SCUM REMOVAL DEVICE AND SCUM REMOVAL METHOD

A scum removal device according to the present disclosure includes a snout, a discharge section, and a suction section. The discharge section is disposed on an extension line of a steel strip entry position on a hot-dip plating bath surface at one side in a steel strip width direction, and discharges a liquid metal for hot dipping. The suction section is disposed on the extension line on the hot-dip plating bath surface at another side in the steel strip width direction, and sucks in the liquid metal for hot dipping. The suction section is configured by a first suction portion and a second suction portion. The first suction portion and the second suction portion are disposed separated from each other at each side of the steel strip width direction extension line of the steel strip entry position on the hot-dip plating bath surface.

TECHNICAL FIELD

The present disclosure relates to a scum removal device and a scum removal method to remove scum floating at the inside of a snout configuring equipment to manufacture hot-dip plated steel sheet.

BACKGROUND ART

In equipment to manufacture hot-dip galvanized steel sheet, if zinc vaporized from a hot-dip galvanizing bath condenses on and adheres to inner walls of a snout (steel strip direct feed pipeline connecting a reduction annealing furnace to a pot of molten zinc), the zinc sometimes forms a scum powder that floats on the galvanizing bath.

Technology is accordingly employed in which a discharge port and a suction port are provided at each of the two steel strip width direction sides of the steel strip inside the snout, a flow is formed in the steel strip width direction, and scum is sucked out through the suction port. However, this is not sufficiently effective, and so technology like the following has been proposed.

For example, Japanese Patent Application Laid-Open (JP-A) No. 2010-229530 (hereinafter referred to as Patent Document 1) discloses a countermeasure to remove floating matter by providing discharge port and suction port pairs, with one pair provided on each of the two thickness direction sides of a steel strip.

Moreover, JP-A No. 2000-064015 (hereinafter referred to as Patent Document 2) and JP-A No. 2014-114484 (hereinafter referred to as Patent Document 3) disclose configurations in which a discharge port is provided on one width direction side of a steel strip to discharge a liquid metal for hot dipping, and a suction port is provided on the other width direction side of the steel strip to suck in the liquid metal for hot dipping.

Moreover, JP-A No. 2003-293107 (hereinafter referred to as Patent Document 4) discloses a configuration in which two discharge ports are provided on one width direction side of a steel strip, and one suction port is provided on the other width direction side of the steel strip.

Moreover, in order to address issues when an injection nozzle is provided for injecting liquid metal for hot dipping, JP-A No. 2014-201817 (hereinafter referred to as Patent Document 5) discloses a configuration in which a dross transfer device is provided to generate waves by moving a plate shaped member to and fro.

SUMMARY OF INVENTION

Technical Problem

However, in the method of Patent Document 1, a flow is generated from one discharge port toward the suction port provided in the steel strip width direction thereof, and a flow is generated from the one discharge port toward the suction port provided in the steel strip thickness direction thereof. This results in part of the scum flowing toward the steel strip surface, and in particular at the two sides in the steel strip width direction, scum readily adheres to the steel strip surface on the side where the discharge port is provided.

Moreover, due to the discharge port being close to the snout wall face, the flow at the wall face is fast, and dislodges scum that has adhered to the wall face. This scum flows out on the bath surface, and readily adheres to the steel strip. This becomes a particular issue because of the large size of the scum dislodged from the snout inner wall face adjacent to the plating bath.

Moreover, Patent Document 2 and Patent Document 3 provide technology to form a flow with directionality from one width direction side of the steel strip to the other width direction side thereof. However, an accompanying current is generated at the hot-dip plating bath surface as the steel strip is drawn into the hot-dip galvanizing liquid. Thus, if the hot-dip zinc plating liquid is simply discharged from one width direction side of the steel strip toward the other width direction side of the steel strip, the effect of the accompanying current will dominate at the suction port side, and scum will flow toward the steel strip surface.

Moreover, although Patent Document 2 proposes a configuration in which a divider plate is install parallel to the steel strip, scum adhered to the divider plate surface readily detaches from the divider plate due to the fast flow in the regulated flow direction, and surface defects are readily generated by the detached scum adhering to the steel strip surface.

Moreover, Patent Document 2 proposes technology to forcibly generate a bath surface flow in a substantially orthogonal direction away from the surface of the steel strip. However, due to a strong flow being generated so as to flow from the two width direction ends of the steel strip in a direction toward the plate width direction center, a problem arises in that inflowing scum readily adheres at the two steel strip width direction end portions of the steel strip.

In the configuration of Patent Document 4, the suction port is provided on an extension line in the width direction, and so there is a concern that the flow from the two discharge ports toward the suction port might draw progressively closer to the steel strip as it flows from the discharge ports toward the suction port.

Moreover, in the configuration of Patent Document 5, waves are generated by moving a plate shaped member to and fro with the dross transfer device, and so floating scum is simply displaced up and down together with the generated waves, and it is not possible to cause active scum flow.

The present disclosure provides a scum removal device and a scum removal method capable of suppressing scum floating on a hot-dip plating bath surface from adhering to a steel strip by suppressing over the entire width of the steel strip.

Solution to Problem

As a result of diligent investigations, the inventors have discovered that scum adhered to snout wall faces in the vicinity of a plating bath surface pose a particular problem in causing steel strip defects when the scum dislodges and adheres to the steel strip. The inventors et al. have discovered that this problem can be prevented by making the scum adhered to the snout wall face at the boundary between the snout inner face and the bath surface more difficult to dislodge, and controlling flow at the bath surface such that even if scum is dislodged, the dislodged scum does not flow to the steel strip surface.

A scum removal device according to a first aspect of the present disclosure includes: a snout, the snout being inserted into a liquid metal for hot dipping in a hot-dip plating pot such that a hot-dip plating bath surface is present inside the snout; a discharge section, the discharge section being disposed on an extension line of a steel strip entry position on the hot-dip plating bath surface at one side in a steel strip width direction, and discharging the liquid metal for hot dipping; and a suction section, the suction section being disposed on the extension line on the hot-dip plating bath surface at another side in the steel strip width direction, and sucking in the liquid metal for hot dipping; the suction section being configured by a first suction portion and a second suction portion, and the first suction portion and the second suction portion being disposed separated from each other at each side of the steel strip width direction extension line of the steel strip entry position on the hot-dip plating bath surface.

The scum removal device according to the present disclosure enables scum floating on the surface of a hot-dip plating bath to be suppressed from adhering to a steel strip.

DESCRIPTION OF EMBODIMENTS

Explanation follows of exemplary embodiments, with reference to the drawings.

FIG. 1illustrates an example of a schematic configuration of plating equipment12provided with one mode of a scum removal device10and a scum removal method according to the present exemplary embodiment. The plating equipment12is equipment to plate a steel strip14having a thickness of from 1 mm to 3 mm, for example. The plating equipment12includes a continuous reduction annealing furnace16to anneal the steel strip14, and a hot-dip plating pot20storing a liquid metal for hot dipping18.

A description will now be given of an example in which molten zinc is employed as the liquid metal for hot dipping18and the steel strip14is galvanized by immersion, however, there is no limitation thereto. For example, the steel strip14can be tinned by employing molten tin, or the steel strip14can be aluminum plated by employing molten aluminum.

A snout22extends from the reduction annealing furnace16. The snout22includes an extension section22A extending in a horizontal direction from the reduction annealing furnace16, and an inclined section22B extending from the extension section22A diagonally downward toward the hot-dip plating pot20. The snout22is formed in a rectangular tube shape surrounding the steel strip14. The leading end portion of the snout22is inserted into the liquid metal for hot dipping18in the hot-dip plating pot20.

The internal space of the snout22is thereby isolated from the exterior, such that the snout22configures a pipeline connecting the reduction annealing furnace16and the hot-dip plating pot20together in an airtight manner.

The internal space of the snout22is filled with a reducing gas to suppress oxidation etc. of the steel strip14, and the steel strip14is immersed in the liquid metal for hot dipping18in the hot-dip plating pot20without coming into contact with air.

A feed roll26is provided at the base end side of the inclined section22B of the snout22, to change a conveyance direction24of the steel strip14diagonally downward. The steel strip14that has been annealed in the reduction annealing furnace16is conveyed with its length direction along the snout22, and drawn into a hot-dip plating bath surface28inside the snout22.

The conveyance path of the steel strip14inside the snout22is determined by the feed roll26and a guide roll30disposed inside the hot-dip plating pot20, thereby stabilizing the position of entry of the steel strip14into the hot-dip plating bath surface28of the liquid metal for hot dipping18. The conveyance direction24of the steel strip14is then changed upward by the guide roll30, and the steel strip14is fed out from the hot-dip plating pot20to a subsequent process.

FIG. 2is a schematic cross-section illustrating in outline a state inside the snout22, as viewed along line2-2ofFIG. 1. Observation windows32are provided at the two sides of the inclined section22B of the snout22in a steel strip width direction KH. The steel strip width direction KH is a direction orthogonal to the conveyance direction24of the steel strip14.

Cameras34are provided at the observation windows32. The cameras34image the way in which the steel strip14is drawn into the hot-dip plating bath surface28at a steel strip entry position29.

The steel strip entry position29is a position at the intersection of the steel strip14and the hot-dip plating bath surface28, or is a position where the steel strip14and the hot-dip plating bath surface28are due to intersect, and forms a straight line with length along the steel strip width direction KH in plan view.

Zinc that vaporizes from the liquid metal for hot dipping18in a plating process condenses and adheres to the inner face of the snout22. Any part of the adhered zinc falling, for example due to vibration caused by oscillation of the bath surface, becomes scum36floating on the hot-dip plating bath surface28.

The scum36adheres to the steel strip14and is a cause of surface defects. The scum removal device10, described in detail below, is accordingly provided inside the snout22to suppress quality defects caused by the scum36.

Scum Removal Device

FIG. 3is an outline cross-section illustrating a state of the hot-dip plating bath surface28inside the snout22as viewed from above (a horizontal section of the snout22and the steel strip14). The steel strip14moves in a direction away from the viewer and into the page inFIG. 3.

The reference numeral60indicates an extension line of the steel strip entry position29, and the extension line60is a straight line passing through a thickness direction center of the steel strip14, and is a hypothetical straight line extension of the steel strip width direction KH. The extension line60is at a position substantially equidistant from one inner wall face22D and another inner wall face22E.

As illustrated inFIG. 2andFIG. 3, a discharge device40is provided on the extension line60of the steel strip14at one width direction side H1of the steel strip14(the left side in the drawings).

The discharge device40includes a circular tube shaped discharge pipe42, bent into a U-shaped profile. The discharge pipe42includes a vertical outside pipe section42A disposed outside the snout22and extending in a vertical direction, and a communication section42B extending from a lower end portion of the vertical outside pipe section42A toward the inside of the snout22. The discharge pipe42includes a vertical inside pipe section42C extending upward from the leading end of the communication section42B and disposed at the inside of the snout22.

The base end portion of the vertical outside pipe section42A of the discharge pipe42extends above the hot-dip plating bath surface28. A motor46is provided at the base end of the vertical outside pipe section42A. A screw48is provided on the drive shaft of the motor46, and the screw48is rotationally driven inside the liquid metal for hot dipping18.

An intake port50is formed to the vertical outside pipe section42A on the opposite side to the snout22at a height position corresponding to the screw48. The liquid metal for hot dipping18that is thereby taken into the vertical outside pipe section42A, through the intake port50open to the outside of the snout22, is fed under pressure by the rotating screw48toward the communication section42B and toward the vertical inside pipe section42C.

As illustrated inFIG. 4, a cuboid shaped discharge nozzle52is provided at a leading end portion of the vertical inside pipe section42C to discharge the liquid metal for hot dipping18at the hot-dip plating bath surface28inside the snout22. A description follows of the discharge nozzle52, taking the direction the liquid metal for hot dipping18is discharged in toward the steel strip14side, as described later, as being the front of the discharge nozzle52.

The discharge nozzle52includes a bottom plate52B formed with a circular hole52A in communication with the vertical inside pipe section42C, and side walls52C extending upward at two side edges of the bottom plate52B. The discharge nozzle52also includes a rear wall52D extending upward at a rear edge of the bottom plate52B, and a top plate52E provided so as to be contiguous to upper edges of the side walls52C and the rear wall52D. An extension plate52F extends from a front edge of the top plate52E toward the bottom plate52B side. A discharge section56is formed between the extension plate52F and the bottom plate52B, opening onto the steel strip14side. As illustrated inFIG. 5, the extension plate52F suppresses ripples from being formed in the liquid metal for hot dipping18as it is discharged from the discharge section56.

As illustrated inFIG. 4, a pair of flow regulation plates58are installed upright on the bottom plate52B. As illustrated inFIG. 5, the flow regulation plates58are formed in rectangular shapes, and are sufficiently tall for upper portions of the flow regulation plates58to be supported by the extension plate52F. The discharge nozzle52is disposed such that a lower side of the discharge nozzle52is at a position in the liquid metal for hot dipping18.

The flow of the liquid metal for hot dipping18discharged from the discharge section56is regulated with enhanced straight line directionality along the steel strip width direction KH by the flow regulation plates58and the side walls52C, as illustrated inFIG. 3andFIG. 6. Moreover, due to the flow of the discharged liquid metal for hot dipping18being regulated by the flow regulation plates58and the side walls52C, the flow speed (the steel strip width direction KH component) of the liquid metal for hot dipping18in the vicinity of the steel strip14is raised in comparison to cases lacking flow regulation, and the scum36is quickly washed away.

The discharge section56is disposed on the extension line60from the steel strip14extending along the steel strip width direction KH, with approximately the width direction center of the discharge section56positioned on the extension line60of the steel strip14. Thus, the discharge device40discharges the liquid metal for hot dipping18, taken in through the intake port50at the outside of the snout22, through the discharge section56from the one width direction side H1of the steel strip14, toward the steel strip14side, such that the liquid metal for hot dipping18flows along the hot-dip plating bath surface28.

Moreover, as illustrated inFIG. 2, a suction device62is provided at another width direction side H2of the steel strip14(the right side in the drawing). The suction device62includes a circular tube shaped suction pipe64bent into a U-shaped profile. The suction pipe64includes a vertical outside pipe64A disposed outside the snout22and extending in a vertical direction, and a communication section64B extending toward the snout22inside from a lower end portion of the vertical outside pipe64A. The suction pipe64also includes a vertical inside pipe64C disposed inside the snout22and extending upward from the leading end of the communication section64B.

The base end portion of the vertical outside pipe64A of the suction pipe64is disposed so as to extend above the hot-dip plating bath surface28. An exhaust port66is opened in the base end portion of the vertical outside pipe64A on the opposite to the snout22, at a height position in the liquid metal for hot dipping18.

A gas supply pipe68is inserted into a base end opening of the vertical outside pipe64A to supply nitrogen gas (N2) fed from a supply source, not illustrated in the drawings. The leading end of the gas supply pipe68reaches a lower portion of the vertical outside pipe64A. The liquid metal for hot dipping18is exhausted through the exhaust port66by the nitrogen gas being supplied through the gas supply pipe68, thereby lowering the internal pressure inside the vertical outside pipe64A. The liquid metal for hot dipping18inside the vertical inside pipe64C flows into the vertical outside pipe64A through the communication section64B due to the lowered internal pressure.

A first suction nozzle71A and a second suction nozzle71B, as illustrated inFIG. 3andFIG. 7are thereby configured at an end portion of the vertical inside pipe64C. A first suction portion72and a second suction portion74are configured by respective openings of the first suction nozzle71A and the second suction nozzle71B. A suction section64H (seeFIG. 3) to suck in the liquid metal for hot dipping18is configured by the first suction portion72and the second suction portion74.

Reference here to a suction section (the first suction portion72and the second suction portion74) indicates openings where nozzles (the first suction nozzle71A and the second suction nozzle71B) are provided to suck in the liquid metal for hot dipping18.

The first suction nozzle71A and the second suction nozzle71B may, for example, be configured by the respective suction pipes64of a pair of the suction devices62. As illustrated inFIG. 8, the suction pipes64are each provided along the up-down direction so as to be separated from each other in a steel strip thickness direction KT (seeFIG. 7). A first pipe64F is configured at an upper end portion of the vertical inside pipe64C of one of the suction pipes64. Moreover, a second pipe64G is configured at an upper end portion of the vertical inside pipe64C of the other of the suction pipes64.

The leading end portion of the first pipe64F is cut at an inclination on the steel strip entry position29side thereof (seeFIG. 7). The plane of the opening is inclined so as to open toward the steel strip entry position29side at the hot-dip plating bath surface28. Namely, the plane of the opening at the leading end portion of the first pipe64F intersects at an angle with the hot-dip plating bath surface28. The leading end portion of the first pipe64F accordingly configures the first suction nozzle71A including the first suction portion72to suck in the liquid metal for hot dipping18.

A leading end portion of the second pipe64G is also cut at an inclination on the steel strip entry position29side thereof (seeFIG. 7). The plane of the opening is inclined so as to open toward the steel strip entry position29side at the hot-dip plating bath surface28. Namely, the plane of the opening at the leading end portion of the second pipe64G intersects at an angle with the hot-dip plating bath surface28. The leading end portion of the second pipe64G accordingly configures the second suction nozzle71B including the second suction portion74to suck in the liquid metal for hot dipping18.

The suction section64H is thereby configured by the first suction portion72and the second suction portion74, to suck in the scum36(seeFIG. 3) floating on the liquid metal for hot dipping18, together with the liquid metal for hot dipping18, so as to remove the scum36.

As illustrated inFIG. 9, the first pipe64F and the second pipe64G may also be configured as bifurcations branching from a main pipe641provided in the liquid metal for hot dipping18(a first modified example). The configuration of the suction device62can be simplified in this case by configuring the main pipe641at the end portion of the vertical inside pipe64C.

Moreover, configurations of the suction nozzles71A,71B are not limited to the profiles given above. An example of a second modified example is illustrated inFIG. 10(in which only a first suction nozzle71C is illustrated) andFIG. 11. Note that the same or equivalent portions to those ofFIG. 3andFIG. 7are appended with the same reference numerals inFIG. 11, and duplicate description is omitted thereof.

Namely, the first suction nozzle71C is provided at the leading end portion of the vertical inside pipe64C. Taking the open direction of the first suction portion72as being the front of the first suction nozzle71C, the first suction nozzle71C includes a bottom plate70B including a circular hole70A in communication with the vertical inside pipe64C, and side walls70C extending upward from the two side edges of the bottom plate70B. Moreover, the first suction nozzle71C includes a rear wall70D provided extending upward from a rear edge of the bottom plate70B, with edges of the rear wall70D contiguous to the side walls70C.

The side walls70C configure flow regulation plates that function to regulate flow of the sucked in liquid metal for hot dipping18along the steel strip width direction KH. Note that a second suction nozzle71D is also configured in a similar manner to the first suction nozzle71C.

Due to the presence of the side walls70C, as illustrated inFIG. 11, an opening width SH1of the first suction nozzle71C (an opening width SH2of the second suction nozzle71D) is fixed, and does not depend on the height of the hot-dip plating bath surface28.

A description now follows regarding a flow regulating function of the flow regulation plates configured by the side walls70C.

As illustrated inFIG. 12, when the suction nozzles71A,71B lack side walls, the liquid metal for hot dipping18surrounding each of suction portions72,74at the center is sucked in. This accordingly allows flows to be generated at the vicinity of inner wall faces22D,22E in the liquid metal for hot dipping18in the snout22.

There is accordingly a need to adjust an amount of the liquid metal for hot dipping18sucked in at the suction portions72,74so that scum adhered to the inner wall faces22D,22E is not dislodged by the flow of the liquid metal for hot dipping18generated in the vicinity of the inner wall faces22D,22E.

Thus, as illustrated inFIG. 13, the suction nozzles71C,71D equipped with flow regulating function by the side walls70C are employed so as to enable the sucking-in direction to be aligned with the steel strip width direction KH.

When doing so, as illustrated inFIG. 14, the flow of liquid metal for hot dipping18in the vicinity of the inner wall faces22D,22E is suppressed by disposing the two suction nozzles71C,71D angled such that each of the suction portions72,74faces the steel strip14side for cases in which the two suction nozzles71C,71D are disposed separated from each other.

As illustrated inFIG. 7andFIG. 11, the first suction nozzle71A or71C and the second suction nozzle71B or71D are disposed such that the approximate center between the pairs of suction nozzles71A,71B,71C,71D is positioned on the extension line60of the steel strip14.

As a result, the first suction portion72of the first suction nozzle71A or71C is disposed on one thickness direction side T1of the steel strip14about a boundary at the extension line60of the steel strip14, and sucks in the liquid metal for hot dipping18at the hot-dip plating bath surface28on the one thickness direction side T1of the extension line60of the steel strip14. Moreover, the second suction portion74of the second suction nozzle71B or71D is disposed on the other thickness direction side T2about a boundary at the extension line60of the steel strip14, and sucks in the liquid metal for hot dipping18at the hot-dip plating bath surface28on the other thickness direction side T2of the extension line60of the steel strip14.

The positional relationship between the snout22, the discharge section56, and each of the suction portions72,74in the scum removal device10will now be described with reference toFIG. 6,FIG. 7, andFIG. 11.

FIG. 6is a diagram indicating the one width direction side H1of the snout22. The discharge section56formed by the discharge nozzle52of the discharge device40is disposed such that the width direction center of the discharge section56in the steel strip thickness direction KT is substantially aligned with the extension line60of the steel strip14, and an opening width TH of the discharge section56in the steel strip thickness direction KT is set to no less than 50 mm. A discharge region TR of the discharge section56is determined by the opening width TH and the placement of the discharge section56.

The discharge section56is also disposed so as to be separated by no less than 100 mm from the inner faces of the snout22facing the steel strip14on entry at the steel strip entry position29. Namely, a separation distance SR1from one end of the discharge section56to the one inner wall face22D of the snout22is no less than 100 mm. Moreover, a separation distance SR2from the other end of the discharge section56to the other inner wall face22E of the snout22is no less than 100 mm, and the separation distance SR1and the separation distance SR2are set so as to be substantially the same dimensions as each other.

FIG. 7andFIG. 11are diagrams illustrating the other width direction side H2of the snout22. The steel strip thickness direction KT center between the first suction nozzle71A,71C and the second suction nozzle71B,71D of the suction device62is disposed so as to be substantially aligned with the extension line60of the steel strip14.

The first suction nozzle71A,71C is set to adjust the amount projecting out from the hot-dip plating bath surface28. The opening width SH1of the first suction portion72of the first suction nozzle71A,71C is thereby no less than 40 mm at the height position of the hot-dip plating bath surface28. Moreover, a separation distance CR1from an edge of the first suction nozzle71A,71C on the side of the extension line60of the steel strip14to the extension line60is no less than 30 mm. Note that due to the first suction nozzle71C including the side walls70C, as described above, the opening width SH1and the separation distance CR1are fixed, and do not depend on the height of the hot-dip plating bath surface28.

The second suction nozzle71B,71D is set to adjust the amount thereof projecting out from the hot-dip plating bath surface28. The opening width SH2of the second suction portion74of the second suction nozzle71B,71D is thereby no less than 40 mm. Moreover, a separation distance CR2from an edge of the second suction nozzle71B,71D on the side of the extension line60the steel strip14to the extension line60is no less than 30 mm. Note that due to the second suction nozzle71D including the side walls70C, as described above, the opening width SH2and the separation distance CR2are fixed, and do not depend on the height of the hot-dip plating bath surface28. The respective suction nozzles71A to71D of the present exemplary embodiment are provided at positions with approximate line symmetry about the extension line60.

The center of the first suction portion72is positioned at the one thickness direction side T1of the end of the discharge section56on the one thickness direction side T1. Moreover, the center of the second suction portion74is positioned at the one thickness direction side T1of the end of the discharge section56on the other thickness direction side T2.

Furthermore, a fourth modified example is illustrated inFIG. 15andFIG. 16.

Namely, a suction nozzle70is provided at a leading end portion of a vertical inside pipe46C. Taking the open direction of each suction portion72,74as the front of the suction nozzle70, the suction nozzle70includes a bottom plate70B including a circular hole70A in communication with the vertical inside pipe64C, and side walls70C extending in a diagonally upward direction from the two side edges of the bottom plate70B, with an upper section of each side wall70C extending in a vertical direction. Moreover, the suction nozzle70includes a rear wall70D provided extending upward from a rear edge of the bottom plate70B with edges of the rear wall70D contiguous to the side walls70C, and a front wall70E provided extending upward from a front edge of the bottom plate70B with edges of the bottom plate70B contiguous to the side walls70C, so as to form a box shape open upward.

Rectangular shaped cutouts70F are formed at the two sides of an upper edge of the front wall70E. A first suction portion72and a second suction portion74are formed by the respective cutouts70F, as examples of a first opening and a second opening open on the steel strip14side. A blocking portion76is configured at a location between the two suction portions72,74by a remaining portion of the upper section of the front wall70E.

A lower edge of each of the suction portions72,74is disposed so as to be at a position below the hot-dip plating bath surface28. Upper edge portions of the side walls70C and the rear wall70D, and an upper edge portion of the blocking portion76of the front wall70E, extend to above the hot-dip plating bath surface28. This enables the scum36floating on the liquid metal for hot dipping18to be sucked in with the liquid metal for hot dipping18through the first suction portion72and the second suction portion74, and to be removed. The liquid metal for hot dipping18is obstructed from being sucked in at the blocking portion76.

As illustrated inFIG. 16, the approximate center of the suction nozzle70in the width direction is disposed at a position on the extension line60of the steel strip14. The first suction portion72of the suction nozzle70is disposed at the one steel strip14thickness direction side T1of the extension line60of the steel strip14, and sucks in the liquid metal for hot dipping18on the one thickness direction side T1of the extension line60of the steel strip14at the hot-dip plating bath surface28. Moreover, the second suction portion74is disposed at the other thickness direction side T2of the extension line60of the steel strip14, and sucks in the liquid metal for hot dipping18on the other thickness direction side T2of the extension line60of the steel strip14at the hot-dip plating bath surface28.

The suction nozzle70is disposed such that the center of the suction nozzle70in the width direction, this being the steel strip thickness direction KT, is substantially aligned with the extension line60of the steel strip14. The location of the suction nozzle70on the extension line60of the steel strip14is blocked off by the blocking portion76.

The opening width SH1of the first suction portion72is no less than 40 mm, and the separation distance CR1from the edge of the suction nozzle70on the width direction center side to the width direction center of the suction nozzle70is no less than 30 mm. Moreover, the opening width SH2of the second suction portion74is no less than 40 mm, and the separation distance CR2from the edge of the suction nozzle70on the width direction center side to the width direction center of the suction nozzle70is no less than 30 mm. The suction nozzle70of the present exemplary embodiment has substantial line symmetry about the width direction center, namely, about the extension line60.

The center of the first suction portion72is positioned at the one thickness direction side T1of the one thickness direction side T1end of the discharge section56. Moreover, the center of the second suction portion74is positioned at the other thickness direction side T2of the other thickness direction side T2end of the discharge section56.

Operation of the scum removal device10and the scum removal method according to the present exemplary embodiment with the configurations described above will now be described in comparison to related technology.

FIG. 17illustrates a most basic configuration in which a discharge section56lacking a function to regulate the flow of discharged liquid metal for hot dipping18is provided at one width direction side H1of a steel strip14, and a suction section84is provided at another width direction side H2of the steel strip14(Comparative Example 1).

FIG. 18illustrates a configuration in which a discharge nozzle52including a flow regulating function performed by the flow regulation plates58and side walls52C illustrated inFIG. 4is employed in place of the discharge section56ofFIG. 17(Comparative Example 2).

FIG. 19illustrates an Example of the present exemplary embodiment including the two suction portions72,74instead of the suction section84ofFIG. 18.

A flow when scum36a,36b,36cadhered to wall faces of a snout22has been dislodged from the same positions on respective wall faces will be described for each of these configurations.

Note thatFIG. 20is a diagram illustrating a state of the hot-dip plating bath surface28in the snout22. An accompanying current is generated at the hot-dip plating bath surface28in the snout22by the liquid metal for hot dipping18being drawn in together with the steel strip14being fed in the conveyance direction24.

In the basic configuration ofFIG. 17(Comparative Example 1), the liquid metal for hot dipping18is discharged in a radial pattern in concentric waves from the discharge section56. Thus in the range where the steel strip14is present, an average flow is generated in the snout22across the entire range of the snout22in the short direction, which is the steel strip thickness direction KT. The flow of the liquid metal for hot dipping18accordingly has a comparatively high flow speed at the wall faces of the snout22. The scum36aadhered to the wall faces of the snout22is accordingly readily dislodged.

Moreover, the flow speed in the steel strip width direction KH in the vicinity of the steel strip14is roughly the same as in the vicinity of the wall faces of the snout22. The flow speed in the steel strip width direction KH is thus not fast enough to cause the scum36ato flow in a direction away from an end portion in the steel strip width direction KH. The scum36ais therefore sucked in toward the steel strip14by the accompanying current of the liquid metal for hot dipping18being drawn in together with the steel strip14, and adheres to the steel strip14, resulting in defects.

Due to the discharge section56including a flow regulating function being employed inFIG. 18, the flow speed in the steel strip width direction KH in the snout22is slower at the vicinity of the wall faces of the snout22, suppressing the scum36bfrom detaching from the wall faces. Moreover, the flow speed in the steel strip width direction KH is high in the vicinity of the steel strip14, causing the scum36bto resist the accompanying current and flow in the steel strip width direction KH. The scum36bcan accordingly be suppressed from adhering to the steel strip14in comparison to the basic configuration ofFIG. 17(Comparative Example 1).

However, even in this method, the scum36bsometimes adheres to the steel strip14on the suction section84side.

Thus, the flow of the hot-dip plating bath surface28was observed, and the position of the scum36badhered to the steel strip14was investigated. From this it was apparent that although a flow substantially in the steel strip width direction KH was generated at a portion slightly away from the steel strip14in the steel strip thickness direction KT, a flow toward an end portion of the steel strip14was generated at the suction section84side.

Thus, as illustrated inFIG. 19, tests were performed with the first suction portion72and the second suction portion74disposed separated from each other in the steel strip thickness direction KT, as an Example of the exemplary embodiment. This enabled the flow toward the end portion of the steel strip14ofFIG. 18to be diverted to a direction away from the steel strip14in the steel strip thickness direction KT, and enabled the scum36cto be sucked into the first suction portion72and the second suction portion74.

Next, preferable placements and operation and advantageous effects of exemplary embodiments of the present invention will be discussed.

Namely, in the scum removal device10, liquid metal for hot dipping taken in from outside the snout22is discharged through the discharge section56, and to form a flow of the liquid metal for hot dipping18in the snout22. The scum36floating inside the snout22is thereby caused to flow toward the first suction portion72and the second suction portion74. When this occurs, in a configuration in which a discharge region TR and a suction region are aligned with each other (for example, the configuration ofFIG. 17), the flow of the liquid metal for hot dipping from the one width direction side H1of the steel strip14toward the other width direction side H2of the steel strip14is drawn in by the accompanying current.

In contrast thereto, the flow of the liquid metal for hot dipping from the discharge section56toward the first suction portion72and the second suction portion74moves away from the steel strip14on progression from the one width direction side H1of the steel strip14to the other width direction side H2of the steel strip14. This suppresses movement of the scum36toward the steel strip14side by being drawn in by the accompanying current together with the liquid metal for hot dipping18toward the steel strip14side, enabling the scum36floating on the hot-dip plating bath surface28to be suppressed from adhering to the steel strip14.

The center of the first suction portion72is positioned at the one thickness direction side T1of the one thickness direction side T1end of the discharge section56. Moreover, the center of the second suction portion74is positioned at the other thickness direction side T2of the other thickness direction side T2end of the discharge section56.

Thus, in comparison to cases in which the suction portions72,74are respectively provided within the discharge region TR, the liquid metal for hot dipping18discharged by the two width direction sides of the discharge section56can also be caused to flow in a direction away from the steel strip14. This enables the floating scum36to be suppressed from adhering to the steel strip14.

Moreover, in the present exemplary embodiment, the first suction portion72and the second suction portion74are disposed separated by no less than 30 mm away from the extension line60of the steel strip14(CR1≥30 mm, CR2≥30 mm). Thus, in comparison to cases in which the two suction portions72,74are provided less than 30 mm away from the extension line60of the steel strip14, the flow of the liquid metal for hot dipping18discharged by the two width direction sides of the discharge section56can be suppressed from approaching the steel strip14due to the accompanying current. This enables the floating scum36to be suppressed from adhering to the steel strip14.

Moreover, the respective opening widths SH1, SH2of the first suction portion72and the second suction portion74are no less than 40 mm. Thus, in comparison to cases in which the opening widths SH1, SH2are less than 40 mm, the region in which the liquid metal for hot dipping18is sucked through the suction portions72,74is widened, thereby raising the removal efficiency of the floating scum36.

In particular, due to employing the suction nozzles71C,71D equipped with the flow regulating function, the suction direction can be aligned with the steel strip width direction KH. The scum adhered to the inner wall faces22D,22E can accordingly be suppressed from dislodging, and also the rate of suction of the liquid metal for hot dipping18at the suction portions72,74can be increased in comparison to cases lacking a flow regulating function.

Disposing the two suction nozzles71C,71D in this configuration at an angle so that the suction portions72,74face the steel strip14side enables a flow of the liquid metal for hot dipping18in the vicinity of the inner wall faces22D,22E to be suppressed (seeFIG. 14).

The discharge section56is separated by no less than 100 mm from the inner faces of the snout22that face the steel strip14entering at the steel strip entry position29(SR1≥100 mm, SR2≥100 mm). Thus, in comparison to cases in which there is a separation of less than 100 mm between the discharge section56and the inner faces, the scum36adhered to the inner faces of the snout22can be suppressed from being dislodged by the flow of liquid metal for hot dipping.

FIG. 21illustrates results of water modeling tests (tests in a water tank) to measure changes in flow speed in the vicinity of an inner face of the snout22when the separation distance SR1from one width direction end of the discharge section56to the one inner wall face22D of the snout22is changed.

The conditions for the water modeling tests are as set out below.

Flow speed in the steel strip width direction KH at the vicinity of the discharge section 56: 250 mm/s.

Position of flow speed measurement in the vicinity of the one inner wall face22D:

the steel strip width direction KH center.

As illustrated inFIG. 21, the flow speed in the vicinity of the inner face (the one inner wall face22D) was confirmed to be lowered by making the separation distance SR1no less than 100 mm, and an effect of preventing dislodging of the scum36adhered to the inner face can be expected.

The opening width TH of the discharge section56was made no less than 50 mm. The discharge rate of liquid metal for hot dipping from the discharge section56was thereby increased in comparison to cases in which the opening width TH was less than 50 mm, enabling an enhanced effect of preventing adherence of the scum36to the steel strip14.

FIG. 22is a table of test results. This table illustrates a first and second comparative example, and a first and second example.

Namely, the first comparative example is a comparative example to test the provision of a discharge section lacking a flow regulating function at the one width direction side H1, and provision of a single suction section on the extension line60of the steel strip14at the other width direction side H2(configuration ofFIG. 17). In the first comparative example a large quantity of scum adhered to the steel strip14, from a central portion of the steel strip14in the steel strip width direction KH toward the suction section side.

In the second comparative example, a flow regulating function (configuration ofFIG. 18) was provided to the discharge section of the first comparative example. In the second comparative example scum mainly adhered to the suction section side end portion of the steel strip14.

The first exemplary embodiment is an example to test provision of a discharge section lacking a flow regulating function at the one width direction side H1, and provision of suction portions separated from each other and forming a pair at the one thickness direction side T1and the other thickness direction side T2about the extension line60of the steel strip14at the other width direction side H2. In the first example, although an extremely small amount of scum was observed adhering to the steel strip14, a dramatic improvement in the amount adhering was achieved.

The second exemplary embodiment is the first exemplary embodiment with a flow regulating function provided to the discharge section (configuration ofFIG. 19). In the second exemplary embodiment scum did not adhere to the steel strip14.

An explanation is given below of the reference numerals.10scum removal device14steel strip18liquid metal for hot dipping22snout22D one inner wall face22E other inner wall face28hot-dip plating bath surface36scum56discharge section60extension line72first suction portion74second suction portionCR1separation distanceCR2separation distanceH1one width direction sideH2other width direction sideKH steel strip width directionKT steel strip thickness directionSH1opening widthSH2opening widthSR1separation distanceSR2separation distanceT1one thickness direction sideT2other thickness direction sideTH opening widthTR discharge region

Supplement

The following aspects may be generalized from the present specification.

Namely, a scum removal device according to a first aspect includes: a snout, the snout being inserted into a liquid metal for hot dipping in a hot-dip plating pot such that a hot-dip plating bath surface is present inside the snout; a discharge section, the discharge section being disposed on an extension line of a steel strip entry position on the hot-dip plating bath surface at one side in a steel strip width direction, and discharging the liquid metal for hot dipping; and a suction section, the suction section being disposed on the extension line on the hot-dip plating bath surface at another side in the steel strip width direction, and sucking in the liquid metal for hot dipping; the suction section being configured by a first suction portion and a second suction portion, and the first suction portion and the second suction portion being disposed separated from each other at each side of the steel strip width direction extension line of the steel strip entry position on the hot-dip plating bath surface.

A scum removal device according to a second aspect is the first aspect, wherein the discharge section includes a flow regulation plate that regulates flow of the discharged liquid metal for hot dipping so as to flow in the steel strip width direction.

A scum removal device according to a third aspect is the first or second aspect, wherein the first suction portion and the second suction portion include flow regulation plates that regulate flow of the discharged liquid metal for hot dipping so as to flow in the steel strip width direction.

A scum removal device according to a fourth aspect is the first or second aspect, wherein: the first suction portion is configured by a first pipe including an opening at a pipe leading end where the liquid metal for hot dipping is sucked in, a plane of the opening being inclined so as to open toward a steel strip entry position side; and the second suction portion is configured by a second pipe including an opening at a pipe leading end where the liquid metal for hot dipping is sucked in, a plane of the opening being inclined so as to open toward the steel strip entry position side.

A scum removal device according to a fifth aspect is the fourth aspect, wherein the first pipe and the second pipe are formed as bifurcations branching from a main pipe.

A scum removal device according to a sixth aspect is any one of the first to third aspects, wherein: the suction section is configured by a suction nozzle including a front wall facing a steel strip entry position side; the front wall of the suction nozzle is formed with: a blocking portion disposed on the extension line at the other side in the steel strip width direction and obstructing sucking in of the liquid metal for hot dipping, a first opening provided at a portion of the front wall at one side of the blocking portion and open toward the steel strip entry position side, and a second opening provided at a portion of the front wall at another side of the blocking portion and open toward the steel strip entry position side; and the first suction portion is configured by the first opening, and the second suction portion is configured by the second opening.

A scum removal device according to a seventh aspect is any one of the first to sixth aspects, wherein the discharge section is disposed at a separation of no less than 100 mm from an inner face of the snout extending along the steel strip entry position.

A scum removal method according to an eighth aspect is used in a snout inserted into a liquid metal for hot dipping in a hot-dip plating pot such that a hot-dip plating bath surface is present inside the snout, the method comprising: discharging the liquid metal for hot dipping at an extension line of a steel strip entry position on the hot-dip plating bath surface at one side in a steel strip width direction; and sucking in the liquid metal for hot dipping at another side in the steel strip width direction on the hot-dip plating bath surface, at positions separated from each other at each side of the steel strip width direction extension line of the steel strip entry position on the hot-dip plating bath surface.

The following other aspects may also be generalized from the present specification.

A first other aspect is “a scum removal device including a suction nozzle to remove scum floating on a hot-dip galvanizing bath, inside a snout connecting a reduction annealing furnace to a pot of molten zinc in equipment to manufacture hot-dip galvanized steel sheet, by sucking in the scum together with molten zinc at a hot-dip galvanizing bath surface, and the suction nozzle including a first suction nozzle disposed on one face side of a steel strip passing through inside the snout, and a second suction nozzle disposed on another face side of the steel strip”.

A second other aspect is “the scum removal device of the first other aspect, wherein the first and second suction nozzles are disposed at a snout inner end portion in a width direction of the steel strip passing through inside the snout”.

A third other aspect is “the scum removal device of the second other aspect, wherein the first and/or the second suction nozzle is disposed at least separated in the steel strip thickness direction by no less than 30 mm from the width direction extension line of the steel strip”.

A fourth other aspect is “the scum removal device of the second or third other aspect, wherein the first and/or the second suction nozzle has an opening size of at least no less than 40 mm in the steel strip thickness direction”.

The entire content of the disclosure of Japanese Patent Application No. 2015-251230 filed on Dec. 24, 2015 is incorporated by reference in the present specification.

Moreover, all publications, patent applications and technical standards mentioned in the present specification are incorporated by reference in the present specification to the same extent as if the individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.