Temperature Range and Control Technology of Electric Arc Furnaces

Temperature Range and Control Technology of Electric Arc Furnaces

Electric arc furnaces (EAFs) are key equipment in modern metallurgical industry, and their internal temperature level and control accuracy directly determine smelting efficiency, energy consumption, and final product quality. By generating a high-temperature electric arc between electrodes and metallic charge materials, electrical energy is efficiently converted into thermal energy, enabling rapid melting of the furnace charge. Depending on the type of metal being processed and specific technological requirements, the operating temperature of an electric arc furnace typically ranges from 1600 °C to 3000 °C, with the exact temperature influenced by raw material composition, smelting stage, and process parameters.

During the smelting of ordinary carbon steel, the furnace temperature is generally maintained within 1600–1750 °C. This temperature range ensures complete melting of the iron–carbon alloy and promotes the transfer of harmful impurities such as sulfur and phosphorus into the slag phase, thereby improving molten steel cleanliness. For stainless steel and other high-alloy steels, due to the higher melting points and complex dissolution behavior of alloying elements, the furnace temperature is usually increased to 1750–1900 °C to ensure sufficient dissolution and homogeneous distribution of chromium, nickel, and other alloying elements. For certain special alloys or superalloys, the smelting temperature may exceed 2000 °C, placing more stringent requirements on the thermal resistance and corrosion resistance of refractory linings.

The core of electric arc furnace temperature control lies in the electrode regulation system. Modern EAFs widely adopt automatic control systems that continuously monitor furnace temperature, current, and voltage, dynamically adjusting electrode positions to regulate arc length and energy input. Proper matching of current and voltage is a key factor in achieving stable temperature control, with typical electrical energy consumption maintained at 400–600 kWh per ton of steel. In combination with infrared temperature measurement devices and computer-based control systems, temperature control accuracy within ±10 °C can be achieved.

Abnormal furnace temperatures can cause serious problems in both production and equipment safety. When the temperature falls below 1550 °C, molten bath fluidity decreases significantly, slag–metal reactions become less efficient, and impurities cannot effectively float and separate, leading to composition inhomogeneity and excessive inclusions in the steel. Conversely, when the temperature exceeds the refractory material’s tolerance limit, magnesia–carbon bricks and other refractories experience accelerated erosion and spalling, which may shorten furnace service life or even result in furnace burn-through accidents. In one steel plant, a failure of the temperature measurement system caused the furnace temperature to rise rapidly to 2100 °C, leading to complete destruction of the furnace bottom refractory lining and economic losses amounting to several million yuan.

In the field of non-ferrous metal smelting, temperature applications of electric arc furnaces show significant differences. Copper and copper alloys are generally smelted at 1100–1250 °C, while aluminum and aluminum alloys, due to their lower melting points, are typically processed at 700–800 °C. These differences arise from the distinct physical and chemical properties of each metal. For example, aluminum electrolysis processes commonly employ low-voltage, high-current power supply modes, and precise temperature control is essential to prevent excessive oxidation of molten aluminum.

The distribution of temperature gradients within the furnace has a direct impact on smelting performance. The region directly affected by the electric arc forms a localized ultra-high-temperature zone, where instantaneous temperatures can exceed 3500 °C, while the temperature at the bottom of the molten bath remains relatively lower. This temperature difference induces natural convection within the molten metal, accelerating compositional homogenization. Operators can optimize high-temperature zone distribution by adjusting electrode positions and configurations. For instance, a special steel enterprise reduced the molten bath temperature gradient from approximately 200 °C to less than 80 °C by adopting a three-electrode eccentric arrangement, significantly improving molten steel quality stability.

With increasingly stringent environmental and energy-efficiency requirements, electric arc furnace temperature control technologies continue to advance. Flue gas waste heat recovery systems can capture thermal energy from exhaust gases at temperatures up to 1200 °C and convert it into steam for power generation. After installing a waste heat boiler system, one enterprise reduced comprehensive energy consumption per ton of steel by 15%. Meanwhile, advanced foamy slag technology reduces radiant heat losses from the electric arc by optimizing slag-forming practices, improving thermal efficiency by approximately 30% and achieving simultaneous benefits in energy savings and temperature stability.

Safety operation standards impose explicit requirements on EAF temperature management. Operators must wear high-temperature protective equipment during furnace observation, and forced cooling systems must be activated immediately when furnace wall temperatures exceed 400 °C. In one foundry, unauthorized shutdown of the furnace cooling water system caused the furnace shell temperature to rise to 600 °C, resulting in severe deformation and significant safety hazards. Currently, routine infrared thermal imaging inspections have become an important preventive maintenance measure, enabling early detection of weak refractory zones and targeted repairs.

In special smelting processes, furnace temperature profiles are subject to more stringent control requirements. For example, vacuum arc remelting (VAR) is conducted under a vacuum level of approximately 10⁻³ Pa, with smelting temperatures typically 200–300 °C higher than those in conventional processes. This environment effectively removes dissolved gases and inclusions from the metal. An aerospace materials enterprise used this process to control oxygen content in titanium alloys below 0.08%, significantly enhancing fatigue strength and service reliability.

The recording and analysis of temperature data form the basis for continuous process optimization. Modern electric arc furnaces are commonly equipped with “black-box” data acquisition systems that comprehensively record temperature variation curves throughout the entire smelting process. By analyzing data from 300 heats, a research institute developed a neural-network-based temperature prediction model that shortened smelting cycles by 8% and reduced energy consumption per ton of steel by 12%. This data-driven intelligent temperature control approach is gradually becoming an important development trend in electric arc furnace technology.