JP5554652B2 - Sheet shutter - Google Patents

Description

  The present invention relates to a sheet shutter that opens and closes a doorway of a building. In particular, the present invention relates to a sheet shutter processed so as to prevent the sheet from being charged.

  The sheet shutter opens and closes the entrance and exit of the building's outer and inner walls. Since the sheet is lightweight and can be opened and closed at high speed, the opening time of the doorway is short, and heat and air do not easily flow out between the spaces defined by the sheet. For this reason, the sealing between the two spaces can be improved, so it can be used in low-temperature warehouses, food processing factories, electronic component production factories, hospitals, etc. that require heat insulation and dustproofness. is set up.

  In general, the upper side of the sheet of the sheet shutter is connected to a rotor pipe, and the rotor pipe is rotated to wind and lower the sheet. The sheet is generally made of a relatively highly insulating material such as a synthetic resin, a reinforcing fiber, or a flame retardant. When such a sheet shutter is installed in a relatively dry atmosphere such as a precision parts production factory, when the sheet wound on the rotor pipe is unwound, the sheet to be unwound and the rotor pipe remain. Static electricity may be generated between the sheet and the sheet to be wound may be charged to about 1000 V or more. When a high potential exists in the sheet as described above, electric discharge may occur, which may lead to problems such as destruction of an electronic device, functional failure of a precision instrument such as a measuring machine, electromagnetic interference, and ignition of a flammable substance. Therefore, as one target of the discharge characteristics of the sheet, it is required that the charging potential is ± 1000 V at the maximum and attenuates to 100 V or less within 2 seconds.

  There has been an attempt to release the charge from the side of the sheet to the rail box as one of the measures for preventing the sheet from being charged or removing static electricity. However, since the side of the seat and the rail box slide at a considerable speed when the seat is raised and lowered, wear and noise at the sliding contact portion become new problems.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a sheet shutter having a sheet antistatic measure or a static electricity removal measure.

The seat shutter as a base of the present invention includes a seat that is raised and lowered at an opening of a building to open and close the opening, a rotor pipe made of a conductive material that winds and lowers the upper end of the sheet, and rotation of the rotor pipe A sheet shutter comprising driving means and a rail box that slidably guides both ends of the sheet in the width direction, wherein the sheet is provided with a discharge line made of a conductive wire or tape. cage, the discharge line that is grounded through the rotor pipe.

  According to the present invention, a discharge line is disposed on the sheet, and the discharge line is connected to the rotor pipe and grounded through the pipe. Thereby, the potential charged on the sheet can be quickly released via the discharge line and the rotor pipe, and charging of the sheet can be prevented. As will be described in detail later, the sheet has a high charging potential mainly in the upper part and the central part. Therefore, it is particularly preferable to discharge through the rotor pipe close to the top of the sheet.

  The upper portion and the central portion of the sheet are portions of about 1500 mm or less from the upper side of the sheet, excluding the upper end portion wound around the rotor pipe even when the sheet is fully opened.

  When the conductivity of the sheet material is improved, the sheet itself is difficult to be charged because it has sufficient conductivity in the thickness direction of the sheet. Further, in a state where the sheet is wound around the rotor pipe, the electric charge generated in the outer sheet flows from the discharge line formed in the sheet in the sheet thickness direction and is discharged to the rotor pipe. In this case, it is not necessary to directly contact the end of the discharge line with the rotor pipe. Of course, it is naturally preferable to bring the discharge line into direct contact with the rotor pipe.

  Furthermore, it is preferable that the distance between the discharge lines in the middle and upper stages of the sheet is set so that the surface resistance is 500 MΩ or less.

In the present invention, the surface resistivity of the sheet is preferably 10 ¹² Ω / m ² or less. From this value, the distance at which the surface resistance value is 500 MΩ or less, at which sufficient charge removal performance is expected, is 500 mm or less. Therefore, it is preferable to dispose each line so that the interval between the discharge lines is 500 mm or less. This makes it difficult for the sheet to be charged when the sheet is opened and closed, and even if it is charged to about 1000 V, the charging potential can be lowered to 100 V or less within 2 seconds, for example, within 0.5 seconds.

  As is clear from the above description, in the sheet shutter of the present invention, since the discharge line that is grounded via the rotor pipe is provided on the sheet, the charge charged on the sheet escapes via the discharge line. For this reason, it is possible to prevent the sheet from being charged and to quickly release the charged charge. Therefore, it is possible to provide a sheet shutter that can be installed in an environment where charging of a sheet becomes a problem, such as in a precision parts factory. Further, since there is no need to attach an extra part such as a sliding contact part, maintenance work and the like do not increase.

It is a figure which shows the structure of the sheet | seat of the sheet shutter of this invention, FIG. 1 (A) is a front view, FIG.1 (B) is a side view, FIG.1 (C) is a side view which expands and shows a discharge line sticking part. It is. It is a figure which shows the whole structure of the sheet shutter of this invention, FIG. 2 (A) is a front view, FIG.2 (B) is a side view. It is a cross-sectional view showing the structure of the rail box of the seat shutter of the present invention. 4A and 4B are diagrams illustrating results of measuring charging characteristics of the sheet shutter of the present invention, in which FIG. 4A is a front view illustrating measurement points of the sheet, FIG. 4B is a graph illustrating measurement results of charging voltage, and FIG. (C) is a graph which shows the measurement result of decay time. FIGS. 5A and 5B are diagrams showing results of measuring charging characteristics of a sheet shutter of a comparative example, FIG. 5A is a front view showing measurement points of a sheet, FIG. 5B is a graph showing measurement results of charging voltage, and FIG. (C) is a graph which shows the measurement result of decay time. FIG. 6A is a graph showing the result of measuring the sheet surface potential of the sheet shutter of the present invention, FIG. 6A is the measurement result at measurement point A, FIG. 6B is the measurement result at measurement point B, and FIG. Indicates the measurement result of measurement point C. It is a graph which shows the result of having measured the sheet surface potential of the sheet shutter of a comparative example, and Drawing 7 (A) shows the measurement result of measurement point A, Drawing 7 (B) shows the measurement result of measurement point B, and Drawing 7 (C). Indicates the measurement result of measurement point C. It is a front view which shows the modification of the sheet | seat of the sheet shutter of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The structure of the sheet shutter will be described with reference to FIGS.
As shown in FIG. 2, the sheet shutter 1 includes a seat 3 that is raised and lowered at an opening of a building to open and close the opening, a drive mechanism 5 that winds up and down the upper end of the sheet 3, and both ends of the sheet 3 in the width direction up and down. The left and right rail boxes 7L and 7R are slidably guided, the main body box 9 is stretched between the upper ends of the rail boxes 7, and the left and right pillars 11 are arranged.
In FIG. 2B, the left side of the sheet 3 is also referred to as the front side, and the right side is also referred to as the back side.

  The drive mechanism 5 includes a rotor pipe 6 and a motor with a speed reducer (not shown) that rotates the rotor pipe 6, and is disposed in the main body box 9. The rotor pipe 6 is made of a conductive material such as aluminum.

As shown in FIG. 1A, the seat 3 has a rectangular shape that is substantially the same in width as the rotor pipe 6 and is long in the rotation direction of the rotor pipe 6. In this example, the sheet 3 has a width of 2 m and a length of 2.5 m. The sheet 3 is made of a relatively light and highly conductive material (for example, a synthetic resin subjected to a conductive treatment, a plastic reinforced fiber, a flame retardant, etc.). As such a sheet, for example, a shutter sheet manufactured by Hiraoka Orizome Co., Ltd. can be used. In this sheet, a vinyl chloride adhesive treatment layer is formed on both surfaces of a polyester plain weave base fabric, a vinyl chloride film layer is formed on the outer surface of the treatment layer, and an acrylic / fluorine antifouling treatment layer is formed on the outer surface of the same layer. Formed. The surface resistivity of the sheet is 10 ¹² Ω / m ² or less, and the electric resistance value in the thickness direction is 10 MΩ or less.

  As shown in FIG. 1B, the lower side of the sheet 3 is folded in a bag shape, and an iron lower pipe 13 is inserted into the folded portion 3a. The lower pipe 13 is a reinforcing member that extends in the width direction of the seat 3. Further, an iron middle stage pipe 15 is also fixed to one surface (in this example, the back surface) of the sheet 3 as a reinforcing member. In this example, the three middle-stage pipes are arranged at a constant interval (in the example, 65 cm). As shown in FIG. 1C, the intermediate pipe 15 is fixed by winding the pipe 15 with the sheet piece 4 and welding both ends of the sheet piece 4 to the sheet 3. These pipes 13 and 15 reinforce the strength in the width direction of the sheet 3 and at the same time serve as weights for lowering.

  The seat 3 is fixed to the rotor pipe 6 at the upper side. When the rotor pipe 6 is driven and rotated by the motor, the seat 3 is wound up and down along the rotor pipe 6. The opening / closing speed of the sheet 3 is, for example, about 1 m / s. As shown in FIG. 1 (A), the upper end 3b of the sheet 3 (a portion having a height H that is one round of the outer periphery of the rotor pipe 6 from the upper side, in this example, a portion that is about 940 mm from the upper side) Even when 3 is wound down and the opening is fully closed, it is still wound around the rotor pipe 6.

As shown in FIG. 1A, a discharge line 20 with a conductive tape is disposed on the front surface of the sheet 3 (the surface that directly contacts the surface of the rotor pipe 6). . As the conductive tape, for example, a flame retardant conductive cloth adhesive tape (2191FR (manufactured by Sumitomo 3M Limited)) can be used. This conductive cloth tape has a structure in which an acrylic conductive adhesive is applied to one side of a conductive cloth nickel-plated on a polyester fiber. The contact resistivity of the tape is 10 ³ to 10 ⁴ Ω / sq 25 mm. In this example, the contact resistance value is obtained when a tape is placed between the electrodes of the gold-plated brass electrode (1 in ² ), a load of 2 kg is applied to one electrode, and a current of 100 mA DC is passed between the electrodes. Measure the voltage. The resistance value is obtained by dividing the measured voltage by 100 mA.

In this example, the discharge line 20 includes one vertical line 21 and three horizontal lines 22A, 22B, and 22C.
The vertical line 21 is substantially T-shaped and has a short horizontal line portion 21a and a long vertical line portion 21b. The horizontal line portion 21a extends in the horizontal direction slightly below the upper end (connection portion with the rotor pipe 6) at the center in the width direction of the seat 3. The vertical line portion 21b extends downward from the upper end (connecting portion with the rotor pipe 6) in the center in the width direction of the seat 3, crosses the horizontal line portion 21a, and further extends to the folded portion 3a at the lower end.
Each horizontal line 22 extends between both side ends on the lower surface of the upper end portion 3b of the seat 3 (the portion wound around the rotor pipe 6 even when the seat is fully closed). Specifically, as shown in FIG. 1C, each horizontal line is attached to the opposite surface of the welded portion 4 a between the sheet piece 4 and the sheet body 3 for attaching the intermediate pipe 15. Since the welded portion 4a is a portion where the sheets 3 overlap and is difficult to bend in the length direction, the tape is hardly peeled off by being attached to the same portion 4a. Thus, in this example, the horizontal line 22 is attached to substantially the same position as the middle pipe 15 (positions of 780 mm, 650 mm, and 610 mm from the lower edge of the sheet 3 when the length of the sheet 3 is 2.5 m). .

  As described above, since the upper end portion 3b of the seat 3 remains wound around the rotor pipe 6 even when the seat is fully closed, the horizontal line portion 21a and the vertical line portion 21b of the vertical line 21 disposed in the same portion. Is always in contact with the rotor pipe 6. Since the rotor pipe 6 is substantially grounded via a bearing or a motor, the vertical line 21 is grounded via the rotor pipe 6 or the like. Since each horizontal line 22 is electrically connected to the vertical line 21 at the intersection, the lines 21 and 22 of the discharge line 20 are grounded via the rotor pipe 6.

As described above, the surface resistivity of the sheet 3 is 10 ¹² Ω / m ² or less. From this value, the distance at which the surface resistance value is 500 MΩ or less, at which sufficient charge removal performance is expected, is 500 mm or less. Therefore, it is preferable to arrange each line so that the interval between each line of the discharge line 20 is 500 mm or less.

  As described above, since the upper end portion 3b of the sheet 3 is wound around the rotor pipe 6 even when the sheet 3 is wound down, the vertical line portion 21b disposed on the upper end portion 3b serves as the rotor pipe. The horizontal line portion 21a is not necessarily provided as long as it is in contact with 6 and is conductive.

  As shown in FIG. 3, the left and right rail boxes 7L and 7R are hollow columns having a square cross-sectional shape. Guide rails 7 a extending in the vertical direction are formed in inner walls facing the left and right sides of the rail box 7. Guides 17 extending in the vertical direction are attached to the edges on both sides of the guide slit 7a. The guide 17 is made of a conductive material (for example, stainless steel). The left and right ends of the lower pipe 13 and the middle pipe 15 enter between the guides 17 through the slits 7a.

  The left and right rail boxes 7L and 7R are provided with sensors (not shown). When the sensor detects a person or a transport vehicle while the sheet 3 is descending, the drive mechanism 5 is activated to automatically wind the sheet 3, and when the detection of the sensor is finished, the sheet 3 is lowered.

  As shown in FIG. 2, the left and right pillars 11 are fixed along the back surfaces of the main body box 9 and the rail box 7. The column 11 is a member made of steel mold or the like, and holds the main body box 9 and the left and right rail boxes 7 upright on the floor surface.

In the sheet shutter 1 of the present invention, since the electrical resistivity of the sheet 3 itself is relatively low, even if the sheet 3 is charged, its charging potential is low. Further, the electric charge escapes to the rotor pipe 6 through the discharge line 20. As described above, since the rotor pipe 6 is substantially grounded, the charge of the sheet 4 is grounded, and the sheet 3 can be prevented from being charged.
Further, when the seat 3 is opened and closed, the side of the seat 3 moves up and down in the rail box 7. At this time, as shown in FIG. 3, the sides of the seat 3 and both ends of the horizontal line 22 of the discharge line 20 are Slid with the guide 17 of the rail box 7. Since the guide 17 is made of a conductive material, it can be expected that the potential of the sheet 3 is directly grounded via the guide 17 or grounded from the discharge line 20 via the guide 17.

Next, with reference to FIG. 4 and FIG. 5, the results of experiments on the influence of the discharge line 20 on the charging characteristics of the sheet 3 will be described.
In this example, using the same sheet as the sheet shutter of FIG. 1, as shown in FIG. 4A, one vertical line and four horizontal lines are within the effective aperture size (width 4100 mm, height 3000 mm). A discharge line consisting of a book was formed. The upper end of the vertical line is connected to the rotor pipe.

As shown in FIG. 4A, the measurement points are three points (a total of 28 points) in the section defined by each line of the discharge line. Specifically, it is an intersection (28 places) between a horizontal line (S1 to S4) passing through the center in the length direction of each section and a line (A to G) dividing the width of each section into four. Attach an electrometer (Staticlon DZ3, manufactured by Sisid Electrostatic Co., Ltd.) to each measurement location, and the front surface of the sheet after opening and closing (the shutter is opened in the initial state) (the outer surface during winding) ) And the time (s) required for decay from the peak voltage to 100 V were measured. The measurement atmosphere was an air temperature of 27.3 ° C. and a humidity of 43%.
As a comparative example, using the same sheet as the sheet shutter of the present invention, as shown in FIG. 5A, the potential was measured at the same measurement location in a sheet shutter not provided with a discharge line. The measurement atmosphere was an air temperature of 23.7 ° C. and a humidity of 48%.

FIGS. 4B and 4C are graphs of measurement results at each measurement point of the sheet shutter of the present invention, and FIGS. 5B and 5C are graphs of measurement results at each measurement point of the sheet shutter of the comparative example. Show. In each figure, (B) shows the charging voltage, and (C) shows the decay time. In each graph, the X axis indicates the position in the width direction, the Y axis indicates the position in the length direction, and the Z axis indicates the potential (V) or time (s).
In this example, from the initial state (shutter open), the potential at each measurement point after performing an operation (opening / closing operation) for full opening after the sheet is fully closed at a normal shutter speed was measured.

The measurement result of the sheet shutter of the present invention will be described with reference to FIGS.
As shown in FIG. 4B, the charging voltage is as low as 0.002 to 0.005 kV or less at each measurement location. The upper part of the sheet (around the S1 line and S2 line) is slightly higher than the lower part, but is sufficiently low at 0.005 kV or less.
As a result, as shown in FIG. 4C, the decay time is 0 s at all measurement points.

The measurement result of the sheet shutter of the comparative example will be described with reference to FIGS.
As shown in FIG. 5B, the charging voltage at each measurement point is 0.002 to 0.23 kV. Also in this example, the upper part of the sheet (around the S1 line and the S2 line) is slightly higher than the lower part, the uppermost S1 line is 0.2 kV or more at all measurement points, and 0. It is around 15 kV. However, the lowest S4 line is sufficiently low, 0.002 to 0.005 kV or less.
As shown in FIG. 5C, at the upper part of the sheet, the decay time is as long as 10 seconds or more.

From these results, the following can be understood.
(1) When the sheet having improved conductivity according to the present invention is used, the charging potential at the time of opening and closing the sheet can be suppressed to ± 1000 V or less without providing a discharge line.
(2) However, when no discharge line is provided, the static elimination characteristics are not sufficient and the decay time is 10 seconds or more.
(3) When a sheet with improved conductivity is used and a discharge line is provided, the charging potential is sufficiently low, about ± 0.05 kV at the maximum, and the decay time is 0 second.
(4) The upper part of the sheet has a higher charging potential than the lower part. The reason for this is considered to be that static electricity is generated by peeling when the sheet is lowered, but if the sheet is continuously lowered in this state, charges are accumulated in the upper part. Therefore, it is considered that the electric charge in the high potential portion can be quickly released by conducting the discharge line to the rotor pipe close to the upper part.

Next, with reference to FIG. 1, FIG. 6, and FIG. 7, the result of measuring the charging characteristics when the opening / closing operation is repeated in the sheet shutter of FIG. 1 will be described.
When an electrometer (electrostatic charge measuring device STATILON DZ3, manufactured by Sicid Electrostatic Co., Ltd.) is attached to the front surface of the sheet 3 of the sheet shutter 1 in FIG. 1, and the sheet shutter is opened and closed (the initial state is set to shutter open). ) Of the sheet 3 was measured. The measurement location is the center (point A) of the section between the vertical line 21 and the top horizontal line 22A and the second horizontal line 22B, and between the vertical line 21 and the second horizontal line 22B and the third horizontal line 22C. And the center (point C) of the section between the vertical line 21 and the third horizontal line 22C and the lower side of the sheet 3 (point B). The measurement atmosphere was a temperature of 26.9 ° C. and a humidity of 53%.
As a comparative example, the same sheet as the sheet shutter of the present invention was used, and the potential was measured at the same measurement location in a sheet shutter without a discharge line.

FIG. 6 shows a graph of measurement results at each measurement point of the sheet shutter of the present invention, and FIG. 7 shows a graph of measurement results at each measurement point of the sheet shutter of the comparative example. (A) of each figure shows A point, (B) shows B point, (C) shows C point. The horizontal axis of the graph represents time (s), and the vertical axis represents potential (V).
From the initial state (shutter opened), the potential was measured by repeating the operation of opening and closing the sheet at the normal shutter speed and then fully opening (opening / closing operation). The interval between the opening and closing operations was an interval at which the charging potential was attenuated to ± 100V.

The measurement result of the sheet shutter of the present invention will be described with reference to FIG.
At point A, as shown in FIG. 6A, the potential is substantially 0 V in the initial state (sheet open state). In a single opening / closing operation, the sheet gradually begins to be negatively charged, reaches about −500V, and immediately returns to 0V. The time from -500 V to 0 V was about 0.5 seconds. A similar result was obtained even when the opening / closing operation was repeated 6 times. In some cases, the charging potential is about -700 V, but even in that case, it returned to 0 V within about 0.5 seconds.

  Also at the point B, as shown in FIG. 6B, almost the same result as the point A was obtained. That is, in one opening / closing operation, the sheet gradually begins to be negatively charged, reaches about −500V, and then returns to 0V. The time from -500 V to 0 V was about 0.5 seconds. A similar result was obtained even when the opening and closing operation was repeated five times.

  At point C, as shown in FIG. 6C, the potential was almost 0 V in the initial state (sheet open state), and the sheet was hardly charged even when the opening / closing operation was performed. Even when charged, it is about −100 V at the maximum, and in this case, it returns to 0 V in about 0.5 seconds.

The measurement result of the comparative example sheet shutter will be described with reference to FIG.
At point A, as shown in FIG. 7A, the potential is substantially 0 V in the initial state (sheet open state). In a single opening / closing operation, the sheet suddenly starts to be negatively charged and reaches −1000V. Thereafter, it gradually attenuated, but it remained charged at about -300 V even after about 20 seconds. For this reason, the opening / closing operation was performed after attenuation to about −300V. Similar results were obtained even when opening and closing operations were repeated.
In the graph, a sudden change in potential that appears before the change in potential in each opening and closing operation is noise.

  At point B, as shown in FIG. 7 (B), almost the same result as point A was obtained.

  At point C, as shown in FIG. 7C, the sheet starts to be negatively charged suddenly in one opening / closing operation, reaches −500 V, and after that, hardly attenuates and after about 20 seconds elapses. It remained charged to about -500V. Similar results were obtained even when opening and closing operations were repeated.

From the above results, the following can be understood.
(1) The sheet shutter 1 according to the present invention has a lower charging potential of the sheet 3 when the sheet is lowered, and the charged potential decay time is shorter than that of the conventional sheet shutter. One target value, that is, the charging potential is ± 1000 V at the maximum and satisfies the requirement to decrease to 100 V within 2 seconds.
(2) The charging potential is higher at the upper portion of the sheet 3 (except for the upper end portion always wound around the rotor pipe 6).

Next, a modification of the discharge line of the sheet shutter of the present invention will be described with reference to FIG.
The discharge line 20 of the sheet 3 </ b> A shown in FIG. 8A is composed of one vertical line 21 and four horizontal lines 22. The vertical line 21 includes a horizontal line portion 21a and a vertical line portion 21b as in the sheet shutter of FIG. 1, and is disposed so as to extend in the center in the width direction of the sheet. On the other hand, the uppermost horizontal line 22A is disposed at a position 200 mm above the attachment position of the uppermost middle pipe 15. The second horizontal line 22B is disposed at the attachment position of the uppermost middle pipe 15. The third horizontal line 22C is disposed at a position 500 mm below the second horizontal line 22B. The fourth horizontal line 22D is disposed at a position 1000 mm below the third horizontal line 22C.
As described above, since the charging potential is higher at the upper part of the sheet 3, in this example, the horizontal line 22 is arranged concentrated on the upper part of the sheet 3.

The discharge line 20 of the sheet 3 </ b> B shown in FIG. 8B is composed of two vertical lines 21 and one horizontal line 22. The interval between the vertical lines 21 </ b> A and 21 </ b> B is 1000 mm, and extends from the upper end of the sheet 3 </ b> B to the push-back portion at the lower end at a target position with respect to the center in the width direction of the sheet 3. The upper end of each vertical line 21 is conducted by a horizontal line 22.
Thus, even if only the vertical line 21 is disposed in the effective opening of the sheet 3B, a target charge attenuation effect can be obtained.

DESCRIPTION OF SYMBOLS 1 Sheet shutter 3 Sheet 4 Sheet piece 5 Drive mechanism 7 Rail box 9 Main body box 11 Pillar 13 Lower pipe 15 Middle pipe 17 Guide 20 Discharge line 21 Vertical line 22 Horizontal line

Claims (4)

A seat that is raised and lowered at the opening of the building to open and close the opening;
A rotor pipe made of a conductive material that winds and lowers the upper end of the sheet;
Rotation driving means of the rotor pipe;
A rail box that slidably guides both ends of the seat in the width direction; and
A sheet shutter comprising:
On the surface of the sheet, a discharge line made of conductive adhesive tape is disposed by sticking ,
A sheet shutter, wherein the discharge line is grounded through the rotor pipe. The discharge line has a vertical line that extends in the vertical direction of the sheet and contacts the surface of the rotor pipe, and a horizontal line that extends in the horizontal direction of the sheet and communicates with the vertical line. The sheet shutter according to claim 1. The surface resistivity of the sheet is 10 ¹² Ω / m ² or less,
In the middle portion, the upper portion of the sheet, the spacing between each line of the discharge line, a sheet shutter according to claim 1 or 2 the surface resistance is characterized in that it is set to be equal to or less than 500Emuomega. The sheet is provided with a middle pipe that is a reinforcing member extending in the lateral direction,
4. The sheet shutter according to claim 2, wherein the horizontal line is attached to a surface opposite to a welded portion between a sheet piece and a sheet main body for attaching the middle pipe. 5.

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