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1. Power supply

(1) Induction furnace Power density configuration. A higher configuration leads to faster melting rates and better energy-saving performance. Whether the electric furnace can maintain a high power factor when supplying power to the furnace is also what distinguishes high-energy-consumption systems from low-energy-consumption ones.

 

(2) The efficiency of induction furnaces and the electrical efficiency of induction coils. (The overall efficiency of advanced foreign induction furnaces can reach as high as 75%, with induction coils achieving efficiencies of up to 85%; domestically, these figures are 73% and 80%, respectively.)

 

(3) Medium-frequency power supply Conversion efficiency varies, with overseas rates ranging from 97% to 98%, and domestic rates approaching 97%. This difference is mainly reflected in the efficiencies of reactance and capacitance.

 

(4) Layout of the electric furnace unit. Factors influencing the layout include the distance between the power source and the furnace body, the length of the copper busbars for power transmission, the length of the water-cooled cables, and the distances between the power supply voltage, the high-voltage transformer, and the point of power supply.

 

2. Molten substance

 

(1) The cleanliness of the furnace charge surface—(if there are 5% impurities, 5% of the electrical energy will be used to melt these impurities)—also affects the lifespan of the furnace lining.

 

(2) Whether the length of the charge material blocks is appropriate affects the electric efficiency and melting quality of the electric furnace. The typical size of the charge material blocks is 200 to 300 mm.

 

(3) Is there liquid metal in the furnace during melting? The residual liquid should account for 15% of the furnace’s capacity. If this proportion is too small, overheating of the molten iron in this portion will be exacerbated; if it’s too large, the effective utilization rate of the molten iron will decline, and unit energy consumption will increase. When the molten iron is drained, both the power factor and the melting rate will decrease.

 

3. Refractory Materials

 

(1) The appropriate thickness of the hot-surface material. Increasing the melting rate can reduce its thickness, but it will shorten the service life, increase furnace-building costs, and heighten safety risks.

 

(2) The correct bottom thickness also affects electrical efficiency and lining life. When the furnace bottom height exceeds the effective coil by 100 mm, the refractory material at the furnace bottom will be severely eroded due to the induction stirring force, thereby significantly reducing its service life.

 

(3) Proper use of backing materials (isolation materials are referred to as backing materials, such as asbestos cloth, etc.).

 

Hazards of using asbestos cloth as a backing material: Asbestos fibers can become lodged in the lungs, and inhalation may increase the risk of cancer. Typically, asbestos cloth has a high moisture content; after prolonged use, the moisture can easily migrate into the quartz sand, causing hardening and cracking. The primary functions of the backing material are to insulate, waterproof, and fireproof the induction coil. The cement layer serves as an isolating barrier, facilitating easy replacement of the furnace lining. On the back side of the hot surface made of quartz sand, we aim for a loose layer—this way, should the hot surface ever be pierced, the molten iron will come to a stop right here. The temperature of the induction coil’s cooling water is a crucial factor in forming this loose layer. If highly insulating asbestos cloth is used and water is added, even trace amounts of boric acid present in the quartz sand can cause it to harden. Mica paper is the best choice in such cases. When treated with high-grade rolled cement, the surface becomes smooth and requires no backing material at all. However, the cement must possess properties that make it easy to process, prevent cracking once dried, and ensure it does not react with acidic substances.

 

 

 

4. Energy saving in the operation process

 

Feeding time: The initial charge of solid furnace materials should reach approximately one-third of the furnace capacity; otherwise, it may affect power output, sparking (discharge), arc formation, and power consumption. It could also lead to cracking on the furnace lining surface, causing severe damage to the neutral refractory materials used in steel casting. When the first batch of materials has reached a molten state and begins to sink, the solid materials should be replenished immediately. This will help compress the softened solids and facilitate their rapid melting. Feeding should proceed normally without causing violent boiling of the liquid metal—such violent boiling indicates that the molten metal is overheated, eroding the furnace walls and consuming the refractory lining material. This method requires that the input power during the melting process be reduced as follows: 20% during the initial feeding stage → 50% when the materials begin to soften → 65% during the feeding process → and finally 100% once the desired temperature profile according to the process requirements has been achieved. At that point, the power supply should be switched off.

 

 

 

5. Improper operation leads to high energy consumption.

 

(1) Superheating of molten metal;

 

(2) Discharging liquid without stopping the furnace is not only unsafe but also incorrect from both an energy consumption and melting process perspective. Typically, induction furnaces are divided into upper and lower sections. When the molten metal level inside the furnace drops below half the height of the upper induction coil, due to changes in resistance, no induced current flows through the upper coil; instead, all the current concentrates on the lower coil, causing the lower molten metal to overheat, erode the furnace walls, and drastically shorten the service life of the furnace lining.

 

(3) High-temperature insulation. Prolonged exposure to high temperatures can alter the metallographic structure, change the phase states of carbon and silicon, and significantly increase the tendency for white cast iron formation in castings, thereby degrading machinability.