A double eccentric soft seal flange butterfly valve

Abstract

The present invention provides a double eccentric soft-sealed flange butterfly valve, comprising a valve body, a valve stem, a valve plate structure capable of sealing the inner cavity of the valve body, and a connecting bracket capable of connecting to a worm gear device; the valve plate structure is arranged in the inner cavity of the valve body, the valve stem is arranged in the axial hole of the valve body, the valve stem is connected to the valve plate structure, the connecting bracket is integrally connected to the valve body, the connecting bracket is arranged at the top end of the axial hole of the valve body, a packing structure capable of sealing the axial hole is arranged in the axial hole of the valve body, and the packing structure is arranged between the valve stem and the valve body. The double eccentric soft-sealed flange butterfly valve described in the present invention solves the problem that, during the manufacturing process of the butterfly valve, a connecting bracket matching the butterfly valve needs to be produced together, and the production process of the connecting bracket requires a relatively high production cost, and the assembly process of the valve body and the connecting bracket also requires a certain cost.

Description

Technical Field

[0001] The invention belongs to the technical field of butterfly valves, and in particular relates to a double eccentric soft sealing flange butterfly valve. Background Art

[0002] Butterfly valve, also known as flap valve, can be used for on-off control of pipeline media. Butterfly valve refers to a valve that opens and closes by rotating the closing part (valve disc or butterfly plate) around the valve shaft. It mainly plays the role of cutting off and throttling on the pipeline. Its main structural forms include centerline butterfly valve, eccentric butterfly valve, double eccentric butterfly valve, triple eccentric butterfly valve, etc. Its advantages are small torque, flexible operation, simple structure and convenient use. Butterfly valve is suitable for pipelines that transport various corrosive and non-corrosive fluid media in engineering systems such as generators, coal gas, natural gas, liquefied petroleum gas, city gas, hot and cold air, chemical smelting and power generation and environmental protection, etc., and is used to regulate and cut off the flow of media; the butterfly valves widely used in the existing market are connected to the turbine worm device through the connecting bracket. In the manufacturing process of the butterfly valve, the connecting bracket matching the butterfly valve needs to be produced together. The production process of the connecting bracket requires a high production cost, and the assembly process of the valve body and the connecting bracket also requires a certain cost, and the stress bearing capacity at the connection position of the butterfly valve and the connecting bracket is weak. Summary of the invention

[0003] In view of this, the present invention aims to propose a double eccentric soft seal flange butterfly valve, which solves the problem that during the manufacturing process of the butterfly valve, a connecting bracket matching the butterfly valve needs to be produced together, and the process of producing the connecting bracket requires a high production cost, and the assembly process of the valve body and the connecting bracket also requires a certain cost;

[0004] And further solves the technical problem of weak stress bearing capacity at the connection position with the connection bracket.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A double eccentric soft-seal flange butterfly valve, comprising a valve body, a valve stem, a valve plate structure capable of sealing the inner cavity of the valve body, and a connecting bracket capable of connecting to a worm gear device;

[0007] The valve plate structure is arranged in the inner cavity of the valve body, the valve stem is arranged in the axial hole of the valve body, the valve stem is connected to the valve plate structure, the connecting bracket is integrally connected to the valve body, the connecting bracket is arranged at the top end of the axial hole of the valve body, the axial hole of the valve body is provided with a packing structure capable of sealing the axial hole, and the packing structure is arranged between the valve stem and the valve body.

[0008] Furthermore, the packing structure includes a plurality of O-rings and a packing gland capable of compressing the O-rings, the packing gland and the plurality of O-rings are both sleeved on the valve stem, the inner wall of the shaft hole is provided with a conical circular groove which tapers from top to bottom, the plurality of O-rings are arranged in the conical circular groove, the packing gland is arranged above the plurality of O-rings, the packing gland is connected to the valve body by bolts, and the tightening direction of the bolts is consistent with the tightening direction of the plurality of O-rings.

[0009] Furthermore, the connecting bracket is symmetrically provided with openings communicating with the outside at both ends thereof, the packing gland is connected to the valve body via two bolts, and one bolt is correspondingly arranged in each of the openings.

[0010] Furthermore, the packing gland includes a sleeve and two pressure plates, the two pressure plates are symmetrically arranged on the left and right sides of the sleeve, each of the pressure plates is fixed to the sleeve, a pressure plate is correspondingly arranged in each of the openings, and each of the pressure plates is correspondingly connected to one of the bolts.

[0011] Furthermore, there are four O-rings.

[0012] Furthermore, the valve plate structure is an arch bridge type valve plate, and the arch bridge type valve plate includes a valve plate bottom plate, an arch bridge plate, a supporting structure and a valve stem sleeve;

[0013] The arch bridge plate is fixedly arranged on the upper end surface of the valve plate bottom plate to form a closed shape. The longitudinal section of the arch bridge plate is a symmetrical first arc structure. The angle between the tangents on both sides of the first arc structure and the horizontal line gradually increases from top to bottom. The angle formed by the tangents on both sides of the top of the first arc structure at the upper end is α, and the angle α is 95 degrees to 175 degrees.

[0014] The supporting structure is arranged between the valve plate bottom plate and the arch bridge plate, one end of the supporting structure is fixedly connected to the arch bridge plate, and the other end of the supporting structure is fixedly connected to the valve plate bottom plate, the valve stem sleeve is fixedly arranged in the middle of the upper end surface of the valve plate bottom plate, the valve stem sleeve is located in the middle of the arch bridge plate, the valve stem sleeve is detachably connected to the valve stem, and a sealing structure is provided at the edge of the valve plate bottom plate.

[0015] Furthermore, the supporting structure includes one or more transverse ribs, multiple vertical ribs and multiple support columns. One or more transverse ribs and multiple vertical ribs are staggered on the upper end surface of the valve plate bottom plate. Each of the transverse ribs and vertical ribs is provided with at least two support columns. The top of each support column is fixedly connected to the arch bridge plate. When there is one transverse rib, the transverse rib is located in the middle of the upper end surface of the valve plate bottom plate. When there are multiple transverse ribs, one transverse rib is located in the middle of the upper end surface of the valve plate bottom plate. The remaining transverse ribs can be arranged on the left side, right side or left and right sides of the transverse rib located in the middle of the upper end surface of the valve plate bottom plate. The multiple transverse ribs are arranged at equal intervals, and the multiple vertical ribs are arranged at equal intervals.

[0016] Furthermore, each of the vertical ribs is perpendicular to each of the transverse ribs, the number of the transverse ribs is an odd number, and the number of the vertical ribs is an even number.

[0017] Furthermore, when the number of the transverse ribs is more than two, the width of the transverse rib located in the middle of the upper end surface of the valve plate bottom plate is 1.2 to 1.5 times the width of the other transverse ribs.

[0018] Furthermore, the connection position between the valve stem sleeve and the arch bridge plate is two second arc structures symmetrically arranged front to back, and the two second arc structures form a dumbbell-shaped structure.

[0019] Furthermore, two of the second arc-shaped structures are provided with rounded corners.

[0020] Furthermore, the transverse ribs, vertical ribs, support columns, arch bridge plates, valve plate bottom plates and valve stem sleeves are all integrally connected.

[0021] Compared with the prior art, the double eccentric soft-seal flange butterfly valve described in the present invention has the following advantages:

[0022] The double eccentric soft-seal flange butterfly valve of the present invention has an integrated design of a connecting bracket and a valve body, which improves the original butterfly valve production process from requiring two sets of molds to only require one set of molds to meet the production needs. The integrated design of the connecting bracket and the valve body can reduce the assembly parts of the butterfly valve, and can further reduce the assembly process of the butterfly valve, thereby greatly reducing the production cost and assembly cost of the butterfly valve. The integrated design of the connecting bracket and the valve body can enhance the stress bearing strength of the connection position of the connecting bracket and the valve body.

[0023] The arch bridge type valve plate in the present scheme can disperse the stress concentration on the valve plate during the actual working process through the first arc structure of the arch bridge plate, thereby effectively avoiding the deflection or structural deformation of the valve plate due to fatigue or exceeding the pressure limit; the arch bridge plate can be effectively supported by the supporting structure, and the supporting structure can reduce the manufacturing material and weight of the valve plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0025] Figure 1 It is a cross-sectional schematic diagram of a double eccentric soft-seal flange butterfly valve according to an embodiment of the present invention;

[0026] Figure 2 This is a schematic structural diagram of a double eccentric soft-seal flange butterfly valve according to an embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of an arch bridge type valve plate structure according to an embodiment of the present invention;

[0028] Figure 4 This is a schematic structural diagram of an arch bridge type valve plate according to an embodiment of the present invention from another angle;

[0029] Figure 5 This is a schematic diagram of a cross-sectional structure of an arch bridge type valve plate according to an embodiment of the present invention;

[0030] Figure 6 This is a schematic diagram of a cross-sectional structure of an arch bridge type valve plate according to an embodiment of the present invention;

[0031] Figure 7 This is a schematic structural diagram of an arch bridge type valve plate according to an embodiment of the present invention from another angle;

[0032] Figure 8 This is a schematic diagram of a supporting structure in an arch bridge type valve plate according to Embodiment 1 of the present invention;

[0033] Fig. 9 This is a schematic diagram of a supporting structure in an arch bridge type valve plate according to the second embodiment of the present invention;

[0034] Fig.10 This is a schematic diagram of a supporting structure in an arch bridge type valve plate described in Example 3 of the present invention.

[0035] Description of reference numerals:

[0036] 10-valve body; 11-connecting bracket; 12-packing structure; 13-bottom end cover; 20-sealing structure; 30-valve stem; 101-valve plate bottom plate; 201-arch bridge plate; 202-connecting plate; 301-valve stem sleeve; 401-transverse rib; 402-vertical rib; 403-support column. DETAILED DESCRIPTION

[0037] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0038] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and the like are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", and the like may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0039] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0040] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0041] A double eccentric soft seal flange butterfly valve, such as Figure 1 As shown, it includes a valve body 10, a valve stem 30, a valve plate structure capable of sealing the inner cavity of the valve body 10, and a connecting bracket 11 capable of connecting a worm gear device. In this embodiment, the worm gear device is an existing turbine worm gear device;

[0042] The valve plate structure is arranged in the inner cavity of the valve body 10, the valve stem 30 is arranged in the axial hole of the valve body 10, the valve stem 30 is connected to the valve plate structure, the connecting bracket 11 is connected to the valve body 10 in an integral manner, the connecting bracket 11 is arranged at the top end of the axial hole of the valve body 10, and a packing structure 12 capable of sealing the axial hole is arranged in the axial hole of the valve body 10, and the packing structure 12 is arranged between the valve stem 30 and the valve body 10. Through the integrated design of the connecting bracket and the valve body, the original butterfly valve production process requires two sets of molds to be opened for production, and it is improved to only need to open one set of molds to meet the production needs. Through the integrated design of the connecting bracket and the valve body, the assembly parts of the butterfly valve can be reduced, and the assembly process of the butterfly valve can be further reduced, thereby greatly reducing the production cost and assembly cost of the butterfly valve. Through the integrated design of the connecting bracket and the valve body, the stress bearing strength of the connection position of the connecting bracket and the valve body can be strengthened;

[0043] The packing structure 12 includes a plurality of O-rings and a packing gland that can compress the O-rings. The packing gland and the plurality of O-rings are both sleeved on the valve stem 30. The inner wall of the shaft hole is provided with a conical circular groove that decreases from top to bottom. The plurality of O-rings are arranged in the conical circular groove. The packing gland is arranged above the plurality of O-rings. The packing gland is connected to the valve body 10 by bolts. The tightening direction of the bolts is consistent with the tightening direction of the plurality of O-rings. In the present embodiment, there are four O-rings. When the O-rings become loose, two bolts can be operated externally to tighten the plurality of O-rings.

[0044] In this embodiment, the O-ring is made of elastic rubber material.

[0045] The connecting bracket 11 has symmetrical openings at both ends thereof, which are connected to the outside. The packing gland is connected to the valve body 10 by two bolts, and one bolt is correspondingly arranged in each opening.

[0046] The packing gland includes a sleeve and two pressure plates, which are symmetrically arranged on the left and right sides of the sleeve, and each pressure plate is fixedly connected to the sleeve. In this embodiment, the sleeve and the two pressure plates are integrally connected, a pressure plate is correspondingly arranged in each opening, and each pressure plate is correspondingly connected to a bolt. When the O-ring becomes loose, the packing gland can be operated outside the valve body 10.

[0047] The valve plate structure is an arch bridge type valve plate, which includes a valve plate bottom plate 101, an arch bridge plate 201, a supporting structure and a valve stem sleeve 301;

[0048] The arch bridge plate 201 is fixed on the upper end surface of the valve plate bottom plate 101 to form a closed shape. The longitudinal section of the arch bridge plate 201 is a symmetrical first arc structure. The angle between the tangents on both sides of the first arc structure and the horizontal line gradually increases from top to bottom. The angle formed by the tangents on both sides of the top of the first arc structure at the upper end is α. Figure 5As shown, the angle α is 95 degrees to 175 degrees, and the first arc structure of the arch bridge plate can disperse the stress concentration on the valve plate during the actual working process, thereby effectively avoiding the deflection or structural deformation of the valve plate due to fatigue or exceeding the pressure limit;

[0049] The supporting structure is arranged between the valve plate bottom plate 101 and the arch bridge plate 201, one end of the supporting structure is fixedly connected to the arch bridge plate 201, and the other end of the supporting structure is fixedly connected to the valve plate bottom plate 101, and the valve stem sleeve 301 is fixedly arranged in the middle of the upper end surface of the valve plate bottom plate 101, and the valve stem sleeve 301 is located in the middle of the arch bridge plate 201. The valve stem sleeve 301 is detachably connected to the valve stem 30, and a sealing structure 20 is provided at the edge of the valve plate bottom plate 101. In this embodiment, the sealing structure is an existing valve plate soft sealing structure.

[0050] In this embodiment, the valve stem 30 includes an upper rotating shaft and a lower rotating shaft. The upper rotating shaft is connected to the upper part of the valve stem sleeve 301 through two cylindrical pins, and the lower rotating shaft is connected to the lower part of the valve stem sleeve 301 through a cylindrical pin. A bottom end cover 13 is provided at the bottom of the lower rotating shaft, and the bottom end cover 13 is connected to the valve body 10 through a locking bolt.

[0051] The supporting structure includes one or more transverse ribs 401, multiple vertical ribs 402 and multiple support columns 403. One or more transverse ribs 401 and multiple vertical ribs 402 are alternately arranged on the upper end surface of the valve plate bottom plate 101. Each transverse rib 401 and vertical rib 402 are provided with at least two support columns 403. The top of each support column 403 is fixedly connected to the arch bridge plate 201. When there is one transverse rib 401, the transverse rib 401 is located in the middle of the upper end surface of the valve plate bottom plate 101. When there are multiple transverse ribs 401, one transverse rib 401 is located in the middle of the upper end surface of the valve plate bottom plate 101. The remaining transverse ribs 401 can be arranged on the left side, right side or left and right sides of the transverse rib 401 located in the middle of the upper end surface of the valve plate bottom plate 101. The multiple transverse ribs 401 are arranged at equal intervals, and the multiple vertical ribs 402 are arranged at equal intervals. The arch bridge plate can be effectively supported by the supporting structure, and the supporting structure can reduce the manufacturing material and weight of the valve plate.

[0052] Each vertical rib 402 is perpendicular to each horizontal rib 401, the number of horizontal ribs 401 is an odd number, and the number of vertical ribs 402 is an even number. When the number of horizontal ribs 401 is more than two, the width of the horizontal rib 401 located in the middle of the upper end surface of the valve plate bottom plate 101 is 1.2 to 1.5 times the width of the other horizontal ribs 401, thereby further strengthening the stress tolerance strength of the front and rear sides of the arch bridge valve plate structure.

[0053] Embodiment 1, as Figure 8 As shown, this is the implementation method for butterfly valve with a diameter of DN800;

[0054] Embodiment 2, as Fig. 9As shown, this is the implementation method for butterfly valve with DN1000 diameter;

[0055] Embodiment three, as Fig.10 As shown, this is the implementation method for a butterfly valve with a diameter of DN1200.

[0056] The connection position between the valve stem sleeve 301 and the arch bridge plate 201 is two second arc structures symmetrically arranged front and back. The two second arc structures form a dumbbell-shaped structure, which can effectively enhance the connection strength between the valve stem sleeve 301 and the arch bridge plate 201. In this embodiment, the two second arc structures are provided with chamfered corners, which can further disperse the stress generated at the connection between the valve stem sleeve 301 and the arch bridge plate 201.

[0057] The transverse ribs 401, vertical ribs 402, support columns 403, arch bridge plates 201, valve plate bottom plates 101 and valve stem sleeves 301 are all integrally connected, which can further enhance the stress tolerance strength of the front and rear sides of the arch bridge valve plate structure, improve the pressure resistance limit of the valve plate structure, and greatly reduce the possibility of deformation of the valve plate structure.

[0058] like Figure 3 As shown, connecting plates 202 capable of lifting are symmetrically provided on the front and rear sides of the arch bridge plate 201, and the valve stem sleeve 301 is arranged between the two connecting plates 202. Each connecting plate 202 is fixedly connected to the arch bridge plate 201. In this embodiment, the connection is integrated, and the valve plate structure can be conveniently moved during the processing through the connecting plate 202.

[0059] How this example works

[0060] First, the supporting structure in the valve plate structure is determined according to the size of the butterfly valve caliber, and the valve plate structure is installed inside the butterfly valve body 10. Three connecting holes are provided on the valve stem sleeve 301. During use, the valve stem sleeve 301 is connected to the valve stem 30 through three cylindrical pins, and the existing turbine worm gear transmission device is connected to the connecting bracket 11. The turbine worm gear transmission device controls the rotation of the valve plate structure through the valve stem 30.

[0061] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A double eccentric soft seal flange butterfly valve, characterized in that: It comprises a valve body (10), a valve stem (30), a valve plate structure capable of sealing the inner cavity of the valve body (10), and a connecting bracket (11) capable of connecting to a worm gear device; The valve plate structure is arranged in the inner cavity of the valve body (10), the valve stem (30) is arranged in the axial hole of the valve body (10), the valve stem (30) is connected to the valve plate structure, the connecting bracket (11) is connected to the valve body (10) in an integral manner, the connecting bracket (11) is arranged at the top end of the axial hole of the valve body (10), a packing structure (12) capable of sealing the axial hole is arranged in the axial hole of the valve body (10), and the packing structure (12) is arranged between the valve stem (30) and the valve body (10); The packing structure (12) comprises a plurality of O-rings and a packing gland capable of compressing the O-rings, the packing gland and the plurality of O-rings are sleeved on the valve stem (30), the inner wall of the shaft hole is provided with a conical circular groove that decreases from top to bottom, the plurality of O-rings are arranged in the conical circular groove, the packing gland is arranged above the plurality of O-rings, the packing gland is connected to the valve body (10) by bolts, and the tightening direction of the bolts is consistent with the tightening direction of the plurality of O-rings; The valve plate structure is an arch bridge type valve plate, and the arch bridge type valve plate comprises a valve plate bottom plate (101), an arch bridge plate (201), a supporting structure and a valve stem sleeve (301); The arch bridge plate (201) is fixedly mounted on the upper end surface of the valve plate bottom plate (101) to form a closed shape. The longitudinal section of the arch bridge plate (201) is a symmetrical first arc-shaped structure. The angle between the tangents on both sides of the first arc-shaped structure and the horizontal line gradually increases from top to bottom. The angle formed by the tangents on both sides of the top of the first arc-shaped structure at the upper end is α, and the angle α is 95 degrees to 175 degrees. The support structure is arranged between the valve plate bottom plate (101) and the arch bridge plate (201), one end of the support structure is fixedly connected to the arch bridge plate (201), and the other end of the support structure is fixedly connected to the valve plate bottom plate (101), the valve stem sleeve (301) is fixedly arranged in the middle of the upper end surface of the valve plate bottom plate (101), the valve stem sleeve (301) is located in the middle of the arch bridge plate (201), the valve stem sleeve (301) is detachably connected to the valve stem (30), and a sealing structure (20) is provided at the edge of the valve plate bottom plate (101); The support structure comprises one or more transverse ribs (401), a plurality of vertical ribs (402) and a plurality of support columns (403). The one or more transverse ribs (401) and the plurality of vertical ribs (402) are alternately arranged on the upper end surface of the valve plate bottom plate (101). At least two support columns (403) are arranged on each transverse rib (401) and vertical rib (402). The top end of each support column (403) is fixedly connected to the arch bridge plate (201). When the transverse rib (401) is a When there are multiple transverse ribs (401), the transverse rib (401) is located in the middle of the upper end surface of the valve plate bottom plate (101); when there are multiple transverse ribs (401), one transverse rib (401) is located in the middle of the upper end surface of the valve plate bottom plate (101), and the remaining transverse ribs (401) can be arranged on the left side, right side or both sides of the transverse rib (401) located in the middle of the upper end surface of the valve plate bottom plate (101); the multiple transverse ribs (401) are arranged at equal intervals, and the multiple vertical ribs (402) are arranged at equal intervals; Each of the vertical ribs (402) is perpendicular to each of the transverse ribs (401), the number of the transverse ribs (401) is an odd number, and the number of the vertical ribs (402) is an even number; When the number of the transverse ribs (401) is more than two, the width of the transverse rib (401) located in the middle of the upper end surface of the valve plate bottom plate (101) is 1.2 to 1.5 times the width of the other transverse ribs (401); The working method is: First, determine the supporting structure in the valve plate structure according to the size of the butterfly valve caliber, and install the valve plate structure into the inside of the butterfly valve body. Three connecting holes are provided on the valve stem sleeve. During use, the valve stem sleeve is connected to the valve stem through three cylindrical pins, and the worm gear transmission device is connected to the connecting bracket. The worm gear transmission device controls the rotation of the valve plate structure through the valve stem.

2. A double eccentric soft seal flange butterfly valve according to claim 1, characterized in that: The connecting bracket (11) is symmetrically provided with openings communicating with the outside at both left and right ends, and the packing gland is connected to the valve body (10) via two bolts, with one bolt correspondingly arranged in each opening.

3. A double eccentric soft seal flange butterfly valve according to claim 2, characterized in that: The packing gland includes a sleeve and two pressure plates, the two pressure plates are symmetrically arranged on the left and right sides of the sleeve, each of the pressure plates is fixed to the sleeve, a pressure plate is correspondingly arranged in each of the openings, and each of the pressure plates is correspondingly connected to one of the bolts.

4. A double eccentric soft seal flange butterfly valve according to claim 3, characterized in that: There are four O-rings.

5. A double eccentric soft seal flange butterfly valve according to claim 4, characterized in that: The connection position between the valve stem sleeve (301) and the arch bridge plate (201) is two second arc structures arranged symmetrically in front and back, the two second arc structures form a dumbbell-shaped structure, and the two second arc structures are provided with rounded corners.

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