic yoke of the induction furnace: The magnetic yoke is made of high-quality silicon steel sheets, arranged around the induction coil to serve as a supporting framework. It also helps confine the stray magnetic flux outside the induction coil, preventing heating of metal components. (3) Water-cooled cable of the induction furnace: Due to frequent tilting of the furnace, the flexible wires of the water-cooled cable are prone to breakage. Loosening of the connection bolts at the terminals can cause current imbalance. Generally, the service life of the water-cooled cable is determined based on the number of furnace tilts, typically three years, after which it needs to be replaced. If the bolts show discoloration, they should be promptly tightened and replaced. (4) The service life of the furnace lining and the reduction in the frequency of furnace rebuilding are important factors for cost reduction. (5) Furnace leakage alarm system for induction furnaces: To ensure safe production, prevent furnace leakage accidents from occurring or escalating, and help assess the condition of the furnace lining and extend the furnace’s lifespan, it is necessary to install a furnace leakage alarm system. Typically, a DC alarm device is used, with the stainless steel wire bottom electrode that comes into contact with the molten iron and the stainless steel plate side electrode separated from the furnace lining induction coil.

　　2. Medium-frequency electric furnace The hydraulic system consists of hydraulic actuators, a control console, tilting hydraulic cylinders, cover hydraulic cylinders, and more. Regularly inspect all seals in the hydraulic system for leaks; if any leaks are found, replace the sealing rings immediately. Moving parts should be lubricated periodically; otherwise, they may easily become damaged.

　　3. The water-cooling system of medium-frequency induction furnaces: To ensure effective cooling and maintain good water quality, it is essential to regularly check for scale buildup. If scale is detected, it should be removed immediately. Generally, the water quality requirements for cooling systems in power-frequency furnaces are as follows: hardness < 10 mg-eq/L, pH between 6 and 9, total dissolved solids with a temperature rise of less than 25°C, and a concentration not exceeding 250 mg/L. For cooling water used in medium-frequency power supplies, the water quality specifications are: hardness < 1.5 mg-eq/L, pH between 7 and 8, resistivity > 4000 Ω·cm, and suspended solids content ≤ 50 mg/L. The circulating water in the circulation tank should be periodically analyzed. When the hardness of the circulating water exceeds 2 mg-eq/L, the entire circulating water in the system should be drained and replaced with fresh water. Cooling towers should also be periodically drained and refilled with fresh softened water to prevent blockages in pipes and nozzles, which could impair cooling efficiency and shorten the service life of the furnace lining.

　　4. Medium-frequency electric furnace The main circuit of the electrical control system and the induction coil should be regularly cleaned to remove external dust. Conductive metal dust and iron particles splashed during steel tapping at the casting plant can accumulate on the outer surfaces of the main copper busbar or the induction coil, reducing their insulation capability and potentially causing discharge and ignition, which can easily lead to damage of electrical components. The connecting screws of the main circuit’s copper busbar also need to be checked and tightened periodically; otherwise, increased contact resistance will result in higher heat generation at the connection points, causing the insulating materials to carbonize and leading to leakage current.