The invention and development of the car-type annealing furnace played a crucial role in human progress. China showcased a relatively advanced copper smelting furnace during the Shang Dynasty, with a furnace temperature reaching 1200°C and an internal diameter of 0.8 meters. During the Spring and Autumn and Warring States periods, people further mastered the technology to control the furnace temperature based on the copper melting furnace, thereby producing cast iron.
In 1794, the world saw the introduction of the straight-tube blast furnace for smelting cast iron. By 1864, the Frenchman Martin applied the regenerative furnace principle of the British Siemens to create a cupola furnace heated by gas fuel. He utilized a regenerative chamber to preheat air and coal gas to temperatures above 1600°C, ensuring the necessary temperature for steelmaking. Around 1900, as electricity supply became sufficient, various resistance furnaces, arc furnaces, and coreless induction furnaces began to be used.
In the 1950s, the development of coreless induction furnaces accelerated. Subsequently, the electron beam furnace emerged, utilizing electron beams to impact solid fuel, enhancing surface heating and melting high-melting-point materials. Hand forging furnaces, used for casting heating, feature a concave槽 filled with coal, with combustion air supplied from the bottom of the槽. Workpieces are buried in the coal for heating. These furnaces have low thermal efficiency and poor heating quality, and are only suitable for heating small workpieces. Later developments included semi-closed or fully enclosed chamber furnaces constructed with refractory bricks, which could use coal, gas, or oil as fuel, or electricity as a heat source, with workpieces heated inside the furnace chamber.
To facilitate heating of large workpieces, a trolley furnace suitable for heating steel ingots and large billets has been introduced, as well as a pit furnace for heating long rods. Since the 1920s, various mechanized and automated furnace types have been presented to improve furnace production rates and labor conditions.
The fuel for the car-type annealing furnace has gradually shifted from solid fuels such as lump coal, coke, and coal powder to gaseous and liquid fuels like blast furnace gas, town gas, natural gas, diesel, and fuel oil, following the development of fuel resources and advancements in fuel conversion technology. Various incineration equipment suitable for the used fuels have also been developed.
The structure, heating technology, temperature control, and furnace atmosphere of the car-type annealing furnace directly affect the quality of the processed products. In the casting heating furnace, increasing the heating temperature of the metal can reduce deformation resistance, but excessively high temperatures can lead to grain growth, oxidation, or overburning, severely impacting the quality of the workpiece. During the heat treatment process, if the steel is heated to a point above the critical temperature and then rapidly cooled, it can increase the hardness and strength of the steel; if it is heated to a point below the critical temperature and cooled slowly, the hardness of the steel can be reduced while its toughness is improved.
To achieve precision in dimensions and a smooth surface finish, or to reduce metal oxidation for purposes such as protecting molds and minimizing machining allowances, various low-oxygen or non-oxygen heating furnaces can be selected. Inside the open flame of a low-oxygen or non-oxygen heating furnace, the incomplete combustion of fuel produces reductive gases, which, when used to heat workpieces, can lower the oxidation burn loss rate to below 0.3%.
Controlled atmosphere furnaces utilize artificially prepared atmospheres that, when introduced into the furnace, enable processes such as gas carburizing, carbonitriding, bright quenching, normalizing, and annealing, all for the purpose of altering the microstructure and improving the mechanical properties of the workpiece. In an active particle furnace, the combustion gases of the fuel or other fluidizing agents applied externally are forcibly passed through a bed of graphite particles or other inert particles, allowing the workpiece buried within to undergo intensive heating and various non-oxidizing heat treatments like carburizing and nitriding. Inside a salt bath furnace, the molten salt serves as the heating medium, preventing oxidation and decarburization of the workpiece. In a cupola furnace, melting cast iron is typically influenced by factors such as coke quality, blowing method, charge conditions, and air temperature, making the melting process unstable and difficult to achieve molten iron. A hot blast cupola can effectively increase the temperature of the molten iron, reduce alloy loss, and decrease the oxidation rate of the molten iron, thereby enabling the production of cast iron.
With the introduction of the coreless induction furnace, the trend is for the cupola furnace to be gradually replaced. This type of induction furnace is not constrained by any cast iron grade and can quickly switch from melting one grade of cast iron to another, which is beneficial for improving the quality of molten iron. Some special alloy steels, such as ultra-low carbon stainless steel and steel used for rolling mill rolls and steam turbine rotors, require the molten steel produced by a basic oxygen furnace or a general electric arc furnace to be further refined in a refining furnace through vacuum degassing and argon stirring to remove impurities, resulting in high-purity, high-capacity molten steel.
Flame furnaces have a wide range of fuel sources, low prices, and can be customized with different structures, which helps reduce production costs. However, they are difficult to control accurately, cause severe environmental pollution, and have low thermal efficiency. Electric furnaces feature uniform temperatures and easy automation, resulting in superior heating quality. According to the method of energy conversion, electric furnaces can be categorized into resistance furnaces, induction furnaces, and arc furnaces. The heating capacity of the furnace per unit time and per unit furnace base area is called the furnace production rate. The faster the furnace heats up and the larger the furnace load, the higher the production rate. Generally, a higher furnace production rate also means a lower unit heat consumption per kilogram of material. Therefore, to reduce energy consumption, it is advisable to operate at full capacity, strive to increase the furnace production rate, and implement active proportion regulation of fuel and combustion air in the combustion equipment to prevent excess or insufficient air. Moreover, efforts should be made to reduce heat loss through the furnace wall, water-cooled components, radiant heat loss from various openings, and heat loss carried away by exhaust gas from the furnace.
The ratio of the heat absorbed by metal or material during heating to the heat supplied into the furnace is known as the furnace thermal efficiency. Continuous furnaces have a higher thermal efficiency than intermittent furnaces due to their higher production rates and continuous operation. The furnace thermal system remains stable, without periodic wall heat loss, and because there is a preheating zone for the furnace material inside the furnace, some of the exhaust gas's residual heat is absorbed by the cold workpieces entering the furnace, thus reducing the temperature of the off-gas.
Actively control furnace temperature, atmosphere, or pressure.
Liquefied gas, natural gas, coke oven gas, city gas, converter gas, mixed gas, blast furnace gas, etc.