Sun, 30 Sep 2018 02:35:09 +0000
History of industrial furnaces
The development of industrial furnaces and the creation and development of industrial furnaces play an important role in human progress.
In China, a relatively perfect copper smelting furnace appeared in the Shang Dynasty. The furnace temperature reached 1200 degrees and the inner diameter of the furnace reached 0.8 meters.
During the Spring and Autumn Period and the Warring States Period, people further mastered the technology of raising furnace temperature on the basis of copper smelting furnace, thus producing cast iron.
In 1794, a straight cupola of molten iron was produced in the world.
Later, in 1864, Martin, a Frenchman, built the first open hearth furnace heated with gaseous fuel, using the principle of the British Siemens regenerative furnace. He uses a regenerator to preheat the air and gas at high temperatures, thus ensuring that the temperature required for steelmaking is more than 1600 degrees Celsius.
Around 1900, the electricity supply gradually became sufficient, and various resistance furnaces, electric arc furnaces and induction furnaces were used.
In 50s twentieth Century, the coreless induction furnace developed rapidly. Then came the electron beam furnace, which uses the electron beam to impact solid fuel, strengthening surface heating and melting high melting point materials.
The earliest furnace for forging heating was a hand forging furnace. Its workspace was a concave groove filled with coal. The air for combustion was supplied from the lower part of the groove. The workpiece was heated in the coal. This kind of furnace has low thermal efficiency, poor heating quality, and can only heat small workpieces, and later developed into a semi-closed or fully closed chamber furnace built of refractory bricks, coal, gas or oil can be used as fuel, but also electricity can be used as a heat source, the workpiece in the furnace heating. For the convenience of heating large workpieces, trolley-type furnaces suitable for heating ingots and billets and well-type furnaces for heating long rods have appeared.
After the 1920s, various types of mechanized and automated furnaces appeared, which could improve the productivity of blast furnaces and labor conditions.
With the development of fuel resources and the progress of fuel conversion technology, the fuel of industrial furnaces has been gradually changed from solid fuels such as lump coal, coke and pulverized coal to gas and liquid fuels such as producer gas, city gas, natural gas, diesel oil and fuel oil, and various combustion devices suitable for the fuel used have been developed.
The structure of industrial furnace, heating process, temperature control and furnace atmosphere will directly affect the quality of products after processing. In the forging furnace, increasing the heating temperature of the metal can reduce the deformation resistance, but too high temperature will cause grain growth, oxidation or overheating, which seriously affects the quality of the workpiece. During heat treatment, 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 the steel is heated to a point below the critical temperature and then cooled slowly, the hardness of the steel can be reduced and the toughness can be increased.
In order to obtain the workpiece with precise size and smooth surface, or to reduce metal oxidation to protect the mold, reduce machining allowance and other purposes, can use a variety of less oxidation-free heating furnace. In an open flame less oxidation heater, the incomplete combustion of fuel is used to produce reductive gas, in which the workpiece is heated, the oxidation burning loss rate can be reduced to less than 0.3%.
Controllable atmosphere furnace is a kind of manufactured atmosphere, through which gas carburizing, carbonitriding, bright quenching, normalizing, annealing and other heat treatment can be carried out to change the metallographic structure and improve the mechanical properties of the workpiece. In a flowing particle furnace, graphite particles or other inert particles are forced to flow through the bed by burning gases of fuel or other fluidizing agents applied externally. Workpiece buried in the particle layer can realize intensified heating, as well as various non-oxidized heating such as carburizing and nitriding. In the salt bath furnace, molten salt solution is used as heating medium to prevent oxidation and decarbonization of the workpiece.
The melting of cast iron in cupola is often affected by coke quality, air supply mode, burden condition and air temperature, which makes the melting process difficult to stabilize and obtain high quality molten iron.
Hot-blast cupola can effectively raise the temperature of molten iron, reduce alloy burning loss, and reduce the oxidation rate of molten iron, thus producing high-grade cast iron.
With the appearance of coreless induction furnace, cupola has been gradually replaced. This induction furnace melting work is not restricted by any cast iron grade, can be melted from one grade of cast iron, quickly converted to another grade of cast iron melting, is conducive to improving the quality of molten iron. Some special alloy steels, such as ultra-low carbon stainless steels and steels for rolls and turbine rotors, need to be melted from open-hearth furnace or ordinary electric arc furnace, through vacuum degassing and argon agitation in the refining furnace to remove impurities, and further refine high purity and large capacity of high quality molten steel.
The flame furnace has a wide range of fuel sources, low price, and is easy to adopt different structures according to local conditions, which is conducive to reducing production costs.
The characteristics of the electric furnace are uniform furnace temperature and easy realization of automatic control, and the heating quality is good. According to the energy conversion mode, the electric furnace can be divided into resistance furnace, induction furnace and electric arc furnace. The furnace heating capacity calculated by unit area per unit area is called furnace productivity. The faster the furnace heating rate and the larger the furnace loading, 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, full-load production should be carried out to maximize furnace productivity, and the combustion device should be automatically proportional to fuel and combustion-supporting air regulation to prevent excess or insufficient air. In addition, the heat storage and heat dissipation loss of the furnace wall, heat loss of water-cooled components, radiation heat loss of various openings, heat loss taken away from the furnace flue gas and so on should be reduced.
The ratio of heat absorbed by a metal or material to the heat supplied to the furnace is called the thermal efficiency of the furnace.
Continuous furnace is more efficient than discontinuous furnace because of its high productivity and uninterrupted operation. The furnace thermal system is in a stable state, and there is no periodic heat storage loss of the furnace wall. In the section of the material, the residual heat of the flue gas is absorbed by the cold part of the furnace, and the temperature of the flue gas from the furnace is reduced. In order to realize automatic control of furnace temperature, furnace atmosphere or furnace pressure.
Gas is liquefied gas, natural gas, coke oven gas, city gas, converter gas, mixed gas, producer gas, blast furnace gas, etc.