JP2012082484A - Method of and device for cooling metallic strip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling method for producing a metallic strip having uniform mechanical properties in a plate width direction without generating shape defects by uniformly cooling the metallic strip.SOLUTION: The relationship of the temperature of the metallic strip with the water amount density in the boundary condition of film boiling and transition boiling is previously obtained when cooling the metallic strip using a cooling device for cooling by spraying a cooling water while controlling the water amount density of the cooling water on the surface of the metallic strip, and the water amount density is controlled so that the metallic strip is cooled in the water amount density given in response to the temperature of the metallic strip as an upper limit on the basis of the above relationship.

Description

  The present invention relates to a cooling method and a cooling device for a metal strip. Specifically, the metal strip is cooled uniformly, thereby making the mechanical properties uniform in the plate width direction without causing shape defects. The present invention relates to a cooling method and a cooling device.

  In recent years, the use of high-tensile steel plates for automobile parts has been promoted in order to improve collision safety, save energy, and protect the environment. When producing high-tensile steel sheets, ferrite and pearlite transformations are usually suppressed by containing austenite phase stabilizing elements such as Ni and Mn, and martensite and bainite structures have been secured. However, since the alloy element content of the high-tensile steel plate increases, the manufacturing cost of the high-super strength steel plate increases.

  If the steel sheet is rapidly cooled after being heated to a predetermined temperature in a continuous annealing facility, a high-tensile steel sheet having a desired strength can be manufactured even if the content of these alloy elements is reduced. Therefore, in the production of high-strength steel plates, it is advantageous that the cooling rate of primary cooling in a continuous annealing facility is high. Therefore, for primary cooling, for example, a method of directly immersing a steel plate in a water-cooled tank, called water quench, A method called water cooling is used which sprays a refrigerant obtained by mixing water and atmospheric gas in a mist form onto a steel sheet. By these methods, the steel sheet is rapidly cooled from 700 to 800 ° C. to 350 ° C. to room temperature.

  When such a rapid cooling treatment is performed on the steel sheet, uneven cooling (temperature unevenness) inevitably occurs in the sheet width direction of the steel sheet. This temperature non-uniformity is magnified by rapid cooling at the time of transition from the film boiling region where a vapor film exists between the steel plate and the refrigerant to the transition / nucleate boiling region where the steel plate and the refrigerant are in direct contact (quenching point). The temperature distribution in the plate width direction is not uniform. As a result, the mechanical property value in the plate width direction of the high-tensile steel plate is not uniform, and a shape defect occurs in the steel plate due to transformation strain in the low-temperature transformation phase.

In Patent Document 1, in the cooling of a high-tensile cold-rolled steel strip heated so as to be recrystallized in a heat treatment furnace equipped with a vertical cooling facility, the temperature of the steel strip ranges from 700 ° C. to a quench point temperature range (350 ° C. ), The water density of the mist cooling is controlled to 150 l / m ² · min or more, and after quenching at a cooling rate of 100 ° C./sec or more, the temperature of the steel strip is lowered to the quench point (350 ° C. ) To 200 ° C., a method of mist cooling with film boiling without transition boiling by controlling the cooling water density to 30 to 150 l / m ² · min is disclosed.

Patent Document 2 discloses an air-water cooling type cooling unit as a control method of an air-water cooling type cooling unit for a strip continuous heat treatment facility capable of continuously cooling to an appropriate temperature while preventing uneven temperature of a steel strip. , The mixing ratio of the gas and the cooling water injected from the injection nozzle for injecting the mixture of the cooling water and the gas toward the steel strip is 0.3 m ³ / at the later stage than the position where the temperature of the steel strip is less than 350 ° C. A method of preventing partial supercooling due to water dripping of the steel strip by setting it to 1 or more is disclosed.

  Further, Patent Document 3 discloses a method for controlling a cooling furnace for a strip continuous heat treatment facility that can stabilize the temperature of a steel strip extracted from a cooling furnace even when the temperature to be cooled is low. In this cooling unit, the steel strip is cooled with water and / or gas, and in the last cooling unit, the steel strip is cooled only with gas, so that the temperature gradient in the vicinity of the target cooling temperature becomes gentle. A method is disclosed in which the temperature of the steel strip on the outlet side of the target cooling furnace is stabilized, the quality of the steel strip is improved, and stable operation is possible.

Japanese Patent No. 4109365 Japanese Patent No. 2647274 JP 05-263148 A

  However, even if the steel strip is cooled by the method disclosed in Patent Documents 1 to 3, film boiling cannot be maintained, and the metal strip and the refrigerant may be brought into contact and rapidly cooled, thereby reliably suppressing temperature unevenness. There was something I couldn't do. In the methods disclosed in Patent Documents 1 to 3, since the steel strip is not cooled with the target water density that maintains film boiling as a target, there is a concern that the productivity of the high-tensile steel plate is lowered. Furthermore, in the methods disclosed in Patent Documents 1 to 3, there is a concern that the steel strip cannot be cooled at a target cooling temperature because the cooling rate of the steel strip is suppressed.

  That is, in the method disclosed in Patent Documents 1 to 3, transition boiling occurs at a temperature lower than 350 ° C., and transition boiling can be avoided by reducing the amount of cooling water or cooling with gas instead of water. It is based on common sense. These methods have two problems.

  The first problem is that the metal strip cannot be cooled at a target cooling temperature in order to reduce the cooling capacity of the subsequent cooling unit. To cool the metal strip at the target cooling rate, reduce the metal strip transport speed to achieve the target cooling temperature to reduce productivity, or increase the cooling capacity of the previous cooling unit. It is conceivable to supplement the cooling capacity of the subsequent cooling unit.

  The second problem is caused by not considering that transition boiling occurs in a temperature range of 350 ° C. or higher. That is, when the water density of the cooling water is high, the quench point temperature rises to 350 ° C. or higher. For this reason, as described above, when the water density of the preceding cooling unit is increased in order to increase the cooling capacity of the preceding cooling unit as a countermeasure for the first problem, transition boiling may occur.

  As described above, in the methods disclosed in Patent Documents 1 to 3, the metal strip cannot be cooled uniformly, and the resulting high-tensile steel sheet has poor shape and variations in mechanical properties in the plate width direction. In the end, the transport speed of the metal strip is lowered, and the productivity of the metal strip is lowered.

  An object of the present invention is to provide a cooling method and a cooling device for cooling a metal strip uniformly, thereby producing a metal strip with uniform mechanical properties in the plate width direction without causing a shape defect. In short, it is to provide a metal strip cooling method and a cooling device that can achieve both high productivity and elimination of temperature unevenness during cooling.

  The present invention uses a water cooling device that cools a metal strip by injecting cooling water, and controls film boiling and transition boiling when cooling the metal strip while controlling the water density of the cooling water on the surface of the metal strip. The relationship between the metal band temperature and the water density in the boundary condition is obtained in advance, and the metal band is cooled at a water density with the upper limit of the water density given according to the temperature of the metal band based on this relationship. And a metal band cooling method characterized by controlling the water density.

  From another point of view, the present invention controls the water density of the surface of the metal strip water cooling device, the temperature information output means for outputting the temperature information of the metal strip, and the cooling water supplied from the water cooling device. A cooling device for a metal strip comprising a control device, wherein the control device outputs temperature information input from the temperature information output means based on the relationship between the temperature of the metal strip and the water density in the boundary condition between film boiling and transition boiling. Accordingly, the metal band cooling device is characterized in that the water density given accordingly is set as an upper limit value, and the water density is controlled so as not to deviate from the upper limit value.

  Furthermore, from another viewpoint, the present invention is a continuous annealing furnace for a metal strip provided with the cooling device according to the present invention described above in the cooling zone of a continuous annealing furnace.

  Since the present invention predicts the temperature of the metal strip using the relationship between the water density and the quench point and performs controlled cooling with a fine water volume density, the temperature unevenness that occurs during the cooling of the metal strip, and the mechanical characteristics caused by this Unevenness and shape defects can be prevented, and this makes it possible to manufacture a metal strip having uniform mechanical properties in the width direction of the metal strip and a good shape with high productivity.

It is a graph which shows the relationship between a water density ratio and a quench point. It is a flowchart which shows the cooling control method of a steel strip. It is a graph which shows the relationship between a water quantity density and a heat transfer coefficient. It is a graph which shows the temperature conditions before and behind the cooling of invention. It is explanatory drawing which shows an example of the cooling device which concerns on this invention. It is a graph which shows the relationship between water quantity density and steel strip exit side temperature. It is a graph which shows the cooling process of the comparative example 1 (at the time of water quantity density constant). It is a graph which shows the cooling process in the comparative example 2 (cooling method of patent document 1). It is a graph which shows the cooling process of the example of this invention (when the control system of this invention is applied).

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.
When the metal strip is cooled using a boiling refrigerant such as water, it always passes through the quench point where the film boiling region moves to the transition / nucleate boiling region. The temperature at the quench point is roughly divided into a refrigerant factor and a coolant target factor.

  Refrigerant-side factors include physical properties such as specific heat, thermal conductivity, and surface tension determined by the type of refrigerant (mainly water in the steel industry), water density and collision speed determined by cooling methods such as spray cooling and laminar cooling, etc. This means a cooling form. The factor to be cooled means the physical properties such as specific heat and thermal conductivity determined by the material, and surface properties determined by roughness and surface scale adhesion.

  However, in the cooling of the metal strip, when the refrigerant to be used and the material to be cooled are determined, the factors that can be controlled among the above-mentioned factors are limited only to the cooling method, and the influence of the water density especially among the cooling methods. Therefore, the flow rate of the cooling water has been controlled even in the prior art.

However, while the temperature at the quench point is determined by the water density, a method for cooling the temperature while accurately predicting and controlling the temperature is not disclosed at present.
FIG. 1 is a graph showing an example of the results of the inventors conducting a steel cooling test and determining the relationship between the water density and the quench point (Tq = f (Q)).

  The graph of FIG. 1 shows changes in the water density and the quench point temperature when the water density is 1 when the quench point temperature is 300 ° C. The quench point temperature is approximately proportional to the water density. You can see that it increases.

  The region of Tq> f (Q) in the graph of FIG. 1 is a quench avoidance region, and in this region, film boiling can be maintained by sandwiching a water vapor layer between the cooling water and the steel material. On the other hand, the region of Tq <f (Q) in the graph of FIG. 1 is a quench generation region, and in this region, since the water density is high, the state becomes a transition boiling state in which the cooling water and the steel material are in direct contact, and film boiling Cannot be maintained.

  In the example shown in FIG. 1, the correlation equation between the water density and the quench point temperature is a linear function. However, since various factors influence as described above, the correlation equation can be a polynomial function, an exponential function, or a logarithmic function. Since it can be a function, its form cannot be limited, but in any case, there is a positive correlation between the water density and the quench point temperature.

  When the present inventors cool a metal strip by injecting cooling water, the relationship between the water density and the quench point temperature is obtained in advance, and the cooling water is maintained so that film boiling can be maintained based on the relationship. It was found that if the upper limit value of the water density is determined, the metal band can be cooled uniformly and reliably without causing transition boiling.

  Here, the temperature referred at the time of cooling is the temperature of the metal strip immediately after being cooled by the water cooling device. If reference is made to the temperature of the metal strip before or during cooling by the water cooling device, the water density is excessive in the metal strip downstream of the location where the temperature of the metal strip is measured, and there is a risk of transition to transition boiling. Because there is.

  Usually, the metal band cooling device is divided into a plurality of cooling zones in the traveling direction of the metal band, and the target temperature of the metal band after cooling by the water cooling device disposed in each cooling zone is set for each cooling zone. Therefore, if the upper limit value of the water amount density is set based on the relationship between the target temperature, the water amount density, and the quench point temperature, transition boiling does not occur.

  However, since the upper limit value of the water density set based on the target temperature is too low, the metal strip may not be cooled to the target temperature. In this case, since the temperature of the metal strip in the cooling device is higher than the target temperature, even if an upper limit value of the water amount density that is appropriately higher than the upper limit value of the water amount density based on the target temperature is set, transition to boiling is not possible. It is not considered.

The method for setting the upper limit value of the water density in this case is shown in the flowchart of FIG.
First, the upper limit value of the water amount density is set based on the target temperature of the metal strip after being cooled by the cooling device.

Next, the difference between the metal band temperature and the target temperature due to this cooling is calculated.
Next, when the temperature of the metal strip is higher than the target temperature by a certain value or more, the upper limit value of the water amount density is set higher and cooling is performed. Even if the upper limit value of the water density is reset, if the temperature of the metal strip is equal to or higher than a certain value and higher than the temperature of the quench point corresponding to the water density, the upper limit value of the water density is set higher again.

  Thereby, even if the temperature of the metal strip is not cooled to the target temperature, the metal strip can be cooled to a temperature closer to the target temperature without shifting to transition boiling. Alternatively, if the cooling capacity is insufficient even if the maximum water density is ensured within the range where transition boiling does not occur, the line speed needs to be reduced, but the reduction allowance can be minimized.

If the temperature of the metal strip is lower than the temperature of the quench point corresponding to the water density, transition boiling has occurred, so care must be taken not to enter this state.
That is, if an excessively high upper limit value of the water amount density is set, transition to boiling will occur, so the upper limit value of the water amount density needs to be set with care. Limit the amount of water density upper limit to be changed at one time, and then check the difference between the metal band temperature and the quench point temperature corresponding to the water density, and set the water density upper limit if necessary. If it repeats, the transition to transition boiling can be prevented reliably.

  The fixed value and the amount of the upper limit value of the water density to be changed at a time can be arbitrarily set. If this constant value is large, it will be difficult to reset the upper limit value of the water density, but if it is too small, for example, even in the steady part where the temperature of the metal strip is stable, it reacts to slight temperature irregularities and increases the amount of cooling water. There is a concern that it may cause a transition to transition boiling.

  If the upper limit of the water density is changed too much, there is an increased risk of transition to transition boiling, but if it is too small, the upper limit of the water density is set many times until the appropriate upper limit of the water density is reached. It takes time to set up. You may make it change the quantity of the upper limit of the water quantity density changed at once by the difference of the temperature of the quenching point corresponding to the temperature of a metal strip, and the water quantity density.

  The temperature of the metal strip may be obtained by calculation instead of actual measurement. Since it takes time to change the water density of the water cooling device and actually change the temperature of the metal strip, it takes time to control the water density based on the measured value of the metal strip temperature. If so, the time required to complete the control becomes so large that it cannot be ignored. When it is obtained by calculation, although it depends on the performance of the computer, an optimum condition can be derived almost instantaneously.

  The calculation elements of this calculation are based on the amount of water in the water cooling device, the water density on the surface of the metal strip, the temperature of the metal strip before cooling by the water cooling device, the thickness of the metal strip, the transport speed of the metal strip, and the material of the metal strip. Examples include physical properties such as thermal conductivity and specific heat, cooling water temperature, heat transfer coefficient, and the like.

  However, the physical property value based on the material may be a constant as long as there is no difference in the material of the metal strip to be processed. Further, the cooling water temperature may be a constant as long as the cooling water temperature is kept constant. Furthermore, since the heat transfer coefficient can also be calculated from the water density and the coolant temperature, this calculated value can be used instead. An example of the calculation result of the heat transfer coefficient is shown in a graph in FIG.

Further, the temperature of the metal strip may be obtained by referring to a table value created in advance. Thereby, the temperature of the metal strip can be derived more quickly than the calculation.
The table value may be the same element as the calculation, but there are elements that can be omitted as in the calculation. The table value can include at least the water amount of the water cooling device, the water amount density of the metal strip, the temperature of the metal strip before cooling by the water cooling device, and the thickness of the metal strip. Thereby, a cooling rate can be derived | led-out and the temperature of the metal strip after cooling can be derived | led-out according to a conveyance speed.

  When the upper limit value of the water density is set based on the temperature of the metal band based on the calculation or the table value, the optimum water density can be set more quickly than in the actual temperature measurement. However, in a steady state, the temperature of the metal strip may be measured and the water density may be controlled based on the measured temperature value. The calculation element used for calculation in the actual cooling device may deviate from the actual value. In such a case, if the actual temperature measurement value is used, control according to the actual state can be performed.

  From the above-described calculation or table value, the temperature of the metal strip immediately after cooling by the water cooling device in the boundary condition between film boiling and transition boiling can be derived according to the temperature of the metal strip before cooling by the water cooling device. An example of this relationship is shown graphically in FIG.

  The condition without cooling in the graph of FIG. 4 is a condition where the temperature before cooling and the temperature after cooling are equal. There is no condition below the condition of no cooling in the graph of FIG. The boundary condition in the graph of FIG. 4 is a boundary condition between film boiling and transition boiling, and is a condition of Tq = f (Q) in the graph of FIG. The boundary condition in the graph of FIG. 4 shows the temperature after cooling of the metal strip when cooling is performed with the water density of the boundary condition of film boiling and transition boiling at the temperature before cooling. Therefore, the conditions under which film boiling can be maintained and cooled are the colored portions between the boundary conditions and no cooling in the graph of FIG.

  If the conveyance speed decreases while maintaining the respective temperatures before and after cooling, the required cooling speed decreases, so the water density required for cooling becomes small, and transition boiling is difficult at low water density. Expand to. That is, if the relationship of the graph of FIG. 4 in the maximum conveyance speed of a metal strip is calculated | required and the target temperature before and behind the cooling by a water cooling apparatus will be defined in the area | region of a coloring part, cooling of the water density which causes transition boiling will be avoided be able to. In addition, when the target temperature is input, the input value of the target temperature may not be accepted unless the temperature condition of the colored portion is satisfied.

  The cooling device may include a plurality of cooling zones divided in the traveling direction of the metal strip, and the above cooling may be performed by a water cooling device arranged for each cooling zone. Thereby, since the target temperature of the metal strip after the cooling of each cooling zone can be set, it becomes possible to set a complicated cooling pattern.

  Furthermore, when the cooling device includes a plurality of divided cooling zones, the temperature of the metal strip before cooling by each cooling zone is set to the temperature of the metal strip immediately after being cooled by the water cooling device in the cooling zone one upstream of this cooling zone. You may substitute by temperature. Thereby, when the metal band cannot be cooled to the target temperature in a certain cooling zone, the cooling condition of the cooling zone downstream of this cooling zone can be adjusted by reflecting the cooling result of this cooling zone.

  The cooling method of the water cooling device of the present invention is preferably a cooling method in which fine water droplets such as air-water cooling or mist cooling are jetted onto the metal band to cool the metal band. Cooling methods that do not fall within the scope of the present invention include, for example, cooling at a large water flow density such that water is on a metal strip as seen on the upstream side of a hot rolling runout table. Such a cooling method does not correspond to the cooling method of the present invention because it passes through the quench point at a high temperature and a high temperature and cools the metal strip in the transition boiling region.

  The type of metal for which the present invention is most effective is steel. Compared to other metal materials, steel has a remarkable change in structure and characteristics depending on the cooling rate, so uniform cooling according to the present invention is most effective.

Next, a cooling device for carrying out the present invention will be described.
FIG. 5 is an explanatory view showing an example of a cooling device according to the present invention.
The cooling device (1) of the present invention includes a water cooling device (2) for cooling the metal strip (8) with water, a temperature information output means (3) for outputting temperature information of the metal strip (8), and a water cooling device (2). It comprises a control device (4) for controlling the water density on the surface of the metal strip (8).

  Further, the cooling device (1) is often configured by being divided into a plurality of cooling zones (5, 6, 7) in the line traveling direction. In the cooling zone (5, 6, 7), a device for cooling the metal strip (8) with a refrigerant is installed. In the present invention, the device for cooling the metal strip (8) whose coolant is water is referred to as a water cooling device (2). In FIG. 5, the description of the devices and information other than the water cooling device (2) in the cooling zone (5, 7) is omitted.

  A water cooling device (2) is comprised by a pump, piping, a spray header, a spray nozzle, etc. The amount of cooling water (9) injected from the water cooling device (2) to the metal strip (8) is instructed by a water amount instruction (11) output from the control device (4).

  The control device (4) determines the density of the amount of water to cool the metal strip (8) based on the temperature information (12) output from the temperature information output means (3), and the metal strip (2) at the place where the water cooling device (2) is installed. The amount of cooling water (9) of the water cooling device (2) corresponding to the conveyance speed of 8) is determined and output as a water amount instruction (11). The temperature information (12) output from the temperature information output means (3) includes, for example, a temperature record (13) before being cooled by the water device (2) of the metal strip, and after being cooled by the water device (2). It is output based on the temperature record (14), the water volume record (15) output by the controller (4), the transport speed of the metal strip (8), and the like. The control device (4) may be one control device (4) for one water cooling device (2), or one control device (4) may perform water cooling for each of the cooling zones (5, 6, 7). The structure which outputs the water quantity instruction | indication (11) according to an apparatus (2) may be sufficient. Further, the temperature information output means (3) may be one temperature information output means (3) in one cooling zone (for example, 6), or one temperature information output means (3) may have a plurality of cooling zones ( The temperature information (12) required for the control device (4) of each cooling zone (5, 6, 7) to set the water density may be output to 5, 6, 7).

  The feature of this cooling device (1) is that the control device (4) stores the relationship between the temperature of the metal strip (8) and the water amount density at the boundary condition (quenching point) between film boiling and transition boiling. Based on the temperature information (12) input from the temperature information output means (3) to the control device (4), a water density that can maintain film boiling is set as an upper limit value, and the range that does not deviate from the upper limit value of the water density By controlling the water content density, the metal strip (8) can be cooled while maintaining film boiling without shifting to transition boiling.

Since the metal strip (8) is cooled while maintaining film boiling, the metal strip (8) is uniformly cooled, and variations in characteristics of the metal strip (8) due to temperature unevenness can be prevented.
The temperature information (12) output from the temperature information output means (3) is, for example, the target temperature of the metal strip (8). In this case, in order to set the upper limit value of the water density of the cooling water (9) according to the target temperature, the cooling water (9) for cooling the metal band (8) in the metal band (8) not cooled to the target temperature. Can be prevented from transitioning to transition boiling.

  The temperature information (12) output from the temperature information output means (3) may be a measured value of the temperature of the metal strip (8), or an estimated value of the temperature of the metal strip (8) based on a calculation or a table value. Good. Thereby, in order to set the upper limit of the amount density of the cooling water (9) according to the temperature of the metal strip (8) conveyed in the cooling device (2), the cooling water (8) for cooling the metal strip (8) 9) can be prevented from transitioning to transition boiling.

  The temperature information (12) of the metal strip (8) output from the temperature information output means (3) is a measured value of the target temperature of the metal strip (8) and the temperature of the metal strip (8), or an operation or table value. It may be both the estimated value of the temperature of the metal strip (8) based. Thus, when the temperature of the metal strip (8) is higher than the target temperature of the metal strip (8) by a predetermined value or more, the water density of the cooling water (9) based on the measured value or estimated value of the temperature of the metal strip (8). By changing the set value to the upper limit value, the temperature of the metal strip (8) can be brought close to the target temperature.

  However, as a result of increasing the water density, the temperature of the metal strip (8) decreases, and the cooling water (9) for cooling the metal strip (8) is likely to shift to transition boiling. Change the setting of the upper limit value of the water density in small increments rather than at once, and check the temperature of the metal strip (8) after the change every time the setting is changed, and the cooling water (9) does not shift to transition boiling ( The difference between the temperature of the metal band (8) and the temperature of the quench point corresponding to the water density is confirmed while confirming that the temperature of the metal band does not become lower than the temperature of the quench point corresponding to the water density of the cooling water at that time) It is desirable to repeat the setting change of the upper limit value of the water amount density of the cooling water (9) until the predetermined range is reached.

  The temperature information (12) is temperature information of the metal strip (8) immediately after cooling by the water cooling device. If the temperature information of the metal strip (8) at a position before or during cooling by the water cooling device is present, the temperature of the metal strip (8) is lower than the temperature information in the metal strip (8) downstream from this position. For this reason, the water density becomes excessive, and transition boiling may occur.

  The calculation elements include the amount of water in the water-cooling device (2), the water density on the surface of the metal strip (8), the temperature of the metal strip (8) before cooling by the water-cooling device (2), and the thickness of the metal strip (8). And the transport speed of the metal strip (8), the thermal conductivity based on the material of the metal strip (8), the physical properties such as specific heat, the water temperature of the cooling water (9), the heat transfer coefficient, and the like.

  However, the physical property value based on the material may be a constant as long as there is no difference in the material of the metal strip (8) to be processed. In addition, the water temperature of the cooling water (9) may be a constant as long as it is a water cooling device (2) in which the water temperature of the cooling water (9) is kept constant. Furthermore, since a heat transfer coefficient can be calculated | required from water quantity density and the water temperature of cooling water (9), it can substitute.

  The table value may be the same element as the calculation, but there are elements that can be omitted as in the calculation. The table values include at least the water amount of the water cooling device (2) or the density of the cooling water amount to the metal strip (8), the temperature of the metal strip (8) before cooling by the water cooling device (2), and the plate thickness of the metal strip (8). And Thereby, a cooling rate can be derived | led-out and the temperature of the metal strip (8) after cooling can be derived | led-out according to the conveyance speed of a metal strip (8).

  Further, in the temperature information (12) output from the temperature information output means (3), a restriction condition such as a colored portion in the graph of FIG. 4 may be imposed on the target temperature. If the relationship between the colored portions in the graph of FIG. 4 at the maximum conveyance speed is satisfied, the cooling water (9) does not undergo transition boiling, so that the film can be cooled while boiling.

  Specifically, the constraint condition is recorded in the recording device, the temperature information output means (3) refers to the constraint condition, and the cooling water (9) that cools the metal strip (8) does not transition and boil. A value higher than the lower limit value of the temperature of the metal strip (8) immediately after cooling by 2) is output as the target value of the temperature of the metal strip (8) immediately after cooling by the water cooling device (2).

  The cooling device (1) is a cooling device (1) divided into a plurality of cooling zones (5, 6, 7) in the metal band (8) conveyance direction, and each cooling zone (5, 6, 7) The water cooling device (2) may be a cooling device (1) that performs cooling based on the cooling water amount control. Thereby, since the target temperature of the metal strip (8) of each cooling zone (5, 6, 7) can be set, it becomes possible to set a complicated cooling pattern.

  Further, when the cooling device (1) is divided into a plurality of cooling zones (5, 6, 7) in the metal band conveyance direction, the temperature of the metal band (8) before cooling by the cooling zones (5, 6, 7). May be the temperature of the metal strip (8) immediately after being cooled by the water cooling device (2) in the cooling zone one upstream of this cooling zone. Then, when the metal strip (8) cannot be cooled to the target temperature in a certain cooling zone, the cooling condition of the cooling zone downstream of this cooling zone can be adjusted to reflect the cooling result of this cooling zone.

  The cooling method of the water cooling device (2) that cools the metal strip (8) is a cooling method that cools the metal strip (8) by spraying fine water droplets such as air-water cooling or mist cooling onto the metal strip (8). As a cooling method not corresponding to this cooling method, for example, cooling of a water flow density with a large flow rate such that water is on a metal band as seen on the upstream side of a hot rolling run-out table can be mentioned. Since such a cooling method is to pass the quench point at a high temperature with a high water density and cool the metal strip in the transition boiling region, the cooling of the water cooling device (2) in the cooling device (1) of the present invention. Does not apply to the method.

  The optimum cooling object for the cooling device (1) of the present invention is a steel strip. Compared to other metal materials, steel has a remarkable change in structure and characteristics depending on the cooling rate. Therefore, uniform cooling by the cooling device of the present invention is most effective.

  The optimum installation location of the cooling device (1) of the present invention is the cooling zone of the continuous annealing furnace. Since the cooling device (1) of the present invention can uniformly cool the metal strip (8) without uneven temperature, the continuous annealing furnace in which the cooling device (1) of the present invention is installed in the cooling zone has uniform characteristics. A metal strip (8) can be produced.

As an example, the results of heat transfer calculation assuming a case where a steel strip having a plate thickness of 1.4 mm at 700 ° C. is cooled in a cooling zone having a total length of 10 m (10 zones) will be described below.
Although this embodiment describes a vertical continuous annealing furnace for thin steel sheets, the present invention can be similarly applied to equipment for operating the cooling conditions for each of the other zones to cool the steel sheets with air or mist. . Moreover, if it processes with the same installation, even if it is metal other than steel, if the correlation type according to the metal is applied, it can implement similarly.

[Comparative Example 1]
FIG. 6 is a graph showing a case where all zones are cooled to 300 ° C. with the same amount of water. The conveyance speed was changed between 80 and 150 mpm for examination. A conveyance speed of 80 mpm and a delivery side steel strip temperature of 300 ° C. are indicated by white circles in FIG. Under this condition, Tq> f (Q), so that the cooling water maintains film boiling on the steel plate. This is because if the conveying speed is 80 mpm, the cooling speed is low and the water density required for cooling is also low, so that the cooling water can be stably and uniformly cooled without transition boiling.

  On the other hand, a conveyance speed of 150 mpm and an outlet steel strip temperature of 300 ° C. are indicated by black circles in the graph of FIG. Since Tq <f (Q) under this condition, the cooling water undergoes transition boiling on the steel sheet, and film boiling cannot be maintained. When the conveyance speed is 150 mpm, the cooling rate is high and the density of water required for cooling is also high. Therefore, when all zones are cooled with the same amount of water, the cooling water undergoes transition boiling.

  In the graph of FIG. 6, when the conveyance speed is 150 mpm, the water density required for cooling is 1.6. Under these conditions, it is shown that film boiling cannot be maintained at 350 ° C. or lower where Tq = f (Q). ing. That is, when trying to pass through the plate at a high speed in order to increase productivity, the required water density increases and the cooling water cannot maintain film boiling.

  FIG. 7 shows the temperature (Tsin) of the metal strip immediately before being cooled by the cooling device in each cooling zone at the conveyance speed of 150 mpm in FIG. 5, the water density setting of each cooling zone, and the cooling device in each cooling zone. The relationship of the temperature (Tsout) of the metal strip immediately after is shown.

  In FIG. 7, the dotted line indicates the temperature of the metal band before and after cooling in one cooling zone in the boundary condition between film boiling and transition boiling. Qmax indicates the water density in the boundary condition between film boiling and transition boiling according to the temperature of the metal strip. White circles indicate the conditions of the temperature of the metal strip immediately before being cooled by the cooling device of each cooling zone and the water density of each cooling zone. In FIG. 7, the water density is constant regardless of the temperature of the metal strip. The white triangle marks indicate the conditions of the temperature of the metal strip immediately before being cooled by the cooling device in each cooling zone and the temperature of the metal strip immediately after being cooled by the cooling device in each cooling zone.

  In the ninth cooling zone, the cooling water transitioned to transition boiling. At this time, the temperature of the metal strip before and after cooling crosses the dotted line, and the water density is equal to or higher than Qmax. When the cooling water shifts from film boiling to transition boiling, the cooling proceeds rapidly, and the temperature unevenness increases with a small amount of water unevenness. If it is assumed that the water amount unevenness of the cooling nozzle used at this time is about ± 10%, a temperature unevenness of ± 22 ° C. occurs.

[Comparative Example 2]
On the other hand, as described in Patent Document 1, a case where the water density is lowered at 350 ° C. or lower is shown in a graph in FIG. 8 as in FIG. The conveyance speed is 150 mpm. Under this condition, the water density in the preceding cooling zone is increased by lowering the water density at 350 ° C. or lower and the cooling capacity is lowered, and the metal strip is finally cooled to 300 ° C. as a whole cooling device.

  In this method, since the amount of cooling water at a high temperature is large, it becomes easy to shift to transition boiling, and the cooling water shifts to transition boiling before the metal strip reaches 350 ° C. For this reason, even if the water density of the cooling water is lowered after the temperature of the metal strip becomes 350 ° C. or less, temperature unevenness has already occurred. In order to reduce the amount of cooling water when the temperature of the metal strip was 350 ° C. or less, the steel plate temperature difference was reheated, and the temperature unevenness was alleviated, but the temperature unevenness of ± 17 ° C. occurred.

[Example of the present invention]
An embodiment of the present invention is shown graphically in FIG. 9 as in FIGS. The conveyance speed and the thickness of the metal strip are 150 mpm and 1.4 mm, which are the same as those in FIGS. The maximum water density by the water cooling device (about 3) is indicated by a bold line. In order to reduce the water density in the cooling zone of the steel sheet to avoid the quench point, to reduce the steel strip temperature to the target temperature in the line, the water capacity density in the initial stage of cooling should be increased to adjust the cooling capacity of the entire line. become. As a result, since the quench point was never passed, the temperature unevenness was very small and improved to ± 6 ° C.

The following method is exemplified for realizing this.
(A) The water density Qmax in the boundary condition between film boiling and transition boiling corresponding to the temperature of the metal band in each cooling zone is set as the upper limit value of the cooling zone water density.
(B) In accordance with the metal zone temperature immediately before cooling in each cooling zone, the temperature of the metal zone immediately after cooling in each cooling zone where the cooling water does not shift to transition boiling is set to the target metal band temperature immediately after cooling in each zone. .

DESCRIPTION OF SYMBOLS 1 Cooling device 2 Water cooling device 3 Temperature information output means 4 Control devices 5, 6, 7 Cooling zone 8 Metal strip 9 Cooling water 11 Water quantity instruction 12 Temperature information 13 Temperature record (before cooling by water cooling device)
14 Temperature record (after cooling with water cooling device)
15 Water results

Claims (15)

  Using a water cooling device that cools the metal strip by injecting cooling water, the boundary condition between film boiling and transition boiling when the metal strip is cooled while controlling the water density of the cooling water on the surface of the metal strip. A relationship between the temperature of the metal band and the water density in advance is obtained in advance, and the metal band is cooled at a water volume density with an upper limit of the water density given according to the temperature of the metal band based on the relationship. In addition, the metal band cooling method is characterized by controlling the water density.   The method for cooling a metal strip according to claim 1, wherein the temperature of the metal strip is a temperature of the metal strip immediately after being cooled by the water cooling device.   The temperature of the metal strip is the target temperature of the metal strip immediately after being cooled by the water cooling device, and the control of the water density is performed by determining the upper limit value of the water density based on the target temperature. The method for cooling a metal strip according to claim 1.   When the temperature of the metal strip immediately after being cooled by the water cooling device is higher than the target temperature of the metal strip by a predetermined value or more, the temperature given according to the water density based on the relationship is subtracted from the temperature of the metal strip. The metal strip cooling method according to claim 3, wherein the upper limit value of the water density is changed to a high value and reset so that the obtained value is in a positive predetermined range.   The method for cooling a metal strip according to any one of claims 1 to 4, wherein the temperature of the metal strip is obtained by calculation.   The metal band cooling method according to any one of claims 1 to 4, wherein the temperature of the metal band is obtained by referring to a table value created in advance.   The lower limit value of the temperature of the metal strip immediately after cooling by the water cooling device in which the cooling water for cooling the metal strip according to the plate thickness of the metal strip and the temperature of the metal strip before cooling by the water cooling device does not transition boiling The method for cooling a metal strip according to any one of claims 3 to 6, wherein the target temperature is higher than the lower limit value.   The metal band cooling method according to any one of claims 1 to 7, wherein the water cooling device is disposed in each of a plurality of cooling zones divided in a traveling direction of the metal band.   Metal strip comprising a metal strip water cooling device, temperature information output means for outputting temperature information of the metal strip, and a control device for controlling the water density on the surface of the metal strip of cooling water supplied from the water cooling device The cooling device according to the present invention is based on the temperature information of the metal strip input from the temperature information output means based on the relationship between the temperature of the metal strip and the water density in the boundary condition between film boiling and transition boiling. A metal band cooling device, wherein a given water density is set as an upper limit value, and the water density is controlled so as not to deviate from the upper limit value.   The metal band cooling device according to claim 9, wherein the temperature information of the metal band is a target temperature of the metal band.   The metal band cooling device according to claim 9, wherein the temperature information of the metal band is a measured value of the temperature of the metal band, or an estimated value of the temperature of the metal band based on a calculation or a table value.   The temperature information of the metal band is a target temperature of the metal band and an estimated value of the temperature of the metal band based on a measured value or calculation or table value of the temperature of the metal band, and the temperature of the metal band is the When the metal band is higher than the target temperature by a predetermined value or more, the estimated value of the temperature of the metal band based on the measured value or calculation or table value of the metal band and the metal band corresponding to the water density based on the relationship The metal band cooling device according to claim 9, wherein the resetting for increasing the upper limit value of the water amount density is repeated until the temperature difference becomes a predetermined positive range.   The metal band cooling device according to any one of claims 9 to 12, wherein the temperature information of the metal band is temperature information of the metal band immediately after cooling by the water cooling device.   The lower limit value of the temperature of the metal strip immediately after cooling by the water cooling device in which the cooling water for cooling the metal strip according to the plate thickness of the metal strip and the temperature of the metal strip before cooling by the water cooling device does not cause transition boiling 14. The metal strip cooling device according to claim 13, further comprising a recording device that records, wherein the target temperature is higher than a lower limit value of the metal strip temperature recorded in the recording device.   The said water cooling apparatus is a cooling device of the metal strip described in any one of Claim 9 to 14 arrange | positioned in each of the some cooling zone divided | segmented in the advancing direction of the said metal strip.

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