JP4547818B2 - Method for controlling the coating amount of hot dip galvanized steel sheet - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling the amount of coating on a hot-dip plated steel sheet when hot metal plating is applied to a continuously running steel strip.
[0002]
[Prior art]
In continuous hot dip plating, the steel strip is continuously pretreated and kept at a high temperature with a predetermined heating pattern, then passed through a plating bath to control the amount of plating, and then cooled to room temperature with a predetermined cooling pattern. This is a typical method.
[0003]
Gas wiping with air is generally performed as a method for controlling the amount of plating adhesion. From the roll in the bath to the top roll, gas wiping must be performed between the roll in the bath and the top roll in the molten metal pot (hot dip plating tank) to solidify the plating surface to a predetermined coating amount. The distance is very long. For this reason, there is a problem that the plating adhesion amount does not fall within the set value unless the predetermined plating adhesion amount control range is increased. In particular, since the hot dip plated steel sheet is welded, there is a problem in corrosion resistance when a large amount of plating is applied, and poor welding occurs when the amount of plating is small. Or, if the plating adhesion amount distribution is made in the plate width direction, there are many problems such as generation of plating cracks during the processing of the steel plate.
[0004]
Many methods have been studied for these problems. Japanese Patent Laid-Open No. 2-265854 discloses a method of controlling the position of a steel strip by moving the position of a roll in a bath called a support roll or a sink roll when the plate shape is not flat but poor. A method is shown in which the amount of plating deposited in the width direction of the steel strip is measured above the wiping nozzle, and the roll position in the bath is controlled so that the data and set value are minimized.
[0005]
Japanese Patent Laid-Open No. 8-199323 discloses a method of measuring the amount of plating adhesion in the plate width direction of a steel strip above a gas wiping nozzle and controlling the plate shape with an electromagnet to make the plating adhesion amount uniform. ing.
[0006]
Further, Japanese Patent Laid-Open No. 6-116696 discloses a method of measuring the amount of plating adhesion above the gas wiping nozzle and independently controlling the pressure of the gas wiping nozzle on the left and right.
[0007]
[Problems to be solved by the invention]
However, the method of changing the position of the roll in the bath as disclosed in JP-A-2-265854 is effective with respect to a simple plate shape defect, but in a steel strip that is usually manufactured, the length of the middle, the level of the ear, and the composite Since some plates have an asymmetric shape such as extension, the amount of plating adhesion cannot be controlled effectively.
[0008]
Although the method of controlling the shape with an electromagnet as disclosed in Japanese Patent Application Laid-Open No. 8-199323 seems to be an effective method at first glance, the length of the steel strip traveling direction is medium in the case of a poorly shaped steel strip, for example, an elongated plate shape. Compared with the extended plate width center and the plate edge, the plate width center is longer, and on the contrary, the plate end is longer than the plate width center, so out-of-plane deformation occurs in these steel strips. is doing. Therefore, even if the position of the steel strip can be changed with an electromagnet, it is difficult to straighten the steel strip that is deformed out of plane, and even if the amount of plating can be flattened somewhat, It is difficult to keep the amount of plating adhesion constant.
[0009]
Furthermore, as in JP-A-6-116696, the method of controlling the position of gas wiping independently on the left and right side is effective only for a steel strip having a simple shape defect.
[0010]
In recent years, the line speed has been increased along with the improvement of the manufacturing technology, but there is no method for stopping the large amount of top dross generated with the increase in speed. Many methods for removing the top dross have been proposed, but the only method for reducing the generation of top dross is to reduce the generation of zinc oxide by nitrogen gas wiping. However, nitrogen gas wiping may cause the operator to run out of oxygen, and there are many problems such as complicated equipment when using a nitrogen seal box, etc. Few.
[0011]
The object of the present invention is to solve the above-mentioned problems of the prior art, and in order to produce a hot dip plated steel sheet having a uniform coating coverage even if a poorly shaped steel strip is passed, The object is to provide a method for controlling the amount of adhesion.
[0012]
[Means for Solving the Problems]
That is, the method for controlling the coating amount of the hot dip plated steel sheet of the present invention has the following characteristics.
[0013]
(1) A gas for wiping the molten metal adhering to the surface of the steel strip pulled up from the molten metal pot to a predetermined plating adhesion amount by air blowing above the molten metal pot when producing a continuous molten plated steel sheet Above the wiping nozzle , the gas wiping nozzle, a DC magnetic field application device for reducing vibration of the steel strip by electromagnetic force , a position detector for detecting the distance from the steel strip, and below the gas wiping nozzle Detects the distance from the steel strip using a position detector using a continuous hot dipping plating system equipped with air cushions to reduce vibration of the steel strip by air blowing , arranged in a staggered manner on the front and back of the steel strip in the running direction , by controlling the air supply flow rate to the magnetic field strength and the air cushion DC magnetic field from the detected value, and controlling the steel strip position, and the top to control the coating weight Coating weight control method for hot dip plated steel sheet, characterized in that to reduce the occurrence of loss.
[0016]
(2) The method for controlling the coating amount of the hot-dip plated steel sheet according to (1) , wherein the air cushion and the DC magnetic field applying device are divided into three or more in the sheet width direction of the steel strip to be passed.
[0017]
(3) The distance between the gas wiping nozzle and the air cushion and the distance between the gas wiping nozzle and the DC magnetic field applying device are within three times the maximum plate width of the steel strip to be passed (1) Or the plating adhesion amount control method of the hot dip galvanized steel sheet as described in (2) .
[0020]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory view showing an embodiment of a continuous hot dipping apparatus used for carrying out the present invention and a plating adhesion amount control method for hot dipped steel sheets of the present invention.
[0021]
The continuous hot dipping equipment shown in FIG. 1 includes a steel strip 4 that is guided and pulled up by a support roll 2 in the molten metal in the molten metal pot 1, and a steel that is pulled up from the molten metal pot 1 above the molten metal pot 1. A gas wiping nozzle 3 for wiping the molten metal adhering to the surface of the band 4 to a predetermined coating amount by air blowing, and the fineness of the steel band 4 by electromagnetic force installed above the gas wiping nozzle 3 The direct current magnetic field application device 7 for reducing the vibration, the position detector 6 for detecting the distance between the steel strip 4 and the steel strip 4 by the air blowing installed below the gas wiping nozzle 3. And an air cushion 5 for reducing frequency vibration.
[0022]
The steel strip 4 is guided to the support roll 2 in the molten metal in the molten metal pot 1 and pulled up. The pulled steel strip 4 is adjusted to a predetermined plating adhesion amount by the gas wiping nozzle 3 and guided to the cooling zone. At this time, the amount of deformation is minimized by performing out-of-plane deformation within the elastic range by arranging the air cushions 5 in a staggered manner so that the defective shape of the steel strip 4 is stabilized before gas wiping. be able to. Further, in order to set the steel strip 4 to a predetermined position of the gas wiping nozzle 3, a position detector 6 by a laser distance meter or a vortex type distance meter is installed above the gas wiping nozzle 3 so that the distance to the steel strip 4 is reached. Is detected and fed back to the pair of DC magnetic field applying devices 7 with the steel strip 4 interposed therebetween, and the plate passing place of the steel strip 4 is adjusted by electromagnetic force. Thereby, the steel strip 4 can drive | work a predetermined plate-passing place.
[0023]
FIG. 4 shows the relationship between the distance between the gas wiping nozzle and the steel strip and the amount of plating applied when a certain nozzle is used. In the range called the potential core of the gas wiping nozzle, there is little fluctuation in the amount of plating, and as the distance between the gas wiping nozzle and the steel strip increases, the amount of plating tends to increase. That is, it increases or decreases depending on the flow rate. The larger the gas flow rate, the higher the wiping gas pressure and the smaller the amount of plating attached. Therefore, in order to obtain a uniform coating amount in the plate width direction of the steel strip to be passed, when the wiping gas pressure is operated at a constant level, the steel strip is passed through the distance between the predetermined gas wiping nozzle and the steel strip. It is desirable to adjust so as to.
[0024]
FIG. 1 shows a control procedure. First, when the plate shape defect of the steel strip 4 has a displacement amount of about 20 mm at maximum in the plate width direction, the amount of out-of-plane deformation in the plate width direction is increased by increasing the pressure of the air cushion 5. Is confirmed by the position detector 6 so as to be within 1 mm, and the set value of the air cushion 5 is determined. Next, since the steel strip 4 between the gas wiping nozzle 3 and the gas wiping nozzle 3 is deformed in the traveling direction by the air cushion 5, it is confirmed by the position detector 6 and the current of the DC electromagnetic application device 7 is controlled. Make sure the steel strip is in place.
[0025]
In order to suppress the shape defect of the steel strip 4 having a complicated shape first, the out-of-plane deformation within the elastic deformation is generated by using the air cushion 5 so as to minimize the defect of the plate shape. The flow rate supplied to the air cushion 5 is controlled. Next, in order to detect the position in the plate width direction of the steel strip 4 whose shape has become stable, the distance from the steel strip 4 is detected by a position detector 6 using a laser distance meter or a vortex-type distance meter. Further, based on the data, the current is controlled so that the electromagnet of the DC electromagnetic application device 7 travels the steel strip 4 at a predetermined position. Finally, the distance between the gas wiping nozzle 3 and the steel strip 4 is detected so that the plating adhesion amount becomes a predetermined amount, and is set to a predetermined gas supply pressure.
[0026]
Further, the control by the air cushion 5 and the DC magnetic field applying device 7 is the same as in the prior art if it is performed uniformly in the plate width direction of the steel strip 4 to be passed, and a sufficient effect cannot be expected. Therefore, it is preferable that the air cushion 5 and the DC magnetic field applying device 7 are divided into three at the center and both ends at the minimum in the plate width direction of the steel strip 4 to be passed and controlled. The distance between the air cushion 5 and the gas wiping nozzle 3 of the DC magnetic field application device 7 cannot be expected to be sufficiently effective when the control position and the gas wiping position are too far apart. It is preferable to install at a distance within 3 times. Even more preferably, it is good to install it at a distance within the maximum plate width equivalent of the steel strip 4 to pass through in order to perform the action stably.
[0027]
Further, by installing the air cushion 5 below the gas wiping nozzle 3, the top generated from the gas wiping nozzle 3 to block the gas flow colliding with the upper surface of the molten metal pot 1 from the gas wiping nozzle 3. Dross can be minimized. Since the gas flow from the air cushion 5 is slower and has a lower flow rate than the gas wiping, the amount of top dross generated is minimized.
[0028]
By performing these controls, not only can the plate width direction of the steel strip 4 through which the front and back plating amount is passed be made uniform, but also the difference in thickness of the plating adhesion on the front and back surfaces can stabilize the plating adhesion amount, In addition, it is possible to manufacture hot-dip plated steel sheets while reducing the occurrence of top dross.
[0029]
FIG. 2 is an explanatory view showing another embodiment of a continuous hot dipping equipment used for carrying out the present invention and a plating adhesion amount control method for hot dipped steel sheets according to the present invention.
[0030]
The continuous hot dipping equipment shown in FIG. 2 includes a steel strip 4 that is guided and pulled up by a support roll 2 in the molten metal in the molten metal pot 1, and a steel that is pulled up from the molten metal pot 1 above the molten metal pot 1. A gas wiping nozzle 3 for wiping the molten metal adhering to the surface of the band 4 to a predetermined coating amount by air blowing, and the fineness of the steel band 4 by electromagnetic force installed above the gas wiping nozzle 3 DC magnetic field application device 7 for reducing vibrations, a position detector 6 for detecting the distance from the steel strip 4, and an air cushion for reducing low-frequency vibrations of the steel strip 4 by air blowing 5.
[0031]
The embodiment shown in FIG. 2 is a preferred form in which one of the two pairs of DC magnetic field applying devices 7 is installed inside the air cushion 5 to save space. Similarly, the position detector 6 is installed in the lowermost air cushion 5 to save space.
[0032]
The steel strip 4 is guided to the support roll 2 in the molten metal in the molten metal pot 1 and pulled up. The pulled steel strip 4 is adjusted to a predetermined plating adhesion amount by the gas wiping nozzle 3 and guided to the cooling zone. At this time, in order to stabilize the shape of the steel strip 4, it is possible to minimize the amount of deformation by performing out-of-plane deformation within the elastic range by arranging the air cushions 5 in a staggered manner with respect to the defective shape. it can. Further, in order to set the steel strip 4 to a predetermined position of the gas wiping nozzle 3, a position detector 6 by a laser distance meter or a vortex type distance meter is installed in the lowermost air cushion 5 to connect the steel strip 4 with the steel strip 4. The distance is detected, and the detected value is fed back to two pairs of DC magnetic field applying devices 7 with the steel strip 4 sandwiched between the upper and lower parts of the air cushion 5 in which the position detector 6 is incorporated. Adjust the plate 4 location. Thereby, the steel strip 4 can drive | work a predetermined plate-passing place.
[0033]
The relationship between the distance between the gas wiping nozzle and the steel strip shown in FIG. 4 and the amount of adhesion of plating is the same in this embodiment. In the embodiment of FIG. 2, the control procedure and the operations and actions of the air cushion 5 and the DC electromagnetic application device 7 are the same as those of the embodiment shown in FIG.
[0034]
FIG. 3 is an explanatory view showing another embodiment of a continuous hot dipping equipment used for carrying out the present invention and a plating adhesion amount control method for hot dipped steel sheets of the present invention.
[0035]
The continuous hot dipping apparatus shown in FIG. 3 includes a pair of DC magnetic field application devices 7 with the steel strip 4 interposed therebetween, and a pair of DC magnetic fields with the air cushion 5, the position detector 6 and the steel strip 4 interposed therebetween. 2 is the same as the continuous hot dipping apparatus shown in FIG. 2 except that the applying device 7 is installed separately. In some cases, the position detector 6 and the direct-current magnetic field applying device 7 are exposed to the atmosphere, so that it is necessary to attach a cooling device (not shown) immediately above the molten metal pot 1, but the operation principle is the same. It goes without saying that the position detector 6 and the DC magnetic field applying device 7 can be made compact by installing them in the same casing.
[0036]
The relationship between the distance between the gas wiping nozzle and the steel strip shown in FIG. 4 and the amount of adhesion of plating is the same in this embodiment. In the embodiment of FIG. 3, the control procedure and the operations and actions of the air cushion 5 and the DC electromagnetic application device 7 are the same as those of the embodiment shown in FIG.
[0037]
【Example】
Example 1
The method for controlling the coating amount of the hot dip galvanized steel sheet according to the present invention was carried out using the continuous hot dip plating equipment shown in FIG. In this example, three air cushions having a traveling direction of 50 mm divided into three in the plate width direction of the steel strip to be passed through, one position detector using a vortex rangefinder, and a pair of DC magnetic field application devices were installed. As a result, by setting the pressure of the air cushion to 200 mmAq, it is possible to stabilize the shape of the 0.8 mm-thick steel strip, and by controlling the steel strip to the center of gas wiping with electromagnetic force, plating The amount of adhesion was up to + 100% in the conventional method with respect to the target, but decreased to within + 20% in the method of the present invention.
[0038]
By installing this air cushion, the pot yield (plating adhesion amount / supply amount) in the conventional method up to 85% is increased to 90% in the method of the present invention, and the top dross is reduced. It was confirmed that there was an effect.
[0040]
【The invention's effect】
As described above, according to the present invention, in the production of a continuous hot dip galvanized steel sheet, a hot dip galvanized steel sheet having a uniform coating amount and a stable steel strip shape can be obtained even if a poorly shaped steel strip is passed through. In order to manufacture, the method of controlling the plating adhesion amount of a hot dipped steel plate can be provided.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an embodiment of a continuous hot dipping equipment used in the practice of the present invention and a method for controlling the amount of coating on a hot dip plated steel sheet of the present invention. FIG. 2 is a continuous view used in the practice of the present invention. Explanatory drawing which shows other embodiment of the hot-dip plating equipment and the plating adhesion amount control method of the hot-dip plated steel sheet of the present invention. FIG. 3 shows the continuous hot-dip plating equipment used for carrying out the present invention and the hot-dip plated steel sheet of the present invention. FIG. 4 is an explanatory diagram showing another embodiment of the adhesion amount control method. FIG. 4 is an explanatory diagram showing the relationship between the distance between the gas wiping nozzle and the steel strip and the plating adhesion amount in the plating adhesion amount control method of the hot dip plated steel sheet of the present invention. Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Molten metal pot 2 Support roll 3 Gas wiping nozzle 4 Steel strip 5 Air cushion 6 Position detector 7 DC magnetic field application apparatus

Claims (3)

A gas wiping nozzle for wiping the molten metal adhering to the surface of the steel strip pulled up from the molten metal pot to a predetermined plating adhesion amount by air blowing above the molten metal pot when producing a continuous molten plated steel sheet A DC magnetic field applying device for reducing vibration of the steel strip by electromagnetic force , a position detector for detecting the distance from the steel strip, and a traveling direction below the gas wiping nozzle Using a continuous hot dipping plating equipment equipped with an air cushion for reducing vibration of the steel strip by air blowing , which is arranged in a staggered manner on the front and back of the steel strip, the distance from the steel strip is detected by a position detector, by controlling the air supply flow rate to the magnetic field strength and the air cushion DC magnetic field from the detected value, and controlling the steel strip position, controls the coating weight to and top dross Coating weight control method for hot dip plated steel sheet, characterized in that to reduce the occurrence. The method for controlling the coating amount of hot-dip plated steel sheets according to claim 1 , wherein the air cushion and the DC magnetic field applying device are divided into three or more in the sheet width direction of the steel strip to be passed. Distance between the distance and the gas wiping nozzle and the gas wiping nozzle and the air cushion and the DC magnetic field application apparatus, according to claim 1 or 2, characterized in that within 3 times the maximum strip width of the strip to be Tsuban Method for controlling the coating amount of hot-dip galvanized steel sheets.

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