JPS60221531A - Method for controlling strip temperature of cooling furnace for continuous annealing installation - Google Patents

Abstract

PURPOSE:To prevent troubles such as defective shape, sheet breakage, etc. by setting and changing stepwise gas jet pressures in such a way that the temp. decreasing rate of the strip for each one cooling roll attains a prescribed value when strip conditions change. CONSTITUTION:The strip 1 is introduced into a cooling furnace 5 and is cooled by a gas jet cooler 8 and a roll cooler 9. When the strip conditions change, the required cooling rate of the gas jet is calculated from the detected values of the strip temp. by a temp. detector 19 and the surface temp. of the rolls 10 and the strip conditions in such a way that the temp. decreasing rate of the strip for each one cooling roll attains the prescribed value or below. The gaseous pressure is set by the calculated value. The set value is maintained till the next timing. The calculation is repeated at every specified period and the set value is changed stepwise until finally the set temp. at which the prescribed strip temp. in the outlet of the cooling furnace is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a) IJ tube temperature control method for a continuous annealing equipment cooling furnace. More specifically, the present invention relates to a method for controlling IJ tube heat retention in a continuous annealing cooling furnace equipped with a roll cooling device and a gas jet cooling device.

Generally, a cold strip (cold rolled steel plate) that has been rolled to a predetermined thickness in a cold rolling facility is heat treated in a continuous annealing facility to impart required mechanical properties. Continuous annealing equipment performs heat treatment by passing the strip continuously through the following steps: heating, soaking, slow cooling, cooling, overaging treatment, and final cooling. It consists of a soaking furnace, slow cooling furnace, cooling furnace, overaging furnace, and final cooling furnace.

FIG. 1 is a diagram showing an example of a heat cycle of a strip heat-treated in a continuous annealing facility, and FIG. 2 is a conceptual diagram showing an example of the overall configuration of the continuous annealing facility. vinegar)
IJ tube 1 is heated at a constant speed by heating furnace 2, soaking furnace 3, and slow cooling furnace 4.
, passing through the cooling furnace 5, over-aging furnace 6, and final cooling furnace 7 in an up-and-down meandering manner, heated and cooled through the heat cycle shown in FIG. 1, and subjected to the required heat treatment. will be sent.

Among the above-mentioned furnaces, the cooling furnace 5 is required to cool the strip at a high cooling rate of, for example, 50 to 1008 C/8, as shown in FIG. This cooling power method includes a method using a gas jet that blows inert gas, a method using water spray or fog,
There is also a method using a cooling roll with a refrigerant flowing inside. Among these, when using water spray or fog, the strip surface comes into contact with water and oxidizes, so field cleaning treatment such as pickling is required, and the disadvantage is that the equipment becomes complex and large-scale. When using a gas jet, the cost of inert gas and the power cost for forming the gas jet are required. Therefore, in general, the cooling power method in continuous annealing equipment cooling furnaces for cold strips involves bringing the high-temperature strip into contact with a cooling roll.
Methods of cooling by contact heat transfer have been found to be advantageous.

However, in this roll cooling method, the refrigerant flows in from one force in the axial direction of the hollow metal cooling roll and flows out from the other force, so the temperature of the refrigerant tends to be uneven in the width direction of the strip, and water When using water (usually water is used due to cost considerations), water may boil if the strip temperature is high. The temperature difference in the width direction causes defects in the product shape. This disadvantage is caused by the uneven contact between the cooling roll and the strip when the original strip plate sent to the continuous annealing equipment has a defective shape or uneven thickness in the width direction, which adds to the stress and causes the product to have an extreme shape. This results in a defect that cannot be corrected even by cold straightening in the post-process, resulting in a defective product.

In order to solve the above-mentioned problems in continuous annealing equipment cooling furnaces, the strip temperature is set by setting the cooling roll and refrigerant line PFt so as to limit the strip temperature drop per cooling roll within the required range. Attempts have been made to provide cooling methods. For example, this is disclosed in Japanese Patent Application Laid-Open No. 59-23826 (Japanese Patent Application No. 57-130457).

However, even with this method, if the strip cooling in the cooling furnace is performed using only the cooling rolls as described above, it is not possible to sufficiently reduce the amount of strip temperature drop per cooling roll, and it is difficult to reduce the temperature drop of the strip per cooling roll. This results in the disadvantage that the number of cooling rolls must be increased and the refrigerant conditions must be precisely controlled for each roll.

Therefore, we installed a gas jet device upstream of the roll cooling device that cools the cooling rolls to increase the cooling capacity of the entire cooling furnace and to reduce the amount of strip temperature drop per cooling roll. , a cooling power method using a combination of gas jets has been considered.

That is, the strip temperature drop amount ΔTs° C. due to the cooling roll in the roll cooling method is given by the following equation 11).

△'rs= CK (〒, -〒W) ・・・・・・・・・
・(1) Here, the thermal impermeability between the Knistrip and the refrigerant (
Kcal/rI? h0C)〒B: Average temperature of the strip part in contact with the cooling roll (''C)〒W: Average temperature of the refrigerant (℃) C: Wrapping angle of the strip on the roll, roll diameter, strip thickness, line A constant determined by the speed (W?h'c/Kcal) In this case, the strip temperature drop amount △Ts may also be the temperature drop amount per roll, and the numerical value will naturally be different (C will change) ) can be considered to be the amount of temperature drop in the entire roll cooling device, which includes multiple cooling rolls.

As is clear from this equation (1), the strip temperature 〒S
The lower ΔTs is, the smaller ΔTs is. Therefore, as described above, the strip temperature drop can be kept within the required range and the drawbacks of the roll cooling method can be avoided. Therefore, as mentioned above, it is considered advantageous in practice to provide a gas jet cooling device upstream of the roll cooling device to lower the strip temperature to a certain degree before starting the roll cooling.

FIG. 3 is a side sectional view showing an example of a cooling furnace conventionally used for carrying out such a combined roll cooling and gas sient cooling method.

In this cooling furnace 5, the strip 1 passes through a gas jet cooling device 8 provided immediately after the entrance of the cooling furnace 5, is blown with inert gas, and is cooled to a required temperature before entering a roll cooling device 9. . In the roll cooling device 9vc, the strip 1 is wound around and brought into contact with the algebraic roll 10, exchanges heat with the refrigerant in the cooling roll 10, is cooled to a required temperature, and is sent out of the cooling furnace 5. Ru.

Note that the reference numeral 11 in the figure is a deflector roll that deflects the strip l in a desired direction.

FIG. 4 is a cross-sectional view of the cooling roll 1O.
0 is formed in a hollow shape by a metal material, and as shown by the arrow in the figure, a refrigerant such as water is introduced from the shaft end of one force of the roll and sent out from the shaft end of the other force, and circulates inside the cooling roll 10. do. A plurality of cooling rolls 10 are arranged in a staggered manner as shown in the figure, and strips 1 are alternately wound around the outer periphery of each roll at a predetermined angle and come into contact with each other, thereby exchanging heat with the refrigerant and cooling the rolls.

Each cooling roll 10 is provided with a drive device 12 for horizontally moving the cooling roll 10, and the operation of this drive device 12 moves the cooling roll 10 forward and backward with respect to the strip 1. Adjust the angle. Note that both axial ends of the cooling roll IO are respectively connected to a refrigerant supply pipe and a refrigerant delivery pipe via rotary joints (not shown).

First, in the gas jet cooling device 8, the blower 13
The cooling gas (preferably using an inert gas such as nitrogen or a reducing gas) pressurized by the strip l
Plenum chambers 1A are provided on both sides with a passageway between them.
VC enters the plenum chamber 14, and is ejected from a number of nozzles 15 provided on opposite sides of the strip 1Vc, and is blown onto both sides of the strip 1 for cooling. The gas jet cooling amount Xi is determined by controlling the opening degree of the damper 18 using the plenum chamber pressure detector 16 and the pressure regulator 17. Note that temperature detectors 1 are provided at the inlet of the cooling furnace 5 and the outlet of the cooling furnace 5, respectively.
Reference numeral 9 is for controlling the cooling amount V+ of the cooling furnace 5 by detecting the entire strip temperature at each location, issuing a control signal, and controlling the cooling amount of the gas shed and the winding angle of the cooling roll 0, etc. . By controlling the amount of jet cooling and the amount of roll cooling in this manner, it is possible to provide an optimal heat cycle to strips of various steel strips and sheet sizes. In other words, when stripping conditions change, for example when the thickness of the leading and trailing strips changes, these controls (materials)
All you have to do is implement the υ control 8 by means.

By the way, the strip in continuous annealing equipment is usually 20
Since the sheet is threaded at a high speed of about 0 to 400 m1m, the time in the cooling furnace 5vc is only about a few seconds. On the other hand, the control response of the winding angle of the cooling roll is extremely slow due to its mechanism and the heat capacity of the roll shell.
It takes more than 120 to change from 0 to 120.

This means that the roll outer surface temperature cannot respond quickly to changing conditions. -The responsiveness of force and gas jet pressure is much more sensitive than this, and a normal change takes about 10 seconds.

Therefore, in the heat treatment of steel types where the plate thickness is relatively thick and statically does not pose a particular problem with the drop in temperature of the string due to roll cooling, the roll winding angle is fixed and the gas jet pressure is It is advantageous to be able to control the process with only one hand, and a good yield can be obtained. However, if the stripping conditions change and, for example, the thickness of the trailing strip becomes thinner than the thickness of the leading strip, it will not be possible to respond immediately to this change due to the delay in the response of the cooling roll as described above, and as will be explained later. In other words, the strip temperature sieve "F lid ΔT8 becomes large, leading to a defective strip shape.

Figure 5 is an example of a diagram showing appropriate conditions for plate thickness whose static characteristics have been calculated in advance for the operation of a cooling furnace equipped with a roll cooling device and a gas jet cooling device as described above.
Figure (a) shows an example of a gas jet precent curve with respect to plate thickness.

In order to simplify the explanation, other stations) IJ Tsubujo Offshore,
For example, the line speed, plate width, target heat cycle, etc. are kept constant. The figure (b) shows the relationship between the plate thickness and the strip temperature drop amount ΔTs, and the broken line in the figure shows the maximum permissible limit value that does not cause defects in the strip shape. Moreover, the same figure (c) shows the relationship between the plate thickness and the same temperature [TR] of the outer surface that is in contact with the strip of the cooling roll.

Figure 6 shows that the conventional operation control method as described above is applied based on the Briscent curve in Figure 5 above, and the strip thickness is 1.0.
It is a diagram showing changes in cooling furnace conditions when changing from 0.8 to 0.8. In this case, the preceding strip (thickness 1
．． Immediately after the welding point between the following strip (011W) and the trailing strip (plate thickness 0.8) passes through the cooling furnace, the gas jet pressure setting value is set based on Fig. 5(a) when the plate thickness is 1.0-. Setting value P
Set value P when plate thickness is 0.81EIB from 'i1. 2
It changes the

Figure 5(b) According to K, statically △Ts<△TSCR(
However, according to the bottom curve in Figure 6, △T
It has been shown that s temporarily exceeds ΔT SCR, which may lead to deterioration of the strip shape. This is because, as mentioned above, the strip temperature TsG at the inlet of the roll cooling device (i.e., the exit of the gas jet cooling device) changes quickly in response to the quick response of the gas jet pressure, whereas the change in the cooling roll surface temperature TR changes rapidly. This is due to the large delay due to the slow response of the cooling roll. In this case, due to the heat capacity of the roll shell, the strip temperature drop ΔT is transiently expressed as the average refrigerant temperature 〒W in equation (1) above and the cooling roll surface temperature [as shown below using TR]. It is appropriate to use the formula (2).

△Ts = CK' (〒5-TR) ・・・・・・・・・
...(2) Here, the reciprocal of the thermal resistance between the K'ni strip and the cooling roll surface (K cal /rr? h'C")
In view of the above circumstances, the present invention has been made in order to eliminate the drawbacks that occur when the stripping conditions change in the conventional cooling furnace operation control force method as described above.
Continuous annealing equipment cooling furnace using a gas jet pressure setting value changing method that can obtain the required final cooling temperature without the strip temperature drop due to roll cooling exceeding the allowable value of the strip shape stability limit. It provides a control force method.

That is, the method of the present invention includes a roll cooling device that cools the strip by bringing the strip into contact with the outer circumferential surface of a cooling roll through which a refrigerant is circulated, as described above, and a nozzle that cools both sides of the strip before the roll cooling device. When cooling the strip in a continuous annealing equipment cooling furnace equipped with a gas shed cooling device that cools the strip by blowing gas, the strip temperature at the inlet and outlet of the cooling furnace and the surface temperature of the cooling roll are detected. If the conditions change, calculate the required cooling rate at the V gas shed so that the strip temperature drop for one cooling roll is below the brittle value based on the detected value and the strip conditions, and use this calculated value to adjust the gas shed pressure. is set, this set value is held until the next calculation timing, and the above calculation is repeated at regular intervals to change the setting in stages. - The above objective can be achieved by reaching the shet pressure setting (vi).

Hereinafter, a method of performing the above-mentioned calculations at regular intervals will be explained. The following description will be made on the assumption that the thickness of the trailing strip is thinner than the thickness of the preceding strip, which is a particular problem among strip conditions as described above.

First, roll cooling equipment personnel loss) IJ tube temperature tolerance T
sci is calculated as follows.

After the welding point between the leading strip and the trailing strip passes through the cooling furnace, the strip temperature drop v:ki△Tsi by the cooling roll at a certain calculation typing (one point in time) is calculated by the following formula (
3).

△'r8i=c2' (TB1-Tui)...
......(3) Here, C2: C (formula (11% formula %)) at the current strip offshore TR1: Detected value of cooling roll surface temperature ('C) TB i
: Average temperature of the strip part in contact with the cooling roll ('C) In the case of normal plate thickness changes, △Tsi<△TSCR unless the gas jet pressure setting is changed before and after passing the welding point.
It is. Therefore, △TSCR=C2' (Tel T
R1) --...(41) The strip temperature can be raised to Td that satisfies the following.Therefore, the maximum eave capacity value TscY of the loss strip temperature exiting the roll cooling furnace at that timing is calculated using the following formula ( 5) You can make a request.

T8Gi = Tst + △T sCR/ 2 --- (
51 Next, the heat transfer coefficient αi of the gas jet is calculated as follows.

The required cooling IQi by the gas jet is calculated using the following formula (1)% where: A Nislip heat transfer area (rr?) Ws: Production volume (rim/h) Cs Nislip specific heat (Kcal /Kg”C; )T
Bli Ni Gas Diend device input device Trostrip temperature detection value) α? Gas jet heat transfer coefficient (Kcal/m'h℃)
TP: Cooling gas temperature (°C) From this equation (6), the gas jet heat transfer plan αi is obtained.

Incidentally, the gas discharge pressure setting value PG1 is expressed as follows:
f is done. That is, the gas jet pressure setting value PGi is the gas jet heat transfer straw α? This is determined by my own formula (7), which I obtained in advance through experimentation.

p. ,=4(.C)b+.

1, ...... (7) Here, a, b, cig) are constants obtained by V experiment, etc.

According to the above calculation, assuming △Ts≦△TSCR tray, repeating the calculation every one foot period, the roll cooling device and loss trimming device TsG will rise.'') VC, change the gas shet pressure set value Pa in stages and change the VC setting. The gas discharge pressure setting value P.i at calculation typing l is held until the next calculation timing i+1.The surface temperature TR of the cooling roll 1 gradually increases (TR□ in Fig. 5(C)).
(from TR□) to a steady value VrL, and the loss strip temperature coming out of the cooling furnace becomes a constant value of 91. Thereafter, a predetermined heat cycle is performed for the new thickness of the strip.

The period of the above calculation may be set to, for example, one to three times the response time to a constant change in the gas jet pressure control system.

Fig. 7 is a side sectional view showing an example of a cooling furnace in which the method of the present invention is applied, corresponding to Fig. 3 above. A roll surface temperature detector 20 and a calculator 21 for performing the above-mentioned calculations are added. P
G is the gas jet pressure setpoint signal.

FIG. 8 is a diagram illustrating the response of the cooling furnace strips when the plate thickness changes when the method of the present invention is carried out.

From this figure, it can be seen that according to the method of the present invention, the amount of strip temperature drop △Ts due to roll cooling does not exceed the allowable limit value △T'sep for strip shape stability, and the strip temperature decreases in a stepwise manner according to the cooling roll surface temperature. It can be seen that the strip temperature is controlled by the gas jet pressure set value that is changed, and a predetermined cooling furnace output loss strip configuration is finally obtained.

As is clear from the above explanation, according to the method of the present invention, as the strip conditions change, the temperature of one strip thermometer due to roll cooling temporarily exceeds the allowable value, resulting in poor shape of the string and even breakage of the strip. 5X will cause a draffle.
! It is possible to perform stable operation of continuous annealing equipment without any problems.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of a heat cycle in continuous annealing equipment, Fig. 2 is a conceptual diagram showing an example of the overall configuration of continuous annealing equipment, and Fig. 3 is a side sectional view showing an example of a conventional cooling furnace. Fourth
Figure 5 is a cross-sectional view showing an example of a cooling roll, Figure 5 is a line diagram showing the appropriate force for notes on plate thickness in a cooling furnace, and Figure 6 1 is an example of the response when plate thickness changes using the conventional method. A line diagram showing,
FIG. 7 is a side cross-sectional view showing one embodiment of a cooling furnace to which the method of the present invention is applied, and FIG. 8 is a diagram showing an example of the response when the plate thickness changes according to the method of the present invention. In the drawings, l is a string, 5 is a cooling furnace, 8 is a gas net cooling device, 9 is a roll cooling device, and io is a cooling roll. Patent Applicant Mitsubishi Heavy Industries, Ltd. Kawasaki Steel Corporation Sub-Agent Patent Attorney Former Ishibe Shibu (and 1 other person) Figure 1, Figure 2, Figure 3! Figure 6 □Saichi

Claims (1)

[Claims] A roll cooling device cools the strip by bringing the strip into contact with the outer circumferential surface of a cooling roll through which a refrigerant is circulated, and a cooling gas is sprayed from a nozzle on both sides of the strip at the front stage of the roll cooling device to cool the strip. In a strip temperature control method for a continuous annealing equipment cooling furnace equipped with a gas jet cooling device, the strip temperature at the inlet and outlet of the cooling furnace and the surface temperature of the cooling roll are detected, and when the strip conditions change, the detected value and the strip temperature are One cooling roll per one condition,
Calculate the required amount of cooling with the gas jet so that the amount of lip temperature drop is below a predetermined value, set the gas jet pressure based on this calculated value, hold this set value until the next calculation timing, and set it at regular intervals. Stretching of a continuous annealing equipment cooling furnace, characterized in that the above calculations are repeated and the settings are changed stepwise for each time the set value is finally reached to obtain a predetermined cooling furnace exit loss strip temperature. , temperature control method.