In order to facilitate the heating of large workpieces, a trolley type furnace suitable for heating steel ingots and large billets has been presented, and a well type furnace has also been presented for heating long rod pieces. After the 1920s, various mechanized and proactive furnace types emerged that could improve furnace production rates and improve labor conditions.

 

With the development of fuel resources and the advancement of fuel conversion technology, the fuel for the trolley type annealing furnace has gradually shifted from solid fuels such as lump coal, coke, and coal powder to gas and liquid fuels such as producer gas, urban gas, natural gas, diesel, and fuel oil. Various incineration equipment suitable for the fuel used has been developed.

 

The structure, heating technology, temperature control, and atmosphere inside the trolley type annealing furnace directly affect the quality of the processed product. In a casting heating furnace, increasing the heating temperature of the metal can reduce deformation resistance, but excessive temperature can cause grain growth, oxidation, or overburning, severely affecting the quality of the workpiece. During the heat treatment process, 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 improved; If heated to a point below the critical temperature and cooled slowly, it can also reduce the hardness of the steel and improve its toughness.

 

In order to obtain workpieces with accurate scale and smooth appearance, or to reduce metal oxidation to protect molds and reduce machining allowances, various types of oxidation free heating furnaces can be selected. In an open flame low oxidation heating furnace, the incomplete combustion of fuel is used to generate restorative gas, and heating the workpiece in it can reduce the oxidation burning loss rate to below 0.3%.

 

A controllable atmosphere furnace is a manually prepared atmosphere that can undergo heat treatment such as gas carburization, carbonitriding, bright quenching, normalizing, annealing, etc. when introduced into the furnace to achieve the goal of changing the metallographic arrangement and improving the mechanical properties of the workpiece. In a movable particle furnace, the combustion gas of fuel or other externally applied fluidizing agents are used to forcibly flow through the graphite particles or other lazy particle layers on the furnace bed. The workpiece can be buried in the particle layer to achieve enhanced heating, and various non oxidation heating methods such as carburization and nitridation can also be carried out. In a salt bath furnace, using molten salt solution as the heating medium can prevent oxidation and decarbonization of the workpiece. Smelting cast iron in cupola is usually affected by coke quality, air supply method, furnace burden and air temperature, which makes the smelting process difficult to be stable and it is difficult to obtain high-quality molten iron. The hot blast cupola can effectively improve 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, the cupola is gradually replaced. The melting operation of this induction furnace is not constrained by any grade of cast iron, and can quickly switch from melting one grade of cast iron to melting another grade of cast iron, which is conducive to improving the quality of molten iron. Some special alloy steels, such as ultra-low carbon stainless steel and steel used for rollers and turbine rotors, require the molten steel produced by open hearth or general electric arc furnaces to be vacuum degassed and stirred with argon gas in the refining furnace to further refine high-quality steel with high purity and large capacity.

 

The fuel used in flame furnaces has a wide range of origins and low prices, making it easy to tailor and adopt different structures, which is beneficial for reducing production costs. However, flame furnaces are difficult to accurately control, causing severe environmental pollution and low thermal efficiency. The electric furnace is characterized by uniform furnace temperature, easy to complete active control and good heating quality. According to the energy conversion method, electric furnaces can also be divided into resistance furnaces, induction furnaces, and electric arc furnaces. The heating capacity of a furnace calculated in units of time and bottom area is called the furnace production rate. The faster the heating speed of the furnace and the larger the loading capacity of the furnace, the higher the production rate of the furnace. In general, the higher the production rate of the furnace, the lower the unit heat consumption per kilogram of material heated. Therefore, in order to reduce energy consumption, it is necessary to produce at full capacity, improve the furnace production rate as much as possible, and implement active share regulation of fuel and combustion air for incineration equipment to prevent excess or lack of air volume. In addition, it is necessary to reduce the loss of heat storage and dissipation on the furnace wall, the heat loss of water-cooled components, the radiation heat loss of various openings, and the heat loss carried away by the flue gas from the furnace.

 

The ratio of the heat absorbed by metals or materials during heating to the heat supplied into the furnace is called the furnace thermal efficiency. Continuous furnaces have higher thermal efficiency than intermittent furnaces because they have a higher production rate and operate continuously. The furnace's thermal system is in a stable state, without periodic wall heat storage loss. Additionally, there is a preheating section inside the furnace, and some residual heat in the flue gas is due to a preheating section inside the furnace. Some residual heat in the flue gas is absorbed by the cold workpiece entering the furnace, reducing the temperature of the flue gas leaving the furnace.

 

To achieve active control of furnace temperature, atmosphere, or pressure. Gas includes liquefied gas, natural gas, coke oven gas, city gas, converter gas, mixed gas, producer gas, blast furnace gas, etc.