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The development of cast iron casting has amply demonstrated the critical importance of selecting the right melting equipment. Although cupola furnaces, as the primary equipment for cast iron melting, continue to be widely used today, they still account for approximately 70% of cast iron parts melted worldwide. Cupola furnace technology has kept pace with advancements in mechanical manufacturing and has made significant progress toward energy conservation, reduced consumption, high quality, efficiency, safety, and environmental protection. In industrially developed countries, a cast iron melting system centered on large-capacity, long-lifespan, and externally heated air cupola furnaces has already taken shape. However, in China, it remains common practice to use cupola furnaces with small capacities, short lifespans, and ambient-air blowing. In recent years, China’s cupola furnace melting industry has begun to shift toward larger capacities, longer furnace lifespans, and externally heated air systems. Long-lifespan, externally heated air cupola furnaces—developed with independent intellectual property rights and tailored to China’s specific production conditions—are now meeting the needs of the country’s growing casting industry. The recommendation by three Chinese government departments regarding externally heated air cupola furnaces clearly points out the direction for the future development of cupola furnaces in China. Currently, China’s cupola furnace melting industry is moving forward at an accelerated pace toward the goals of energy conservation, reduced consumption, high quality, efficiency, safety, and environmental protection. Induction furnaces, as melting equipment, have been used for decades in both pure cast iron melting and duplex melting processes. China has accumulated extensive experience in manufacturing and applying power-frequency and medium-frequency induction furnaces, achieving remarkable progress in many areas—including induction coil design, frequency conversion technology, integrated control systems, and circulating cooling technologies. An increasing number of manufacturers are adopting induction furnaces for both melting and holding operations.
The melting mechanisms of cupola furnaces and induction furnaces differ significantly, leading to substantial differences in their performance and, consequently, their adaptability to various production processes. The type of cast iron parts—such as grade, production volume, mechanical processing requirements—as well as the production method, the types and states of charge materials, and the skill level of melting operations and production management all impose distinct demands on the performance of melting equipment. Only when the performance characteristics of the melting equipment are perfectly aligned with the specific production conditions can we achieve a high-quality, efficient, energy-saving, consumption-reducing, safe, and environmentally friendly production process, thereby attaining superior technical and economic indicators.
In iron casting, should a cupola furnace or an induction furnace be used?
How do you choose between a cupola furnace and an induction furnace? Only by understanding the cupola furnace and... Induction furnace Only after understanding the melting characteristics can the right decision be made.
1. Melting Characteristics
1.1 Metallurgical Performance and Molten Iron Quality: It is widely acknowledged that the metallurgical performance of a cupola furnace is significantly superior to that of an induction furnace. Inside the cupola furnace, temperatures exceeding 1700°C, along with coke, slag, and...
The metallurgical environment created by the furnace gas plays a positive role in influencing the compositional changes of both the iron charge and the molten iron. Through process control, it is possible to increase carbon and silicon content, significantly reduce the burn-off of alloying elements, and lower the sulfur gain rate. In particular, large-capacity, externally heated, long-life cupola furnaces demonstrate an even stronger ability to stabilize and improve the quality of the molten iron. Inside the cupola furnace, although the molten iron remains superheated for only a few minutes, its droplet and fine-stream-like nature provides an ample surface area for contact with coke, slag, and furnace gas, enabling efficient heat absorption, temperature rise, and mass transfer. The superheating temperature of the molten iron can reach up to 1600℃.
Above: The sulfur content of the molten iron tapped from the furnace can be controlled below 0.06%. Both the molten iron and the slag exhibit excellent fluidity, which facilitates the transfer of metal oxides from the molten iron into the slag. The molten iron spends a short time overheating in the furnace; it contains approximately 0.005% oxygen and about 0.06% sulfur. The high-melting-point compounds formed by these elements can serve as nucleation substrates. After tapping, the molten iron contains a large number of self-generated crystal nuclei. The grain-refining effect achieved through inoculation treatment is particularly pronounced for high-grade gray cast irons.
The induction furnace operates at a maximum temperature of around 1600℃, which is lower than that of the cupola furnace. When using carbon-increasing agents, it is difficult for these agents to dissolve and disperse uniformly, and during crystallization, they tend to form flaky or blocky graphite. The molten iron remains superheated for as long as 1 hour, and with electromagnetic stirring in place, the number of foreign crystal nuclei available for eutectic crystallization is significantly reduced due to their dissolution and reaction. The sulfur content is approximately 0.03%, and the oxygen content is about 0.002%. Because there are fewer nucleation sites, the degree of supercooling in the iron increases, resulting in a superheat level that is 40℃ to 50℃ higher than in the cupola furnace under the same carbon equivalent. Consequently, thin sections of castings are prone to white cast iron formation and exhibit poor machinability. Moreover, the castings have a strong tendency to shrink, making them susceptible to cracking; thick-walled sections are particularly vulnerable to defects such as shrinkage porosity, shrinkage cavities, and inclusions. Conventional inoculation methods have limited effectiveness, so it is necessary to use high-dose, highly efficient inoculants and apply multiple inoculation treatments.
1.2 Process Performance
1D Production Capacity and Adaptability to Output Requirements: Currently, cupola furnaces with melting rates ranging from 1 ton/hour to 100 tons/hour are in widespread use. If production demands dictate, melting rates can even exceed 1 ton/hour or fall below 100 tons/hour. For any given specification of cupola furnace, its melting rate can be adjusted within the corresponding range without compromising normal smelting performance, with adjustment margins typically spanning 10% to 20% increase or decrease. Consequently, a single cupola furnace can easily meet the output requirements of virtually any production scale. Since the overall efficiency of a cupola furnace improves as its melting rate increases, large-capacity, long-lifespan, and externally heated cupola furnaces offer even greater overall efficiency. Therefore, cupola furnaces are particularly well-suited for large-scale, high-volume production. Induction furnaces used for smelting can currently be manufactured with individual capacities reaching nearly 100 tons, fully capable of meeting the needs of large-scale production. However, expanding the installed electrical capacity often presents a significant hurdle that many enterprises find difficult to overcome. As a result, induction furnaces are more suitable for medium- and small-scale production.
2) Product Adaptability: Cupola furnaces can melt cast irons—including gray cast iron, ductile iron, compacted graphite iron, white cast iron, and certain alloyed cast irons and ferroalloys. They can also be used to melt certain ores (such as stone materials) for the production of rock wool, cast stone, and similar products. The molten iron temperature from a cupola furnace can be precisely controlled at around 1550℃, making it suitable for casting parts ranging in weight from a few grams to tens of tons. Induction furnaces, on the other hand, can melt a wide variety of commonly used grades of steel and non-ferrous metals. Specifically when it comes to producing cast iron parts, induction furnaces exhibit superior product adaptability compared to cupola furnaces. Induction furnaces can melt various types of high-alloy cast irons—such as high-chromium cast iron—that cupola furnaces are unable to handle.
3) Adaptability to Production Methods: The cupola furnace operates on a continuous melting process, with molten iron continuously flowing out of the furnace at a steady rate. In contrast, the induction furnace employs an intermittent melting process, delivering molten iron—equal in volume to the furnace’s capacity—at regular intervals. Thus, for production methods involving parallel operations, the cupola furnace is more suitable; whereas for production methods based on staged operations, the induction furnace is better suited. Although using a combination of multiple induction furnaces and controlling the sequence of melting and iron tapping can also enable parallel operations, such multi-furnace configurations will lead to increased energy consumption, additional auxiliary equipment requirements, larger floor space needs, and greater burdens on production management.
④ Adaptability to Charge Materials: Due to its inferior metallurgical capabilities, the electric furnace exhibits far less adaptability to charge materials compared to the cupola furnace. It is essential to use clean, rust-free charge materials, and the composition of the charge must meet the required chemical specifications for the molten iron; it is not possible to rely on the melting process itself to achieve the desired composition of the molten iron. When melting high-carbon cast iron using low-carbon charge materials, both the properties of the carbon-increasing agent and the amount of carbon added are subject to strict limitations. Consequently, the proportion of scrap steel in the charge material is also restricted. In contrast, the cupola furnace demonstrates remarkable adaptability to a wide variety of charge materials and can entirely use scrap steel as its charge for melting high-carbon cast iron. In particular, automotive scrap steel—being lightweight and thin—is expected to gradually become the primary metallic charge material for casting in the future. However, this type of scrap steel is unsuitable for electric furnaces, whereas the cupola furnace can readily handle it. The use of automotive scrap steel is of great significance for promoting a circular economy and reducing the cost of charge materials for casting. Even low-quality, impure charge materials can be used in cupola furnaces.
In induction furnace charge composition, the proportion of pig iron should not be too high. Under the temperature conditions of an induction furnace, the coarse graphite flakes present in pig iron are difficult to fully dissolve into the molten iron, instead forming fine graphite grains. During solidification of the molten iron, these fine graphite grains serve as nucleation sites, giving rise to primary graphite. Such graphite appears in blocky or flaky forms, which can adversely affect the mechanical properties of cast iron. Typically, the amount of pig iron used in induction furnaces is around 10%; if it exceeds 20%, the mechanical properties of the cast iron will become difficult to guarantee. When producing ductile iron and high-grade gray cast iron, to avoid the occurrence of inherited defects, the proportion of return scrap should also not be too high. Due to differences in adaptability to charge materials, the cost of charge materials for induction furnaces tends to be higher than that for cupola furnaces when producing the same products.
1.3 Impact on the Environment
1D—Primary sources of pollution. Both cupola furnaces and induction furnaces emit dust and harmful gases; however, the dust from cupola furnaces contains a significantly higher proportion of coarse particles, primarily coke particles, whereas the flue dust from induction furnaces consists of fine particles. Due to the combustion of coke in cupola furnaces, the emissions of SO2 and CO2 in the flue gas are greater, and the volume of flue gas is also larger. Cupola furnaces do not produce electromagnetic pollution, whereas induction furnaces generate substantial electromagnetic interference. Induction furnaces also pose a heavier thermal radiation hazard than cupola furnaces. The flue dust from cupola furnaces is mainly discharged outside the plant premises, while the flue dust from induction furnaces is confined within the plant building. From an environmental protection perspective, dust removal systems can effectively address the pollution issues associated with cupola furnaces. Currently, emerging technologies such as reverse-flue dust cleaning and slag granulation offer a viable pathway for the harmless and resource-based treatment of pollutants generated by cupola furnaces. However, at present, induction furnaces do not yet possess similar advantages in pollution control.
2) Energy requirements. The cupola furnace uses coke as its fuel, with a consumption rate of approximately 100 kg of coke (with a fixed carbon mass fraction of 85%) per ton of molten iron. When completely burned, coke releases a calorific value of 2,896 W. In contrast, the induction furnace uses electricity as its energy source, consuming about 2,160 W (600 kWh) per ton of molten iron. If we compare this to coal consumption, since 1 kg of coke is equivalent to 1.25 kg of coal, each ton of molten iron corresponds to a coal consumption of 125 kg. Similarly, since 1 kWh of electricity requires 0.36 kg of coal, each ton of molten iron corresponds to a coal consumption of 216 kg. Currently, China’s power generation structure is dominated by thermal power, meaning that induction furnaces consume more non-renewable resources—by over 70%—than cupola furnaces. Consequently, the resulting pollutant emissions from induction furnaces also exceed those from cupola furnaces. Moreover, while volatile matter from coking coal can be utilized as a chemical feedstock, the volatile matter in coal used for power generation, which could serve as a chemical feedstock, is instead burned off. As China’s power generation structure evolves, the current situation will change, and the energy structure of cupola furnaces will likewise undergo transformation. For example, cupola furnaces equipped with plasma-assisted air injection can reduce coke consumption by more than 60%. Correspondingly, emissions of pollutants and heat loss will also be significantly reduced. There are already successful examples of cupola furnaces that use non-coke fuels such as natural gas, coal gas, electricity, or fuel oil to provide heat, and research aimed at improving performance and enhancing practical applicability is ongoing. Provided that melting performance remains unchanged, optimizing the energy structure of cupola furnaces will further highlight their inherent advantages.
From the perspective of energy utilization in production, the thermal efficiency of a cupola furnace is about 40%.
Approximately 60% of the energy is utilized in induction furnaces, while cupola furnaces perform slightly worse, falling below induction furnaces. However, when it comes to resource-based energy consumption per ton of molten iron, cupola furnaces actually consume significantly less than induction furnaces. The heat losses in a cupola furnace include physical heat carried away by flue gases, latent chemical heat stored in CO, heat dissipated from the furnace body, and residual heat from slag and furnace lining materials. In contrast, the heat losses in an induction furnace consist mainly of heat radiated from the furnace body and the furnace opening, as well as resistive heat from the induction coil carried away by cooling water. Regarding the recovery of these lost heats, cupola furnaces offer greater feasibility and higher benefits compared to induction furnaces. For instance, technologies such as external hot air supply, extended furnace life, and waste-heat boilers for flue gases—currently successfully implemented in China—have already led to substantial reductions in heat losses. As the number of large-capacity cupola furnaces continues to rise, China’s energy consumption per ton of molten iron in cast iron smelting will decline significantly, making it entirely achievable to catch up with and surpass the world’s advanced standards.
1.4 Impact of Furnace Structure and Associated Equipment on Melting Performance Different structures and associated equipment of cupola furnaces result in significant differences in performance. During production, the appropriate cupola furnace structure and supporting equipment can be selected based on factors such as the grade of castings, composition of charge materials, production volume, and manufacturing process. Cupola furnaces exhibit strong adaptability in terms of both structure and associated equipment; ranging from conventional cupolas with ambient-air supply, standard lining, single-shift manual operation, to advanced, externally heated, lining-free cupolas with extended service life and fully automated operation—there are numerous diverse cupola systems available to choose from. Induction furnaces, classified as crucible furnaces, primarily serve the functions of melting and superheating. Changes in their structural design have relatively little impact on these core functions. Therefore, during production, one should select production conditions solely based on the fundamental functions of the induction furnace, rather than choosing the furnace itself according to specific production requirements.
In double-furnace melting, the quality of the molten iron is primarily determined in the cupola furnace rather than in the induction furnace. Molten iron tapped at low temperatures is difficult to refine into high-quality iron in the induction furnace. Therefore, it is crucial not to lower the quality requirements for the molten iron produced in the cupola furnace—especially ensuring that the molten iron entering the induction furnace maintains a sufficiently high temperature, such as above 1400°C. Otherwise, castings are prone to defects. Castings made from pig iron melted in electric furnaces are susceptible to defects such as shrinkage porosity, shrinkage cavities, and inclusions. Electric-furnace castings also exhibit significant contraction stresses, making them more likely to develop crack-type defects. In this regard, the cupola furnace has an advantage, while the electric furnace is at a disadvantage.
2 Equipment Investment
The composition of cupola melting systems varies considerably. Taking a melting capacity of 10 tons per hour as an example, a single-shift, ambient-air-fed cupola furnace equipped with a charging machine costs approximately 300,000 yuan, whereas a long-life, externally heated air-fired furnace without lining sells for about 3.5 million yuan. The prices of cupola furnaces also differ depending on their melting performance and production conditions, providing enterprises with more diverse and suitable options for making rational choices.
The metallurgical capabilities of induction furnaces are relatively limited; therefore, the melting performance of induction furnaces with different designs does not vary significantly. The primary factors behind price differences lie in brand and quality. Moreover, the requirements for production conditions are fairly consistent across different models. Consequently, you cannot select an induction furnace based on your specific production conditions—instead, you must adapt your production conditions to meet the furnace’s requirements. Similarly, you cannot choose an induction furnace solely based on the characteristics of your products or charge materials. For a 10-ton medium-frequency induction furnace used for melting, if you plan to melt one batch per hour, the required installed electrical capacity would be 7,000 kV/A. The price of domestically produced equipment is approximately 2.5 million yuan, excluding the costs associated with increasing power capacity and the possibility of such upgrades.
The 10-ton medium-frequency holding furnace used for duplex melting: At a holding temperature of 1450℃, the medium-frequency power supply requires 800 kW, and the equipment quotation is RMB 788,000. When heating up by 100℃ in 15 minutes, the medium-frequency power supply needs 2000 kW, and the equipment quotation is RMB 1,037,000. Table 1 shows a comparison of investment costs for melting workshop equipment in two recently constructed casting projects in China. As shown in Table 1, in terms of one-time equipment costs for the melting workshop, duplex melting is 20% to 40% lower than single-induction-furnace melting; single cupola-furnace melting has the lowest equipment investment. However, the latter two methods require larger floor space and higher civil engineering costs.

3 Selection of Melting Equipment
The proper selection of melting equipment has a significant impact on the overall efficiency of production. Although China is a major producer of castings, its iron-melting equipment remains relatively backward. The excessive number of small-capacity cupola furnaces has led to a situation characterized by high energy consumption, high material consumption, severe pollution, low product quality, and low profitability. Particularly in recent years, the inappropriate rise in the prices of coke and furnace charge materials, coupled with increasingly stringent environmental regulations, has posed considerable challenges to the survival of small- and medium-sized enterprises that already operate with low profitability. It is undoubtedly correct to embark on a path of reform—including shifting away from traditional cupola-furnace iron-melting methods—to enhance efficiency and secure survival and development. The key question, however, lies in how to choose the appropriate iron-melting method. Table 2 provides a comparative analysis of the characteristics of cupola furnaces and induction furnaces from a production-technology perspective, which can serve as a useful reference. Production technology and overall efficiency are closely interconnected; thus, the fundamental basis for equipment selection should be the comprehensive efficiency of the equipment in actual production. When making specific choices, one should carefully analyze and calculate from all aspects that influence overall efficiency, taking into account the actual production conditions and anticipated development trends, in order to arrive at the optimal solution.