KR20020049465A - Method for controlling the amount of the strip plating - Google Patents

Abstract

PURPOSE: A method for controlling a plating amount of a strip is provided to prevent generation of excessive plating at the welding part between a preceding coil and a following coil by forming a control logic appropriately harmonizing a blowing pressure of a wiping gas and a distance between an air knife and a strip. CONSTITUTION: The method for controlling a plating amount of a strip comprises the steps of determining a plating amount of a following coil; increasing a distance between the following coil and an air knife; and increasing a blowing pressure for blowing air from the air knife, wherein the distance is derived from the following equation 1: £Equation 1|D=axCW+bxV+c, where D is a distance(mm) between the strip and the air knife, CW is a target plating adhesion amount(g/m¬2), V is a transfer speed of the strip(m/min), and a, b and c are constants, the blowing pressure is derived from the following equation 2:£Equation 2|CW=e¬a·V¬b·P¬c·D¬d, where CW is a plating adhesion amount(g/m¬2), V is a transfer speed of the strip(m/min), P is a pressure of a wiping gas(kgf/cm¬2), D is a distance between the strip and the air knife(mm), and a, b, c and d are constants.

Description

Method for controlling the amount of the strip plating}

The present invention relates to a method for controlling the amount of plating in the hot dip galvanizing process, and more particularly, the target plating adhesion amount of the leading coil and the trailing coil due to the characteristics of a continuous line working by welding the preceding coil and the trailing coil. In the case of different, that is, when the target plating amount of the preceding coil is high and the target plating amount of the trailing coil is low, or when the target plating amount of the preceding coil is low and the target plating amount of the trailing coil is high, the plating amount generated by the difference in the plating amount before and after the welded portion. The present invention relates to a plating deposition control method for minimizing deviation (over-attachment or under-attachment).

In general, the hot dip galvanizing process is performed by passing the hot dip zinc 4 in the plating bath 5 through the strip 2, as shown in FIG. In addition, the coating amount on the surface of the strip 2 is determined by the line speed of the strip 2, the blowing pressure of the wiping gas blown out of the air knife 1, the strip 2 and It is determined by the distance between the air knifes 1.

In general, the plating amount is proportional to the feeding speed and the spacing between the strip 2 and the air knife 1 and inversely proportional to the blowing pressure of the wiping gas. At this time, the feed rate is usually a limiting factor determined in the heating furnace for the purpose of adjusting the temperature of the strip. Therefore, the adjustment operation of the plating deposition amount is mainly performed by adjusting the blowing pressure of the wiping gas and the interval between the strip 2 and the air knife 1.

Therefore, when there is a difference in the target plating adhesion amount of each of the preceding coil and the following coil, in particular, when the target plating adhesion amount of the trailing coil is higher than that of the preceding coil, the blowing pressure of the wiping gas corresponding to the time point at which the weld passes is adjusted.

However, as shown in FIG. 2, since the blowing pressure of the wiping gas is PID (proportional, derivative, integral) control to prevent pressure unevenness, the target set value is reached after a certain time. Therefore, as shown in FIG. 3, under-carrying portions whose plating deposition amount is not controlled by the elapsed time are generated.

In addition, the coating amount can be controlled by adjusting the gap between the strip 2 and the air knife 1, but if the gap is too narrow, there is a risk of collision between the strip 2 and the air knife 1, and the gap is too wide. If so, the blowing pressure of the wiping gas should be increased relatively. However, higher than necessary high pressure operations may degrade the quality of the plating surface to be plated on the surface of the strip.

On the other hand, as shown in Figure 4, when there is a difference in the target plating amount before and after the weld, in particular, when the target plating amount of the relatively low leading coil and the relatively high trailing coil is connected to the welding portion to reach the air knife A method of blowing a wiping gas at a preset blowing pressure has been used.

And, as shown in FIG. 5, when the target plating deposition amount is relatively high, the leading coil and the relatively low trailing coil are connected, the wiping gas is blown at the blowing pressure set when the welding portion of the coil passes through the air knife. The method is being used.

However, the above-described schemes, as shown in Figures 4 and 5, there is a problem that the excessive plating occurs near the weld portion of the strip to consume zinc more than necessary.

The present invention has been made to solve the conventional problems as described above, by configuring a control logic (Logic) to properly match the blowing pressure of the wiping gas and the gap between the air knife and the strip to the target plating deposition amount is different An object of the present invention is to provide a coating amount control method in a coil welding part for preventing overplating from occurring in a welding part between a preceding coil and a trailing coil.

1 schematically shows a general plating apparatus.

Figure 2 is a graph showing the response characteristics of the gap between the strip and the air knife and the pressure of the wiping gas.

3 is a graph showing the relationship between response time and plating deposition amount.

Figure 4 is a graph showing the response characteristics according to the target plating amount change.

5 is a graph showing the response characteristics according to the target plating amount change.

6 is a flow chart of the plating amount control logic before and after welding according to the present invention.

7 is a flow chart of a control system according to the present invention.

8 is a graph showing the response characteristics according to the target plating amount change according to an embodiment of the present invention.

9 is a graph showing the response characteristics according to the target plating amount change according to another embodiment of the present invention.

In order to achieve the above object, according to the present invention, the air is blown from the air knife to a strip in which the target coil has a relatively low leading coil and a relatively high trailing coil are welded and travels at a predetermined feed rate through the plating bath. The method for controlling the plating amount of the strip by determining the plating amount of the trailing coil, increasing the interval between the trailing coil and the air knife, and increasing the blowing pressure for blowing air from the air knife In steps,

The interval is the following [formula 1],

D = a × CW + b × V + c .............. Derived from (1),

Where D is the distance between the strip and the air knife (mm), CW is the target plating amount (g / m ² ), V is the feed rate of the strip (m / min), and a, b and c are constants Is,

The blowing pressure is the following [formula 2],

CW = e ^a · V ^b · P ^c · D ^d .............. Derived from (2),

Where CW is the coating weight (g / m 2), V is the feed rate of the strip (m / min), P is the wiping gas pressure (kgf / cm 2), and D is the distance between the strip and the air knife ( mm), and a, b, c, and d are constants.

In addition, according to another embodiment of the present invention, by blowing the air from the air knife to the strip that is welded to the relatively high leading coil and relatively low trailing coil, the target plating amount is passed through the plating bath running at a predetermined feed speed The method for controlling the plating amount of the strip includes determining a plating amount of the trailing coil, reducing a gap between the trailing coil and an air knife, and increasing a blowing pressure for blowing air from the air knife. Made up of

The interval is the following [formula 1],

D = a × CW + b × V + c .............. Derived from (1),

Where D is the distance between the strip and the air knife (mm), CW is the target plating amount (g / m ² ), V is the feed rate of the strip (m / min), and a, b and c are constants Is,

The blowing pressure is the following [formula 2],

CW = e ^a · V ^b · P ^c · D ^d .............. Derived from (2)

Where CW is the coating weight (g / m 2), V is the feed rate of the strip (m / min), P is the wiping gas pressure (kgf / cm 2), and D is the distance between the strip and the air knife ( mm), and a, b, c, and d are constants.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention.

Referring to FIG. 6, which shows the plating amount control algorithm and the plating amount control system before and after the weld, according to an embodiment of the present invention, coil information such as the thickness, width, and plating amount of the coil is provided from the upper calculator to the controller. As a result of the information received from the upper calculator, when the plating amount of the trailing coil is increased as compared with the preceding coil, the newly calculated interval is set as the pressure at the time when the weld passes the air knife, and then the gap according to the pressure change is compensated. .

For example, when the target plating amount of the trailing coil decreases, the blowing pressure of the air knife is preferentially adjusted before the weld passes through the air knife, and the gap compensation between the strip and the air knife is performed according to the blowing pressure change. And a space | interval is adjusted at the time when a welding part passes an air knife.

7 shows a plating amount control algorithm before and after welding according to the present invention.

Commonly performed in the step-by-step implementation of the algorithm is to check the coil information. That is, after receiving the information on the coil from the upper calculator, the control device determines whether to control the execution by determining whether the plating amount of the trailing coil is increased or decreased.

Example 1

This embodiment is a case where the weld portion between the relatively low leading coil and the relatively high trailing coil passes through the air knife.

As shown in FIG. 8, when the target plating amount is increased, the interval of the air knife should be widened and the pressure should be lowered. However, since the response speed of the pressure is slow, in order to quickly control the plating amount, the interval is first widened to a pre-calculated set value D _NEW to secure an increased coating amount. The next pressure is lowered gradually until it reaches the default setting and the gap is gradually narrowed accordingly.

Referring to FIG. 7, once the plating amount of the trailing coil is determined, the pressure value P _NEXT and the gap value D _NEXT , which should be set once, are calculated. If the target plating amount of the trailing coil is increased, in order to match the plating amount, the temporary gap value D _NEXT necessary under the current line speed and pressure P is given by the following formula (1) and the feed rate (V) of the current strip. And the target plating amount CW.

D = a × CW + b × V + c .............. (1),

Where D is the distance between the strip and the air knife (mm), CW is the target plating amount (g / m ² ), V is the feed rate of the strip (m / min), and a, b and c are constants to be.

On the other hand, since the general coating weight (CW) is represented by the formula of the following [Equation 2], the pressure value (P _NEXT ) to work in the trailing coil can be derived using the following [Equation 2].

^{CW = e a · V b ·} P c · D d .............. (2),

Where CW is the coating weight (g / m 2), V is the feed rate of the strip (m / min), P is the wiping gas pressure (kgf / cm 2), and D is the distance between the strip and the air knife ( mm) and a, b, c and d are constants.

That is, when the welding part waits for passing through the air knife and then passes through the air knife, the newly set interval value D _NEW and the current pressure value P _NEXT are set. At this time, the pressure remains the same, but the spacing becomes wider, so that the plating amount is increased in an instant.

Therefore, in order to gradually lower the pressure to the pressure value P _NEXT to be originally set, the pressure value P _NEW is calculated through the above [Equation 2]. At this time, if the amount of change of pressure value (P _NEW ) for lowering the pressure stepwise becomes large, the interval is controlled quickly, but the response of the pressure is delayed. The lower limit pressure value P _NEW corresponding to the corrected target plating amount (ie, target plating amount-lower limit value) modified so as not to deviate from the lower limit of is derived from the above [Equation 2].

At this time, the new pressure value with the pressure value (P _NEXT) is smaller than the pressure value (P _NEXT) The stepwise lower pressure value calculated in this manner (P _NEW) is to the original setting has to go to a pressure to do the original settings (P _NEW ).

On the other hand, in order to calculate the response time required to stabilize the pressure, that is, the time required to maintain the pressure value (P _NEW ) from the pressure value (P _NEXT ) is calculated using the pressure response function equation of the following [Equation 3] do.

t = aln (P) + b .............. (3),

Where t is the required time (sec), P is the wiping gas pressure (kgf / cm 2), and a and b are constants.

In addition, a stepwise interval value D _NEW corresponding to the stepwise pressure value P _NEW is calculated by Equation 1 above.

In addition, when the calculated pressure value P _NEXT and the interval value D _NEXT are set at the same time, the pressure and the gap are simultaneously reduced, and thus the plating amount is not affected by the offset action. At this time, the to reach the step of pressure values the pressure value (P _NEXT) need wait phase pressure value (P _NEW), the original setting for the response time (t) required to reach the (P _NEW), 7 As shown, continue to lower the pressure in stages. This process is terminated when the _stepped pressure value P _NEW and the pressure value P _NEXT originally set should be the same.

Example 2

This embodiment is a case where the weld portion between the relatively high leading coil and the relatively low trailing coil passes through the air knife.

As shown in FIG. 9, when the target plating amount is changed from the high coil to the low coil, the gap between the air knife should be reduced and the pressure should be increased. However, due to the slow response speed of pressure, in order to quickly control the coating amount, the pressure and the gap are gradually increased while maintaining the plating amount, and then the pressure is maintained as the weld passes through the air knife and the gap is pre-calculated. By setting the setting value (D _NEW ) and controlling it quickly, the reduced plating amount is ensured.

Referring to FIG. 7 again, once the plating amount of the trailing coil is determined, the pressure value P _NEXT and the interval value D _NEXT to be set once are calculated using the above [Equation 1] and [Equation 2]. And, if the target plating amount of the trailing coil decreases, the time t required to reach the new pressure value P _NEW at the current working pressure value P _NEXT is calculated by the above [Equation 3]. This is to estimate how far the weld should be from the air knife. That is, the position x to be set is calculated by multiplying the feed rate of the strip by the pressure response delay time t.

Therefore, it waits until a welding part reaches the setting position x. Then, when the welded portion arrives at the set position x, the interval value D _NEW to be controlled step by step is calculated from the above expression (1). At this time, if the gap between the welded portion and the air knife is widened at random, the plating amount is largely attached, so the upper limit value of the plating amount is set. That is, the interval value D _NEW to be set is calculated using Equation 1 on the basis of the target plating amount plus the upper limit value.

The pressure P _NEW corresponding to the calculated interval D _NEW is calculated in Equation 2 above. At this time, in case the calculated pressure (P _NEW) is greater than the current pressure (P _NEXT), change in the pressure (P _NEW) calculating the current pressure (P _NEXT), intervals (D _NEW) for the [formula 2] Recalculate

In addition, the air after the response time (t) of the calculated pressure (P _NEW) is calculated from the above Equation 3, the set pressure (P _NEW) and the distance (D _NEW) for the next time (t). That is, if the pressure value (P _NEW ) to be set step by step matches the pressure value (P _NEXT ) to be originally set, no further control is required, so wait until the weld reaches the air knife.

Then, when the welding part arrives at the air knife, it sets the calculated set interval value _NEXT that should be applied to the trailing coil.

Therefore, the air knife interval is rapidly narrowed and the plating deposition amount is drastically reduced to compensate for the response delay of the wiping gas pressure.

The present invention compensates the response delay to the setting of the wiping gas pressure in the air knife interval when the target plating amount is different before and after the welded portion of the preceding coil and the trailing coil, and the plating deposition amount variation (excess caused by the plating deposition amount before and after the weld) is excessive. By minimizing adherence or underattachment, the zinc plating amount is prevented from being excessively attached more than necessary, thereby reducing the zinc consumption.

The foregoing is merely illustrative of the preferred embodiments of the present invention and those skilled in the art to which the present invention pertains may make modifications and changes to the present invention without departing from the spirit and gist of the invention as set forth in the appended claims. It should be recognized.

Claims (4)

A method of controlling the plating amount of a strip by blowing air from an air knife to a strip in which a target plating amount having a relatively low leading coil and a relatively high trailing coil are welded and traveling at a predetermined feed speed through a plating bath, Determining the plating amount of the trailing coil; Increasing the spacing between the trailing coil and the air knife; Increasing blowing pressure for blowing air from the air knife; The interval is the following [formula 1], D = a × CW + b × V + c .............. Derived from (1), Where D is the distance between the strip and the air knife (mm), CW is the target plating amount (g / m ² ), V is the feed rate of the strip (m / min), and a, b and c are constants Is, The blowing pressure is the following [formula 2], CW = e ^a · V ^b · P ^c · D ^d .............. Derived from (2) Where CW is the coating weight (g / m 2), V is the feed rate of the strip (m / min), P is the wiping gas pressure (kgf / cm 2), and D is the distance between the strip and the air knife ( mm), and a, b, c, and d are constants. The method of claim 1, Delay time (t) for reaching the blowing pressure represented by the above [Equation 2] is the following [Equation 3], t = a · ln (P) + b .............. derived from (3), Where t is the required time (sec), P is the wiping gas pressure (kgf / ㎠), a, b is a strip plating amount control method characterized in that the constant. A method of controlling the plating amount of a strip by blowing air from an air knife to a strip in which a target plating amount of relatively high leading coil and a relatively low trailing coil are welded and traveling through a plating bath and traveling at a predetermined feed speed, Determining the plating amount of the trailing coil; Reducing the gap between the trailing coil and the air knife; Increasing blowing pressure for blowing air from the air knife; The interval is the following [formula 1], D = a × CW + b × V + c .............. Derived from (1), Where D is the distance between the strip and the air knife (mm), CW is the target plating amount (g / m ² ), V is the feed rate of the strip (m / min), and a, b and c are constants Is, The blowing pressure is the following [formula 2], CW = e ^a · V ^b · P ^c · D ^d .............. Derived from (2) Where CW is the coating weight (g / m 2), V is the feed rate of the strip (m / min), P is the wiping gas pressure (kgf / cm 2), and D is the distance between the strip and the air knife ( mm), and a, b, c, and d are constants. The method of claim 3, Delay time (t) for reaching the blowing pressure represented by the above [Equation 2] is the following [Equation 3], t = a · ln (P) + b .............. derived from (3), Where t is the required time (sec), P is the wiping gas pressure (kgf / ㎠), a, b is a strip plating amount control method characterized in that the constant.