JP3787320B2 - Method and apparatus for controlling alloying in hot dip galvanizing line - Google Patents

Description

表１から明らかなとおり、本発明により優れた耐パウダリング性及びめっき密着性を得ることができた。
【００３２】
【発明の効果】
本発明によれば、誘導加熱装置出側に放射型板温計を設けてめっき鋼板の板温を測定し、その測定結果に基づいて誘導加熱装置への投入電力量を制御しようとする従来技術において問題であっためっき鋼板表面の放射率変動に起因する誘導加熱装置出側での放射板温計による正確な板温の測定が実用上困難であり従って精度の良い合金化制御ができないという問題も解消でき、さらに、メッキ機ワイピング条件による誘導加熱装置入側めっき鋼板温度の変動があっても、本発明の方法によれば誘導加熱装置出側めっき鋼板温度を正確に補正することができるので定常操業状態において正確な加熱温度を得ることが可能になった。
【００３３】
また、誘導加熱装置における加熱コイル効率を逆算して実績データーとして蓄積することが可能になり、したがって、過渡期においても、実績データーとして蓄積された加熱効率などのデーターを使用することによりライン通板条件に応じた投入電源量指令を優先して制御することにより、電源量指令に時間的遅れを無くし合金化不足を生じることなく合金化メッキ制御を行うことができるようになった。
【００３４】
さらに、保熱帯の後段部分に設置される放射板温計は、従来のように保熱帯の出側であって保熱帯と冷却装置の間に設けた場合に比較して、メッキ鋼板が外気との接触や後設の冷却装置からの冷風等の影響を受けて板温が降下し始めている途中の状態の温度を測定しているのではなく、炉内条件がほぼ一定の保熱帯内であるので精度良く板温を測定することができる。従って、板サイズや通板速度に影響されず正確な板温を測定することができるようになったので、メッキ密着性及び加工性に優れた合金メッキ鋼板を安定して製造することが可能となった。
【００３５】
さらに本発明による傾斜保熱では、保熱時間中に漸次板温が低下するので地金との境界近くに生成するΓ相の生成を抑制することができ、優れためっき密着性を得ることができるようになる。
【００３６】
また、誘導加熱装置によってめっき鋼板を５２０℃〜５６０℃の高温に急速に再加熱することによって、合金化に必要な保熱時間を短縮することが可能になるので、合金化処理装置をコンパクトにできる。
【図面の簡単な説明】
【図１】本発明の溶融亜鉛めっき設備の一実施例を示す図である。
【図２】本発明の電力指令設定器１５における演算ロジックを示す図である。
【図３】本発明の保熱帯の制御の一例を示す図である。
【図４】本発明における合金化サイクルと従来法を示す図である。
【図５】本発明と従来法のζ相／δ_１相比と加工性の関係を示す図である。
【図６】従来の溶融亜鉛めっき設備の例を示す説明図である。
【符号の説明】
１：鋼板 ２：溶融亜鉛浴
３：シンクロール ４：メッキ機
５：誘導加熱装置 ６：電力制御装置
７：保熱帯 ８：保熱帯制御装置
９：電源装置 １０：放射型板温計、
１１：気水冷却装置 １２：トップロール
１３：放射型板温計 １４：板温計補正演算器
１５：電力指令 １６ａ，１６ｂ：炉温計
１７：板温指示計 １８：放射型板温計
１９：電熱ヒーター ２０：炉温制御装置
２１：放射型板温計[0001]
BACKGROUND OF THE INVENTION
The present invention relates to alloying control in which a galvanized layer is alloyed by rapid cooling after heating and heat-retaining a steel plate immediately after plating in a continuous hot dip galvanizing line for steel plates. Material size, material, plating The present invention relates to an alloying control method and apparatus in a hot dip galvanizing line capable of performing optimum alloying control according to the product type.
[0002]
[Prior art]
FIG. 6 is a view showing an example of a conventional continuous hot dip galvanizing line. In FIG. 6, the steel plate 1 is pulled vertically upward through the sink roll 3 in the hot dip zinc pot 2 and adjusted to a predetermined plating thickness by the plating machine 4. The plating machine 4 employs a gas wiping method or a wiping method using electromagnetic force. The plated steel sheet 1 adjusted to a predetermined plating thickness by the plating machine 4 is subsequently reheated by the induction heating device 5 and then heated by the heat retention zone 7 equipped with the electric heater 19 for a predetermined time. The alloying treatment of the plating layer is performed by the above. The plated steel sheet 1 exiting the retentive zone 7 is rapidly cooled in the air / water cooling device 11 and sent to the next process via the top roll 12.
[0003]
In the induction heating device 5 and the tropical retentive zone 7, in order to perform an optimal alloying process, a radial plate thermometer 13 is provided on the exit side of the induction heating device 5, and based on the measurement result of the radial plate thermometer 13. For example, Japanese Patent No. 3074933 proposes a method of controlling the amount of electric power supplied to the induction heating device 5 by the power control device 6 so that the temperature of the plated steel sheet becomes a predetermined temperature.
[0004]
In addition, in the tropical zone 7, the plate temperature indicator 17 is used to output the tropical zone on the exit side of the tropical zone 7 and based on the measurement result of the radial plate thermometer 21 provided between the tropical zone 7 and the cooling device 11. There has been proposed a method for controlling the input power from the plate temperature indicator 17 to the heat retention zone 7 so that the plate temperature at the side becomes a predetermined temperature.
[0005]
Moreover, in order to prevent the so-called powdering in which the plating layer of the bent portion at the time of processing or the like is peeled off in a powdery state in the plated steel sheet, as shown by the broken line in FIG. In the alloying treatment of galvanization, a method of rapidly heating to a predetermined temperature t1 ° C. by an induction heating device and subsequently maintaining the temperature at t1 ° C. in a tropical region has been adopted. Further, as disclosed in JP-A-4-341550, after the basis weight control is completed, the plate is heated to a plate temperature of 500 ° C. or more and 600 ° C. or less in the first stage heating alloying process, and then unalloyed. It has been proposed to complete the alloying process by heating in a plate temperature range of 510 ° C. or lower and 470 ° C. or higher in the second stage heating alloying process in this state. It was considered effective to be within seconds.
[0006]
[Problems to be solved by the invention]
However, as shown in FIG. 6, a radiation-type plate thermometer 13 is provided on the outlet side of the induction heating device, the plate temperature of the plated steel plate 1 is measured, and the amount of electric power supplied to the induction heating device 5 is controlled based on the measurement result. However, a definite defect was inherent in the above. That is, after the plated steel sheet 1 is reheated by the induction heating device 5, alloying of the plating layer proceeds in the process of heat retention for a predetermined time in the retentive zone 7, and almost alloyed in the latter stage of the retentive zone. At the stage when the plating is completed, the surface irradiance of the alloyed plated steel sheet converges to a substantially constant value depending on the plating bath components. However, the emissivity of the plating surface immediately after induction heating depends on the plating thickness and heating temperature. Therefore, it is practically difficult to measure the accurate plate temperature with the radiation plate thermometer on the induction heating device exit side.
[0007]
In addition, based on the measurement result of the radial plate thermometer 21 provided on the exit side of the retentive zone 7 and between the retentive zone 7 and the cooling device 11, the plate temperature on the outgoing side of the retentive zone becomes a predetermined temperature. As described above, in the technology for controlling the input power from the plate temperature indicator 17 to the retentive zone 7, the plated steel sheet 1 is brought into contact with the outside air from the time of leaving the retentive zone 7, cold air from the subsequent cooling device 11, etc. Since the plate temperature starts to fall under the influence, the plate temperature measured by the radiation type plate thermometer 21 provided between the heat retaining zone 7 and the cooling device 11 is measured in the middle of the temperature drop. Since the temperature drop changes depending on the line passing conditions such as the thickness of the steel sheet and the line passing speed, the measured temperature of the radial plate thermometer 21 correctly represents the holding temperature of the plated steel sheet 1 in the retentive zone 7. It was difficult.
[0008]
On the other hand, the temperature of the entrance side plated steel sheet of the induction heating device is determined in the process in which the plated steel sheet exiting the hot dipping bath passes through a gas wiping type plating machine and the plating thickness is adjusted to a predetermined thickness. The plating steel plate temperature at the inlet side of the induction heating device changes depending on the plating wiping conditions such as the gas pressure and flow velocity of the machine wiping nozzle, so that the power output of the induction heating device is the same and the heating rate in the induction heating device is constant. Even if it exists, since the plated steel plate temperature on the induction heating device exit side changes, it is difficult to accurately control the plated steel plate temperature on the induction heating device exit side.
[0009]
In addition, in the conventional alloying method, it has been difficult to obtain a high-quality alloyed steel sheet that has both adhesion and powdering resistance and is excellent in slidability with a mold during press working. That is, in the alloying process of the plated steel sheet, alloy layers are formed in the order of Γ phase, δ ₁ phase, ζ phase, and η phase from the bare metal side. The alloying phases in γ are almost δ ₁ phase and ζ phase, and a slight Γ phase remains on the bare metal side. In order to maintain excellent plating adhesion and good workability, it is important to keep the ratio of δ ₁ phase and ζ phase within a certain range by making the degree of alloying (Fe%) appropriate. . For example, an alloy plating layer having excellent workability can be obtained by setting the ζ phase / δ ₁ phase ratio to 0.1 to 0.2. When the degree of alloying is low, that is, when the ζ phase / δ ₁ phase ratio is large, a relatively soft ζ phase (FeZn ₁₃ ) is formed on the surface layer of the plating layer, which becomes a sliding resistance during press working and causes press cracking. Cause it to happen. On the other hand, when the degree of alloying is high, that is, when the ζ phase / δ ₁ phase ratio is small, a Γ phase (Fe ₅ Zn ₂₁ ) is generated at the boundary surface between the metal and the plating layer, and the Γ phase breaks during the press working and is plated. The problem of poor adhesion occurs. This ζ phase / δ ₁ phase ratio is shown in FIG. 5 in comparison with the difference in temperature pattern of the alloying treatment cycle. Under the constant heat retention indicated by the wavy line in FIG. 4 of the conventional method, the ζ phase / δ ₁ phase ratio becomes large, and it is difficult to maintain good workability. In addition, with regard to the suppression of Γ phase formation, which is important for improving plating adhesion, the conventional method makes it easy for Γ phase to grow due to overalloy due to the high temperature of the plated steel sheet on the tropical rain discharge side. There was a problem that plating adhesion was hindered. On the other hand, in the method disclosed in JP-A-4-341550, when the heating time in the second stage is performed in a short time of 3 seconds or less, the heating plate temperature is set to 600 in the first heating in order to complete the alloying process. There is a need for heating to a high temperature around 0 ° C., and a device having a strong heating capability is required for the first heating device, which increases the equipment cost.
[0010]
Therefore, the present invention provides an alloying control method and apparatus for a hot dip galvanizing line capable of accurately controlling the alloying process in a hot dip galvanizing facility for steel sheets.
[0011]
[Means for Solving the Problems]
The alloying control method in the hot dip galvanizing line according to the present invention is a method of plating a steel plate with a hot dip galvanizing bath, adjusting the plating thickness to a predetermined thickness, then reheating it with an induction heating device, and installing an electric heater. In the alloying control method in the hot dip galvanizing line that is held for a predetermined time and subsequently cooled, the required heating in the induction heating device based on the preset target plate temperature and passage condition on the outlet side of the induction heating device The amount of electric power supplied to the induction heating device is calculated by further adding the heating coil efficiency to the required heating amount, and a plate thermometer near the exit side in the warmer and a plurality of furnaces in the warmer zone Using the measurement results by the thermometer, the plate temperature on the outlet side of the induction heating device is calculated, the target plate temperature is corrected based on the calculated value, the input electric energy is corrected, and the temperature is again set to 520 ° C. to 560 ° C. Heated, It was subjected to gradient heat retaining lowering the reheating temperature of the serial 520 ° C. to 560 ° C. gradual plate temperature 511 ℃ ~522 ℃ during heat-keeping time, 250 ° C. to 300 ° C. The cooling rate 30 ° C. / sec or more until in that rapid cooling it characterized.
[0012]
The alloying control device of the present invention is an induction heating device that heats a hot-dip galvanized steel sheet, and an alloying control device for a hot-dip galvanizing facility that sequentially has a cooling zone and a cooling zone. Calculate the required heating amount in the induction heating device based on the target plate temperature and the passing plate conditions on the device exit side, and further command the electric power input to the induction heating device by adding the heating coil efficiency to the required heating amount A power command setter is provided, and a thermometer is provided in the vicinity of the exit side in the heat retention zone and a furnace thermometer is provided at a plurality of locations in the heat retention zone, and the measurement results obtained by the plate thermometer and the furnace thermometer are used to A plate temperature correction calculator for calculating the plate temperature at the induction heating device outlet side is provided, and the target plate temperature of the power command setter is corrected based on the calculated value in the plate temperature correction calculator to the induction heating device. again the input power amount in compensation to 520 ℃ ~560 ℃ Heat the 520 ° C. was subjected to gradient heat retaining lowering the gradual plate temperature 511 ℃ ~522 ℃ from reheating temperature to 560 ° C. during the heat-keeping time, cooling rate 30 ° C. up to 250 ° C. to 300 ° C. / it characterized in that no such rapid cooling in seconds or more.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
FIG. 1 is a view showing an embodiment of the hot dip galvanizing equipment of the present invention. In FIG. 1, the steel plate 1 enters the molten zinc bath 2, and then is pulled upward through the sink roll 3, and the zinc layer adhering to the soaked plated steel plate 1 is adjusted to a predetermined adhesion amount by the plating machine 4. Be controlled. The steel sheet 1 having the adjusted plating thickness is reheated to a temperature of about 500 ° C. to 570 ° C. by the induction heating device 5 and is subsequently maintained at the tropical region 7. Thereafter, the plated steel sheet 1 is cooled by the air / water cooling device 11 and sent to the next process through the top roll 12.
[0015]
As for the input power to the induction heating device 5, the set value S1 calculated and set by the power command setter 15 is transmitted to the power control device 6, and the input power amount to the induction heating device 5 is controlled. At this time, the temperature Pt2 of the plated steel plate is actually measured by the radial plate thermometer 10 which is a rear stage portion of the tropical zone 7 and is installed in the tropical zone 7, and at the same time, the inside of the furnace which is measured by the furnace thermometers 16a and 16b. Using the temperature results Pfa and Pfb, the plate temperature correction calculator 14 calculates the plate temperature Pt1 on the outlet side of the induction heating device. That is, the heat transfer amount Q from the plated steel sheet in the tropical zone 7 can be expressed as Q = Qr + Qc, where Qr is the heat transfer amount due to radiation, and Qc is the heat transfer amount due to convection, and is obtained by the following equations.
[0016]
Qr = 4.88 × 10 ⁻⁸ × φcg × {(Ts + 273) ⁴ − (Ts−Tg + 273) ⁴ } × A
Qc = α × (Ts−Tf) × A
here,
φcg: Gas radiation coefficient Ts: Plated steel plate temperature Tf: Temperature inside the retentive furnace (Pfa, Pfb)
Tg: Logarithmic average temperature difference α: Convection heat transfer coefficient A: Surface area of plated steel plate in the tropical zone On the other hand, the temperature change Qs due to the heat quantity of the plated steel plate in the tropical zone is W, the processing amount of the steel plate is W, and the specific heat of the steel plate is Cs Then, Qs = W × Cs × (Ptl−Pt2).
[0017]
Therefore, if φcg and α are obtained in advance by calculation, the furnace temperature Tf in the corresponding zone is known by obtaining the temperature retention results Pfa and Pfb of the tropical retentive furnace, and the induction heating device outlet plate is obtained from Qs = Qr + Qc. The temperature Ptl is obtained. The induction heating device outlet side plate temperature result calculation value Ptl calculated in this way is transmitted to the power command setter 15.
[0018]
Further, the electric heater 19 installed in the retentive zone 7 is supplied with electric power by the retentive control device 8 so that the furnace temperature results Pfa and Pfb become a predetermined set furnace temperature in the furnace temperature control device 20. Be controlled. The gas and liquid injection amounts of the air-water cooling device 11 are controlled so that the measurement results obtained by the radiation-type plate thermometer 18 match the preset plate temperature range of 250 ° C. to 350 ° C.
[0019]
FIG. 2 is a diagram showing arithmetic logic in the power command setter 15 of the present invention. First, the required heating amount is calculated from the processing amount obtained from line passing data such as plate thickness, plate width, and line speed, and the difference ΔT between the induction heating device inlet plate temperature and the target plate temperature. The At this time, the plate temperature at the inlet of the induction heating device is obtained by calculating the temperature drop until the steel plate leaves the plating bath, passes through the gas wiping portion and enters the induction heating device, by heat transfer calculation. Furthermore, the power input command is output using the heating coil efficiency (η) in the induction heating device. Here, the power input command is corrected and output by correcting the actual plate temperature calculation value Pt1. The At this time, the correction by the actual plate temperature calculation value Ptl is corrected only at the time of steady operation in which the threading plate size does not change. That is, the heating coil efficiency in the induction heating apparatus can be obtained in advance by a performance test. Further, based on the correction by the actual plate temperature calculation value Ptl according to the present invention, the plate of the plated steel plate is used. The heating efficiency of the induction heating device can be calculated backwards for each thickness and plate width and accumulated as data. Therefore, by using the heating efficiency data accumulated in this way, more accurate electric energy setting and alloying control are possible even in the transition period when the plate thickness and width change when the steel plate connection part passes. Thus, it is possible to prevent the occurrence of defective parts such as unalloyed plating due to response delay.
[0020]
Example 2
FIG. 3 is a diagram showing an example of the control of the tropical zone of the present invention. In FIG. 3, after the steel plate 1 enters the molten zinc bath 2, the steel plate 1 is pulled upward through the sink roll 3, and the zinc layer adhering to the soaked plated steel plate 1 is adjusted to a predetermined adhesion amount by the plating machine 4. Be controlled. The plated steel sheet 1 is reheated to a temperature of about 500 ° C. to 570 ° C. by the induction heating device 5, and then the temperature is maintained in the retentive zone 7. Thereafter, the plated steel sheet 1 is rapidly cooled by the air / water cooling device 11 so that the temperature of the plated steel sheet is 250 ° C. to 350 ° C. at a cooling rate of 30 ° C./second or more, and is sent to the next process through the top roll 12. . At this time, excessive generation of the Γ phase in the plating layer can be suppressed by rapidly cooling the plated steel sheet temperature to 250 ° C. to 350 ° C. This is because rapid cooling can prevent the plating layer from being easily overalloyed by the latent heat of the alloyed plated steel sheet.
[0021]
As described in the first embodiment, the input power to the induction heating device 5 is preset according to the steel plate size and the plate passing speed so that the temperature of the plated steel plate on the outlet side of the induction heating device 5 is T1 ° C. Is done.
[0022]
Moreover, the electric heater 19 equipped in the inside of the tropical retentive zone 7 is passed through the furnace temperature control device 20 by the tropical retentive control device 8 so that the temperature of the plated steel plate near the outlet side of the tropical retentive zone 7 becomes T2 ° C. Input power is controlled. Thus, the furnace temperature can be controlled more accurately by using an electric heater as a heat source for the tropical region. In the air-water cooling device 11, the temperature of the plated steel sheet is controlled so as to match the plate temperature set value in the range of 250 ° C to 350 ° C by adjusting the injection amounts of the gas and the liquid refrigerant.
[0023]
FIG. 4 shows a temperature pattern of the alloying treatment cycle according to the present invention. Conventionally, the plated steel sheet reheated by the induction heating device has been maintained at a constant temperature within the tropical region as indicated by the broken line in FIG. In this invention, when it is set as the plating steel plate temperature T1 in the induction heating apparatus exit side and the plating steel plate temperature T2 in the tropical retentate exit side, heat retention is implemented as T1-T2 = Δt.
[0024]
Here, Δt is obtained by the following equation.
[0025]
Δt = C1, C2, C3, exp {n · w}
However,
C1: Coefficient determined by the Al concentration in the bath (0.9 to 1.O)
C2: Coefficient determined by the amount of added components such as Mn and Si in the original plate (0.5 to 1.5)
C3: Constant (500 to 900)
n: Coefficient (-0.04 to -0.06)
w: Zinc adhesion amount (g / m ² )
For example, zinc adhesion amount w = 55 g / m ² , C1 = 0.9 when Al concentration in the bath = 0.09%, C2 = 1.0, C3 = 700, n = −0. In the case of 05, from the above equation, it is required to perform a gradient heat retention of Δt = about 40 ° C. The coefficient C1 is determined by the Al concentration in the bath. C1 = 0.9 when the Al concentration in the bath is 0.09% or less, and C1 = 1.0 when the Al concentration in the bath is 0.1% or more. desirable.
[0026]
The coefficient C2 depends on the amount of added components such as Mn and Si in the original plate, and the reaction with zinc on the surface of a high-tensile steel plate in which the content of these components increases is slow, so C2 is 1.5 at maximum. In addition, when plating a soft cold-rolled steel sheet, an optimum value can be obtained in the range of 0.5 to 1.0. C3 is a constant unique to the hot dip galvanizing line and is determined according to the retention time in the tropical zone, etc., so if the retention time in the tropical zone is 7 seconds, C3 = 900, but the retention time is, for example, 15 seconds or more C3 = 500 can be obtained. As the coefficient n, an optimum value is selected in the range of -0.04 to -0.06.
[0027]
As described above, in order to maintain excellent plating adhesion and good workability, it is important to keep the ratio of the δ ₁ phase and the ζ phase within a certain range. For example, an alloy plating layer having excellent workability can be obtained by setting the ζ phase / δ ₁ phase ratio to 0.1 to 0.2. This ζ phase / δ ₁ phase ratio is shown in FIG. 5 in comparison with the difference in temperature pattern of the alloying treatment cycle. Under the temperature pattern of the conventional method, whereas as shown in broken line ζ phase / [delta] ₁ phase ratio is increased, the present invention ζ is inclined retaining heat by phase / [delta] ₁ phase ratio of 0.1 Since it can control to the appropriate range of -0.2, the plated steel plate excellent in workability can be obtained.
[0028]
Furthermore, in the gradient heat retention according to the present invention, since the plate temperature gradually decreases during the heat retention time, the generation of the Γ phase generated near the boundary with the metal can be suppressed, and the thickness of the Γ phase is less than 0.6 μm. Therefore, excellent plating adhesion can be obtained.
[0029]
In addition, by rapidly reheating the plated steel sheet to a high temperature of 520 ° C. to 560 ° C. with the induction heating device 5, it becomes possible to shorten the heat retention time required for alloying, so the alloying treatment device is compact. The advantage of being able to be obtained can be obtained. For example, when performing an alloying treatment with a plating adhesion amount of 30 to 60 g / m ² and a plating layer iron amount of 7 to 13% and the remaining zinc, a heat retention time of 20 to 25 seconds is required in the conventional uniform temperature maintaining method. However, according to the method of the present invention, the alloying process can be completed in 8 to 10 seconds.
[0030]
Next, four examples of the present invention are shown in Table 1 in comparison with comparative examples. In Table 1, a flat steel plate (plate thickness 0.7 mm, plate width 1050 mm) is continuously plated, the amount of adhesion is controlled by gas wiping just above the bath, and a 430 ° C plated steel strip is introduced into the induction heating device. And reheated. The induction heating device employs high frequency induction heating of 100 KHz, and the tropical rain is equipped with an electric heater. In the rapid cooling, the plated steel strip after the alloying treatment was directly cooled by air-water jet.
[0031]
[Table 1]

As apparent from Table 1, excellent powdering resistance and plating adhesion can be obtained by the present invention.
[0032]
【The invention's effect】
According to the present invention, a radiation type thermometer is provided on the outlet side of the induction heating device to measure the plate temperature of the plated steel plate, and based on the measurement result, the conventional technique for controlling the amount of power input to the induction heating device In practice, it is practically difficult to accurately measure the plate temperature with a radiant plate thermometer on the exit side of the induction heating device due to the emissivity fluctuation on the surface of the plated steel plate. In addition, even if there is a fluctuation in the temperature of the induction-plated steel sheet on the induction heating device due to the wiping conditions of the plating machine, the method of the present invention can accurately correct the temperature of the induction-plated steel sheet on the outlet side of the induction heating device. It has become possible to obtain an accurate heating temperature in a steady operation state.
[0033]
In addition, it is possible to back-calculate the heating coil efficiency in the induction heating device and accumulate it as actual data. Therefore, even in the transition period, by using data such as the heating efficiency accumulated as actual data, the line passing plate By preferentially controlling the input power amount command according to the conditions, the alloying plating control can be performed without causing a time delay in the power amount command and causing insufficient alloying.
[0034]
Furthermore, the radiant plate thermometer installed in the latter part of the tropics is compared with the case where the radiating plate thermometer is located on the exit side of the tropics and is provided between the tropics and the cooling device as in the conventional case. The temperature in the middle of the plate temperature is starting to drop due to the influence of cold air coming from the cooling system and the cooling device installed later is not measured. Therefore, the plate temperature can be measured with high accuracy. Therefore, the accurate plate temperature can be measured without being affected by the plate size and the plate passing speed, and it is possible to stably produce an alloy plated steel plate having excellent plating adhesion and workability. became.
[0035]
Furthermore, in the gradient heat retention according to the present invention, since the plate temperature gradually decreases during the heat retention time, it is possible to suppress the formation of the Γ phase generated near the boundary with the metal and to obtain excellent plating adhesion. become able to.
[0036]
In addition, it is possible to shorten the heat retention time required for alloying by rapidly reheating the plated steel sheet to a high temperature of 520 ° C. to 560 ° C. by means of an induction heating device, so that the alloying processing device can be made compact. it can.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of a hot dip galvanizing facility of the present invention.
FIG. 2 is a diagram showing arithmetic logic in a power command setter 15 of the present invention.
FIG. 3 is a diagram showing an example of the control of the tropical zone of the present invention.
FIG. 4 is a diagram showing an alloying cycle and a conventional method in the present invention.
FIG. 5 is a graph showing the relationship between the ζ phase / δ ₁ phase ratio and workability of the present invention and the conventional method.
FIG. 6 is an explanatory view showing an example of a conventional hot dip galvanizing facility.
[Explanation of symbols]
1: Steel plate 2: Molten zinc bath 3: Sink roll 4: Plating machine 5: Induction heating device 6: Power control device 7: Insulation zone 8: Insulation zone controller 9: Power supply device 10: Radiation type plate thermometer,
11: Air-water cooling device 12: Top roll 13: Radiation type thermometer 14: Plate thermometer correction calculator 15: Electric power command 16a, 16b: Furnace thermometer 17: Plate temperature indicator 18: Radiation type thermometer 19 : Electric heater 20: Furnace temperature control device 21: Radiation type plate thermometer

Claims (2)

Steel sheet plated with molten zinc plating bath was adjusted to a predetermined plating thickness, induction heating and reheating the apparatus, and held for a predetermined time, the electric heater equipped with holding tropical subsequently cooled galvanizing line In the alloying control method in
An induction heating device that calculates a required heating amount in the induction heating device based on a preset target plate temperature and a passing plate condition on the outlet side of the induction heating device that is set in advance, and further takes the heating coil efficiency into consideration with the required heating amount And calculating the plate temperature on the outlet side of the induction heating device using the measurement results by the plate thermometer near the outlet side in the heat retention zone and the furnace thermometers at multiple locations in the heat retention zone, Based on the calculated value, the target plate temperature is corrected, the input electric power is corrected, the plate is gradually reheated from 520 ° C. to 560 ° C. , and gradually heated during the heat retention time. A method of controlling alloying in a hot dip galvanizing line, characterized in that, after performing gradient heat retention to lower the temperature to 511 ° C to 522 ° C , rapid cooling is performed at a cooling rate of 30 ° C / second or more from 250 ° C to 300 ° C. . In an induction heating device for heating a hot dip galvanized steel sheet, a hot spring, an alloying control device for a hot dip galvanizing facility having a cooling zone in sequence,
An induction heating device that calculates a required heating amount in the induction heating device based on a preset target plate temperature and a passing plate condition on the outlet side of the induction heating device that is set in advance, and further takes the heating coil efficiency into consideration with the required heating amount A power command setter is provided to command the amount of power input to the inside. A plate thermometer is provided in the vicinity of the exit, and a thermometer is provided at a plurality of locations in the tropical region. The plate thermometer and the furnace thermometer A plate temperature correction calculator that calculates the temperature at the outlet side of the induction heating device is provided using the measurement results obtained by the calculation, and the target plate temperature of the power command setter is corrected based on the calculated value in the plate temperature correction calculator. Then, the amount of electric power applied to the induction heating device is corrected and reheated to 520 ° C. to 560 ° C., and the gradual plate temperature is changed from 520 ° C. to 560 ° C. during the heat retention time. After applying the gradient heat retention to lower the temperature, the cooling rate is from 250 ° C to 300 ° C. Alloying controller in galvanizing line, characterized in that no such rapid cooling at 30 ° C. / sec or more.

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