An industrial furnace is a thermal equipment that heats a material or a workpiece by using the heat of fuel combustion or electric energy in industrial production. Broadly speaking, the boiler is also an industrial furnace, but it is customarily not included in the scope of industrial furnaces.
The main components of the industrial furnace are: industrial furnace masonry, industrial furnace exhaust system, industrial furnace preheater and industrial furnace combustion device. There are many types of industrial furnaces used in the machinery industry. There are cupola furnaces, induction furnaces, resistance furnaces, electric arc furnaces, vacuum furnaces, open hearth furnaces, and crucible furnaces for smelting metals in foundries; sand-type drying ovens and iron alloys with baked sand types. Furnaces and casting annealing furnaces, etc.; in forging workshops, there are various heating furnaces for heating steel ingots or slabs before forging, and heat treatment furnaces for stress relief after forging; in the metal heat treatment workshop, there are various annealings to improve the mechanical properties of workpieces. Heat treatment furnaces for normalizing, normalizing, quenching and tempering; in welding workshops, preheating furnaces for welding parts and post-welding tempering furnaces; heating furnaces for sintering metals in powder metallurgy plants.
Industrial furnaces are also widely used in other industries such as metal melting furnaces, ore sintering furnaces and coke ovens in the metallurgical industry; distillation furnaces and cracking furnaces in the petroleum industry; generators in the gas industry; cement kiln and glass in the silicate industry. Glass annealing furnace; baking oven for food industry.
The creation and development of industrial furnaces play a very important role in human progress. In China, there have been relatively sophisticated copper furnaces in the Shang Dynasty. The furnace temperature reached 1200°C and the furnace inner diameter reached 0.8 meters. During the Spring and Autumn Period and the Warring States period, people further mastered the technique of raising the temperature of the furnace on the basis of the copper melting furnace, thereby producing cast iron.
In 1794, a straight cylindrical cupola melting cast iron appeared in the world. Then, in 1864, the Frenchman Martin used British Siemens's regenerative furnace principle to build a front-side steelmaking open hearth heated with gaseous fuel. He used a regenerator to preheat the air and gas at a high temperature, thus ensuring the temperature above 1600°C required for steelmaking. Around 1900, the electrical energy supply gradually became sufficient and various resistance furnaces, electric arc furnaces and cored induction furnaces began to be used.
In the 1950s, coreless induction furnaces developed rapidly. Later, electron beam furnaces emerged that used electron beams to impact solid fuels to enhance surface heating and melt high melting point materials.
The furnace used for forging and heating has earlier been a hand forging furnace. Its working space is a concave groove. The tank is filled with coal. The combustion air is supplied from the lower part of the tank and the workpiece is buried in the coal and heated. This type of furnace has low thermal efficiency, poor heating quality, and can only heat small parts. It will later be developed into a semi-closed or fully enclosed hearth furnace made of refractory bricks. Coal, gas or oil can be used as fuel. Electric energy can also be used as a heat source, and the workpiece is heated in the furnace.
In order to facilitate the heating of large-sized workpieces, a trolley furnace suitable for heating steel ingots and large billets has also emerged, and pit furnaces have also appeared for heating long rods. After the 1920s, a variety of mechanized and automated furnaces that can increase furnace productivity and improve working conditions have emerged.
The fuel of industrial furnaces also follows the development of fuel resources and advances in fuel conversion technology, and the use of lump coal, coke, pulverized coal, and other solid fuels has gradually shifted to gases such as producer gas, city gas, natural gas, diesel oil, and fuel oil. Liquid fuels, and various combustion devices adapted to the fuel used have been developed.
The structure, heating process, temperature control and furnace atmosphere of industrial furnaces will directly affect the quality of processed products. In a forging furnace, increasing the heating temperature of the metal can reduce the deformation resistance. However, if the temperature is too high, grain growth, oxidation, or overheating will occur, which will seriously affect the quality of the workpiece. In the heat treatment process, if the steel is heated to a point above the critical temperature and then suddenly cooled, the hardness and strength of the steel can be increased; if it is slowly cooled after being heated to a point below the critical temperature, the steel hardness can be made. Decrease increases toughness.
In order to obtain accurate and smooth surface parts, or to reduce metal oxidation to protect the mold, reduce the processing allowance, etc., you can use a variety of less oxidation furnace. In an open-flame, less oxidatively-heated furnace, incomplete combustion of the fuel produces a reducible gas, and heating the workpiece therein can reduce the oxidative loss rate to less than 0.3%.
Controllable atmosphere furnace is the use of artificially prepared atmosphere, into the furnace for gas carburizing, carbonitriding, bright quenching, normalizing, annealing and other heat treatment: in order to achieve the purpose of changing the microstructure, improve the mechanical properties of the workpiece. In the fluidized particle furnace, the combustion gas of the fuel or other fluidizing agent externally applied forcibly flows through the graphite particles or other inert particle layers on the hearth, and the workpiece is buried in the particle layer to achieve enhanced heating, and can also be infiltrated. Carbon, nitridation and other non-oxidation heating. In a salt bath furnace, molten salt solution is used as a heating medium to prevent oxidation and decarburization of the workpiece.
The melting of cast iron in cupola furnaces is often affected by the quality of coke, air supply method, charging conditions, and air temperature, making it difficult to stabilize the smelting process and making it difficult to obtain high-quality molten iron. Hot air cupola can effectively increase the temperature of molten iron, reduce the burning loss of alloy, and reduce the oxidation rate of hot metal, so as to produce advanced cast iron.
With the advent of coreless induction furnaces, cupolas have gradually been replaced. This induction furnace's smelting work is not limited by any grade of cast iron and can be quickly converted from smelting a grade of cast iron to smelting another grade of cast iron, which helps improve the quality of the molten iron. Some special alloy steels, such as ultra-low carbon stainless steels and steels for rolls and turbine rotors, require molten steel smelted from open hearth furnaces or general electric arc furnaces to be further refined by vacuum degassing and argon agitation in the refining furnaces. High-purity, large-capacity high-quality molten steel.
Industrial furnaces are divided into two types according to the heating mode: one is a flame furnace (or a fuel furnace), and the workpiece is heated by the combustion heat of a solid, liquid, or gaseous fuel in the furnace; the second type is an electric furnace in the furnace The electrical energy is converted into heat for heating.
The flame furnace has a wide range of fuel sources and low prices. It is easy to adopt different structures according to local conditions and is beneficial to reducing production costs. However, the flame furnace is difficult to achieve accurate control, and it has serious environmental pollution and low thermal efficiency. The characteristics of the electric furnace are that the furnace temperature is uniform and the automatic control is easy, and the heating quality is good. According to the energy conversion method, the electric furnace can be further divided into resistance furnace, induction furnace and electric arc furnace.
Industrial furnaces can be divided into two categories according to the thermal system: one is the intermittent furnace, also called the cycle furnace, which is characterized by the intermittent production of the furnace. The furnace temperature changes during each heating cycle, such as chamber furnaces and tables. Car-type furnaces, well-type furnaces, etc. The second category is continuous furnaces, which are characterized by the continuous production of furnaces and the division of temperature within the furnace. During the heating process, the temperature in each zone is constant, and the workpiece gradually enters the high-temperature heating zone from the low-temperature preheating zone, such as a continuous heating furnace and a heat treatment furnace, a ring furnace, a step furnace, and a oscillating hearth furnace. Wait.
Furnace heating capacity calculated in units of furnace floor area per unit of time is referred to as furnace productivity. The faster the furnace warms up and the greater the furnace load, the higher the furnace productivity. In general, the higher the furnace productivity, the lower the unit calorie consumption per kilogram of heating material. Therefore, in order to reduce energy consumption, full-load production should be performed to maximize the productivity of the furnace. At the same time, automatic adjustment of fuel and combustion air is applied to the combustion device to prevent excess or insufficient air volume. In addition, the heat storage and heat loss of the furnace wall, the heat loss of water-cooled components, the loss of radiant heat from various openings, and the loss of heat away from the flue gas are also reduced.
The ratio of the amount of heat that is absorbed when the metal or material is heated to the amount of heat that is supplied to the furnace is called the furnace thermal efficiency. Continuous furnaces have higher thermal efficiency than discontinuous furnaces because the productivity of continuous furnaces is high and they work without interruption. The furnace thermal system is in a stable state, there is no periodic heat storage loss in the furnace walls, and there is a pre-heat in the furnace. In the section of the hot charge, the residual heat of the flue gas is due to the section of the furnace where there is a preheated charge. The residual heat of the flue gas is absorbed by the cold workpieces entering the furnace, which reduces the temperature of the flue gas from the furnace.
In order to make the furnace temperature constant and achieve the specified heating rate, it is necessary to determine the excellent furnace type structure in addition to the process requirements, preheater and furnace type, fuel and combustion device type, industrial furnace exhaust, etc. The flow and pressure of the fuel and combustion air, or the controllable variables such as electric power, are mutually adjusted by various control units to achieve automatic control of furnace temperature, furnace atmosphere, or furnace pressure.
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