Peep window, snout with peep window, and method for preventing foreign matter from adhering to the peep window.

Abstract

To provide: a peephole capable of suppressing foreign matter adhesion to a window part while preventing a view from the window part from being interrupted; a snout having the same; and method for preventing fumes from adhering to the peephole.SOLUTION: A peephole 7 for checking the inside of a housing 5 includes a window part 8; a header 9; a cylindrical spacer part 10 for connecting the header 9 with the housing 5 at a preset interval; an aperture part 11 provided between the header 9 and the spacer part 10 and having an inner diameter smaller than that of the spacer part 10; and a supply port for supplying gas having a pressure higher than that of the inside of the housing 5 to the header 9.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a viewing window, a snout with a viewing window, and a method for suppressing foreign matter adhesion to a viewing window. In particular, in a continuous hot dip plating line for thin steel sheets, it relates to a viewing window for observing the inside of a snout for a plating bath, a snout with a viewing window, and a method for suppressing foreign matter adhesion to the viewing window.

Background Art

[0002] In order to observe a closed space such as the inside of a snout for a plating bath, a viewing window may be provided in the snout. For example, in the case of a continuous hot dip plating line for thin steel sheets, a viewing window for observing the liquid level of the plating bath inside the snout is provided on the wall surface of the snout in order to investigate the cause of troubles related to the surface properties of the plating and to suppress them.

[0003] However, in such a viewing window provided on the wall surface of the snout, poor visibility due to the adhesion of metal fumes, that is, metal fine particles generated in the plating bath or the snout, to the inside of the window part in the viewing window has been a problem.

[0004] Devices and methods for solving such problems have been conventionally studied. For example, Patent Document 1 describes a viewing window for looking into the inside of a plasma ash melting furnace. The viewing window has a header part where a window material is provided and a communication path that communicates with the header part inside the furnace, and is configured to blow purge gas into the header part. Further, the inner diameter of the communication path is set smaller than the inner diameter of the header part. Therefore, in the viewing window of Patent Document 1, the flow rate of the purge gas flowing through the communication part toward the inside of the furnace increases, thereby preventing the backflow of the furnace gas into the header part and suppressing the adhesion of fumes to the window material. Also, Patent Document 2 describes a monitoring device inside a snout provided with a valve between the viewing window and the snout. In that device, by closing the valve, it is possible to suppress the adhesion of fumes to the inside of the window part.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2003-021326 [Patent Document 2] Publication number 02-048420 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the viewing window described in Patent Document 1, as mentioned above, the flow velocity of the purge gas is increased by making the inner diameter of the communication passage smaller than the inner diameter of the header section, thereby preventing backflow of furnace gas into the header section and suppressing the adhesion of fumes to the inside of the window section. However, in order to sufficiently prevent backflow of furnace gas with the purge gas, it is necessary to make the overall diameter of the communication section even narrower and further increase the flow velocity of the purge gas. However, such a configuration has the drawback that the view when looking into the furnace from the viewing window is obstructed by the communication section.

[0007] Furthermore, even with a method like the one shown in Patent Document 2, which completely blocks fumes by installing a valve or rotary shutter between the viewing window and the snout, there is a possibility that gas from inside the snout may flow into the viewing window when the valve is opened to check the inside of the snout, causing fumes to adhere to the viewing window.

[0008] The present invention was made to solve the above problems, and aims to provide a viewing window, a snout with a viewing window, and a method for suppressing fume adhesion to a viewing window, which can suppress obstruction of the view from the window while suppressing the adhesion of foreign matter to the window. [Means for solving the problem]

[0009] To achieve the above objectives, the present invention [1] A viewing window comprising a window portion and a header portion on which the window portion is formed, wherein the viewing window is used to check the inside of the housing through the window portion, comprising a cylindrical spacer portion that connects the header portion and the housing at a predetermined distance apart, a constricted portion provided between the header portion and the spacer portion and having an inner diameter smaller than the inner diameter of the spacer portion, and a supply port that supplies gas to the header portion at a pressure higher than the internal pressure of the housing. [2] The viewing window according to [1] above, further comprising a suppression device located inside the header portion that covers at least a portion of the window portion to suppress the adhesion of foreign matter to the window portion. [3] The viewing window according to [1] above, further comprising a removal device inside the header portion for removing foreign matter adhering to the window portion. [4] The viewing window described in [1] above, where d is the outer diameter of the window portion, A is the inner diameter of the spacer portion, a is the inner diameter of the aperture portion, B is the distance between the window portion and the housing, and b is the distance from the window portion to the aperture portion, and the relationship (ad) / b > (Ad) / B is satisfied. [5] The viewing window described in [1] above, wherein the diameter of the header portion is larger than the diameter of the spacer portion. [6] The suppression device is a shutter, which is the peephole described in [2] above. [7] The removal device is a wiper, which is the viewing window described in [3] above. [8] A snout with a viewing window, having the viewing window described in [1] above, and the tip of which is in contact with the plated bathtub. [9] A method for suppressing foreign matter adhesion to a viewing window according to any one of [1] to [7] above, wherein the gas is supplied from the supply port to the header portion to generate a gas flow toward the housing side via the throttling portion and the spacer portion, and the movement of foreign matter toward the header portion from the housing is suppressed by the gas flow. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress obstruction of the view from the window while suppressing the adhesion of foreign matter to the window portion of the viewing window. As a result, it is possible to observe a wide area inside the housing from the window, and running costs such as cleaning and maintenance of the viewing window can be reduced. [Brief explanation of the drawing]

[0011] [Figure 1] This is a side cross-sectional view showing an example of a continuous hot-dip galvanizing line. [Figure 2] This is a view from the direction of arrow α shown in Figure 1. [Figure 3] This is a cross-sectional view showing an example of a viewing window according to the present invention. [Figure 4] This is a cross-sectional view showing another example of a viewing window according to the present invention. [Modes for carrying out the invention]

[0012] (First Embodiment) Embodiments of the present invention will be described below. Figure 1 is a side cross-sectional view showing an example of a continuous hot-dip galvanizing line. The continuous hot-dip galvanizing line 1 shown in Figure 1 is a line that performs plating on the surface of a strip-shaped thin steel sheet (hereinafter referred to as "thin sheet") 3 by continuously immersing it in the molten plating stored in the plating bath 2. In the example shown in Figure 1, a cylindrical snout 5 is connected to the exit end of the heat treatment furnace 4 in the direction of transporting the thin sheet 3. The heat treatment furnace 4 can be a continuous annealing furnace as an example. The thin sheet 3 is transported inside the heat treatment furnace 4 by a transport device (not shown). The end of the snout 5 opposite to the heat treatment furnace 4 in the longitudinal direction is immersed in the molten plating stored in the plating bath 2. This is to avoid oxidation of the surface of the thin sheet 3 if it is exposed to the outside air. In other words, the inside of the snout 5 is not open to the outside and is a closed space where it is difficult to monitor the inside from the outside during use. The snout 5 corresponds to the housing of the present invention. Hot-dip plating refers to the process of melting metals in a liquid phase, such as zinc, aluminum, lead, tin, or their alloys, at a temperature above their melting point.

[0013] Figure 2 is a view along the α arrow shown in Figure 1. As shown in Figures 1 and 2, a sink roll 6 is positioned below the surface of the molten plating liquid. The thin plate 3 is wrapped around the sink roll 6 so that it passes under the sink roll 6 in the vertical direction of the plating bath 2. This ensures that the thin plate 3 is reliably immersed in the molten plating, and the sink roll 6 changes the direction of travel of the thin plate 3 upwards in the vertical direction, allowing the plated thin plate 3 to be lifted out of the plating bath 2.

[0014] The snout 5 is provided with a viewing window 7 according to this embodiment for observing the molten plating liquid level. Figure 3 is a cross-sectional view of the viewing window 7 according to this embodiment. The viewing window 7 shown in Figure 3 comprises a window portion 8 made of a transparent material such as glass, and a header portion 9 on which the window portion 8 is provided. The header portion 9 is connected to the snout 5 via a cylindrical spacer portion 10, and the header portion 9 and the snout 5 are separated from each other by the length of the spacer portion 10. This is to avoid the situation where foreign matter such as fumes generated in the plating bath 2 adheres to the window portion 8, making it difficult to observe the molten plating liquid level. Therefore, the length of the spacer portion 10 is preferably such that fumes do not easily reach the window portion 8, and this can be determined, for example, by experiment.

[0015] The header part 9, for example, has a hollow box shape, and a window part 8 is integrally provided at the center of one surface in the height direction (the left - right direction in FIG. 3). A substantially circular opening that penetrates in the plate thickness direction is formed on the surface of the header part 9 opposite to the window part 8, and the peripheral part of the opening functions as a flange part. Specifically, the header part 9 has a hollow cylindrical shape, and a substantially circular window part 8 is provided at the center of the upper surface of the header part 9, that is, the center of the left - hand side surface in the left - right direction of FIG. 3. A substantially circular opening is formed at the center of the bottom surface of the header part 9, that is, the center of the right - hand side surface in the left - right direction of FIG. 3, and a spacer part 10 is connected to this opening. The inner diameter a of the opening is set smaller than the inner diameter A of the spacer part 10. Therefore, the opening functions as a throttle part 11 that narrows the fluid flow path between the header part 9 and the snout 5 via the spacer part 10.

[0016] One end in the length direction of the spacer part 10 is connected, for example, by welding to a through - hole 12 formed on the outer peripheral surface of the snout 5. The inner diameter of the through - hole 12 is set to be approximately the same as the inner diameter A of the spacer part 10. Specifically, the spacer part 10 is welded to the outer peripheral surface of the snout 5 with the center of the through - hole 12 substantially coinciding with the center axis of the spacer part 10.

[0017] A flange part that protrudes outward in the radial direction is formed at the other end in the length direction of the spacer part 10. In the example shown in FIG. 3, with the central axis of the header part 9 and the central axis of the spacer part 10 substantially coinciding, the flange part of the header part 9 and the flange part of the spacer part 10 are overlapped with each other via a packing 13, and they are connected by bolts 14.

[0018] An opening is formed through the outer peripheral surface (side surface) of the header portion 9 in the plate thickness direction, and a gas pipe 15 is communicated with the opening. The gas pipe 15 is connected to a gas supply source not shown. Gas is supplied from the gas supply source to the inside of the header portion 9 through the gas pipe 15 and the opening formed on the side surface of the header portion 9. That is, the opening formed on the outer peripheral surface of the header portion 9 functions as a gas supply port. The gas is preferably an inert gas such as nitrogen, carbon dioxide, or a rare gas. Also, the pressure of the inert gas is preferably at least approximately the same as the pressure inside the snout 5, and more preferably higher than the pressure inside the snout 5. This is because if the pressure of the inert gas is lower than the pressure inside the snout 5, the pressure inside the header portion 9 will drop below the pressure inside the snout 5, making it easier for fumes to enter the header portion 9. And this may cause fumes to adhere to the window portion 8, so this is to avoid that.

[0019] Also, inside the header portion 9, a fume removal device for removing fumes when fumes adhere to the surface of the window portion 8 (hereinafter referred to as the inner surface) is provided in the header portion 9. Examples of the removal device include a wiper that wipes the inner surface of the window portion 8 to remove fumes, and a cleaning device that blows high-pressure cleaning fluid onto the inner surface of the window portion 8 to blow off and remove fumes. FIG. 3 shows an example when the removal device is a wiper 16, and the wiper 16 is arranged inside the header portion 9.

[0020] A rod 17 is connected to the wiper 16. In the example shown in FIG. 3, the rod 17 extends in the radial direction of the header portion 9, and the tip of the rod 17 protrudes outside the header portion 9. That is, an opening is formed through the side surface of the header portion 9 in the plate thickness direction, and the rod 17 is passed through the opening so as to be movable in the radial direction of the header portion 9. In addition, in order to maintain the airtight state of the header portion 9, a packing not shown is provided between the opening and the rod 17.

[0021] A handle 18 is provided at the tip of the rod 17. The system is configured so that fumes adhering to the inner surface of the window section 8 can be removed by the wiper 16 by gripping the handle 18 and pushing it towards the header section 9, and then pulling it back to its original position. Alternatively, the wiper 16 may be configured to operate automatically instead of being operated manually. For example, a motor or fluid pressure cylinder (not shown) can be connected to the handle 18 or the tip of the rod 17 to transmit power. The motor or fluid pressure cylinder can then be driven by a timer (not shown) to operate the wiper 16, or the drive of the motor or fluid pressure cylinder can be controlled by a control device (not shown) to operate the wiper 16.

[0022] Here, the sizes of each component of the viewing window 7 will be explained. The outer diameter D of the header section 9 is set to be larger than the inner diameter A of the spacer section 10 and the inner diameter of the through hole 12. Also, in this embodiment, the inner diameter a of the aperture section 11 is set to be greater than or equal to the outer diameter d of the window section 8 (a≧d). Furthermore, the value obtained by subtracting the outer diameter d of the window section 8 from the inner diameter a of the aperture section 11 and dividing it by the height b of the header section 9 in the left-right direction in Figure 3 is set to be larger than the value obtained by subtracting the outer diameter d of the window section 8 from the inner diameter A of the spacer section 10 and dividing it by the height B of the viewing window 7 in the left-right direction in Figure 3 ((ad) / b>(Ad) / B). By doing this, it is possible to suppress the obstruction of the field of view when looking into the inside of the snout 5 from the window section 8 by the aperture section 11 and the spacer section 10. In Figure 3, the range of the field of view when looking into the inside of the snout 5 from the window section 8 is indicated by a dashed line.

[0023] (Effects / Actions) The thin sheet 3 is heat-treated in the heat treatment furnace 4 shown in Figure 1, and the thin sheet 3 is transported to the plating bath 2 via a snout 5 by a transport device (not shown) without being exposed to the outside air. The thin sheet 3 is then immersed in the molten plating and plated. The molten plating stored in the plating bath 2 is a liquid-phase metal molten at a high temperature. Therefore, metal fumes may be generated in the plating bath 2. These fumes are fine metal particles, and these particles are heavier than the air inside the snout 5. The high temperature mentioned above means a temperature at least above the melting point of the metal used for molten plating.

[0024] Meanwhile, at the surface of the molten plating, the air is heated, creating an updraft. As a result, the fumes move upwards in the vertical direction within the snout 5 due to the updraft.

[0025] On the other hand, inert gas is continuously or intermittently supplied to the header section 9 of the viewing window 7 via a gas pipe 15 from a gas supply source (not shown), creating a gas flow of inert gas from the header section 9 to the snout 5 side. Since the inner diameter a of the throttling section 11 is smaller than the inner diameter of the header section 9, the inert gas is less likely to flow out of the header section 9 to some extent, and as a result, the internal pressure of the header section 9 is kept at a high state, i.e., positive pressure.

[0026] Furthermore, the inner diameter a of the throttling section 11 is smaller than the inner diameter A of the spacer section 10, which is the inner diameter of the through hole 12. Therefore, when the gas flow passes through the throttling section 11, its flow velocity increases compared to the flow velocity of the gas flow upstream of the throttling section 11 in the direction of inert gas flow. This increased-velocity gas flow then flows into the snout 5 via the spacer section 10.

[0027] At the connection point between the spacer section 10 and the snout 5, the upward airflow containing the aforementioned fumes and the gas flow of the inert gas collide. The gas flow of the inert gas pushes the fumes and the air containing the fumes towards the snout 5, thus suppressing the inflow of air containing the fumes into the spacer section 10. Furthermore, even if air containing the fumes does flow into the spacer section 10, the spacer section 10 has a certain length, and the gas flow of the inert gas within the spacer section 10 pushes the air containing the fumes back towards the snout 5. Therefore, it is possible to suppress the movement of fumes from the inside of the spacer section 10 towards the header section 9.

[0028] Furthermore, the gas flow velocity of the inert gas is highest in the throttling section 11. In the throttling section 11, the high-velocity gas flow pushes the fumes back, making it difficult for the fumes to pass through the throttling section 11. In addition, the header section 9 is kept under positive pressure as described above. Therefore, this also helps to prevent fumes from entering the header section 9. If fumes do enter the header section 9 and adhere to the inner surface of the window section 8, grasp the handle 18, push the handle 18 towards the header section 9, and then pull it back to its original position. By doing so, the fumes adhering to the window section 8 can be removed by the wiper 16.

[0029] Furthermore, in this embodiment, as described above, by making the inner diameter a of the throttling section 11 smaller than the inner diameter A of the spacer section 10, the flow velocity of the inert gas flow is maximized in the throttling section 11, thereby suppressing the intrusion of fumes into the header section 9. In other words, without reducing the inner diameter A of the entire spacer section 10, that is, without making the inner diameter A of the spacer section 10 the same size as the inner diameter a of the throttling section 11, only the inner diameter of the throttling section 11 located between the spacer section 10 and the header section 9 is reduced. With this configuration, while suppressing the intrusion of fumes into the header section 9, it is possible to suppress the obstruction of the view when looking into the inside of the snout 5 from the window section 8 by the spacer section 10, compared to the case where the inner diameter A of the entire spacer section 10 is reduced. As a result, the inside of the snout 5 can be observed over a wide area from the window section 8.

[0030] Thus, according to the first embodiment, it is possible to suppress the adhesion of fumes to the inner surface of the window portion 8 and the fogging of the window portion 8 caused by the adhesion of fumes to the inner surface of the window portion 8. Furthermore, even if fumes do adhere to the window portion 8, they can be easily removed by the wiper 16. Therefore, according to the first embodiment, the field of view of the viewing window 7 is ensured, and the liquid level of the molten plating can be reliably observed. In addition, since the viewing window 7 can be easily cleaned at any time, the running costs of the viewing window 7 can be reduced accordingly.

[0031] (Second Embodiment) Figure 4 is a cross-sectional view showing another example of the viewing window according to the present invention. The example shown in Figure 4 is one in which a suppression device is provided on the viewing window 7 to cover the window portion 8 and suppress the adhesion of fumes. The header portion 9 shown in Figure 4 is a hollow rectangular prism shape. The suppression device is, for example, a shutter 19 that covers at least a part of the window portion 8, and in the example shown in Figure 4, it is provided between the wiper 16 and the aperture portion 11 in the height direction (left-right direction in Figure 4) of the viewing window 7. The shutter 19 is, for example, a thin, flat member, and is rectangular or square in shape, which is about the same as the cross-sectional shape of the header portion 9, and its size is about the same as the size of the inside of the header portion 9. The shutter 19 enters the inside of the header portion 9 by an actuator and exits from the header portion 9 to be housed in the shutter housing (hereinafter referred to as the housing) 20. Therefore, the length of the shutter 19 in the vertical direction in Figure 4 is set to be about the same as the inner diameter of the header portion 9.

[0032] An example of an actuator is a rack and pinion device 21. The rack and pinion device 21 comprises a pinion gear 22 and a rack 23 on which gear teeth that mesh with the pinion gear 22 are formed. A power source (not shown) is connected to the pinion gear 22 in a manner that allows torque transmission, and the pinion gear 22 rotates in response to the torque transmitted from the power source. As the pinion gear 22 rotates, the rack 23 moves either towards the header section 9 or to the opposite side. In the example shown in Figure 4, the rack 23 moves in the vertical direction in Figure 4. A shutter 19 is connected to the rack 23 via a connecting section 24. The power source mentioned above can be, for example, a motor.

[0033] In the example shown in Figure 4, the housing 20 extends in the vertical direction in Figure 4, and one end of the housing 20 in the vertical direction is integrated with the outer circumferential surface of the header portion 9. An opening is formed at one end of the housing 20 that communicates with the interior of the header portion 9, and the shutter 19 enters and exits the interior of the header portion 9 through this opening. An opening is formed at the other end of the housing 20 through which the connecting portion 24 enters and exits the interior of the housing 20. To maintain the airtight state of the housing 20, a packing 25 is provided at the opening at the other end of the housing 20. The other configurations are the same as those shown in Figure 3, so the same reference numerals as in Figure 3 are used and their descriptions are omitted.

[0034] (Effects / Actions) In the second embodiment shown in Figure 4, if the molten plating liquid level is not observed through the viewing window 7, the power source described above is activated, for example, by an operator, and the pinion gear 22 is rotated in the forward direction by the torque generated by the power source. As a result, the rack 23 that meshes with the pinion gear 22 moves downward in the vertical direction of Figure 4. The shutter 19 is connected to the rack 23 via the connecting part 24. Therefore, as described above, when the rack 23 moves downward in the vertical direction of Figure 4, the shutter 19 retracts from the housing 20 and enters the interior of the header section 9. The shutter 19 then comes into contact with the inner surface of the header section 9 on the side opposite to the housing 20, and its movement stops. As a result, the window section 8 is covered by the shutter 19, so even if fumes enter the header section 9, they will not adhere to the window section 8.

[0035] In contrast, when observing the molten plating liquid level through the viewing window 7, the pinion gear 22 is rotated in the opposite direction to the forward direction by the power source. In other words, the shutter 19 retracts from the header section 9 and is housed inside the housing 20 by the opposite principle to the one described above. Then, an inert gas is supplied to the inside of the header section 9 via the gas pipe 15, and, as in the first embodiment, the entry of fumes into the inside of the header section 9 and the adhesion of fumes to the window section 8 are suppressed.

[0036] Thus, in the second embodiment shown in Figure 4, the adhesion of fumes to the window portion 8 of the viewing window 7 can be suppressed by opening the shutter 19 when observing the molten plating liquid surface and closing the shutter 19 at other times. Therefore, when the molten plating liquid surface is not being observed, the supply of inert gas can be stopped. In other words, running costs can be reduced by stopping the supply of inert gas. Furthermore, when the shutter 19 is opened to observe the molten plating liquid surface, as described above, inert gas is supplied to the inside of the header portion 9, so the same operation and effect as in the first embodiment can be obtained.

[0037] It should be noted that the present invention is not limited to the embodiments described above. In Figure 3, a wiper 16 is provided on the side of the header section 9 opposite to the gas pipe 15, but the installation positions of the gas pipe 15 and wiper 16 are not limited. Also, the actuator shown in Figure 4 may be a hydraulic cylinder or an air cylinder instead of the rack and pinion device 21. Furthermore, in the embodiments described above, the observation window of the present invention was explained using a continuous hot-dip galvanizing line for thin sheets equipped with a snout as a housing as an example, but the observation window of the present invention can be applied to things other than snouts. For example, it can be applied to various housings such as melting furnaces where it is difficult to monitor the inside.

[0038] Furthermore, in Figure 3, a wiper 16 as a removal device is provided inside the header section 9, and in Figure 4, both a wiper 16 as a removal device and a shutter 19 as a suppression device are provided inside the header section 9. However, it is also possible to configure the header section 9 to have only a suppression device such as a shutter 19, without providing a removal device such as a wiper 16 inside. Even with a configuration in which only a shutter 19 is provided inside the header section 9, the adhesion of fumes to the window section 8 of the viewing window 7 can be suppressed, similar to each embodiment. [Explanation of symbols]

[0039] 1. Continuous hot-dip galvanizing line 2. Plating Bathtub 3 thin plate 4. Heat treatment furnace 5. Snout (an example of a game cabinet) 6 Sync Roll 7 Peephole 8 Window section 9. Header section 10 Spacer section 11 Aperture section 12 Through holes 13 Gasket 14 volts 15 Gas pipes 16. Wiper (an example of a removal device) 17 Rods 18 handle 19. Shutter (an example of a suppression device) 20 Shutter Housing 21. Rack and pinion device 22 Pinion Gear 23 racks 24 Connecting part 25 Packing

Claims

1. It comprises a window portion and a header portion on which the window portion is formed, and is a viewing window through which the inside of the housing can be viewed, A cylindrical spacer portion connects the header portion and the housing at a predetermined distance, A constricted portion is provided between the header portion and the spacer portion, and has an inner diameter smaller than the inner diameter of the spacer portion. The header section is provided with a supply port for supplying gas at a pressure higher than the internal pressure of the housing. A viewing window in which the inner diameter of the diaphragm is greater than or equal to the outer diameter of the window.

2. The viewing window according to claim 1, further comprising a suppression device located inside the header portion that covers at least a portion of the window portion to suppress the adhesion of foreign matter to the window portion.

3. The viewing window according to claim 1, further comprising a removal device inside the header portion for removing foreign matter adhering to the window portion.

4. A viewing window according to claim 1, where d is the outer diameter of the window portion, A is the inner diameter of the spacer portion, a is the inner diameter of the diaphragm portion, B is the distance between the window portion and the housing, and b is the distance from the window portion to the diaphragm portion, and the relationship (a-d) / b > (A-d) / B is satisfied.

5. The viewing window according to claim 1, wherein the diameter of the header portion is larger than the diameter of the spacer portion.

6. The suppression device is a shutter, as described in claim 2.

7. The removal device is a wiper, as described in claim 3.

8. The viewing window according to claim 3, wherein the removal device is a cleaning device that sprays a high-pressure cleaning fluid onto the window portion.

9. A handle connected to the wiper, A motor and a fluid pressure cylinder connected to the handle in a manner that can transmit power, The viewing window according to claim 7, further comprising a timer or control device for operating the wiper by driving the motor or fluid pressure cylinder.

10. A snout with a viewing window, having the viewing window described in claim 1, the tip of which is in contact with a plated bathtub.

11. A method for suppressing the adhesion of foreign matter to a viewing window according to any one of claims 1 to 9, The gas is supplied from the supply port to the header section to generate a gas flow toward the housing side via the throttling section and the spacer section. A method for suppressing the adhesion of foreign matter to a viewing window, wherein the movement of foreign matter from the housing toward the header portion is suppressed by the gas flow.

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