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Application of Graphite Electrode in Steelmaking Electric Arc Furnace

Graphite electrodes are mainly used as conductive materials in electric smelting furnaces. Compared with other conductive materials, the biggest advantage of graphite electrode material is that it has good electrical and thermal conductivity and better toughness, can accept the impact of larger current and does not soften or melt at high temperatures. It is used as a conductive material in the steel-making electric arc furnace, and the heat energy is transferred to the charge through arc discharge to melt the steel scrap. In the submerged arc furnace for smelting yellow phosphorus and industrial silicon, the electric energy is transferred into the charge through the electrode, and the charge itself is melted by the electric resistance heating of the charge.

The Advantages of Electric Arc Furnace for Steelmaking

Compared with other steelmaking methods, electric arc furnace steelmaking has its unique advantages. Electric arc furnace steelmaking is heated by an electric arc, and its temperature can be as high as 2 000 ℃ or more. This exceeds the maximum temperature that other steelmaking furnaces can reach when burning and heating with general fuel. The thermal efficiency is higher than that of the open hearth and converter steelmaking methods. Heating with electric energy can also accurately control the temperature and can use various elements (including aluminum, iron, and other elements that are easily oxidized) to alloy steel. Various types of high-quality steel and alloy steel are smelted, such as ball-bearing steel, stainless acid-resistant steel, high-speed tool steel, electrical steel, heat-resistant steel and alloys, and magnetic materials.

At present, electric furnace smelting adopts the traditional alkaline electric arc furnace steelmaking method. The process consists of “refilling the furnace-charging-smelting (including melting period and oxidation period)-refining outside the furnace (reduction period)-tapping-continuous casting” and so on.

According to relevant data, with the continuous improvement of ultra-high power electric arc furnaces and related technologies, the electrode consumption dropped from 6.5 kg/t to 1.2 kg/t from 1965 to 2000. The power consumption is reduced from 630 kW. h/t to 290 kW. h/t and the tapping time is reduced from 180 min to 40 min.

Artificial graphite electrodes — High-Quality Graphite Electrodes for Steelmaking

Characteristics Requirements of Graphite Electrode Materials for Steelmaking Electric Arc Furnaces

When investigating the adaptability of graphite electrodes to steel-making electric arc furnaces, the physical and chemical properties of the materials, the matching accuracy of the electrode and the joint, the reliability of the connection, and the length of the adaptable equipment (the up and down stroke of the electrode) should be analyzed one by one. Among them, the pear blossom properties of graphite electrode materials include mechanical properties, electrothermal properties, electrical conductivity, and oxidation resistance. In addition, it is necessary to understand and master the power transmission mode, smelting method, and process of the equipment.

It is very important to correctly understand the basic characteristics of graphite electrode materials. The characteristics of different grades of graphite electrodes are basically determined by the raw materials and manufacturing methods used.

Graphite electrodes should have at least the following properties on the smelting furnace. (1) Must be able to withstand the arc current required by the steelmaking process. (2) Continuous arc generation must be maintained.

In addition, the electrode should be able to be used in a wide temperature range (that is, it can be used in a state of rapid cooling and rapid heating). In the comprehensive evaluation of the performance of the graphite electrode, the thermal shock resistance index is used as the basic standard to measure the resistance of the electrode tip.

Thermal shock resistance refers to the ability of a material to resist damage under rapid cold and rapid heat. It is a comprehensive reflection of the performance of graphite electrodes.

Compared with other conductive materials, graphite electrodes have some excellent or irreplaceable characteristics under high-temperature conditions. Graphite electrodes can be used at relatively high temperatures (sublimation temperature of 3650°C), and are the only high-temperature conductive materials that can withstand high temperatures. There is no other material that can replace them in actual use. The strength of graphite increases as the temperature rises at high temperatures. Compared with other metals, graphite has the lowest coefficient of thermal expansion. When studying the characteristics of graphite electrodes, especially the thermal stress and vibration of the connection part, the coefficient of thermal expansion and the electrical resistivity is regarded as one of the most important indicators. Therefore, it is very important to choose petroleum coke with a low CTE value to produce graphite electrodes.

The Influence of Steelmaking Technology Progress on the Consumption of Graphite Electrodes

With the large-scale and ultra-high power of steelmaking electric arc furnaces, many improvements have been made to domestic UHP electric arc furnaces. For example, molten steel is reserved at the bottom of the furnace, and long-arc bubble slag submerged arc operation is used for drainage (the power transmission system is low current and high voltage). The foaming slag operation mainly reduces the radiation of the electric arc to the furnace wall and creates conditions for the long arc operation. The long-arc operation can effectively utilize power, that is, increase power factor, increase thermal efficiency, shorten smelting time and reduce electrical energy consumption. The improvement of thermal efficiency shortens the time for melting scrap steel and smelting. The use of long arc operation increases the vibration caused by the arc but can basically avoid the collapse of the electrode during the good penetration. After the current is reduced, the tip consumption of the electrode can be reduced. In addition, shortening the smelting time in an oxidizing atmosphere means that the side consumption of the electrode is also reduced. Coupled with the auxiliary electrode spray cooling, the electrode consumption of the UHP arc furnace is greatly reduced. From the level of over 2kg/t at the end of the last century to the level of 1.5 kg/t. Sometimes, it even reaches the level of 1.2~1.3 kg/t, which is especially in line with the characteristics of high production and low consumption in China’s steel industry in recent years.

In addition, the application of technologies such as out-of-furnace refining, scrap preheating, and addition of molten iron has contributed to the reduction of electrode consumption. The automatic control of electrode lifting protection makes the phenomenon of electrode breakage caused by human operation less and less.

The advancement of steelmaking technology has brought about a substantial reduction in electrode consumption, making imported electrodes of uniform material competitive advantage. It is a top priority for domestic carbon companies to break through the quality of large-size ultra-high-power electrodes as soon as possible and strive to reduce steelmaking consumption. To learn more about graphite electrodes for steelmaking electric arc furnaces, please contact us.

Large Diameter Graphite Electrodes in DC Arc Furnace

The physical performance requirements of large-scale, UHP graphite electrodes, with the introduction and continuous expansion of DC electric arc furnaces in my country, are of great significance for the best use of electric arc furnaces and reducing electrode consumption. Therefore, in order to promote the development of the electric furnace steelmaking industry, it is also extremely necessary for the development of large-scale, ultra-high power electrodes. Next, we will learn more about the application and cost-saving of graphite electrodes in electric arc furnaces from two aspects: the best use conditions of the electrodes in the DC arc and the physical properties of large-size graphite electrodes for DC electric arc furnaces.

uhp graphite electordes for Arc Furnaces

The Best Use Conditions of Electrodes in DC Electric Furnace

A certain electrode diameter corresponds to the best current load. Only in this way can the consumption of the electrode be the lowest, the utilization rate is the highest, and the role of the electrode can be fully and effectively played. H. Hagd et al. proposed two calculation criteria for a certain electrode diameter corresponding to the maximum current load. The first criterion is to calculate the current load capacity by considering only the thermal load; the second criterion is to calculate the current load capacity by calculating the mechanical stress through the thermal load.

Figure 5 shows the maximum tangential tensile stress of the φ600mm electrode at different current intensities. The calculation takes into account the conical shape of the electrode tip. The experimental results show that the maximum current load of the φ600mm electrode is about 85kA, and the maximum tangential tensile stress value generated at this time is 22MPa. When the current load is 62kA, the maximum tangential tensile stress on the outer surface of the electrode at the connection is 11.2MPa. This value is the lowest current intensity value at which the connection is broken, the electrode is peeled off, and the crack grows.

Fig. 6 is the upper limit of the current load corresponding to a certain diameter electrode obtained according to the thermal interception load (first criterion). Fig. 7 is the upper limit of the current load corresponding to a certain straight electrode obtained by calculating the mechanical stress (the second criterion) through the thermal load. Comparing the current load limit values obtained by the two criteria, the results are relatively consistent and satisfy the linear relationship. In practical applications, the second criterion is more important when the results obtained are applied to electric furnace electrodes. Because the second criterion is the result derived from thermal stress, and thermal stress is often one of the important reasons for electrode failure and connection damage.

The performance of graphite electrodes and nipples produced in my country is definitely different from that of H.Hagel calculation electrodes. Therefore, our application of this criterion can only use its linear relationship, and the general trend should be consistent.

Physical Properties of Large-Size Graphite Electrodes for DC Electric Solitary Furnace

With the increasing number of high-power and large-capacity DC electric furnaces, the electrode diameter is getting larger and larger, up to φ800mm, and the current interception is getting higher and higher, reaching 150kA. It is very important to choose a suitable electrode quality standard to meet the needs of high-power and large-capacity electric furnaces. All practical and theoretical studies have obtained the same results, and the performance of large-scale graphite electrodes needs to be improved even more. This requires attention to the selection of raw materials and the establishment of advanced production processes.

Higher requirements are put forward on the physical properties of large-size electrodes used in DC electric arc furnaces.

(1) The resistivity is further reduced. In this way, the power loss (I2R) is small, and a reasonable temperature gradient can also be obtained. This requires a higher graphitization temperature to ensure a decrease in resistivity.

(2) The coefficient of thermal expansion should be low. Since the graphite electrode and the graphite electrode nipple at the connection site have different thermal expansion properties in the axial and radial directions, the temperature at the nipple is higher and the thermal stress is greater. Under the premise of low thermal expansion coefficient, the axial and radial thermal expansion coefficient of the electrode should be slightly greater than or equal to the nipple and should satisfy αpTp-αNTN ≥ 0. Among them, αp is the thermal expansion coefficient of the electrode; Tp is the temperature of the electrode; αN is the thermal expansion coefficient of the nipple; TN is the temperature of the nipple. In this way, the thermal stress value is reduced. To achieve this, there must be advanced technology, raw materials, and formula to ensure.

(3) The thermal conductivity should be high. The high thermal conductivity allows the electrode to dissipate heat quickly, and the radial temperature gradient is small, which is also beneficial to improve the thermal stress. The thermal conductivity should be above 200W/m·K.

(4) It must have a certain strength. The electrode must have a certain strength, and the strength of the nipple is higher than that of the electrode. Large-size electrodes have a large weight. In order to ensure a reasonable current flow, there should be a higher pressure on the connection end surface. If the strength is insufficient, the connection thread will be damaged, local cracks will occur prematurely, and the failure rate will be accelerated. At the same time, we also hope that the modulus of elasticity should be low, so that the thermal stress σ = EaT is also reduced. Therefore, both strength and elastic modulus should be considered. The strength can be improved through process control, selection of reasonable formulas and raw materials, and multiple dipping processes.

(5) The porosity should be low. For electrodes, excessive surface porosity will increase oxidation and increase electrode consumption. Porosity can be improved by the surface treatment process.

Configuration of Graphite Electrodes for Steelmaking Electric Arc Furnaces

In the configuration of Graphite Electrodes for Steelmaking Electric Arc Furnaces, it is necessary to follow the basic principle of “normal power electric furnaces with ordinary power graphite electrodes, high-power electric furnaces with high-power graphite electrodes, and ultra-high-power electric furnaces with ultra-high-power graphite electrodes“.

Configuration Scheme of the Graphite Electrode for AC Steelmaking Electric Arc Furnace

For AC steelmaking electric arc furnace,

The 10~30t electric furnace is equipped with graphite electrodes with a diameter of 300~400mm.
The 30-50t electric furnace is equipped with graphite electrodes with a diameter of 450mm.
The 60~80t electric furnace is equipped with graphite electrodes with a diameter of 500mm.
The 100~170t electric furnace is equipped with graphite electrodes with a diameter of 550~600mm.
The 200t electric furnace is equipped with graphite electrodes with a diameter of 600~700mm.
The 250~300t electric furnace is equipped with a 700mm diameter graphite electrode.

RS High Quality Graphite Electrode — RS High-Quality Graphite Electrode

Configuration Scheme of the Graphite Electrodes for DC Steelmaking Electric Arc Furnace

For DC steelmaking electric arc furnace,

The 30t electric furnace is equipped with graphite electrodes with a diameter of 450mm.
The 60t electric furnace is equipped with graphite electrodes with a diameter of 500mm.
70~80t electric furnace is equipped with graphite electrodes with a diameter of 600mm.
The 100~130t electric furnace is equipped with a 700mm diameter graphite electrode.
The 150t electric furnace is equipped with graphite electrodes with a diameter of 750mm.

uhp graphite electrode — UHP graphite electrode

Rongsheng Group, one of the graphite electrodes suppliers, provides you with Graphite Electrodes for Steelmaking Electric Arc Furnaces.

FAQ1 How to choose the electrode correctly in the electric arc furnace steelmaking?

According to the design characteristics of the electric arc furnace, reasonably select the electrode that meets the production of the electric arc furnace, and select the product with the best cost performance. It is very necessary to carefully select the electrode suitable for each furnace. The special performance of the steelmaking furnace, the feeding method, the maximum current intensity, the length of the electrode column under the holder, the distance between the sidewall of the furnace and the electrode circumference, etc., are all factors that must be considered when choosing the electrode for the electric arc furnace.

FAQ2 Why is the electrode required to be parallel and centered with the top hole of the furnace cover when steelmaking in an electric arc furnace?

The electrode column and the top hole of the furnace cover should be centered. The electrode column should avoid friction with the furnace cover, otherwise, friction with the furnace cover during lifting and lowering will cause the furnace cover to break the electrode. For AC furnaces, the three-phase electrode columns should be kept as parallel as possible.

FAQ3 What effect does the resistivity performance have on the use of electrodes in steelmaking?

The resistivity of the graphite electrode is a physical index that reflects the conductivity of the electrode and is related to the manufacturing process of the electrode. The country has qualitatively specified values for the resistivity of graphite electrodes of different specifications. Generally speaking, when steel mills choose electrodes of certain specifications, they must choose the resistivity range specified by the national metallurgical standards. Too high resistivity will cause the electrode to become red and hot when it is energized, and increase electrode oxidation consumption.

350-500mm Quasi-Ultra High Power Graphite Electrodes

In 2002, some customers have asked whether a new variety of graphite electrodes with properties between UHP graphite electrodes and HP graphite electrodes could be manufactured? In this way, it can not only meet the production needs of ultra-high power refining furnaces but also have a relatively large price drop compared to the UHP electrode. However, there is a carbon company that fulfills these customers’ demands. They have developed a new variety of graphite electrodes between ultra-high power graphite electrodes and high-power graphite electrodes, quasi-ultra high power graphite electrodes. This graphite electrode product requires various physical and chemical performance indexes to reach or be close to the UHP graphite electrode, but the production cost is greatly reduced so that the sales price also drops significantly.

Brief Introduction of Quasi-Ultra High Power Graphite Electrode

The properties of quasi-ultra high power graphite electrodes are between the high power graphite electrodes and ultra-high power graphite electrodes, close to those of UHP graphite electrodes, which can meet the demand of UHP graphite electrodes for LF and high power graphite electrodes for electric are furnace, and reduce the cost of the production of HP graphite electrodes and ultra-high power graphite. The technologic processes for φ350 ~ φ500mm quasi-ultra high power graphite electrodes were introduced, which were made from imported high-ranking/ordinary needle cokes to a scale in some carbon manufacturer. The results show that the properties of products obtained are close to those of ultra-high power graphite electrodes, and can meet the demand of ultra-high power graphite electrodes for LF.

Characteristics of Quasi-Ultra High Power Graphite Electrode

(1) The calcined coke produced by China’s domestic petroleum coke and the imported ordinary-grade needle coke is mixed in a certain proportion. The physical and chemical indexes of the produced quasi-ultra-high-power graphite electrodes have all met the requirements of the enterprise standard Q/140200DNT001-2007 “Quasi-ultra-high-power graphite electrodes“, and the trial production effect has reached the expected target.

(2) The sample analysis report proves that the performance index of the quasi-ultra-high-power graphite electrode is close to that of ultra-high-power graphite electrode, which can meet the production needs of ultra-high-power refining furnace.

(3) Finally, because part of the raw materials used by China-made petroleum coke, the production cost of quasi-ultra-high-power graphite electrodes is significantly lower than that of ultra-high-power graphite electrodes. Therefore, the selling price of quasi-ultra high-power graphite electrodes has also been reduced. From the customer’s perspective, it can effectively reduce the production cost of ultra-high power refining furnaces.

What are Graphite Electrodes?

What are graphite electrodes? Graphite electrodes are kind of conductive material in electric arc furnace steelmaking production. The graphite electrodes are mainly made of petroleum coke and needle coke as raw materials, and coal pitch is used as a binder, and is made by calcination, batching, kneading, pressing, roasting, graphitization, and machining. Due to some special properties of graphite. It is a conductor that releases electrical energy in the form of an electric arc to heat and melt the charge in the electric arc furnace. According to its quality index, it can be divided into rp graphite electrode, high power graphite electrode and ultra high power graphite electrode.

What are the graphite electrodes?

Rp graphite electrode, produced with ordinary grade petroleum coke. Graphitization temperature is low, its resistivity is high, the coefficient of linear expansion is large, and its thermal shock resistance is poor, so the current density is allowed to be low.

HP graphite electrode, produced with high-quality petroleum coke (or low-grade needle coke). Sometimes the electrode body needs to be dipped. Its physical and mechanical properties are higher than those of ordinary power graphite electrodes, such as low resistivity, which allows a large current density.

UHP graphite electrodes must be produced with high-grade needle coke. And the graphitization heat treatment should be carried out in the internal graphitization furnace. The graphitization temperature is as high as 2800 ~ 3000 ° C. Therefore, the resistivity is lower, allowing greater current density, the linear expansion coefficient is smaller, and has excellent thermal shock resistance.

The main raw material for the production of graphite electrodes is petroleum coke. A small amount of pitch coke can be added to rp graphite electrodes, and the sulfur content of petroleum coke and pitch coke cannot exceed 0.5%. Needle coke is also needed when producing high-power or ultra-high-power graphite electrodes. The main raw material for the production of aluminum anodes is petroleum coke, and the sulfur content should be controlled not more than 1.5% to 2%. Petroleum coke and asphalt coke should meet the relevant national quality standards.

Graphite Electrode used in DC Electric Arc Furnace

The development of electric furnace steelmaking technology, the enlargement of electric furnaces, the increase of electric power per unit furnace capacity and the use of DC electric arc furnaces have constantly put forward new requirements for the variety and performance of graphite electrodes. The use of high-power and ultra-high-power electric furnace steelmaking can shorten the furnace melting time, improve production efficiency, reduce power consumption and reduce graphite electrode consumption.

RS Graphite Electrode Manufacturers

RS Group, one of the Graphite electrode manufacturers, supply rp, hp, uhp graphite electrodes to the steelmaking plant. And our customer has been more than 60 countries anf areas all over the world. If you are want to buy the rp graphite electrode, please contact us, we will reply you as soon as possible.

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