JPH08199324A - Steel plate temperature control method in alloying furnace - Google Patents

Abstract

(57) [Summary] [Purpose] In the alloying furnace, the heating zone inlet side plate temperature or the heating zone outlet side plate temperature is obtained without using a radiation thermometer or heat transfer calculation, and the heat retaining zone outlet side plate temperature is determined as the heating zone outlet side plate temperature. It is intended to provide a method capable of controlling the steel plate temperature by the heating zone outlet side plate temperature, which is effective even when the operating conditions are changed, in the case of performing the feedback control as it is. [Structure] In an alloying furnace, a heating zone entrance side plate temperature or a heating zone exit side plate temperature is obtained from the impedance of an induction heating heater, and the input power of each induction heating heater is obtained to control the steel sheet temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the temperature of a steel sheet when an alloy-plated steel sheet is produced using an induction heating furnace and a heater-type heat-retaining furnace in a continuous hot-dip galvanized steel sheet production facility. is there.

[0002]

2. Description of the Related Art Galvanized steel sheets are used as steel sheets for automobiles, steel sheets for home appliances, etc. because they are excellent in corrosion resistance, paintability and press formability. For alloy galvanized steel sheets, pass the steel sheet through a hot dip zinc bath, adjust the plating thickness to an appropriate level with a wiping device installed directly above the zinc bath, then heat to about 500 to 550 ° C in a heating zone, and further preserve the heat. It is generally manufactured by making the plating layer an alloy layer of iron and zinc by keeping the temperature isothermal.

An important point in this process is to control the temperature of the galvanized steel sheet in order to prevent alloy shortage and overalloying of the alloy layer to control the alloying degree of the plated layer within an appropriate range.

Conventionally, the alloy combustion furnace uses a gas combustion heating method. In the case of the gas combustion heating method, the temperature of the steel sheet is controlled by adjusting the furnace temperature, and the method has already been established.

In recent years, there has been an attempt to shift to an induction heating method from the viewpoint of quality improvement by rapid heating and environmental protection.

For example, Japanese Patent Laid-Open No. 3-199365 discloses an induction heating method and an open flame. By combining with the heating method,
A plate temperature control technique of an alloying furnace when heating a steel plate is disclosed. Regarding the technology disclosed in the above publication, FIG.
The steel plate 20 discharged from the annealing furnace 21 is
Zinc enters the zinc bath pot 22, is attached with zinc, is pulled up from the pot 22, the amount of zinc attached is adjusted by the wiping nozzle 23, and passes through the heating zone 24, holding zone 25, and cooling zone 26 of the alloying furnace to reach the steel plate surface. An alloy layer is formed. In the alloying furnace, the heating zone 24 includes a first heating zone 27 of an induction heating system and then a second heating zone 28 of an open flame heating system.
It consists of Then, the electric power or voltage is adjusted so that the first heating zone 27 of the induction heating system reaches the set value, and the furnace temperature is adjusted so that the second heating zone 28 of the direct heating system reaches the furnace temperature set value. Is.

[0007]

In the case of the above induction heating method, the steel plate temperature is a function P = F (t, w, s, ΔT) / E.
It is controlled by turning on the electric power calculated by the FF (t = plate thickness, w = plate width, s = line speed,
ΔT = amount of temperature rise, EFF = heating efficiency). However, this has the following problems.

(1) Since the temperature rise amount in this function is the difference between the target plate temperature on the heating zone exit side and the heating zone entrance side plate temperature, the heating zone entrance side plate temperature must be accurately calculated to calculate the temperature rise amount. Need to get However, the method using a radiation thermometer is difficult to measure due to the clouding of the lens surface of the radiation thermometer due to the scattering of zinc and the attenuation of the radiation energy due to the low emissivity of the steel sheet.

Further, the method of calculating by taking into consideration the natural cooling in the idle running section from the zinc bath to the heating zone and the cooling by wiping air is difficult to set the heat transfer function, and this method is also difficult.

(2) Further, since the heating efficiency and constants of the electric power obtained by the above function are slightly different depending on the operating conditions, the heating zone outlet side plate temperature is detected and compared with the target plate temperature. Need to be corrected. However, the steel sheet on the heating zone exit side is in the process of alloying, and the emissivity of the steel sheet changes significantly, so it is difficult to measure with a radiation thermometer.

Therefore, a method is conceivable in which the plate temperature is measured on the heat retaining side outlet side where the emissivity fluctuation is small, and the plate temperature is regarded as the heating zone outlet side plate temperature (normally, the heating zone outlet side plate temperature and the heat retaining side outlet plate are operating conditions. Since the temperature is the same, the target temperature of the heat retaining zone is set to the same value as the target plate temperature on the heating zone exit side. However, when the operating conditions such as width and line speed change, the heat capacity of the heat retaining zone is large. Therefore, the warming tropical outlet side plate temperature fluctuates due to the delay in the response time of the furnace temperature, and the warming tropical outlet side plate temperature ≠ the heating zone outgoing side plate temperature. There is a problem that you can not.

Therefore, in order to solve the above-mentioned problems, the present invention finds a heating zone inlet side plate temperature or a heating zone outlet side plate temperature in an alloying furnace without using a radiation thermometer or heat transfer calculation. Provided is a method of controlling a steel plate temperature by the heating zone outlet side plate temperature which is effective even when the operating conditions are changed, when the outlet side plate temperature is regarded as the heating zone outlet side plate temperature for feedback control.

[0013]

According to the present invention, in an alloying furnace, the heating zone inlet side plate temperature or the heating zone outlet side plate temperature is obtained from the impedance of the induction heating heater, and the input power of each induction heating heater is obtained to obtain the steel sheet temperature. Is to control.

[0014]

[Function] The accuracy of the electric power supplied to the induction heating heater can be improved by calculating the input electric power by using the heating zone entrance side plate temperature or the heating zone exit side plate temperature obtained from the impedance of the induction heating heater. .

Even if the warming tropical outlet side plate temperature fluctuates due to changes in operating conditions, accurate feedback control can be maintained by using the heating zone outlet side plate temperature calculated as the heating zone outlet side actual plate temperature.

[0016]

Embodiment An embodiment of the present invention will be described with reference to FIG.

The steel sheet 2 continuously fed to the zinc pot 1 is coated with molten zinc 3 and adjusted to an appropriate plating thickness by a wiping device 4 installed immediately above the zinc bath, and then heated by a heating zone 5. The plating layer becomes an alloy layer of iron and zinc by being heated to about 500 to 550 ° C. and being kept isothermally in the heat retaining zone 6.

In the present invention, the steel plate 2 is the heating zone 5
Induction heating is carried out at 1, and heat is held by a heater at the heat retaining zone 6. And a zinc pot 1 a warming 6
Further, temperature detectors 8, 9 and 11 are respectively provided on the outlet side of the warming zone and the induction heating heater is controlled by the input power control device 7. In addition, the heater 12 of the warming zone is the furnace temperature controller 1
It is controlled by 0.

In the induction heating type heating zone 5, a required number of induction heating heaters (IH) No. 1 to No. n heaters are provided, and the supply power of each heater is controlled by the input power control device to control the plate temperature.

In the present invention, the heating zone entrance side plate temperature and the heating zone exit side plate temperature are determined by the impedance of the induction heating heater (IH). In this regard, referring to FIG. 2, the plate temperature and the impedance of the induction heating heater The relationship will be described.

As is apparent from FIG. 2, the average plate temperature Tn (° C) of the n-th induction heating heater section is correlated with the impedance Z (Ω) (= supply voltage / current) of the induction heating heater. . Focusing on this fact, the heating zone entry side temperature from the impedance of the induction heater to (T _IACT) and heated home use plate temperature (T _OACT), can be obtained from Equation 1 and Equation 2.

Formula 1 T _IACT = Tn-Pn (Tn + 1-Tn) / (Pn + Pn
+1) Formula 2 T _OACT = Tn + Pn (Tn-Tn-1) / (Pn + Pn
Here -1), T _IACT: heating zone entry side temperature T _OACT: heating home use plate temperature Tn: n-th stage of the induction heater of the average metal temperature Pn: input power above into the n-th stage of the induction heater From the equation, the heating zone entrance side plate temperature is obtained by calculating the impedance of the induction heating heaters of the first and second stages, and the plate of the induction heating heater part of each stage is obtained from the impedance-plate temperature characteristics collected in advance. Calculate the temperature, calculate the temperature rise of the first stage heater from the plate temperature difference between the induction heating heaters,
The heating zone entrance side plate temperature can be obtained by subtracting the plate temperature from the step.

Similarly, the heating zone outlet side plate temperature can be obtained by the equation (2).

Thus, from the impedance-plate temperature characteristics,
By measuring the impedance of the induction heater, the heating zone entrance side plate temperature or the heating zone exit side plate temperature can be accurately obtained, and as a result, the input power of the induction heating heater can be obtained accurately.

Then, the input power can be obtained by the following equation (see FIG. 3).

First, the base power (TP
The calculation of B) is performed.

Formula 3 TPB = J × t × W × ρ × Q × 10 ³ / EFF where, t: plate thickness (mm) W: plate width (mm) ρ: specific gravity of steel plate (kg / mm ³ ) Q : Specific heat of steel plate (kw · sec / kg · ° C) EFF: Heating efficiency (function of plate thickness / plate width) J: Constant When the base power is calculated, then the input power is calculated according to the operating conditions by the following formula. Done.

Equation 4 Ptw = TPB × S (T _OTAR −T _IACT ) / 60 + K [k
W] Here, S: Line speed (m / min) T _OTAR : Target plate temperature (° C) T _IACT : Heating zone entrance side plate temperature (° C) K: Corrected power (kW) Power obtained by the above calculation Then, the correction power K is calculated by the following equation.

Formula 5 K = TPB × S × (T _OTAR −T _OACT ) / 60 where T _OACT : Heating _{zone outlet} side plate temperature (° C) By repeating the equations 4 and 5, the heating zone target plate temperature and actual result are obtained. The correction amount of input power is calculated from the deviation of the plate temperature and corrected.

Next, the control when the operating conditions are changed by using the above plate temperature will be described with reference to FIG.

The heating zone outlet side plate temperature T _OACT is _subjected to feedback control using the warming zone outlet side plate temperature (section), and the heating zone outlet side plate temperature is obtained from the impedance of the induction heater by the above-mentioned method. When the temperature of the heat retaining zone fluctuates and deviates from the target furnace temperature ± a, the actual strip temperature on the heating zone outlet side is switched from the heat retaining zone outlet side temperature to the sheet temperature obtained by the above method (section), heat retaining zone When the furnace temperature returns to the target furnace temperature ± a, the heating zone outlet-side actual plate temperature is switched to the heat retention outlet-side plate temperature (section). At this time, the correction amount of the input power is calculated and corrected from the deviation between the heating zone target plate temperature and the actual plate temperature.

[0032]

The plate temperature can be accurately controlled.

In the present invention, the steel plate temperature is controlled by utilizing the plate temperature on the heating zone entrance side or the heating zone exit side, which is obtained from the impedance of the induction heating heater, so that accurate feedback control can be performed. Further, even if the warming tropical outlet side plate temperature changes due to changes in operating conditions, accurate feedback control can be maintained by applying the heating zone outlet side plate temperature obtained from the impedance as the heating zone outlet side actual plate temperature.

[Brief description of drawings]

FIG. 1 is a schematic view of an alloying furnace applied to the present invention.

FIG. 2 is a diagram showing the relationship between impedance and plate temperature.

FIG. 3 is a diagram showing a calculation procedure of input power.

FIG. 4 is a graph showing changes in target plate temperature when the present invention is applied when operating conditions change.

FIG. 5 is a schematic view of a conventional alloying furnace.

[Explanation of symbols]

1,22 Zinc pot 2,20 Steel plate 3,22
Zinc bath 4,23 Wiping device 5,24 Heating zone
6,25 Heat insulation 7 Input power control device 8, 9, 11 Temperature detector
10 Heat-retaining furnace temperature controller 12 Heat-retaining heater
21 annealing furnace 26 cooling zone 27 first heating zone of induction heating system 28 second heating zone of direct flame heating method

Claims (2)

[Claims] 1. A method of controlling a steel sheet temperature by electric power supplied to a heating zone composed of an induction heating heater of an alloying furnace, wherein the impedance of the induction heating heater at each stage is obtained, and the impedance plate temperature characteristic is correlated. , The plate temperature of the induction heating heater of each stage is calculated, and the heating amount of each stage is calculated from the plate temperature difference between the adjacent induction heating heaters. A method for controlling a steel sheet temperature, which comprises obtaining the plate temperature on the heating zone entrance side or the heating zone exit side from subtraction or addition, and obtaining the input power using the plate temperature on the heating zone entrance side or the heating zone exit side. 2. A method of controlling a steel sheet temperature by electric power applied to a heating zone composed of an induction heating heater of an alloying furnace, wherein a warming temperature outgoing side sheet temperature is used as a heating zone outgoing side sheet temperature, and this is fed back to determine the steel sheet temperature. In controlling
When the warming zone temperature is out of the target furnace temperature range, the heating zone outlet side actual plate temperature is switched from the warming zone outlet side plate temperature to the heating zone outlet side plate temperature obtained in claim 1, and the warming zone furnace temperature falls within the target furnace temperature range. A method for controlling a steel plate temperature, characterized in that the actual strip temperature on the outlet side of the heating zone is switched to the strip temperature on the heat retaining side when returning.