KR20220163733A - Control Method of Coating Weight of molten metal in Continuous Hot Dip Coating Line - Google Patents

Abstract

The present invention relates to a coating weight control method for a continuous molten metal facility, which can always obtain uniform accuracy, comprising the steps of: setting a reference distance; executing coating weight control by a coating weight estimation model formula; calculating a distance between an air knife nozzle and a steel plate; and executing coating weight control with a calculated target coating weight.

Description

Coating weight control method of continuous molten metal equipment {Control Method of Coating Weight of molten metal in Continuous Hot Dip Coating Line}

The present invention relates to a method for controlling the coating weight of a continuous molten metal facility capable of adjusting the coating mass per unit area coated in real time when a metal plate passes through a bath containing molten metal.

In general, continuous hot-dip plating equipment consists of a snout and a dip roll in a coating bath, and is mainly applied to pickling galvanizing lines (PGL) and continuous galvanizing lines (CGL).

In this continuous hot-dip plating facility, a metal strip passed through a furnace is continuously immersed in a molten metal bath to form a coating layer, and after the coating amount or thickness is adjusted by an air knife, tempering It is a device that forms a plating layer by coating a metal strip while going through a rolling mill (SPM) and a shape corrector (T/L).

In such a continuous hot-dip plating facility, the hot-dip plating material coming up on the steel sheet S passing through the molten metal bath is cut to a predetermined thickness by an air knife installed on the top of the bath surface.

That is, the thickness of the hot-dip plating layer depends on the spray pressure of the air knife installed and used in the line and the distance between the nozzle and the metal plate, and also depends on the conveying speed of the metal plate. In actual operation, the target coating thickness is determined for the steel plate being transported, and the transport speed is also determined. Therefore, the distance between the steel plates or the pressure of the air knife is adjusted to match the plating thickness with respect to the set feed rate.

Since the plating layer buried on the surface of the steel sheet is still in a molten state, a technology for accurately measuring the thickness of the plating layer at the rear end of the air knife has not yet been established. That is, since an appropriate measuring device capable of measuring the thickness of non-solidified hot-dip metal has not yet been technically put into practical use, the plating thickness at this point cannot be known.

The plating thickness meter currently in operation is a room temperature measurement method, and is installed and operated at a downstream point (about 100m or more rear end), which is a point where the molten metal plating layer is sufficiently cooled. Therefore, the plating thickness can be measured only when the metal plate is transported from the air knife point for a certain period of time and reaches the downstream plating thickness sensor position. Therefore, even if the distance or pressure is changed to match the coating amount at the time when the new coating amount is set, the result cannot be known immediately, and can be known through the sensor only after a certain period of time.

For this reason, real-time feedback control, which is commonly used, cannot be executed, and during this time, the operator has no choice but to set the distance or pressure using the operator's experience or a relational expression derived empirically. The plating thickness for the changed condition is checked at the moment when the steel plate reaches the position of the sensor at the time when the changed distance or pressure is applied.

The main point of view here is to minimize the error of the plating thickness and maintain the plating quality by matching the target plating amount.

Registered Patent No. 10-1688384 (registered on December 15, 2016) Registered Patent No. 10-0815814 (registered on March 14, 2008) Registered Patent No. 10-1017830 (registered on February 18, 2011)

The present invention has been made to solve the above problems,

The accuracy of coating thickness in the hot-dip plating process is directly related to the quality of the steel sheet and the reduction in production cost. The coating thickness can be obtained only when the distance and pressure are accurately set for a given feed rate, and given operating conditions, that is, the coating thickness and feed rate The object of the present invention is to provide a method for controlling the coating weight of a continuous molten metal facility to accurately derive the distance and pressure in real time.

The method for controlling the coating weight of a continuous molten metal facility according to the present invention includes (a) a pressure operating range for the spray pressure of an air knife, an air knife nozzle, and a steel plate in order to calculate an operating set value for a target coating weight using a coating weight estimation model formula; setting a distance operation range for the distance between the spaces and setting a reference distance within the distance operation range; (b) After calculating the spray pressure value by substituting the reference distance into the spray pressure estimation model formula, if the calculated spray pressure value is within the pressure operating range, the coating amount is controlled by the target coating amount calculated by the coating weight estimation model formula. executing; (c) fixing the operation setting injection pressure value as the upper or lower limit of the pressure operation range when the injection pressure value in step (b) is out of the pressure operation range; (d) calculating the distance between the air knife nozzle and the steel plate by substituting the upper or lower limit of the pressure operation range in step (c) into a model formula for estimating the distance between the air knife nozzle and the steel plate; (e) if the distance between the air knife nozzle calculated by the distance estimation model formula and the steel plate is within the distance operating range, executing coating weight control with the target coating weight calculated by the gold weight estimation model formula; And (f) when the distance between the air knife nozzle and the steel plate calculated by the distance estimation model formula is out of the distance operating range, the distance between the air knife nozzle and the steel plate is fixed at the upper limit value or the lower limit value of the distance operating range , the step of executing coating weight control with the target coating weight calculated by the coating weight estimation model formula.

The coating weight estimation model equation according to the present invention is characterized in that it is defined by Equation 1.

――――――수학식 1

―――――― Equation 1

Here, P: air knife spray pressure, Pa: surrounding atmospheric pressure, Cw: coating thickness, V: line feed speed, L: distance between air knife nozzle and steel plate, H: distance between air knife nozzle and molten metal surface

m: gas constant of air knife injection fluid (= 1.4), K: constant, α: velocity influence index, β: pressure influence index, γ: distance influence index δ: height influence index

The injection pressure estimation model equation according to the present invention is characterized in that it is defined by Equation 2.

――――――수학식 2

―――――― Equation 2

The distance estimation model equation according to the present invention is characterized in that it is defined by Equation 3.

――――――수학식 3

――――――Equation 3

In order to increase the hit rate for the coating weight estimation model formula according to the present invention, the exponents α, β, γ, δ and coefficient K included in the coating weight estimation model formula are calculated through learning using performance values operated for a certain period of time in Equation 4 It is characterized by optimizing by.

――――――수학식 4

――――――Equation 4

here,

, L' = Ln (L), H'= Ln(H), K'= Ln(K)Cw' = Ln (Cw),

, L' = Ln (L), H' = Ln (H), K' = Ln (K)

According to the present invention, the pressure operation range is 0.3 bar to 0.7 bar, the distance operation range is 7 mm to 13 mm, and the reference distance is set to 10 mm.

The method for controlling the coating amount of a continuous molten metal facility according to the present invention accurately adjusts the coating thickness to a target value for a given operating condition, so that the quality of the coated steel sheet and the cost of work can be reduced.

In addition, since the present invention is realized by a dedicated control system, operator's intervention is unnecessary, and uniform accuracy can always be obtained.

1 is a perspective view showing a continuous molten metal facility according to the present invention;
Figure 2 is a conceptual diagram showing the plating process by the continuous molten metal equipment according to Figure 1;
3 is a conceptual diagram showing a coating weight control system of a continuous molten metal facility according to the present invention;
4 is a logic flow diagram showing a coating weight control method according to the present invention;
Figure 5 is a schematic diagram showing the control process of the coating weight control system according to the present invention.

In order to explain the present invention and the operational advantages of the present invention and the objectives achieved by the practice of the present invention, the following describes a preferred embodiment of the present invention and references it.

First, the terms used in this application are used only to describe specific embodiments, and are not intended to limit the present invention, and singular expressions may include plural expressions unless the context clearly indicates otherwise. In addition, in this application, terms such as "comprise" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other It should be understood that the presence or addition of features, numbers, steps, operations, components, parts, or combinations thereof is not precluded.

In describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description will be omitted.

As shown in FIGS. 1 to 5, the system for controlling the coating thickness of a continuous molten metal line for implementing the method for controlling the coating weight of a continuous molten metal facility according to the present invention is configured as follows.

An air knife 10 that cuts off the plating material on the steel plate S, a pressure measuring sensor 20 mounted on a pipe for spraying fluid of the air knife 10 to measure the spray pressure in real time, and an air knife ( 10), a room temperature plating thickness measurement sensor 50 (hereinafter referred to as a 'plating amount measurement sensor') for measuring the plating thickness (Cw_fb) in real time in a state in which the material plated on the metal plate is solidified, and an air It is configured to include a distance adjusting device 30 for adjusting the distance between the knife and the steel plate, and a height adjusting device 40 for adjusting the height of the air knife from the molten surface.

In addition, the calculator 70 calculates the pressure and distance from the coating weight estimation model formula in real time and derives a new coating weight estimation model formula through predetermined learning using existing operation data, and the steel plate S is the air knife 10 Calculate the time required to transfer from the point to the position of the coating amount measurement sensor 50, collect and store signals from various sensors such as the pressure measurement sensor 20 - the coating amount measurement sensor 50 - the distance measurement sensor, and store the collected data It is configured to include a main controller 60 that transmits to the calculator 70 in real time and controls the pressure set value and the distance set value transmitted from the calculator 70 in real time.

In the plating thickness control system configured as described above, the spraying unit sprays the spraying fluid on the surface of the steel sheet S with a certain pressure to cut off the plating layer. This injection unit is composed of an air knife 10 equipped with a spray nozzle and a blower or pressure control valve 80 for sending spray fluid to maintain a predetermined pressure in the spray nozzle chamber of the air knife.

In addition, when the pressure setting value is input to the main controller 60, the pressure controller 61 controls the blower or the pressure control valve 80 so that the injection fluid can be injected at a constant pressure through the air knife 10.

At this time, the pressure controller 61 receives feedback of the pressure measured by the pressure sensor 20 in real time and controls it to be the same as the pressure set using the blower or the pressure control valve 80.

In the present invention, the coating amount (Cw), the line conveying speed (V) (hereinafter referred to as 'feeding speed'), the spray pressure (P) of the air knife 10 (hereinafter referred to as 'injection pressure'), the air knife 10 and the steel plate) (S) (hereinafter referred to as 'distance') and the height (H) of the air knife 10 from the molten surface (hereinafter referred to as 'height'). Same as Equation 1.

Here, P: air knife injection pressure, Pa: surrounding atmospheric pressure, Cw: plating thickness, V: line transfer speed, L: distance between air knife nozzle and steel plate, H: distance between air knife nozzle and molten metal surface, m: The gas constant of the fluid sprayed with the air knife (= 1.4), K: constant, α: velocity influence index, β: pressure influence index, γ: distance influence index, δ: height influence index.

The coating weight estimation model was derived through fluid engineering analysis, and the moving speed (V), coating weight setting value (Cw), spray pressure (P), distance (L) and height (H) measured at the same time for the air knife The exponents α, β, γ, δ, and the coefficient K inherent in the function are estimated using many operating performance values (Cw_fb) consisting of .

In actual operation, the line feed rate (V) is determined according to the type of steel and the size (thickness, width) of the steel sheet, and a target coating amount (Cw_ref) is determined for each steel sheet (S). In addition, the height (H) of the air knife can be appropriately set according to the operating experience.

In this case, the molten plating solution adhering to the surface of the steel plate S transported in the vertical direction through the bathtub flows down by its own weight until the steel plate reaches the air knife 10 . Therefore, the amount of molten metal liquid adhering to the steel sheet varies according to the distance from the bath surface. Accordingly, when the height (H) from the bath surface to the air knife changes, the thickness of the molten plating solution attached to the steel plate S and flowing into the air knife point changes. If there is a lot of inflowing molten plating solution, a higher blowing pressure is required when the air knife cuts to a certain thickness.

However, in the present invention, as described above, the height (H) of the air knife is properly set according to the operating experience, but if necessary, the height of the air knife is adjusted by controlling the height adjusting device 40 by the height controller 65 It is also possible to control the coating amount by adjusting.

Through this, the coating weight control method of the continuous molten metal facility is implemented through steps (a) to (f) as shown in FIGS. 1 to 5.

First, in step (a) (S100) according to the present invention, the pressure operating range (0.3 bar ~ 0.7 bar) and the distance operation range (7mm to 13mm) for the distance (L) between the air knife nozzle and the steel plate, and the reference distance (10mm) is set within the distance operation range.

In addition, in step (b) (S200), the spray pressure (P) value is calculated by substituting the reference distance into the spray pressure estimation model formula, and then calculated through the coating weight estimation model formula when the calculated spray pressure value is within the pressure operating range. Coating weight control is executed with the set target coating weight (Cw_ref).

In addition, in step (c) (S300), if the injection pressure (P) value in step (b) (S200) is out of the pressure operation range, the operation is set to the upper limit value (0.7bar) or lower limit value (0.3bar) of the pressure operation range. It is fixed at the injection pressure value.

In this case, in step (d) (S400), the distance between the air knife nozzle and the steel plate (L ) will be computed.

When the calculated distance (L) between the air knife nozzle and the steel plate is within the distance operation range, the coating weight control is performed with the target coating weight (Cw_ref) calculated through the coating weight estimation model formula (e) (S500).

In addition, in step (f) (S600), if the distance (L) between the air knife nozzle and the steel plate calculated by the distance estimation model formula is out of the distance operating range, the distance (L) between the air knife nozzle and the steel plate is set as the upper limit of the distance operating range It is fixed as the value (13mm) or the lower limit value (7mm), and coating weight control is executed with the target coating weight (Cw_ref) calculated through the coating weight estimation model.

In this case, the coating weight estimation model equation is defined as Equation 1 as described above.

In addition, during actual operation, the feed rate (V) of the steel sheet and the target coating weight (Cw_ref) for this steel sheet are determined according to the production plan, and the height (H) of the air knife can be changed within a certain range according to operation experience.

In order to meet the target coating amount (Cw_ref) for a given speed, the spraying pressure (P) and the distance (L) of the air knife are adjusted. The estimated model equations for the spraying pressure and distance are Equations 2 and 3, respectively.

Here, the exponents α, β, γ, δ and the coefficient K are constants respectively, and many operational data combinations, namely coating amount (Cw), line speed (V), air knife spray pressure (P), air knife nozzle and It is obtained by estimating by applying the least squares method from the distance (L) and height (H) between steel plates (|k=1,...,n). The plating materials in the hot-dip plating process vary, such as zinc, zinc-aluminum mixture, and aluminum-silicon mixture, and the combination of α, β, γ, δ, and K varies depending on the plating material. Here, the coating amount, line speed, and pressure can be taken as accurate values as measured values, but the distance between the air knife nozzle and the steel plate may cause some error depending on the accuracy of the installation work of the equipment and the bending amount, which is the longitudinal deformation of the steel plate. The error between the actual physical distance and the distance measured by the length sensor installed in the facility is called bias. This amount of bias is obtained indirectly by changing the amount of bias until the exponent γ related to the distance is estimated to be 1.0. Once this amount of bias is determined, it can be permanently used.

On the other hand, the pressure operating range is determined by the capacity of the device for supplying injection fluid, and is generally limited to 0.3 bar to 0.7 bar, and the distance operating range is limited to 7 mm to 13 mm. The basic distance can be set to 10mm as the median value of the distance operating range.

A flow chart for the control difference using the pressure operating range, distance operating range, and reference distance is shown in FIG. 4, and will be described in detail below.

First, it is necessary to determine the spray pressure and distance that realizes the target coating weight for a given moving speed. In general, considering the shape and vibration width of the steel plate, the distance (L) between the steel plate and the air knife nozzle is at least 7 mm or more, and the default value is 10 mm. The pressure operation range for controlling the coating amount (Cw) is set to 0.3 bar to 0.7 bar as described above for the coating surface quality, and the distance operation range is set to 7 mm to 13 mm. If the pressure is too low, the plating quality deteriorates, and if the pressure is too high, fragments of the molten plating solution that have not yet solidified may be generated and clog the air knife nozzle.

When the feed rate (V) of the line and the target coating weight (Cw_ref) are transmitted to the calculator 70, the calculator 70 calculates a pressure suitable for the coating weight estimation model. At this time, the distance L is basically set to 10 mm as described above. The injection pressure P is calculated by Equation 2 as described above, that is, the injection pressure estimation model equation.

At this time, if the calculated pressure is between 0.3 bar and 0.7 bar, the calculated pressure is applied to the main controller 60 to execute pressure control by the pressure controller 61, and the coating amount for the actual measured pressure actual value (P_fb) will measure

If the calculated pressure exceeds 0.7 bar, the pressure setting value is fixed at 0.7 bar, and the distance (L) is recalculated from Equation 3, that is, the distance estimation model equation. If the calculated distance is within the range of 7 mm to 10 mm, the distance set value (L_ref) is applied to the distance controller 63 to control the coating amount. Also, if the calculated distance is within 7mm, the distance is fixed at 7mm and the coating weight control is executed.

If the calculated pressure is predicted to be within 0.3 bar, the pressure setting value (P_ref) is fixed to 0.3 bar, and the distance is recalculated from the distance estimation model equation (Equation 3). In this case, if the calculated distance is within the range of 10 mm to 13 mm, the distance set value (L_ref) is applied to the distance controller 63 to control the coating amount. However, if the calculated distance exceeds 13mm, the distance is fixed at 13mm and coating weight control is executed.

In this case, the exponents α, β, γ, and δ inherent in the coating weight model function are constants physically determined by the mutual behavior of the spraying air and the coating layer, and the coefficient K varies depending on the shape of the air knife and the type of spraying fluid. These exponents and coefficients are obtained as follows.

As described above, when the natural logarithm is taken on the left and right sides of the coating weight estimation model equation function of Equation 1, the following multivariate linear function equation, that is, Equation 4 is derived.

, L' = Ln (L), H'= Ln(H), K'= Ln(K) 이다.Where, Cw' = Ln (Cw),

, L' = Ln (L), H' = Ln (H), K' = Ln (K).

The coefficients α, β, γ, δ, and K' of this linear function are the feed rate (V), coating weight actual value (Cw), spray pressure (P), and distance (L) at the same point collected during a certain operating period. It can be calculated online or offline by applying the least squares method using a combination of data such as , height (H). Even after these indices and coefficients are determined once, since the characteristics of the air knife change minutely due to deformation of the shape of the air knife over time, they are periodically re-estimated and replaced in order to continuously maintain the coating weight accuracy.

As such, the present invention has been described with reference to one embodiment shown in the drawings, but this is only exemplary, and those skilled in the art can make various modifications and equivalent other embodiments therefrom. will understand

Therefore, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

10: air knife
20: pressure measuring sensor
30: distance control device
40: height adjustment device
50: coating weight measurement sensor
60: main controller
61: pressure controller 63: height controller
65: distance controller
70: calculator (model formula for estimating plating amount)

Claims (6)

(a) In order to calculate the operating set value for the target coating weight using the coating weight estimation model formula, a pressure operating range for the spray pressure of the air knife and a distance operating range for the distance between the air knife nozzle and the steel plate are set, and the distance Setting a reference distance within the operating range (S100);
(b) calculating the spray pressure value by substituting the reference distance into the spray pressure estimation model formula, and then executing the coating amount control according to the coating amount estimation model formula when the calculated spray pressure value is within the pressure operation range ( S200);
(c) when the injection pressure value in step (b) is out of the pressure operation range, fixing the operation setting injection pressure value as the upper limit value or the lower limit value of the pressure operation range (S300);
(d) calculating the distance between the air knife nozzle and the steel plate by substituting the upper or lower limit of the pressure operation range in step (c) into a model formula for estimating the distance between the air knife nozzle and the steel plate (S400);
(e) executing coating weight control according to the coating weight estimation model formula when the distance between the air knife nozzle and the steel plate calculated by the distance estimation model formula is within the distance operating range (S500); and
(f) When the distance between the air knife nozzle and the steel plate calculated by the distance estimation model formula is out of the distance operating range, the distance between the air knife nozzle and the steel plate is fixed at the upper or lower limit of the distance operating range, Executing coating weight control according to the coating weight estimation model formula (S600);
A method for controlling the coating weight of a continuous molten metal facility comprising a.
According to claim 1,
The method for controlling the coating weight of a continuous molten metal facility, characterized in that the coating weight estimation model is defined by Equation 1.

―――――― Equation 1
Here, P: air knife spray pressure, Pa: surrounding atmospheric pressure, Cw: coating thickness, V: line feed speed, L: distance between air knife nozzle and steel plate, H: distance between air knife nozzle and molten metal surface
m: gas constant of air knife injection fluid (= 1.4), K: constant, α: velocity influence index, β: pressure influence index, γ: distance influence index δ: height influence index
According to claim 2,
The method for controlling the coating weight of a continuous molten metal facility, characterized in that the injection pressure estimation model is determined by Equation 2.

―――――― Equation 2
According to claim 3,
The method for controlling the coating weight of a continuous molten metal facility, characterized in that the distance estimation model is defined by Equation 3.

――――――Equation 3
According to claim 1,
In order to increase the hit rate for the coating weight estimation model formula, the exponents α, β, γ, δ and coefficient K contained in the coating weight estimation model formula are optimized by Equation 4 through learning using actual performance values operated for a certain period of time. Coating weight control method of continuous molten metal equipment, characterized in that.

――――――Equation 4
here,
Cw' = Ln (Cw),

, L' = Ln (L), H' = Ln (H), K' = Ln (K)
According to any one of claims 1 to 5,
The pressure operation range is 0.3 bar to 0.7 bar, the distance operation range is 7 mm to 13 mm, and the reference distance is set to 10 mm.

Images