How many types of casting electric furnaces are there?
Electric furnace is a heating furnace that converts the electric energy in the furnace into heat to heat the workpiece. Compared with fuel furnaces, the advantages of electric furnaces are: the atmosphere in the furnace is easy to control, and can even be vacuumed; the material is heated quickly, the heating temperature is high, and the temperature is easy to control .
Advantage ·
Electric furnace is a heating furnace that converts the electric energy in the furnace into heat to heat the workpiece. Compared with fuel furnaces, the advantages of electric furnaces are: the atmosphere in the furnace is easy to control, and can even be vacuumed; the material is heated quickly, the heating temperature is high, and the temperature is easy to control ; The production process is easier to achieve mechanization and automation; good labor and hygiene conditions; high thermal efficiency; good product quality; and more environmentally friendly is a good product for increasingly serious environmental problems. Electric furnaces in the metallurgical industry are mainly used for smelting, heating and heat treatment of iron and steel, ferroalloys, and non-ferrous metals. Industrial-scale electric furnaces appeared at the end of the 19th century. Since the 1950s, due to the increase in demand for advanced metallurgical products and the decline in electricity costs with the development of the power industry, the proportion of electric furnaces in metallurgical furnace equipment has increased year by year. Electric furnaces can be divided into resistance furnaces, induction furnaces, electric arc furnaces, plasma furnaces, electron beam furnaces, etc.
Type introduction ·
Resistance furnace
An electric furnace that uses Joule heat generated by current passing through a conductor as a heat source. According to the method of electric heat generation, resistance furnaces are divided into direct heating and indirect heating. In the direct heating resistance furnace, the current passes directly through the material. Because the electric heating power is concentrated on the material itself, the material is heated quickly, which is suitable for processes that require rapid heating, such as the heating of forging blanks. This kind of resistance furnace can heat the material to a very high temperature. For example, the carbon material graphitization electric furnace can heat the material to more than 2500°C. The direct heating resistance furnace can be made into a vacuum resistance heating furnace or a protective gas resistance heating furnace. In powder metallurgy, it is often used for sintering tungsten, tantalum, niobium and other products. Attention should be paid when using this kind of furnace for heating:
①In order to heat the material uniformly, the conductive cross section and conductivity of each part of the material are required to be consistent;
②Since the resistance of the material itself is quite small, in order to achieve the required electric heating power, the working current is quite large, so the power transmission electrode and the material should be in good contact to avoid arcing to burn the material, and the resistance of the power transmission bus should be small to reduce circuit loss ; Most resistance furnaces are indirect heating resistance furnaces, which are equipped with a resistor body specially used to realize the electric-heat conversion, called an electric heating body, which transfers heat energy to the materials in the furnace.
The most commonly used electric heaters are iron-chromium-aluminum heaters, nickel-chromium heaters, silicon carbide rods and molybdenum disilicide rods, silicon carbide rods, and zirconium diboride ceramic composite heaters. According to needs, the atmosphere in the furnace can be ordinary atmosphere, protective atmosphere or vacuum. Generally, the power supply voltage is 220 volts or 380 volts, and an intermediate transformer with adjustable voltage should be equipped if necessary. Single-phase power supply for small furnaces (<10 kW) and three-phase power supply for large furnaces. For materials with single varieties and large batches, continuous furnace heating should be used. Most resistance furnaces with furnace temperature lower than 700□ are equipped with blowers to strengthen heat transfer in the furnace and ensure uniform heating. The resistance furnace used to melt fusible metals (lead, lead-bismuth alloys, aluminum, magnesium and their alloys, etc.) can be made into a crucible furnace; or into a reverberatory furnace with a molten pool, with an electric heating element installed on the top of the furnace. The electroslag furnace is a resistance furnace that realizes electrothermal transformation from molten slag.
Induction furnace
Introduction of Induction Furnace An electric furnace that uses the induction electric heating effect of materials to heat or melt materials. The basic component of the induction furnace is an induction coil wound with a copper tube. An alternating voltage is applied to both ends of the induction coil to generate an alternating electromagnetic field. The conductive material is placed in the induction coil, and the eddy current is generated in the material due to electromagnetic induction. The electrical energy is converted into heat energy to heat the material by the action of resistance; therefore, it can also be considered Induction heating is a direct heating type resistance heating.
The characteristic of induction heating is that the electric heating power (current distribution) transformed in the heated material is very uneven, with the largest surface and the smallest center, which is called the skin effect. In order to improve the electric heating efficiency of induction heating, the power supply frequency should be appropriate. Small smelting furnaces or the surface heating of materials use high frequency electricity, and large smelting furnaces or deep penetration heating of materials use medium frequency or power frequency electricity. The induction coil is a load with a considerable inductance, and its power factor is generally very low. In order to improve the power factor, the induction coil is generally connected in parallel with an intermediate frequency or high frequency capacitor, which is called a resonant capacitor. The gap between the induction coil and the material should be small. The induction coil should be made of a square copper tube with water cooling in the tube. The inter-turn gap of the induction coil should be as small as possible and the insulation should be good. Induction heating device is mainly used for heating and casting of steel, copper, aluminum and zinc, etc., with fast heating, less burning loss, high degree of mechanization and automation, and suitable for configuration on automatic operation lines.
Features of induction furnace series heating furnace:
(1) The heating speed is fast, the production efficiency is high, the oxidation decarbonization is less, and the cost of materials and forging dies is saved.
Since the principle of intermediate frequency induction heating is electromagnetic induction, the heat is generated in the workpiece itself. Ordinary workers can perform continuous forging tasks ten minutes after going to work with the intermediate frequency electric furnace, without the need for professional furnace firing workers to perform furnace firing and sealing work in advance . There is no need to worry about the waste of heated billets in the coal furnace caused by power outages or equipment failures. Due to the fast heating speed of this heating method, there is very little oxidation. Compared with the coal-fired furnace, each ton of forgings can save at least 20-50 kilograms of steel raw materials, and the material utilization rate can reach 95%. Because this heating method heats uniformly and the temperature difference between the core and the surface is extremely small, the life of the forging die is greatly increased in forging, and the surface roughness of the forging is also less than 50um.
(2) The working environment is superior, improving the labor environment of workers and the company's image, pollution-free, and low energy consumption.
Compared with coal stoves, workers will no longer be bake and smoked by coal stoves in the scorching sun, and can meet the requirements of various indicators of the environmental protection department. At the same time, it can establish the company's external image and the future development trend of the forging industry. . Induction heating is the most energy-saving heating method in electric heating furnaces. The power consumption of forgings per ton heated from room temperature to 1100°C is less than 360 degrees.
(3) The heating is uniform, the temperature difference between the core and the surface is extremely small, and the temperature control accuracy is high.
The induction heating furnace has the advantages of small size, light weight, high efficiency, excellent thermal processing quality and favorable environment. It is rapidly eliminating coal-fired furnaces, gas furnaces, oil-fired furnaces and ordinary resistance furnaces. It is a new generation of metal heating equipment.
Industrial applications of induction melting furnaces include crucible furnaces (coreless induction furnaces) and furnaces (cored induction furnaces). The crucible is made of refractory material or steel, and the capacity ranges from several kilograms to dozens of tons. The smelting feature is that the melt in the crucible is subjected to electromotive force, which forces the liquid level of the molten pool to bulge, and the melt flows from the center of the liquid level to the surroundings, causing a circulating flow. This phenomenon is called electrokinetic effect, which can make the melt composition uniform. The disadvantage is that the slag is biased to the periphery and the coverage is poor. Compared with the furnace furnace, the crucible furnace is flexible in operation, the melting temperature is high, but the power factor is low, and the power consumption is high. The inductor of the furnace is composed of an iron core, an induction coil and a furnace lining. The melting groove is one or two belt-shaped annular grooves, which are filled with melt connected to the molten pool. In principle, the furnace can be regarded as an iron core transformer with only one turn of the secondary coil and short-circuit. The induced current flows in the molten channel melt to achieve electrothermal transformation.
In production, after each furnace of metal smelting is completed, the molten pool cannot be emptied, otherwise it will dry out easily, and a part of the melt must be reserved as the next furnace. The temperature of the melting channel is higher than that of the molten pool, and it is subject to the erosion of the melt flow, so the furnace lining of the melting channel is easily damaged. In order to facilitate maintenance, the inductors of modern furnaces are made into easy-to-replace assembly parts. The capacity of the furnace ranges from several hundred kilograms to more than one hundred tons. The furnace is supplied with power frequency electricity. Since the iron core made of silicon steel sheet is used as the magnetic path, the electric efficiency and power factor are very high. Furnace furnace is mainly used for the melting of cast iron, copper, zinc, brass, etc. It can also be used as a mixed melt to store and heat the melt.
Electric arc furnace
An electric furnace that uses arc heating to smelt metals and other materials. According to the heating method, it is divided into three types: ①Indirect heating electric arc furnace. The arc is generated between the two electrodes, does not touch the material, and heats the material by thermal radiation. This kind of furnace is noisy and low in efficiency, and is gradually eliminated. ②The electric arc furnace is directly heated. The electric arc is generated between the electrode and the material and directly heats the material; the steel-making three-phase electric arc furnace is the most commonly used direct heating electric arc furnace. ③Submerged arc electric furnace, also known as reduction electric furnace or submerged electric furnace. One end of the electrode is buried in the material layer to form an arc in the material layer and use the resistance of the material layer to heat the material; it is often used for smelting iron alloys.
Vacuum electric arc furnace
It is an electric furnace that uses an electric arc to directly heat and smelt metal in a vacuumed furnace body. The gas in the furnace is thin, and the arc is mainly generated by the vapor of the molten metal. In order to stabilize the arc, DC power is generally supplied. According to the characteristics of smelting, it is divided into metal remelting furnace and casting furnace. According to whether the electrode is consumed (melted) during the smelting process, it is divided into consumable furnaces and non-consumable furnaces. Most of the industrial applications are consumable furnaces. The vacuum electric arc furnace is used to smelt special steel, active and refractory metals such as titanium, molybdenum, and niobium.
Arc electric heating can be considered as arc resistance electric heating. Stable arc (arc resistance) is a necessary condition for the normal production of the furnace. AC electric arc furnaces usually use power frequency electricity. In order to stabilize the arc, there must be proper inductive reactance in the furnace power supply circuit, but the presence of inductive reactance will reduce the power factor and electrical efficiency. Reducing the current frequency is the way to develop AC electric arc furnace. The arc resistance value is quite small. In order to obtain the necessary heat, the furnace needs a considerable working current. Therefore, the resistance of the short network of the furnace should be as small as possible to avoid excessive circuit loss. For a three-phase electric arc furnace, the impedance of the three phases should be close to the same to avoid unbalanced three-phase load.
Plasma furnace
An electric furnace that uses plasma generated when the working gas is ionized for heating or smelting. Plasma-generating devices, usually called plasma guns, are classified into arc plasma guns and high-frequency induction plasma guns. Pass the working gas into the plasma gun. The gun has a device that generates an electric arc or high-frequency (5-20 MHz) electric field. After the working gas is acted on, it ionizes to generate a plasma composed of electrons, positive ions, and a mixture of gas atoms and molecules. . After the plasma is ejected from the nozzle of the plasma gun, a high-speed and high-temperature plasma arc flame is formed, and the temperature is much higher than that of a general arc. The most commonly used working gas is argon, which is a monoatomic gas, easy to ionize, and is an inert gas that can protect materials. The working temperature can be as high as 20,000 degrees; it is used for smelting special steel, titanium and titanium alloys, superconducting materials, etc. Furnace types include water-cooled copper crystallizer furnace, hollow cathode furnace, plasma furnace with induction heating, plasma furnace with refractory lining, etc.
Electron beam furnace
An electric furnace that bombards materials with high-speed electrons to heat them and melt them. In the vacuum furnace shell, the cathode is heated by a low-voltage electric filament to make it emit electrons. The electron beam is accelerated by the high-voltage electric field that accelerates the anode, bombarding the metal material at the anode, and transforming electrical energy into heat. Because the electron beam can be highly dense through the electromagnetic focusing device, it can generate very high temperatures in the bombarded parts of the material. The electron beam furnace is used to smelt special steel, refractory and active metals.
Electric stove
Electric heating furnace can use metal heating element or non-metal heating element to generate heat source. Its simple structure and wide range of uses are its main features. It can be widely used in annealing, normalization, quenching, tempering, carburizing and carburizing and nitriding. Wait. The main metal heating elements include Ni-Cr heating wires (the most common, the highest is used up to 1200 ℃), Mo-Si alloys and pure metals such as W, Mo; non-metal heating elements include SiC (the most common, the highest can be heated to 1600 ℃ ), LaCrO3 and graphite rods (can be heated to 2000 ℃ under vacuum or protective atmosphere).
advantage:
1) It is easier to get high temperature compared with fuel furnace.
2) It can be heated from inside the material to increase the temperature.
3) It is easy to use in controllable atmosphere furnace and vacuum furnace.
4) Electric furnace has no exhaust heat loss of fuel furnace, so it has high thermal efficiency.
5) Easy to control the temperature, easy to remote control and fine adjustment.
6) It can be heated quickly.
7) Good operation performance and no pollution to the environment.
shortcoming:
1) The cost of power distribution equipment needs to be increased.
2) The cost of electricity is high.
3) When the resistance heating temperature exceeds 1000°C, the refractory material may conduct electricity, and insulation needs to be paid attention to.
Develop ·
In 2010, China's manufacturing industry accounted for 19.8% of global manufacturing output, slightly higher than the US's 19.4%, ranking first in the world. The rapid development of China's manufacturing industry has driven the development of China's oven, furnace and electric furnace manufacturing industries. According to statistics from the National Bureau of Statistics, in 2010, the number of enterprises above designated size in the oven, furnace and electric furnace manufacturing industries increased to 308, achieving a total industrial output value of 16.288 billion yuan, a year-on-year increase of 30.79%; achieving sales revenue of 16.387 billion yuan, a year-on-year increase of 32.63% ; Realized a total profit of 1.043 billion yuan, a year-on-year increase of 79.17%.
70%-80% of parts in the automobile and tractor industries require heat treatment, while 100% of tools, cutting tools and bearing products require heat treatment. The service life of some civil light industrial metal products is also improved by heat treatment. At the same time, the fastener industry, bearing industry, chain industry, tool industry, automobile, tractor, and motorcycle parts industry all rely on the improvement of heat treatment quality to enhance their competitiveness. With the continuous development of China’s industry, my country has 400,000-500,000 tons of thermal processing will be added. In addition, most of the domestic ovens, furnaces and electric furnaces are obsolete and backward, and will tend to be eliminated and updated. my country’s demand for thermal processing equipment is very strong. The development prospects of electric furnaces are promising.
