The creation and development of vacuum furnace plays an important role in human progress.In the shang dynasty, a relatively perfect copper smelting furnace appeared in China, with a temperature of 1200℃ and an inner diameter of 0.8 meters.In the spring and autumn period and the warring states period, people further mastered the technology of raising furnace temperature on the basis of melting copper furnace, thus producing cast iron.
In 1794, the world appeared the straight barrel cupola for smelting cast iron.Later, in 1864, Martin, a Frenchman, used the regenerative furnace principle of Siemens, an Englishman, to build the first steelmaking open-hearth furnace heated by gas fuel.He used the regenerator to preheat the air and gas at a high temperature, ensuring the temperature needed to make steel above 1600 ° c.Around 1900, electric power 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 came the electron-beam furnace, which used beams of electrons to blast solid fuel, enhancing surface heating and melting materials with high melting points.The first furnaces used for forging heating were hand forgings. The working space was a concave groove filled with coal. Air for burning was supplied from the lower part of the groove.This kind of furnace is very low thermal efficiency, heating quality is not good, and can only heat small workpiece, later developed into a firebrick built into the semi-closed or fully closed chamber furnace furnace, can use coal, gas or oil as fuel, can also be used as a heat source, the workpiece in the furnace heating.
In order to heat large workpieces, trolley furnaces for heating ingot and billet have appeared, and well furnaces for heating long rods have appeared.After 20 th century 20 th century appeared again to be able to raise productivity of furnace and improve all sorts of mechanization, automation furnace type.With the development of fuel resources and the progress of fuel conversion technology, solid fuels such as block coal, coke and pulverized coal are gradually converted into producer gas, city gas, natural gas, diesel, fuel oil and other gas and liquid fuels.
The structure, heating technology, temperature control and atmosphere of the vacuum furnace 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 overburning, seriously affecting the quality of the workpiece.During heat treatment, if the steel is heated to a point above the critical temperature and then cooled suddenly, the hardness and strength of the steel can be increased.If it is heated to a point below the critical temperature and then cooled slowly, the hardness of the steel will be reduced and the toughness will be increased.
In order to obtain accurate size and smooth surface of the workpiece, or in order to reduce metal oxidation to achieve protection of the mold, reduce the machining margin, can be used a variety of less oxidation heating furnace.In an open flame less oxidization-free reheating furnace, using the incomplete combustion of fuel to produce reducing gas, heating the workpiece can reduce the oxidization-burning rate to less than 0.3%.
Controlled vacuum furnace is the atmosphere of artificial preparation, through the furnace can be carburizing, carbonitriding, bright quenching, normalizing, annealing and other heat treatments: to change the microstructure, improve the mechanical properties of the workpiece.In a moving particle furnace, the combustion gas of fuel, or other fluidizing agent applied externally, is used to force through the graphite particles or other inert particle layer on the hearth. The workpiece buried in the particle layer can be heated intensively, and various non-oxidized heating such as carburizing and nitriding can also be carried out.In the salt bath furnace, the molten salt liquid is used as the heating medium to prevent the oxidation and decarburization of the workpiece.
The smelting of cast iron in cupola is often affected by coke quality, air supply mode, burden condition and air temperature.The hot air cupola can effectively increase the temperature of molten iron, reduce the burning loss of alloy and reduce the oxidation rate of molten iron, thus producing high grade cast iron.
With the appearance of coreless induction furnace, cupola has the tendency to be replaced gradually.The smelting operation of this induction furnace is not restricted by any cast iron grade, and it can quickly change from smelting one grade of cast iron to smelting another, which is beneficial to improve the quality of molten iron.Some special alloy steels, such as ultra-low carbon stainless steels and those used in roll and turbine rotors, require molten steel from open hearth or electric arc furnaces to be removed by vacuum degasser and argon in the refining furnace to further refine high purity, high capacity high quality steel.
The fuel source of flame furnace is wide, the price is low, it is convenient to adopt different structure according to local conditions, which is beneficial to reduce the production cost, but flame furnace is difficult to realize accurate control, serious pollution to the environment, low thermal efficiency.Electric furnace is characterized by uniform temperature and easy to achieve automatic control, heating quality is good.According to the way of energy conversion, electric furnace can be divided into resistance furnace, induction furnace and arc furnace.The furnace heating capacity calculated in units of floor area per unit time is called furnace productivity.The faster the furnace heats up, the larger 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, full capacity production should be carried out and furnace productivity should be increased as far as possible. At the same time, automatic proportional adjustment of fuel and auxiliary air should be implemented for combustion devices to prevent excess or insufficient air volume.In addition, it is necessary to reduce the heat storage and cooling loss of the furnace wall, the heat loss of the water-cooled components, the radiant heat loss of various openings, and the flue gas taken away from the furnace
Heat loss, etc.
In order to make the furnace temperature is constant and the implementation rules of heating speed, except must according to the technological requirements, preheater and furnace used mechanical type, fuel and combustion device categories, such as vacuum grate smoke method determine the excellent furnace type structure, the need for fuel and combustion air flow and pressure, or electric power controllable variables through a variety of control units such as mutual adjustment, in order to realize the furnace temperature and furnace atmosphere or automatic control of furnace pressure.The gas is liquefied gas, natural gas, coke oven gas, city gas, converter gas, mixed gas, producer gas, blast furnace gas and so on.