JP7134591B2 - Continuous hot-dip galvanizing method and continuous hot-dip galvanizing equipment - Google Patents

Description

The present invention relates to a continuous hot-dip galvanizing method and a continuous hot-dip galvanizing apparatus for hot-dip galvanizing a steel sheet and heating the hot-dip galvanized steel sheet with an induction heating device to alloy the hot-dip galvanized layer.

In a continuous hot-dip galvanizing apparatus for continuously galvanizing a steel plate, the steel plate is passed through a hot-dip zinc bath and then heated to form an alloyed layer of zinc and iron on the surface layer of the hot-dip galvanized layer. Heating of the steel sheet during alloying is performed by induction heating using high-frequency current, and LF (Longitudinal Flux: parallel magnetic flux) method is generally adopted as induction heating (see Patent Document 1). In the LF method, a high-frequency current (primary current) is passed through an induction coil that surrounds the steel plate to generate magnetic flux parallel to the direction in which the steel plate advances. The resulting eddy currents accumulate to generate an induced current in the opposite direction to the primary current, thereby heating the steel plate without contact.

JP-A-6-330276

In addition to the above-mentioned LF method, TF (Transverse
Flux: vertical magnetic flux) method. In the TF method, an inductor (a good magnetic material) wound with an induction coil is placed on both sides of a steel plate. An induced current is generated along the route, which heats the steel plate.
Conventionally, the LF method has been adopted as an induction heating method for alloying, as described in Patent Document 1, but at present, steel types that are not easy to heat by the LF method are being manufactured. For these reasons, introduction of the TF method as an induction heating method for alloying is also under consideration.

By the way, when alloying is performed by induction heating, a force acts along the surface of the steel sheet, and thin steel sheets are especially susceptible to deformation. When the steel sheet is deformed, the hot-dip galvanized layer formed on the steel sheet is also affected and deformed. The deformation of the steel sheet is resolved when the steel sheet passes through the induction heating device, but the deformation of the coating is not resolved, and only the unevenness due to the deformation remains on the surface of the hot-dip galvanized steel sheet (hereinafter referred to as hot-dip galvanized steel sheet). sometimes.
When the hot-dip galvanized layer of the steel sheet is alloyed by adopting the TF method as the induction heating method, streak patterns extending in the width direction of the hot-dip galvanized steel sheet may occur.

The present invention has been made in view of this point, and is capable of producing a steel sheet in which the hot-dip galvanized layer is heated and alloyed by induction heating of the TF method and has no streak pattern. An object of the present invention is to provide a plating method and a continuous hot-dip galvanizing apparatus.

In order to achieve the above object, the present invention provides a continuous hot dip galvanizing method for hot dip galvanizing a steel sheet, heating the hot dip galvanized steel sheet with a heating device, and alloying the hot dip galvanized layer, The heating device includes a TF heating device that performs induction heating at least by a vertical magnetic flux method, and includes a step of controlling the temperature of the steel plate so that the temperature of the steel plate that has passed through the heating device decreases. , the temperature of the hot-dip galvanized layer of the steel sheet after a predetermined time of 0.5 seconds or more has passed after passing through the TF heating device is 510 ° C. or more and 545 ° C. or less , and the predetermined time of 0.5 seconds or more The temperature drop rate of the steel sheet is controlled so that the temperature of the hot-dip galvanized layer 2 seconds after the elapse of time is 500° C. or more and 540° C. or less , and the temperature is extended in the width direction and at a pitch of 5 to 10 mm in the sheet threading direction. It is characterized by smoothing the hot-dip galvanized layer, which is produced when a streak pattern having a length of 50 to 200 mm in the sheet width direction passes through the TF heating device .

The heating device has an LF heating device that performs heating by a parallel magnetic flux method, and after the steel plate is heated by the LF heating device until the temperature of the hot-dip galvanized layer of the steel plate reaches 480 ° C., the heated steel plate is It is preferable to heat to a predetermined temperature by the TF heating device.

It is preferable to blow gas onto the hot-dip galvanized layer of the steel sheet that has passed through the TF heating device to smooth the hot-dip galvanized layer.

Preferably, a contacting member is brought into contact with the hot-dip galvanized layer of the steel sheet that has passed through the TF heating device to smooth the hot-dip galvanized layer.

According to another aspect of the present invention, there is provided a continuous hot-dip galvanizing apparatus for hot-dip galvanizing a steel sheet, heating the hot-dip galvanized steel sheet with a heating device, and alloying the hot-dip galvanized layer, The apparatus has a TF heating device that performs induction heating at least by a vertical magnetic flux method, and controls the temperature of the steel plate so that the temperature of the steel plate that has passed through the heating device decreases, wherein the TF heating device The temperature of the hot-dip galvanized layer of the steel sheet after a predetermined time of 0.5 seconds or more after passing through the steel sheet reaches 510 ° C. or higher and 545 ° C. or lower , and the hot-dip galvanized layer 2 seconds after the predetermined time has elapsed. The temperature reduction rate of the steel sheet is controlled so that the temperature of the layer is 500 ° C. or higher and 540 ° C. or lower , and the stripes extending in the width direction of the plate and having a pitch of 5 to 10 mm in the plate passing direction and a length in the width direction of 50 to 200 mm It is characterized by comprising a temperature control device for smoothing the hot-dip galvanized layer generated when the pattern passes through the heating device .

The heating device has an LF heating device that performs heating by a parallel magnetic flux method, the LF heating device heats the steel sheet until the temperature of the hot-dip galvanized layer of the steel sheet reaches 480 ° C., and the TF heating device It is preferable to heat the steel plate heated by the LF heating device to a predetermined temperature.

It is preferable to include a smoothing device for blowing gas onto the hot-dip galvanized layer of the steel sheet that has passed through the TF heating device to smooth the hot-dip galvanized layer.

It is preferable to provide a smoothing device for smoothing the hot-dip galvanized layer by contacting the hot-dip galvanized layer of the steel sheet that has passed through the TF heating device.

According to the continuous hot-dip galvanizing method and the continuous hot-dip galvanizing apparatus of the present invention, it is possible to produce a steel sheet in which the hot-dip galvanized layer is heated and alloyed by induction heating of the TF method and has no streak pattern. .

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the outline of the continuous hot-dip galvanizing apparatus which concerns on embodiment of this invention. FIG. 2 is a diagram showing an outline of the TF heating furnace of FIG. 1; 1. It is a figure which shows an example of the temperature change of the steel plate passed through the continuous hot-dip galvanizing apparatus of FIG. It is a figure which shows the outline of the continuous hot-dip galvanizing apparatus which concerns on the 2nd Embodiment of this invention. 5 is a diagram showing an example of temperature change of a steel sheet that is passed through the continuous hot-dip galvanizing apparatus of FIG. 4. FIG. It is a figure which shows the outline of the continuous hot-dip galvanizing apparatus which concerns on the 3rd Embodiment of this invention. 7 is a diagram showing an example of temperature change of a steel sheet that is passed through the continuous hot-dip galvanizing apparatus of FIG. 6. FIG. It is a figure which shows the outline of the continuous hot-dip galvanizing apparatus based on the 4th Embodiment of this invention. It is a figure which shows the outline of the continuous hot-dip galvanizing apparatus based on the 5th Embodiment of this invention. It is a figure which shows the outline of the continuous hot-dip galvanizing apparatus which concerns on the 6th Embodiment of this invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

(First embodiment)
FIG. 1 is a schematic diagram of a continuous hot-dip galvanizing apparatus according to a first embodiment of the present invention.
In the continuous hot-dip galvanizing apparatus 1 shown in the figure, a steel sheet H is introduced into a hot-dip galvanizing bath 2 after being annealed in an annealing furnace (not shown).
The steel sheet H introduced into the hot-dip galvanizing bath 2 is turned upward by sink rolls 3 provided in the bath 2, and warped by support rolls 4, and then pulled out of the hot-dip galvanizing bath 2. be
A wiping gas is sprayed from the gas wiping nozzle 5 toward both sides of the hot-dip galvanized steel sheet H to adjust the coating amount.

The steel plate H with the adjusted coating weight passes through a damping device 6 that suppresses the vibration of the steel plate H. As shown in FIG. The damping device 6 may have a function to regulate the angle of the steel plate H with respect to the alloying heating furnace 7 in addition to the function of suppressing the vibration of the steel plate H.
As a method for suppressing vibration and regulating the angle by the vibration damping device 6, a method of blowing a high temperature gas (for example, 450° C. or higher) to the end portion of the steel plate H is conceivable. Alternatively, a method using electromagnetic force may be used.
Further, for example, a roller heated to 450° C. or more may be brought into contact with the end portion of the steel plate H to suppress the vibration of the steel plate H and regulate the angle of the steel plate H. Although the hot-dip galvanized layer of the steel sheet H is deformed by contact with rollers, the viscosity of the hot-dip galvanized layer decreases while the steel sheet H is being passed through the TF heating furnace 7. The deformed portion of the plating layer returns to the state before deformation. The width of the roller is, for example, 5 to 10 mm.

Note that the wiping gas from the gas wiping nozzle 5 may be used to suppress the vibration of the steel plate H and to regulate the angle without providing the damping device 6 described above.
Also, without providing the damping device 6, the amount of intermesh (roll pushing amount) of the support rolls 4 may be adjusted to suppress the vibration of the steel plate H and regulate the angle.

After passing through the damping device 6, the steel plate H is heated in a TF heating furnace 7 as a heating device according to the present invention, and the temperature is raised to 550±10° C., for example. The TF heating furnace 7 heats the steel plate H by induction heating of the TF method as described later. pass.

The hot-dip galvanized layer of the steel sheet H is alloyed while the steel sheet H reaches the upper roll 9 from the TF heating furnace 7 via the temperature control device 8 . The temperature controller 8 keeps the hot-dip galvanized layer in a low-viscosity state by controlling the rate of temperature drop. Methods for controlling the temperature drop rate include a method using combustion gas using a burner, etc., a method using high-temperature (e.g., 450 ° C. or higher) gas, a method using radiant heat, heat insulating materials and suppression of gas upward flow (weirs and hot gas There is a method of using a seal) together.
The alloyed steel plate H is cooled by a cooling device (not shown), and the passing direction is changed by the upper roll 9 .

By alloying the hot-dip galvanized layer in this manner, the weldability, corrosion resistance, pressability, etc. of the steel sheet H can be improved.

FIG. 2 is a diagram schematically showing the TF heating furnace 7, FIG. 2A is a schematic side view of the TF heating furnace 7, and FIG. It is a schematic cross-sectional view in.

The TF heating furnace 7 is provided, for example, as shown in FIG. 2, so that E-shaped cores 71 and 72, which are E-shaped in side view and cross-sectional view, face each other with the steel plate H interposed therebetween.
The E-shaped cores 71 and 72 are composed of ferromagnetic cores such as ferrite, laminated electromagnetic steel sheets, and amorphous alloys. Further, the E-shaped cores 71 and 72 have induction coils 73 and 74 wound around the center protrusions 71a and 72a.

The induction coils 73 and 74 are made of a conductor such as copper and connected to a power source (not shown). A magnetic flux M generated by the induction coils 73 and 74 penetrates the steel plate H in the thickness direction. In the TF heating furnace 7, an induced current perpendicular to this magnetic flux M is generated in the plate surface of the steel plate H, and the steel plate H is heated by the induced current. That is, the TF heating furnace 7 heats the steel sheet H by induction heating of the TF method. A similar heating effect can be obtained by any method other than the method shown in FIG.

FIG. 3 is a diagram showing an example of temperature change of the steel sheet H passing through the continuous hot dip galvanizing apparatus 1. As shown in FIG. The vertical axis in FIG. 3 indicates the temperature of the steel sheet H, and the horizontal axis indicates the elapsed time after the steel sheet H is withdrawn from the hot-dip galvanizing bath 2 .
As described above, the continuous hot-dip galvanizing apparatus 1 uses TF induction heating to raise the temperature to the alloying temperature. Therefore, after the alloying is completed, the surface of the hot-dip galvanized steel sheet H may have a streak pattern extending in the sheet width direction. For example, a pattern with a pitch of 5 to 10 mm in the sheet threading direction, a length of 50 to 200 mm in the sheet width direction, and a height of several μm may occur.

Therefore, in the continuous hot-dip galvanizing apparatus 1, as shown in FIG. The hot-dip galvanization of the steel sheet H is maintained in a low-viscosity state. Therefore, while the hot-dip galvanized steel sheet H passes through the temperature control device 8, the hot-dip galvanized layer of the steel sheet H is smoothed. Therefore, the height of the streak pattern generated on the surface of the hot-dip galvanized steel sheet H can be set to less than 1 μm to make the streak pattern inconspicuous.

The temperature control device 8 controls the temperature of the hot-dip galvanized layer after a predetermined time has passed since it passed through the TF heating furnace 7 as a heating device so that the temperature of the hot-dip galvanized layer reaches a predetermined temperature or higher, and the hot-dip galvanized layer is stopped after a predetermined second after the predetermined time. The temperature drop rate of the steel plate H is controlled so that the temperature of the layer is equal to or higher than another predetermined temperature.
The predetermined time is the time necessary for homogenizing the elemental composition of the hot-dip galvanized layer as a whole, eliminating the deformation of the steel sheet when passing through the induction heating part, and stabilizing the shape. Tend to equalize/dissolve. Since the effect of smoothing is reduced unless the elemental composition is uniform and deformation is eliminated, the predetermined time is preferably 0.5 seconds or longer, more preferably 1 second or longer, which is required for uniformity and deformation elimination. In addition, the upper limit of the predetermined time is that the steel plate reaches the exit side end of the temperature control device 8 after the predetermined time has passed since the steel sheet passed through the exit side end of the TF heating furnace 7 and the above predetermined seconds have passed. It's time to go through
Also, the predetermined second is 2 seconds. In specifying the target cooling rate, that is, the temperature drop rate, of the steel sheet in this embodiment, it is necessary to measure the temperature at intervals of time. Therefore, 2 seconds can be used as the predetermined second as described above. The above time interval is determined by the area where the thermometer can be installed.
Further, the predetermined temperature and the another predetermined temperature are 510° C. and 500° C., respectively.
Therefore, the temperature control device 8, for example, sets the temperature of the hot-dip galvanized layer to 510° C. or higher one second after passing through the TF heating furnace 7, and increases the temperature of the hot-dip galvanized layer to 500° C. three seconds after passing through the TF heating furnace 7. The temperature drop rate of the steel plate H is controlled so as to achieve the above.
More specifically, for example, when the steel type of the steel sheet H has a high non-magnetic content, the temperature control device 8 controls the temperature of the hot-dip galvanized layer one second after passing through the TF heating furnace 7 to The temperature drop rate of the hot-dip galvanized steel sheet H is suppressed so that the temperature is in the range of 510° C. or higher and 545° C. or lower, and the temperature 3 seconds after passing through the TF heating furnace 7 is in the range of 500° C. or higher and 540° C. or lower. .
When the temperature of the steel sheet H one second after passing through the TF heating furnace 7 is 545° C. or higher, or when the temperature three seconds after passing is 540° C. or higher, the transformation of the structure of the steel plate H occurs in part, and the material changes.
Further, when the temperature 1 second after passing through the TF heating furnace 7 is less than 510°C or when the temperature 3 seconds after passing is less than 500°C, the viscosity of the hot-dip galvanizing increases. , and the smoothing effect is no longer exhibited. Even if the temperature 1 second after passing through the TF heating furnace 7 is 510° C. or higher and 545° C. or lower, the smoothing effect is not exhibited even if the temperature 3 seconds after passing is lower than 500° C. .

(Second embodiment)
FIG. 4 is a diagram showing an outline of a continuous hot-dip galvanizing apparatus according to a second embodiment of the present invention. FIG. 5 is a diagram showing an example of temperature change of the steel sheet H passing through the continuous hot dip galvanizing apparatus 1 of FIG. The vertical axis in FIG. 5 indicates the temperature of the steel sheet H, and the horizontal axis indicates the elapsed time after the steel sheet H is pulled out of the hot-dip galvanizing bath 2 .

The continuous hot-dip galvanizing apparatus 1 of FIG. 4 is provided with a heating device 10 having a TF heating furnace 7 and a temperature raising device 11, unlike the configuration of the same device of the first embodiment.
The temperature raising device 11 of the heating device 10 further heats the hot-dip galvanized steel sheet H heated by the TF heating furnace 7 to raise the temperature, and is provided between the TF heating furnace 7 and the temperature control device 8. there is The heating method in the temperature raising device 11 includes, for example, a method using combustion gas using a burner or the like, a method using high-temperature gas, and a method using induction heating such as the LF method.

In the continuous hot-dip galvanizing apparatus 1 shown in FIG. 4, as shown in FIG. is heated to a predetermined temperature, that is, the alloying temperature. During this temperature rise, the viscosity of the hot-dip galvanized steel sheet H is low. Therefore, the streak pattern in the sheet width direction generated on the surface of the hot-dip galvanized steel sheet H during heating in the TF heating furnace 7, that is, during induction heating by the TF method, can be reduced during the temperature rise. After the temperature is raised by the temperature raising device 11, the temperature control device 8 suppresses the temperature drop rate of the hot-dip galvanized steel sheet H to maintain the hot-dip galvanized steel sheet H in a low-viscosity state. As a result, while the hot-dip galvanized steel sheet H passes through the temperature control device 8, the hot-dip galvanized layer of the steel sheet H is further smoothed. Therefore, the small streak pattern generated on the surface of the hot-dip galvanized steel sheet H can be further reduced and the streak pattern can be eliminated.

When the heating device 11 heats the hot-dip galvanized steel sheet H by induction heating of the LF method, a streak pattern occurs on the surface of the steel sheet H, but the streak pattern does not extend in the sheet width direction, Also, by setting the power supply frequency to a high frequency, the streak pattern can be made very small.

The temperature raising device 11 heats the hot-dip galvanized steel sheet H for 1 second, for example, and raises the temperature by 5°C or more to raise the temperature of the hot-dip galvanized layer to, for example, 550±10°C. The reason for raising the temperature by 5° C. or higher is as follows. That is, since an error of about ±5° C. is expected in measuring the temperature of the molten coating on the steel plate H moving at high speed, the temperature is raised by 5° C. or more so as to reliably raise the temperature. The upper limit of the temperature rise is 600° C., and if this temperature is exceeded, overalloying at the steel plate-plating interface rapidly progresses, which is undesirable because it causes peeling of the plating such as powdering. Moreover, it is preferable that the heating time in the temperature raising device 11 is 1 second or longer. This is because at around 550° C., it takes one second or more for the fluidity of the hot-dip galvanizing on the steel sheet H to stabilize, that is, for the state of the hot-dip galvanizing on the steel sheet H to become uniform. be.

Further, the temperature control device 8 in the present embodiment operates, for example, after a predetermined time has elapsed after passing through the heating device 10, that is, the temperature raising device 11, in other words, after a predetermined time has elapsed since the end of heating by the temperature raising device 11. In the above, the temperature of the hot-dip galvanized layer of the hot-dip galvanized steel sheet H becomes 510° C. or higher, and the temperature of the hot-dip galvanized layer becomes 500° C. or higher two seconds after the elapse of the predetermined time. control the rate.
More specifically, the temperature control device 8, for example, the temperature of the hot-dip galvanized layer one second after passing through the temperature raising device 11 is in the range of 510 ° C. or higher and 545 ° C. or lower. The temperature drop rate of the hot-dip galvanized steel sheet H is controlled so that the temperature after 3 seconds is in the range of 500° C. or more and 540° C. or less.

(Third embodiment)
FIG. 6 is a diagram showing an outline of a continuous hot-dip galvanizing apparatus according to a third embodiment of the present invention. FIG. 7 is a diagram showing an example of temperature change of the steel sheet H passing through the continuous hot-dip galvanizing apparatus 1 of FIG. The vertical axis in FIG. 7 indicates the temperature of the steel sheet H, and the horizontal axis indicates the elapsed time after the steel sheet H is pulled out of the hot-dip galvanizing bath 2 .

The continuous hot-dip galvanizing apparatus 1 of FIG. 6 is provided with a heating device 13, which has an LF heating furnace 14 and a TF heating furnace 7, unlike the configuration of the same device of the first embodiment. The LF heating furnace 14 is an LF heating device that performs induction heating by the LF method, and is provided upstream of the TF heating furnace 7 and downstream of the damping device 6 . A temperature control device 8 is provided downstream of the TF heating furnace 7 .

In the continuous hot-dip galvanizing apparatus 1 of FIG. 6, as shown in FIG. 7, the hot-dip galvanized steel sheet H is first heated to the alloying temperature, that is, another predetermined temperature lower than the predetermined temperature, by the LF heating furnace 12, and then heated by the TF. The furnace 7 heats to the alloying temperature. Therefore, when heating to the alloying temperature, the time for heating in the TF heating furnace 7, that is, induction heating by the TF method can be shortened. It is possible to reduce the streak pattern in the sheet width direction that occurs on the surface of the steel sheet H. Then, the temperature control device 8 controls the temperature drop rate of the hot-dip galvanized steel sheet H to maintain the hot-dip galvanized steel sheet H in a low-viscosity state. As a result, while the hot-dip galvanized steel sheet H passes through the temperature control device 8, the hot-dip galvanized layer of the steel sheet H is smoothed. Therefore, the small streak pattern generated on the surface of the hot-dip galvanized steel sheet H can be further reduced and the streak pattern can be eliminated.

The LF heating furnace 12 heats the steel plate H until the temperature of the hot dip galvanized layer of the hot dip galvanized steel plate H reaches 480° C., for example. Thereafter, the TF heating furnace 7 heats the hot-dip galvanized steel sheet H heated by the LF heating furnace 12 until the hot-dip galvanized layer reaches 550±10°C.

Further, the temperature control device 8 in the present embodiment, for example, after a predetermined time has elapsed after passing through the heating device 13, that is, the TF heating furnace 7, the temperature of the hot-dip galvanized layer of the hot-dip galvanized steel sheet H is 510° C. or higher. At the same time, the temperature drop rate of the hot-dip galvanized steel sheet H is controlled so that the temperature of the hot-dip galvanized layer becomes 500° C. or higher two seconds after the elapse of the predetermined time.
More specifically, the temperature control device 8 sets the temperature of the hot-dip galvanized layer one second after passing through the TF heating furnace 7 to be in the range of 510 ° C. or higher and 545 ° C. or lower. The temperature drop rate of the hot-dip galvanized steel sheet H is controlled so that the temperature after 3 seconds is in the range of 500° C. or more and 540° C. or less.

(Fourth embodiment)
FIG. 8 is a diagram showing an outline of a continuous hot-dip galvanizing apparatus according to a fourth embodiment of the present invention.
The continuous hot-dip galvanizing apparatus 1 of FIG. 8 includes a smoothing device 15 instead of the temperature control device 8 of the same device of the first embodiment.

The smoothing device 15 smoothes the surface of the steel plate H, and is provided downstream of the TF heating furnace 7 . As a smoothing method, a method of blowing a high-temperature (for example, 450° C.) gas is conceivable.
Since the continuous hot-dip galvanizing apparatus 1 shown in FIG. 8 is provided with the above-described smoothing device 15, it is possible to eliminate streak patterns formed on the surface of the hot-dip galvanized steel sheet H by induction heating of the TF method.

(Fifth embodiment)
FIG. 9 is a diagram showing an outline of a continuous hot-dip galvanizing apparatus according to a fifth embodiment of the present invention.
A continuous hot-dip galvanizing apparatus 1 of FIG. 9 has a configuration in which the temperature control device 8 is removed from the same apparatus of the first embodiment.

In the continuous hot-dip galvanizing apparatus 1, the power supply frequency for the TF heating furnace 7 is not kept constant but varied.
When the power supply frequency for the TF heating furnace 7 is constant at 25 kHz, for example, a pattern with a pitch of 5 to 10 mm in the sheet passing direction, a length of 50 to 200 mm in the width direction, and a height of several μm is melted after alloying. It occurs on the surface of the galvanized steel sheet H. On the other hand, when the power supply frequency for the TF heating furnace 7 is set to 250 kHz, for example, streak patterns are generated on the surface of the steel sheet H at a pitch of 1 to 3 mm in the sheet passing direction. Further, when the power frequency for the TF heating furnace 7 is set to 2.5 kHz, for example, stripe patterns are generated on the surface of the steel sheet H at a pitch of 15 to 30 mm in the sheet passing direction. Therefore, in the continuous hot-dip galvanizing apparatus 1, the power supply frequency for the TF heating furnace 7 is not constant, but is changed, specifically, for example, between 2.5 kHz and 250 kHz every few seconds. As a result, the streak pattern formed on the surface of the steel sheet H cannot be visually determined.

(Sixth embodiment)
FIG. 10 is a diagram showing an outline of a continuous hot-dip galvanizing apparatus according to a sixth embodiment of the present invention.
The continuous hot-dip galvanizing apparatus 1 of FIG. 10 includes a smoothing device 15 in addition to the configuration of the same apparatus of the first embodiment.

The smoothing device 15 smoothes the surface of the steel plate H and is provided downstream of the temperature control device 8 . As a smoothing method, a method of blowing a high-temperature (for example, 450° C.) gas onto the surface of the steel plate H can be considered. However, the method is not limited to this method, and a method of bringing a roller or blade heated to a high temperature (for example, 450° C.) into contact with the surface of the steel plate H may be used.

In the continuous hot dip galvanizing apparatus 1 of FIG. 10, since the smoothing device 15 is provided downstream of the temperature control device 8, even if a streak pattern remains on the surface of the steel plate H after passing through the temperature control device 8, the remaining streaks The pattern can be eliminated by the smoothing device 15 .

INDUSTRIAL APPLICABILITY The present invention is useful for a technique of alloying a hot-dip galvanized layer of a steel sheet by TF induction heating.

DESCRIPTION OF SYMBOLS 1... Continuous hot-dip galvanizing apparatus 2... Continuous hot-dip galvanizing bath 3... Sink roll 4... Support roll 5... Gas wiping nozzle 6... Vibration damping device 7... TF heating furnace 8... Temperature control device 9... Upper roll 10... Heating device REFERENCE SIGNS LIST 11: Temperature raising device 12: LF heating furnace 13: Heating device 14: LF heating furnace 15: Smoothing device

Claims (8)

A continuous hot-dip galvanizing method comprising hot-dip galvanizing a steel plate and heating the hot-dip galvanized steel plate with a heating device to alloy the hot-dip galvanized layer,
The heating device has a TF heating device that performs induction heating at least by a vertical magnetic flux method,
including a step of controlling the temperature of the steel plate so that the temperature of the steel plate that has passed through the heating device decreases,
In the step of controlling, the temperature of the hot-dip galvanized layer of the steel sheet after a predetermined time of 0.5 seconds or more after passing through the TF heating device becomes 510 ° C. or higher and 545 ° C. or lower, and the 0.5 The temperature drop rate of the steel sheet is controlled so that the temperature of the hot-dip galvanized layer is 500° C. or higher and 540° C. or lower two seconds after the predetermined time of at least seconds has elapsed, and the Continuous hot-dip galvanizing characterized by smoothing the hot-dip galvanized layer generated when a streak pattern having a pitch of 5-10 mm and a length of 50-200 mm in the width direction of the plate passes through the TF heating device. Method. The heating device has an LF heating device that performs heating by a parallel magnetic flux method,
After heating the steel sheet by the LF heating device until the temperature of the hot-dip galvanized layer of the steel sheet reaches 480° C., the heated steel sheet is heated to a predetermined temperature by the TF heating device. The continuous hot-dip galvanizing method described in . 3. The continuous hot-dip galvanizing method according to claim 1 , wherein the hot-dip galvanized layer of the steel sheet that has passed through the TF heating device is sprayed with gas to smooth the hot-dip galvanized layer. 3. The continuous hot-dip galvanizing method according to claim 1 , wherein a contacting member is brought into contact with the hot-dip galvanized layer of the steel sheet that has passed through the TF heating device to smooth the hot-dip galvanized layer. A continuous hot-dip galvanizing apparatus for hot-dip galvanizing a steel sheet and heating the hot-dip galvanized steel sheet with a heating device to alloy the hot-dip galvanized layer,
The heating device has a TF heating device that performs induction heating at least by a vertical magnetic flux method,
A device for controlling the temperature of the steel plate so that the temperature of the steel plate that has passed through the heating device decreases, wherein the steel plate melts after a predetermined time of 0.5 seconds or more has elapsed after passing through the TF heating device. The temperature drop rate of the steel sheet is adjusted so that the temperature of the galvanized layer is 510 ° C. or higher and 545 ° C. or lower and the temperature of the hot dip galvanized layer two seconds after the predetermined time has elapsed is 500 ° C. or higher and 540 ° C. or lower. The hot-dip galvanized layer was formed when a streak pattern extending in the sheet width direction, with a pitch of 5 to 10 mm in the sheet passing direction and a length of 50 to 200 mm in the sheet width direction passed through the TF heating device. A continuous hot-dip galvanizing apparatus comprising a smoothing temperature control device. The heating device has an LF heating device that performs heating by a parallel magnetic flux method,
The LF heating device heats the steel sheet until the temperature of the hot-dip galvanized layer of the steel sheet reaches 480 ° C.,
6. The continuous hot-dip galvanizing apparatus according to claim 5 , wherein the TF heating device heats the steel sheet heated by the LF heating device to a predetermined temperature. 7. The continuous hot-dip galvanizing apparatus according to claim 5 , further comprising a smoothing device for smoothing the hot-dip galvanized layer by blowing gas onto the hot-dip galvanized layer of the steel sheet that has passed through the TF heating device. . 7. The continuous hot-dip galvanizing according to claim 5 or 6 , further comprising a smoothing device for smoothing the hot-dip galvanized layer by coming into contact with the hot-dip galvanized layer of the steel sheet that has passed through the TF heating device. Device.

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