Various electric furnace knowledge summary

Electric Furnace

　　Electric furnace is a heating furnace that converts the electric energy in the furnace into heat to heat the workpiece. Compared with the fuel furnace, the advantages of electric furnace include: the atmosphere in the furnace is easy to control, and it can even be pumped into vacuum; the material is heated up quickly, the heating temperature is high, and the temperature is easy to control.

Advantages

　　Electric furnace is the heating furnace which converts the electric energy in the furnace into heat to heat the workpiece, compared with the fuel furnace, the advantages of electric furnace are: the atmosphere in the furnace is easy to control, even can be pumped into a vacuum; the material is heated quickly, the heating temperature is high, the temperature is easy to control; the production process is easy to realize the mechanization and automation; the labor hygiene conditions are good; the thermal efficiency is high; the quality of the product is good; and more environmentally friendly to the environmental problems that are becoming more and more serious. It is a good product for the increasingly serious environmental problems. Metallurgical industry electric furnace is mainly used for iron and steel, ferroalloys, non-ferrous metals, such as melting, heating and heat treatment. 19th century the end of the emergence of industrial-scale electric furnaces, since the 1950s, due to the growth of demand for high-level metallurgical products and the cost of electricity with the development of the power industry and the decline in the ratio of electric furnaces in the metallurgical furnace equipment increased year by year. Electric furnace can be divided into resistance furnace, induction furnace, electric arc furnace, plasma furnace, electron beam furnace and so on.

Types

　　Resistance Furnace

　　Resistance Furnace is an electric furnace that uses the Joule heat generated by passing electric current through a conductor as a heat source. According to the way of generating electric heat, resistance furnace is divided into direct heating and indirect heating. In the direct heating resistance furnace, the electric current passes through the material directly, because the electric heating power is concentrated in the material itself, so the material is heated very quickly, and it is suitable for the process that requires rapid heating, such as the heating of forging billet. This kind of resistance furnace can heat the material to a very high temperature, such as graphitization of carbon materials electric furnace, can heat the material to more than 2500 ℃. Direct heating resistance furnace can be made into a vacuum resistance heating furnace or through the protective gas resistance heating furnace, in powder metallurgy, commonly used in sintering tungsten, tantalum, niobium and other products. The use of this furnace heating should be noted:

　　① In order to make the material heated uniformly, the conductive cross-section and conductivity of each part of the material is required to be consistent;

　　Industrial resistance furnace

　　② due to the material's own resistance is quite small, in order to achieve the required electric power, the working current is quite large, so feed the electrode and material contact to be good, so as not to start the arc burn material, and feed the resistance of the bus bar to be small, in order to reduce the loss of the circuit; most of the resistance furnace is indirectly heated resistor furnace, which is equipped with a special used to realize the electrical - thermal transformation of the resistor body, known as the electro-thermal body, which transfers thermal energy to the furnace material.

　　The furnace shell is made of steel plate, and the furnace chamber is lined with refractory materials such as ceramic fiber, and the materials are placed inside.

The most commonly used electric heaters are ferrochromium-aluminum electric heaters, nickel-chromium electric heaters, silicon carbide rods and molybdenum disilicide rods, silicon-carbon rods, and zirconium diboride ceramic composite heaters. According to the need, the furnace atmosphere can be ordinary atmosphere, protective atmosphere or vacuum. General power supply voltage 220 V or 380 V, if necessary, equipped with adjustable voltage intermediate transformer. Small furnaces (<10 kW) single-phase power supply, large furnaces three-phase power supply. For a single species, the batch size of materials, it is appropriate to use a continuous furnace heating. Furnace temperature below 700 □ resistance furnace, most of the device blower, in order to strengthen the furnace heat transfer, to ensure uniform heating. Used for melting fusible metals (lead, lead-bismuth alloy, aluminum and magnesium and its alloys, etc.) of the resistance furnace, can be made into a crucible furnace; or made into a reflecting furnace with a melting pool, installed on the top of the furnace with an electric heater. Electroslag furnaces are resistance furnaces in which the electrothermal transformation is realized by a dissolved slag (see Electroslag Remelting).

　　Induction Furnace

　　Induction furnace introduction to use the material of the induction of electric heat effect and make the material heating or melting of the electric furnace. The basic part of the induction furnace is the induction loop wound with copper tubing. Induction loop on both sides of the AC voltage, generating alternating electromagnetic field, conductive materials placed in the induction loop, due to electromagnetic induction in the material to produce eddy currents, by the role of resistance and electrical energy into heat to heat the material; therefore, can also be considered as induction heating is a direct heating type of resistance heating.

　　Induction heating is characterized by the transformation of the heated material in the electric power (current distribution) is very uneven, the surface of the largest, the center of the smallest, known as the skin effect. In order to improve the thermal efficiency of induction heating, the power supply frequency should be appropriate, small melting furnace or surface heating of materials using high-frequency electricity, large melting furnace or deep penetration of the material heating using intermediate-frequency or industrial-frequency electricity. Induction loop is a fairly large inductance load, its power factor is generally very low. In order to improve the power factor, the induction loop is generally connected in parallel with medium-frequency or high-frequency capacitors, known as resonant capacitance. The gap between the induction loop and the material should be small, the induction loop should be made of square copper tube, the tube is cooled by water, the gap between the turns of the induction loop should be as small as possible, and the insulation should be good. Induction heating device, mainly used for heating and melting casting of steel, copper, aluminum and zinc, etc., fast heating, less burnout, high degree of mechanization and automation, suitable for configuration in the automatic operating line.

　　Induction furnace series heating furnace features

　　Fast heating speed, high production efficiency, less oxidization and decarburization, saving material and mold cost.

　　Because the principle of medium frequency induction heating is electromagnetic induction, the heat is generated in the workpiece itself, the ordinary workers can carry out the continuous work of forging task after ten minutes of working with the medium frequency electric furnace, and there is no need to burn the furnace professional workers to burn the furnace and seal the furnace work in advance. There is no need to worry about the waste phenomenon caused by power failure or equipment failure of the coal furnace has been heated billet. Because of the heating method of heating speed, so the oxidation is very little, each ton of forgings and burning coal furnace compared to save at least 20-50 kg of steel raw materials, the material utilization rate of up to 95%. Because of the heating mode heating uniformity, core surface temperature difference is very small, so in the forging also greatly increase the life of the forging die, the roughness of the surface of the forgings is less than 50um.

Superior working environment, improve the labor environment of workers and the company's image, no pollution, low energy consumption

　　Induction heating furnace and coal furnace, compared with the workers will not be subjected to the hot sun under the coal furnace baking and smoke, but also to meet the requirements of the environmental protection department of the indicators, and at the same time to establish the company's external image and the future development trend of the forging industry. Induction heating is the most energy-saving heating in the electric heating furnace from room temperature to 1100 ℃ tons of forgings consume less than 360 degrees.

Uniform heating, very small temperature difference between the core and the surface, high precision temperature control

　　Induction heating furnace has a small size, light weight, high efficiency, excellent thermal processing quality and favorable environment and other advantages are rapidly eliminating coal-fired furnace, gas furnace, fuel furnace and ordinary resistance furnace, is a new generation of metal heating equipment.

　　Industrial applications of induction melting furnace crucible furnace (coreless induction furnace) and melting ditch furnace (core induction furnace), see Figure 2 induction furnace furnace structure schematic. The crucible is made of refractory material or steel, with a capacity from a few kilograms to tens of tons. The melting is characterized by the crucible melt by the electric force, forcing the melt pool liquid surface raised, the melt from the liquid surface center flow to the surrounding area and cause the circulation flow. This phenomenon is called electric effect, can make the melt composition uniform, the disadvantage is that the slag is biased toward the periphery, poor coverage. Compared with the melting ditch furnace, crucible furnace operation flexibility, high melting temperature, but the power factor is low, high power consumption. Melting groove furnace inductor by the iron core, induction ring and melting groove furnace lining composition, the melting groove for one or two band ring ditch, which is full of melts and melting pool connected to the melt. In principle, the groove furnace can be regarded as the secondary only one turn coil and short-circuit core transformer. The induced current flows in the melt in the trench, which realizes the electro-thermal transformation.

　　In production, after each furnace metal melting is completed, the melt pool can not be emptied, otherwise it will be easy to dry out, and must retain a part of the melt as the next furnace starting melt. Melting ditch temperature is higher than the melt pool, but also to withstand the melt flow scouring, so the melting ditch furnace lining is easily damaged, in order to facilitate maintenance, the modern furnace inductor made of easy-to-replace fittings. Melting ditch furnace capacity from a few hundred kilograms to more than a hundred tons. Melting ditch furnace for industrial frequency electricity, due to the iron core made of silicon steel sheet for the magnetic flux path, electrical efficiency and power factor are very high. Melting ditch furnace is mainly used for cast iron, copper, zinc, brass and other melting, but also as a mixing Shanghai, used to store and heat the melt.

　　Electric arc furnace

　　The use of electric arc heat effect melting metal and other materials of the electric furnace (Figure 3 electric arc furnace type). According to the heating method is divided into three types: ① indirect heating arc furnace. Arc generated between the two electrodes, without contacting the material, relying on thermal radiation to heat the material. This kind of furnace noise, low efficiency, gradually eliminated. ② direct heating arc furnace. Arc generated between the electrode and the material, direct heating of the material; steelmaking three-phase arc furnace is the most commonly used direct heating arc furnace (see arc furnace steelmaking). ③ submerged arc furnace, also known as reduction furnace or mineral heat furnace. One end of the electrode is buried in the material layer, forming an electric arc in the material layer and using the material layer's own resistance to heat the material; commonly used in smelting ferroalloys (see ferroalloy furnace)

　　Vacuum electric arc furnace

　　Vacuum electric arc furnace is an electric furnace that uses electric arc to heat the molten metal directly in the vacuum furnace body. Furnace gas thin, mainly by the molten metal vapor arc, in order to stabilize the arc, generally for direct current. According to the melting characteristics, divided into metal remelting furnace and casting furnace. According to the melting process whether the electrode consumption (melting), divided into self-consumption furnace and non-self-consumption furnace, most of the industrial applications are self-consumption furnace. Vacuum arc furnaces are used for melting special steels, active and refractory metals such as titanium, molybdenum and niobium (see vacuum metallurgy).

　　Electric arc heating can be thought of as arc resistance heating. Stabilization of the electric arc (arc resistance) is necessary for normal furnace production. AC arc furnaces usually use industrial frequency electricity, in order to stabilize the arc, the furnace power supply circuit to have the appropriate inductive resistance, but the presence of inductive resistance will reduce the power factor and electrical efficiency. Reduce the current frequency is the way to develop the AC arc furnace. Arc resistance resistance value is quite small, in order to obtain the necessary heat, the furnace requires a fairly large operating current, so the resistance of the furnace short network should be as small as possible, so as to avoid excessive circuit losses. For three-phase arc furnace, to make the three-phase impedance close to the same, so as not to unbalance the three-phase load.

Plasma Furnace

　　An electric furnace that uses plasma generated when the working gas is ionized for heating or melting. The device that generates the plasma is usually called a plasma gun, and there are two types of plasma guns: arc plasma guns and high-frequency induction plasma guns. The working gas into the plasma gun, the gun has an electric arc or high-frequency (5 to 20 MHz) electric field device, the working gas is ionized by the action, generated by the electrons, positive ions, and gas atoms and molecules mixed plasma. Plasma from the plasma gun nozzle, the formation of high-speed high-temperature plasma arc flame, the temperature is much higher than the general arc. The most commonly used working gas is argon, which is a monoatomic gas that is easily ionized and an inert gas that protects materials. The working temperature can be as high as 20000□; it is used for melting special steel, titanium and titanium alloy, superconducting materials and so on. Furnace types include water-cooled copper crystallizer furnaces, hollow cathode furnaces, plasma furnaces with induction heating, and plasma furnaces with refractory linings (see Plasma Metallurgy).

　　Electron beam furnace

　　Electron beam furnace with high-speed electron bombardment of the material to heat the melting of the electric furnace (Figure 4 electron beam furnace schematic). In the vacuum furnace shell, with a low voltage electric filament heating cathode, so that the emission of electrons, electron beams accelerated by the accelerating anode of the high-voltage electric field and accelerated movement, bombardment of metal materials located in the anode, so that the electrical energy into thermal energy. Because the electron beam can be highly concentrated by electromagnetic focusing device, so the material can be bombarded in the part of the high temperature. Electron beam furnaces are used for melting special steel, refractory and active metals.

　　Electric furnaces for industrial use are categorized into two types: cyclic operation furnaces and continuous operation furnaces.

　　Periodic operation furnace is divided into: box furnace, sealed box furnace, pit-type furnace, bell-type furnace, cart furnace, dumping drum furnace.

　　Continuous operation of the furnace is divided into: kiln car furnace, pusher furnace, roller furnace, vibration bottom furnace, rotary furnace, step furnace, traction furnace, continuous roller 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, etc. ...

　　Electric Furnace

　　Electric furnace can use metal heaters or non-metallic heaters to generate heat source, its simple structure, very wide range of uses is its main feature, can be widely used in annealing, normalizing, quenching, tempering, carburizing and carburizing nitriding, and so on. The main metal heaters include Ni-Cr electric hot wire (the most common, up to 1200 ℃), Mo-Si alloy and W, Mo and other pure metals; non-metallic heaters include SiC (the most common, up to 1600 ℃), LaCrO3 and graphite rods (vacuum or protective atmosphere can be heated to 2000 ℃).

　　Advantages:

　　1) Easily obtain high temperatures compared to fuel furnaces.

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

　　(3) Easy to use in controlled atmosphere furnaces and vacuum furnaces.

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

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

　　6） It can be heated quickly.

　　7） It has good operation performance and does not pollute the environment.

Disadvantages:

　　1) Requires additional distribution equipment costs.

　　2) High cost of electricity.

　　3) When the resistance heating temperature exceeds 1000 ℃, the refractory material may conduct electricity, need to pay attention to the insulation problem.

Development

　　In 2010, China's manufacturing sector accounted for 19.8% of global manufacturing output, slightly higher than the United States' 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 industry. According to the National Bureau of Statistics data statistics, in 2010 the national oven, furnace and electric furnace manufacturing industry above-scale enterprises increased to 308, realizing industrial output value of 16.288 billion yuan, an increase of 30.79%; to achieve sales revenue of 16.387 billion yuan, an increase of 32.63%; to achieve total profits of 1.043 billion yuan, an increase of 79.17%.

　　Automobile, tractor industry 70% -80% of the parts need to heat treatment processing, tools, cutting tools and bearing products are 100% need for heat treatment, some civil light metal products, the vast majority of the service life, also rely on heat treatment to improve. At the same time, the fastener industry, bearing industry, chain industry, tooling industry, automotive, tractor, motorcycle parts and components industry are relying on the improvement of the quality of heat treatment to enhance the competitive strength of the industry, with the continuous development of China's industry, within the past decade, China's annual addition of 400,000-500,000 tons of thermal processing, in addition to the majority of the domestic oven, furnace, furnace and furnace equipment is old and backward, will tend to phase out the update, China's demand for heat treatment equipment is very strong, and the heat treatment equipment is very strong. The demand for thermal processing equipment is very strong, the development of China's ovens, furnaces and electric furnaces is promising.

Extension method

　　In order to protect and extend the use of electric furnaces, must pay attention to the following matters:

　　(1) Regularly check whether the connection of each connector of the electric furnace and controller is good.

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

　　(3) The controller is limited to 0-50 ℃ ambient temperature.

 　   (4) furnace and controller use, shall not exceed the rated power, furnace temperature shall not exceed the maximum operating temperature, prohibit the wet workpiece loaded into the furnace chamber, containing ultra-high moisture heated workpiece should be pre-drying.

　　(5) Keep the inside of the furnace chamber clean, the furnace metal oxides, slag and impurities should be removed in a timely manner, loading and unloading of workpieces should be careful.

Types of Furnaces

　　Industrial Furnace

　　Industrial furnace: divided into electric furnaces and combustion furnaces (the narrow sense of the industrial furnace refers to combustion furnaces)

　　The main products of seven 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, lining, heat-resistant components

　　1. Divided into two categories of cyclic and continuous

　　2. The characteristics of the periodic furnace:

　　A. Charge at the same time to join the same time to take out

　　B. Heating the charge is basically immobile (except for special circumstances: such as drum furnace, roller-hearth furnace)

　　C. Strive for uniform temperature in the working area

Classification of resistance furnace

　　Bogie Furnace Sintering Furnace Tempering Furnace Annealing Furnace Solid Fusion Furnace Hardening Furnace Carburizing Furnace Nitriding Furnace Smelting Furnace Brazing Furnace Salt Bath Furnace Roller Barrel Furnace Mesh Belt Furnace Vacuum Furnace Laboratory Furnace Medium and High Frequency Furnace Drying Furnace Covered Furnace Pusher Furnace Casting Furnace Fuel Furnace Kiln Furnace Ammonia Breakdown Furnace Glass Furnace

　　Continuous Resistance Furnaces

　　A. Pusher Type Furnaces

　　B. Conveyor Furnaces

　　C. Mesh Belt Furnaces (for annealing, sintering, brazing and solution treatment of thin and small parts. Structure similar to conveyor belt furnace)

　　D. Continuous rotary furnace

　　E. Roller-hearth furnace (material disk moving on rollers)

Structure

　　The whole set of electric furnace equipment contains medium frequency power cabinet, compensation capacitor, furnace body (two) and water-cooled cable, reducer. Furnace body consists of four parts: furnace shell, induction coil, furnace lining, tilting furnace gearbox, etc. Furnace shell is made of non-magnetic material, induction coil is a spiral cylinder made of rectangular hollow tube, and cooling water is passed inside the tube during melting. The coil leads to the copper row and water-cooled cable connection, the furnace lining is close to the induction coil, made of quartz sand compacted and sintered, the tilting of the furnace body by the tilting furnace gearbox direct rotation. Tilting furnace gearbox is a two-stage turbine speed, self-locking performance, smooth and reliable rotation, emergency power failure to see the collector tilting furnace, to avoid danger. The control of the motor of the tilting gearbox of the two furnaces can be selected through the furnace selector switch, and the switch box with four-core rubber wires enables the operator to stand in a suitable position for the tilting and resetting of the furnace to carry out the pointing control.

Operation regulations

　　1, the operator must understand the following points:

　　A, the structure and performance of the furnace and its auxiliary equipment.

　　B, distribution system, control system layout and the location of safety devices, etc..

　　C、Operating process and safety operation regulations.

　　2、Pre-operation preparation check

　　A. Whether the power supply of the equipment is normal or not, whether there is any broken phase, short circuit or bare wire, etc..

　　B. Check whether the contact at the grounding device wiring is good.

　　C, check whether there is damage to the heating element, whether the contact of the connection is good, and whether there is contact with the furnace body and shell.

　　D, check the temperature control system for irregularities.

　　E, check the furnace door lift, cart in and out of normal operation.

　　3、Workpieces with corrosive, volatile and explosive gases are strictly prohibited to enter the furnace body for processing, so as not to affect the service life of the heating element and refractory materials and cause explosions and other accidents.

　　4、The electric furnace shall not run over temperature, otherwise it will shorten the service life of the equipment.

　　5、Workpieces are stacked evenly and should be about 100-150mm away from the heating element.

　　6, too much oxidized skin of the workpiece into the furnace before the need to remove, available wire brush brush down.

　　7, barbaric operation is strictly prohibited, the workpiece should be placed lightly to avoid impact.

　　8, the use of electric furnace operators shall not leave their posts without authorization, must always pay attention to the working condition of the furnace is normal.

　　9, the electric furnace in the loading and unloading of the workpiece, you must first cut off the power supply of the heating element to ensure the safety of the operator.

　　10, the oxides of the furnace chamber (including under the wire of the electric furnace) should be frequently cleaned up, at least once a week or five times a furnace. Under the furnace floor can be compressed air blow.

       11、Resistance wire, such as after use, shall not be collision folding, in order to avoid breakage.

　　12, electric furnace motor need to be regularly checked, add lubricants, etc., pay attention to the use of safety.

　　13、Regularly check the use of heating elements. Heating element after short-term use will not be folded, collision. If not yet serious corrosion and break, can be used with the same material (or wire itself) as a welding rod, using acetylene gas for heating and welding, welding rod using 50% white cloud powder mixture, if the heating element can not be used in serious corrosion, it should be replaced.

　　14, regular calibration of the meter, thermocouple deviation, to prevent the meter, thermocouple error caused by the temperature measurement is not correct and affect product quality.