JP2794676B2 - A method for controlling the coating weight of hot-dip differential plating. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for applying a thick plating to a steel strip by hot dip plating.
The present invention relates to a method for controlling the amount of plating on the front and back surfaces in a short time as intended.

(Prior art) Conventionally, hot-dip galvanized steel sheets and hot-dip aluminum coated steel sheets have generally been coated with the same amount of coating on the front and back surfaces. However, in this case, excessive corrosion protection is applied to the surface that does not require much corrosion resistance. Therefore, in order to reduce costs and improve meltability, in recent years, there has been an increasing demand for products having a different thickness of plating, which does not require much corrosion resistance and has a smaller amount of plating on the back surface than on the front surface.

As shown in FIG. 6, a pair of gas injection nozzles 2 are arranged opposite to each other above the hot-dip plating bath, and the nozzle gap D is kept constant. The gas is sprayed at different pressures on the front and back surfaces of the rising steel strip 3 so as to vary the amount of coating on the front and back of the steel strip. At this time, the gas injection nozzles 2 on both sides are arranged such that both ends are usually equidistant from the passing position of the steel strip 3. In FIG. 6, 4 is a snout, 5 is a dipping roll, and 6 is a vibration preventing roll of the steel strip 3.

By the way, since the amount of coating on the front and back of the product having a different thickness differs depending on the application and the customer, the gas pressure blown to the front and back of the steel strip must be changed at the time of switching.
It is necessary to change the gas pressure also when switching from plating with the same coating weight on both sides to plating with a different thickness. This pressure change
Conventionally, tension applied to steel strip 3, steel strip 3 and gas injection nozzle 2
If other plating conditions, such as the interval between the plating, are constant, assuming that the coating weight will decrease in response to an increase in pressure, increase the pressure if you want to reduce the coating weight, and increase the pressure if you want to increase the coating weight Was low. In general, the gas pressure is controlled by the pressure in the gas injection nozzle 2.

(Problems to be Solved by the Invention) By the way, if the gas pressures on the front and back sides are both changed at the time of switching, or the gas pressure on either side is changed, the pressure difference between the front and back sides of the steel strip changes. However, when a change occurs in the pressure difference, since the steel strip 3 rising from the plating bath 1 acts only on the tension, the passing position of the steel strip 3 fluctuates, and it turns out that the amount of plating applied on the front and back does not meet the target. did. For example, when reducing the amount of adhesion only on the back side while keeping the amount of adhesion on the front side the same, if only the gas pressure on the back side is increased while the gas pressure on the front side is kept at the pressure before switching, FIG. As shown by the dotted line, the steel strip 3 is pushed to the front side, and the threading position changes. When the passing position changes, the distance from the gas injection nozzle 2 to the steel strip 3 on the front and back also changes, the gas pressure blown on the front and back of the steel strip also changes, and the plating adhesion amount on the front and back also changes. This tendency is remarkably observed when the steel strip 3 is a thin plate. However, conventionally, this tendency was neglected. Therefore, when the steel strip 3 is switched, the product is expected to be obtained until the measurement result of the coating weight is obtained. And a different adhesion amount.

The present invention has been made in view of the above circumstances, and provides an adhesion control method capable of immediately achieving a target plating adhesion even if the gas pressure blown to the front and back of a steel strip is changed.

(Means for Solving the Problems) According to the present invention, each coating weight distribution surface on the front and back of the steel strip according to the gas injection pressure change of each nozzle is calculated in advance, and first, the front and back surfaces of the coating weight distribution surface are calculated. Calculate the deposition distribution curve of each target plating deposition amount, and then calculate the projected intersection points of both distribution curves on the front and back nozzle gas injection pressure surfaces, and further determine the front and back gas injection pressures from the intersection, and find the obtained gas By setting the gas injection pressure on the front surface side and the gas injection pressure on the back surface side as the injection pressure, the target plating adhesion amount can be immediately achieved.

(Function) When gas with different pressures is blown to the front and back of the steel strip under the condition that the nozzle interval on both sides is constant, and the thickness of the steel strip is changed, even if the pressure of the gas blown to the front and back or one of the two sides changes, Assuming that the plate position does not change, the amount of plating changes with a constant curve corresponding to the gas pressure. The reference adhesion curve in FIG. 1 schematically shows the relationship between the adhesion and the gas pressure in such a state, focusing on one surface of the steel strip. That is, when the gas pressure is low, the amount of adhesion does not change much even if the pressure changes, but changes considerably when the gas pressure exceeds a certain level. However, it does not change much as the pressure increases. In this curve, if the thickness difference plating does not have much difference in the adhesion amount between the front and back, the gas pressure blown to the front and back of the steel strip is set to the part where the change in the adhesion amount is large. If the amount is small, the pressure on the back side is set to a portion where the change in the amount of adhesion is small due to the gas pressure as shown in the figure.

However, for example, when the gas pressure on the back side is changed while the gas pressure on the front side is kept constant, the passing position of the steel strip is actually changed due to the effect, and the interval between the gas injection nozzle is also changed. I will. When the interval between the steel strip and the gas injection nozzle changes in this way, even if the blowing gas pressure is constant,
Since the wiping force of the gas pressure applied to the steel strip changes depending on the interval, the amount of plating changes.

Even if the gas pressure on the front side of the steel strip is kept constant as described above, if the gas pressure on the back side is changed, the change affects the amount of adhesion on the front side. Simply changing the gas pressure on the back side does not provide a target-differential-thickness plated product.

The change in the amount of deposition on the front side due to the change in gas pressure on the back side is such that when the gas pressure on the back side is increased, the steel strip approaches the gas injection nozzle arranged on the front side, so that the front side deposition amount is As shown in the reduced adhesion curve of FIG.
Conversely, when the backside gas pressure is lowered, the gas is separated from the front side gas injection nozzle, so that the frontside adhesion amount increases as shown by the increase adhesion amount curve. The surface adhesion amount of increase or decrease, so varies in response to changes in the backside gas pressure, when changing the backside gas pressure in a state where the surface-side gas pressure constant P ₁ in Figure 2, the rear surface lower portion side gas pressure is from the surface side gas pressure P _1, since the steel strip separated from the gas jet nozzle of the surface,
The surface-side adhesion amount becomes the increase adhesion amount curve in FIG. 1, and the surface-side adhesion amount becomes larger than the reference adhesion amount. For example, when the back side gas pressure is P ₀ , the reference adhesion amount that should be W ₀ increases to W ₁ and increases by W ₁ −W ₀ . On the other hand, higher portion than the surface side gas pressure P ₁ is the back side gas pressure, so close to the gas injection nozzle surface side, it decreased adhesion amount curve, surface coating weight is less than the reference deposition amount. For example, the backside gas pressure P ₂ in Figure 2, which becomes W ₀ at the reference deposition amount is reduced and W _2, decreases by W ₀ -W _2. This variation of the surface-side adhesion amount with respect to the reference adhesion amount is established regardless of the surface-side gas pressure.

Therefore, when the back side gas pressure is lower than the front side gas pressure, the front side gas pressure is increased to make the front side adhesion amount equal to the reference adhesion amount, and conversely, the back side gas pressure is increased. When the pressure is higher than the pressure, it is necessary to lower the gas pressure on the surface side in order to make the surface side deposition amount the same as the reference deposition amount.

FIG. 3 generally shows how much the front side gas pressure must be changed in order to make the front side adhesion amount the reference adhesion amount when the back side gas pressure is changed.

That is, in FIG. 3, the horizontal axis X indicates the front side gas pressure, the vertical axis Y indicates the back side gas pressure, and the vertical axis Z indicates the surface plating adhesion amount. The distribution of the amount of side adhesion is shown three-dimensionally.
When the gas pressure on the front and back is equal to _Pn , the adhesion amount on the front and back becomes uniform. However, changing the backside gas pressure and lower than P _n, since the back side gas pressure in the second figure corresponds to the case lower than the surface side gas pressure, surface adhesion amount is more than the reference coating weight W _n . Therefore, equal adhesion amount rays surface adhesion amount becomes equal to the reference deposition amount W _n is shifted in the direction of the surface side gas pressure is high, if the backside gas pressure was low as P ₅ [Delta] P _x1
Only the surface side gas pressure must be increased. on the other hand,
If the back side gas pressure is higher than _Pn, it corresponds to the case where the back side gas pressure is higher than the front side gas pressure in FIG.
Surface coating weight is less than the reference coating weight W _n. Therefore,
In this case, an equal coating weight line surface adhesion amount becomes equal to the reference deposition amount W _n is shifted in the direction of the surface side gas pressure is low,
The backside gas pressure must be lowered surface-side gas pressure only [Delta] P _x2 is when high as P _6. From these facts, a line having the same amount of adhesion on the surface side is a curved line with respect to a straight reference adhesion amount line (dashed-dotted line), assuming that the steel strip has not moved. Such a curve
If the back side gas pressure is changed variously, it is created corresponding to it.If the curve corresponding to the back side gas pressure change is created innumerably, it becomes a curved surface and the surface side adhesion amount distribution curved surface becomes can get.

Although the above description has been made with a focus on the surface-side adhesion amount when the back-side gas pressure is changed, the same applies to the back-side adhesion amount when the front-side gas pressure is changed. If the amount of backside adhesion is changed to a certain amount, the isotherm line becomes a curved curve as shown in FIG. 4, and if the curve corresponding to the front side gas pressure change is created, Thus, a curved surface with a distribution of the amount of adhesion on the back side is obtained.

Superposed so that the surface-side adhesion amount distribution curved surface and the back side coating weight distribution curved surface obtained as above horizontal axis X, vertical axis Y coincide, such as the amount of deposition in Figure 3 is W _n When the amount deposited in adhesion amount line and Figure 4 projects an equal coating weight line to be W _m to the plane of the horizontal axis X- vertical axis Y, the projection line of the two such as adhesion amount lines, points as Figure 5 Cross at C.

Since the front-side isoadhesion line and the back-side isoadhesion line are established regardless of the surface-side gas pressure and the back-side gas pressure, respectively, FIG. Projection lines can be drawn. The projection line intersection of the number of equi-adhesion lines on the front side and the back side obtained in this way, if the gas pressure on the front and back is set to the pressure corresponding to the intersection, the plating adhesion on the front and back intersect. It means that it is the one of the equi-adhesion curve. Therefore, if this is used, the gas pressures on the front and back sides that correspond to the adhesion amounts can be set by previously determining the adhesion amounts on the front and back. For example, in FIG. 5, when it is desired to set the front-side adhesion amount to W _n and the back-side adhesion amount to W _m , follow an equi-adhesion amount line of W _n and W _m to find a point C where the two intersect. Determine the gas pressures on the front and back corresponding to
the _x, can be the front and back by setting the backside gas pressure to P _y in the amount of deposition of target.

The line having the same amount of adhesion on the front side or the back side as shown in Fig. 4 differs depending on other plating conditions such as the thickness of the steel strip and the passing speed. If it is stored in the control device, the front and back gas pressures can be easily set.

By the way, as described with reference to FIG. 1, when the amount of adhesion on the front surface side or the back surface side is extremely reduced, the gas pressure is set to a high pressure. As can be seen, even if the gas pressure is slightly changed on both the front side and the back side, the backside adhesion amount does not change and overlaps the reference adhesion amount line. Therefore, the backside gas pressure can be increased or decreased in accordance with the increase or decrease of the front surface gas pressure, and the passing plate position can be kept constant. This is effective in preventing the steel strip from vibrating when the threading position is generally changed.

(Example) In the case of hot-dip galvanizing a cold-rolled steel strip with a thickness of 0.27 mm while passing it through each gas injection nozzle-steel strip interval of 12 mm at the front and back at a speed of 120 m / min, etc., as shown in FIG. Compared with the conventional method in which the thickness curve is created, the thickness difference plating is performed by setting the gas pressure on the front and back sides using it, and the gas pressure on the back side is not changed but the gas pressure on the back side is changed. . Table 1 shows the results.

(Effects of the Invention) As described above, according to the method of the present invention, the target adhesion amount can be immediately obtained when switching from double-sided equivalent amount plating to differential thickness plating or when changing the front and back adhesion amount in differential thickness plating. Quality and yield are improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the change in the amount of plating applied when the passing position of the steel strip does not change and when it changes. FIG. 2 is a graph showing a variation in the amount of deposition on the front side when the gas pressure on the rear side is changed while the gas pressure on the front side is kept constant. FIG. 3 is a graph showing an equi-adhesion amount line when the gas pressure on the front surface side and the gas pressure on the rear surface side is changed to a certain value. FIG. 4 is a graph showing an equi-adhesion amount line when the gas pressure on the front surface side and the gas pressure on the rear surface side is changed and the adhesion amount on the back surface becomes a constant value. FIG. 5 is a graph showing the relationship between the front-side gas pressure and the front-side equi-adhesion line and the relationship between the back-side gas pressure and the rear-side equi-adhesion line. FIG. 6 shows a thickness difference plating method using a gas injection nozzle. 1 ... Hot-dip plating bath, 2 ... Gas injection nozzle, 3 ... Steel strip, 4 ... Snout, 5 ... Dipping roll, 6 ... Anti-vibration roll, D ... Nozzle interval,

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhiro Majima 5 Ishizu Nishimachi, Sakai City, Osaka Nisshin Steel Co., Ltd. Inside Hanshin Works (72) Inventor Miki Higashino 631-1, Kameido, Koto-ku, Tokyo Inside Seiko Electronic Industry Co., Ltd. (56) References JP-A-61-143573 (JP, A) JP-B-56-5823 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 2/00 -2/40

Claims (2)

(57) [Claims] A gas injection nozzle is disposed above a hot-dip plating bath, and gas having different pressures is blown onto the front and back of the steel strip rising from the plating bath with the nozzle interval kept constant, thereby plating the front and back of the steel strip. When varying the amount of adhesion,
Each plating weight distribution curve on the front and back of the steel strip according to the gas injection pressure change of each nozzle on the front and back is calculated in advance, and first, the weight distribution curve of each target plating weight on the front and back on the plating weight distribution curve is obtained. Next, the projected intersection of both distribution curves on the front and back nozzle gas injection pressure surfaces is determined, and the front and back gas injection pressures are determined from the intersection, and the front and back gas injection pressures are set to the determined gas injection pressure. A method for controlling the coating amount of hot differential thickness plating. 2. The plating method according to claim 1, wherein the plating amount on the lower side of the distribution curve of the coating amount hardly changes even if the gas injection pressure is changed, in accordance with the increase or decrease of the gas injection pressure on the front side. 2. The method according to claim 1, wherein the gas jet pressure on the side is increased or decreased to keep the rising and passing position of the steel strip constant.