JP3261714B2 - Method for controlling alloying of galvanized steel sheet - Google Patents

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 alloying in a continuous galvannealed steel sheet manufacturing line.

[0002]

2. Description of the Related Art Generally, an alloying treatment of a hot-dip galvanized steel sheet is performed through a process of heating, soaking, and cooling. As a conventional technique, as disclosed in Japanese Patent Application Laid-Open No. 1-252761, “Sheet temperature control device of alloying furnace for hot dip galvanizing”, alloying conditions include steel type, aluminum concentration in plating bath, zinc adhesion amount, and the like. An alloying target heating temperature is set in consideration of the alloying heating temperature and soaking time, and an operation signal is output based on the deviation between the actual plate temperature of the sheet thermometer and the target temperature to achieve the target temperature. There has been proposed a control method using a sheet temperature control device.

Similarly, Japanese Patent Application Laid-Open No. Sho 62-180050, entitled "Method of controlling alloying of hot-dip galvanized steel sheet,"
A control method using a sheet temperature control device to set the alloying target heating temperature in consideration of the alloying target heating temperature, the soaking time, and the aluminum concentration in the film as the alloying conditions, and to realize the sheet temperature. Has been proposed.

However, in order to set an appropriate alloying heating temperature and soaking time, it is not sufficient to consider only the above-mentioned alloying conditions. Since the rate and the optical diffusion state of the surface fluctuate greatly, accurate sheet temperature measurement is difficult, and alloying control by a sheet temperature control device that attempts to control the sheet temperature based on the actual and target deviations is realized. It was very difficult, and in fact, most operations were based on the experience and judgment of operators.

[0005] One of the conditions affecting the alloying state is the temperature of the sheet entering the plating bath. However, when the sheet thickness, the sheet width or the speed is changed, the furnace inertia of the annealing furnace is large. Therefore, it is not possible to immediately reach the predetermined entry plate temperature. For this reason, a transient change in the alloying state occurs, and the quality of the fluctuating portion deteriorates, resulting in instability of the quality, and the removal of the portion deteriorates the yield.

[0006]

The problem to be solved by the present invention is that the alloying state is not determined solely by the conditions of the prior art, but the product type of the alloy plating to be produced, the plating bath temperature and the steel sheet. And the residence time in the plating bath depending on the temperature of the sheet entering the plating bath and the passing speed of the steel sheet, and furthermore, the cooling amount of the steel sheet from the plating bath to the alloying heating furnace. For this reason, in order to manufacture alloy-plated steel sheets with stable quality, it is not enough to maintain a constant alloying heating temperature, and the alloying heating temperature is changed by changing the various alloying conditions described herein. There is a need.

[0007] The sheet temperature measurement at the exit side of the alloying furnace is as follows.
Difficulty due to large changes in emissivity and surface diffusion, plate temperature feedback using a plate temperature controller cannot be implemented, and other methods for operating the alloying furnace must be solved. No. For this reason, it is appropriate to obtain the operation amount of the alloying heating furnace that achieves the alloying heating target temperature by heat transfer calculation.

Further, among conditions affecting the alloying state, the control of the sheet temperature entering the plating bath has a slow response,
Since it takes time to stabilize at a predetermined temperature in an excessive state in the change of the sheet thickness, the sheet width or the speed, the alloy is designed to predict or detect the transient change of the approaching sheet temperature and correct the effect. It is necessary to operate the heating furnace.

[0009]

As a means for solving the above-mentioned problems, the present invention provides an alloying treatment equipment for an galvanized steel sheet which comprises an alloying heating furnace, a soaking holding furnace and a cooling furnace. Of residence time and soaking time in plating bath depending on product type, steel type, zinc deposition amount, aluminum concentration in plating bath, plating bath temperature, steel plate temperature entering steel plate, and sheet passing speed The alloying control method for galvannealed steel sheet is to determine the target temperature and soaking time for alloying heating for alloying treatment by the amount of cooling of the steel sheet from the plating bath to the alloying heating furnace. is there.

[0010] Further, among the above alloying conditions, when the thickness, width or speed of the steel sheet is changed, the influence of the transient fluctuation of the sheet temperature of the steel sheet entering the plating bath on the alloying state is determined. This is a method for controlling the alloying of a galvannealed steel sheet in which the alloying heating temperature is controlled in accordance with the transient fluctuation in order to correct the effect.

[0011]

The operation of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing equipment for alloying a hot-dip galvanized steel sheet. Figure 2 shows target plate temperature and holding cooling of the alloying furnace
It is a figure which shows the switch point from a soaking | uniform-heating holding | maintenance in a furnace to cooling.

In FIG. 1, 1 is an annealing furnace, 2 is a sheet thermometer,
3 is a snout, 4 is a galvanizing bath, 5 is a galvanizing bath thermometer, 6 is a gas throttle nozzle, 7 is an alloying heating furnace, 8 is a holding cooling furnace (soaking and holding furnace) , and 9 is alloying. A control device, 10 is an alloying heating furnace unit control device, 11 is a holding cooling furnace unit control device, 12 is an annealing furnace control device, and 13 is an alloying degree meter.

First, the alloying control device 9 determines the type of product, the type of steel, the amount of zinc deposited, the aluminum concentration in the plating bath, the temperature of the plating bath, the temperature of the steel sheet entering the plating bath, the speed of passing the steel sheet, and The alloying heating furnace 7 as shown in FIG. 2 is obtained by using the residence time in the plating bath, the soaking time, and the amount of cooling of the steel sheet from the plating bath 4 to the alloying heating furnace 7 according to the speed. The target plate temperature and the switching point from the soaking to the cooling in the holding cooling zone are determined. Next, the alloying heating furnace 7
From the target sheet temperature and the sheet temperature on the entry side of the alloying heating furnace 7, the required heat quantity to be supplied to the alloying heating furnace 7 is obtained, and the operation amount for controlling the alloying heating furnace 7 is calculated. Then, the manipulated variable is set in the alloying furnace control unit 10 and the switching point from the soaking holding to the cooling is set in the soaking furnace unit 11.

Further, in a transient state in which the sheet thickness, the sheet width or the speed is changed, a transient change of the sheet temperature entering the plating bath 4 is predicted or detected by the sheet thermometer 2 to cancel the influence. A fine adjustment amount of the alloying heating temperature that can be obtained is obtained, and a fine operation amount of the alloying heating furnace 7 is calculated and set from the temperature in the same manner as described above.

[0015]

EXAMPLE In this example, a case where an induction heating device is used as an alloying heating furnace will be described as an example. From various studies to date, the alloying state is affected by several factors. FIG. 3 shows the effects of the aluminum concentration in the bath, the plating bath temperature, the plate temperature entering the plating bath, the alloying temperature, and the soaking time on the alloying state. Further, similarly to the conditions shown in FIG. 3, the residence time in the bath and the pre-cooling amount of the alloying furnace also affect the alloying state.

From the above relationship, a standard heat cycle as shown in FIG. 2 for obtaining an appropriate alloying state in a predetermined product type is firstly determined. However, it cannot be changed to the point where the temperature is continuously switched from the soaking to the cooling, and only some intermittent values can be selected for the time when the feeding speed is determined. Therefore, the alloying target heating temperature T for obtaining a predetermined alloying state is given by the following equation (1) in consideration of the actual soaking time.

[0017]

(Equation 1)

Further, a heat transfer calculation represented by the following equation (2) is performed to obtain dT.

[0019]

(Equation 2)

Since it is difficult to measure the temperature of Ti at the point where the steel sheet enters the plating bath, the measured value of the sheet thermometer attached to the exit side of the annealing furnace and the heat transfer calculation shown in the following equation (3) are used. perform calculations stacked by, to calculate the value.

[0021]

(Equation 3)

Next, the operation amount of the alloying heating furnace 7 is calculated based on the alloying target heating temperature T obtained from the equation (1). In this calculation, in order to calculate the amount of heat input to the alloying heating furnace 7, the induction heating device is used using the following equation (4), using the inlet-side plate temperature of the alloying heating furnace 7 calculated when dT is obtained. The power input to the alloying furnace is determined and set in the alloying furnace unit control device 10.

[0023]

(Equation 4)

FIG. 4 shows an example of setting the input power to the induction heating device determined as described above. FIG. 4 is a diagram for explaining a control example in a steady state according to the present invention .
Line speed of 1000mm steel plate increased from 50 to 60 mpm
This is a changed example . The top diagram shows how the line speed changes.
The second, third, and fourth figures from the top
The soaking time corresponding to the line speed change,
The change of the stay time and the cooling amount before the alloying heating furnace are shown. Obedience
If the line speed is changed, the power
The setting is a simple speed proportional setting.
Was large (each of the sixth from the top and the bottom of the figure)
Broken line). Soaking time, soaking time, before alloying furnace
Since the change in the cooling amount affects the degree of alloying, the present invention
Is 5 from the top to compensate for the effects of these changes.
As shown in the second figure, the alloying target temperature is changed. This
Change the target temperature of
Are set as shown by the solid line in FIG. The bottom figure
Indicates the degree of alloying obtained by the method of the present invention. As is apparent from this figure, simply changing the input power in proportion to the speed takes into consideration the soaking time, the residence time in the bath, and the effect of the cooling before the alloying furnace 7 on the alloying reaction. However, the degree of alloying varies, but the present invention makes it possible to stably control the alloying state. Further, according to the present invention, a stable alloying state can be ensured even when the bath temperature, the aluminum concentration in the bath, and the plate temperature entering the plating bath fluctuate.

Further, when the thickness, width or speed of the plating is changed, the control response of the temperature of the sheet entering the plating bath is slow and causes a transient fluctuation. As shown in FIG. Is detected by the sheet thermometer 2 or the like and the input power of the induction heating device is sequentially changed according to the present invention, so that a stable alloying state can be obtained even in a transient state. FIG.
FIG. 3 is a diagram for explaining a control example in a transient state according to the present invention .
At a line speed of 50 mpm and a steel plate size of 1.0 mm
× board width 1000mm → board thickness 0.8mm × board width 1000m
It is an example that has changed to m . The top figure shows how the thickness changes.
And the second figure from the top corresponds to the above-mentioned thickness change.
The change of the plating bath entry plate temperature is shown. The thickness is 1.0 →
When the thickness is reduced to 0.8mm, the plating bath enters at the part where the thickness changes
The temperature drops sharply, and then the temperature gradually decreases
It returns to the entry plate temperature. The change of the entering plate temperature at the plate thickness change part is
Affects the degree of alloying. Conventionally, alloys in the transient state
Target temperature and induction heater power setting to achieve it
Does not take into account the change of the entering plate temperature in the plate thickness change section
Was. Therefore, the deviation of the degree of alloying from the target value is large.
(Each broken line from the third to the bottom figure from the top).
In the present invention, it is necessary to correct the influence of the change in the entry plate temperature.
As shown by the solid line in the third figure from the top,
Change the temperature. In response to this change in target temperature, induction
The heater power is set as shown by the solid line in the fourth diagram from the top.
Set. The solid line at the bottom is the alloy obtained by the method of the present invention.
Indicates the degree of conversion.

Incidentally, even in a gas heating type alloying furnace,
This method can be applied, and in the procedure described above, the operation amount (for example, the target furnace temperature or the gas combustion amount, etc.) of the gas furnace that can achieve the target plate temperature is obtained by heat transfer calculation. Only good.

[0027]

As described above, according to the present invention,
Even if various factors affecting the alloying change, the alloying state can be controlled stably, an alloyed hot-dip galvanized steel sheet having excellent quality can be stably manufactured, and the yield can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing equipment for alloying a hot-dip galvanized steel sheet.

FIG. 2 is a view showing a target plate temperature of an alloying heating furnace and a switching point from soaking to cooling in a holding cooling zone.

FIG. 3 shows the effects of the aluminum concentration in the bath, the plating bath temperature, the temperature of the sheet entering the plating bath, the alloying temperature, and the soaking time on the alloying state.

FIG. 4 is an example of control in a steady state according to the present invention.

FIG. 5 is an example of control in a transient state according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Annealing furnace 2 Sheet thermometer 3 Snout 4 Galvanizing bath 5 Galvanizing bath thermometer 6 Gas throttle nozzle 7 Alloying heating furnace 8 Holding cooling furnace 9 Alloying control device 10 Alloying heating furnace single control device 11 Holding cooling furnace alone Control device 12 Annealing furnace control device 13 Alloying degree meter

Claims (2)

(57) [Claims] In a process for alloying a hot-dip galvanized steel sheet by an alloying treatment facility comprising an alloying heating furnace, a soaking holding furnace and a cooling furnace, a product type, a steel type, a zinc adhesion amount, and an aluminum content in a plating bath. The change of the residence time in the plating bath and the soaking time by the concentration, the plating bath temperature, the plate temperature of the steel plate entering the plating bath and the passing speed of the steel plate, and the cooling amount of the steel plate from the plating bath to the alloying heating furnace A method for controlling alloying of a galvannealed steel sheet, characterized by determining a target temperature for alloying heating and a soaking time for alloying treatment. 2. Determine the effect of a transient change in the sheet temperature of the steel sheet entering the plating bath on the alloying state when the thickness, width or speed of the steel sheet is changed among the alloying conditions. 2. The method according to claim 1, wherein the alloying heating temperature is controlled in accordance with the transient fluctuation to correct the influence.
The method for controlling alloying of a galvannealed steel sheet according to the above.