KR101006077B1 - Apparatus and method for cooling hot-dip galvanized steel plate - Google Patents

Abstract

The present invention relates to an apparatus and method for cooling a steel plate plated with alloyed molten zinc in a cracking furnace.

The cooling apparatus of the present invention has a delta (δ) to a natural cooling zone for alloying the hot-dip galvanized steel sheet heated to a temperature of 480 ° C. or higher while cooling through natural cooling, and to a plated layer surface of the plated steel sheet passing through the natural cooling zone. Crack formed of a forced cooling zone for forcibly cooling the plated steel sheet such that a temperature difference (ΔT) defined in Equation 1 below satisfies the range of 100 to 250 ° C so that further alloying growth can be suppressed when the phase is formed. in; And a cooling member for forcibly cooling the plated steel sheet passing through the forced cooling zone.

[Equation 1]

△ T = cracked steel plate temperature (℃)-cracked steel plate temperature (℃)

[Thickness of material: 0.5 ~ 3.2t, plate speed: 180mpm or less due to crack of plated steel sheet]

Molten Zinc, Plating, Steel Sheet, Cracking, Cooling, Alloying, Cold, Spraying

Description

Cooling device and cooling method for alloyed hot-dip galvanized steel sheet {APPARATUS AND METHOD FOR COOLING HOT-DIP GALVANIZED STEEL PLATE}

The present invention relates to a cooling apparatus and a cooling method of an alloyed hot-dip galvanized steel sheet, in particular, in the surface treatment process by controlling the alloying state of the hot-dip galvanized steel sheet rapidly passing through the crack as the line speeds up (powdering) occurs The present invention relates to an apparatus and a method for cooling an alloyed hot-dip galvanized steel sheet so as to prevent undesirably.

The surface treatment of steel plate is applied for the purpose of extending the life of the product and improving its characteristics, and has been developed as one of the main technologies supporting steel demand in various fields such as automobiles, home appliances, construction, civil engineering, and containers.

Hot-dip galvanizing method widely used in this surface treatment, as shown in Figure 1, consists of the main process passing through the cooler 6 and the Top Roll (7).

The degree of alloying of the steel sheet manufactured as described above is determined based on the alloying degree (F%) of the plating layer as a main index, and the alloy phases constituting the plating layer-zeta (ζ) phase, delta (δ) phase, and gamma (γ) phase -Affects the properties such as workability and powdering depending on the ratio. Here, the zeta (ζ) phase disappears near the exit of the crack zone, and the delta (δ) phase occupies most of the plating layer with little change after generation.

However, the gamma (γ) phase is formed at the base iron interface and grows with an increase in temperature and time. The growth of the gamma (γ) phase increases as alloying of the plating layer proceeds, in particular, as the plating steel sheet passes through the crack zone. Additional growth will occur in the vicinity of the exit being completed, which will affect the powdering.

Therefore, it is important to maintain the appropriate temperature so that the cracking zone 5 is alloyed with the plated steel sheet in consideration of the material, the plating conditions, the moving speed of the line, and the like. Alloying of the plated steel sheet (S) should be properly completed.

However, the conventional crack zone 5 has a problem that it is not possible to control the alloying state of the molten zinc plated steel sheet (S). For example, in recent years, the line speed is increased due to the improvement of production technology. The conventional crack zone 5 as described above naturally cools the steel sheet coated with molten zinc through a long section, and is suitable for speeding up the line. It is not possible to lower the temperature of the steel sheet (S), thereby causing the hot steel sheet (S) in contact with the top roll (7) to act as a cause of powdering and plating layer peeling occurs.

In addition, in the prior art, the hot-dip galvanized steel sheet S passing through the cracks 5 is rapidly cooled by water cooling in the mist cooler 6, resulting in incomplete alloy plating layer formation and powdering and plating layer peeling due to thermal shock. There was a problem leading to the outbreak.

Therefore, in the technical field, there is a need to develop a technology for a cooling apparatus for a plated steel sheet that can be applied to a cracked furnace so that alloying can be appropriately performed according to the type, physical properties, etc. of the hot-dip galvanized steel sheet which proceeds at high speed in the cracking furnace. It has been emerging.

The present invention has been proposed to solve the above-mentioned conventional problems, by cooling the plated steel sheet so as to control the proper alloying state of the hot-dip galvanized steel sheet passing through the crack quickly by the speed of the line is generated powdering of the plated steel sheet It is an object of the present invention to provide a cooling apparatus and method for alloying hot-dip galvanized steel sheet that can prevent the lead in advance, thereby improving the quality and productivity of the coated steel sheet.

The present invention for achieving the above object,

When the delta (δ) phase is formed up to the natural cooling zone for alloying the hot-dip galvanized steel sheet heated to a temperature of 480 ° C. or higher while cooling through natural cooling, and the plated layer surface of the plated steel sheet passing through the natural cooling zone, A crack consisting of a forced cooling zone for forcibly cooling the plated steel sheet so that the alloying growth can be suppressed so that the temperature difference ΔT defined in Equation 1 below satisfies the range of 100 to 250 ° C .; And

It relates to a cooling device for alloyed hot-dip galvanized steel sheet comprising a; cooling member configured to cool the plated steel sheet passing through the forced cooling zone.

[Equation 1]

△ T = cracked steel plate temperature (℃)-cracked steel plate temperature (℃)

[Thickness of material: 0.5 ~ 3.2t, plate speed: 180mpm or less due to crack of plated steel sheet]

In the present invention, it is preferable to set the temperature difference ΔT defined by Equation 1 to 130 to 160 ° C.

In addition, the plated steel sheet in the forced cooling zone is preferably 450 ℃ or less, more preferably discharged by cooling to a temperature in the range of 420 ~ 350 ℃.

In addition, the cooling member in the present invention, a plurality of injection pipe is installed in the forced cooling zone and configured to spray cold air to the plated steel sheet passing through the forced cooling zone; A distribution header connected to distribute cold air to a plurality of injection pipes respectively installed in the forced cooling zone; And an intake fan forcibly inhaling outside air to blow cold air into the distribution header.

The cooling member is preferably configured to increase the cooling rate of the plated steel sheet toward the rear end of the forced cooling zone.

In the present invention, the forced cooling zone is preferably composed of two or more stages.

In addition, in the present invention, the respective injection pipes are preferably arranged horizontally at regular intervals along the traveling direction of the plated steel sheet.

In this case, the injection pipe is preferably made of a front injection pipe and a rear injection pipe provided with a slit-type injection nozzle to evenly spray cold air to the front and rear of the plated steel sheet, the distribution header is the front, rear injection pipe It consists of a front distribution header and a rear distribution header, respectively, to distribute the cold air, the front and rear distribution header is more preferably connected to the horizontal branch pipe branched to both sides of the intake fan.

And at least one exhaust port formed in the crack furnace to exhaust heat generated by cold spraying of the injection nozzle in the forced cooling zone; And a door rotatably connected to the crack furnace to open and close the exhaust port. Furthermore, it is preferable to further include an opening / closing cylinder connecting the door with the crack to adjust the opening and closing angle of the door.

In addition, the injection pipe is made of a front injection pipe and a rear injection pipe so as to inject cold air into the front and rear of the plated steel sheet, respectively, the distribution header to distribute the cold air to the front and rear injection pipe, respectively, the front distribution header and the rear distribution It consists of a header, the front and rear distribution header is connected to the horizontal branch pipes respectively provided in the forced cooling zone of the multi-stage, a plurality of injection pipes installed in each of the forced cooling zone is connected to each of the front and rear distribution header The horizontal branch pipes of the forced cooling zones are preferably connected to vertical branch pipes connected to the intake fan.

In addition, the plurality of spray pipes installed in the forced cooling zone is preferably alternately provided with a wide and small injection nozzle formed to spray cold air to the plated steel plate formed in a wide and small width.

In addition, the spray pipe installed in the forced cooling zone is preferably configured to increase the amount of cold air sprayed on the plated steel sheet in the exit direction of the forced cooling zone.

In addition, the cooling device of the hot-dip galvanized steel sheet of the present invention,

A plurality of injection amount control valves for adjusting the amount of cold air injection in the respective injection pipes; A temperature measuring unit measuring a surface temperature of the plated steel sheet at the outlet of the crack; An air amount control unit outputting a control signal for opening and closing the injection amount control valve so as to reduce a deviation between the measured temperature and a predetermined target temperature; And a valve control unit controlling opening and closing of each injection amount control valve according to a control signal of the air amount control unit. It is preferred to further include.

Furthermore, it is more preferable to further include a speed control unit for controlling the fan rotational speed of the intake fan in accordance with a control signal of the air volume control unit.

In the present invention, the air amount control unit preferably outputs a control signal for the fan rotational speed of the intake fan after the respective injection amount control valve is opened (closed).

In addition, the air volume control unit preferably outputs a control signal to the valve control unit so that the injection amount of the cold air injected into the plated steel sheet gradually increases from the multi-stage cooling zone to the rear end.

Furthermore, the present invention,

Transferring the plated steel sheet into a cracking furnace for alloying the hot-dip galvanized steel sheet;

Intake fan sucks cold air from the outside and transfers it to the spray pipe through the distribution header, and sprays the cold air onto the plated steel plate through a cold air spray nozzle which is provided in the spray pipe and faces the front and rear surfaces of the plated steel sheet being transferred into the crack furnace. Making;

Measuring the surface temperature of the plated steel sheet at the exit to the crack;

Calculating a deviation between the measured surface temperature and a predetermined target temperature;

When the deviation occurs to output the opening and closing control signal of the injection amount control valve for adjusting the injection amount of the cold air injected to the plated steel sheet to reduce the deviation, the injection amount of the cold air injected into the plated steel plate toward the rear end of the crack Outputting the open / close control signal to increase step by step; And

And controlling the injection amount of cold air injected into the plated steel sheet by controlling the opening and closing of the injection amount control valve according to the control signal.

Furthermore, the cooling method of the present invention,

After controlling the injection amount of cold air injected into the plated steel sheet,

Determining whether all the injection amount control valves are opened or closed; Outputting a control signal for a fan rotational speed of the intake fan to reduce the deviation when the injection amount control valves are all opened and closed; And controlling an air blowing amount of cold air blown from the intake fan by controlling a fan rotation speed of the intake fan according to the control signal. It may further include.

In an embodiment of the present invention, the step of spraying cold air to the plated steel sheet being transferred, it is preferable to spray in the width direction of the front and rear of the plated steel sheet.

And in the present invention, the step of outputting the opening and closing control signal of the injection amount control valve, if the measured temperature is higher than the target temperature outputs a control signal for the opening (open) of the injection amount control valve, if the low injection rate adjustment It is desirable to output a control signal for the close of the valve.

At this time, if the measured temperature is higher than the target temperature, and outputs a control signal to increase the number of opening the injection amount control valve (open), if it is low to increase the number of closing the injection amount control valve (close) It is more preferable to output a control signal.

According to the present invention by cooling the plated steel sheet to maintain the desired alloying state for the hot-dip galvanized steel sheet that passes through the crack quickly by the high speed of the line to prevent the occurrence of powdering of the coated steel sheet in advance to improve the quality and productivity It can be effective.

In addition, according to the present invention, since the amount of cold air injection of the injection nozzle and the amount of cold air introduced from the outside are controlled according to the temperature of the plated steel sheet measured at the inlet and the outlet of the crack, the cooling control can be performed in real time according to the material of the plated steel sheet. There is.

In addition, according to the present invention, the cooling efficiency of the hot-dip galvanized steel sheet can be maximized by increasing the cooling step by step toward the rear end portion of the crack according to the characteristics of steel grade, wide, narrow, and component of the hot-dip galvanized steel sheet, thereby providing excellent plating. Alloying of the steel plate and surface quality of the plating layer can be attained.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

2 is a front view of a cooling apparatus of a hot dip galvanized steel sheet according to an embodiment of the present invention.

Referring to FIG. 2, the cooling apparatus of the hot-dip galvanized steel sheet according to the present invention includes a cracking furnace 100 formed of a natural cooling zone 120 and a forced cooling zone 140, and a plate passing through the forced cooling zone 140. It includes a cooling member for cooling the steel sheet. At this time, the cooling member is preferably configured to increase the cooling rate in the exit direction to the plated steel sheet passing through the forced cooling zone 140.

And in the present invention, the cooling member, the distribution header for connecting the plurality of injection pipes 200 and the plurality of injection pipes 200 configured to inject cold air to the plated steel sheet passing through the forced cooling zone 140 ( It may be configured to include an intake fan 700 for blowing cold air to the 300 and the distribution header (300).

In the present invention, the crack furnace 100 alloys the steel plate (S) plated with molten zinc and reacts the alloying of the steel plate (S) plated with molten zinc through ordinary air cooling and the natural It consists of a forced cooling zone 140 for cooling the plated steel sheet (S) to control the alloying growth of the plated steel sheet (S) passed through the cooling zone (120).

The crack furnace 100 is provided with an inlet 102 and an outlet 104 to allow the entry and exit of the plated steel sheet (S) to be transported by the drive of the top roll of the upper, between the hot-dip galvanized steel sheet (S) is continuous The natural cooling zone 120 and the forced cooling zone 140 passing through are formed to maintain the ideal alloying temperature. In addition, the crack furnace 100 may be supported by a plurality of horizontal frames 12 and vertical frames 14 to be embedded in the chamber 18.

In the present invention, the natural cooling zone 120 is a section for reacting the alloying of the plated steel sheet (S) after the hot-dip galvanized steel sheet (S) is heated in a heater, in this natural cooling zone 120 is approximately 500 ~ 650 ℃ The plated steel sheet (S) heated in the range is subjected to the alloying reaction while air-cooling at a cooling rate of 5 ~ 6 ℃ / s.

The forced cooling zone 140 controls the alloying growth of the plated steel sheet S passing through the natural cooling zone 120. In the forced cooling zone 140, the forced cooling zone 140 passes through the natural cooling zone 120. When the delta (δ) phase is formed up to the plated layer surface of the plated steel sheet s, the plated steel sheet is formed such that the temperature difference ΔT defined in Equation 1 is in the range of 100 to 250 ° C. to suppress further alloying growth. Forced cooling

[Equation 1]

ΔT = Entry plated steel sheet temperature to crack (℃)-Side plated steel plate temperature to crack (℃)

[However, material thickness: 0.5 ~ 3.2t, plate speed: 180mpm or less due to cracking of plated steel sheet]

That is, in the present invention, when the delta (δ) phase is formed to the plated layer surface of the plated steel sheet (s), that is, after the time of proper alloying, the plated layer is removed by cooling the plated steel sheet to a desired temperature range to suppress further alloying reaction. The thickness of the gamma (gamma) phase in the plating layer which becomes the cause can be effectively controlled. If ΔT defined in Equation 1 is less than 100 ° C., the above-described additional alloying reaction cannot be avoided, and thus, the thickness of the gamma (γ) phase in the plating layer may increase, thereby causing problems such as peeling of the plating layer. And the suppression of the above-mentioned alloying reaction is theoretically effective as ΔT is large, but the upper limit is limited to 250 ° C in consideration of the limitation of the realistic cooling system.

More preferably, ΔT defined by Equation 1 is limited to 130 to 160 ° C., but a plating layer having excellent characteristics may be obtained through suppression of the alloying reaction described above in this range.

In the present invention, from the above-described point of view, the forced cooling zone 140 is preferably discharged by cooling the plated steel sheet (s) to 450 ℃ or less, more preferably discharged by cooling to a temperature range of 350 ~ 420 ℃ It is.

In addition, in the present invention, the cooling member may include a plurality of injection pipes 200 installed in the forced cooling zone 140 and configured to spray cold air onto the plated steel sheet s passing through the forced cooling zone.

In the present invention, the forced cooling zone 140 may be formed in two or more stages including the first forced cooling zone 141 and the second forced cooling zone 142, or as a single zone instead of multiple stages. Can be done. However, in any case, it is preferable to configure the injection pipe 200 to increase the cold air injection amount toward the rear end to the rear of the forced cooling zone 140. For example, in the multi-stage forced cooling zone 140 including the first forced cooling zone 141 and the second forced cooling zone 142, the injection pipe 200 is arranged so that the injection amount of cold air increases from the front end to the rear end. It is preferable to. When the plated steel sheet is forcibly cooled in the forced cooling zone 140 having the arrangement of the injection pipes 200, excellent alloying degree can be obtained and surface quality characteristics of the plated layer can be very excellent.

On the other hand, in the present invention for the above-described cooling pattern may be configured such that the number of the injection pipe 200 is gradually increased toward the rear end in the multi-stage forced cooling zone 140.

In addition, it may be configured to narrow the width between the adjacent injection pipe 200 toward the rear end in the forced cooling zone 140 of the multi-stage.

Alternatively, the cold air ejection outlet diameter of the injection nozzle 202 provided in the injection pipe 200 may be increased step by step toward the rear end of the forced cooling zone 140 of the multistage. The distance between the injection pipe 200 and the plated steel sheet S may be closer to the rear end of the cooling zone 140 in steps.

In addition, each of the forced cooling zones (141, 142) is provided with a spray pipe 200 having a spray nozzle 202 is arranged horizontally to spray cold air to the front and rear of the plated steel sheet (S), such a minute As shown in FIG. 5, the yarn pipe 200 preferably includes a front injection pipe 210 and a rear surface of the plated steel sheet S, each having a spray nozzle 202 to spray cold air to the front surface of the plated steel sheet S. It may be made of a rear injection pipe 220 is provided with a spray nozzle 202 to spray cold air. 2 and 3, the pair of front and rear spray pipes 200 may be formed in plural numbers arranged at regular intervals along the advancing direction of the plated steel sheet S, and each of the spray nozzles 202 may be provided. In the axial direction of each of the injection pipes 200, that is, in the width direction of the steel plate is formed in a long and narrow slit shape it is possible to evenly spray cold air to the front and rear of the plated steel sheet (S).

Further, in the present invention, a plurality of injection pipes 200 provided with a wide injection nozzle 202a is disposed in the first forced cooling zone 141, whereas the second forced cooling zone 142 has a different injection width. The nozzles 202c are arranged at regular intervals, and between them, the injection pipes 200 provided with the wide and narrow injection nozzle pairs 202a and 202b are alternately arranged so that the nozzles 202c are wide and narrow as necessary. It is preferable to inject cold air into the plated steel sheet (S). Looking at the injection pipe 200 of the second forced cooling zone 142 with reference to Figures 3 and 6, a pair of left and right injection pipe consisting of a wide injection nozzle 202a and a narrow injection nozzle (202b) ( 200 may be arranged in six stages, the pair of injection pipes 200 may be disposed relatively close to the plated steel sheet (S) to improve the cooling capacity of the second forced cooling zone (142). have. Therefore, the plated steel sheet S sequentially passing through the first forced cooling zone 141 and the second forced cooling zone 142 is formed of a predetermined degree of alloying and surface quality by cold air injected through the injection nozzle 202. It can be controlled while cooling step by step to obtain a.

In addition, the cooling apparatus of the present invention in the injection nozzle 202 in the heat generated in the first forced cooling zone 141 and the second forced cooling zone 142, that is, the forced cooling zone 141, 142 of the multi-stage It may include an exhaust port (141a, 142a) for exhausting the heat generated while the plated steel sheet (S) is cooled by the injected cold air, each exhaust port (141a, 142a) is a first forced cooling zone ( 141 and the second forced cooling zone 142 are formed in the crack furnace 100 is located so that the heat is not exhausted through the outlet 104 of the crack furnace 100.

In addition, the exhaust ports 141a and 142a may be formed in plural along the traveling direction of the plated steel sheet S so as to efficiently exhaust the heat generated by the cold air injection of the injection nozzle 202 to the outside of the crack furnace 100. In addition, the door 150 may be configured to be opened and closed. The door 150 may be rotatably installed on one side of the crack path 100 by the rotation shaft 152 to open and close the exhaust ports 141a and 142a. In addition, the door 150 may be automatically opened and closed and the opening and closing angle by the opening and closing cylinder 160, for this purpose, one end of the rotating shaft 152 is connected to the connection link 154, the opening and closing the connection link 154 The operating rod 162 of the cylinder 160 may be connected. By operating the opening / closing cylinder 160, the operation rod 162 opens or closes the door 150 by rotating the rotation shaft 152 while pushing or pulling the connection link 154.

In addition, in the present invention, the cooling member may include a distribution header 300 for distributing cold air to the plurality of injection pipes 200 installed in the forced cooling zone 140.

As shown in FIGS. 2 and 4, the distribution header 300 is vertically connected to both sides of the plurality of front injection pipes 210 installed in the forced cooling zones 141 and 142 to distribute cold air. A pair of front distribution headers 310 and a plurality of rear distribution headers 320 may be configured to be vertically connected to both sides of the plurality of rear injection pipes 220 to distribute cold air.

As shown in FIG. 4, the front distribution header 310 and the rear distribution header 320 are connected to the horizontal branch pipes 400 that are bent to both front and rear sides, respectively, of each of the forced cooling zones 141 and 142. As shown in FIG. 2, the horizontal branch pipe 400 may be connected to a vertical branch pipe 500 connected to the intake fan 700. In addition, the horizontal branch pipes 400 of the forced cooling zones 141 and 142 are supported by a plurality of pipe shoes 410 installed in the horizontal frame 12, and the vertical portion connecting the horizontal branch pipes 400 to each other. The engine 500 may be optionally provided with a balance damper 510 to adjust the balance of the amount of cold air flow flowing into the first forced cooling zone 141 and the second forced cooling zone 142.

In addition, in the present invention, the cooling member may include an intake fan 700 for forcibly inhaling outside air (cold air) outside the chamber 18 and blowing it to the distribution header 300.

Both ends of the intake fan 700 are bent downward to be connected to one end of the connection pipe 600 connected to the vertical branch pipe 500. An intake pipe 710 connected to the outside while penetrating the side wall 16 of the chamber 18 is connected to the intake fan 700 to inhale outside air relatively cold compared to the inside of the chamber 18, and to intake the outside air forcibly. Is blown to the distribution header 300 through the connecting pipe 600, the vertical branch pipe 500 and the horizontal branch pipe 400. In addition, a filter 712 is installed in the intake pipe 710 to filter foreign substances such as dust contained in the outside air. Optionally, the air volume damper 610 may be installed at one end of the connection pipe 600 to which the intake fan 700 is connected, and in this case, the air volume of the intake fan 700 may be adjusted.

The other end of the connection pipe 600 is connected to the auxiliary intake fan 720 and is activated when the intake fan 700 is overloaded or broken. The auxiliary intake fan 720 is connected to the outside while passing through the side wall of the chamber 100. The intake pipe 730 may be connected to intake cold outside air compared to the inside of the chamber 10. In addition, the auxiliary intake pipe 730 is provided with a filter 732 may filter foreign substances such as dust contained in the outside air. In addition, a check valve 620 may be installed at the other end of the connection pipe 600 to prevent a phenomenon in which outside air sucked from the intake fan 700 flows back to the auxiliary intake fan 720.

The above-described intake fan 700 (preferably including the auxiliary intake fan 720) forcibly sucks outside air by fan rotation and blows it out through the connection pipe 600 and the branch pipes 400 and 500. The rotation speed of the fan of the intake fan 700 is controlled by the speed control unit 40 to be described later to control the air blowing amount.

On the other hand, the cooling device of the present invention,

A plurality of injection amount control valves 230 respectively formed in the plurality of injection pipes 200; A temperature measuring part 10 for measuring the surface temperature of the plated steel sheet S at the exit side of the crack furnace 100; An air quantity control unit 20 for outputting a control signal using the measured surface temperature; And a valve control unit 30 for controlling the injection amount control valve 230, respectively. Furthermore, in the above configuration, it may be configured to further include a speed control unit 40 for controlling the fan rotational speed of the intake fan 700.

The injection amount control valve 230 is installed in the plurality of injection pipes 200 to adjust the injection amount of cold air injected into the plated steel sheet (S) through the injection nozzle 202 of each injection pipe 200. This is for adjusting the injection amount of cold air injected through the injection nozzles 202 provided in the plurality of injection pipes 200 according to the surface temperature of the plated steel sheet S measured at the exit 104 of the crack furnace 100. will be. Further, by adjusting the left and right injection balance of the injection nozzle 202 in a balanced manner, it may be possible to prevent the cold phenomenon from being drawn to any part of the plated steel sheet (S). The injection amount control valve 230 is controlled by the valve control unit 30 its operation.

The temperature measuring unit 10 is installed at the outlet 104 of the crack furnace 100 to measure the surface temperature of the plated steel sheet (S) exiting the crack furnace 100. This is because the surface temperature of the plated steel sheet S at the outlet 104 of the crack furnace 100 is closely related to the alloying degree of the plated steel sheet S. For cooling control. The surface temperature measured by the temperature measuring unit 10 is input to the air quantity control unit 20.

The air volume controller 20 calculates a deviation between the measured surface temperature of the plated steel sheet S and a target temperature input from the host computer 50, and reduces the deviation, such as the valve controller 30 and the speed controller 40. Outputs a predetermined control signal. Preferably, the air amount control unit 20 outputs a control signal for opening and closing the injection amount control valve 230 to the valve control unit 30 so as to reduce the deviation value between the target temperature and the measured surface temperature of the plated steel sheet (S). . Further, optionally, the air amount controller 20 outputs a control signal for the fan rotational speed of the intake fan 700 to the speed controller 40.

The valve control unit 30 and the speed control unit 40 control the opening and closing of the injection amount control valve 230 and the fan rotation speed of the intake fan 700 according to the control signal of the air amount control unit 20, respectively. For example, when the measured surface temperature is higher than the target temperature, the injection amount control valve 230 is controlled to increase the cold air injection amount to reduce the deviation, and the fan rotation speed is increased. This lowers the surface temperature and approaches the target temperature. Here, the opening and closing speed of the injection amount control valve 230 and the fan rotation speed is preferably set appropriately according to the steel grade, physical properties, line speed, measured surface temperature and the like of the plated steel sheet.

At this time, the air volume control unit 20 primarily outputs a control signal for opening and closing the injection amount control valve 230, and secondly outputs a control signal for the fan rotational speed of the intake fan 700. Specifically, when the deviation between the target temperature and the measured surface temperature of the plated steel sheet (S) occurs by reducing the deviation primarily through the opening and closing of the injection amount control valve 230, the injection amount control valve 230 If the deviation does not decrease even if all the opening and closing, that is, all open or closed, it is preferable to reduce the deviation by adjusting the fan rotational speed of the intake fan 700 secondary.

On the other hand, the upper computer 50 presets the target temperature of the plated steel sheet S in consideration of the steel grade, width, thickness, physical properties, line speed, etc. of the plated steel sheet S being transferred from the crack furnace 100. And it is transmitted to the air volume control unit 20. This target temperature may be set differently according to the characteristics of the plated steel sheet (S).

Hereinafter, the overall operation of the hot-dip galvanized steel sheet cooling apparatus according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The hot-dip galvanized steel sheet S passing through the heater by driving the top roll is transferred into the crack furnace 100 and flows into the inlet 102 of the crack furnace 100 and passes through the natural cooling zone 120. The hot-dip galvanized steel sheet (S) is slowly cooled naturally while performing an alloying reaction while passing through the cooling zone 120. Subsequently, when the plated steel sheet S flowing through the natural cooling zone 120 and introduced into the first forced cooling zone 141 forms a delta (δ) phase up to the surface of the plated layer, the first forced cooling is suppressed to further suppress alloying growth. In the zone 141 and the second forced cooling zone 142, the plated steel sheet s is forcedly cooled to a range satisfying Equation (1).

To this end, the outside air intake through the intake pipe 710 in sequence by the operation of the intake fan 700, the connecting pipe 600, the vertical branch pipe 500, the horizontal branch pipe 400, the distribution header 300 While passing through the injection pipe 200, the cold air supplied to the injection pipe 200 is injected to the front and rear of the plated steel sheet (S) through the injection nozzle (202). At this time, cold air may be gradually injected to the plated steel sheet S gradually from the first forced cooling zone 141 to the second forced cooling zone 142, for example, to the second forced cooling zone 142. Increasing the number of injection pipes 200 for cold air injection step by step, narrowing the width between the injection pipes 200 step by step, increasing the cold air injection outlet of the injection nozzle 202 step by step, or injection nozzle This can be achieved by bringing the distance between 202 and the plated steel sheet S in steps.

On the other hand, the temperature measuring unit 10 installed in the outlet 104 of the crack path 140 measures the surface temperature of the plated steel sheet (S) exiting to the outlet 104. The measured surface temperature is input to the air volume controller 20. The air volume controller 20 compares the target temperature of the plated steel sheet S input from the upper computer 50 with the surface temperature measured by the temperature measuring unit 10 to calculate the deviation. Subsequently, a predetermined control signal for opening / closing the injection amount control valve 230 is output to the valve control unit 30 so as to reduce the deviation. In addition, a predetermined control signal for the fan rotational speed of the intake fan 700 is selectively output to the speed controller 40 so as to reduce the deviation.

Furthermore, the valve control unit 30 primarily controls the injection amount control valve 230 to adjust the injection amount of cold air injected to the plated steel sheet S through the injection nozzle 202 according to the control signal of the air amount control unit 20. When the opening and closing of the injection amount control valve 230 is not able to reduce the deviation, that is, even if the opening or closing all the injection amount control valve 230 (close) when the deviation can not be reduced Secondly, the speed controller 40 controls the fan rotational speed of the intake fan 700 in order to adjust the air flow rate of the cold air by forcibly sucking the cold air from the outside according to the control signal of the air volume control unit 20.

At this time, it is preferable that the injection amount control valve 230 installed in each injection pipe 200 is controlled to open and close at each stage so as to take much or less heat amount according to the material characteristics of the plated steel sheet (S). In this way, the heat generated when the plated steel sheet S is cooled by the cold spray of the injection nozzle 202 is exhausted through the exhaust port 141a opened by the operation of the door 150, and the outlet 104 of the crack path 100 is discharged. The exhaust of the furnace is prevented. That is, the door 150 closing the exhaust port (141a), as shown in Figure 7a, the operation rod 162 is operated by the operation of the opening and closing cylinder 160 to push the connection link 154, the connection link 154 Rotating shaft 152 connected to the rotation is to open the exhaust port (141a). In addition, the door 150 may maximize the exhaust of heat by opening the exhaust port 141a completely as shown in FIG. 7C.

In addition, the balance damper 510 installed in the vertical branch pipe 500 connecting the horizontal branch pipe 400 of the first forced cooling zone 141 and the second forced cooling zone 142 as described above is provided from the intake fan 700. Controls the flow of intaken cold air. That is, by adjusting the balance damper 510, the amount of cold air blowing in the first forced cooling zone 141 and the second forced cooling zone 142 can be controlled.

In addition, the auxiliary intake fan 720 is operated at the time of failure of the intake fan 700, and does not interfere with cooling control of alloying growth of the plated steel sheet S, and a check valve 620 is installed at the connection pipe 600 to provide an intake fan ( Backflow of the outside air taken in by 700 is prevented.

On the other hand, Figure 8 is a control flow chart for cooling the hot-dip galvanized steel sheet according to an embodiment of the present invention.

Referring to Figure 8, the hot-dip galvanized steel sheet cooling method of the present invention transfers the plated steel sheet (S) to the crack furnace 100 for alloying the hot-dip galvanized steel sheet and suck the cold air from the outside in the intake fan 700 the crack In the process of spraying cold air to the plated steel sheet (S) being transferred from the furnace. First, the surface temperature of the plated steel sheet S which is transferred from the crack furnace 100 and exits through the outlet 104 is measured by the temperature measuring unit 10 (S100). The temperature measuring unit 10 outputs the measured surface temperature to the air quantity control unit 20.

Subsequently, the air volume controller 20 compares the target temperature of the plated steel sheet S set in advance by the upper computer 50 with the surface temperature measured by the temperature measuring unit 10 to calculate a deviation between the two temperatures (S102 and S104). ). If a deviation occurs, the control signal for opening and closing the injection amount control valve 230 is output to the valve control unit 30 so as to reduce the deviation (S106). The valve control unit 30 controls the opening and closing of the injection amount control valve 230 according to the control signal of the air amount control unit 20 (S108). At this time, it is determined whether the injection amount control valve 230 is already open or closed (ie, all open or closed) (S110), and if not already opened or closed, the injection amount control valve 230 according to the corresponding control signal Open and close the (S112). Subsequently, the process proceeds to step S100 again to measure the surface temperature of the plated steel sheet S again at the outlet of the crack furnace 100 in the temperature measuring unit 10.

If the injection amount control valve 230 is already opened and closed at step S110, the air volume control unit 20 outputs a control signal for the fan rotational speed of the intake fan 700 to the speed control unit 30 because the injection amount control valve 230 is already opened and closed. (S114). As a result, the speed controller 40 adjusts the fan rotation speed of the intake fan 700 according to the control signal (S116).

On the other hand, the injection amount control valve 230 is provided in each of the plurality of injection pipe (200). Such a plurality of injection amount control valve 230 is preferably opened and closed step by step for each position. The opening and closing rate of the injection amount control valve 230 is appropriately set in accordance with the deviation of the surface temperature and the target temperature in the air amount control unit 20.

Hereinafter, the present invention will be described in detail through a preferred embodiment.

Example 1

TABLE 1

ingredient C N Ti Nb Sol.Al B Mn P Si S Less than 50ppm Less than 100ppm 100-600 ppm 30-200 ppm 0.01 ~ 0.1wt% 20ppm or less Less than 0.2wt% Less than 300ppm 0.001 ~ 0.1wt% Less than 200ppm

The steel specimen having a thickness of 0.7t having the composition as shown in Table 1 was annealed under normal conditions and then immersed in a hot dip galvanizing bath. Then, after heating the hot-dip galvanized plated steel sheet having a plated layer of approximately 39.7 ~ 42.6g / m ² thickness on the surface through a heater, using the crack furnace of the present invention consisting of a natural cooling zone and a forced cooling zone After cooling under the cooling conditions of, the plated layer characteristics of the produced hot-dip galvanized steel sheet was evaluated. And for comparison, after the hot-dip galvanized steel sheet having a plating layer of the thickness was prepared using a conventional cracking furnace to perform air cooling, the characteristics of the plating layer of the plated steel sheet was also evaluated.

Meanwhile, the length of the crack furnace used in this experiment was 32m, and the plate speed was controlled to 140mpm due to the crack of the plated steel sheet. In addition, the entry and exit plated steel sheet temperature to the crack, the temperature difference (ΔT) defined by the above Equation 1 is shown in Table 2 below.

TABLE 2

Entry temperature due to crack
(℃) Exit temperature by crack
(℃) Temperature difference
(△ T) Top Roll Temperature
(℃) Conventional One 515 425 90 313 2 512 418 94 316 3 513 420 93 317 Invention One 515 411 104 310 2 514 404 110 304 3 514 396 118 298 4 514 407 107 306 5 514 403 111 303 6 514 380 134 286 7 512 379 133 284

And to evaluate the alloying degree (using wet analysis) and powdering (powdering) of the plated steel sheet produced by this method, the results are shown in Figure 9, and also, the cross-sectional picture of the plated layer of each of the evaluated test pieces also shown in Figure 10 (ag) and FIG. 11 (ac). Specifically, Figure 9 is a view showing the alloying degree and powdering (powdering) of the 0.7t thin material manufactured using the cooling device of the present invention compared with the conventional material. 10 (a-g) shows a cross-sectional texture picture of the plating layer of the inventive materials of FIG. 9, and FIG. 11 (a-c) shows a cross-sectional texture picture of the plating layers of the conventional materials of FIG.

First, as shown in Figure 9, Inventive materials 1-7 (b1 ~ b7) and conventional materials 1-3 (a1 ~ a3) produced using the cooling apparatus of the present invention in terms of alloying degree of the plated steel sheet produced It can be seen that it falls within the appropriate range. However, considering the powdering (powdering) aspect, it can be seen that the powdering (powdering) peeling width of the conventional materials is larger than the invention.

This can be easily seen by the analysis of Figure 10 (ag) and Figure 11 (ac), specifically in the case of the invention material (1-7) of the present invention of Figure 10 (ag) in the cooling process using the cooling device of the present invention The growth of the gamma (γ) phase in the plating layer is suppressed, but in the case of the conventional material (1-3) of FIG. 11 (ac), the thickness of the gamma (γ) phase is increased, which may cause problems such as peeling of the plating layer. 10 (a-g) correspond to the invention material 1-7 in order, and FIG. 11 (a-c) corresponds to the conventional material 1-3. In addition, as shown in Figure 9, in the case of the present invention, it can be seen that the powdering (powdering) peeling width also decreases as the degree of alloying decreases, and better powdering (powdering) when the temperature deviation is ΔT 130 ℃ or more It can be seen that it shows characteristics.

(Example 2)

[Table 3]

ingredient C N Ti Nb Sol.Al B Mn P Si S Less than 80ppm Less than 100ppm 100-600 ppm 30-200 ppm 0.01 ~ 0.1wt% 20ppm or less Less than 0.3wt% Less than 500ppm 0.001 ~ 0.1wt% Less than 200ppm

The steel specimen of thickness 1.4t having the composition as shown in Table 2 was annealed under normal conditions and then immersed in a hot dip galvanizing bath. Then, after heating the hot-dip galvanized plated steel sheet having a plated layer of approximately 41.4 ~ 45.2g / m ² thickness on the surface through a heater, using the crack furnace of the present invention consisting of a natural cooling zone and a forced cooling zone After cooling under the cooling conditions of, the plated layer characteristics of the produced hot-dip galvanized steel sheet was evaluated. And for comparison, after the hot-dip galvanized steel sheet having a plating layer of the thickness was prepared using a conventional cracking furnace to perform air cooling, the characteristics of the plating layer of the plated steel sheet was also evaluated.

Meanwhile, the length of the crack furnace used in this experiment was 32m, and the plate speed was controlled to 75mpm due to the crack of the plated steel sheet. In addition, the entry and exit plated steel sheet temperature to the crack, the temperature difference (ΔT) defined by the above Equation 1 is shown in Table 4 below.

[Table 4]

Entry temperature due to cracking (℃) Exit temperature by cracking (℃) Temperature difference (△ T) Top roll temperature (℃) Conventional One 514 424 90 313 Invention One 515 371 143 281 2 515 363 152 273 3 515 363 152 275

And to evaluate the alloying degree (using wet analysis) and powdering (powdering) of the plated steel sheet produced by this method, the results are shown in Figure 12, and also the cross-sectional picture of the plated layer of each of the evaluated test pieces also shown in Figure 13 It is shown in (ad). Specifically, Figure 12 is a view showing the alloying degree and powdering (powdering) of the 1.4t thick material manufactured by using the cooling apparatus of the present invention compared with the conventional material, Figure 13 (ad) is a test of Figure 12 A cross sectional photograph of the plated layer of the ashes is shown.

As shown in FIG. 12, Inventive Materials 1-3 (b1 to b3) and Conventional Materials 1 (a) prepared under predetermined cooling conditions using the cooling apparatus of the present invention are appropriate in terms of alloying degree of the manufactured plated steel sheet. It can be seen that it belongs to the range. However, in consideration of the powdering (powdering) aspect, it can be seen that the powdering (powdering) peeling width in the case of the conventional material is larger than the invention material.

That is, as shown in Figure 13 (ad), in the case of the inventive material (1-3), the growth of the gamma (γ) phase in the plating layer is suppressed in the cooling process using the cooling apparatus of the present invention, Figure 11 (ac In the case of the conventional material (1), the thickness of the gamma (γ) is increased, which may cause problems such as peeling of the plating layer. On the other hand, in Fig. 10 (a), the conventional material 1 corresponds to the invention material 1-3 in Fig. 10 (b-c).

(Example 3)

A steel specimen having a thickness of 0.7t having the composition as shown in Table 1 of Example 1 was annealed under normal conditions and then immersed in a hot dip galvanizing bath. Subsequently, after heating the hot-dip galvanized plated steel sheet having a plating layer having a thickness of approximately 46 g / m ² on the surface through a heater, it is composed of a multi-stage forced cooling zone composed of a natural cooling zone and a first and second forced cooling zones. After cooling using the crack furnace of the present invention, the plated layer properties of the produced hot-dip galvanized steel sheet was evaluated. Meanwhile, the length of the crack furnace used in this experiment was 32m, and the plate speed was controlled to 140mpm due to the crack of the plated steel sheet.

First, although the cooling conditions belong to the scope of the present invention, after cooling the plated steel sheet by changing the cooling mode in the forced cooling zone, the characteristics of the plated steel sheet were evaluated. Specifically, a full cooling material is obtained through full cooling to cool the entire forced cooling zone, and also control cooling to increase the amount of cold air sprayed toward the rear end of the forced cooling zone. The control coolant was prepared through the). In addition, as a comparison to the conventional soaking (Soaking) material produced through the conventional air cooling in the cracking furnace was also manufactured.

The alloying degree of the alloy plated material specimens prepared as described above is shown in FIG. 14 by measuring the degree of alloying for the left side, the center, and the right side of the plated steel sheet. As shown in FIG. 14, it can be seen that the full cooling material and the control cooling material manufactured using the cooling apparatus of the present invention have superior alloying degree of the plating layer compared with the conventional soaking material.

In addition, in terms of alloying degree, it can be seen that the full cooling material has slightly better characteristics than the control cooling material.

On the other hand, when the alloy plated steel sheet is applied to the outer plate material of the automotive steel sheet, it is required to be excellent in the roughness and surface uniformity of the surface of the plating layer as well as the alloying degree described above. Figure 15 (a-c) is a surface SEM and three-dimensional surface image to show the surface layer uniformity according to the cooling mode of the test material. Specifically, FIG. 15 (a) shows a conventional soaking material, 15 (b) shows a control cooling material of the present invention, and 15 (c) shows a full cooling material of the present invention.

As shown in Figure 15 (a-c), in the case of the soaking material, it can be seen that the surface properties of the plating layer as a whole is not good. And the full cooling material shows better surface quality than the soaking material, but the surface quality is somewhat lower than the control cooling material.

That is, as can be seen from Fig. 14 and 15 (ac), the full cooling material of the present invention is advantageous in terms of alloying degree of the plating layer, but the control coolant of the present invention is excellent in the overall aspect considering the surface quality characteristics of the plating layer. It can be seen that it shows characteristics.

In other words, in the cooling apparatus of the present invention, it is possible to more effectively manufacture the plated steel sheet having excellent surface quality as well as alloying by cooling the plated steel sheet by increasing the amount of cold air to the rear end of the forced cooling zone.

DETAILED DESCRIPTION The drawings and the detailed description of the invention are merely exemplary of the present invention, which are used only for the purpose of illustrating the present invention and are used to limit the scope of the invention as defined in the claims or claims. no. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Hot-dip galvanized steel sheets used in automobiles and the like are treated as a matter of which the quality of the plating layer is very important. When powdered peeling occurs in such a plated steel sheet, it leads to a fatal defect in product quality. Therefore, in the actual industrial site, it is important to control the alloying state of the steel plate coated with molten zinc in the surface treatment process to significantly reduce the powdered peeling width of the plated steel sheet. To this end, there is a continuous need for a technique of cooling a hot-dip galvanized steel sheet to an appropriate temperature.

Applying the cooling apparatus and method of the hot-dip galvanized steel sheet of the present invention to properly cool the hot-dip galvanized steel sheet that passes through the crack furnace to control the alloying state of the coated steel sheet, thereby preventing the occurrence of powdering in advance. can do. Therefore, the present invention can be very usefully used in the surface treatment process.

1 is an exemplary view showing a conventional hot dip galvanizing method.

Figure 2 is a side view of the hot-dip galvanized steel sheet cooling apparatus according to the present invention.

Figure 3 is a side view of the hot-dip galvanized steel sheet cooling apparatus according to the present invention.

4 is a plan view of the hot-dip galvanized steel sheet cooling apparatus according to the present invention.

5 is a cross-sectional view taken along the line A-A of FIG.

6 is a cross-sectional view showing main parts of a second forced cooling zone according to an embodiment of the present invention;

7a to 7c is an operation of the door according to an embodiment of the present invention.

8 is a flow chart showing a hot-dip galvanized steel sheet cooling method according to the present invention.

9 is a view showing the alloying degree and powdering properties of the 0.7t thin material manufactured using the cooling device of the present invention in comparison with the conventional material.

Figure 10 (a-g) is a cross-sectional texture picture of the plating layer of the inventive material of Figure 9;

Figure 11 (a-c) is a cross-sectional texture picture of the plating layer of the conventional materials of Figure 9;

12 is a view showing the alloying degree and powdering properties of the 1.4t thick material manufactured using the cooling device of the present invention in comparison with the conventional material.

Figure 13 (a-d) is a cross-sectional structure photograph of the plating layer of the test materials of the present invention of Figure 12.

14 is a view showing a change in alloying degree for each cooling mode.

15 (a-c) is a surface SEM and three-dimensional surface image to show the plating layer surface uniformity according to the cooling mode of FIG.

Explanation of symbols on the main parts of the drawings

10: temperature measuring unit 20: air volume control unit

30: valve control unit 40: speed control unit

100: cracked 120: natural cooling zone

140: forced cooling zone 150: door

160: opening and closing cylinder 200: injection pipe

202: injection nozzle 230: injection amount control valve

300: distribution header 400: horizontal branch pipe

500: vertical branch pipe 600: connector

610: air volume damper 700: intake fan

Claims (22)

When the delta (δ) phase is formed up to the natural cooling zone for alloying the hot-dip galvanized steel sheet heated to a temperature of 480 ° C. or higher while cooling through natural cooling, and the plated layer surface of the plated steel sheet passing through the natural cooling zone, A crack consisting of a forced cooling zone for forcibly cooling the plated steel sheet so that the alloying growth can be suppressed so that the temperature difference ΔT defined in Equation 1 below satisfies the range of 100 to 250 ° C .; And And a cooling member for forcibly cooling the plated steel sheet passing through the forced cooling zone. [Equation 1] ΔT = temperature of plated steel sheet in crack zone (℃)-temperature of plated steel sheet in crack zone (℃) [However, material thickness: 0.5 ~ 3.2t, plate speed: 180mpm or less due to cracking of plated steel sheet] The method of claim 1, The cooling member may include a plurality of injection pipes for injecting cold air into the plated steel sheet passing through the forced cooling zone; A distribution header connected to distribute cold air to the plurality of injection pipes, respectively; And an intake fan forcibly drawing outside air to blow cold air into the distribution header. The method of claim 1, Cooling apparatus of the alloyed hot-dip galvanized steel sheet, characterized in that the temperature difference (ΔT) is forced cooling the plated steel sheet to satisfy the 130 ~ 160 ℃ range. The method of claim 1, Cooling apparatus for the galvanized hot-dip galvanized steel sheet, characterized in that the discharged by cooling the plated steel sheet to a temperature in the range of 420 ~ 350 ℃ in the forced cooling zone. The method of claim 1, And the cooling member is configured to increase the cooling rate in the exiting direction of the forced cooling zone with respect to the plated steel sheet passing through the forced cooling zone. The method of claim 2, The forced cooling zone is composed of a plurality of stages including at least a first forced cooling zone and a second forced cooling zone, the injection pipe installed in the forced cooling zone increases the amount of cold air injection to the plated steel plate in the exit direction of the forced cooling zone. Cooling apparatus for alloyed hot-dip galvanized steel sheet, characterized in that configured to be. The method of claim 2, Each of the injection pipe is a cooling device for alloyed hot-dip galvanized steel sheet, characterized in that it is arranged horizontally at regular intervals along the traveling direction of the plated steel sheet. The method of claim 7, wherein The spray pipe is a cooling device for alloyed hot-dip galvanized steel sheet characterized in that it comprises a front injection pipe and a rear injection pipe is provided with a slit injection nozzle to evenly spray cold air to the front and rear of the plated steel sheet, respectively. The method of claim 2, The distribution header is composed of a front distribution header and a rear distribution header connected to distribute cold air to the front and rear injection pipes, respectively, and the front and rear distribution headers are connected to horizontal branch pipes branched to both sides of the intake fan. Cooling apparatus for alloyed hot dip galvanized steel sheet. The method of claim 1, At least one exhaust port formed in the crack furnace to exhaust heat generated by cooling the plated steel sheet of the cooling member in the forced cooling zone; And A door rotatably connected to the crack passage to open and close the exhaust port; Cooling apparatus of alloyed hot-dip galvanized steel sheet further comprising a. The method of claim 10, Cooling apparatus for the alloyed hot-dip galvanized steel sheet further comprises a opening and closing cylinder for connecting the door and the crack to adjust the opening and closing angle of the door. The method of claim 2, The injection pipe is composed of a front injection pipe and a rear injection pipe so as to inject cold air into the front and rear of the plated steel sheet, respectively, and the distribution header is configured as a front distribution header and a rear distribution header to distribute cold air to the front and rear injection pipes, respectively. The front and rear distribution headers are connected to horizontal branch pipes respectively provided in the forced cooling zone, The plurality of injection pipes installed in the forced cooling zone are connected to each of the front and rear distribution headers, and the horizontal branch pipe of the forced cooling zone is connected to a vertical branch pipe connected to the intake fan. Device. The method of claim 6, Cooling apparatus of the alloyed hot-dip galvanized steel sheet, characterized in that the plurality of spray pipes installed in the at least one forced cooling zone is provided with a wide and small injection nozzle alternately formed to spray cold air to the plated steel sheet formed in a wide and small width . The method of claim 2, A plurality of injection amount control valves for adjusting the amount of cold air injection in the respective injection pipes; A temperature measuring unit measuring a surface temperature of the plated steel sheet at the outlet of the crack; An air amount control unit outputting a control signal for opening and closing the injection amount control valve so as to reduce a deviation between the measured temperature and a predetermined target temperature; And A valve control unit controlling opening and closing of each injection amount control valve according to a control signal of the air amount control unit; Cooling apparatus of alloyed hot-dip galvanized steel sheet further comprising a. The method of claim 14, Cooling apparatus for the alloyed hot-dip galvanized steel sheet further comprises a speed control unit for controlling the fan rotational speed of the intake fan in accordance with a control signal of the air volume control unit. The method of claim 15, The air flow rate control unit cooling the alloying hot-dip galvanized steel sheet, characterized in that for outputting a control signal for the fan rotational speed of the intake fan after each injection amount control valve is opened (closed). The method of claim 14, And the air amount control unit outputs a control signal to the valve control unit such that the amount of cold air injected into the plated steel sheet increases step by step from the cooling zone to the rear end thereof. Transferring the plated steel sheet into a cracking furnace for alloying the hot-dip galvanized steel sheet; Intake fan sucks cold air from the outside and transfers it to the spray pipe through the distribution header, and sprays the cold air onto the plated steel plate through a cold air spray nozzle which is provided in the spray pipe and faces the front and rear surfaces of the plated steel sheet being transferred into the crack furnace. Making; Measuring the surface temperature of the plated steel sheet at the exit to the crack; Calculating a deviation between the measured surface temperature and a predetermined target temperature; When the deviation occurs to output the opening and closing control signal of the injection amount control valve for adjusting the injection amount of the cold air injected to the plated steel sheet to reduce the deviation, the injection amount of the cold air injected into the plated steel plate toward the rear end of the crack Outputting the open / close control signal to increase step by step; And Controlling the injection amount of cold air injected into the plated steel sheet by controlling the opening and closing of the injection amount control valve according to the control signal; Cooling method of alloyed hot-dip galvanized steel sheet comprising a. The method of claim 18, After controlling the injection amount of cold air injected into the plated steel sheet, Determining whether all the injection amount control valves are opened or closed; Outputting a control signal for a fan rotational speed of the intake fan to reduce the deviation when the injection amount control valves are all opened and closed; And Controlling the fan speed of the cold air blown from the intake fan by controlling a fan rotation speed of the intake fan according to the control signal; Cooling method of alloyed hot-dip galvanized steel sheet further comprising a. The method of claim 18, Injecting cold air into the plated steel sheet being transferred, Cooling method of the alloyed hot-dip galvanized steel sheet, characterized in that the spraying in the width direction of the front and rear of the plated steel sheet. 21. The method of claim 20, Outputting the opening and closing control signal of the injection amount control valve, If the measured temperature is higher than the target temperature, and outputs a control signal for the open (open) of the injection amount control valve, if the low alloyed melting, characterized in that for outputting a control signal for the close (close) of the injection amount control valve Cooling method of galvanized steel sheet. The method of claim 21, If the measured temperature is higher than the target temperature, output a control signal to increase the number of opening the injection amount control valve; if low, control to increase the number of closing the injection amount control valve. Cooling method of alloyed hot-dip galvanized steel sheet, characterized in that for outputting a signal.

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