Industrial furnaces are thermal equipment that heats materials or workpieces in industrial production using heat from fuel combustion or electrical energy conversion. Broadly speaking, a boiler is also an industrial furnace, but it is customary not to include it in industrial furnaces.
The main components of industrial furnaces are: industrial furnace masonry, industrial furnace exhaust system, industrial furnace preheater and industrial furnace combustion equipment. There are many types of industrial furnaces used in the mechanical industry. In the foundry, there are cupolas, induction furnaces, electric resistance furnaces, electric arc furnaces, vacuum furnaces, open furnaces, furnaces, etc. for melting metals; sand drying furnaces and ferroalloys with baking sand type Oven and casting annealing furnaces; in the forging workshop, there are various heating furnaces for pre-forging heating of steel ingots or billets, and heat treatment furnaces for stress relief after forging; in metal heat treatment workshops, various annealings for improving the mechanical properties of workpieces , normalizing, quenching and tempering heat treatment furnace; in the welding workshop, there are pre-weld preheating furnace and post-weld tempering furnace for weldment; in the powder metallurgy workshop there is a furnace for sintering metal.
Industrial furnaces are also widely used in other industries, such as metal smelting furnaces, ore sintering furnaces and coke ovens in the metallurgical industry; distillation furnaces and cracking furnaces in the petroleum industry; furnaces in the gas industry; cement kiln and glass melting in the silicate industry, Glass annealing furnace; baking oven for food industry, etc.
The creation and development of industrial furnaces plays an important role in human progress. In China, a relatively perfect copper smelting furnace appeared in the Shang Dynasty. The furnace temperature reached 1200 ° C and the inner diameter of the furnace reached 0.8 m. During the Spring and Autumn Period and the Warring States Period, people further mastered the technology of increasing the furnace temperature on the basis of the copper melting furnace, thus producing cast iron.
In 1794, a straight cylindrical cupola of molten iron appeared in the world. Later, in 1864, the Frenchman Martin used the principle of regenerative furnaces of the British Siemens to build the first steel-making flat furnace heated with gaseous fuel. He uses a regenerator to preheat the air and gas at a high temperature, thus ensuring temperatures above 1600 °C for steelmaking. Around 1900, the power supply was gradually increased, and various resistance furnaces, electric arc furnaces and core induction furnaces were used.
In the 1950s, coreless induction furnaces developed rapidly. Later, electron beam furnaces were used to use electron beams to impact solid fuels, which enhanced surface heating and melting of high melting point materials.
The furnace used for forging heating is the first hand forging furnace. The 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 for heating. The furnace has low thermal efficiency, poor heating quality, and can only heat small workpieces, and later developed into a semi-closed or fully enclosed furnace chamber furnace made of refractory bricks, which can be used as fuel for coal, gas or oil. Electric can also be used as a heat source, and the workpiece is heated in the furnace.
In order to facilitate the heating of large workpieces, a trolley type furnace suitable for heating steel ingots and large billets has appeared, and a pit furnace has appeared in order to heat the elongated rods. After the 1920s, various mechanized and automated furnace types that improved furnace productivity and improved working conditions appeared.
The fuel of industrial furnaces is gradually changed from the use of solid fuels such as lump coal, coke and pulverized coal to gas of producer gas, city gas, natural gas, diesel oil, fuel oil, etc., along with the development of fuel resources and advances in fuel conversion technology. Liquid fuels, and various combustion devices have been developed that are compatible with the fuel used.
The structure of the industrial furnace, the heating process, the temperature control and the atmosphere in the furnace all directly affect the quality of the processed product. In the forging furnace, increasing the heating temperature of the metal can reduce the deformation resistance, but if the temperature is too high, it will cause grain growth, oxidation or over-burning, which seriously affects the quality of the workpiece. During 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 heated to a point below the critical temperature and then slowly cooled, the hardness of the steel can be increased. Reduce the toughness.
In order to obtain a workpiece with a precise size and a smooth surface, or to reduce metal oxidation to protect the mold and reduce the machining allowance, various less oxidation-free furnaces can be used. In the open flameless oxidation-free heating furnace, incomplete combustion of the fuel is used to generate a reducing gas, and heating the workpiece therein can reduce the oxidation loss rate to 0.3% or less.
The controlled atmosphere furnace is an artificially prepared atmosphere, which can be subjected to heat treatment such as gas carburizing, carbonitriding, bright quenching, normalizing, annealing, etc. in order to achieve the purpose of changing the metallographic structure and improving the mechanical properties of the workpiece. In the flowing particle furnace, the combustion gas of the fuel or other fluidizing agent applied externally 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 or osmosis. Various non-oxidative heating such as carbon and nitriding. In the salt bath furnace, the molten salt solution is used as a heating medium to prevent oxidation and decarburization of the workpiece.
The melting of cast iron in the cupola is often affected by conditions such as coke quality, air supply mode, charge condition and air temperature, making the smelting process difficult to stabilize and difficult to obtain high quality molten iron. The hot air cupola can effectively increase the temperature of the molten iron, reduce the burning of the alloy, and reduce the oxidation rate of the molten iron, thereby producing a high-grade cast iron.
With the advent of coreless induction furnaces, cupolas have gradually been replaced. The melting of this induction furnace is not limited by any cast iron grade. It can be converted from cast iron of one grade and quickly converted to cast iron of another grade, which is beneficial to improve the quality of molten iron. Some special alloy steels, such as ultra-low carbon stainless steels and steels for rolls and steam turbine rotors, need to be smelted in open hearth furnaces or general electric arc furnaces, and are further refined by vacuum degassing and argon agitation in the refining furnace. High-quality steel with high purity and large capacity.
Industrial furnaces are divided into two types according to heating methods: one is a flame furnace (or a fuel furnace), which heats the workpiece with the heat of combustion of solid, liquid or gaseous fuel in the furnace; the second type is an electric furnace in the furnace. Convert electrical energy to heat for heating.
The flame furnace has a wide source of fuel and low price. It is convenient to adopt different structures according to local conditions, which is conducive to reducing production costs. However, the flame furnace is difficult to achieve precise control, causing serious environmental pollution and low thermal efficiency. The electric furnace is characterized by uniform furnace temperature and easy automatic control, and the heating quality is good. According to the energy conversion mode, the electric furnace can be further divided into an electric resistance furnace, an induction furnace and an electric arc furnace.
Industrial furnaces can be divided into two categories according to the thermal system: one type is intermittent type furnace, also called periodic type furnace, which is characterized by intermittent production of furnace, and the furnace temperature changes during each heating cycle, such as chamber furnace and table. The car type furnace, the pit type furnace, etc.; the second type is a continuous type furnace, which is characterized in that the furnace is continuously produced, and the temperature section is divided in the furnace. During the heating process, the temperature of each section is constant, and the workpiece gradually enters the high temperature heating zone from the low temperature preheating zone, such as continuous heating furnace and heat treatment furnace, ring furnace, step furnace, vibrating bottom furnace. Wait.
The furnace heating capacity calculated in units of unit time per unit time is called furnace productivity. The faster the furnace is heated and the higher the furnace load, the higher the furnace productivity. In general, the higher the furnace productivity, the lower the unit heat consumption per kilogram of material heated. Therefore, in order to reduce energy consumption, production should be carried out at full capacity, and the productivity of the furnace should be increased as much as possible. At the same time, automatic proportional adjustment of fuel and combustion air should be performed on the combustion device to prevent excess or insufficient air. In addition, it is necessary to reduce the heat storage and heat loss of the furnace wall, the heat loss of the water-cooled components, the radiant heat loss of various openings, and the heat loss from the flue gas.
The ratio of the heat absorbed by a metal or material as it is heated to the heat supplied to the furnace is called the furnace thermal efficiency. The continuous furnace has higher thermal efficiency than the intermittent furnace. Because the continuous furnace has high productivity and is uninterrupted, the furnace heat system is in a stable state, there is no periodic furnace wall heat storage loss, and there is a pre-heating inside the furnace. In the section of the hot charge, the residual heat of the flue gas is due to a section of the preheating charge inside the furnace, and the residual heat of the flue gas is absorbed by the cold workpiece entering the furnace, which lowers the temperature of the flue gas leaving the furnace.
In order to keep the furnace temperature constant and achieve the specified heating rate, in addition to determining the excellent furnace structure according to the process requirements, preheater and furnace mechanical type, fuel and combustion device type, industrial furnace exhaust method, etc., The flow and pressure of the fuel and combustion air, or 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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