The creation and development of vacuum furnaces plays an important role in human progress. China in the Shang Dynasty appeared a more perfect copper smelting furnace, furnace temperature reached 1200 ℃, the furnace diameter of 0.8 meters. In the Spring and Autumn Period, people in the melting furnace on the basis of further grasp the technology to improve the furnace temperature, which produced a cast iron.
In 1794, the world appeared a cast iron cast iron straight cupola. After 1864, the French Martin used the British Siemens’ regenerative furnace principle, built the first gas-fired furnace with gas fuel heating. He used the regenerator to preheat the air and gas at high temperatures, thus ensuring the temperature required for steelmaking at temperatures above 1600 ° C. 1900 years ago, the power supply gradually enough to start using a variety of resistance furnace, electric arc furnace and a core induction furnace.
In the 1950s, the coreless induction furnace developed rapidly. Later, there has been an electron beam furnace, the use of electron beams to impact the solid fuel, can strengthen the surface heating and melting high melting point of the material. The furnace for forging heating is the first hand forging furnace, the working space is a concave groove, the tank filled with coal, combustion air from the lower part of the tank supply, the workpiece buried in the coal heating. The heat efficiency of this furnace is very low, the heating quality is not good, and can only heat a small workpiece, after the development of refractory brick with semi-closed or fully enclosed furnace chamber furnace, you can use coal, gas or oil as fuel , Can also be used as a heat source, the workpiece on the furnace heating.
In order to facilitate the heating of large parts, there have been suitable for heating steel ingots and large billet trolley furnace, in order to heat the long bar also appeared in the pit furnace. Since the 1920s, there have been various mechanized and automated furnaces that have improved furnace productivity and improved working conditions. The fuel of the industrial furnace is also gradually changed from the use of solid fuels such as lump coal, coke and pulverized coal, gas such as gas, city gas, natural gas, diesel oil, fuel oil, etc., with the development of fuel resources and the progress of fuel conversion technology. Liquid fuel, and developed a variety of combustion devices compatible with the fuel used.
Vacuum furnace structure, heating process, temperature control and furnace atmosphere, will directly affect the quality of processed products. In the forging furnace, to improve the heating temperature of the metal, can reduce the deformation resistance, but the temperature is too high will cause grain growth, oxidation or over burning, seriously affecting the quality of the workpiece. In the heat treatment process, if the steel heated to a certain point above the critical temperature, and then suddenly cooling, can improve the hardness and strength of steel; if heated to a critical point below the critical temperature after the slow cooling, but also the hardness of steel Reduce the toughness to improve.
In order to obtain a precisely sized and smooth surface of the workpiece, or in order to reduce the metal oxidation in order to achieve the protection of mold, reduce the processing margin and other purposes, you can use a variety of non-oxidation furnace. In the less flame-free heating furnace, the use of incomplete combustion of fuel to produce reducing gas, in which the workpiece can increase the oxidation burn rate reduced to 0.3% or less.
Controlled vacuum furnace is the use of artificial preparation of the atmosphere, into the furnace can be gas carburizing, carbonitriding, bright quenching, normalizing, annealing and other heat treatment: to achieve changes in the microstructure, improve the mechanical properties of the purpose of the workpiece. In the flowing particle furnace, the use of fuel combustion gas, or other externally applied other fluidizing agent, forced through the furnace bed of graphite particles or other inert particle layer, the workpiece buried in the particle layer can be enhanced heating can also be infiltration Carbon, nitriding and other non-oxidative heating. In the salt bath furnace, with molten salt as a heating medium, to prevent the workpiece oxidation and decarbonization.
Cast iron in the cupola, often by the coke quality, air supply, charge conditions and air temperature and other conditions, so that the melting process is difficult to stabilize, easy access to high-quality hot metal. Hot air cupola can effectively improve the hot metal temperature, reduce alloy burns, reduce the rate of molten iron oxidation, which can produce high-grade cast iron.
With the emergence of coreless induction furnace, cupola has been gradually replaced by the trend. The melting of this induction furnace is not subject to any grade of cast iron, can be smelt from a grade of cast iron, and soon converted to another grade of cast iron, is conducive to improving the quality of molten iron. Some special alloy steels, such as ultra-low carbon stainless steel and steel for rolls and steam turbines, require molten steel melted from a flat or general electric arc furnace to be refined by vacuum degassing and argon in the refining furnace High-purity, high-capacity high-quality molten steel.
Flame furnace fuel source is wide, low price, easy to take different conditions according to local conditions, is conducive to reducing production costs, but the flame furnace is difficult to achieve precise control, serious environmental pollution, thermal efficiency is low. Electric furnace is characterized by uniform furnace temperature and easy to achieve automatic control, heating quality. 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 in unit time unit floor area is called furnace productivity. The faster the furnace heats up, 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 material. Therefore, in order to reduce energy consumption, should be full load production, as far as possible to improve the furnace productivity, while the combustion device to implement fuel and combustion air automatic adjustment to prevent excessive or insufficient air. In addition, but also to reduce the furnace wall heat and heat loss, heat loss of water-cooled components, a variety of openings of radiation heat loss, away from the furnace smoke away heat loss.
In order to make the furnace temperature constant and to achieve the required heating rate, in addition to the process requirements, preheater and furnace mechanical type, fuel and combustion equipment category, vacuum furnace exhaust method to determine the excellent furnace structure, Fuel and combustion air flow and pressure, or control variables such as electrical power through a variety of control units to adjust each other to achieve furnace temperature, furnace atmosphere or furnace pressure of the automatic control. Gas for liquefied petroleum gas, natural gas, coke oven gas, city gas, converter gas, mixed gas, furnace gas, blast furnace gas.