JP2008231484A - Continuous hot dip galvanization apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous hot dip galvanizing apparatus capable of manufacturing a high-quality plated steel sheet free of a surface defect by performing the galvanizing in a manner as to prevent the adhesion of foreign matters, such as suspended dross in a snout to the surface of the steel sheet. <P>SOLUTION: The continuous hot dip galvanizing apparatus is equipped with guide plates installed so as to hold a steel sheet immersed into the continuous hot dip galvanizing bath through the snout in-between by opening the distance from the steel sheet in the positions above and below inclusive of the plating bath surface and a pump and injection nozzles for discharging molten zinc from the center of the guide plates. The apparatus includes a pump and suction nozzle for sucking the suspended matter on a molten zinc and plating bath at the end of the guide plates. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a continuous hot dip galvanizing apparatus for steel plates, and in particular, maintains a good bath surface state without floating substances such as dross on the plating bath surface in the snout during continuous hot dip galvanizing, and a plated steel sheet caused by the floating substances The present invention relates to a continuous hot dip galvanizing apparatus that can prevent surface defects.

  As shown in FIG. 1, the conventional continuous hot dip galvanizing apparatus advances a steel plate 1 annealed in a continuous annealing furnace from a turn-down roll 5 into a snout 2 connected to the continuous annealing furnace and introduces it into a hot dipping bath 3. And it is comprised so that a hot dipping can be performed by letting the inside of a hot dipping bath pass through the sink roll 4. FIG. Usually, the inside of the snout is shielded from the atmosphere and is kept in a non-oxidizing atmosphere such as nitrogen gas to prevent oxidative contamination of the steel sheet surface. Since this non-oxidizing atmosphere contains a small amount of oxygen and moisture, the oxygen and moisture react with the molten metal on the surface of the plating bath to inevitably generate floating dross. In addition, Fe eluted from the steel sheet into the plating bath reacts with Al added in a small amount to the bath to improve plating adhesion, thereby generating dross. It is known that these dross floats on the surface of the plating bath and adheres to the surface of the steel sheet continuously introduced into the plating bath, causing a plating defect called dross soot.

  As a preventive measure, many techniques for removing floating dross in the snout have been proposed.

  For example, as a plating device that provides both a molten zinc suction port and a supply port in the snout, creates a flow of molten zinc toward the suction port and removes dross, the width of the steel plate in the snout that leads the steel plate to the molten metal bath One metal pump is arranged at each end of the direction, one is a discharge type in the snout, the other is a suction type in the snout, and the metal pump of the discharge type in the snout has a variable discharge port height, and There has been proposed a molten metal plating apparatus in which discharge ports are arranged one by one on the front and back surfaces of the steel plate in the snout in parallel to the steel plate surface and the metal bath surface (see, for example, Patent Document 1). In addition, as a plating device that brings fresh molten metal without dross into contact with the steel sheet introduced into the plating bath, the steel plate immersed in the hot dip galvanizing bath is guided at the upper and lower positions including the plating bath surface. A continuous hot dip galvanizing apparatus has been proposed, characterized in that it is provided with a pump and an injection nozzle for guiding, discharging and overflowing molten zinc between the guide plate and the steel plate. Reference 2).

  In addition, a specific bath flow is forcibly generated in the snout to prevent floats other than the plating metal from drifting on the surface of the steel plate immersed in the plating bath, and the unevenness of the line strip-like gloss on the steel plate surface. As a method of preventing the occurrence, a partition plate is provided in the snout parallel to the steel plate, and a unidirectional bath surface flow parallel to the steel plate surface is forcibly generated from one end of the steel plate toward the other end. A method for producing a hot-dip Zn—Al—Mg-based plated steel sheet having an excellent surface appearance has been proposed (see, for example, Patent Document 3).

  However, in patent document 1, there exists a problem that the floating dross of the peripheral part in a snout adheres to the steel plate surface by the flow from a pump, and in patent document 2, in order to overflow the molten zinc of a plating bath, a big pump capability is provided. There is a problem that is needed. Moreover, in patent document 3, since the bath surface flow is compulsorily produced | generated over the full width of a steel plate, there exists a problem that there exists a possibility that it may contact with the steel plate full width when a flow distance is long and a floating substance exists.

JP 2003-293107 A JP-A-2-11747 JP 2000-64015 A

  In view of the above situation, in the continuous hot dip galvanizing apparatus, the present invention provides a guide plate with a predetermined distance from the steel plate on both the front and back sides of the steel plate introduced into the plating bath, and the steel plate and the guide plate from the center of the guide plate. High quality plating without surface defects by preventing molten foreign matter such as floating dross in the snout from adhering to the steel plate surface and preventing contact between the guide plate and the steel plate by discharging molten zinc during It is an object of the present invention to provide a continuous hot dip galvanizing apparatus capable of producing a steel plate.

  The present inventor has provided a guide plate so as to sandwich the steel plate on both the front and back sides of the steel plate immersed in the plating bath and at the upper and lower positions including the plating bath surface, and freshly melted zinc from the center of the guide plate. By discharging and sucking foreign matter such as molten zinc and dross from both ends of the guide plate, the steel plate immersed in the plating bath can always be in contact with fresh molten zinc, and high quality plating without surface defects The present invention was completed by finding that a steel plate was obtained.

The gist of the present invention is as follows.
(1) In a continuous hot dip galvanizing apparatus for steel sheets heat-annealed in a reducing atmosphere of a continuous annealing furnace, a steel sheet immersed in a hot dip galvanizing bath through a snout is placed at the upper and lower positions including the plating bath surface. A guide plate installed so as to be sandwiched at a distance; a pump and a spray nozzle for discharging molten zinc from the center of the guide plate; and on the molten zinc and plating bath at the end of the guide plate A continuous hot-dip galvanizing apparatus comprising a pump and a suction nozzle for sucking the suspended matter.

  (2) The continuous hot-dip galvanizing apparatus as described in the above item (1), wherein the distance between the steel plate and the guide plate is 30 to 70 mm.

  (3) The continuous hot-dip galvanizing apparatus as described in (1) or (2) above, wherein the guide plate has a ceramic film formed on the surface thereof.

  (4) The continuous hot-dip galvanizing apparatus according to any one of (1) to (3) above, wherein a heating device is installed in the snout.

  (5) The continuous hot-dip galvanizing apparatus according to any one of (1) to (4) above, wherein a pair of rolls for sandwiching the steel sheet is provided in the hot-dip plating bath.

  According to the continuous hot dip galvanizing apparatus of the present invention, a steel plate immersed in a plating bath can always come into contact with fresh hot galvanized material, and foreign matters such as dross floating on the bath surface may adhere to the steel plate surface. Since it can prevent, it becomes possible to manufacture a high quality plated steel plate without a surface defect stably.

Moreover, the heating effect with respect to a guide plate, a plating bath surface, and a floating dross is acquired by heating a snout wall. For this reason, the temperature drop of the guide plate can be prevented, the dross can be prevented from sticking to the guide plate, and the flow state of the floating dross on the surface of the plating bath can be maintained. it can.
Furthermore, since the roll in the bath that sandwiches the steel plate in the bath can be prevented, the vibration of the steel plate and the warp of the steel plate can be prevented, so that the steel plate can be prevented from coming into contact with the guide plate and generating wrinkles.

  Hereinafter, the apparatus of the present invention will be described in detail with reference to the drawings.

  FIG. 2 is a cross-sectional view showing the outline of the continuous hot dip galvanizing apparatus of the present invention, and FIG. 3 shows a plan view of the outline of the continuous hot dip galvanizing apparatus.

  As shown in FIG. 2, the steel sheet 1 is annealed in a continuous annealing furnace, immersed in a plating bath from a snout 2 that leads to a hot dip galvanizing bath, and continuously hot dip galvanized. In addition, this invention apparatus is applicable to hot dip galvanization, zinc alloy plating (Zn-Mg-Al type | system | group, Zn-Mg-Al-Si type | system | group), etc.

  A guide plate 6 is installed in parallel with the steel plate so as to sandwich the steel plate with a gap with the steel plate 1 at the upper and lower positions including the plating bath surface 9 so that dross floating on the plating bath surface does not contact the steel plate. Protected.

The guide plate is preferably a surface having low wettability and reactivity with molten zinc. For example, a steel plate in which a ceramic sprayed coating is formed on the surface of a stainless steel plate or a heat resistant steel plate can be used. Examples of the ceramic include CaO—SiO ₂ and ZrO ₂ —SiO ₂ —CaO ceramics. And as thickness of a ceramic membrane | film | coat, the range of 150-500 micrometers is preferable. This is because if the thickness is less than 150 μm, the life of the film is poor, while if it exceeds 500 μm, the film tends to peel due to the difference in thermal expansion between the substrate of the guide plate and the ceramic.

  Note that an undercoat may be provided under the ceramic film to enhance the adhesion of the film.

  As shown in FIG. 2, the guide plate 6 is installed on the front and back surfaces of the steel plate in parallel with the steel plate so as to sandwich the steel plate 1 with a gap of 100 mm or less, preferably 30 to 70 mm from the steel plate 1 to be plated Is done. The gap should be narrow, but the steel plate has vibration (blur) and warpage. If it is narrow, the steel plate and the guide plate will come into contact with each other and wrinkles will occur on the surface of the steel plate. Therefore, the lower limit is preferably 30 mm. Further, the gap is 100 mm or less due to the structure of the apparatus, but if it is too wide, the flow of the plating bath flow and the floating dross flow in the guide plate is effectively secured unless the capacity of the pump for forming the discharge flow is increased. Therefore, it is preferable to be 70 mm or less.

  Further, the guide plate 6 can be fixedly installed on the snout 2 or the plating bath, and the upper limit of the height protruding on the plating bath surface 9 and the depth immersed under the plating bath surface is particularly limited. It is not necessary to do this, but it is preferable that the thickness is 500 mm or less in view of the structure of the plating apparatus. In addition, the lower limit is preferably 25 mm or more in consideration of the variation of the bath surface that occurs during continuous plating, similarly to the snout immersion depth. And it is preferable that the two guide plates have the same shape, the width is larger than the steel plate width, and the molten zinc discharged from the injection nozzle needs to flow into the suction nozzle. It is.

  As shown in FIG. 3, the molten zinc pumped up by the pump is discharged from the center of the guide plate 6 into the gap between the guide plate and the steel plate by the injection nozzle 10.

  A part of the molten zinc discharged from the injection nozzle flows toward both ends of the steel plate as indicated by arrows along the gap between the guide plate and the steel plate.

  Since suction nozzles 11 connected to a pump are provided at both ends of the guide plate, molten zinc and suspended matter on the plating bath are sucked by this. For this reason, the steel sheet is always brought into contact with fresh molten zinc, and contact with floating matter (foreign matter) such as floating dross is prevented.

  That is, the molten zinc discharged from the center of the guide plate flows compulsorily along the steel plate surface from the center of the steel plate toward the end of the steel plate, and even if there are floating substances, There is only the possibility of contact, and surface defects are less likely to occur. Moreover, since the forced flow distance of molten zinc is half of the width of the steel plate, it can be made to flow more easily than forced flow of the full width of the steel plate.

  FIG. 4 is a diagram illustrating an arrangement relationship between the guide plate and the injection nozzle.

  As shown in FIG. 4A, the injection nozzle 10 is provided with a window 12 in the guide plate 6, and molten zinc is discharged from the window into the gap between the guide plate and the steel plate by the injection nozzle. The discharge direction of molten zinc from the injection nozzle is preferably discharged at an injection angle of at least 30 degrees with respect to the steel plate. This facilitates flowing the molten zinc toward the end of the steel plate.

  Further, instead of providing a window in the guide plate, as shown in FIG. 4 (b), a concave portion is formed by curving the central portion of the guide plate outward, and an injection nozzle 10 is disposed in the concave portion. Alternatively, molten zinc may be discharged.

  The injection nozzle is connected to a pump (metal pump) (not shown) by piping, and the pumped-up molten zinc is discharged from the injection nozzle. A known pump may be used as the pump.

  As shown in FIG. 5, the suction nozzle 11 is provided with suction nozzles 11 at both ends of the guide plate 6, and sucks the molten zinc and floating dross discharged from the injection nozzle 10 in the direction of the arrow. 11 can be sucked. The suction nozzle is provided on the plating bath surface, and the position of the suction nozzle can be moved up and down in accordance with the vertical movement of the plating bath surface.

  Further, the suction nozzle is connected to a pump (metal pump) by piping, and the suction nozzle acts by driving the pump.

  The steel plate introduced into the plating bath is unavoidably vibrated, and the steel plate may be warped. When the steel plate vibrates or warps, wrinkles are generated on the surface of the steel plate in contact with the guide plate installed at a distance from the front and back surfaces of the steel plate. Therefore, as shown in FIG. A steel plate is sandwiched between a pair of in-bath rolls 7 immersed in the steel plate to prevent vibration and warpage of the steel plate. In addition, you may provide the roll which clamps a steel plate on a plating bath surface as needed.

  Furthermore, in the present invention, it is preferable to install a snout wall heating device (heater) 8 to heat the snout wall. When the snout wall is heated, a heating effect is generated from the heated snout wall to the guide plate, the plating bath surface layer, and the floating dross. As a result, the temperature of the guide plate can be prevented from lowering, the solidification of the plating bath surface can be prevented, and the dross floating on the plating bath surface can be held in a softened state to prevent the guide plate and the snout wall from sticking to each other. . Furthermore, since the floating dross is in a softened state, the floating dross can be easily sucked by the suction nozzles provided at both ends of the guide plate.

  Since the temperature of the hot dip galvanizing bath is usually set to about 450 ° C., the heating temperature of the snout wall is preferably adjusted to a temperature 10 to 100 ° C. higher than the temperature of the plating bath. When the temperature is lower than 10 ° C, the effect of supplying heat to the guide plate, the plating bath surface layer and the floating dross is insufficient. On the other hand, when heated to a high temperature range exceeding 100 ° C, the metal vapor from the plating bath solidifies and accumulates. It is not preferable.

  As a heating device for heating the snout wall, an electric resistance heating element, an electromagnetic induction heating device, a gas combustion burner, or the like can be used.

  The temperature control of the heating device that heats the snout wall is performed by feeding back the detection signals of the bath temperature measuring thermometer and the snout type temperature measuring thermometer to the temperature control device of the snout heating device. This can be achieved by controlling the output of the device.

  Using the continuous hot dip galvanizing apparatus shown in FIG. 2, hot dip galvanization is performed on a steel plate having a plate width of 1000 mm and a plate thickness of 0.7 mm at a line speed of 120 m / min and a hot dip galvanizing bath set at a plating bath temperature of 450 ° C. went. In order to prevent vibration of the steel plate, the steel plate was sandwiched between rolls in a bath and passed.

Since the snout depth was 200 mm, a metal pump suction port was provided at a depth of 400 mm below the surface of the molten zinc bath outside the snout, and the molten zinc sucked from this suction port was set at a gap of 50 mm. In the gap between the steel plate and the steel plate, it was discharged from an injection nozzle installed at the center of the guide plate. The discharge rate was 20 × 10 ⁻³ m ³ / min. On the other hand, the bath surface was sucked from suction nozzles provided at both ends of the guide plate. During the plating, the snout wall was heated to 470 ° C. with a heating device.

  When the surface of the plated steel sheet obtained by continuous hot dip galvanizing was investigated, surface defects such as dross wrinkles were not present on the surface, and a high-quality plated steel sheet was obtained.

It is a figure which shows the conventional continuous hot dip galvanizing apparatus. It is sectional drawing which shows the outline | summary of the continuous hot dip galvanizing apparatus of this invention. It is a top view which shows the outline | summary of the continuous hot dip galvanizing apparatus of this invention. It is a figure which shows the arrangement | positioning relationship between a guide plate and an injection nozzle. It is a figure which shows the arrangement | positioning state of an absorption nozzle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Snout 3 Hot-dip galvanizing bath 4 Sink roll 5 Turn-down roll 6 Guide plate 7 Roll in bath 8 Heater 9 Bath surface 10 Injection nozzle 11 Suction nozzle 12 Window 13 Recessed part

Claims (5)

  In a continuous hot dip galvanizing apparatus for steel sheets that have been heat-annealed in a reducing atmosphere in a continuous annealing furnace, the steel sheets that are immersed in the hot dip galvanizing bath through the snout are spaced apart from the steel plate at the upper and lower positions including the plating bath surface. A guide plate installed so as to be sandwiched between, a pump and a spray nozzle for discharging molten zinc from the center of the guide plate, and the floating material on the molten zinc and the plating bath at the end of the guide plate A continuous hot-dip galvanizing apparatus comprising a pump for sucking and a suction nozzle.   The continuous hot-dip galvanizing apparatus according to claim 1, wherein the distance between the steel plate and the guide plate is 30 to 70 mm.   The continuous hot dip galvanizing apparatus according to claim 1 or 2, wherein the guide plate has a ceramic film formed on a surface thereof.   The continuous hot-dip galvanizing apparatus according to claim 1 or 2, wherein a heating device is installed in the snout.   The continuous hot-dip galvanizing apparatus according to any one of claims 1 to 3, wherein a pair of rolls for sandwiching the steel plate is provided in the hot-dip plating bath.

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