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Introduction to Continuous Annealing of Packaging Steel Strip
by：Hongmei
2021-03-15
Introduction to Continuous Annealing of Packaging Steel Strip
The annealing furnace in the continuous hot-dip galvanizing line for packaging steel strip is actually similar to the general straight-through continuous annealing furnace. In the improved Sendzimir method, it consists of three basic parts: a preheating furnace, a reduction furnace, and a cooling section. The end of the annealing furnace is fixed by a rigid beam, so that when the furnace body is heated, it can rely on the pulley installed at the bottom of the furnace body to slide on the fixed track, so that the furnace body can expand freely in the direction of the steel belt entrance. Generally, the thermal expansion rate of the annealing furnace body is about 0.05%.
The length of annealing furnace is comprehensively determined according to the productivity of the unit and other parameters, so each operation line is different.
The original hot-dip galvanized sheet passes through the annealing furnace to achieve two goals. First, the steel strip must be heated to a certain temperature in the annealing furnace. Firstly, the strip steel is preheated to the recrystallization temperature in the preheating furnace, and then the strip steel is heated to above the recrystallization temperature in the reduction furnace and kept warm and soaked. Finally, the steel strip is cooled to the temperature of the zinc pot in the cooling section. The heating curve is shown in Figure 61. Second, make the steel strip have a clean active surface without oxides, and make the strip steel hermetically enter the zinc pot for hot-dip galvanizing.
When is in production, the annealing furnace is filled with hydrogen-containing protective gas, and it is always operated under positive pressure. The iron oxide scale on the surface of the steel strip is reduced by hydrogen in the reduction furnace, and water vapor is generated at the same time. If water vapor accumulates in the furnace. Too much, not only can not play a reducing effect, but will cause the strip to oxidize. Therefore, the water vapor must be removed in time to keep the protective gas in the furnace updated. Fresh protective gas is mainly introduced from the end of the annealing furnace, and then flows toward the entrance of the annealing furnace against the running direction of the steel strip, thus achieving the above-mentioned purpose of renewing the protective gas.
According to experience, it is more appropriate to keep the furnace pressure of the preheating furnace and reduction furnace at 3-5 and 7-8 mm water column respectively. If the music in the furnace is too high, it will be unfavorable to the sealing of the furnace, which will cause excessive waste of protective gas due to tight air leakage. However, if the pressure in the furnace is controlled too low, there is a danger of negative pressure.
Production practice has proved that the furnace pressure mainly depends on the amount of gas combustion exhaust gas in the preheating furnace. The furnace pressure can be properly controlled by controlling the outflow of exhaust gas. Attempts to control the furnace pressure by adjusting the amount of protective gas introduced are not feasible.
At present, there are three ways to control the furnace pressure. One is to use a larger preheating furnace entrance, and then use a curtain made of glass wool or asbestos and other sweet and hot materials to hang on the furnace mouth. In this way, the amount of exhaust gas in the furnace can be adjusted by the rising or falling amount of the curtain, so as to achieve the purpose of controlling the furnace pressure. The second is that the beam uses a narrower entrance to the furnace, and there are one or two skylights on the top of the preheating furnace entrance area, so that the pressure in the furnace can be controlled by lifting or falling the skylights. The third is to control the pressure in the furnace. The exhaust gas generated by the heating furnace is discharged to the outside of the factory through the flue. In this way, an electric butterfly valve is installed on the cross section of the smoke inlet. By controlling the angle of the butterfly valve, the amount of exhaust gas in the preheating furnace can be effectively controlled to achieve The purpose of accurately controlling the furnace pressure, this is
A more advanced method.
The annealing furnace in the continuous hot-dip galvanizing line for packaging steel strip is actually similar to the general straight-through continuous annealing furnace. In the improved Sendzimir method, it consists of three basic parts: a preheating furnace, a reduction furnace, and a cooling section. The end of the annealing furnace is fixed by a rigid beam, so that when the furnace body is heated, it can rely on the pulley installed at the bottom of the furnace body to slide on the fixed track, so that the furnace body can expand freely in the direction of the steel belt entrance. Generally, the thermal expansion rate of the annealing furnace body is about 0.05%.
The length of annealing furnace is comprehensively determined according to the productivity of the unit and other parameters, so each operation line is different.
The original hot-dip galvanized sheet passes through the annealing furnace to achieve two goals. First, the steel strip must be heated to a certain temperature in the annealing furnace. Firstly, the strip steel is preheated to the recrystallization temperature in the preheating furnace, and then the strip steel is heated to above the recrystallization temperature in the reduction furnace and kept warm and soaked. Finally, the steel strip is cooled to the temperature of the zinc pot in the cooling section. The heating curve is shown in Figure 61. Second, make the steel strip have a clean active surface without oxides, and make the strip steel hermetically enter the zinc pot for hot-dip galvanizing.
When is in production, the annealing furnace is filled with hydrogen-containing protective gas, and it is always operated under positive pressure. The iron oxide scale on the surface of the steel strip is reduced by hydrogen in the reduction furnace, and water vapor is generated at the same time. If water vapor accumulates in the furnace. Too much, not only can not play a reducing effect, but will cause the strip to oxidize. Therefore, the water vapor must be removed in time to keep the protective gas in the furnace updated. Fresh protective gas is mainly introduced from the end of the annealing furnace, and then flows toward the entrance of the annealing furnace against the running direction of the steel strip, thus achieving the above-mentioned purpose of renewing the protective gas.
According to experience, it is more appropriate to keep the furnace pressure of the preheating furnace and reduction furnace at 3-5 and 7-8 mm water column respectively. If the music in the furnace is too high, it will be unfavorable to the sealing of the furnace, which will cause excessive waste of protective gas due to tight air leakage. However, if the pressure in the furnace is controlled too low, there is a danger of negative pressure.
Production practice has proved that the furnace pressure mainly depends on the amount of gas combustion exhaust gas in the preheating furnace. The furnace pressure can be properly controlled by controlling the outflow of exhaust gas. Attempts to control the furnace pressure by adjusting the amount of protective gas introduced are not feasible.
At present, there are three ways to control the furnace pressure. One is to use a larger preheating furnace entrance, and then use a curtain made of glass wool or asbestos and other sweet and hot materials to hang on the furnace mouth. In this way, the amount of exhaust gas in the furnace can be adjusted by the rising or falling amount of the curtain, so as to achieve the purpose of controlling the furnace pressure. The second is that the beam uses a narrower entrance to the furnace, and there are one or two skylights on the top of the preheating furnace entrance area, so that the pressure in the furnace can be controlled by lifting or falling the skylights. The third is to control the pressure in the furnace. The exhaust gas generated by the heating furnace is discharged to the outside of the factory through the flue. In this way, an electric butterfly valve is installed on the cross section of the smoke inlet. By controlling the angle of the butterfly valve, the amount of exhaust gas in the preheating furnace can be effectively controlled to achieve The purpose of accurately controlling the furnace pressure, this is
A more advanced method.
