Advantages and Disadvantages of Induction Furnace

In the past 30 years, the application of induction furnaces in the steel casting industry has developed rapidly, of course due to its many advantages, but on the other hand, it also has many disadvantages. When selecting it as smelting equipment, it is necessary to conduct comprehensive analysis and research, strives to maximize its strengths and avoid its weaknesses, and must not join in the excitement and catch up with the trend. After selecting the equipment, it is necessary to have a comprehensive understanding of its characteristics and strive to continuously improve the quality of casting products on the basis of energy conservation and emission reduction.

The following is a brief analysis of the advantages and disadvantages of induction furnace melting of cast steel for reference.

1. Advantages of Induction Furnace

In terms of casting steel smelting, compared to electric arc furnace smelting, using a crucible-type induction furnace has many advantages, such as:

(1) Although induction furnaces are also high-power power consuming devices, their interference to the power grid is much smaller than that of electric arc furnaces;

(2) In terms of the impact on the environment, the smelting process has low noise and relatively low emissions of smoke, gas, dust, and waste residue;

(3) In terms of resource utilization, charging materials (including various alloy elements added) have a low burning loss and high yield. The amount of slag-making material is much smaller, and electrodes are not used;

(4) In terms of metallurgical functions, due to the electromagnetic stirring effect, the composition of the molten steel is relatively uniform, the temperature of the molten steel is also relatively uniform, and temperature control is relatively convenient. There is no carbon increase caused by the electrode. Because there is no high-temperature effect of electric arc, there is no problem that nitrogen is easily absorbed by molten steel due to its dissociation at high temperatures;

(5) The investment in equipment is relatively small, and the area occupied is relatively small;

(6) It is easier to automate jobs.

2. Disadvantages of Induction Furnace

Due to the above advantages, the application of crucible induction furnaces in steel casting has developed rapidly since the 1980s. However, crucible induction furnaces also have their unique shortcomings that restrict their development‘ "How to avoid weaknesses?" It is a subject that process technicians must face. To avoid shortcomings, one should have a full understanding of these shortcomings.

(1) Problems with Refractory Furnace Lining

Refractory furnace lining is an important component of a crucible induction furnace, ensuring its normal operation is crucial to the reliability, economic efficiency, safety, and even the metallurgical quality of cast steel products.

The energy used for melting in a crucible-type induction furnace is transmitted to the metal in the furnace through the refractory lining by the magnetic flux generated by the induction coil. As the thickness of the refractory furnace lining increases, the magnetic flux leakage increases, and the output power, power factor, and electrical efficiency of the inductor decrease. In order to minimize the compensation of reactive power by balancing capacitors and improve electrical efficiency, it is necessary to minimize the thickness of refractory furnace lining as much as possible. Therefore, in various furnaces for steelmaking, the thickness of the refractory lining of induction furnaces is much smaller than that of any furnace type, but the operating conditions are much harsher than those of other furnace types.

1) The inner surface of the furnace lining is in contact with molten steel at a high temperature, while the outer surface is connected to a water-cooled induction coil. However, the temperature gradient in the thin furnace lining is very large.

2) The continuous stirring of the molten steel in the furnace due to electromagnetic effects enhances the flushing of the molten steel against the furnace lining, as well as the erosion of the suspended oxides on the furnace lining. Moreover, the stirring effect also increases the possibility of the molten steel absorbing gases.

3) If the furnace lining is not sufficiently compacted or sintered well, molten steel may seep into the cracks of the furnace lining during the melting process. Due to the induction heating effect, the seeped molten steel will not solidify in the cracks, but will continue to deepen in the cracks until it contacts the coil, causing a short circuit, or even causing a major safety accident.

Therefore, strict requirements must be imposed on the performance, particle size distribution, lining construction, and sintering of furnace lining refractory materials, without any carelessness.

(2) Problems with Metallurgical Functions

"The metallurgical function of crucible induction furnace smelting cast steel is much worse than that of electric arc furnace smelting. Therefore, in the early stage, it can only be used for smelting steel with general metallurgical quality requirements and manufacturing small steel castings.". After the 1980s, with the continuous improvement of equipment and refractory materials, mild oxidation boiling can be implemented during the smelting process to enhance its metallurgical function. The scope of application has gradually expanded to high-quality low-alloy steel, high-alloy steel, and even ultra-low carbon stainless steel and various high-temperature alloys. However, the low metallurgical function of induction furnace smelting cannot be ignored.

1) Induction furnace melting, in which the slag is melted by the heat transmitted by the molten steel. The temperature of the slag is lower than the temperature of the molten steel, and it cannot be subjected to oxidation refining and diffusion deoxidation through various metallurgical reactions between the molten steel and the slag, as in electric arc furnace melting.

2) Electric arc furnace melting, the molten pool is shallow basin type, and the diameter of the slag line is about 4-5 times the depth of the molten pool; "The crucible type induction furnace is used for melting. The molten pool is cylindrical in shape, and the diameter of the molten pool is smaller than its depth. The ratio of the two is about 0.6 to 0.75.". It can be seen that the interface between molten steel and slag during induction furnace melting is much smaller than that during electric arc furnace melting, making it impossible to utilize the metallurgical reaction between molten steel and slag for smelting operations.

Therefore, when steel casting enterprises adopt induction furnace melting, the requirements for furnace charge must be very strict: all kinds of raw materials must be accurately informed of their chemical composition; The amount of charging materials shall be determined by calculation; Scrap steel and furnace feed must be dry, free of sediment and oil contamination; The maximum size of the charging material cannot be greater than 1/2 of the size of the inner chamber of the crucible.

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