An electric arc furnace is an electric furnace that utilizes the electrical heating generated by electric arcs to smelt metals. Within an electric arc furnace, one or more electric arcs are present. Through the action of arc discharge, electrical energy is transformed into heat energy, providing the necessary heat to warm the smelting materials. Due to the high arc temperature, substantial electrothermal transformation capacity, high electrothermal efficiency, and ease of controlling furnace atmosphere and operation, electric arc furnaces are widely employed in industrial settings, particularly suitable for smelting refractory and advanced materials.
Industrial electric arc furnaces can be classified into three primary categories. The first type is the direct electric arc furnace, where the arc occurs between the electrode and the melted charge, heating the charge directly through arc contact. This category includes three-phase steelmaking electric arc furnaces, DC electric arc furnaces, and vacuum consumable furnaces. The second type is the indirect electric arc furnace, where the arc occurs between two specialized electrode rods, and the charge is heated indirectly through heat transfer from the arc. This type is mainly used for smelting copper and copper alloys but has been largely replaced by other smelting furnaces due to drawbacks such as high noise and poor smelting quality. The third type is the submerged arc furnace.
An arc is a phenomenon of gas conduction, commonly referred to as arc discharge (gas conduction phenomena are termed gas discharge in physics). Other phenomena within gas discharge include glow discharge and spark discharge. Arc discharge is a self-excited discharge characterized by low voltage (only tens of volts), high current density (up to hundreds of amperes per square centimeter), continuous emission of dazzling arc light, substantial heat generation, and high temperature.
The electric arc in an electric arc furnace primarily involves the conduction phenomenon of gas (including metal vapor) excited by electrons emitted from a hot cathode. For gas conduction to occur, ionization must take place to produce charged particles, including positively charged positive ions and negatively charged electrons or negative ions. The total positive charge carried by the gas ions equals the total negative charge, hence the term plasma; the arc is also referred to as arc plasma.
Gas ionization in an electric arc furnace generally arises from the following causes:
Collision Ionization: Electrons emitted from the cathode due to high temperature collide with gas molecules on their path to the anode, causing the molecules to acquire ionization energy and dissociate into positive ions and electrons. This transforms neutral molecules into charged particles.
Thermal Ionization: At high temperatures, gas molecules possess significant kinetic energy. When they collide with one another, they gain energy and ionize, a process known as thermal ionization.
Photoionization: The energy irradiated by atomic absorption of light can also excite atoms to an ionized state. However, photoionization is generally not the primary method of gas ionization.
Electric Field-Induced Ionization: Under the influence of an electric field, charged particles such as positive ions, electrons, or negative ions that have been ionized from the gas move toward the positive and negative poles, respectively, and are accelerated by the electric field force, increasing their kinetic energy. When these charged particles collide with gas molecules, they cause further ionization, generating new charged particles. These new charged particles are also accelerated by the electric field force and move toward the poles, causing additional ionization upon collision with gas molecules. This process is known as chain ionization.
The degree of ionization caused by an electric field primarily depends on the intensity of the electric field and the free path of the particles. Greater electric field strength results in more work done by the electric field force on the charged particles, increasing their kinetic energy and enhancing the ionization degree upon collision. The free path is also related to gas density and the volume of the charged particles themselves; lower density results in a longer free path. Therefore, gas ionization caused by an electric field is higher under vacuum conditions. Electrons, being much smaller in volume than ions, have a longer free path and are more likely to ionize molecules or atoms. In other words, electrons play a major role in gas ionization caused by an electric field.
It should be noted that within an arc, there is an ionization process where neutral gas molecules dissociate into positive ions and electrons, as well as a recombination process where positive ions capture electrons and recombine into neutral molecules. Under certain conditions, these two processes reach dynamic equilibrium, maintaining a certain degree of ionization.
We are a professional electric furnace manufacturer. For further inquiries, or if you require submerged arc furnaces, electric arc furnaces, ladle refining furnaces, or other melting equipment, please do not hesitate to contact us at susie@aeaxa.com
