Patent Publication Number: US-8113139-B2

Title: Gas wiping apparatus having adjustable gas guide

Description:
TECHNICAL FIELD 
     The present invention relates to a gas wiping apparatus for coating a molten metal such as molten zinc on the surface of a steel strip, in which the molten metal solution deposited on the steel strip is wiped to adjust a coating thickness of the steel strip. More particularly, the present invention relates to a multi-nozzle gas wiping apparatus which can wipe the surface of the coated steel strip passing through a hot dipping bath filled with a molten metal by a high speed gas jet to restrain the molten metal from splashing even at a high-speed and adjust a coating thickness (coating thickness) of the coated steel strip stably and uniformly. 
     BACKGROUND ART 
     A steel strip, especially a coated steel strip obtained by coating a specific molten metal, e.g., molten zinc onto a cold-rolled steel strip, is highly corrosion-resistant and has aesthetic appearance. 
     Especially, lately, this coated steel strip has been utilized in electronic products or automobiles, thus calling for development of a manufacturing method for a higher-quality coated steel strip. 
     The steel strip is chiefly coated by virtue of continuous hot dip galvanizing. 
     For example, as shown in  FIG. 1 , a coil steel strip (cold-rolled steel strip) S uncoiled from a pay off reel is thermally treated in a furnace through a welder and an entry looper. Then the coil steel strip S passes through a hot dipping bath  110  filled with molten zinc  112  through a snout  114  to be coated. 
     Next, the steel sheet passes through a gas wiping apparatus  120  (or an air knife) disposed over a molten level of the hot dipping bath. In this case, the molten metal solution (zinc) of the steel strip S is adequately worn from surfaces thereof by a high-pressure air or a non-active gas such as nitrogen, which will be hereinafter referred to as ‘gas’, blown onto the steel strip. This allows the steel strip to be adjusted in its coating thickness as shown in A of  FIG. 1 . 
     Afterwards, a gauge  130  measures whether the steel strip is coated to an appropriate coating thickness. The measured value is fed back to adjust a gas ejection pressure of the gas wiping apparatus  120  and an interval between the steel strip S and the gas wiping apparatus  120 , thereby continuously controlling a coating amount of the steel strip. 
     Here, reference signs  116  and  118  in  FIG. 1 , which are not described, indicate a sink roll for guiding the steel strip into the hot dipping bath and a stabilizing roll for suppressing vibration of the steel strip. 
     As described above, the gas wiping apparatus (air knife)  120  is the important equipment for determining a coating thickness of the steel strip to meet consumer&#39;s demand. 
       FIG. 2  illustrates splashing of a molten metal solution (molten zinc) which occurs in a gas wiping apparatus  120 . 
     As shown in  FIG. 2 , a high-speed high-pressure gas is ejected through outlets  122  e.g., slits formed between upper and lower lips of the gas wiping apparatus  120 , to collide against surfaces of the steel strip. Here, molten metal particles, e.g., molten zinc particles, (which will be hereinafter referred to as zinc chips) deposited on the steel strip are splashed due to gas moving upward and downward at a high speed. 
     For example, in  FIG. 2 , the gas ejected from the gas outlets at a high pressure and a high speed causes a negative pressure area to be formed around the outlets owing to the gas traveling fast so that the zinc chips d are splashed from the surfaces of the coated steel strip. 
     Meanwhile, currently, to boost production of the coated steel strip, the steel strip is made to move at a higher speed. Also, to lower costs of the steel strip, a molten metal layer is required to be coated on the steel strip to a thickness as small as possible within a desired extent. 
     In the case of thin coating, greater portions of the molten metal should be worn from the surfaces of the coated steel strip passing through the hot dipping bath as indicated with reference numeral  110  of  FIG. 1 . Therefore, this requires gas to move at a higher speed, thereby increasing a collision pressure. 
     However, as described above, the higher speed of the gas ejected proportionally aggravates splashing of the zinc chips so that the gas is limitedly increased in its ejection speed. 
     The zinc chips d splashed as described above are deposited on or around the outlets of the gas wiping apparatus, causing the gas to be ejected with non-uniform distribution along a width direction of the steel strip. This results in defective coating of the steel strip. 
     Therefore, to restrain the molten metal from splashing during thin coating, currently the steel strip moves at a lower speed to be coated, thus limiting a high-speed travel of the steel strip and eventually degrading production of the steel strip. 
     Lately, a major concern with the gas wiping apparatus  120  is to eject the gas at a high speed and a high pressure while moving the steel strip faster and maximally suppressing the zinc chips from splashing which adversely affects product quality. 
     Conventionally, several technologies with regards to the gas wiping apparatus have been proposed to suppress the zinc chips from splashing. However, these technologies entail a complicated separate structure other than the gas wiping apparatus. Also, with the technologies, the zinc chips are not effectively prevented from splashing in an actual coating process. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the foregoing problems of the prior art and therefore an aspect of the present invention is to provide a multi-nozzle gas wiping apparatus, which can wipe the surface of a steel strip passing through a hot dipping bath filled with molten metal by a high speed gas jet while suppressing zinc chips from being scattered even during a high-speed coating. 
     Another aspect of the invention is to provide a multi-nozzle gas wiping apparatus, in which multiple uniform pressure spaces (chambers) are formed to ensure a gas jet to be sprayed uniformly through the multiple nozzle unit along a width direction of a steel strip, and also turbulent components of the gas jet are inhibited to allow the jet to be sprayed stably. 
     Technical Solution 
     According to an aspect of the invention, the gas wiping apparatus includes a body containing a high pressure gas; and a multiple nozzle unit disposed at the body to eject the high pressure gas onto a surface of a moving coated steel strip. 
     Preferably, the body is configured as a chamber defining a space for containing the high pressure gas supplied through a gas feed pipe which is connected to the body, and gas exhaust holes are perforated in a side wall of the chamber, where the multiple nozzle unit is installed, to spray the high pressure gas therethrough. 
     More preferably, the body has a partition wall for dividing the space for containing the high pressure gas into first and second uniform pressure spaces, wherein the partition wall has gas passage holes perforated therein. 
     The multiple nozzle unit includes a main nozzle disposed at the side wall of the chamber of the body to communicate with the gas exhaust holes in the chamber; and at least one auxiliary nozzle disposed over and under the main nozzle, respectively, to communicate with the gas exhaust holes. 
     Preferably, the main nozzle includes one nozzle, and the auxiliary nozzle includes first and second auxiliary nozzles disposed over and under the main nozzle, respectively. 
     Also, the gas wiping apparatus further includes a third uniform pressure space formed inside the main nozzle, communicating with the second uniform pressure space of the chamber through the gas exhaust holes. 
     The main nozzle and the auxiliary nozzle include upper and lower lips joined to the side wall of the chamber, the upper and lower lips defining main and auxiliary gas outlets. 
     The main and auxiliary gas outlets are disposed at a predetermined interval sequentially from the chamber, in a moving direction of the steel strip. 
     The chamber of the body includes a chamber body containing the high pressure gas therein; and a lip support unit disposed at the chamber body and provided therein with the lips of the multiple nozzle unit. 
     The lip support unit includes lip supports having the upper and lower lips of the main and the auxiliary nozzles slantingly and movably engaged therewith; and a support body having gas exhaust orifices for exhausting the high pressure gas contained in the chamber toward the gas exhaust outlets formed between the lips, the support body integrally connected to the lip supports to support the wiping device against load. 
     The gas wiping apparatus further includes a first gas guide disposed in the uniform pressure spaces of the chamber and configured to adjust an amount of the high-pressure gas flowing to the main and auxiliary nozzles. 
     The first gas guide includes guide plates which are rotatably connected to a corresponding one of the lip supports for supporting the main nozzle in the lip support unit, the guide plates installed rotatably in the chamber by a driving unit vertically associated therewith. 
     The driving unit is disposed on the side wall of the chamber not to interfere with a flow of the high-pressure gas and comprises a driving cylinder having the guide plates connected thereto. 
     The gas wiping apparatus further includes a second gas guide disposed in the uniform pressure spaces of the chamber and configured to allow the high-pressure gas to flow to the main nozzle and the auxiliary nozzle at a uniform amount. 
     The second gas guide comprises the guide plates which define a gas passage opening in the second uniform pressure space while forming a fourth uniform pressure space therebetween. 
     Advantageous Effects 
     In a multi-nozzle gas wiping apparatus according to the invention, the surface of a steel strip passing through a hot dipping bath filled with a molten metal is wiped by a high speed gas jet. Meanwhile, zinc chips are effectively prevented from splashing even during a high speed coating, thereby increasing productivity of the coating process. 
     Moreover, multiple uniform pressure spaces (chambers) are formed inside the gas wiping apparatus to ensure a gas jet to be sprayed uniformly through the multiple nozzle unit along a width direction of the steel sheet. Also, turbulent components of the jet are inhibited to ensure the jet to be sprayed stably. 
     Therefore, the gas wiping apparatus having the multiple nozzle unit prevents zinc chips from splashing by adjusting a coating thickness of the steel sheet. This also allows the gas to be ejected uniformly along a width direction of the steel sheet, ultimately enhancing coating quality of the steel strip. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view illustrating an example of a conventional continuous hot dip galvanizing apparatus; 
         FIG. 2  is a view illustrating splashing of zinc chips in a conventional gas wiping apparatus (air knife); 
         FIG. 3  is a schematic configuration view illustrating a multi-nozzle gas wiping apparatus according to the invention; 
         FIG. 4  is a view illustrating a gas wiping by the multi-nozzle gas wiping apparatus according to the invention; 
         FIG. 5  is a graph illustrating collision pressures of wiping gases on a steel strip in a conventional single nozzle apparatus and a multiple nozzle apparatus of the invention, respectively; 
         FIGS. 6(   a ) and ( b ) are graphs illustrating negative pressures generated around a corresponding nozzle in the conventional single nozzle apparatus and a multiple nozzle apparatus of the invention, respectively, in which  FIG. 6(   a ) is a graph illustrating negative pressures generated at levels 10 cm up and down from the nozzle; and ( FIG. 6(   b ) is a graph illustrating negative pressures generated at levels 20 cm up and down from the nozzle; 
         FIG. 7  is a view illustrating operation of a three-nozzle gas wiping apparatus according to the invention; 
         FIG. 8  is a configuration view illustrating a multi-nozzle gas wiping apparatus according to a preferred embodiment of the invention; 
         FIG. 9  is an exploded perspective view of  FIG. 8 ; 
         FIG. 10  is a configuration view illustrating a multi-nozzle gas wiping apparatus according to another embodiment of the invention; 
         FIG. 11  is a partial rear view of  FIG. 10 ; 
         FIG. 12  is a partially broken perspective view of  FIG. 10 ; and 
         FIG. 13  is a structural view illustrating a multi-nozzle gas wiping apparatus according to further another embodiment of the invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The present invention will now be described in detail. 
     A gas wiping apparatus (or an air knife) adjusts a coating thickness of a steel strip. In the gas wiping apparatus, a high-pressure gas (air or inactive gas) is blown at a high speed through a nozzle thereof to collide against a steel strip, thereby generating a collision pressure. 
     Here, the higher pressure of the gas sprayed causes gas particles to move more dynamically, thereby wiping a coating layer of the steel strip to a small thickness. 
     Also, as the steel strip travels faster, more gas should participate in wiping per unit time so that the gas should be ejected at a higher pressure or at a higher speed. 
     For example, when it comes to a gas wiping for adjusting a coating thickness of the steel strip, the coating thickness is varied according to a moving speed of the steel strip, a pressure and speed of the gas sprayed from the nozzle and a gap between the steel strip and the nozzle. 
     However, in a case where the steel strip needs to be coated thinly, the steel strip can move faster by spraying the gas from the nozzle at a higher pressure and accordingly increasing a collision pressure of the gas with respect to the steel strip. 
     Here, high-speed gas particles collide against the steel strip and are redirected to move along a length direction of the steel strip at a high speed. The gas flowing along a length direction of the steel strip generates shear stress on surfaces of a molten metal deposited on the steel strip. The gas will be hereinafter referred to as a ‘wall jet’. 
     Therefore, when such shear stress surpasses surface tension of a molten coating layer of the steel strip, particles of the molten coated layer fall off, causing metal chips or zinc chips to be splashed as shown in  FIG. 2 . 
     Meanwhile, in the conventional gas wiping apparatus using a single nozzle shown in  FIG. 2 , for example, the zinc chips are splashed, when the steel strip travels at a speed of 160 mpm and is coated to a coating thickness up to 40 g/m 2 . 
     Therefore, when the steel strip moves at a speed of at least 160 mpm, in the conventional gas wiping apparatus (air knife), the steel strip is hardly coated to a coating thickness of up to 40 g/m 2 . 
     That is, with a rapidly rising demand for the coated steel strip for use in, e.g., automobiles or electric products, high-speed coating or thin coating has faced a limitation. 
     Therefore, the gas wiping apparatus of this invention ensures the steel strip to be coated to a small thickness even at a high speed. 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
     First,  FIG. 3  illustrates basic configuration of a multi-nozzle gas wiping apparatus  1 . 
     As shown in  FIG. 3 , the gas wiping apparatus  1  having the multiple nozzle unit includes a body  10  for containing a high-pressure gas (air or inactive gas) and a multiple nozzle unit  30  installed at the body to eject the high-pressure gas onto a moving, coated steel strip. 
     Here, the body  10  is configured as a chamber defining a space  20  for containing the high-pressure gas therein. Such a chamber is joined to a frame which fixes the apparatus to both sides of the moving steel strip. 
     Also, gas exhaust holes  12   a  are perforated in a side wall  12  of the chamber, where the multiple nozzle unit  30  is installed, to spray the high pressure gas therethrough. 
     Moreover, the body  10  has a horizontal partition wall  14  for dividing the space  20  into first and second uniform pressure spaces  20   a  and  20   b . The partition wall  14  has gas passage holes perforated therein. 
     Preferably, as will be explained in detail below, the body  10  further includes a third uniform pressure space  20   c  formed inside a main nozzle  32 , communicating with the second uniform pressure space  20   b  of the chamber through the gas exhaust holes  12   a.    
     Therefore, referring to  FIG. 3 , the gas is provided at a high pressure through a high pressure feed pipe  18  which is connected to a side wall ( 16  of  FIG. 9 ) of the chamber  10  or to an upper part thereof. When the gas is fed through the high pressure feed pipe  18  connected, the gas is fed to the second uniform pressure space  20   b  from the first uniform pressure space  20   a  through the gas passage holes  14   a . Subsequently, the gas is exhausted to the third uniform pressure space  20   c  disposed inside the main nozzle  32  through the gas exhaust holes  12   a  perforated in the side wall of the chamber. 
     In this fashion, the high-pressure gas is distributed uniformly to each of the uniform pressure spaces and then sprayed through the main nozzle  32  and first and second auxiliary nozzles  34  and  36  of the multiple nozzle unit  30 . 
     That is, the high-pressure gas is ejected uniformly along a width direction of the steel strip through the main nozzle  32  and the first and second auxiliary nozzles  34  and  36 , thus allowing the steel strip to be coated with a uniform thickness. 
     As shown in  FIG. 3 , the multiple nozzle unit  30  is disposed at the side wall of the chamber to communicate with the gas exhaust holes  12   a  perforated in the side wall  12  of the chamber  10 . Also, the multiple nozzle unit  30  includes the main nozzle  32  for adjusting a coating thickness of the steel strip and the first and second auxiliary nozzles  34  and  36  disposed over and under the main nozzle  32  to connect to the gas exhaust holes. Here, the auxiliary nozzles  34  and  36  serve to prevent the molten metal from splashing. 
     That is, according to characteristics of the invention, the gas wiping apparatus  1  includes the main nozzle  32  and at least one auxiliary nozzle, preferably, the first and second auxiliary nozzles  34  and  36  sequentially disposed over and under the main nozzle  32 . 
     Reference signs  32   c ,  34   c  and  36   c  in  FIG. 3 , which are not described, denote gas exhaust outlets of the nozzles. 
       FIG. 4  illustrates gas colliding against a steel strip when sprayed through a multiple nozzle unit  30  including a main nozzle  32  and at least one auxiliary nozzle (first auxiliary nozzle)  34 . 
     That is, as shown in  FIG. 4 , a main gas G 1  sprayed from the main nozzle  32  collides against surfaces of the steel strip S to adjust a coating thickness thereof. A gas G 2  sprayed from the first auxiliary nozzle  34  surrounds the main gas G 1 , thereby preventing zinc chips (metal chips) from splashing as described with reference to  FIG. 2 . 
     For example, the gas sprayed from the main nozzle may have greater shear stress along a length direction of the steel strip than surface tension of a coating layer. However, in this case, the gas ejected from the first auxiliary nozzle surrounds the main gas from the main nozzle, thereby preventing zinc chips from splashing caused by the gas ejected from the main nozzle. 
     Then,  FIG. 5  illustrates a collision pressure of gas with respect to a steel strip in a case where a conventional single nozzle is employed, and main and auxiliary nozzles are adopted together, respectively. 
     That is, as shown in  FIG. 5 , in a case where the auxiliary nozzle is employed, the collision pressure of the gas with respect to the steel strip in a moving direction of the steel strip is higher than in a case where only the single nozzle (indicated with ‘no auxiliary nozzle’) is employed. 
     That is, according to the invention, the gas ejected from the main nozzle and the gas ejected from the auxiliary nozzle cooperatively increase a collision pressure of the entire gas with respect to the steel strip. At the same time, the gas ejected from the auxiliary nozzle prevents zinc chips from splashing. 
     Therefore, when a coating amount is adjusted with the gas ejected at an identical speed in the conventional single nozzle and the main and auxiliary nozzles, respectively, the collision pressure of the sprayed gas with respect to the steel strip is increased in the gas wiping apparatus  1  of the invention, assuring the steel strip to be coated thinly while suppressing zinc chips from splashing. 
       FIGS. 6   a  and  6   b  illustrate negative pressures generated at levels 10 cm and 20 cm from the center of the nozzle with respect to a moving direction of a steel strip. 
     That is, as shown in  FIG. 6   b , in a case where the main nozzle  32  and the auxiliary nozzles  34  are employed, the wall jet is insufficiently decreased in its speed. This generates a negative pressure resulting from the high speed flow of gas in areas a bit away from a collision point along a length direction of the steel strip, i.e., 20 cm up and down from the center of the nozzles. This potentially causes the zinc chips to splash. 
     However, as shown in  FIG. 6   a , a negative pressure due to the high-speed flow of gas hardly occurs in areas less away from the collision point along a length direction of the steel strip, i.e., 10 cm up and down from the center of the nozzle. 
     Accordingly, as shown in  FIG. 3 , preferably, the second auxiliary nozzle  36  is installed together with the first auxiliary nozzle  34 . This increases an ambient pressure and eliminates a negative pressure partially generated on the steel strip around the nozzles of the gas wiping apparatus (air knife), thereby forming an activated positive pressure. This prevents zinc chips from splashing on the entire molten coating layer of the steel strip. 
       FIG. 7  illustrates distribution of gas sprayed in a most desirable case where a main nozzle  32  and first and second auxiliary nozzles  34  and  36  are employed in a multi-nozzle gas wiping apparatus  1 . 
     The main nozzle  32  and the first auxiliary nozzle  34  of the multiple nozzle unit  30  eject gases G 1  and G 2  necessary for gas wiping which meets high-speed thin coating conditions. 
     The second auxiliary nozzle  36  ejects a gas G 3  at a relatively lower speed than the main nozzle and the first auxiliary nozzle. Thus, gas particles sprayed from the main nozzle at a high speed, collide against the steel strip, and are mixed with gas particles ejected from at least the second auxiliary nozzle (preferably first and second auxiliary nozzles) at a lower speed to decrease the overall gas speed. This accordingly allows the wall jet to move at a lower speed along a length direction of the steel strip. This weakens shear stress and thus restrains zinc chips from splashing. 
       FIGS. 8 to 13  illustrate detailed structures of a multi-nozzle gas wiping apparatus  1  of the invention, whose basic functions have been explained above. 
     First,  FIGS. 8 and 9  illustrate a gas wiping apparatus  1  including a lip support unit  24  according to another embodiment of the invention of  FIG. 3 . 
     For example, the body  10  of the invention described above is configured as a chamber, and includes a space  20  for containing a high-press gas composed of first to third uniform pressure spaces  20   a ,  20   b  and  20   c , a chamber body  22  fixed to the fixing frame and a lip support unit  24  provided to the chamber body and having a main nozzle and first and second auxiliary nozzles. 
     Here, the lip support unit  24  includes lip supports  26  and a support body  28 . The lip supports  26  have upper and lower lips of the main, first and second nozzles  32 ,  34  and  36  slantingly and movably engaged therewith. The support body  28  has gas exhaust orifices  28   a  for exhausting the high-pressure gas toward gas exhaust outlets and is integrally connected to the lip supports to support the wiping device against load. 
     Therefore, in the gas wiping apparatus  1  according to the modified embodiment of the invention as shown in  FIGS. 8 and 9 , the lip support unit  24  constitutes a main body to sustain load. Accordingly, to render the chamber body  22  of the invention sufficiently strong, a thickness of the chamber body  22  engagingly fixed to the lip support unit  24  does not need to exceed that of a chamber body of a conventional gas wiping apparatus. 
     Here, to build the chamber body  22 , flanges f with three bent pieces  22   a ,  22   b , and  22   c  are assembled together by bolts and nuts to enable separate components to be installed therein in a case where the gas wiping apparatus undergoes maintenance and repair, or is fabricated. The upper and lower pieces  22   a  and  22   c  of the chamber are connected to the upper and lower lip supports  26  of the lip support unit, respectively. 
     Meanwhile, the main nozzle  32  and the first and second auxiliary nozzles  34  and  36  include the main lip  32   a  and  32   b  and the first and second upper and lower lips  34   a,    34   b ;  36   a ,  36   b  which can be assembled and dissembled on the lip supports  26  of the lip support unit  24 . These main, first and second upper and lower lips are slantingly installed on slanted surfaces of the lip supports  26 . 
     Here, the lips have slits h perforated therein to bolt the lips therethrough on the slanted surfaces of the lip supports  26 . This allows the lips to be adjustably positioned. 
     As a result, as shown in  FIGS. 8 and 9 , in the gas wiping apparatus  1  of the invention, a main outlet  32   c  is formed at a distal end of the central main lips  32   a  and  32   b . First auxiliary outlets  34   c  are formed between the main lips and the first upper and lower auxiliary lips  34   a  and  34   b . Likewise, second auxiliary outlets  36   c  are formed between the first auxiliary upper and lower lips  34   a  and  34   b  and the second upper and lower auxiliary lips  34   a ,  34   b ,  36   a  and  36   b , respectively. 
     What is important, the main outlet  32   c  is located most adjacent to the steel strip and then the first and second auxiliary outlets  34   c  and  36   c  of the first and second auxiliary nozzles are located next to the main outlet  32   c  sequentially. 
     Therefore, when gases are ejected at an identical speed, the gas ejected from the main outlet exhibits a greatest collision pressure with respect to the steel strip, followed by the first and second auxiliary nozzles. When it comes to the speed of the gas sprayed onto the steel strip, the gas is most slowly ejected from the second auxiliary outlet which is located at a greatest distance. 
     That is, as shown in  FIG. 7 , the gas ejected from the main outlet and the first auxiliary outlets adjusts a coating thickness of the steel strip. Meanwhile, the gas ejected from the first and second auxiliary outlets decreases the wall jet, thereby restraining zinc chips from splashing. 
     Here, reference numeral  16  of  FIG. 9  denotes a side wall of the body (chamber)  10 . 
       FIGS. 10 to 12  illustrate gas wiping apparatuses  1  according to other embodiments of the invention. 
     As shown in  FIG. 10 , the gas wiping apparatus according to the modified embodiment of the invention further includes a first gas guide  50  disposed in the second uniform pressure space of the chamber and configured to adjust an amount of a high-pressure gas flowing to main and auxiliary nozzles. 
     The first gas guide  50  includes guide plates  50   a  and  50   b  which are rotatably connected to a corresponding one of lip supports  26  for supporting the main nozzle  32 . The guide plates  50   a  and  50   b  are installed rotatably in the second uniform pressure space by a driving unit  52  or a driving cylinder vertically associated therewith. 
     Therefore, the guide plates  50   a  and  50   b  are pivoted about a lip support unit by the driving cylinder  52 . This adjusts the amount of an internal gas flowing to the first and second auxiliary nozzles  34  and  36 . 
     Meanwhile, the driving unit  52  or the drive cylinder, as shown in  FIGS. 11 and 12 , is disposed vertically in a protrusion  16   a  formed on a side wall  16  of the body (chamber)  10  and inside a cover  51  not to interfere with a flow of the high-pressure gas. Also, the driving cylinder  52  has the guide plates connected thereto. 
     Consequently, with the driving cylinder operated, the guide plates  50   a  and  50   b  are rotated about a hinge point of the lip support unit to adjust an amount of the gas flowing to the first and second auxiliary nozzles  34  and  36 . 
     Here, although not designated with reference numerals in the drawings, rods of the driving cylinder are connected to the guide plates, respectively, in a structure having slits and hinge pins which can move in response to the rotation of the guide plates. 
     Meanwhile, in a case where the driving cylinder  52  is moved by the stroke of the rods that operate identically, the upper and lower guide plates are rotated at an identical amount. On the other hand, in a case where the driving cylinder  52  is driven separately, the upper and lower guide plates can be separately adjusted in their rotational amount. 
       FIG. 13  illustrates a gas wiping apparatus  1  according to further another embodiment of the invention. 
     The gas wiping apparatus according to this modified embodiment of the invention further includes a second gas guide  54 , i.e., guide plates disposed in a second uniform pressure space of the chamber and configured to allow a high-speed gas to flow to main and auxiliary nozzles at a uniform amount. 
     In consequence, the second guide plates  54  define a gas passage opening in the second uniform pressure space while forming a fourth uniform pressure space  20   d  therebetween. This ensures the gas to be ejected from the main nozzle and the first and second auxiliary nozzles with uniform distribution even despite a change in the flow rate or pressure of the gas. 
     INDUSTRIAL APPLICABILITY 
     As set forth above, according exemplary embodiments of the invention, a multi-nozzle gas wiping apparatus can wipe the surface of a steel strip passing through a hot dipping bath filled with molten metal by a high-speed gas jet. Moreover, the molten metal is inhibited from splashing even during a high-speed coating, and eventually, a coating thickness (coating amount) of the steel strip can be adjusted stably and uniformly. 
     While the present invention has been shown and described in connection with the preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.