JPH1143758A - Cooling method in alloying treatment process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a metallic material excellent in surface appearance uniformity by selecting whether it is suitable as a means between mist cooling and air cooling in accordance with the size of cooling loads discriminated by the heat transfer coefficient required for cooling and cooling a metallic material applied with hot-dip metal plating. SOLUTION: The sheet temp. of a steel sheet 10 applied with plating is measured by a sheet temp. gauge 40 at the outlet side of a heat holding zone 34, and from the line rate at this time, the sheet thickness, the outlet side objective sheet temp. in a cooling zone 36 and a parameter of a host computer, the heat transfer coefficient is computed. A controller 50 discriminates the size of cooling loads from the magnitude of the heat transfer coefficient, and whether mist cooling is executed or air cooling is executed is selected. In the case that the cooling loads is big, the speed of revolution of an air fan 52 is made certain, the sheet temp. is measured by a sheet temp. gauge 42, and the opening degree of a flow rate valve 58 is adjusted by a flow rate controller 56 so as to regulate the quantity of water detected by a flow rate gauge 54 to prescribed value. In the case that the cooling loads are small, the flow rate adjusting valve 58 is perfectly closed to regulate the quantity of water to zero, the air fan 52 is adjusted by a pressure controller 62 so as to regulate the air pressure in a pressure sensor 60 to the objective value, and the sheet temp. is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cooling method in an alloying process, and more particularly to a method for cooling a wide range of line speeds and sheet thicknesses, which is suitable for use in producing hot-dip galvanized steel sheet. The present invention relates to a cooling method in an alloying process.

[0002]

2. Description of the Related Art Generally, in an apparatus for alloying a hot-dip galvanized steel sheet, as shown in FIG. And heated almost uniformly by a heating zone 32 by electric induction or gas, and thereafter, an alloy layer was formed by a preservative layer 34,
Rapid cooling is performed in the cooling zone 36. In the figure, 22 is
For example, a snout for shielding the steel sheet 10 in a reducing atmosphere introduced from an annealing furnace (not shown) from the atmosphere, 24
Is a sink roll immersed in a galvanizing bath 20;
38 is a top roll.

In cooling in the cooling zone 36,
Since rapid cooling is required to suppress a flower pattern called spangle which may occur on the surface of the steel sheet and to make the surface appearance uniform, for example, as described in JP-A-5-9697, air and water are removed. Mixed mist cooling (also referred to as air-water cooling) is performed, and alcohol mist cooling is performed as in JP-A-62-253775.

[0004]

However, the mist cooling is sufficiently effective for cooling requiring a large heat transfer coefficient, such as rapid cooling, but otherwise, for example, when the line speed is low. On the other hand, when a thin steel plate or the like is used, overcooling occurs, and water remains on the surface of the steel plate, which may cause dropping of cooling water or other equipment such as rolls. Also, the water on the steel plate is transferred to the roll surface,
The steel plate slips on the roll and impairs the surface appearance,
Alternatively, the central portion of the roll contacted by the steel sheet is excessively cooled, and the radius of the central portion of the roll is made relatively small due to the difference in the amount of thermal expansion, so that the effect of preventing the roll crown from meandering is lost. There was a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and enables cooling over a wide range of line speeds and plate thicknesses, eliminates water residue and meandering on the metal surface, and has excellent surface appearance uniformity. It is an object to provide a metal material.

[0006]

According to the present invention, when cooling a metal material plated with a molten metal in a cooling zone in an alloying process, mist cooling is performed when a cooling load is large,
When the cooling load is small, the above problem is solved by performing air cooling.

Further, the magnitude of the cooling load is determined based on the magnitude of a heat transfer coefficient required for cooling.

According to the present invention, the determination of the cooling load is made based on, for example, the heat transfer coefficient, so that the inlet side plate temperature, the outlet side target plate temperature, the cooling length, the refrigerant temperature, the line speed, the plate thickness, After calculating the heat transfer coefficient from the strip density, the specific heat of the strip, etc., the mist cooling and air cooling are switched at a certain threshold, so that the metal material such as a steel plate does not become overcooled, and the mist cooling does not occur. Since air cooling is performed in a region that cannot be cooled by the method, no water remains on the surface of the metal material, and meandering and slippage of a steel plate or the like can be suppressed.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the configuration of a cooling control device for carrying out the present embodiment.

In the present embodiment, when the steel sheet 10 reaches the exit side of the preservation zone 34, the steel sheet 1 is measured by the sheet thermometer 40.
A sheet temperature of 0 is measured, and a heat transfer coefficient is calculated from the line speed, the sheet thickness, the target sheet temperature on the outlet side of the cooling zone 36 at that time, and parameters of a host computer (not shown).
It is determined whether to perform mist cooling or air cooling.

FIG. 2 shows the control load range of the present invention. The switching determination thresholds (heat transfer coefficients) α and β can be provided for each cooling method and steel type. If the thresholds α and β are exceeded, the cooling method is switched. Threshold α for switching to air cooling when the current cooling method is mist cooling
Can be, for example, α = 100 kcal / m ² · hr · ° C. When the current cooling method is air cooling, the threshold β for switching to mist cooling is, for example, β = 150
kcal / m ² · hr · ° C.

Here, the reason why hysteresis is provided for switching between mist cooling and air cooling by changing the values of α and β is as follows.
This is to suppress cooling unevenness due to plate temperature fluctuation when switching the cooling method.

When mist cooling is selected by the control device 50, for example, the air flow rate is kept constant, and the water flow rate is used as the operation end. Specifically, while the rotation speed of the air fan 52 is kept constant, the plate temperature is measured by the plate thermometer 42 on the outlet side of the cooling zone 36, and the amount of water detected by the flow meter 54 is adjusted according to the result. The flow controller (FIC) 56 is set to a predetermined value.
To adjust the opening of the flow control valve 58.

On the other hand, when air cooling is selected by the control device 50, the flow control valve 58 is fully closed to set the water volume to zero, the rotation speed of the air fan 52 is set to the operation end, and the cooling zone 36 is set.
The pressure controller (PIC) 62 adjusts the rotation speed of the air fan 52 so that the air pressure detected by the pressure sensor 60 becomes a target value in accordance with the plate temperature measured on the outlet side of
Control the sheet temperature.

In the drawing, reference numeral 64 denotes a flow controller 56 and a pressure controller 62 in accordance with the output of the plate thermometer 42.
Is a temperature controller (TIC) for giving a target value to the temperature controller.

In the present embodiment, the sheet temperature on the outlet side of the cooling zone 36 detected by the sheet thermometer 42 is used as a flow controller 56.
And the feedback to the pressure controller 62, it is possible to perform high-precision cooling control. Note that, for example, at the time of air cooling, a fixed set value may be input to the pressure controller 62 to perform open-loop control.

Further, in the present embodiment, since the heat transfer coefficient is used to determine the switching of the cooling load, the switching can be determined with high accuracy. The criterion for determining the magnitude of the cooling load is not limited to the magnitude of the heat transfer coefficient. For example, the cooling water flow rate or the air pressure may be used for determining the cooling load. Specifically, for example, when the cooling water flow rate becomes equal to or lower than a predetermined lower limit value by mist cooling, the process shifts to air cooling. On the other hand, when the air pressure becomes equal to or higher than a predetermined upper limit value by air cooling, the mist cooling is performed. A transition can be made to cooling.

In the above embodiment, the mist cooling is controlled by the amount of water, and the air cooling is controlled by the rotation speed of the air fan. However, the control method of the mist cooling and the air cooling is not limited to this. .

In the above embodiment, the present invention
Although it was applied to the cooling of hot-dip galvanized steel sheet, the application of the present invention is not limited to this.By the other hot-dip metal other than zinc, during the alloying process during the plating of other metal materials other than the steel sheet. Obviously, the invention is equally applicable to cooling.

[0021]

According to the present invention, a cooling method is selected according to a cooling load at the time of cooling in the alloying process, so that a wide range of line speeds and sheet thicknesses can be cooled.
Further, since no water remains on the surface of the metal material, slipping and meandering of the metal plate on the roll can be suppressed. Further, by these actions, there is an excellent effect that a galvanized steel sheet having excellent surface appearance uniformity can be stably provided.

According to the experiment conducted by the inventor, as shown in FIG. 3, by switching to air cooling, supercooling was eliminated, so that a dirt generation area could be avoided, and a factor inhibiting first-class quality could be reduced. Further, the plate temperature control accuracy was improved, the area where Zn pickup flaws were generated could be avoided, and similarly, the inhibition factor could be reduced.

[Brief description of the drawings]

FIG. 1 is a pipeline diagram showing a configuration of a cooling control device for implementing an embodiment of the present invention.

FIG. 2 is a diagram showing a reference for switching between mist cooling and air cooling in the embodiment.

FIG. 3 is a diagram showing the effect of the present invention.

FIG. 4 is a cross-sectional view showing a configuration of an apparatus for alloying a hot-dip galvanized steel sheet, which is an example of an object to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Steel plate 20 ... Galvanizing bath 30 ... Gas nozzle 32 ... Heating zone 34 ... Preservation zone 36 ... Cooling zone 40, 42 ... Plate thermometer 50 ... Control device 52 ... Air fan 54 ... Flow meter 56 ... Flow controller (FIC) 58 ... Flow control valve 60 ... Pressure sensor 62 ... Pressure controller (PIC) 64 ... Temperature controller (TIC)

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Jun Morizumi 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. 1-chome (without address) Inside Kawasaki Steel Corporation Mizushima Works

Claims (2)

[Claims] When cooling a metal material plated with a molten metal in a cooling zone in an alloying process, mist cooling is performed when a cooling load is large, and air cooling is performed when a cooling load is small. Characteristic cooling method in alloying process. 2. The method according to claim 1, wherein the magnitude of the cooling load is determined based on the magnitude of a heat transfer coefficient required for cooling.