1794, a straight tube furnace for smelting cast iron appeared in the world. Later, in 1864, Martin, a Frenchman, built the first steel-making flat kiln heated by gas fuel by using the regenerative kiln principle of Siemens Company in Britain. He used the regenerator to preheat the air and gas at high temperature, so as to ensure the temperature above 1600℃ required for steelmaking. 1900 or so, the power supply is gradually sufficient, and various resistance furnaces, electric arc furnaces and cored induction furnaces are used.
In 1950s, coreless induction furnaces developed rapidly. Later, electron beam kiln appeared, which can strengthen surface heating and melt high melting point materials by using electron beam to impact solid fuel.
The furnace used for forging heating was originally a hand forging furnace, and its working space was a concave groove filled with coal. Air for combustion was supplied from the lower part of the groove, and the workpiece was buried in coal for heating. This kind of kiln has low thermal efficiency and poor heating quality, and can only heat small workpieces. Later, it developed into a semi-closed or fully enclosed chamber kiln made of refractory bricks, which can use coal, gas or oil as fuel or electricity as heat source, and the workpiece is heated in the kiln chamber.
In order to facilitate the heating of large workpieces, there are trolley furnaces suitable for heating steel ingots and billets, and there are also well furnaces for heating long bars. After the 1920s, various mechanized and automated kiln types appeared, which can improve the productivity and working conditions of the kiln.
With the development of fuel resources and the progress of fuel conversion technology, the fuel of industrial kilns has 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 adapted to the fuels used have been developed.
The structure, heating technology, temperature control and atmosphere of industrial kiln will directly affect the quality of processed products. In forging heating furnace, increasing the heating temperature of metal can reduce the deformation resistance, but too high temperature will cause grain growth, oxidation or overheating, which will seriously affect the quality of workpiece. In the heat treatment process, if the steel is heated above the critical temperature and then suddenly cooled, the hardness and strength of the steel can be improved; If it is heated to a point below the critical temperature and then cooled slowly, the hardness of steel can be reduced and the toughness can be improved.
In order to obtain the workpiece with accurate size and smooth surface, or to reduce the metal oxidation protection mold and reduce the machining allowance, various less oxidation heating furnaces can be used. In an open-flame furnace with less oxidation heating, reducing gas is produced by incomplete combustion of fuel, and the oxidation loss rate can be reduced to below 0.3% by heating the workpiece.