JP2000317513A - Method for controlling coiling temperature of hot-rolled steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coiling temp. control method of a hot-rolled steel sheet, with which the coiling temp. is controlled so as to match to a target temp. at high accuracy, even in the case the coiling temp. is in the low temp. range, such as 400-500 deg.C, or even in the case a scale thickness on the steel sheet is thick or the steel sheet has the large ratio of heavy component, such as Si, Ni, related to the scale thickness. SOLUTION: The temp. TMHF of min. heat flux point changed from a film boiling state to a transition boiling state, and the temp. TCHF of critical heat flux point changed from the transition boiling state to a nuclear boiling state on the water-cooling surface of the hot-rolled steel sheet with respect to a prescribed sampling point, are estimated, respectively. Further, the boiling state of the water-cooling surface is estimated from the relation of respective temperatures TMHF and TCHF of the min. heat flux point and the critical heat flux point, and the temperature of water-cooling surface of the hot-rolled steel sheet, and the heat transfer coefficient of the water-cooling is calculated from a model formula of the heat transfer coefficient of the water-cooling according to the estimated boiling state. Then this heat transfer coefficient of the water-cooling surface to the prescribed sampling point is calculated by using this heat transfer coefficient of the water-cooling.

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 a winding temperature of a hot-rolled steel sheet for cooling a steel sheet to be hot-rolled to a desired winding temperature on a run-out table.

[0002]

2. Description of the Related Art In a hot rolling process of a steel sheet, a steel sheet after finish rolling is transported from a finish rolling mill to a winder by a run-out table by a water-cooling device provided above and below the run-out table. After being cooled to a temperature, it is wound up by a winder. In hot rolling of a steel sheet, the manner of cooling after the finish rolling is an important factor that determines the mechanical properties of the steel sheet.

[0003] In this cooling control, the water injection into the steel sheet surface by a number of water cooling devices (cooling banks) installed downstream of the finishing mill is turned on / off by opening and closing a valve, or injected by a flow control valve. This is done by increasing or decreasing the amount of water. For example, while inputting the instantaneous actual values such as the sheet thickness, the sheet width, the conveying speed of the steel sheet, the finishing outlet temperature, and the winding temperature to the computer, the target winding temperature can be realized based on the calculation result. This is performed by controlling on / off of the cooling bank.

[0004] However, in a hot rolling mill, usually, accelerated rolling is performed, so that not only the material conveying speed is changed, but also the finishing outlet temperature is constantly fluctuated due to skid marks and the like. The boiling state of the water-cooled surface fluctuates depending on the surface temperature and surface properties. Therefore, it is an important subject in manufacturing a hot-rolled steel sheet to accurately control the winding temperature with respect to these disturbances.

As a method of controlling the winding temperature in response to the disturbance, there is, for example, a control method disclosed in Japanese Patent Application Laid-Open No. 58-221606. In this control method, first, the material temperature and the sheet thickness are sampled and measured at a fixed time interval or a fixed distance interval at the finishing mill outlet, and the sampling points are tracked until the sampling points reach the winding thermometer. Then, the following calculation is performed for all sampling points sampled up to the current time.

(1) The material temperature is measured to determine the amount by which each sampling point moves in one sampling cycle, and the position of each sampling point is corrected to the current position. (2) Find the cooling bank where the sampling point is located, input the actual water injection pattern, find the material temperature at this sampling point, calculate the heat transfer coefficient at each sampling point from each formula, and further calculate the heat transfer coefficient at each sampling point. Correct the material temperature to the current temperature. (3) Predict future speed changes from the set values of the finishing mill's acceleration rate, deceleration rate, and acceleration / deceleration timing, and predict the predicted passage time of each cooling bank until this sampling point reaches the winding thermometer. .

(4) An actual water injection pattern of each cooling bank is input, and a predicted winding temperature is calculated using a predicted passage time of each cooling bank. (5) If the predicted winding temperature does not match the target temperature, the scheduled injection of the cooling bank downstream from this sampling point so that the target winding temperature is reached, according to the predetermined priority of the water injection bank. Change the pattern. The winding temperature is controlled by outputting the thus obtained water injection pattern for all sampling points at a necessary timing.

FIG. 1 is a schematic diagram showing an outline of a cooling facility for performing the above-described winding temperature control. The steel sheet 1 coming out of the finishing mill 2 is cooled on the run-out table 3 by the cooling devices 4 and 5.
It is cooled by water injection from the chiller and wound up by the winder 6.
At this time, the temperature of the steel sheet before cooling is measured by the thermometer 7,
The temperature of the steel sheet after cooling is measured by the thermometer 8. The take-up temperature controller 9 is basically a feed-forward controller, which predicts and calculates the temperature after cooling (the take-up temperature), and makes a note from the cooling devices 4 and 5 so that the calculated value matches the target value. Determine the amount of water.

In the above-described method for cooling a steel sheet, it is important how accurately the temperature at each sampling point of the steel sheet can be estimated. An error usually occurs in the calculation for making this estimation. The main factor of this error is the accuracy of estimating the heat transfer coefficient of water cooling used for temperature calculation.

Conventionally, with respect to the heat transfer coefficient of water cooling, JP-A 9-10822 discloses, as disclosed in JP-A-9-216011 Patent Publication, water density of the cooling water of the top-bottom surface of the steel sheet W _t , W _b [m ³ / m ² min], the conveyance speed V of the steel sheet V [m / min], and the water temperature _Tw [° C.] of the cooling water.
From the heat flux q _wt , q _wb [Kcal / m ² hr] determined from the above, and the heat transfer coefficients h _wt , h _wb [Kc
al / m ² hr ° C.] has been widely used. That is,
Equations (3) and (4) for the heat transfer coefficient derived from Equations (1) and (2), which represent the upper and lower heat fluxes, have been used.

[0011]

(Equation 1)

Here, T _t , T _b : surface temperature [° C.] of the steel plate (upper surface / lower surface), Z _t , Z _b : adjustment coefficient [−], t: suffix representing the upper surface, b: suffix representing the lower surface Characters.

FIG. 2 is a graph expressing the equation (1) or the equation (2) with the surface temperature of the steel sheet on the horizontal axis and the heat flux on the vertical axis. As is clear from FIG. 2, the heat flux is
It is treated to be constant regardless of the surface temperature of the steel sheet.

[0014]

However, in the production of a high-tensile hot-rolled steel sheet, the winding temperature is set as low as 400 to 500 ° C. depending on the required strength. However, it is known that in such a temperature range where the steel sheet temperature is low, the boiling phenomenon in the cooling process is in a transition boiling state in which a transition from film boiling to nucleate boiling occurs.

FIG. 3 shows the behavior of a boiling curve in which the degree of superheat (= surface temperature of steel sheet−saturation temperature of cooling water) is plotted on the horizontal axis and the heat flux is plotted on the vertical axis. In the cooling process, the state changes from the film boiling state to the transition boiling state, and further to the nucleate boiling state. It can be seen that the heat flux rapidly increases in the transition boiling state. The point at which the film boiling state changes to the transition boiling state is called a minimum heat flux point (MHF point), and the point at which the transition boiling state changes to the nucleate boiling state is called a critical heat flux point (CHF point).

The conventional heat transfer coefficient formula is based on an empirical formula obtained at a relatively high winding temperature (approximately ≧ 550 ° C.), that is, a film boiling state. Winding temperature 400 required for production of high tension hot rolled steel sheets, etc.
It is difficult to use for temperatures up to 500 ° C. Therefore, the winding temperature control itself has low accuracy, and automatic control is difficult.

In order to cope with such a problem, Japanese Patent Publication No. Hei 6-248 discloses that water is injected from upper and lower cooling headers in a high temperature region in which cooling water is boiling, and only a lower surface of a steel plate is injected in a transition boiling region. It has been proposed to perform cooling of the steel sheet in a stable state by performing the above.

In Japanese Patent Application Laid-Open No. 9-10822,
As shown in FIG. 4, focusing on the fact that the behavior of the cooling curve greatly differs depending on the element components related to the difference in the scale thickness generated on the steel sheet surface, that is, the Si weight component, basically, Equation (3), 4) It is proposed that the heat transfer coefficient equation given in the form of the equation can be handled by adjusting the correction coefficient for each cooling bank.

This is because, in the high Si steel, as shown in FIG. 5, the sub-scale layer (FeO—Fe ₂ SiO ₄ ) develops, so that the oxide scale formed on the surface of the steel sheet remains after the finish rolling. This is because it is necessary to cope with an increase in the cooling rate caused by the scale thickness being larger than that of the general material and the surface roughness of the steel sheet being rough.

As described above, in the cooling process of the steel sheet, the temperature at which the film boiling state changes to the transition boiling state, that is, the minimum heat flux point (MHF point) changes according to the subcooling degree of the cooling water. As shown in Japanese Unexamined Patent Publication No. 9-10822, the thickness varies depending on the thickness and surface roughness of the steel sheet, that is, the surface properties.

However, in the method disclosed in Japanese Patent Publication No. 6-248, there is no concrete method for estimating the transition boiling state. In addition, since the method of using the cooling device is restricted, there are problems such as the inability to uniformly cool the upper and lower surfaces and the performance of the cooling device cannot be fully exhibited.

Further, in the method disclosed in Japanese Patent Application Laid-Open No. 9-10822, it is necessary to adjust the correction coefficient for each cooling bank. It is difficult to cope with a change in.

The present invention has been made to solve such a problem, and its object is to provide:
In order to control the amount of cooling water injected into the hot-rolled steel sheet on the run-out table and make the winding temperature of the hot-rolled steel sheet coincide with the target temperature, the water-cooled surface of the hot-rolled steel sheet at a predetermined sampling point on the run-out table When calculating the heat transfer coefficient, the boiling point of the water-cooled surface is calculated by applying the model formula of the water-cooled heat transfer coefficient according to the boiling state of the water-cooled surface to the sampling point and calculating the water-cooled heat transfer coefficient to this sampling point. Accurately determine the heat transfer coefficient of the water-cooled surface, which rapidly changes due to the change in the state, even if the winding temperature is in the low temperature range of 400 to 500 ° C, and the scale thickness of the steel plate is related to the thick steel plate or scale thickness. An object of the present invention is to provide a method for controlling a winding temperature of a hot-rolled steel sheet that controls a winding temperature so as to match a target temperature with high accuracy even for a steel sheet having a large weight component such as Si and Ni.

[0024]

According to a first aspect of the present invention, there is provided a method for controlling a winding temperature of a hot-rolled steel sheet, wherein when a hot-rolled steel sheet conveyed to a winder by a run-out table is water-cooled with cooling water, the predetermined temperature on the run-out table is reduced. Using the heat transfer coefficient of the water-cooled surface of the hot-rolled steel sheet at the sampling point, a predicted value of the winding temperature of the hot-rolled steel sheet is calculated, and the heat value on the run-out table is adjusted so that the predicted value matches the target value. In the method for controlling the winding temperature of a hot-rolled steel sheet for controlling the amount of water injected into the steel sheet, the boiling state of the water-cooled surface of the hot-rolled steel sheet at the predetermined sampling point may be a film boiling state, a nucleate boiling state, or a transition boiling state. A first step of estimating whether the state is a state, and a second step of calculating the heat transfer coefficient of the water cooling surface with respect to the predetermined sampling point from a model equation of the heat transfer coefficient of water cooling according to the estimated boiling state. To include And it features.

According to a second aspect of the present invention, in the first step of the first aspect, the temperature of the water-cooled surface of the hot-rolled steel sheet and the subcooling degree of the cooling water with respect to the predetermined sampling point are determined. Calculating the temperature of the minimum heat flux point at which the film boiling state changes to the transition boiling state, and the temperature of the critical heat flux point at which the transition boiling state changes to the nucleate boiling state, according to the degree of subcooling. Estimating the boiling state of the water-cooled surface at the predetermined sampling point from the relationship between the respective temperatures of the heat flux point and the critical heat flux point and the temperature of the water-cooled surface of the hot-rolled steel sheet.

According to a third aspect of the present invention, in the method of the first aspect, the first step is to determine a temperature of a water-cooled surface of the hot-rolled steel sheet and a subcooling degree of the cooling water with respect to the predetermined sampling point. The minimum heat flux point at which the film boiling state changes to the transition boiling state, and the temperature of the critical heat flux point at which the transition boiling state changes to the nucleate boiling state, according to the calculating step and the subcooling degree and the scale thickness of the hot-rolled steel sheet, respectively. Estimating, and estimating the boiling state of the water-cooled surface at the predetermined sampling point from the relationship between the respective temperatures of the minimum heat flux point and the critical heat flux point and the temperature of the water-cooled surface of the hot-rolled steel sheet. It is characterized by the following.

According to a fourth aspect of the present invention, in the first step of the first aspect, the temperature of the water-cooled surface of the hot-rolled steel sheet and the subcooling degree of the cooling water with respect to the predetermined sampling point are determined. The minimum heat flux point at which the film boiling state changes to the transition boiling state, and the transition boiling state changes to the nucleate boiling state, according to the calculating step and the subcooling degree and the weight component of the elemental component related to the scale thickness of the hot-rolled steel sheet. Estimating the temperature of the changing critical heat flux point, respectively;
Estimating the boiling state of the water-cooled surface at the predetermined sampling point from the relationship between the temperatures of the minimum heat flux point and the critical heat flux point and the temperature of the water-cooled surface of the hot-rolled steel sheet.

In the present invention, the boiling state of the water-cooled surface of the hot-rolled steel sheet with respect to the sampling point is estimated, and the heat transfer coefficient of the water-cooled surface is calculated using a model equation of the water-cooled heat transfer coefficient according to the boiling state.

In the present invention, when estimating the boiling state,
Depending on the subcooling degree of the cooling water, or according to the subcooling degree and the scale thickness of the hot-rolled steel sheet, or according to the subcooling degree and the weight component of the elemental component related to the scale thickness of the hot-rolled steel sheet, the film boiling state From the minimum heat flux point at which the transition boiling state changes to the transition boiling state, and the critical heat flux point at which the transition boiling state changes to the nucleate boiling state. Estimate the boiling state of the surface.

Thus, by accurately estimating the heat flux of water cooling which rapidly changes with the change of the boiling state of the water-cooled surface of the steel material, the heat transfer coefficient of water cooling is accurately calculated, and the winding of the hot-rolled steel sheet is accurately calculated. It is possible to accurately predict the taking temperature. Therefore, even for a hot-rolled steel sheet having a low winding temperature of 400 to 500 ° C., the winding temperature can be controlled with high accuracy.

According to a fifth aspect of the present invention, in the method for controlling the winding temperature of a hot-rolled steel sheet according to any one of the second to fourth aspects, the second step estimates the boiling state in the first step as a film boiling state. If this is the case, the step of calculating the heat transfer coefficient of the water-cooled surface from the degree of subcooling, the water density of the cooling water, and the transport speed of the hot-rolled steel sheet. The step of calculating the heat transfer coefficient of the water-cooled surface from the temperature of the water-cooled surface of the rolled steel sheet, the water temperature of the cooling water, the water density of the cooling water, and the transport speed of the hot-rolled steel sheet. If it is estimated, the solid-liquid contact area ratio of the water-cooled surface is determined from the surface temperature of the hot-rolled steel sheet, and the heat transfer coefficient at the minimum heat flux point and the heat The value between the transmission rate and the Characterized in that it is a step of calculating a heat transfer coefficient of the water-cooled surface for the ring points.

In a sixth aspect of the present invention, in the method for controlling a winding temperature of a hot-rolled steel sheet according to any one of the second to fourth aspects, the second step estimates a boiling state in the first step as a film boiling state. If this is the case, the step of calculating the heat transfer coefficient of the water-cooled surface from the degree of subcooling, the water density of the cooling water, and the transport speed of the hot-rolled steel sheet. The step of calculating the heat transfer coefficient of the water-cooled surface from the temperature of the water-cooled surface of the rolled steel sheet, the water temperature of the cooling water, the water density of the cooling water, and the transport speed of the hot-rolled steel sheet. If it is estimated, the solid-liquid contact area ratio of the water-cooled surface is determined from the surface temperature of the hot-rolled steel sheet, and the heat transfer coefficient at the minimum heat flux point and the heat The weighted average value with the transmission rate is Characterized in that it is a step of calculating a heat transfer coefficient of the water-cooled surface for the sampling point.

In the present invention, in the case of a transition boiling state,
The solid-liquid contact area ratio is determined from the surface temperature of the steel sheet, and the value between the heat transfer coefficient at the minimum heat flux point and the heat transfer coefficient at the critical heat flux point, or weighted, is calculated according to the solid-liquid contact area ratio. The average value is calculated as the heat transfer coefficient of the water-cooled surface with respect to the sampling point.

Thus, even when the cooling behavior is different from that of a general steel sheet due to a large scale thickness or a large weight component such as Si and Ni related to the scale thickness, a change in the boiling state of the water-cooled surface of the steel material is obtained. By accurately estimating the water-cooling heat flux that rapidly changes with the above, it is possible to accurately calculate the water-cooling heat transfer coefficient and accurately predict the winding temperature of the hot-rolled steel sheet. Therefore, even for a hot-rolled steel sheet having a large scale thickness and a hot-rolled steel sheet having a large weight component such as Si and Ni related to the scale thickness, the winding temperature can be controlled with high accuracy.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to a case in which the winding temperature is controlled in a run-out table cooling facility having 14 cooling banks as shown in FIG. In the run-out table cooling system shown in FIG. 6, the temperature of the steel sheet (rolling finish temperature) before cooling is measured by a thermometer 7 provided on the exit side of the finish rolling mill 2, and between the No. 6 bank and the No. 7 bank. The temperature of the steel sheet during cooling (intermediate temperature) is measured by the thermometer 10 provided. Further, the temperature of the steel sheet after cooling (winding temperature) is measured by a thermometer 8 provided on the entrance side of the winding machine 6. The controller 9 takes in the actual value of the rolling finish temperature from the thermometer 7 and
Alternatively, the actual value of the transport speed of the steel sheet is taken in from the winder 6. Using various performance values including these, the controller 9
Performs the following processing.

First, the current temperature of the steel sheet 1 is calculated. In the winding temperature control of this embodiment, the calculation of the predicted temperature of the steel sheet is particularly important. In calculating the temperature of the steel sheet, a one-dimensional heat conduction model in the thickness direction is used. Steel plate temperature is (5)
It is given by the heat conduction equation shown in the equation.

[0037]

(Equation 2)

Here, T: steel sheet temperature [° C.], t: time [h]
r], y: position in the thickness direction of the steel sheet [m], c: specific heat [K
cal / kg ° C.], ρ: density [kg / m ³ ], κ: thermal conductivity [Kcal / mhr ° C.] Here, the boundary condition of the steel sheet surface is as follows:
According to equation (7).

[0039]

(Equation 3)

Here, q _t , q _b : heat flux on the upper and lower surfaces [Kcal / m ² hr], d: plate thickness of the steel plate [m] Here, the heat fluxes q _t , q _b on the upper surface and the lower surface are Using the heat transfer coefficients of water cooling, radiation, and convection [Kcal / m ² hr ° C.], they are expressed by the following equations (8) and (9), respectively.

[0041]

(Equation 4)

[0042] However, T _w: temperature [℃], T _a: where ambient temperature [℃], the heat transfer coefficient h _rt radiation, h _rb, the heat transfer coefficient of convection h
_at and _hab are respectively given as follows.

[0043]

(Equation 5)

Ρ: Stefan-Boltzma
nn constant, ε: emissivity [-], β _t , β _b : constant

Water-cooled heat transfer coefficients h _wt , h _wb [Kcal / m
² hr ° C.] is determined by determining the boiling state of the water-cooled surface according to the surface temperature of the steel sheet. In the first example of determining the boiling state, the minimum heat flux point (MHF
Point) and the critical heat flux point (CHF point). When the surface temperature of the steel sheet is equal to or higher than the estimated minimum heat flux point, it is determined that the film is in a boiling state, and between the minimum heat flux point and the critical heat flux point. In some cases, it is determined that the state is a transition boiling state. Cooling water subcooling Δ
T _SUB [° C] is the cooling water saturation temperature T _SAT [° C] (in the case of water, 100 ° C under atmospheric pressure) and the cooling water temperature _Tw [° C].
And from equation (14).

[0046]

(Equation 6)

The temperature T _MHF [° C.] at the minimum heat flux point and the temperature T _CHF [° C.] at the critical heat flux point are determined by the subcooling degree Δ of the cooling water.
From T _SUB , estimation is performed using the equations (15-A) and (16-A).

[0048]

(Equation 7)

Here, T _m0 , T _c0 , K _M1 , K _c1 : constants.

Another example of determining the boiling state will be described below. From the subcooling degree of the cooling water and the weight component (Si weight component or Ni weight component, etc.) of the scale thickness or the element component related to the scale thickness, from the minimum heat flux point (MHF point)
And the critical heat flux point (CHF point). When the surface temperature of the steel sheet is equal to or higher than the estimated minimum heat flux point, it is determined that the film is in a boiling state, and when the temperature is between the minimum heat flux point and the critical heat flux point. Is determined to be a transition boiling state.

The temperature T _MHF [° C.] at the minimum heat flux point and the temperature T _CHF [° C.] at the critical heat flux point are determined by subcooling Δ
When estimating from T _SUB and scale thickness δ [μm],
It is calculated by the formulas (15-B) and (16-B).

[0052]

(Equation 8)

Where K _M2 and K _{c2 are} constants. In addition, when estimating from the subcooling degree ΔT _SUB of the cooling water and the weight component of the element component related to the scale thickness, for example, the Si weight component w _Si [%] or the Ni weight component w _Ni [%], C)
It is calculated by the formula and the formula (16-C).

[0054]

(Equation 9)

Here, K _M3 , K _M4 , K _c3 , K _c4 : constants. In the formulas (15-C) and (16-C), both the Si weight component (w _Si ) and the Ni weight component (w _Ni ) are used, but either one is used. May be. As for the element components, other element components can be similarly handled as long as they relate to the scale thickness.

Since the scale thickness δ varies depending on the type of steel and the manufacturing conditions, for example, the surface scale thickness of a steel sheet is measured for each type of steel and manufacturing conditions, and an appropriate value is obtained from a consolidated table. Set it.

After estimating the boiling state as described above,
The heat transfer coefficient of water cooling is calculated according to each boiling state as follows.

[Film Boiling State] Upper surface: When T _t ≧ T _MHF , Lower surface: When T _b ≧ T _MHF , it is estimated that the film is in a boiling state, and the water-cooled heat transfer coefficients are _expressed by equations (17) and (18). Ask from.

[0059]

(Equation 10)

[0060] However, W _t, W _b: water density of the cooling water [m
³ / m ² min], V: steel sheet speed [m / min],
B _t , B _b , D: constants. The heat transfer coefficient determined by the equations (17) and (18) is determined by the water density of the cooling water, the transport speed of the steel sheet, and the degree of subcooling, and does not depend on the surface temperature of the steel sheet. In particular, the heat flux at the minimum heat flux point (T _t = T _MHF , T _b = T _MHF ), that is, the minimum heat flux q _{MHF, t} , q _{MHF, b} is (1
It can be obtained by the equations (9) and (20).

[0061]

[Equation 11]

[Nucleate boiling state] Upper surface: When T _t ≤ T _CHF , Lower surface: When T _b ≤ T _CHF , the nucleate boiling state is estimated, and the water-cooled heat transfer coefficients are _expressed by equations (21) and (22). Ask from.

[0063]

(Equation 12)

[0064] However, A _t, A _b: constant. In particular, the heat flux at the critical heat flux points (T _t = T _CHF , T _b = T _CHF ), that is, the critical heat fluxes q _{CHF, t} and q _{CHF, b} are given by the following equation (23).
It is obtained by the formula.

[0065]

(Equation 13)

[Transition boiling state] Upper surface: When T _CHF <T _t <T _MHF , lower surface: T _CHF <T _b
When <T _MHF , it is estimated to be in a transition boiling state. The transition boiling state is considered to be a state in which the film boiling state and the nucleate boiling state are mixed, and the spatial ratio of the water-cooled surface in the nucleate boiling state, that is, the spatial ratio of heat transfer by solid-liquid contact (spatial average) )think of. FIG. 7 is an explanatory view of the solid-liquid contact area ratio. The solid-liquid contact (nucleate boiling) is performed at a ratio f, and a vapor film is present (film boiling) at a ratio (1-f). The solid-liquid contact area ratios f _t and f _b [−] are expressed as (2) as a function of the surface temperature of the steel sheet.
Equations 5) and (26) are given.

[0067]

[Equation 14]

As is apparent from the equations (25) and (26), the solid-liquid contact area ratio is 0 at the minimum heat flux point and 1 at the critical heat flux point.
Becomes FIG. 8 shows that T _w = 40, T _SAT = 100, T _m0 = 51,
The _graph shows changes in the solid-liquid contact area ratio when T _c0 = 134, K _m1 = 8.0, and K _c1 = 2.71. In the cooling process, the solid-liquid contact area ratio increases below the minimum heat flux point and becomes 1 at the critical heat flux point.

FIG. 9 shows that T _w = 40, T _SAT = 100, T
_m0 = 46, _Tc0 = 129, _Km1 = 8.0, _Kc1 = 2.71, _KM3 =
Steel type A ( _wSi = 0.04%) as a low Si steel and steel type B as a high Si steel when K _c3 = 130 and K _M4 = K _c4 = 0.
(W _Si = 0.81%) shows the change in the solid-liquid contact area ratio. The surface scale thickness of steel type A is about 5 to 10 μm, and the surface scale thickness of steel type B is about 20 μm. In the cooling process, the solid-liquid contact area ratio increases below the minimum heat flux point and becomes 1 at the critical heat flux point. Further, in the case of steel type B having a large scale thickness, the minimum heat flux point and the critical heat flux point are about
It has moved to the high temperature side of 100 ° C.

Heat flux q in transition boiling state_{trans, t}, Q
_{trans, b}Is the solid-liquid contact area ratio f_t, F _bUsing the following
Give by expression.

[0071]

(Equation 15)

FIG. 10 shows the change of the heat flux in the transition boiling state. In the transition boiling region of the cooling process, the heat flux changes linearly from the minimum heat flux to the critical heat flux according to the change in the solid-liquid contact area ratio. From the above heat flux, the heat transfer coefficient of water cooling can be obtained by the equations (29) and (30).

[0073]

(Equation 16)

Based on the above formula, the finite difference method, or
Calculate the steel sheet temperature using the approximate expression of the analytical solution.

FIG. 11 shows a sheet thickness of 4.04 mm and a sheet width of 149.
This is an example in which winding temperature control is performed on a 5-mm hot-rolled steel sheet by a conventional method using heat transfer equations (3) and (4). The conventional heat transfer formulas (3) and (4) are based on an empirical formula in a temperature range where the winding temperature is relatively high, that is, in a film boiling range (generally ≧ 550 ° C.). When the take-up temperature is in the transition boiling range of 440 ° C., it is difficult to use, and the difference between the calculated value of the take-up temperature and the actual value is severe. In this case, when automatic control of the winding temperature is performed, the calculated winding temperature is aimed at the target winding temperature, but since the calculated winding temperature and the actual winding temperature are significantly different, as a result, Winding temperature control accuracy is poor,
It is out of temperature for the entire length.

FIG. 12 shows a steel type B (thickness:
(2.6 to 2.9 mm) shows the correlation between the calculated temperature and the actual temperature by the conventional method using the heat transfer equations (3) and (4). As is clear from the figure, the calculated temperature deviates from the actual temperature by 100 ° C or more, and automatic control cannot be performed. Therefore, in such a case, the water injection control must be performed manually.

The conventional heat transfer equations (3) and (4) are based on an empirical equation in a temperature range where the winding temperature is relatively high, that is, in a film boiling range (generally ≧ 550 ° C.). As described above, when the winding temperature is in the transition boiling range of 450 ° C., it is difficult to use. Further, in the case of steel type B, which is a high Si steel, the minimum heat flux point moves to the high temperature side and the change from the film boiling state to the transition boiling state occurs faster than that of a general material (low Si steel). The divergence between the calculated value of the temperature and the actual value is further increased.

FIG. 13 shows a winding temperature control example 1 according to the present invention.
FIG. 14 shows a winding temperature control example 2 according to the present invention. In control example 1, a hot-rolled steel sheet having a thickness of 3.52 mm and a width of 1140 mm was controlled to a target temperature of 450 ° C., and control example 2 was a heat-rolled steel sheet having a thickness of 2.65 mm and a width of 722 mm. This is a rolled steel sheet whose winding temperature is controlled to a target temperature of 420 ° C.

The temperature error in the middle part of the control example 1 is 4 ° C., and the temperature deviation in the middle part of the control example 2 is −5 ° C., and the calculation accuracy is good. Therefore, the winding temperature is ±
It is controlled with an accuracy of 20 ° C., which indicates that the present invention is extremely effective. Please note that in implementing the above,
^{_{A t = 1.4 × 10 6,}} A b = 0.8 × 10 6, B t =
1.167 × 10 ³ , B _b = 0.667 × 10 ³ , D =
1.667 × 10 ^-3, using T _a = 25 becomes the value.

FIG. 15 shows the correlation between the calculated value of the winding temperature and the actual value according to the present invention. In the temperature range where the winding temperature is 400 to 450 ° C., even for steel type A which is a low Si steel, high S
It can be seen that there is also a calculation accuracy of ± 20 ° C. for steel type B, which is i-steel, and that it has sufficient accuracy for automatically controlling the winding temperature control.

FIG. 16 shows an example of controlling the winding temperature of steel type A according to the present invention, and FIG. 17 shows an example of controlling the winding temperature of steel type B according to the present invention. The control example of steel type A is as follows: sheet thickness 2.96 mm, sheet width 7
The winding temperature of a 98 mm hot-rolled steel sheet is controlled to a target temperature of 420 ° C., and the control example of steel type B is a sheet thickness of 2.94 m.
The winding temperature of a hot-rolled steel sheet having a width of 1008 mm and a target temperature of 430 ° C. was controlled.

In both control examples, the deviation of the calculated temperature in the middle part is small, and the calculation accuracy of the method according to the present invention is good. Therefore, the winding temperature is controlled at a temperature of ± 20 ° C. over the entire length. This indicates that the present invention is extremely effective in controlling the winding temperature of a hot-rolled steel sheet having a large surface scale such as a high Si steel. Incidentally, when the above implementations, A _t =
1.4 × 10 ⁶ , _Ab = 0.8 × 10 ⁶ , _Bt = 1.1
67 × 10 ³ , B _b = 0.667 × 10 ³ , D = 1.6
67 × 10 ⁻³ and _a value of _Ta = 25 are used.

In the above embodiment, when predicting and calculating the temperature of the steel sheet, the heat transfer equation in the transition boiling region was used for both the upper and lower surfaces, but on the lower surface of the steel sheet, the sprayed cooling water reaches the surface of the steel sheet. After that, since it does not flow down due to gravity and does not stay on the surface of the steel sheet, or it is very little, a heat transfer type in the transition boiling region only on the upper surface may be used. Use of the heat transfer equation in the transition boiling region only on the upper surface is also effective in improving the accuracy of calculating the temperature of the steel sheet, and is included in the present invention.

In the above embodiment, the heat transfer coefficient is fixed in the film boiling region.
Other than such a method, the same effect can be obtained even when the heat flux is handled at a constant value in the film boiling region, which is included in the present invention. Further, in the above embodiment,
In the nucleate boiling region, the heat flux is handled so as to be constant, but the heat flux may be reduced so as to be lower than the critical heat flux point.

The effect of using the heat transfer equation in the transition boiling region has a similar effect in cooling control in a cooling system for a thick steel plate, which is a kind of hot-rolled steel plate, and is included in the present invention. It is.

In the description of the above embodiment, high Si steel is taken up. However, even in Ni-containing steel, as the Ni content (Ni weight component) increases, the minimum heat flux point moves to the high temperature side and the cooling rate increases. The present invention is also effective for such steel types.

[0087]

As described above, the method for controlling the winding temperature of a hot-rolled steel sheet according to the present invention controls the amount of cooling water injected into the hot-rolled steel sheet on the run-out table to reduce the winding temperature of the hot-rolled steel sheet. In order to match the target temperature, when calculating the heat transfer coefficient of the water-cooled surface of the hot-rolled steel sheet at a predetermined sampling point on the run-out table, a model of the heat transfer coefficient of water cooling according to the boiling state of the water-cooled surface at the sampling point Since the heat transfer coefficient of the water-cooled surface of the hot-rolled steel sheet at this sampling point is calculated by applying the formula, the heat transfer coefficient of the water-cooled surface, which rapidly changes due to the change in the boiling state of the water-cooled surface, is accurately calculated and taken up. Temperature 40
Even in a low temperature range of 0 to 500 ° C., a steel sheet having a large steel sheet scale thickness, or Si related to the scale thickness,
Even with a steel sheet having a large weight component such as Ni, the excellent effect that the winding temperature is controlled so as to match the target temperature with high accuracy, and a steel sheet having desired mechanical properties can be manufactured. Play.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an outline of a cooling facility that executes winding temperature control on a run-out table.

FIG. 2 is a diagram showing a relationship between a steel sheet surface temperature and a heat flux in the conventional art.

FIG. 3 is a diagram showing a boiling curve.

FIG. 4 is a diagram showing cooling curves of a low Si steel and a high Si steel.

FIG. 5 is an explanatory diagram of a residual scale in a high Si steel.

FIG. 6 is a schematic diagram showing an outline of a run-out table cooling system that executes winding temperature control according to the present invention.

FIG. 7 is an explanatory diagram of a solid-liquid contact area ratio.

FIG. 8 is an explanatory diagram showing a change in a solid-liquid contact area ratio.

FIG. 9 is an explanatory diagram of a change in the solid-liquid contact area ratio of steel type A and steel type B having different scale thicknesses.

FIG. 10 is an explanatory diagram of a modeled heat flux change used in the winding temperature control method of the present invention.

FIG. 11 is an explanatory diagram of a control result by a conventional winding temperature control.

FIG. 12 is a view showing a correlation between a calculated value of a winding temperature of a high Si steel (steel type B) and an actual value by a conventional method.

FIG. 13 is an explanatory diagram of a control result of a winding temperature control example 1 according to the method of the present invention.

FIG. 14 is an explanatory diagram of a control result of winding temperature control example 2 according to the method of the present invention.

FIG. 15 is a diagram showing a correlation between calculated values and actual values of the winding temperature of low Si steel (steel type A) and high Si steel (steel type B) according to the method of the present invention.

FIG. 16 is an explanatory diagram of a control result of a winding temperature control example of steel type A according to the method of the present invention.

FIG. 17 is an explanatory diagram of a control result of a winding temperature control example of steel type B according to the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Finish rolling mill 3 Run-out table 4, 5 Cooling device 6 Winding machine 7 Thermometer 8 Thermometer 9 (winding temperature) controller 10 Thermometer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hisashi Tachibana 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka F-term in Sumitomo Metal Industries, Ltd. (reference) 4E024 BB07 FF01 GG10 4K043 AA01 BA05 CB01 EA07 FA03 FA13 GA10

Claims (6)

[Claims] When a hot-rolled steel sheet conveyed to a winder by a run-out table is water-cooled with cooling water, a heat transfer coefficient of a water-cooled surface of the hot-rolled steel sheet with respect to a predetermined sampling point on the run-out table is used. A method for controlling a winding temperature of a hot-rolled steel sheet in which a predicted value of a winding temperature of a hot-rolled steel sheet is calculated and the amount of water injected into the hot-rolled steel sheet on a run-out table is controlled so that the predicted value matches a target value. A first step of estimating whether the boiling state of the water-cooled surface of the hot-rolled steel sheet at the predetermined sampling point is a film boiling state, a nucleate boiling state, or a transition boiling state, and according to the estimated boiling state. A second step of calculating a heat transfer coefficient of the water-cooled surface with respect to the predetermined sampling point from a model equation of the heat transfer coefficient of the water-cooled sheet. 2. The method according to claim 1, wherein the first step includes calculating a temperature of a water-cooled surface of the hot-rolled steel sheet with respect to the predetermined sampling point and a subcooling degree of the cooling water. Estimating the minimum heat flux point at which the transition boiling state is reached, and the temperature of the critical heat flux point at which the transition boiling state is shifted to the nucleate boiling state, respectively, the temperature of the minimum heat flux point and the critical heat flux point, and the hot rolled steel sheet Estimating a boiling state of the water-cooled surface at the predetermined sampling point from a relationship with the temperature of the water-cooled surface of the hot-rolled steel sheet. 3. The first step includes calculating a temperature of a water-cooled surface of the hot-rolled steel sheet and a sub-cooling degree of the cooling water with respect to the predetermined sampling point, and calculating the sub-cooling degree and the scale thickness of the hot-rolled steel sheet. Accordingly, estimating the temperature of the minimum heat flux point at which the film boiling state changes to the transition boiling state, and the temperature of the critical heat flux point at which the transition boiling state changes to the nucleate boiling state, respectively, and calculating the minimum heat flux point and the critical heat flux point. Estimating the boiling state of the water-cooled surface at the predetermined sampling point from the relationship between the respective temperatures and the temperature of the water-cooled surface of the hot-rolled steel plate. Temperature control method. 4. The method according to claim 1, wherein the first step includes calculating a temperature of a water-cooled surface of the hot-rolled steel sheet and the sub-cooling degree of the cooling water with respect to the predetermined sampling point, and calculating the sub-cooling degree and the scale thickness of the hot-rolled steel sheet. Estimating the minimum heat flux point at which the film boiling state changes to the transition boiling state and the temperature of the critical heat flux point at which the transition boiling state changes to the nucleate boiling state, respectively, according to the weight component of the relevant elemental component; Estimating a boiling state of the water-cooled surface with respect to the predetermined sampling point from a relationship between respective temperatures of the flux point and the critical heat flux point and the temperature of the water-cooled surface of the hot-rolled steel sheet. The method for controlling a winding temperature of a hot-rolled steel sheet according to the above. 5. The method according to claim 1, wherein the second step includes the step of: estimating a boiling state as a film boiling state in the first step;
Calculating the heat transfer coefficient of the water-cooled surface from the degree of subcooling, the water density of the cooling water, and the conveying speed of the hot-rolled steel sheet. If the nucleate boiling state is estimated in the first step, the water-cooling Surface temperature, cooling water temperature, cooling water volume density and the heat transfer rate of the hot-rolled steel sheet is a step of calculating the heat transfer coefficient of the water-cooled surface, when the transition boiling state is estimated in the first step, The solid-liquid contact area ratio of the water-cooled surface is determined from the surface temperature of the hot-rolled steel sheet, and according to the solid-liquid contact area ratio, the heat transfer coefficient at the minimum heat flux point and the heat transfer coefficient at the critical heat flux point The method for controlling the winding temperature of a hot-rolled steel sheet according to any one of claims 2 to 4, wherein the step of calculating a value between the two values as a heat transfer coefficient of the water-cooled surface with respect to the predetermined sampling point. 6. The method according to claim 1, wherein in the first step, when the boiling state is estimated to be a film boiling state in the first step,
Calculating the heat transfer coefficient of the water-cooled surface from the subcooling degree, the water volume density of the cooling water, and the conveying speed of the hot-rolled steel sheet. If the nucleate boiling state is estimated in the first step, the water cooling of the hot-rolled steel sheet is performed. Surface temperature, cooling water temperature, cooling water volume density and the heat transfer rate of the hot-rolled steel sheet is a step of calculating the heat transfer coefficient of the water-cooled surface, when the transition boiling state is estimated in the first step, The solid-liquid contact area ratio of the water-cooled surface is determined from the surface temperature of the hot-rolled steel sheet, and according to the solid-liquid contact area ratio, the heat transfer coefficient at the minimum heat flux point and the heat transfer coefficient at the critical heat flux point are determined. 5. The method according to claim 2, further comprising calculating a weighted average value as a heat transfer coefficient of the water-cooled surface with respect to the predetermined sampling point.