JP3202512B2 - Wiping method and apparatus in continuous galvanizing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas wiping method in continuous hot-dip galvanizing capable of equalizing the amount of hot-dip zinc deposited on the front and back of a steel strip to be plated and performing gas wiping with high efficiency. It concerns the device.

[0002]

2. Description of the Related Art Generally, in a wiping method in a continuous hot-dip galvanizing facility, as shown in FIG. 2, a steel strip 2 that has exited an annealing furnace 13 passes through a snout 14 and then is stored in a hot-dip zinc pot 1. The support roll 5 is immersed in the support roll 15 and is turned by the sink roll 4, supported by the in-bath support roll 5 and the on-bath support roll 6, and rises vertically. The molten zinc adhering to the front and back of the steel strip 2 is wiped by a wiping gas injected from a pair of wiping nozzles 3 arranged on the bath surface of the molten zinc 15 with the vertically rising steel strip 2 interposed therebetween, and a predetermined amount is applied. The plating is controlled so as to provide the basis weight (see, for example, JP-A-4-285146).

In this case, usually, the amount of plating applied to the steel strip 2 is controlled by adjusting the injection amount of the wiping gas or the distance between the wiping nozzle 3 and the steel strip 2.

[0004]

In the conventional gas wiping method, the steel strip 2 to be wiped by the wiping nozzle 3 when manufacturing a steel strip having a small thickness and a wide width is shown in FIG. In some cases, the steel strip 2 tends to be stretched in the abdomen, and a phenomenon that a warped shape defect occurs may occur.

When such a warp occurs in the steel strip 2, it becomes difficult to bring the wiping nozzle 3 sufficiently close to the steel strip 2, and therefore, the wiping gas must be increased in order to obtain the same coating weight. And energy losses increase. In particular, when controlling the thin coating amount, the situation where the thin coating amount cannot be controlled unless the steel strip speed is lowered, which greatly impairs the productivity of the equipment.

[0006] When the warp shape defect occurs, the distance between the wiping nozzle 3 and the surface of the steel strip 2 is naturally slightly shifted and becomes non-uniform in the plate width direction. A quality defect, such as non-uniformity, will result. In order to maintain the lower limit of the coating weight, there is a problem that the average coating weight must be set to be much larger than the lower limit of the coating weight and controlled, resulting in a large loss of the zinc used.

[0007] The present invention prevents the problem of the prior art, that is, the unevenness of the distance between the wiping nozzle and the steel strip due to the warpage generated in the steel strip, thereby making the basis weight of the steel strip to be plated uniform. It is an object of the present invention to provide a wiping method and apparatus in continuous hot-dip galvanizing that can perform gas wiping with high efficiency.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made as a result of intensive studies to solve the above-mentioned problems, and as a result, the cause of the warpage has been identified, thereby leading to the development of the present invention. However, it is as follows. Upon invention of claim 1, wherein for achieving the above object, wiping the molten zinc in a continuous galvanizing attached to both sides of the plated steel strip by injecting the wiping gas from gas wiping nozzles, the Occurs on plated steel strip
Next to a wavy warp in the section of the strip in the thickness direction
When the wave height, which is the difference between the height of the matching peak and the valley, exceeds 2 mm
Only heating the wiping gas to, and satisfies the following relationship gas temperature T _G Wa <br/> Ipingugasu during the heating (℃) said relative thickness of the plated steel strip D (mm) This is a wiping method in continuous galvanizing.

The wiping gas temperature T _G (° C.) ≧ −400 D + 400 According to the second aspect of the present invention, the wiping gas injected from the gas wiping nozzle is supplied to the steel strip having a thickness of 0.9 m.
2. Heating is performed only when the temperature is equal to or less than m.
It is a wiping method in the continuous galvanizing described.

[0010] The present invention 請 Motomeko 3 described, wiping in air, continuous galvanizing of claim 1 or 2, wherein the use of a mixed gas of nitrogen or air and nitrogen as wiping gas Is the way.

[0011] According to a fourth aspect of the invention, the wiping unit in the continuous galvanizing wiping the molten zinc adhering to the sides of the plated steel strip by ejecting a wiping gas injected from the gas wiping nozzle, said wiping and <br/> heater installed in the middle of the pipe system for supplying gas, before which is arranged in the pipe downstream of the heater
A thermocouple for measuring the temperature of the wiping gas;
Based target gas temperature T _G of Pingugasu the relationship:
A calculator to calculate, and a target gas temperature T calculated by the calculator
_G is set, and the wiping
If the temperature of the temperature measurement signal is lower than the target gas temperature _TG ,
A controller for inputting a heating power increase signal to the heater.
Then , the edge of the steel strip to be plated is supercooled from the center part , and the wavy warp in the steel strip thickness direction cross section occurs .
A wiping device for continuous hot-dip galvanizing, characterized in that the wave height, which is the difference between the heights of adjacent peaks and valleys, is reduced. Serial _{T G (℃) ≧ -400 D} + 400

[0012]

[Action] Several causes were considered for the cause of warpage of the steel strip, but as a result of research, it was found that the cause was as follows. First, a phenomenon in which the edge of the steel strip 2 is supercooled from the center occurs at the time of wiping.
Is biased toward the edge of the steel strip, and the central part of the steel strip has a shape like a loose belly stretch. The slack in the central portion of the steel strip becomes a wavy warp as shown in FIG. 3 due to the pressure of the wiping gas injected from the in-bath support roll 5, the on-bath support roll 6, and the wiping nozzle 3.

Further, the cause of supercooling of the edge portion of the steel strip during wiping is mainly caused by the flow of the wiping gas in the edge direction before and after the wiping and the supercooling at the edge portion due to the suction of the outside air gas. . According to research, the temperature difference between the steel strip edge and the central part of the steel strip due to supercooling varies depending on the sheet thickness, etc., but is about 5 to 20 ° C., and this temperature difference causes the warpage shown in FIG. It became clear that a shape defect of the steel strip having a wave height H of about 1 to 3 mm occurred. The present invention
The above-mentioned wave height H of the warp is as shown in FIG.
In the steel strip thickness direction cross-section generated in the steel strip to be plated
A wave that is the height difference between adjacent peaks and valleys in a wavy warp
Shows the height H.

[0014] not by this wave-like occurrence, wasting or spending the energy of wiping can not be brought close to wiping nozzle 3 to sufficiently strip 2, the distance between the wiping nozzle 3 tip and the steel strip 2 and uniform Therefore, the amount of galvanized coating in the sheet width direction of the steel strip 2 becomes non-uniform, and a problem has occurred that a large amount of zinc is wasted unnecessarily in order to guarantee the lower limit of the galvanized coating.

Therefore, as a result of repeated studies to solve this problem, it is very difficult to make the flow of the wiping gas injected from the wiping nozzle uniform, and therefore, in the present invention, the wiping gas is heated and injected. Another object of the present invention is to prevent the cooling of the edge portion of the steel strip and sufficiently reduce the wave shape caused by the warpage of the steel strip. First, since the heating cost of the wiping gas increases even if the temperature of the wiping gas is increased unnecessarily, the wave height H of the warp without any hindrance was determined by an operation experiment. It was found that the amount of zinc deposited was almost uniform with no deviation, and the wiping nozzle could be sufficiently close to the steel strip.

Next, in order to keep the wave height H of the warp at 2.0 mm or less in the normal operation range, the gas wiping temperature should be set at some degree.
The experiment was performed by changing the thickness, width, speed of the steel strip, zinc deposition amount, etc. of the steel strip, and the following results were obtained. Strip width, strip speed and zinc coverage of the strip have little to do with the normal operating range. The strip thickness is directly related to the ease of cooling of the steel strip, so the wiping gas temperature is kept at room temperature and the strip width is 1000 to 1600 mm , and the strip speed is 60 to 140 m.
/ Min, and a specific weight of zinc of 20 to 60 g / m ² (one side), a detailed experiment was performed, and the result shown in FIG. 4 was obtained. That is, in FIG. 4, when the thickness of the steel strip increases, the wave height H due to the warp of the steel strip also decreases, and when the thickness exceeds 0.9 mm, the wave height H of the warp is 2.0 mm or less even at a normal wiping gas temperature. Thus, operational problems due to the wave shape do not occur. Conversely, when the thickness of the steel strip is reduced, the degree of supercooling at the edge of the steel strip increases, and accordingly, the wave height H of the warp also increases.

Subsequently, at each thickness of the steel strip, the wave height H of the warp is set to 2.0 m by increasing the temperature of the wiping gas.
The experiment was conducted to see if it can be suppressed to less than m. FIG. 5 shows an example of the experimental result. In FIG. 5, for example, the thickness of the steel strip is 0.7 m.
m, the gas wiping temperature must be lower in the normal operating range.
If the temperature is 120 ° C or higher, the wave height H of the warp is the target range.
It turned out that it can be made less than 0mm.

The wave height H of the warp is 2.0 m for each thickness of the steel strip.
FIG. 6 shows the minimum temperature of the wiping gas temperature to be set to m or less. FIG. 6 shows the wiping gas temperature T _G.
(° C.), assuming that the plate thickness is D (mm), it was found that the wave height H of the warp can be reduced to 2.0 mm or less if _TG ≧ −400 D + 400.

Although inexpensive air is suitable as the wiping gas, nitrogen gas or a mixed gas of air and nitrogen gas is also suitable.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic explanatory view showing an arrangement of a continuous hot-dip galvanizing apparatus used in an embodiment of the present invention. As shown in FIG. 1, the steel strip 2 to be plated out of the annealing furnace 13 passes through a snout 14, is immersed in molten zinc 15 stored in a molten zinc pot 1, turned by a sink roll 4, and It stands vertically by being supported by the middle support roll 5 and the on-bath support roll 6. The molten zinc adhering to the front and back of the steel strip 2 is wiped by wiping with a wiping gas injected from a pair of wiping nozzles 3 disposed on the bath surface of the molten zinc 15 with the vertically rising steel strip 2 interposed therebetween. Controlling to a predetermined plating weight is the same as in the conventional example shown in FIG.

In the present invention, a heater 8 is provided in the middle of a pipe 7 for supplying a wiping gas from a wiping blower 9 to a pair of wiping nozzles 3. The temperature of the wiping gas heated by the heater 8 is measured using a thermocouple 10 disposed on the pipe 7 on the downstream side of the heater 8. The target gas temperature T _G (° C.) of the wiping gas satisfies the relation of T _G (° C.) ≧ −400 D + 400 using the steel strip thickness D (mm) by the computer 12 that controls the continuous galvanizing equipment. And set it in the controller 11. For example, when the thickness of a steel strip is D = 0.7 mm, T _G (° C.) ≧ −
400 set to D + 400 = -400 × 0.7 × 400 = 120 ℃ become so for example T _G specific range 125 to 135 ° C. over 120 ° C. The.

After the wiping gas supplied from the wiping blower 9 to the pipe 7 is heated by the heater 8 provided in the middle of the pipe 7, the wiping gas is supplied to the wiping nozzle 3 to be injected and adhered to the front and back of the steel strip 2. Wiping the molten zinc. At this time, the temperature of the wiping gas heated by the heater 8 is measured by the thermocouple 10, and the temperature measurement signal is input to the controller 11.

The controller 11 determines whether or not the temperature of the input temperature measurement signal falls within the temperature range of 125 to 135 ° C. set by the computer 12. If the temperature is lower than 125 ° C., a heating power increase signal is output. Conversely, if the temperature is higher than 135 ° C., a heating power reduction signal is input from the controller 11 to the heater 8, and the heater 8 controls heating based on these signals to set the predetermined temperature 125 to 135.
Keep at ° C.

Steel strip thickness 0.7 mm, strip width 1300 mm, steel strip speed
When performing continuous hot-dip galvanizing of the steel strip 2 under the conditions of 120 m / min and a zinc adhesion amount of 45 g / m ² (one side), the air supplied to the wiping nozzle as the wiping gas by the heater 8 is set in the range of 125 to 135. When heated to ℃, the wave height H of the warp can be reduced to 2 mm or less, and the tip of the wiping nozzle can be brought closer to the steel strip.
As a result, the usage amount of the wiping gas could be reduced although it was several percent. In addition, the coating weight was uniform in the width direction of the steel strip, and gas wiping was performed with high efficiency.

The heater 8 may be a heater provided with an electric heater, but may be a heat-exchange type heater utilizing combustion exhaust gas of an annealing furnace usually installed in a continuous galvanizing facility. The most significant effect of the practice of the present invention is a reduction in the average amount of zinc deposition. Since the variation in the amount of zinc deposition in the conventional method was reduced, the average zinc deposition was reduced to about 0.5 to 2.0 g / m ² (one side). It became possible to reduce.

As a result, as shown in FIG. 7, according to the method of the present invention, a heating cost for heating the wiping gas by the heater is required as compared with the conventional method, but depending on the thickness of the steel strip. It can be seen that the production cost can be minimized when the calculated wiping gas is used.

[0027]

As described above, according to the present invention, in continuous hot-dip galvanizing, after wiping gas injected from a gas wiping nozzle is heated to a temperature set based on the thickness of a steel strip, the steel strip is heated. Since the molten zinc adhering to the front and back surfaces was wiped, the hot-dip galvanizing with a uniform basis weight could be performed with high efficiency while preventing the warp of the steel strip.

As a result, the amount of molten zinc used is reduced,
Manufacturing costs are reduced.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an arrangement of a continuous galvanizing apparatus of the present invention.

FIG. 2 is a schematic explanatory view showing an arrangement of a conventional continuous galvanizing apparatus.

FIG. 3 is an explanatory diagram showing a warp state of a steel strip in a wiping nozzle portion.

FIG. 4 is a diagram showing a relationship between a thickness D (mm) of a steel strip and a wave height H (mm) of a warp.

FIG. 5 is a diagram showing a relationship between a wiping gas temperature T _G (° C.) and a wave height H (mm) of steel strip warpage.

FIG. 6 shows the thickness D (mm) of the steel strip and the wiping gas temperature T _G.
FIG. 3 is a diagram showing the relationship with (° C.).

FIG. 7 shows a zinc reduction cost with respect to a wiping gas temperature,
It is a diagram which shows a heating cost and a manufacturing cost comparing the method of this invention with the conventional method.

[Explanation of symbols]

 Reference Signs List 1 molten zinc pot 2 steel strip 3 wiping nozzle 4 sink roll 5 support roll in bath 6 support roll on bath 7 piping 8 heater 9 wiping blower 10 thermocouple 11 controller 12 computer 13 annealing furnace 14 snout 15 molten zinc

Claims (4)

(57) [Claims] 1. A cross-section in a thickness direction of a steel strip to be plated when a molten wiping gas is sprayed from a gas wiping nozzle in a continuous hot-dip galvanizing to wipe molten zinc adhering to the front and back of the steel strip to be plated. In
A wave that is the height difference between adjacent peaks and valleys in a wavy warp
Apply the wiping gas only when the height exceeds 2 mm.
Heating and the gas temperature T of the wiping gas at the time of the heating
_G (° C.) wiping method in continuous galvanizing, characterized by satisfying the below <br/> SL relationship the relative thickness of the plated steel strip D (mm). Note Wiping gas temperature T _G (° C) ≧ −400 D + 400 Wherein the wiping gas injected from the gas wiping nozzle, wiping in claim 1 Symbol placement of continuous galvanizing, characterized in that the thickness of the plated steel strip is heated only when the 0.9mm or less Method. Wherein air as wiping gas wiping method in continuous galvanizing of claim 1 or 2, wherein the use of a mixed gas of nitrogen or air and nitrogen. 4. A wiping apparatus for continuous hot-dip galvanizing for wiping molten zinc adhering to the front and back surfaces of a steel strip to be plated by injecting a wiping gas injected from a gas wiping nozzle, wherein a piping system for supplying the wiping gas is provided. and the installed heater in the middle, under the heater
Temperature of the wiping gas provided in the pipe on the flow side
And a target gas temperature of the wiping gas.
A calculator for calculating the degree _TG based on the following relational expression;
The target gas temperature _TG calculated by the calculator is set, and the thermocouple is set.
The temperature of the wiping gas temperature signal measured at
If the temperature is lower than the target gas temperature _TG ,
It has a controller that inputs to the heater, and the steel strip in the thickness direction is cut when the edge of the steel strip to be plated is supercooled from the center.
Of the peaks and valleys adjacent to each other
A wiping device for continuous hot-dip galvanizing , wherein a wave height as a difference is reduced. Serial _{T G (℃) ≧ -400 D} + 400