JPS639570B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control method and device for a cooling furnace for continuous annealing equipment, and includes a gas jet cooling device that cools the strip by blowing cooling gas onto the strip, and a cooling device that cools the strip by bringing the strip into contact with a cooling roll. It is useful for use in a cooling furnace having a roll cooling device.

FIG. 1 is an example of a heat cycle of a strip (cold rolled steel sheet) that is heat treated in a continuous annealing facility. That is, the strip is heat treated in the following order: heating → soaking → slow heating → cooling → overaging → final cooling. Therefore, the continuous annealing equipment is composed of a heating furnace 1, a soaking furnace 2, a slow-heating furnace 3, a cooling furnace 4, an overaging furnace 5, and a final cooling furnace 6, as shown in Fig. 2, in accordance with the above heat cycle. has been done. The temperature of the strip 7 moving up and down in each furnace 1 to 6 is detected by a strip temperature detector 8, and the heating and cooling means of each furnace are operated to obtain a heat cycle as shown in FIG. be done.

The cooling furnace 4 shown in Fig. 2 has a cooling rate of 50~
A high cooling capacity of 100°C/sec is required. An example of a device having such a high cooling capacity is a roll cooling device as shown in FIG.

The roll cooling device will be explained with reference to FIGS. 3 and 4. First, as shown in FIG.
These cooling rolls 9a, 9
It is cooled by contact heat transfer with b, 9c, 9d, and 9e. The roll drive devices 10a, 10b are
By driving the cooling rolls 9b and 9d in the vertical direction in FIG. 3, the winding angle of the strip 7 is adjusted and the winding angle between the cooling rolls 9a to 9e and the strip 7 is adjusted. Change the cooling capacity by changing the contact length. A refrigerant flows through the cooling rolls 9a to 9e, and as shown in FIG. 4, a refrigerant 11 circulates between the heat exchanger 12 and the cooling rolls 9a to 9e. That is, the refrigerant 11 in the cooling rolls 9a to 9e is sent to the refrigerant tank 14 through the drain pipe 13, and is further sent to the refrigerant tank 14 through the pump 1.
5 to the heat exchanger 12 for cooling, and the cooled refrigerant 11 is supplied through the supply pipe 16 into the cooling rolls 9a to 9e. The temperature of the refrigerant 11 that has been cooled and passes through the supply pipe 16 is measured by a refrigerant temperature detector 17.
Based on this detection result, the refrigerant temperature controller 18 controls the opening and closing of the control valve 19 to control the heat exchanger 1.
The amount of cooling water flowing into 2 is controlled. Thereby, the temperature of the refrigerant 11 flowing into the cooling rolls 9a to 9e is set to a predetermined value.

In the above-mentioned roll cooling device, a cooling method has been proposed in which the strip temperature drop amount ΔT _S (°C) due to roll cooling is limited so as not to disturb the shape of the strip in the width direction. (Special application 1987-
No. 129069). Here, ΔTs is expressed by the following equation (1).

_ΔTS = CK ( _S − _W ) (1) However, K: Heat transfer rate between the refrigerant and the strip (Kcal/m ²
h℃) _S : Average temperature of the strip in contact with the cooling roll (℃) _W : Average temperature of the refrigerant (℃) C: Roll diameter, wrapping angle (contact length), strip speed, thickness, Constant determined by specific weight and specific heat (m ² h°C/Kcal) From the above equation (1), it can be seen that if the strip temperature can be lowered, _ΔTS will be smaller and the shape of the strip in the width direction will be better. Based on this knowledge, a cooling facility as shown in FIG. 5 has been proposed which is equipped with a gas jet device upstream of the roll cooling device in order to reduce the strip temperature. To explain the cooling equipment having such a structure in detail, a gas jet device is provided upstream of the roll cooling device, and the strip 7 is cooled by the gas jet device and then cooled by the roll cooling device. The gas jet cooling system is equipped with plenum chambers 20 facing each other with a strip 7 in between, and a blower 21.
The cooling gas pressurized in the plenum chamber 20
It is blown out at high speed from a nozzle 22 provided in the strip 7 to cool the strip 7. The pressure inside the plenum chamber 20 is detected by a plenum chamber pressure detector 23, and based on this detected value, a damper 25 is controlled by a plenum chamber pressure regulator 24, thereby controlling the flow rate of the cooling gas. On the other hand, the roll cooling device is equipped with cooling rolls 9a to 9d, and roll drive devices 10a to 10d that move the cooling rolls 9a to 9d in the left and right directions in the figure. The roll position is detected by the roll position detector 26, and based on this detected value, the roll drive devices 10a to 10d are operated by the roll position control device 27, and the positions of the cooling rolls 9a to 9d are adjusted. When the positions of the cooling rolls 9a to 9d change, the wrapping angle of the strip 7 changes, and the strip 7 and the cooling rolls 9a to 9d change in position.
The contact length with 9d changes, and the amount of cooling heat in the roll cooling device changes. Furthermore, the speed of the strip 7 is detected by a line speed detector 28, and the speed of the strip 7 is detected by a line speed detector 28.
The final cooling temperature of is detected by a strip temperature detector 29. In addition, in FIG. 5, 30a and 30b are deflector rolls.

In the cooling furnace shown in FIG. 5, the manipulated variables for controlling the final cooling temperature of the strip 7 to a predetermined value include the contact length (roll winding angle) between the strip 7 and the cooling rolls 9a to 9d in the roll cooling device and the refrigerant There are 11 temperatures and a flow rate of the cooling gas in the gas jet cooling system.

However, the response time required to adjust the contact length and refrigerant temperature in the roll cooling device is much longer than the time it takes for the strip 7 to pass through the cooling furnace (several seconds). For example, changing the roll wrap angle from 60 degrees to 120 degrees to change the contact length takes about 2 minutes, and for refrigerant temperature it takes about 10 minutes at 90% response time. Moreover, it is difficult to improve these responsiveness because of the following restrictions. That is, the cooling rolls 9a to 9d
When moving the strip, it is necessary to avoid adversely affecting the tension control system of the strip 7.
The moving speed of the cooling rolls 9a to 9d is restricted, resulting in low responsiveness. Moreover, the responsiveness of the refrigerant temperature is most controlled by the residence time in the cooling rolls 9a to 9d. Therefore, it would be possible to improve responsiveness by reducing the internal volume of the roll or increasing the refrigerant flow rate to shorten the residence time, but this is also difficult. In other words, in order to increase the contact length between the cooling roll and the strip in order to increase the cooling efficiency, the outside diameter of the roll must be increased, and the internal volume of the roll cannot be made very small.
Furthermore, the cooling flow rate is limited because the diameter of the refrigerant supply pipe provided in the roll bearing cannot be made very large.

Therefore, in a cooling furnace like the one shown in Figure 5, the response of the contact length and refrigerant temperature in the roll cooling device is poor, and when annealing conditions such as strip thickness change, the contact length (roll wrapping angle) ) or when changing the refrigerant temperature setting, there is a drawback that the predetermined heat cycle may be temporarily deviated from. When such a deviation occurs, the strip that has been cooled during that time becomes defective, resulting in a decrease in yield.

In view of the above-mentioned prior art, the present invention provides a method and method for cooling a strip to a predetermined final cooling temperature with good responsiveness even when annealing conditions change in a cooling furnace equipped with a roll cooling device and a gas jet cooling device. The purpose is to provide equipment. The gist of the present invention to achieve the above object is that in a continuous annealing equipment cooling furnace that combines a roll cooling device and a gas jet cooling device, when changing the contact length between the strip and the cooling roll in the roll cooling device or the refrigerant temperature setting, In order to compensate for these low responses, the contact length or refrigerant temperature during the transient response is detected, and based on this detected value, the cooling gas flow rate of the gas jet cooling device is controlled to compensate for the excess or deficiency caused by the above-mentioned low response. It is in.

The present invention has been made with attention to the following points. In other words, the response time of the cooling gas flow rate (in the example shown in FIG. 5, the pressure inside the plenum chamber 20) of the gas jet cooling device is
The response time is approximately 1 second, which is determined by the response of the operating end such as the rotation speed of the blower 21 and the rotation speed of the blower 21, and is sufficiently faster than the response time of the contact length and refrigerant temperature.

First, the principle of the present invention will be explained with reference to FIG. 6 while comparing it with a conventional example. In the same figure, the required amount of heat removal from the strip is Q _S target (Kcal/h),
The amount of cooling heat generated by the cooling roll of the roll cooling device
Q _R (Kcal/h), the amount of cooling heat by the cooling gas of the gas jet cooling device is Q _G (Kcal/h), and the actual amount of heat removed is Q _S real (Kcal/h). The prior art will be explained with reference to FIG. 6a. In steady state (before time t ₁ )
Q _S target = Q _S real (= Q _G + Q _R ). By the way, when the annealing conditions change at time t ₁ and the required heat removal Q _S target changes (increases in this case), the responsiveness of the roll cooling heat Q _R is poor;
Between time t ₁ and t ₂ , Q _S target≠Q _S real
This results in insufficient cooling. Therefore, in the present invention, as shown in FIG. 6b, after the time _t1 when the annealing conditions change, the cooling gas flow rate is increased to increase the gas cooling heat amount Q _G , and even after the conditions have changed, Q _S target
= Q _S real. In this case, the gas cooling heat quantity Q _G reaches its maximum at time t ₁ , then gradually decreases, and returns to a steady state (same state as before t ₁ ) after time t ₂ when the roll cooling heat quantity Q _R becomes stable again. I have to.

The present invention will be specifically explained below.

In the cooling furnace shown in FIG. 5, the basic equation of the cooling characteristic of the gas jet cooling device is expressed by the following equation (2), and the basic equation of the cooling characteristic of the roll cooling device is expressed by the following equation (3).

cγdvdT _S /dx=α(Tg- _S )×2 (2) _cγdvdS /dx=K( _W - _S ) (3) Here, _S : Strip temperature (℃) Tg: Cooling gas temperature (℃) T _W : Refrigerant temperature (°C) α: Heat transfer coefficient of cooling gas (Kcal/m ² h°C) K: Heat transfer coefficient between strip and refrigerant
(Kcal/m ² h℃) c: Strip specific heat (Kcal/Kg℃) γ: Strip specific weight (Kg/m ³ ) d: Plate thickness (m) v: Speed (m/h) x: Length (m ) By solving the above equations (2) and (3), the strip temperature can be calculated using the following equation (4),
It is expressed as (5).

T _SG = Tg (T _SI - Tg) EXP (-αL/cγdv) (4) T _SR = _W + (T _SG - _W ) EXP (-K・θ・π/180・D _R /2・N _R / cγdv)(
5) Here, T _SI : Inlet strip temperature (determined from target heat cycle) (℃) T _SG : Gas jet cooling device outlet strip temperature (℃) T _SR : Outlet strip temperature = final cooling temperature (℃) L: Gas jet cooling device cooling length (m) θ: Roll wrapping angle (corresponding to the contact length between the strip and the cooling roll) (deg) N _R : Number of cooling rolls D _R : Outside diameter of the cooling roll (m) Further, for example, the following formula (6) The heat transfer coefficient α of the cooling gas and the pressure P are related in advance by an empirical formula of the form:

P=a ₁ α ^a2 + a ₃ (6) where P: Pressure inside the plenum chamber 20 (mmH ₂ O) a ₁ , a ₂ , a ₃ : constants Therefore, the above equations (4) to (6) can be Using this method, a pressure setting value P is determined so that _the final cooling temperature _TSR of the strip 7 becomes the target value, with respect to the roll wrap angle θ or the coolant temperature TW during the transient response. If the gas jet cooling device is controlled to achieve the pressure setting value P obtained in this way, the characteristics shown in FIG. 6b will be obtained, and changes in the condition settings can be quickly followed.

In order to perform such calculations and control, a calculation device 31 is provided as shown in FIG. This calculation device 31 includes annealing conditions such as strip dimensions, line speed, and target heat cycle, as well as refrigerant temperature signals and roll position signals (contact length between the cooling roll and the strip) from the refrigerant temperature detector 17 and roll position detector 27. ) is input. Then, the arithmetic unit 31 calculates the above-mentioned equations (4) to (6),
A cooling temperature set value signal a, a roll position set value signal b, and a gas jet pressure set value signal c such that Q _S target = Q _S real are output. Of course, the signals a and b are input to the roll cooling device to control the amount of cooling heat Q _R caused by the roll cooling device, and the signal c is input to the gas jet cooling device to control the amount of cooling heat Q _G caused by this. Furthermore, if there is a change in the setting of the roll wrap angle or refrigerant temperature, a gas jet pressure setting value signal c is outputted so as to compensate for excess or insufficient cooling of the roll cooling device by the gas jet cooling device during the transient response.

FIG. 7 shows an example of a time response estimation when the calculation and setting change of the gas jet pressure set value signal c is performed periodically. Figure 7a is the set value of the roll winding angle, Figure 7b is the actual value of the roll winding angle, Figure 7c is the gas jet pressure set value, Figure 7d is the gas pressure set value, and Figure 7e is the outlet. The actual values of the strip temperatures are respectively shown, and the target value of the outlet strip temperature changes from T ₁ to T ₂ at time t ₁ . The cycle of the above calculation and setting change may be set to, for example, the 70% response time when changing the gas jet pressure setting value. Of course, this period does not need to be constant; for example, the calculation may be performed and the setting may be changed when the upper and lower limits of the final cooling temperature are exceeded. However, in Figure 7, the strip load and refrigerant temperature are constant, but the annealing condition, or in this case the target value of the final cooling temperature, changes from T ₁ to T ₂ , so the setting of the roll wrap angle is changed at the same time. This is an example of a case. For simplicity, it is assumed that the gas jet pressure changes in a ramp-like manner as the set value changes. Moreover, the dotted line in FIG. 7e is the time response when the control of the present invention is not performed, and from this characteristic it can be seen that according to the present invention, the responsiveness of the final cooling temperature is dramatically improved.

FIG. 8 shows a cooling furnace that is provided with a plenum chamber 20 that blows out cooling gas from a blower 21, facing the cooling rolls 9a to 9d, and performs roll cooling and jet cooling.The present invention can also be applied to such a cooling furnace. Needless to say, it can be applied in the same way.

As specifically explained above in conjunction with the embodiments, according to the present invention, the low responsiveness of the roll winding angle (corresponding to the contact length between the strip and the cooling roll) or the refrigerant temperature can be reduced to the high responsiveness of the cooling gas flow rate. By ensuring this, the final cooling temperature can be controlled to a predetermined value as quickly as possible, and yield can be improved.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram showing the heat cycle of a strip heat treated in continuous annealing equipment, Fig. 2 is a block diagram showing the continuous annealing equipment, Figs. 3 and 4 are block diagrams showing the roll cooling device, and Fig. The figure is a block diagram showing an example in which the present invention is applied to a cooling furnace having a roll cooling device and a gas jet cooling device, FIG. 6a is a characteristic diagram showing the characteristics of the prior art, and FIG. 6b is a characteristic diagram showing the characteristics of the present invention. FIG. 7 is a characteristic diagram showing various characteristics in the embodiment shown in FIG. 5, and FIG. 8 is a configuration diagram showing another example of the cooling furnace. In the drawings, reference numeral indicates a roll cooling device, reference numeral indicates a gas jet cooling device, numeral 4 indicates a cooling furnace, numeral 7 indicates a strip, and 9a
~9e is a cooling roll, 10a~10d is a roll drive device, 11 is a refrigerant, 12 is a heat exchanger, 17 is a refrigerant temperature detector, 18 is a refrigerant temperature controller, 19 is a control valve, 20 is a plenum chamber, and 21 is a blower ,
24 is a plenum chamber pressure regulator, 25 is a damper, 26 is a roll position detector, 27 is a roll position controller, 28 is a line speed detector, 29 is a strip temperature detector, 31 is a calculation device, and a is a cooling temperature setting value signal, b is the roll position set value signal, c
is the gas jet pressure setpoint signal.

Claims (1)

[Claims] 1. A gas jet cooling device that cools the strip by blowing cooling gas onto the strip, and a cooling roll that cools the strip by bringing the strip into contact with the outer peripheral surface of a cooling roll through which a refrigerant flows. In combination with a roll cooling device that cools the strip, the final cooling temperature of the strip can be set to a predetermined value by controlling the cooling gas flow rate in the gas jet device, the contact length between the cooling roll and the strip in the roll cooling device, or the temperature of the refrigerant. In the temperature control method for continuous annealing equipment cooling furnaces, when changing the contact length or refrigerant temperature in the roll cooling device from one set value to another, the contact length or refrigerant temperature during transient response is It is characterized by detecting the refrigerant temperature and controlling the cooling gas flow rate of the gas jet cooling device based on this detected value so as to compensate for excess or insufficient cooling of the cooling roll due to a low response of the contact length or refrigerant temperature. Temperature control method for continuous annealing equipment cooling furnace. 2. A gas jet cooling device that cools the strip by blowing cooling gas onto the strip, a gas jet control device that controls the flow rate of the cooling gas, and a strip on the outer peripheral surface of a cooling roll through which a refrigerant flows. a roll cooling device for cooling the strip by contacting the strip; a contact length control device for controlling the contact length between the cooling roll and the strip; a refrigerant temperature control device for controlling the temperature of the refrigerant; The set values of the cooling gas flow rate, contact length, and refrigerant temperature are calculated to obtain a predetermined final strip cooling temperature according to annealing conditions such as line speed and target heat cycle, and control signals based on these calculated values are applied to each of the strips. Calculate the cooling gas flow rate to obtain a predetermined final cooling temperature based on the detected value of the contact length or refrigerant temperature during a transient response when changing the setting of the contact length or the temperature of the refrigerant. 1. A temperature control device for a continuous annealing equipment cooling furnace, comprising: a calculation device that provides a control signal based on a value to the gas jet control device.