electric stove

  Electric furnace: Electric heating equipment that uses electric heating to achieve the intended technological purpose (such as smelting, melting, heating, heat treatment, sintering, drying, etc.) is called an electric furnace. The industrial furnaces that use the electrothermal effect to provide heat are divided into industrial furnaces and household furnaces. Industrial furnaces are divided into resistance furnaces and induction furnaces. With the development of modern industrial technology, induction furnaces have become the most energy-efficient electric conversion in electric furnaces. The heating method is widely used in many fields such as family, medicine, chemical industry, metallurgy, etc.

Electric furnace advantages

  Compared with the fuel furnace, the advantages of the electric furnace are: the atmosphere in the furnace is easy to control, and even can be evacuated; 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; the labor hygiene conditions are good; the thermal efficiency is high ; Good product quality, etc. Electric furnaces in the metallurgical industry are mainly used for smelting, heating and heat treatment of steel, ferroalloys, non-ferrous metals, etc. At the end of the 19th century, industrial-scale electric furnaces appeared. Since the 1950s, the proportion of electric furnaces in metallurgical furnace equipment has increased year by year due to the increase in demand for advanced metallurgical products and the decline in electricity costs with the development of the power industry. Electric furnaces can be divided into resistance furnaces, induction furnaces (Shenzhen photoelectric furnaces), electric arc furnaces, plasma furnaces, electron beam furnaces, etc.

Resistance furnace

  An electric furnace that uses Joule heat generated by current passing through a conductor as a heat source. According to the electric heating method, the resistance furnace is divided into direct heating and indirect heating. In the direct heating resistance furnace, the current flows directly through the material. Because the electric heating power is concentrated on the material itself, the material is heated very quickly. It is suitable for processes that require rapid heating, such as forging billet heating. This 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 □. 

 

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 to sinter tungsten, tantalum, niobium and other products. When using this furnace for heating, attention should be paid to: ① To make the material heated uniformly, the conductive cross-section and conductivity of each part of the material are required to be consistent; The contact between the power transmission electrode and the material should be good, so as not to burn the material from the arc, and the resistance of the power transmission bus should be small to reduce the circuit loss; Too low. One of his shortcomings when the resistance furnace's thermal efficiency is not high.

  Most resistance furnaces are indirect heating resistance furnaces, which are equipped with a resistor body specifically designed to realize the electrical-thermal transition, called the electric heating body, which transfers heat energy to the materials in the furnace (Figure 1 Indirect heating resistance furnace).

This electric furnace shell is made of steel plate, the furnace is lined with refractory materials, and the materials are placed inside. The most commonly used heating elements are iron chromium aluminum heating elements, nickel chromium heating elements, silicon carbide rods and molybdenum disilicide rods. According to needs, the atmosphere in the furnace can be ordinary atmosphere, protective atmosphere or vacuum. The general power supply voltage is 220 volts or 380 volts. If necessary, configure an intermediate transformer with adjustable voltage. Single-phase power supply for small furnaces (<10 kW), three-phase power supply for large furnaces. For materials with a single variety and large batches, continuous furnace heating should be used. Resistance furnaces with furnace temperature below 700 □, most of them are equipped with blowers to enhance heat transfer in the furnace and ensure even heating. The resistance furnace used for melting fusible metals (lead, lead-bismuth alloy, aluminum, magnesium and their alloys, etc.) can be made into a crucible furnace; or a reverberatory furnace with a melting pool, and an electric heating body is installed on the furnace roof. The electroslag furnace is a resistance furnace that realizes electrothermal conversion by dissolving slag (see electroslag remelting).

Induction furnace

An electric furnace that uses the induction electrothermal effect of materials to heat or melt the materials. The basic component of the induction furnace is an induction coil wound with a copper tube. The AC voltage is applied at both ends of the induction coil to generate an alternating electromagnetic field. The conductive material is placed in the induction coil. Due to the electromagnetic induction, eddy current is generated in the material, and the electrical energy is converted into heat energy to heat the material due to the resistance. Therefore, it can also be considered Induction electric heating is a kind of direct heating resistance electric heating. Domestic famous manufacturer 

The characteristic of induction electrothermal is that the electrothermal 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-scale smelting furnaces or high-frequency electricity is used to heat the surface of the materials, and large-scale smelting furnaces or medium-frequency or industrial frequency electricity is used for the deep penetration of materials. The induction coil is a load with a relatively large 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 capacitors, called compensation capacitors. The gap between the induction ring and the material should be small. The induction ring should be made of square copper tube. The tube is cooled by water. The gap between the turns of the induction ring should be as small as possible and the insulation should be good. The induction heating device is mainly used for heating and melting casting of steel, copper, aluminum and zinc. It has fast heating, less burning loss, high degree of mechanization and automation, and is suitable for being configured on automatic operation lines.

Features of induction furnace series heating furnace

Fast heating speed, high production efficiency, less oxidation decarburization, saving materials and forging die cost

Because the principle of medium frequency induction heating is electromagnetic induction, its heat is generated in the workpiece itself. Ordinary workers can use the medium frequency electric furnace to work continuously for forging tasks ten minutes after work, without the need for professional furnace workers to perform furnace and seal furnace work . There is no need to worry about the waste of the coal furnace's heated billets due to power outages or equipment failures. Due to the rapid heating rate of this heating method, there is very little oxidation, and at least 20-50kg of steel raw materials are saved per ton of forgings and coal-fired furnaces, and the material utilization rate can reach 95%. Due to the uniform heating of this heating method and the extremely small temperature difference on the core surface, the life of the forging die is also greatly increased in forging, and the roughness of the forging surface is also less than 50um.

Excellent working environment, improve workers' working environment and company image, no pollution, low energy consumption

Compared with coal stoves, induction heating furnaces will not allow workers to be exposed to the baking and fumigation of coal stoves under the hot sun, but also meet the requirements of various indicators of the environmental protection department, while establishing the company's external image and the future development of the forging industry trend. Induction heating is the most energy-efficient heating method in electric heating furnaces. The power consumption per ton of forgings heated from room temperature to 1100°C is less than 360 degrees.

Even heating, minimal temperature difference on the core surface, and high temperature control accuracynduction heating generates heat in the workpiece itself, so the heating is uniform, and the temperature difference on the core surface is extremely small. The application of temperature control system can achieve precise temperature control and improve product quality and pass rate.

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, fuel oil furnaces and ordinary resistance furnaces. It is a new generation of metal heating equipment.

Industrial melting furnaces used in the industry include crucible furnaces (coreless induction furnaces) and melting furnaces (core induction furnaces). The crucible is made of refractory material or steel, and its capacity ranges from several kilograms to tens of tons. The smelting feature is that the melt in the crucible is subjected to electromotive force, forcing the liquid level of the molten pool to protrude, and the melt flows from the center of the liquid level to the surroundings, causing circulating flow. This phenomenon is called the electromotive 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 ditch furnace, the crucible furnace has flexible operation, high melting temperature, but low power factor and high power consumption. The inductor of the melting ditch furnace is composed of an iron core, an induction ring and a melting ditch furnace lining. The melting ditch is one or two band-shaped annular ditch, which is filled with melt connected with the molten pool. In principle, the ditch furnace can be regarded as an iron-core transformer with only one coil in the secondary and short circuit. The induced current flows in the melt of the ditch, and the electrothermal transformation is realized.

In the production, after the melting of each furnace is completed, the molten pool cannot be emptied, or it is easy to dry up, and a part of the melt must be retained as the starting melt for the next furnace. The temperature of the molten ditch is higher than that of the molten pool, and it also bears the erosion of the melt flow, so the furnace lining is easy to be damaged. For easy maintenance, the inductor of the modern furnace is made of easy-to-replace assembly parts. The capacity of the furnace is from several hundred kilograms to more than one hundred tons. The ditch furnace supplies power frequency power. Since the iron core made of silicon steel sheet is used as the magnetic path, the electric efficiency and power factor are very high. Melting ditch furnace is mainly used for melting cast iron, copper, zinc, brass, etc. It can also be used as a mixed melting furnace to store and heat the melt.

Electric arc furnace

Electric furnace using arc heat effect to smelt metal and other materials (Fig. 3 type of electric arc furnace). There are three types according to the heating method: ① Indirect heating electric arc furnace. The arc is generated between the two electrodes, does not contact the material, and heats the material by thermal radiation. This kind of stove is noisy and has low efficiency, and is gradually being eliminated. ② Directly heating the electric arc furnace. An 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 (see Electric Arc Furnace Steelmaking). ③ Submerged arc electric furnace, also known as reduction electric furnace or mine thermal electric furnace. One end of the electrode is buried in the material layer, forming an arc in the material layer and heating the material by the resistance of the material layer; commonly used for smelting iron alloy (see iron alloy electric furnace), smelting ice nickel, copper ice (see nickel, copper), and producing calcium carbide (Calcium carbide), etc.

Vacuum arc furnace

Is an electric furnace that directly heats and smelts metal in an evacuated furnace body with an electric arc. 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, direct current is generally supplied. According to the melting characteristics, it is divided into metal remelting furnace and casting furnace. According to whether the electrode is consumed (melted) in the smelting process, it is divided into consumable furnaces and non-consumable furnaces. Most of the industrial applications are consumable furnaces. Vacuum arc furnace is used to melt special steel, active and refractory metals such as titanium, molybdenum, niobium (see vacuum metallurgy).

Arc electric heating can be regarded as arc resistance electric heating. Arc (arc resistance) stability is a necessary condition for normal furnace production. AC arc furnaces usually use power frequency power. To stabilize the arc, the furnace power supply circuit must have appropriate inductance, but the presence of inductance will reduce the power factor and electrical efficiency. Reducing the current frequency is the way to develop AC arc furnaces. 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 furnace short network should be as small as possible to avoid excessive circuit losses. For the 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 a working gas is ionized to heat or melt. Devices that generate plasma are usually called plasma guns, and there are two types of arc plasma guns and high-frequency induction plasma guns. The working gas is passed into the plasma gun. The gun has a device that generates an arc or a high-frequency (5-20 MHz) electric field. The working gas is ionized after the action and generates a plasma composed of electrons, positive ions, and 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 the general arc. The most commonly used working gas is argon, which is a monoatomic gas, easy to ionize, and an inert gas, which can protect the material. The working temperature can be as high as 20000 □; used for melting special steel, titanium and titanium alloy, superconducting materials, etc. Furnace types include a water-cooled copper crystallizer furnace, a hollow cathode furnace, a plasma furnace equipped with induction heating, and a plasma furnace with refractory lining (see Plasma Metallurgy).

Electron beam furnace

An electric furnace heated and melted by bombarding the material with high-speed electrons (Figure 4 electron beam furnace schematic). In the vacuum furnace shell, the cathode is heated with a low-voltage electric filament to emit electrons. The electron beam is accelerated by the high-voltage electric field of the accelerated anode, bombards the metal material located on the anode, and converts the electrical energy into heat. Because the electron beam can be highly dense through the electromagnetic focusing device, it can generate a high temperature in the area where the material is bombarded. The electron beam furnace is used to melt special steel, refractory and active metals.ndustrial electric furnaces are classified into two categories: periodic operation furnaces and continuous operation furnaces.

Periodic operation furnace is divided into: box furnace, sealed box furnace, pit furnace, bell jar furnace, trolley furnace, dumping roller furnace.

Continuous operation furnace is divided into: kiln car furnace, push rod furnace, roller hearth furnace, vibrating hearth furnace, rotary hearth furnace, walking furnace, traction furnace, continuous drum furnace, conveyor belt furnace and so on. The conveyor belt furnace can be divided into: mesh belt furnace, stamping chain plate furnace, casting chain plate furnace and so on. ..

Electric stove

Electric furnace

The electric heating furnace can use metal heating elements or non-metallic heating elements to generate heat sources. 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 electric heating wire (most common, up to 1200℃), Mo-Si alloy and W, Mo and other pure metals; non-metallic heating elements include SiC (most common, can be heated up to 1600 ℃ ), LaCrO3 and graphite rod (can be heated to 2000 ℃ under vacuum or protective atmosphere).

1. The advantages of electric furnace

1) Compared with fuel furnace, it is easy to get high temperature.

2) It can be heated from the inside of the material to increase its temperature.

3) Easy to use in controlled atmosphere furnace and vacuum furnace.

4) The electric furnace does not have the heat loss of exhaust gas from the fuel furnace, so the thermal efficiency is high.

5) Easy to control temperature, convenient for remote control and fine adjustment.

6) Fast heating is possible.

7) Good operation performance and no pollution to the environment.

2. The shortcomings of the electric furnace

1) Need to increase the cost of power distribution equipment.

2) High electricity cost.

3) When the resistance heating temperature exceeds 1000 °C, the refractory material may conduct electricity, and attention must be paid to the insulation problem.

The main types of electric furnace

One. Industrial furnace

Industrial furnace: divided into electric furnace and combustion furnace (in a narrow sense, industrial furnace refers to combustion furnace)wo. main productsSeven categories: resistance furnace, induction furnace, vacuum furnace, electron beam furnace, heat treatment (or melting) unit, heat treatment auxiliary equipment, combustion furnace.

three. Resistance furnace: three major components: heater, furnace lining, heat-resistant components

1. Divided into two types of periodic and continuous

2. Characteristics of periodic furnace:

A. Charges are added and taken out at the same time

B. The furnace material is basically fixed during heating (except for special cases: such as drum furnace and roller hearth furnace)

C. Strive for uniform temperature in the work area

3. Classification of periodic resistance furnace

A. Box furnace

B. Trolley furnace (divided into self-propelled and traction), used for annealing, the workpiece cools with the furnace after heating

C. Pit furnace

D. Hood furnace (mainly used for annealing, heating hood can be moved)

E. Bottom-lift hood furnace (fixed hood, lifting base, suitable for large furnaces)

F. Rotary hearth furnace

G. Sealed box furnace (also known as multi-purpose furnace, which can carry out heat treatment processes such as carburization, smooth quenching, carbonitriding, etc .. It is heated by a radiant tube, which is a resistance wire fixed by a refractory ceramic disc and mounted in a sealed heat-resistant steel pipe In this structure, the atmosphere in the furnace will not affect the heating element)

4. Continuous resistance furnace

A. Push furnace

B. Conveyor furnace

C. Mesh belt furnace (suitable for annealing, sintering, brazing and solution treatment of thin and small parts. The structure is similar to conveyor belt furnace)

D. Continuous rotary furnace (drum furnace)

E. Roller hearth furnace (the tray moves on the roller)

F. Rotary hearth furnace

Electric furnace transformer Electric furnace transformer is a transformer designed to provide power for various electric furnaces. Industrial electric furnace transformers can be roughly divided into three categories: resistance furnace transformers, electric arc furnace transformers and induction furnace transformers.

Resistance furnace transformers are used in resistance furnaces and salt bath furnaces for heating, heat treatment, powder metallurgy sintering, non-ferrous metal melting, etc. of mechanical parts. Due to the electricity of its heating element.