JPH06108166A - Method for controlling cooling - Google Patents

Abstract

PURPOSE:To restrain the strip temp. from exceeding the allowance range in a cooling zone and to improve the quality of a product by securing the stable cooling capacity operation while effectively utilizing a CC zone having a small cooling capacity in spite of various kind conditions of a material to be cooled. CONSTITUTION:In the cooling control method for cooling the material 2 to be cooled in the rapid cooling (GJC) zone using cooling gas blow 11 and the slow cooling (CC) zone using a cooling tube 12, when the cooling capacity of the material to be cooled passing through the slow cooling zone is lower than the max. furnace hearth load in the preset slow cooling zone, the strip temp. on the outlet side of the rapid cooling zone is controlled basing on the relation being almost proportional to the CC zone furnace hearth load. When the cooling capacity of the material to be cooled passing through the slow cooling zone according to the variation, etc., of various kind conditions of the material to be cooled exceeds the max. furnace hearth load, the strip temp. on the outlet side of the rapid cooling zone is obtd. basing on the preset max. furnace hearth load to control the strip temp. on the outlet side of the rapid cooling zone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling control method used for various strip transfer lines including a continuous hot-dip galvanizing line, and particularly for transferring a cooling zone composed of a rapid cooling zone and a slow cooling zone. The present invention relates to a cooling control method having a function of appropriately controlling the temperature of a material to be cooled while taking into consideration the cooling capacity of the slow cooling zone in response to changes in the plate thickness of the material to be cooled, transfer speed, and the like.

[0002]

2. Description of the Related Art Conventionally, in cooling a strip in a continuous transfer line for continuously transferring the strip, a rapid cooling zone using a cooling gas blow {hereinafter, referred to as GJC (Control Jet)
The strip can be cooled to a predetermined temperature by passing it through a cooling zone composed of a "Col-oling) zone" and a slow cooling zone (hereinafter referred to as "CC (Control Cooling) zone") using a cooling tube. Has been done.

By the way, in such a continuous transfer line, the cooling capacity is different between the GJC band and the CC band from the viewpoints of their applications and functions. For example, in the case of the GJC band, the cooling capacity is large, but temperature unevenness easily occurs in the width direction of the strip. On the other hand, in the case of the CC band, although the cooling capacity is small, a uniform temperature can be obtained in the width direction and the length direction of the strip.

Therefore, in this type of strip transfer line, in order to satisfy the cooling conditions of the steel types and to perform uniform cooling while considering the cooling capacity of each cooling zone, a GJC zone is provided on the upstream side of the line. A cooling control method is adopted in which a strip is installed and the strip is cooled significantly, while a CC band is installed on the downstream side of the line for uniform cooling. As one of them, for example, a cooling control method for a continuous melting plating line is proposed, and a cooling furnace as shown in FIG. 1 described later is used.

In the cooling furnace of this plating line, the strip passes through the GJC band which constitutes the cooling furnace. At this time, the cooling gas is applied from the cooling gas blow to the strip for forced convection transfer cooling, and the furnace wall and the strip. The radiant heat transfer cooling is performed so that the cooling temperature difference between the strip on the inlet side and the strip on the outlet side is about 200 ° C. Subsequently, the strip moves from the GJC zone to the CC zone which constitutes the cooling furnace. Here, the temperature difference between the strip on the inlet side and the strip on the outlet side is GJC because the heat transfer cooling is mainly performed between the furnace wall and the strip. Cooling is performed to about 100 ° C., which generally has a smaller cooling capacity than the strip.

[0006]

However, in the CC band as described above, since radiation heat transfer cooling is used, there is a limit to the amount of heat that can be cooled by the furnace temperature lower limit value. This is a constraint on the amount of cooling heat per unit width (this is called the hearth load). Therefore, the upper limit of the amount of cooling heat to be removed in the CC band is determined by the hearth load constraint. On the other hand, in the GJC band, the target plate temperature on the GJC band exit side is fixed. As a result, the following problems arise in controlling the cooling temperature of the strip in the continuous transfer line.

That is, when the strip size (eg, plate thickness, plate width, etc.) or the transfer speed is changed, the CC
Since there is a restriction on the amount of cooling heat of the zone, so-called plate temperature deviation occurs, which is outside the required cooling temperature on the CC zone exit side. Therefore, in order to avoid this plate temperature deviation, the operator erroneously thinks about the strip transfer speed and sometimes the GJC.
Although it is artificially operated to change the target plate temperature on the take-out side, efficiency (ton / hr) down is unavoidable, and the plate temperature is also off due to an operation error, which adversely affects the product quality. There is a problem giving.

The present invention has been made in view of the above-mentioned circumstances, and it is possible to change various conditions of the material to be cooled by controlling the plate temperature on the outlet side of the GJC band while considering the cooling heat quantity characteristic of the CC band. It is an object of the present invention to provide a cooling control method that enables optimum cooling heat quantity operation in the CC band, suppresses plate temperature deviation in the cooling band, and greatly contributes to product quality improvement.

[0009]

In order to solve the above problems, the invention according to claim 1 is a cooling system for cooling a material to be cooled by a GJC band using a cooling gas blow and a CC band using a cooling tube. In the control method, a cooling control method for determining the outlet plate temperature of the GJC band from the cooling heat quantity characteristic of the CC band and at least the transfer speed, density, specific heat and the like of the material to be cooled, and controlling the outlet plate temperature of the GJC band. is there.

Next, the invention corresponding to claim 2 is a GJC band using a cooling gas blow and a CC using a cooling tube.
In the cooling control method of cooling the cooled material by the zone, the maximum hearth load of the CC zone is set in advance, when the cooling heat amount of the cooled material passing through the CC zone is less than or equal to the maximum hearth load, the CC zone The GJ is almost proportional to the hearth load.
When the outlet plate temperature of the C zone is controlled and the cooling heat amount of the cooled material passing through the CC zone exceeds the maximum hearth load due to changes in various conditions of the cooled material, etc., it is preset. This is a cooling control method in which the outlet plate temperature of the GJC band is obtained based on the maximum hearth load, and the outlet plate temperature of the GJC band is controlled.

[0011]

Therefore, according to the invention of claim 1, by taking the measures as described above, the G heat quantity characteristic of the CC band having a small cooling capacity and the change of various conditions of the material to be cooled are taken into consideration.
Since the outlet plate temperature of the JC band is determined, it is possible to cover the insufficient cooling of the CC band and suppress the plate temperature deviation.

Next, the invention according to claim 2 is, when the cooling heat amount of the material to be cooled passing through the CC zone is less than the maximum hearth load, the outlet plate of the GJC zone so as to be proportional to the CC zone hearth load. The temperature is controlled, and C changes with changes in various conditions of the material to be cooled.
When the amount of cooling heat of the material to be cooled that passes through the C zone exceeds the maximum hearth load, the amount of heat that cannot be removed in the CC zone is GJC.
By lowering the temperature of the strip output side plate, stable operation of the CC band having a small cooling capacity can be performed in an optimal state, so that the plate temperature deviation can be avoided in advance and a high quality cooled material can be obtained. . INDUSTRIAL APPLICABILITY The present invention is particularly effective in the case of controlling the cooling zone outlet side plate temperature with high accuracy, as in a molten zinc plating line.

[0013]

EXAMPLE An example of the cooling control method according to the present invention will be described below.

For the cooling zone in which the GJC zone and the CC zone are combined, it is necessary to perform cooling control while paying sufficient attention to the cooling heat quantity characteristic of the CC zone having a small cooling capacity. Therefore, the present invention is implemented based on the following control method and knowledge.

(1) First, regarding the control method, in order to effectively operate the CC band having a small cooling capacity, the control method is divided into two parts based on the cooling heat quantity characteristic of the CC band. One of them is C
It is effective utilization up to the upper limit of cooling heat (maximum hearth load) of the C band, and the other one is to take measures when the upper limit of the cooling heat amount of the CC band, that is, the maximum hearth load is exceeded. I need to think.

Therefore, in the GJC zone, the GJC zone outlet side plate temperature is set so as to be proportional to the CC zone hearth load up to the CC zone cooling heat amount upper limit. On the other hand, when the maximum hearth load of the CC zone is exceeded, the cooling heat amount cannot be removed in the CC zone. At this time, therefore, in the GJC zone, the plate temperature on the outlet side of the GJC zone is changed by the cooling heat amount that cannot be removed in the CC zone. By lowering it, a control method that covers the cooling heat amount is implemented.

(2) Next, it is necessary to change the target plate temperature on the GJC banding side in order to set the plate temperature on the CC banding side to a constant target value when the size of the strip or the transfer speed is changed. At this time, G which is in the process of cooling the cooling furnace
The issue is whether the JC strip outlet side plate temperature can be operated within a wide allowable temperature range.

Incidentally, for example, in a hot dip galvanizing line, the plate temperature on the GJC band side is about ± 40 ° C, while the plate temperature on the CC band outlet side is about ± 10 ° C. Has a temperature range. Therefore, in the strip transfer line, even if the GJC zone and the CC zone are regarded as one cooling furnace and the plate temperature on the GJC zone exit side is controlled, no problem occurs in the material of the strip.

Therefore, the method of the present invention implements the cooling control method as described in the above (1) based on the knowledge of the above (2). At this time, the plate temperature on the GJC zone exit side is the cooling heat quantity of the CC zone. In addition to the characteristics, it is determined from the following relational expressions including strip transfer speed, density, specific heat, etc.

That is, in determining the strip temperature on the GJC strip exit side, the cooling heat quantity Q [k cal / h] of the strip passing through the CC strip is determined from the strip thickness, strip width and transfer speed.
r], and if the cooling heat quantity Q of this CC band is equal to or less than the maximum hearth load Qmax [k cal / hr · m], the plate will have a cooling heat quantity almost proportional to the cooling capacity (ton / hr) of the CC band. Set the temperature. That is, when the amount of cooling heat per unit width Q / W [kcal / hr · m] ≦ hearth load Qmax [kcal / hr · m], T _GJ = T _CC + (K / C _p ) ... ( 1) Determine the GJC strip output side plate temperature T _GJ (° C) from the following relational expression.

However, T _CC (° C): CC band target plate temperature,
K: constant (proportional constant between cooling heat quantity and ton / hr), ρ
_Fe [kg / m ³ ]: Density of the strip, C _p [k cal / kg
• k]: Specific heat of the strip. On the other hand, when the cooling heat quantity Q in the CC band exceeds the maximum hearth load Qmax [kcal / hr · m], the cooling heat quantity is set to Qmax and the plate temperature on the GJC band exit side is determined. That is, when the cooling heat quantity per unit width Q / W [kcal / hr · m]> hearth load Qmax [kcal / hr · m], T _GJ = T _CC + {Qmax / (t · v · ρ _Fe · C _p )} (2) Determine the plate temperature T _GJ (° C) on the GJC banding side from the following relational expression. However, Qmax [kcal / hr · m]: hearth load,
t [m]: plate thickness, v [m 2 / hr]: transfer speed.

Therefore, by adopting the cooling control method as described above, when the cooling heat quantity of the strip passing through the CC zone is less than the maximum hearth load, the GJC zone exit side is proportional to the CC zone hearth load. The upper limit of the cooling heat quantity to be removed in the CC zone when the cooling heat quantity of the strip in the CC zone exceeds the maximum hearth load due to changes in conditions such as strip size and transfer speed, etc. That is, since the maximum hearth load is set and the GJC zone outlet side plate temperature is set, stable operation can be performed under optimal conditions even in the CC zone with a small cooling capacity. In addition, the temperature in the strip width direction can be made uniform and a high quality strip can be obtained.

Next, an apparatus to which the above cooling control method is applied will be described with reference to FIGS. 1 and 2. 1 is a diagram showing the configuration of a cooling furnace used in a molten zinc plating line and other continuous strip transfer lines, and FIG. 2 is a diagram showing the configuration of a cooling temperature control device including the cooling furnace.

That is, such a cooling furnace has a GJC band and a C
The strips 2 are arranged so as to be connected to the C band in an appropriate form, and the guide rolls 1, ... Are arranged in the GJC band and the CC band with a required positional relationship, so that the strip 2 guides the guide rolls 1 ,. A transfer line is formed so as to form a meandering shape. Then, thermometers 3 and 4 are installed on the respective output sides of the GJC band and the CC band. Reference numeral 5 is a furnace shell representing the form of the furnace.

Next, the cooling temperature control device including the cooling furnace is
As shown in FIG. 2, gas blowers 11 and 11 are installed on the inlet side and the outlet side of the GJC band, respectively, and the cooling gas mediums sent from the outside through the pressure control valves 21 and 21 are supplied to the gas blowers 11 and 11, respectively. With strip 2
On the other hand, cooling tubes 12, 12 are arranged on the inlet side and the outlet side of the CC band side, respectively.
Similarly, the cooling mediums sent from the outside via the flow rate control valves 31 and 31, respectively, are passed through the cooling tubes 12 to perform radiation transfer cooling.

The cooling temperature control device 20 has a combination configuration of cascade control + feedforward control,
Specifically, the strip size and the transfer velocity, which are disturbance factors, are taken in, and other necessary parameters and constants are used to perform the calculations of the above formulas (1) and (2) and other required calculations to determine the GJC band and The target plate temperature calculation unit 30 using a process computer or the like for obtaining the target plate temperature in the CC band, the GJC band side target plate temperature calculated by the target plate temperature calculation unit 30 and the GJC band output side thermometer 3 are detected. A temperature controller 22 for obtaining a GJC strip output side target pressure by performing an adjustment calculation such as PI or PID based on a deviation from the GJC strip output side detected temperature, and a CC band side target similarly obtained by the target plate temperature calculation unit 30. Plate temperature and CC
There is provided a flow rate controller 32 for obtaining a CC output side target flow rate by performing an adjustment calculation such as PI or PID based on the deviation from the CC output side detected temperature detected by the output side thermometer 4.

Further, this cooling temperature control device is required based on the target pressure and the discharge pressures from the pressure detectors 23 and 24 provided in the cooling gas medium supply passages on the GJC zone inlet side and the outlet side. Pressure regulators 25 and 26 that output pressure operation signals, and flow rate detectors 33 and 34 that are provided in the target medium flow rate and the cooling medium supply path on the CC band inlet side and outlet side
Flow rate controllers 35 and 36 for outputting a required flow rate operation signal based on the detected flow rate from the pressure regulators 35 and 36, and the pressure control valves 21 and 21 are operated based on the pressure operation signals from the pressure regulators 35 and 36. Operate, while the flow controller 35,36
The flow rate control valves 31 and 31 are operated based on the flow rate control signal from.

Therefore, the conventional ones to which the cooling control method and the cooling temperature control device of the present invention as described above are not applied,
As shown in FIG. 3 (a), when the strip transport speed increases at time t1, the GJC band target plate temperature and the actual temperature are the same, even though the cooling heat amount needs to be increased. Then, the upper limit of the cooling capacity is exceeded and cooling cannot be performed. Therefore, the actual temperature rises on the CC band exit side, and the plate temperature deviation occurs.

On the other hand, according to the cooling control method and the cooling temperature control device of the present invention, when the upper limit of the cooling capacity of the CC band is exceeded due to the increase of the transfer speed of the strip as shown in FIG. 3 (b), By lowering the target plate temperature on the GJC outlet side, the CC strip outlet side plate temperature can be made to follow the target plate temperature, and the strip quality is not affected by changing the transfer speed. It goes without saying that this applies not only to the transfer speed of the strip, but also to changes in the strip size and other disturbance factors.

Next, FIG. 4 shows the strip transfer speed 85r.
pm is constant, and the strip size is as follows: a plate thickness 0.66 x plate width 1280 mm, roll plate thickness 0.81 x plate width 1
It is a figure which shows the relationship of GJC zone target board temperature and actual temperature, and CC zone target board temperature and actual temperature when it changes in the order of 213 mm, Har plate thickness 0.71 x board width 1130 mm.

That is, in this cooling control, the CC band target plate temperature is changed each time the strip size is changed, and the optimum GJ is changed each time the CC band target plate temperature is changed.
The purpose is to set the C-band target plate temperature.
It can be seen that the target plate temperature in the C band follows well,
Optimal operation can be secured even in the CC band having a small cooling capacity. The present invention can be variously modified and implemented without departing from the scope of the invention.

[0032]

As described above, according to the present invention, C
By controlling the temperature of the cooled material on the GJC strip exit side in accordance with the restriction of the cooling heat quantity of the C zone, while effectively changing the various conditions of the cooled material, the CC zone with a small cooling capacity can be effectively used. It is possible to provide a cooling control method which can ensure stable cooling heat quantity operation, can suppress the plate temperature deviation in the cooling zone, and can greatly contribute to the improvement of product quality.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a cooling furnace to which a cooling control method according to the present invention is applied.

FIG. 2 is a configuration diagram of a cooling temperature control device including a cooling furnace to which the method of the present invention is applied.

FIG. 3 is a diagram for explaining a plate temperature state depending on whether or not the method of the present invention is applied.

[Fig. 4] CC band and GJ accompanying strip size change
The figure explaining the change state of the target board temperature and actual value of C zone.

[Explanation of symbols]

2 ... Strip (material to be cooled), 3, 4 ... Thermometer, 11 ...
Guy blow, 12 ... Cooling tube, 20 ... Cooling temperature control device, 22 ... Temperature controller, 23, 24 ... Pressure detector, 2
5, 26 ... Pressure controller, 30 ... Target plate temperature calculation unit, 32
... Temperature controller, 33,34 ... Flow rate detector, 35,36 ...
Flow controller.

Claims (2)

[Claims] 1. A cooling control method for cooling a material to be cooled by a rapid cooling zone using a cooling gas blow and a slow cooling zone using a cooling tube, wherein the cooling heat quantity characteristic of the slow cooling zone and at least the transfer of the material to be cooled. A cooling control method, characterized in that the outlet plate temperature of the rapid cooling zone is obtained from the speed, density, specific heat, etc., and the outlet plate temperature of the rapid cooling zone is controlled. 2. A cooling control method for cooling a material to be cooled by a rapid cooling zone using a cooling gas blow and an annealing zone using a cooling tube, wherein a maximum hearth load of the annealing zone is set in advance, When the cooling heat amount of the cooled material passing through the cold zone is less than or equal to the maximum hearth load, the outlet plate temperature of the rapid cooling zone is controlled in a relationship substantially proportional to the CC zone hearth load, while When the cooling heat amount of the cooled material passing through the slow cooling zone exceeds the maximum hearth load due to changes in various conditions, etc., the output of the rapid cooling zone is set based on the preset maximum hearth load. A cooling control method, wherein the side plate temperature is obtained and the outlet plate temperature of the rapid cooling zone is controlled.