Basic knowledge of electric furnace

Electric furnace is a heating furnace that converts electric energy in the furnace into heat to heat the workpiece. What else do you know about electric furnaces? The following is the basic knowledge of electric furnace that I have compiled for your reference and understanding. I hope you like it!

First, the advantages of electric furnace

Electric furnace is a heating furnace that converts electric energy in the furnace into heat to heat the workpiece. Compared with the oil-burning furnace, the advantages of electric furnace are: the atmosphere in the furnace is easy to control, and even vacuum can be pumped; The material is heated quickly, the heating temperature is high, and the temperature is easy to control; The production process is easy to realize mechanization and automation; Good labor hygiene conditions; High thermal efficiency; Good product quality; But also more environmentally friendly, and is a good product for the increasingly serious environmental problems. In metallurgical industry, electric furnaces are mainly used for smelting, heating and heat treatment of steel, ferroalloy and nonferrous metals. At the end of 19, an industrial-scale electric furnace appeared. Since 1950s, with the development of electric power industry, the demand for advanced metallurgical products has increased, the electricity bill has decreased, and the proportion of electric furnace in metallurgical furnace equipment has increased year by year. Electric furnaces can be divided into resistance furnaces, induction furnaces, arc furnaces, plasma furnaces and electron beam furnaces.

Secondly, the types of electric furnaces are introduced.

electric resistance furnace

An electric furnace in which current passes through a conductor to generate Joule heat as a heat source. According to the electric heating mode, resistance furnaces are divided into direct heating and indirect heating. In a directly heated resistance furnace, the current passes directly through the material. Because the electric heating power is concentrated in the material itself, the material is heated quickly, and it is suitable for processes that need rapid heating, such as the heating of forging blanks. This kind of resistance furnace can heat the material to a very high temperature, such as graphitization electric furnace of carbon material, which can heat the material to above 2500℃. Directly heated resistance furnace can be made into vacuum resistance heating furnace or shielding gas resistance heating furnace, which is often used to sinter tungsten, tantalum, niobium and other products in powder metallurgy. Attention should be paid to when heating with this furnace:

(1) In order to heat the material evenly, it is required that the conductive cross section and conductivity of each part of the material are consistent;

Industrial resistance furnace

(2) Because 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 contact between the transmission electrode and the material is better, avoiding arcing and burning the material, and the resistance of the transmission bus is small, thus reducing the circuit loss; Resistance furnaces are mostly indirect heating resistance furnaces, which are equipped with resistors specially used to realize electrothermal conversion, called electrothermal bodies, and transfer heat energy to materials in the furnace.

The shell of this electric furnace is made of steel plate, and the hearth is lined with refractory materials such as ceramic fibers, and the materials are placed inside.

The most commonly used electric heaters are iron-chromium-aluminum electric heaters, nickel-chromium electric heaters, silicon carbide rods and molybdenum disilicide rods, silicon carbide rods and zirconium diboride ceramic composite heaters. According to requirements, the atmosphere in the furnace can be ordinary atmosphere, protective atmosphere or vacuum. The general power supply voltage is 220 volts or 380 volts, and an intermediate transformer with adjustable voltage is provided when necessary. Small furnace (

Induction furnace

Introduction of induction furnace An electric furnace that heats or melts materials by using the inductive electrothermal effect of materials. The basic component of induction furnace is induction coil wound with copper tube. An AC 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 eddy current is generated in the material due to electromagnetic induction, which is converted into heat energy through resistance to heat the material. Therefore, induction heating can also be considered as a kind of direct heating resistance heating.

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 skin effect. In order to improve the electric heating efficiency of induction heating, the power frequency should be appropriate. Small melting furnaces use high frequency electricity to heat the surface of materials, while large melting furnaces use medium frequency or power frequency electricity to heat the materials deeply. Induction coil is a load with considerable inductance, and its power factor is generally very low. In order to improve the power factor, induction coils are generally connected in parallel with intermediate frequency or high frequency capacitors, which are called resonant capacitors. The gap between the induction coil and the material should be small. The induction coil should be made of square copper tube, and the tube should be cooled with water. The turn-to-turn gap of induction coil should be as small as possible and the insulation should be good. Induction heating device, mainly used for heating and casting steel, copper, aluminum and zinc, has the advantages of fast heating speed, less burning loss, high mechanization and automation, and is suitable for automatic production lines.

Characteristics of induction furnace series heating furnace

Fast heating speed, high production efficiency, less oxidation and decarbonization, saving materials and forging die costs.

Because the principle of medium frequency induction heating is electromagnetic induction, and its heat is generated in the workpiece itself, ordinary workers can continue forging tasks ten minutes after they go to work with the medium frequency electric furnace, without the need for professional furnace burners to seal the furnace in advance. Don't worry about the waste of heating blanks caused by power failure or equipment failure. Because of this heating method, the temperature rises rapidly, and there is little oxidation. Compared with coal-fired furnaces, each ton of forgings saves at least 20-50 kilograms of steel raw materials, and the material utilization rate can reach 95%. Because this heating method is uniform and the temperature difference between the core and the surface is extremely small, the life of the forging die is greatly prolonged during forging, and the roughness of the forging surface is less than 50um.

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

Compared with the coal stove, the induction heating furnace will not be smoked by the coal stove in the scorching sun, and it can meet the requirements of the environmental protection department, and at the same time establish the external image of the company and the future development trend of the forging industry. Induction heating is the most energy-saving heating method in electric heating furnace, and the power consumption per ton of forgings is less than 360 degrees when heated from room temperature to 1 100℃.

Uniform heating, minimal temperature difference between the core and the surface, and high temperature control accuracy.

Induction heating furnace has the advantages of small volume, light weight, high efficiency, good hot working quality and environmental friendliness. It is rapidly replacing coal-fired furnaces, gas-fired furnaces, oil-fired furnaces and ordinary resistance furnaces, and is a new generation of metal heating equipment.

Industrial induction melting furnaces include crucible furnace (coreless induction furnace) and trough furnace (cored induction furnace), as shown in Figure 2. Crucibles are made of refractory materials or steel, and the capacity varies from several kilograms to dozens of tons. Its melting characteristic is that the melt in the crucible is subjected to electrodynamics, which forces the liquid level of the molten pool to rise, and the melt flows around from the center of the liquid level, resulting in circulation. This phenomenon is called electrodynamic effect, which can make the melt composition uniform, but the disadvantage is that the slag is biased to the periphery and the coverage is poor. Compared with trough furnace, crucible furnace has flexible operation and high melting temperature, but low power factor and high power consumption. The inductor of trough smelting furnace consists of iron core, induction coil and trough lining. The trough is one or two belt-shaped annular troughs, and the melt communicated with the molten pool is filled in the trough. In principle, the trough smelting furnace can be regarded as an iron core transformer with only one turn of coil in secondary short circuit. The induced current flows in the melt channel to realize electrothermal transformation.

In production, after each heat of metal smelting, the molten pool should not be emptied, otherwise it will easily dry up, and a part of the melt must be reserved as the initial melt of the next heat. The temperature of the melting tank is higher than that of the molten pool, and at the same time it is eroded by the melt flow, so the inner lining of the melting tank is easy to be damaged. In order to facilitate maintenance, the inductor of modern furnace is made into an easily replaceable component. The capacity of trough smelting furnace ranges from several hundred kilograms to more than one hundred tons. Power frequency power is provided by melting tank furnace. Because the iron core made of silicon steel sheet is used as the magnetic circuit, the electric efficiency and power factor are very high. The trough smelting furnace is mainly used for smelting cast iron, copper, zinc, brass and so on. It can also be used as a mixed melting pot to store and heat the melt.

electric arc furnace

An electric furnace that uses the thermal effect of electric arc to melt metals and other materials (Figure 3 Arc furnace type). According to the heating mode, it can be divided into three types: ① indirect heating electric arc furnace. An arc is generated between two electrodes, and the material is heated by thermal radiation without contact. This kind of stove is noisy and inefficient, and it is gradually being eliminated. ② Direct-heated electric arc furnace. An arc is generated between the electrode and the material, which directly heats the material; Three-phase EAF is the most commonly used direct heating EAF (see EAF steelmaking). ③ Submerged arc furnace, also known as reduction furnace or submerged arc furnace. One end of the electrode is buried in the material layer to form an arc in the material layer, and the material is heated by the resistance of the material layer itself; Commonly used for smelting ferroalloy (see ferroalloy electric furnace)

vacuum arc furnace

It is an electric furnace in which molten metal is directly heated by electric arc in a vacuum furnace. The gas in the furnace is thin, and the arc is mainly generated by the vapor of molten metal. In order to stabilize the arc, direct current is usually 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 can be divided into consumable furnaces and non-consumable furnaces, and most of them are consumable furnaces in industry. Vacuum arc furnace is used to smelt special steel, active and refractory metals, such as titanium, molybdenum and niobium (see vacuum metallurgy).

Arc electric heating can be considered as arc resistance electric heating. The stability of arc (arc resistance) is a necessary condition for the normal production of the furnace. AC arc furnaces usually use power frequency electricity. In order to stabilize the arc, there should be proper inductance in the power supply circuit of the furnace, but the existence of inductance will reduce the power factor and electrical efficiency. Reducing current frequency is the development direction of AC arc furnace. The resistance of arc resistance is quite small. In order to obtain the necessary heat, the furnace needs a considerable working current, so the resistance of the short network of the furnace should be as small as possible to avoid excessive circuit loss. For three-phase EAF, the three-phase impedance should be close to the same, so as to avoid unbalanced three-phase load.

Plasma heating furnace

An electric furnace that is heated or smelted by the plasma generated when the working gas is ionized. Devices that generate plasma are usually called plasma guns, including arc plasma guns and high-frequency induction plasma guns. The working gas is introduced into a plasma gun, which is equipped with a device for generating an arc or a high-frequency (5-20 MHz) electric field. The working gas is ionized after being acted, and a plasma composed of a mixture of electrons, positive ions and gas atoms and molecules is generated. 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 the general arc. The most commonly used working gas is argon, which is a monatomic gas, easy to ionize and an inert gas, which can protect materials. The working temperature can be as high as 20000□; Used for smelting special steel, titanium and titanium alloys, superconducting materials, etc. Furnace types include water-cooled copper crystallizer, hollow cathode furnace, induction heating plasma furnace and refractory lining plasma furnace (see plasma metallurgy).

Electron beam furnace

An electric furnace that bombards materials with high-speed electrons to heat and melt them (as shown in Figure 4, an electron beam furnace). In the vacuum furnace shell, the cathode is electrically heated by a filament with low voltage to emit electrons. The electron beam is accelerated by the high-voltage electric field of the accelerating anode, bombarding the metal material at the anode, and converting electric energy into heat energy. Because the electron beam can pass through the high-density electromagnetic focusing device, high temperature can be generated at the bombarded part of the material. Electron beam furnaces are used to melt special steels, refractories and active metals.

Industrial electric furnaces are divided into two categories: periodic operation furnaces and continuous operation furnaces.

Cyclic operation furnaces are divided into box furnaces, sealed box furnaces, well furnaces, hood furnaces, trolley furnaces and tilting drum furnaces.

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

electric fire

Electric heating furnace can use metal heater or nonmetal heater to generate heat source. Its main features are simple structure and wide application. It can be widely used in annealing, normalizing, quenching, tempering, carburizing and nitriding. The main metal heating elements are nickel-chromium heating wire (the most common, the highest temperature is 1200℃), molybdenum-silicon alloy and pure metals such as W and Mo. Non-metallic heating elements include SiC (most commonly, which can be heated to 1600℃), LaCrO3 and graphite rod (which can be heated to 2000℃ in vacuum or protective atmosphere).

Advantages:

1) Compared with the oil-fired furnace, it is easy to have high temperature.

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

3) It is convenient to be used in controlled atmosphere furnace and vacuum furnace.

4) The electric furnace has no waste heat loss of the oil-burning furnace, and the thermal efficiency is high.

5) It is easy to control the temperature, which is convenient for remote control and fine adjustment.

6) It can be heated quickly.

7) Good operation performance and no environmental pollution.

Disadvantages:

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

2) High power cost.

3) When the resistance heating temperature exceeds 1000℃, the refractory may conduct electricity, so attention should be paid to insulation.

develop

In 20xx, China's manufacturing industry accounted for 19.8% of global manufacturing output, slightly higher than that of the United States, ranking first in the world. The rapid development of manufacturing industry in China has promoted the development of oven, furnace and electric furnace manufacturing industry in China. According to the statistics of the National Bureau of Statistics, in 20 10, the number of enterprises above designated size in oven, smelting furnace and electric furnace manufacturing increased to 308, achieving a total industrial output value of1628.8 billion yuan, a year-on-year increase of 30.79%; Realized sales income of 654.38+06.387 billion yuan, a year-on-year increase of 32.63%; The total profit was 654.38+0.43 billion yuan, a year-on-year increase of 79. 17%.

70%-80% parts in automobile and tractor industries need heat treatment, while 65,438+000% tools, cutters and bearing products need heat treatment. The service life of some civil light industrial metal products is mostly improved by heat treatment. At the same time, 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 competitive strength. With the continuous development of China's industry, China will add 400,000-500,000 tons of thermal processing capacity every year in the past decade. In addition, domestic ovens, stoves and electric furnaces are mostly outdated and backward, and there will be a trend of being eliminated and updated. The demand for thermal processing equipment in China is very strong, and ovens in China will be heated.

Extension method

In order to protect and prolong the service life of electric furnace, the following matters must be paid attention to:

(1) Regularly check whether the connection between the electric furnace and the controller is good.

(2) The electric furnace and controller must work in a place where the relative humidity does not exceed 85% and there are no conductive dust, explosive gas and corrosive gas that can damage metal insulation and electronic components.

(3) The working environment temperature of the controller is limited to 0-50℃.

(4) When the electric furnace and controller are used, they shall not exceed the rated power, and the furnace temperature shall not exceed the maximum use temperature. It is forbidden to load wet workpieces into the furnace, and the heated workpieces with ultra-high moisture should be dried in advance.

(5) Keep the furnace clean, remove metal oxides, slag and impurities in time, and be careful when loading and unloading workpieces.

Three, the classification of electric furnace

industrial furnace

Industrial furnace: divided into electric furnace and combustion furnace (industrial furnace in narrow sense refers to combustion furnace)

The main products are divided into seven categories: resistance furnace, induction furnace, vacuum furnace, electron beam furnace, heat treatment (or melting) unit, heat treatment auxiliary equipment and combustion furnace.

3. Resistance furnace: three parts: heater, furnace lining and heat-resistant parts.

1. can be divided into two categories: periodicity and continuity.

2. The characteristics of the cycle furnace:

A. simultaneously adding and taking out furnace charges

B. When heating, the charge is basically motionless (except in special circumstances, such as roller hearth furnace and roller hearth furnace).

C. strive for uniform temperature in the working area.

Four, the classification of resistance furnace

Trolley furnace sintering furnace tempering furnace annealing furnace solid furnace quenching furnace carburizing furnace normalizing furnace nitriding furnace melting furnace brazing furnace salt bath furnace roller furnace mesh belt furnace vacuum furnace experimental furnace high frequency furnace drying furnace bell furnace push rod furnace melting furnace fuel furnace ammonia decomposition furnace glass furnace.

Continuous resistance furnace

A. propulsion furnace

B. conveyor belt furnace

C mesh belt furnace (suitable for annealing, sintering, brazing and solution treatment of thin and small parts. Similar in structure to a conveyor belt furnace)

D. continuous rotary drum furnace

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

structure

The whole set of electric furnace equipment includes intermediate frequency power cabinet, compensation capacitor, furnace body (two sets), water-cooled cable and reducer. The furnace body consists of four parts: furnace shell, induction coil, furnace lining and tilting reducer. The furnace shell is made of non-magnetic material, and the induction coil is a spiral cylinder made of rectangular hollow tube, and cooling water is introduced into the tube during melting. The copper bar leading out the coil is communicated with the water-cooled cable, the furnace lining is close to the induction coil, and the induction coil is sintered by compacted quartz sand. The tilting of the furnace body is directly driven by the tilting gear box to rotate. The tilting gear box is a two-stage turbine with good self-locking performance and stable and reliable rotation. When there is an emergency power failure, it is necessary to stop working and tilt the furnace to avoid danger. The motor control of the tilting reduction box of two furnaces can be selected by furnace selection switch, and the switch box of four-core rubber wire can make the operator stand in a suitable position to control the tilting and reset of the furnaces.

Operation guide

1, the operator must know the following points:

First, the structure and performance of electric furnace and its auxiliary equipment.

B. Layout of power distribution system, control system and location of safety devices, etc.

C, operation process and safety operation procedures.

2, check the preparation work before operation

A, whether the power supply of the equipment is normal, whether there is phase failure, short circuit or bare wire, etc.

B, check whether the grounding device connection contact is good.

C, check whether the heating element is damaged, whether the joints are in good contact, and whether there is contact with the furnace body and shell.

D, check whether the temperature control system is abnormal.

E, check the oven door lifting, the car in and out of operation is normal.

3. It is forbidden to process workpieces with corrosive, volatile and explosive gases in the furnace, so as not to affect the service life of heating elements and refractories and cause accidents such as explosion.

4. The electric furnace can't run over temperature, otherwise it will shorten the service life of the equipment.

5. Workpieces should be stacked evenly, and the distance from the heating element is about100-150 mm. ..

6. Workpieces with too many scales need to be removed before entering the furnace, and can be brushed with a wire brush.

7, it is forbidden to barbaric operation, the workpiece should be put down gently, to avoid collision.

8. When using the electric furnace, the operator shall not leave his post without authorization, and must always pay attention to whether the working state of the electric furnace is normal.

9. When the electric furnace is loading and unloading workpieces, the power supply of the heating element must be cut off first to ensure the safety of the operators.

10, furnace oxide (including electric furnace wire) should be cleaned frequently, at least once a week or once every five furnaces. Compressed air can be blown into the bottom of the furnace.

1 1. If resistance wires are used, they should not collide and bend to avoid breaking.

12, the electric furnace motor should be checked regularly, lubricated, and pay attention to safety.

13, regularly check the use of heating elements. After short-term use, the heating element should not bend or collide. If it is not seriously corroded and broken, the same material as the electric furnace wire (or the electric furnace wire itself) can be used as covered electrode, and acetylene gas is used for heating and welding, and 50% white cloud powder is used in covered electrode. If the heating element is seriously corroded and cannot be used, it should be replaced separately.

14. Regularly check the deviation between the instrument and thermocouple to prevent the incorrect temperature measurement caused by the error between the instrument and thermocouple from affecting the product quality.

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