On 2018-08-08 14:48:54
Precautions before and after use of trolley type annealing furnace
The creation and development of trolley type annealing furnace plays a very important role in human progress. In the Shang Dynasty, China presented a relatively complete copper smelting furnace with a temperature of 1200 ℃ and an inner diameter of 0.8m. In the spring and Autumn period and the Warring States period, people further grasped the technology of improving furnace temperature on the basis of copper melting furnace, and then produced cast iron.
In 1794, the world presented a straight barrel Cupola for smelting cast iron. In 1864, the French Martin used the principle of Siemens' regenerative furnace to create the first open hearth furnace for steelmaking heated by gas fuel. He used the regenerator to preheat the air and gas at high temperature, thus ensuring the temperature above 1600 ℃ required for steelmaking. Around 1900, the power supply was gradually sufficient, and various resistance furnaces, electric arc furnaces and cored induction furnaces were used.
In 1950s, coreless induction furnace was developed rapidly. Then there was the electron beam furnace, which used the electron beam to impact the solid fuel and strengthened the surface heating and melting of high melting point materials. The earliest furnace used for casting heating was the hand forging furnace. Its working space was a concave groove filled with coal. The air for burning was supplied from the lower part of the groove, and the workpiece was buried in the coal for heating. This kind of furnace has low thermal efficiency and poor heating quality. It can only heat small workpieces. In the future, it will be a semi closed or fully closed chamber furnace built of refractory bricks. It can use coal, gas or oil as fuel, or electricity as heat source, and the workpieces will be heated in the furnace.
In order to facilitate the heating of large workpieces, a trolley type furnace suitable for heating ingots and large billets is presented, and a well type furnace is also presented for heating long rod parts. After the 1920s, various mechanized and active furnace types which can improve the furnace production rate and labor conditions were presented.
Along with the development of fuel resources and the progress of fuel conversion technology, the fuel of trolley type annealing furnace is gradually changed from solid fuel such as lump coal, coke and coal powder to gas and liquid fuel such as producer gas, city gas, natural gas, diesel oil and fuel oil, and various incineration equipment suitable for the fuel used is developed.
The structure, heating technology, temperature control and atmosphere of the trolley type annealing furnace will directly affect the product quality after processing. In the casting furnace, improving the heating temperature of metal can reduce the deformation resistance, but too high temperature will cause grain growth, oxidation or overburning, which will seriously affect the quality of workpiece. In the process of heat treatment, if the steel is heated to a certain point above the critical temperature and then cooled suddenly, the hardness and strength of the steel can be improved; if the steel is heated to a certain point below the critical temperature and cooled slowly, the hardness of the steel can be reduced and the toughness can be improved.
In order to obtain the workpiece with accurate scale and smooth surface, or to reduce the metal oxidation to protect the mold and reduce the machining allowance, various kinds of less oxidation-free heating furnaces can be selected. In the open flame less oxidation furnace, the recovery gas is produced by incomplete combustion of fuel, in which the oxidation loss rate can be reduced to less than 0.3% by heating the workpiece.
Controlled atmosphere furnace is a kind of atmosphere which is prepared manually. It can be used for heat treatment such as gas carburizing, carbonitriding, bright quenching, normalizing, annealing, etc. in order to change the metallographic arrangement and improve the mechanical properties of workpieces. In the active particle furnace, the burning gas of fuel or other fluidizing agent applied externally is used to forcibly flow through the graphite particles or other lazy particles layer on the hearth, and the workpiece buried in the particle layer can complete the strengthening heating, as well as various non oxidation heating such as carburizing and nitriding. In the salt bath furnace, the molten salt is used as the heating medium to prevent the oxidation and decarburization of the workpiece. The melting of cast iron in cupola is usually affected by the quality of coke, air supply method, charge condition and air temperature, which makes the melting process difficult to be stable and 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, so as to produce high-grade cast iron.
With the appearance of coreless induction furnace, cupola will be replaced gradually. The smelting operation of this induction furnace is not restricted by any cast iron grade. It can quickly change from smelting one grade of cast iron to smelting 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 for rolls and turbine rotors, need to remove impurities from the molten steel melted in open hearth furnace or general electric arc furnace through vacuum degassing and argon agitation in the refining furnace to further refine high-purity and high-capacity high-quality molten steel.
The flame furnace has a wide range of fuel sources and low price, which is convenient to adopt different structures for tailoring, and is conducive to reducing production costs. However, it is difficult to complete accurate control of the flame furnace, resulting in severe environmental pollution and low thermal efficiency. The characteristics of electric furnace are uniform furnace temperature, easy to complete active control and good heating quality. According to the method of energy conversion, electric furnace can be divided into resistance furnace, induction furnace and electric arc furnace. The furnace heating capacity calculated by unit time unit furnace bottom area is called furnace yield. The faster the furnace temperature rises and the larger the furnace load, the higher the furnace yield. In general, the higher the furnace yield, the lower the unit heat consumption per kilogram of material. Therefore, in order to reduce energy consumption, it is necessary to produce at full capacity, improve furnace production rate as much as possible, and adjust the active share of fuel and combustion supporting air for incineration equipment together to prevent excess or lack of air. In addition, the loss of heat storage and heat dissipation of furnace wall, heat loss of water-cooling components, radiation heat loss of various openings, heat loss of flue gas taken away from the furnace, etc. shall be reduced.
The ratio of the heat absorbed by a metal or material when it is heated to the heat supplied to the furnace is called furnace thermal efficiency. The thermal efficiency of continuous furnace is higher than that of intermittent furnace, because the production rate of continuous furnace is high and the furnace is operated continuously, the furnace thermal system is in a safe and stable state, there is no periodic loss of heat storage on the furnace wall, but also because there is a preheating furnace charge section in the furnace, some of the residual heat of flue gas is because there is a preheating furnace charge section in the furnace, some of the residual heat of flue gas is the cooling into the furnace The temperature of the flue gas from the furnace is reduced due to the absorption of the workpiece. To complete the active control of furnace temperature, atmosphere or pressure.
Gas is liquefied gas, natural gas, coke oven gas, city gas, converter gas, mixed gas, producer gas, blast furnace gas, etc.