JP4894326B2 - Molten metal plating equipment for steel sheet - Google Patents

Description

  The present invention relates to a molten metal plating apparatus for steel sheets, and more particularly to a molten metal plating apparatus for steel sheets provided with a premelt pot for supplying molten metal bath components to a molten metal tank for plating molten metal.

  A general method for producing a molten metal (for example, Zn, Al, Mn, Pb and alloys thereof) plated steel sheet is as follows. That is, after the surface of the cold-rolled steel sheet is cleaned in a pretreatment step, the steel sheet is heat-annealed in a non-oxidizing or reducing atmosphere, and then cooled without being oxidized to a temperature suitable for plating, and then a plating bath Soak continuously. Excess molten metal adhering to the surface of the steel sheet in the bath is removed by an adhesion amount adjusting device such as gas wiping to adjust the adhesion amount and cooling.

  And manufacture of this plated steel plate is normally performed by adding another kind of metal in the molten metal which is a main component. For example, in a typical product, a small amount of Al is added to molten Zn which is a main component in molten zinc plating (including alloyed molten zinc plated steel sheet), and in the molten aluminum plating, molten Al which is the main component. A small amount of Si is generally added therein. The reason for the addition is to suppress the growth of a hard and brittle alloy layer at the interface between the molten metal and the base steel sheet and to improve the plating adhesion. However, in order to moderately suppress the growth of the alloy layer, the amount added must be controlled within an appropriate range.

  In the case of a hot-dip galvanized steel sheet, the added Al reacts with the steel sheet preferentially over Zn in the hot-dip zinc bath, and an Al-enriched layer (Fe-Al intermetallic compound) is formed at the interface between the plated layer and the base steel sheet. ) Is suppressed, thereby making it possible to manufacture an alloyed hot-dip galvanized steel sheet with good adhesion. In order to develop good adhesion, it is necessary to control the Al concentration in the molten zinc bath within a predetermined concentration range.

  The hot dip galvanizing bath is not only reduced by adhering to the steel plate and taken out of the galvanizing tank, but also decreases due to the removal of dross out of the galvanizing tank. is there. Since Al is consumed for (1) preferential generation of an Al-enriched layer, (2) generation of dross, and the like, the reduction rate is increased. Therefore, as a replenishment method, conventionally, a Zn ingot containing a target or higher concentration of Al and a pure Zn ingot are put into the plating bath.

  However, in the Al replenishment method using the ingot, it takes time until the ingot put into the plating bath dissolves and diffuses in the plating bath and becomes a uniform plating bath, and all the ingot dissolves and diffuses. Since the Al concentration in the bath continues to decrease until the next ingot is charged, there is a problem that the Al concentration in the plating bath varies greatly corresponding to the pitch at which the ingot is charged. That is, when the Al concentration in the plating bath fluctuates as described above, the generation of the Al-enriched layer described above becomes non-uniform and stable plating quality cannot be obtained.

  Therefore, in order to solve such a problem, Patent Document 1 uses a plurality of premelt pots that melt and hold the replenishment components in advance, and from the premelt pot with respect to the required concentration of replenishment components and the reduction amount of the plating bath. Using at least one pre-melt pot in which the components are replenished in the plating tank, or in which the replenishment components are previously melted and held, and at least one hopper containing a metal lump or metal powder of the replenishment components A component replenishment method for a plating bath is disclosed, wherein the component is replenished to the plating tank from the premelt pot and hopper so as to correspond to the concentration of the replenishing component and the reduction amount of the plating bath.

  Further, Patent Document 2 uses a plurality of pre-melt pots or at least one hopper in which the replenishing components are previously melted and held, and in the plating bath so as to correspond to the necessary concentration of the replenishing components and the reduction amount of the plating bath. A plating bath characterized in that a component is supplied from the premelt pot or the premelt pot and a hopper to the mixing tank provided, and the component is replenished by spraying into the plating bath from the mixing tank using an injection nozzle. Discloses a method of supplementing ingredients.

  However, in the methods of Patent Document 1 and Patent Document 2, the concentration of the components varies in the vicinity of the supply place for supplying the replenishment component to the plating bath and other places, and the concentration distribution in the plating tank becomes uneven, There was a problem that the plating quality was uneven throughout the steel plate.

  Further, as a method for supplying components to the plating bath, there is a method of supplying molten plated metal from the pre-melt pot or mixing tank disclosed in Patent Document 3 to the entire plate width direction of the portion where the plated steel plate enters the plating bath. Although it is disclosed, defects such as ash and scratches occur due to fluctuations in the intruding wavefront due to the direct supply of molten metal to the part into which the steel sheet enters.

There are many prior arts related to the pre-melt pot associated with the plating bath, but many of them disclose methods for adjusting the concentration of components in the pre-melt pot when supplying molten metal from the pre-melt pot to the plating bath. However, in view of the arrangement of the in-bath facilities in the plating bath, there has been no current situation regarding an optimum molten metal supply device.
Japanese Patent Laid-Open No. 1-165553 JP-A-2-104649 JP 7-238358 A

  The present invention solves the problems of the prior art described above, and when supplying molten metal from a premelt pot to a plating tank, a product having excellent plating quality can be obtained without segregating the components of the molten metal. It aims at providing the molten metal plating apparatus of a steel plate.

In order to achieve the above-mentioned object, the present inventors have intensively studied a conventional plating bath facility.
As a result, we noticed that the flow in the plating tank is very important to make the concentration of the components uniform, and as a countermeasure against this, properly arranging the connecting pipe for supplying molten metal from the premelt pot to the plating tank. Inspired. The present invention is based on this idea.

  The gist of the present invention for solving the above problems is as follows.

  (1) A molten plating bath for holding a molten metal bath containing a plurality of components, one or more primet pots for supplying molten metal bath components to the molten plating bath, and melting in the molten plating bath In a molten metal plating apparatus for a steel plate comprising a connecting pipe for communicating a metal bath and molten metal in each of the pre-melt pots, an opening for leading the molten metal bath component of the connecting pipe into the molten metal bath in the molten plating tank The steel sheet molten metal plating apparatus is characterized in that the section is installed at an interval so as to be equal to or greater than the maximum steel sheet width on the steel sheet intrusion portion side of the molten plating tank.

  (2) An opening for leading the molten metal bath component of the connecting pipe into the molten metal bath in the molten plating bath is installed at a position deeper than the snout immersion depth in the molten metal bath (1). ) Steel plate molten metal plating equipment.

  (3) The flow of the molten metal bath component derived from the opening is regulated between the opening for extracting the molten metal bath component of the connecting pipe into the molten metal bath of the molten plating tank, and the snout and the steel plate. (1) or (2) a molten metal plating apparatus for a steel plate, wherein a baffle plate is installed.

  According to the present invention, the opening for deriving the molten metal bath component into the molten metal bath in the molten plating bath is installed at an interval so as to be equal to or greater than the maximum width of the steel plate on the steel plate intrusion portion side of the molten metal bath. Therefore, it is possible to prevent the problem of non-uniformity of the molten metal component concentration in the molten plating tank and fluctuation of the molten metal bath surface that occurs when the molten metal bath is supplied from the premelt pot to the molten plating tank. The plating quality can be stabilized, and the occurrence of defects such as ash and scratches can be prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing a main part of a molten metal plating apparatus for a steel sheet according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AA in FIG. FIG. 3 is a schematic view for explaining the structure of the inner portion of the connecting pipe in the molten plating tank, and is a cross-sectional view taken along the line BB in FIG. 1 to 3, 1 is a molten metal bath, 2 is a molten metal bath, 3 is a snout, 4 is a sink roll, 5 is a premelt pot, 6 is a connecting pipe, 7 is a baffle plate, 8 is a metal ingot, 9 Are strips (steel plates), 11 and 12 are pre-melt pot 5 side openings and molten metal tank 1 side openings of the connecting pipe 6, respectively. The metal ingot 8 is held up and down by a lifting tool of a metal ingot throwing device (not shown).

  The molten plating tank 1 holds the molten metal bath 2, and the steel plate 9 is immersed and passed through the steel plate 9. The premelt pot 5 dissolves the molten metal bath component supplied to the molten plating tank 1 and holds the molten metal bath 2a. The pre-melt pot 5 is disposed on the side of the molten plating tank 1, and the molten metal bath 2 of the molten plating tank 1 and the molten metal bath 2 a of the pre-melt pot 5 are connected by a connecting pipe 6.

  On the side of the molten plating tank 1 of the connecting pipe 6, a branch pipe branched in the width direction of the steel plate 9 along the wall surface of the molten plating tank 1 is provided, and an opening 12 is provided at each branch pipe end. In this invention, the opening part 12 is arrange | positioned so that the space | interval of this opening part 12 may become more than the steel plate maximum width. That is, each opening part 12 is arrange | positioned so that it may be located outside the steel plate edge part of the maximum width. Here, the outside means that the pass line is located at a position farther from the top of the plating apparatus with reference to the center in the width direction of the steel plate (two-dot chain line CC in FIG. 2) (also in the following description). The same).

  Since the molten metal bath 2 of the molten plating tank 1 and the molten metal bath 2a of the premelt pot 5 are connected by the connecting pipe 6, when the molten metal 2a is not replenished from the premelt pot 5 to the molten metal bath 1 The liquid level in the molten plating tank 1 and the liquid level in the premelt pot 5 are at the same level. When the molten metal bath 2a is supplied from the premelt pot 5 to the molten metal bath 1, the metal ingot 8 of the premelt pot 5 is lowered. When the metal ingot 8 is lowered, the liquid level of the premelt pot 5 rises and a liquid level difference is generated between the molten plating tank 1 and the premelt pot 5, and the molten metal 2 a in the premelt pot 5 passes through the opening 11. It is introduced into the connecting pipe 6 and led out from the opening 12 into the molten plating tank 1. When the liquid level in the molten plating tank 1 and the liquid level in the premelt pot 5 become the same liquid level, the transfer of this liquid is stopped. Moreover, the part immersed in the primet pot 5 of a metal ingot melt | dissolves. Since the transfer of this liquid utilizes the liquid level difference between the molten plating tank 1 and the pre-melt pot 5, the transfer of this liquid does not cause fluctuation of the wave front in the molten metal bath 2 in the molten metal bath 1, and the snout. As a result, defects such as ash adhesion and scratches caused by the fluctuation of the wave front in the plate 3 are not generated.

  In the molten metal plating, it is particularly important to obtain stable plating quality that the molten metal bath components in the vicinity of the snout 3 where the steel plate 1 enters the molten metal tank 1 are uniform.

  The molten metal bath 2 in the vicinity of the snout 3 is caused by the flow of the steel sheet as it enters the molten metal tank 1, and the steel plate passage area on the snout 3 side (hatching area between the steel sheet 9 and the sink roll 4 in the snout 3 in FIG. 2). ). If the molten metal 2a replenished from the premelt pot 5 flows into the steel plate passage area in the vicinity of the snout 3 before being sufficiently diffused into the molten metal bath 2 in the molten plating tank 1, it can be seen, for example, by molten zinc plating. Stable plating quality cannot be obtained, for example, the generation of the Al-enriched layer becomes non-uniform. In the apparatus of the present invention, the molten metal 2a replenished from the premelt pot 5 is melted in the molten plating tank 1 by installing the gaps between the openings 12 at the ends of the branch pipes to be equal to or greater than the maximum width of the steel plate. It is suppressed from flowing into the steel plate passage area near the snout 3 before being sufficiently diffused into the metal bath 2, and the molten metal 2 a supplied from the premelt pot 5 is melted in the molten plating tank 1 into the steel plate passage area. A sufficiently diffusive mixture flows in the metal bath 2. As a result, the non-uniformity of the concentration of the plating metal component that occurs when the molten metal bath 2a is supplied from the pre-melt pot 5 to the molten plating bath 1 can be prevented, and the plating quality of the steel sheet can be stabilized.

  If the molten metal bath 2 of the molten plating tank 1 and the molten metal bath 2a of the premelt pot 5 are communicated by the connecting pipe 6, the vertical positions of the openings 11 and 12 of the connecting pipe 6 are not particularly limited. A part of the openings 11 and 12 may be on the bath surface, but the steel plate before the molten metal bath 2a replenished from the premelt pot 5 to the molten plating tank 1 is not sufficiently diffused into the molten metal bath 2. In order to suppress the flow in the vicinity of the plating bath intruding portion of the metal or prevent dross or the like existing on the bath surface of the premelt pot 5 from being brought into the molten plating tank 1, the opening 11 and the opening 12 are provided. Is preferably provided so as to be immersed in the bath surface position or in the bath, and the opening 12 is more preferably installed at a position deeper than the immersion depth of the snout 3 in the molten metal bath 2. In this apparatus, the opening 11 on the pre-melt pot 5 side of the connecting pipe 6 is provided at a position where the upper end is at the bath surface level, and the opening 12 on the plating metal tank 1 side is the snout 3 in the molten metal bath 2. It is provided at a position deeper than the immersion depth.

  The openings 11 and 12 of the connecting pipe 6 are not only arranged near the wall surface of the molten plating tank 1 facing the steel plate surface behind the snout 3 as in the apparatus according to this embodiment, but also on the front side (in FIG. 1). The sink roll 4 may be disposed on the left side of the rising portion of the steel plate 9 after the plate passing direction is changed.

  The connecting pipe 6 can be manufactured using a known material having corrosion resistance and heat resistance, such as ceramics, for the molten metal dissolved in the premelt pot 5 and the molten metal held in the molten plating tank 1. Further, the outside of the portion of the connecting pipe 6 outside the bath may have a heat insulating structure. The cross-sectional size / shape of the connecting pipe 6 and the opening size / shape of the openings 11 and 12 are not particularly limited. An appropriate one can be adopted according to the amount of molten metal component to be replenished.

  In order to further enhance the action of preventing the molten metal bath 2a supplied from the premelt pot 5 to the molten plating tank 1 from flowing near the plating bath intrusion portion of the steel plate before sufficiently diffusing in the molten metal bath 2. More preferably, a baffle plate 7 that restricts the flow of the molten metal bath led out from the opening 12 is installed between the opening 12 of the connecting pipe 6 and the snout 3 and the steel plate 9.

  It is preferable that the baffle plate 7 has an upper end on the bath surface or on the bath surface, and the lower end is preferably disposed so as to be deeper than the opening 12 and the snout 3, and is in contact with the opening 12 and the sink roll 4. It is more preferable to install it so that it is below the line connecting the steel plate traveling path in the bath. Since the temperature difference in the bath increases as the location of the opening becomes deeper, the depth is preferably within the depth of the sink roll axis from the bath surface.

  The baffle plate 7 is disposed so that the widthwise end of the baffle plate 7 is disposed outside the opening 12 of the connection pipe 6 and is disposed outside the end of the snout width direction. It is preferable to install so that it may become more than the maximum dimension (external dimension) of the parts 12 and 12, and more than snout width.

  In this apparatus, the baffle plate 7 is disposed between the snout 3 and the opening 12 of the connecting pipe 6, the upper end thereof is installed on the bath surface, and the lower end thereof is deeper than the opening 12. The part is installed in contact with the wall surface of the molten plating tank 1.

  The baffle plate 7 can be manufactured using a known material having corrosion resistance and heat resistance, such as ceramics, for the molten metal held in the molten plating tank 1. The baffle plate 7 may not be a flat plate. An appropriate shape can be adopted depending on the installation location of the opening 12.

  In the apparatus described above, the entire connecting pipe 6 is installed so as to be submerged under the bath surface. However, as shown in FIG. 4, the openings 11 ′ and 12 ′ of the connecting pipe 6 ′ are submerged under the bath surface. If it installs so, parts other than opening part 11 'and 12' of connecting pipe 6 'may be the structure arrange | positioned on the bath surface.

  In the present invention, one or more are installed according to the type of the molten plated steel sheet for producing the premelt pot connected to the molten plating tank by the connecting pipe as described above.

  Hereinafter, a method for producing a hot-dip galvanized steel sheet using the molten metal plating apparatus for steel sheets according to the embodiment of the present invention will be described.

  In the apparatus of FIG. 1, the steel plate 1 is immersed and passed from the snout 3 into the plating bath 2 of the molten plating tank 1, and after the direction of the passing plate is changed by the sink roll 3 in the bath, the steel plate 1 is pulled up from the plating bath 2. The amount of zinc adhesion is controlled by a gas wiping nozzle (not shown), and further processing such as spangle adjustment processing and alloying processing is performed as necessary to obtain a desired hot-dip galvanized steel sheet.

  For example, the bath composition of the molten zinc plating is 0.1 to 0.2 mass% Al—Zn. A molten metal bath (hereinafter referred to as a plating bath) 2 having the above composition is held in the molten metal tank 1, and the Al concentration of the plating bath 2 is controlled within the above concentration range. When the hot-dip galvanized steel sheet is produced in this way, the plating bath 2 adheres to the steel sheet and is taken out of the tank and removed as dross outside the tank. In order to keep the liquid level constant, it is necessary to replenish the plating bath.

  The composition of the decreasing plating bath is not the same as the plating bath 2 held in the molten plating bath 1. Since Al is consumed as an Al-enriched layer formed at the interface between the plating layer and the steel sheet substrate, and is removed as dross as Fe2Al5, the reduction rate of Al is higher than that of Zn. Therefore, the Al concentration of the plating bath to be supplied needs to be higher than the Al concentration of the plating bath 2 held in the molten plating tank 1.

  The plating bath is replenished from the premelt pot. Two premelt pots are installed, the first premelt pot melts and holds the pure zinc ingot, and the second premelt pot melts and holds the Al—Zn alloy ingot. The connecting pipe of the first premelt pot has the arrangement shown in FIG. 1, and the connecting pipe of the second premelt pot has the arrangement shown in FIG.

  As the Al—Zn alloy, for example, a 0.3 to 0.5 mass% Al—Zn alloy is used. By adjusting the ratio of the amount of molten metal supplied from the first premelt pot and the second premelt pot, the Al concentration of the plating bath 2 held in the molten metal tank 1 is controlled, and the liquid level of the molten plating tank 1 Is kept at a constant liquid level. At that time, the proportion of the replenishment amount of the Al—Zn alloy held in the second pre-melt pot is increased so as to compensate for the decrease amount of Al that is greatly reduced as compared with Zn, for example, Al of the plating bath to be replenished. By setting the concentration to about 8 to 12 mass%, the Al concentration of the plating bath 2 held in the molten plating tank 1 can be controlled within a predetermined concentration range.

  If the plating bath is replenished from the pre-melt pot using the apparatus of the present invention, the unevenness of the Al concentration in the plating bath in the molten plating tank 1 is eliminated, so that the plating quality can be stabilized and the plating bath surface is fluctuated. Therefore, the occurrence of defects such as ash and scratches can be prevented.

When performing hot dip galvanizing on steel sheets of various dimensions within the range of thickness: 0.4 to 3.2 mm × width 750 to 1850 mm in a continuous hot metal plating line, using an apparatus having the following conditions I to V: The ratio of defective plating was compared. Here, the plating defect rate was calculated based on the following criteria by visually confirming an alloying defect portion in a surface inspection room on the exit side of the hot dip galvanizing line.
Plating defect rate (%) = Plating defect steel plate weight (t) / Production steel plate weight (t) × 100
[Plating equipment conditions]
I: The ingot is put directly into the main pot without using the premelt pot.
II: The ingot is melted in the premelt pot, and the main pot side opening in the connecting pipe between the premelt pot and the main pot is located in the center of the steel plate at a position shallower than the snout immersion depth on the steel plate intrusion side of the main pot side wall. Placed opposite the part.
III: The ingot is melted in the premelt pot, and the main pot side opening in the connecting pipe between the premelt pot and the main pot is a steel plate at a position shallower than the snout immersion depth on the steel plate intrusion side of the main pot side wall. Are arranged at two locations with an interval equal to or greater than the maximum width (see FIG. 2).
IV: The ingot is melted in the premelt pot, and the main pot side opening in the connecting pipe between the premelt pot and the main pot is a steel plate at a position deeper than the snout immersion depth on the steel plate intrusion side of the main pot side wall. Are arranged at two locations with an interval equal to or greater than the maximum width (see FIGS. 2 and 3).
For V: IV, a baffle plate immersed from the bath surface to a position deeper than the opening is disposed between the snout and the main pot side opening.

  The plating defect rate under each condition was 1.05% for I, 0.95% for II, 0.62% for III, 0.47% for IV, and 0.29% for V.

  As mentioned above, although the example which manufactures a hot dip galvanized steel sheet using the apparatus of the present invention was explained, the apparatus of the present invention not only manufactures a hot dip galvanized steel sheet, but also a molten metal plated steel sheet containing a plurality of components, for example, It can be widely used as an apparatus for producing a molten metal plated steel sheet containing Zn, Al, Mn, Pb and alloys thereof.

  The apparatus of the present invention can be used as an apparatus for producing a molten metal plated steel sheet containing a plurality of components, for example, a molten metal plated steel sheet containing Zn, Al, Mn, Pb and alloys thereof.

It is a schematic sectional drawing which shows the principal part of the molten metal plating apparatus of the steel plate which concerns on embodiment of this invention. It is an AA section arrow sectional view of Drawing 1. It is the schematic explaining the structure in the fusion plating tank of a connection pipe. It is a schematic sectional drawing which shows the principal part of the molten metal plating apparatus of the steel plate which concerns on another embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molten metal tank 2, 2a Molten metal bath 3 Snout 4 Sink roll 5 Premelt pot 6, 6 'Connection pipe 7 Baffle plate 8 Metal ingot 9 Steel plate 11, 11', 12, 12 'Opening

Claims (2)

A molten plating bath for holding a molten metal bath containing a plurality of components, one or a plurality of prime pots for supplying molten metal bath components to the molten plating bath, and a molten metal bath in the molten plating bath; In the molten metal plating apparatus for a steel plate provided with a connecting pipe for communicating the molten metal in each premelt pot, an opening for leading the molten metal bath component of the connecting pipe into the molten metal bath in the molten plating tank, An opening for introducing the molten metal bath component of the connecting pipe into the molten metal bath in the molten plating bath; A molten metal plating apparatus for a steel sheet , wherein a baffle plate for restricting a flow of a molten metal bath component derived from the opening is provided between the snout and the steel sheet . The opening for leading the molten metal bath component of the connecting pipe into the molten metal bath in the molten plating bath is installed at a position deeper than the snout immersion depth in the molten metal bath. Steel plate molten metal plating equipment.

Images