Sealing ring for strong alkali electrolytic cell

Abstract

The application discloses a sealing ring for a strong-alkali electrolytic cell, wherein the sealing ring body is a three-element ethylene-propylene rubber annular elastic sealing element, and the cross section of the sealing ring body comprises a high-cross-linking-density layer, a cross-linking-density gradual transition layer and a low-cross-linking-density layer along the thickness direction. The high-cross-linking-density layer is located at the medium contact side, and the dense three-dimensional cross-linking network thereof inhibits the penetration of alkali liquor; the low-cross-linking-density layer is located at the core, the molecular chain segment has a large freedom degree of movement, and the compression permanent deformation is small, so that the elastic recovery force is continuously provided; the gradual transition layer continuously transitions the cross-linking density along the thickness direction, and eliminates the interlayer shear stress in the temperature cycle. The layers are integrally combined through co-sulfurization to form a co-cross-linking network.

Description

Technical Field

[0001] This invention relates to the field of rubber seal technology, and more specifically, to a sealing ring for use in strong alkali resistant electrolytic cells. Background Technology

[0002] In alkaline water electrolysis hydrogen production systems, a sealing ring is installed in the sealing groove of the electrolyzer frame. The sealing ring relies on the pre-tightening force of the flange bolts to generate elastic compression deformation, forming contact stress on the sealing surface to prevent leakage of potassium hydroxide solution and hydrogen produced during electrolysis from the electrolyzer. Existing sealing rings are typically made of fluororubber or EPDM rubber through a one-time molding and vulcanization process, resulting in uniform cross-linking density across the sealing ring's cross-section.

[0003] Under long-term operating conditions, the chemical erosion and mechanical loads experienced by different regions of the sealing ring cross-section vary. When the cross-linking density is uniform throughout the sealing ring cross-section, increasing the overall cross-linking density to enhance the surface's resistance to alkali penetration reduces the degree of freedom of molecular chain movement in the core region, leading to increased compression set, insufficient elastic recovery, and a gradual decrease in contact stress on the sealing surface. Conversely, reducing the overall cross-linking density to ensure the core's elastic recovery results in insufficient barrier capacity of the surface cross-linking network against alkali molecules, leading to a higher alkali penetration rate and causing the surface rubber to swell and soften. Furthermore, in renewable energy-coupled alkaline water electrolysis hydrogen production systems, the electrolyzer frequently starts and stops due to power fluctuations, causing the sealing ring to repeatedly undergo temperature cycles. If there are abrupt changes in cross-linking density between adjacent regions, the difference in thermal expansion concentrates at the abrupt interface, forming interfacial shear stress. After numerous temperature cycles, chemical bonds at the interface undergo fatigue fracture, resulting in microscopic peeling gaps and loss of the sealing ring's gradient protection function. Existing sealing rings with uniform cross-linking density cannot simultaneously meet the dual requirements of resistance to media erosion and long-term sealing resilience. Summary of the Invention

[0004] This invention provides a sealing ring for strong alkali resistant electrolytic cells, solving the technical problem that uniform cross-linked density sealing rings in related technologies cannot simultaneously meet the dual requirements of resistance to media erosion and long-term sealing and rebound under strong alkali, high temperature and frequent start-stop conditions.

[0005] This invention discloses a sealing ring for a strong alkali resistant electrolytic cell, used for installation in the sealing groove of the electrolytic cell frame and elastically compressing under the preload of flange bolts to form sealing contact stress. The sealing ring includes a sealing ring body, which is a ring-shaped elastic seal made of EPDM rubber. The cross-section of the sealing ring body includes at least a high crosslinking density layer and a low crosslinking density layer along its thickness direction. The high crosslinking density layer is located on the side of the sealing ring body's cross-section facing the electrolytic cell medium after installation, and the crosslinking points between the EPDM rubber molecular chains in the high crosslinking density layer are densely distributed, forming a dense three-dimensional crosslinking network. The low crosslinking density layer is located in the core region of the sealing ring body's cross-section that withstands compression deformation, and the crosslinking points between the EPDM rubber molecular chains in the low crosslinking density layer are sparsely distributed. The high crosslinking density layer and the low crosslinking density layer are integrally bonded through a co-crosslinking network formed by co-vulcanization.

[0006] Furthermore, in the cross-section of the sealing ring body, a cross-linking density gradient transition layer is provided between the high cross-linking density layer and the low cross-linking density layer. The cross-linking density gradient transition layer is annular and sandwiched between the inner side of the high cross-linking density layer and the outer side of the low cross-linking density layer. The cross-linking point density between the EPDM rubber molecular chains in the cross-linking density gradient transition layer continuously decreases along its thickness direction from the side closer to the high cross-linking density layer to the side closer to the low cross-linking density layer. There is no abrupt change in cross-linking density within the thickness range of the cross-linking density gradient transition layer.

[0007] Furthermore, at the interface between the crosslinking density gradient transition layer and the high crosslinking density layer, the crosslinking density of the side of the crosslinking density gradient transition layer closer to the high crosslinking density layer matches the crosslinking density of the high crosslinking density layer, and the two form a co-crosslinking network during co-vulcanization to achieve chemical bonding; at the interface between the crosslinking density gradient transition layer and the low crosslinking density layer, the crosslinking density of the side of the crosslinking density gradient transition layer closer to the low crosslinking density layer matches the crosslinking density of the low crosslinking density layer, and the two form a co-crosslinking network during co-vulcanization to achieve chemical bonding; from the high crosslinking density layer through the crosslinking density gradient transition layer to the low crosslinking density layer, the crosslinking density is continuously and gradually distributed, and there is no interface with abrupt changes in crosslinking density.

[0008] Furthermore, the high cross-linking density layer is a thin-walled annular shell that extends continuously along the outer contour of the medium contact side of the sealing ring body cross section; the low cross-linking density layer fills the core space enclosed by the high cross-linking density layer.

[0009] Furthermore, the cross-section of the sealing ring body is an O-shaped cross-section, the high cross-linking density layer is continuously distributed along the outer half-circumference arc surface of the O-shaped cross-section, covering the arc surface area of ​​the O-shaped cross-section facing the medium, and the low cross-linking density layer occupies the inner half-circumference area of ​​the O-shaped cross-section away from the medium.

[0010] Furthermore, the sealing ring body has a rectangular cross-section, the high cross-linking density layer covers one side of the rectangular cross-section facing the medium and a portion of the end face area adjacent to that side, forming a U-shaped thin-walled shell that encloses the medium contact side of the rectangular cross-section, and the low cross-linking density layer fills the internal space enclosed by the U-shaped thin-walled shell.

[0011] Furthermore, the cross-section of the sealing ring body has an asymmetrical outer contour. The outer contour of the medium contact side where the high cross-linking density layer is located is geometrically different from the outer contour of the compression deformation side where the low cross-linking density layer is located, so that the sealing ring body can only be placed into the sealing groove with a unique orientation during installation.

[0012] Furthermore, the asymmetrical outer contour is that the curvature of the arc surface on the medium contact side of the cross-section of the sealing ring body is different from the curvature of the arc surface on the compression deformation side; or, one side of the cross-section of the sealing ring body is provided with a positioning flange that protrudes radially, and the other side is a smooth arc surface, and the positioning flange cooperates with the positioning groove correspondingly opened on the groove wall of the sealing groove to define the installation orientation of the sealing ring body.

[0013] Furthermore, the wall thickness of the high cross-linking density layer is less than the thickness of the low cross-linking density layer along the compression direction; in the total thickness of the sealing ring body cross section along the compression direction, the combined thickness of the low cross-linking density layer and the cross-linking density gradient transition layer is greater than the wall thickness of the high cross-linking density layer.

[0014] Furthermore, at the interface between the high crosslinking density layer and the low crosslinking density layer, the EPDM rubber molecular chains in the two rubber compounds participate in a co-crosslinking reaction during vulcanization, forming a co-crosslinking network spanning the two layers at the interface, thus chemically bonding the high crosslinking density layer and the low crosslinking density layer together.

[0015] This invention solves the technical problem of the mutual constraint between the resistance to media erosion and elastic recovery ability of a uniform crosslinking density sealing ring under strong alkaline, high-temperature, and frequent start-stop conditions by setting a high crosslinking density layer, a crosslinking density gradient transition layer, and a low crosslinking density layer along the thickness direction in the cross-section of the sealing ring body. The following technical effects are achieved: The high crosslinking density layer is located on the media contact side. Its dense three-dimensional crosslinking network reduces the penetration rate of alkaline molecules and inhibits the swelling and softening of the surface rubber by the alkaline solution, ensuring that the surface hardness and volume of the media contact side remain stable under long-term alkaline immersion conditions; The low crosslinking density layer is located in the core of the cross-section. Its molecular chain segments have a large degree of freedom of movement and small compression set, enabling it to continuously provide elastic recovery force under long-term compressive loads, maintaining the contact stress on the sealing surface; The crosslinking density gradient transition layer causes the crosslinking density within the cross-section to continuously and gradually change along the thickness direction, corresponding to a continuous transition in the coefficient of thermal expansion. The thermal stress generated by temperature cycling is dispersed within the continuous thickness range of the gradient transition layer, reducing the interfacial shear stress borne by the co-crosslinking network between layers, reducing the risk of interlayer peeling gaps, and helping the sealing ring maintain its gradient protection function and the stability of the sealing contact stress under frequent start-stop conditions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the overall structure of the sealing ring body of the present invention; Figure 3 This is a cross-sectional view of the sealing ring body of the present invention; Figure 4 This is a schematic diagram of the sealing ring body of the present invention with an added positioning flange; Figure 5 This is a schematic diagram showing the fit between the positioning flange and the positioning groove of the sealing ring of the present invention.

[0017] In the diagram: sealing ring body-1, high cross-linking density layer-2, low cross-linking density layer-3, cross-linking density gradient transition layer-4, positioning flange-5, electrolytic cell frame-6, sealing groove-7, positioning groove-8, flange-9, flange bolt-10. Detailed Implementation

[0018] In an alkaline water electrolysis hydrogen production system, a sealing ring is installed in the sealing groove 7 of the electrolyzer frame 6. The sealing ring relies on the pre-tightening force of the flange bolts 10 to generate elastic compression deformation, forming contact stress on the sealing surface to prevent the potassium hydroxide solution and hydrogen gas generated by electrolysis from leaking out of the electrolyzer. Existing sealing rings are usually made of fluororubber or EPDM rubber through compression molding and vulcanization in one step, and the cross-linking density is uniform throughout the cross-section of the sealing ring.

[0019] Under long-term operating conditions, the chemical corrosion and mechanical loads experienced by different regions of the sealing ring cross-section vary. The surface region of the sealing ring cross-section, which is in direct contact with potassium hydroxide solution, is continuously subjected to alkali wetting, with alkali molecules penetrating and diffusing into the cross-section along the gaps between rubber molecular chain segments. When the cross-linking density is uniform throughout the sealing ring cross-section, the cross-linking network in the surface region is insufficient to block alkali molecules, resulting in a higher alkali penetration rate, causing the surface rubber to swell and soften, and reducing surface hardness. Simultaneously, the core region of the sealing ring cross-section, which is subjected to compressive deformation caused by the preload of the flange bolts 10, needs to maintain elastic recovery capability under long-term compressive loads to continuously provide sealing contact stress. When the core region and the surface region use the same uniform cross-linking density, increasing the overall cross-linking density to enhance the surface's resistance to alkali penetration reduces the degree of freedom of molecular chain segment movement in the core region, increases permanent compression deformation, and reduces elastic recovery force. This leads to a gradual attenuation of contact stress on the sealing surface, ultimately forming a micro-leakage channel for hydrogen at the sealing interface.

[0020] Furthermore, in alkaline water electrolysis hydrogen production systems coupled with renewable energy, the electrolyzer frequently starts and stops due to power fluctuations, causing the sealing ring to repeatedly experience temperature cycles from room temperature to operating temperature. When regions with varying cross-linking densities exist within the sealing ring's cross-section, these regions exhibit different coefficients of thermal expansion due to their different cross-linking densities, resulting in asynchronous thermal expansion and contraction during temperature cycling. If there is a sudden change in cross-linking density between adjacent regions, the difference in thermal expansion caused by temperature cycling concentrates at the abrupt interface, forming interfacial shear stress. After numerous temperature cycles, the chemical bonds at the interface gradually fatigue and break, creating microscopic peeling gaps between adjacent regions. The alkaline solution then bypasses the highly cross-linked areas on the surface and directly penetrates into the core through these gaps, leading to the loss of the overall gradient protection function of the sealing ring.

[0021] like Figure 1-5 As shown in the embodiment, a sealing ring for a strong alkali-resistant electrolytic cell is provided. This sealing ring is installed in the sealing groove 7 of the electrolytic cell frame 6 and undergoes elastic compression deformation under the preload of the flange bolts 10 to form a sealing contact stress. The sealing ring body 1 is a ring-shaped elastic seal made of EPDM rubber. The cross-section of the sealing ring body 1 includes at least a high cross-linking density layer 2 and a low cross-linking density layer 3 along its thickness direction. The high cross-linking density layer 2 is located on the side of the sealing ring cross-section facing the electrolytic cell medium after installation, and the low cross-linking density layer 3 is located in the core region of the sealing ring cross-section that withstands compression deformation. The high cross-linking density layer 2 and the low cross-linking density layer 3 are integrally bonded through a co-cross-linking network formed by co-vulcanization.

[0022] Specifically, the high crosslinking density layer 2 is a thin-walled annular shell that extends continuously along the outer contour of the medium contact side of the sealing ring cross-section. The crosslinking points between the EPDM rubber molecular chains in the high crosslinking density layer 2 are densely distributed, forming a dense three-dimensional crosslinking network. This dense three-dimensional crosslinking network reduces the gaps between molecular chain segments. When alkali molecules diffuse into the cross-section along the gaps between chain segments, the diffusion path of the alkali molecules is repeatedly blocked and deflected by the dense crosslinking nodes. The penetration rate is significantly lower than that of rubber with uniform crosslinking density, thus inhibiting the swelling effect of alkali on the rubber surface and enabling the high crosslinking density layer 2 to maintain stable surface hardness and volume under long-term alkali immersion conditions.

[0023] A low-crosslinking density layer 3 fills the core space enclosed by a high-crosslinking density layer 2. In the low-crosslinking density layer 3, the crosslinking points between the EPDM rubber molecular chains are sparsely distributed, and the molecular chain segments retain a large degree of freedom of movement. When the preload of the flange bolts 10 is transmitted to the sealing ring body 1 through the flange 9, the low-crosslinking density layer 3, due to its large degree of freedom of movement of its molecular chain segments, bears the main elastic deformation in the sealing ring cross-section. Under long-term continuous compressive load, the low-crosslinking density layer 3 exhibits small permanent compressive deformation and can continuously provide elastic recovery force, maintaining sufficient contact stress on the sealing surface.

[0024] At the interface between the high crosslinking density layer 2 and the low crosslinking density layer 3, the EPDM rubber molecular chains in the two rubber compounds participate in the co-crosslinking reaction during the vulcanization process, forming a co-crosslinking network across the two layers at the interface, connecting the two layers together by chemical bonding, and preventing the layers from separating under working load.

[0025] It should be understood that the sealing ring body 1 is installed in the sealing groove 7 of the electrolytic cell frame 6. The sealing groove 7 is an annular groove formed on the electrolytic cell frame 6. The groove wall of the sealing groove 7 provides radial constraint to the sealing ring body 1, and the bottom surface of the sealing groove 7 provides axial support to the sealing ring body 1. The flange 9 face is located on the opening side of the sealing groove 7. After the flange bolts 10 are tightened through the bolt holes on the flange 9, the flange 9 face presses against the end face of the sealing ring body 1, converting the bolt preload into a compressive load on the sealing ring body 1. During installation, the high cross-linking density layer 2 of the sealing ring body 1 faces the potassium hydroxide solution inside the electrolytic cell, and the low cross-linking density layer 3 faces the direction of compression deformation. The potassium hydroxide solution contacts the outer surface of the high cross-linking density layer 2 in the sealing ring body 1, and the hydrogen gas generated by electrolysis is blocked by the contact stress formed between the flange 9 face and the sealing groove 7.

[0026] In some embodiments, the sealing ring body 1 has an O-shaped cross section, the high cross-linking density layer 2 is continuously distributed along the outer half-circumferential arc surface of the O-shaped cross section, covering the arc surface region of the O-shaped cross section facing the medium, and the low cross-linking density layer 3 occupies the inner half-circumferential region of the O-shaped cross section away from the medium.

[0027] In some embodiments, the sealing ring body 1 has a rectangular cross-section, the high cross-linking density layer 2 covers one side of the rectangular cross-section facing the medium and a portion of the end face area adjacent to that side, forming a U-shaped thin-walled shell that covers the medium contact side of the rectangular cross-section, and the low cross-linking density layer 3 fills the internal space enclosed by the U-shaped thin-walled shell.

[0028] In some embodiments, the cross-section of the sealing ring body 1 has an asymmetrical outer contour. The outer contour of the medium contact side where the high cross-linking density layer 2 is located is geometrically different from the outer contour of the compression deformation side where the low cross-linking density layer 3 is located, so that the sealing ring body 1 can only be placed into the sealing groove 7 with a single orientation during installation, thereby ensuring that the high cross-linking density layer 2 faces the medium side. The asymmetrical outer contour may be that the curvature of the arc surface on the medium contact side is different from that on the compression deformation side, or it may be that one side of the cross-section has a radially protruding positioning flange 5 while the other side is a smooth arc surface. The positioning flange 5 cooperates with the corresponding positioning groove 8 opened on the groove wall of the sealing groove 7, defining the installation orientation of the sealing ring body 1.

[0029] Furthermore, to eliminate the concentrated interfacial shear stress generated during temperature cycling due to abrupt changes in crosslinking density between the high crosslinking density layer 2 and the low crosslinking density layer 3, a crosslinking density gradient transition layer 4 is provided between the high crosslinking density layer 2 and the low crosslinking density layer 3 in the cross-section of the sealing ring body 1. The crosslinking density gradient transition layer 4 is annular and sandwiched between the inner surface of the high crosslinking density layer 2 and the outer surface of the low crosslinking density layer 3. The crosslinking point density between the EPDM rubber molecular chains in the crosslinking density gradient transition layer 4 continuously decreases along its thickness direction from the side closer to the high crosslinking density layer 2 to the side closer to the low crosslinking density layer 3, and there is no abrupt change in crosslinking density within the thickness range of the crosslinking density gradient transition layer 4.

[0030] At the interface between the crosslinking density gradient transition layer 4 and the high crosslinking density layer 2, the crosslinking density of the side of the crosslinking density gradient transition layer 4 closer to the high crosslinking density layer 2 is close to that of the high crosslinking density layer 2. During co-curing, they form a co-crosslinking network and achieve chemical bonding. Similarly, at the interface between the crosslinking density gradient transition layer 4 and the low crosslinking density layer 3, the crosslinking density of the side of the crosslinking density gradient transition layer 4 closer to the low crosslinking density layer 3 is close to that of the low crosslinking density layer 3. During co-curing, they also form a co-crosslinking network and achieve chemical bonding. Therefore, in the cross-section of the sealing ring, from the high crosslinking density layer 2 through the crosslinking density gradient transition layer 4 to the low crosslinking density layer 3, the crosslinking density exhibits a continuous and gradual distribution, without any abrupt changes in crosslinking density at the interface.

[0031] It should be understood that the coefficient of thermal expansion of EPDM rubber is related to its crosslinking density. In regions with higher crosslinking density, the movement of molecular chain segments is constrained by the crosslinking points, resulting in a lower coefficient of thermal expansion; in regions with lower crosslinking density, the movement of molecular chain segments has greater freedom, resulting in a higher coefficient of thermal expansion. In the crosslinking density gradient transition layer 4, the crosslinking density changes continuously and gradually along the thickness direction, and the corresponding coefficient of thermal expansion also changes continuously and gradually along the thickness direction from a lower value near the high crosslinking density layer 2 to a higher value near the low crosslinking density layer 3. During temperature cycling, the amount of thermal deformation at various points within the sealing ring cross-section transitions smoothly along the thickness direction, the thermal strain difference between adjacent micro-layers is minimal, and no concentrated interfacial shear stress is generated.

[0032] Furthermore, in order to minimize the impact of the high cross-linking density layer 2 on the overall elastic compressive performance of the sealing ring while ensuring its resistance to alkali penetration, the wall thickness of the high cross-linking density layer 2 is less than the thickness of the low cross-linking density layer 3 along the compression direction. The high cross-linking density layer 2 occupies only a thin layer area on the medium contact side of the sealing ring cross-section, serving as a barrier against alkali penetration. The majority of the thickness of the sealing ring cross-section is occupied by the low cross-linking density layer 3 and the cross-linking density gradient transition layer 4, so that the elastic response of the sealing ring body 1 under compressive load mainly depends on the elastic characteristics of the low cross-linking density layer 3.

[0033] How to use the sealing ring body 1: The sealing ring body 1 is placed into the sealing groove 7 of the electrolytic cell frame 6, with the high cross-linking density layer 2 facing the medium space inside the electrolytic cell. The groove wall of the sealing groove 7 constrains the radial position of the sealing ring body 1, and the bottom surface of the sealing ring body 1 abuts against the bottom surface of the sealing groove 7.

[0034] In some embodiments, when the cross-section of the sealing ring body 1 has an asymmetrical outer contour or a positioning flange 5, the sealing ring body 1 is placed into the sealing groove 7 along the direction in which the positioning flange 5 is aligned with the positioning groove 8 on the wall of the sealing groove 7. The positioning flange 5 is embedded in the positioning groove 8, which limits the installation orientation of the sealing ring body 1 and ensures that the high cross-linking density layer 2 faces the medium side.

[0035] Tighten the flange bolts 10, and the flange 9 moves axially and presses against the end face of the sealing ring body 1, applying a pre-tightening compression force to the sealing ring body 1. The pre-tightening compression force is transmitted through the flange 9 to the end face of the sealing ring body 1, and then along the thickness direction of the sealing ring cross-section towards the bottom surface of the sealing groove 7. In the pre-tightening compression force transmission path, the high cross-linking density layer 2, due to its dense cross-linking network and restricted molecular chain segment movement, produces a smaller amount of compressive deformation; the cross-linking density gradient transition layer 4 produces a gradual compressive deformation corresponding to its local cross-linking density; and the low cross-linking density layer 3, due to its large degree of freedom of molecular chain segment movement, bears the largest proportion of elastic compressive deformation in the cross-section. After the sealing ring body 1 is compressed as a whole, sealing contact stress is formed on the contact surfaces with the flange 9, the bottom surface of the sealing groove 7, and the groove wall.

[0036] After the electrolytic cell is put into operation, it is filled with potassium hydroxide solution and heated to the operating temperature, generating hydrogen gas during electrolysis. The potassium hydroxide solution contacts the outer surface of the high cross-linking density layer 2 in the sealing ring body 1, and the alkali molecules diffuse into the cross-section along the gaps between the EPDM rubber molecular chains in the high cross-linking density layer 2. The dense cross-linking nodes in the high cross-linking density layer 2 hinder the diffusion path of the alkali molecules, keeping the penetration rate at a low level and inhibiting the swelling of the surface rubber by the alkali solution. The low cross-linking density layer 3 continuously provides elastic recovery force under compression, maintaining the contact stress on the sealing surface and preventing hydrogen gas from leaking outward along the sealing interface.

[0037] When the electrolytic cell is frequently started and stopped due to power fluctuations, the sealing ring body 1 repeatedly undergoes temperature cycles from room temperature to operating temperature. During the heating phase, transient temperature gradients are generated in different regions of the sealing ring cross-section due to the time difference in heat conduction, resulting in varying degrees of thermal expansion in each region; during the cooling phase, different regions experience varying degrees of thermal contraction. The cross-linking density gradient transition layer 4 in the sealing ring cross-section ensures that the coefficient of thermal expansion varies continuously along the thickness direction throughout the cross-section, and the difference in thermal deformation between adjacent micro-layers is minimal. The thermal stress generated by the temperature cycle is dispersed across the continuous thickness range of the cross-linking density gradient transition layer 4 rather than concentrated at a particular interface. During repeated temperature cycles, the shear stress borne by the co-crosslinking network between layers is far below the fatigue limit of the co-crosslinking network, and no interlayer peeling gaps are generated within the sealing ring cross-section. The penetration barrier function of the high cross-linking density layer 2 against alkali solution and the elastic recovery function of the low cross-linking density layer 3 are both maintained continuously.

[0038] In this embodiment, the sealing ring body 1 has regions with different cross-linking densities along the thickness direction in the cross section, and the alkali penetration resistance and elastic recovery function are respectively assigned to the regions at different positions in the cross section, thus overcoming the contradiction between the resistance to media erosion and the elastic recovery ability in a sealing ring with uniform cross-linking density.

[0039] Specifically, the high cross-linking density layer 2 is located on the medium contact side of the sealing ring cross-section. The dense three-dimensional cross-linking network of the high cross-linking density layer 2 reduces the gaps between molecular chain segments. The diffusion path of alkali molecules along the gaps between chain segments is blocked by a large number of cross-linking nodes, reducing the penetration rate. Therefore, it inhibits the swelling and softening of the rubber surface by the alkali, allowing the surface hardness and volume of the sealing ring on the medium contact side to remain stable under long-term alkali immersion conditions. The low cross-linking density layer 3 is located in the core region of the sealing ring cross-section. The molecular chain segments of the low cross-linking density layer 3 have a large degree of freedom of movement and small compression set. Therefore, it can continue to provide elastic recovery force under long-term bolt preload, maintaining the contact stress on the sealing surface and preventing hydrogen leakage along the sealing interface.

[0040] Furthermore, the cross-linking density gradient transition layer 4, located between the high cross-linking density layer 2 and the low cross-linking density layer 3, ensures that the cross-linking density within the cross-section changes continuously and gradually along the thickness direction without abrupt interfaces. Consequently, the corresponding coefficient of thermal expansion also changes continuously along the thickness direction. Therefore, during temperature cycling caused by frequent start-stop cycles, the thermal deformation at various points within the cross-section transitions smoothly along the thickness direction. The thermal expansion differences caused by temperature cycling are dispersed within the continuous thickness range of the cross-linking density gradient transition layer 4, resulting in minimal thermal strain difference per unit thickness. The interfacial shear stress borne by the co-crosslinking network between layers is far below the fatigue limit of the co-crosslinking network. Therefore, after numerous temperature cycles, no interlayer peeling gaps are generated within the cross-section of the sealing ring, and the penetration path of the alkali solution is continuously and completely blocked by the high cross-linking density layer 2. The sealing ring maintains its gradient protection function and long-term stability of the sealing contact stress under frequent start-stop conditions.

[0041] As can be seen, the sealing ring of this embodiment, through the gradient distribution of cross-linking density within the cross-section and the continuous transition of the cross-linking density gradient transition layer 4, takes into account the alkali penetration resistance of the medium contact side, the elastic recovery capability of the core, and the structural integrity of the interlayer during temperature cycling within the same sealing ring. This solves the technical problem that a sealing ring with uniform cross-linking density cannot simultaneously meet the dual requirements of resistance to medium erosion and long-term sealing and rebound under strong alkali, high temperature, and frequent start-stop conditions.

[0042] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A sealing ring for a strong alkali resistant electrolytic cell, used for installation in a sealing groove (7) of an electrolytic cell frame (6) and elastically compressing under the pre-tightening force of flange bolts (10) to form a sealing contact stress, characterized in that, include: The sealing ring body (1) is a ring-shaped elastic seal made of EPDM rubber. The cross section of the sealing ring body (1) includes at least a high cross-linking density layer (2) and a low cross-linking density layer (3) along the thickness direction. The high cross-linking density layer (2) is located on the side of the sealing ring body (1) facing the electrolytic cell medium after installation. The cross-linking points between the EPDM rubber molecular chains in the high cross-linking density layer (2) are densely distributed, forming a dense three-dimensional cross-linking network. The low crosslinking density layer (3) is located in the core region of the sealing ring body (1) that is subjected to compression deformation in the cross section. The crosslinking points between the EPDM rubber molecular chains in the low crosslinking density layer (3) are sparsely distributed. The high crosslinking density layer (2) and the low crosslinking density layer (3) are integrated through a co-crosslinking network formed by co-sulfurization.

2. The sealing ring for a strong alkali-resistant electrolytic cell according to claim 1, characterized in that, In the cross section of the sealing ring body (1), a cross-linking density gradient transition layer (4) is provided between the high cross-linking density layer (2) and the low cross-linking density layer (3). The cross-linking density gradient transition layer (4) is in the shape of an annular sheet and is sandwiched between the inner side of the high cross-linking density layer (2) and the outer side of the low cross-linking density layer (3). The cross-linking point density between the EPDM rubber molecular chains in the cross-linking density gradient transition layer (4) decreases continuously along its thickness direction from the side closer to the high cross-linking density layer (2) to the side closer to the low cross-linking density layer (3). There is no abrupt change in the cross-linking density within the thickness range of the cross-linking density gradient transition layer (4).

3. The sealing ring for a strong alkali-resistant electrolytic cell according to claim 2, characterized in that, At the contact interface between the crosslinking density gradient transition layer (4) and the high crosslinking density layer (2), the crosslinking density of the crosslinking density gradient transition layer (4) on the side closer to the high crosslinking density layer (2) matches the crosslinking density of the high crosslinking density layer (2), and the two form a co-crosslinking network to achieve chemical bonding during co-sulfurization; at the contact interface between the crosslinking density gradient transition layer (4) and the low crosslinking density layer (3), the crosslinking density of the crosslinking density gradient transition layer (4) on the side closer to the low crosslinking density layer (3) matches the crosslinking density of the low crosslinking density layer (3), and the two form a co-crosslinking network to achieve chemical bonding during co-sulfurization; from the high crosslinking density layer (2) through the crosslinking density gradient transition layer (4) to the low crosslinking density layer (3), the crosslinking density is continuously and gradually distributed, and there is no interface with abrupt change in crosslinking density.

4. The sealing ring for a strong alkali-resistant electrolytic cell according to claim 1, characterized in that, The high cross-linking density layer (2) is a thin-walled annular shell that extends continuously along the outer contour of the medium contact side of the cross section of the sealing ring body (1); the low cross-linking density layer (3) fills the core space enclosed by the high cross-linking density layer (2).

5. The sealing ring for a strong alkali-resistant electrolytic cell according to claim 1, characterized in that, The sealing ring body (1) has an O-shaped cross section. The high cross-linking density layer (2) is continuously distributed along the outer half-circumference arc surface of the O-shaped cross section, covering the arc surface area facing the medium in the O-shaped cross section. The low cross-linking density layer (3) occupies the inner half-circumference area away from the medium in the O-shaped cross section.

6. The sealing ring for a strong alkali-resistant electrolytic cell according to claim 1, characterized in that, The sealing ring body (1) has a rectangular cross-section. The high cross-linking density layer (2) covers one side of the rectangular cross-section facing the medium and a portion of the end face area adjacent to that side. It forms a U-shaped thin-walled shell that encloses the medium contact side of the rectangular cross-section. The low cross-linking density layer (3) fills the internal space enclosed by the U-shaped thin-walled shell.

7. The sealing ring for a strong alkali-resistant electrolytic cell according to claim 1, characterized in that, The sealing ring body (1) has an asymmetrical outer contour. The outer contour of the medium contact side where the high cross-linking density layer (2) is located is geometrically different from the outer contour of the compression deformation side where the low cross-linking density layer (3) is located, so that the sealing ring body (1) can only be placed into the sealing groove (7) with a unique orientation during installation.

8. The sealing ring for a strong alkali-resistant electrolytic cell according to claim 7, characterized in that, The asymmetrical outer contour is that the curvature of the arc surface on the medium contact side of the cross section of the sealing ring body (1) is different from the curvature of the arc surface on the compression deformation side; or, one side of the cross section of the sealing ring body (1) is provided with a positioning flange (5) protruding radially, and the other side is a smooth arc surface. The positioning flange (5) cooperates with the positioning groove (8) correspondingly opened on the groove wall of the sealing groove (7) to limit the installation orientation of the sealing ring body (1).

9. The sealing ring for a strong alkali-resistant electrolytic cell according to claim 2, characterized in that, The wall thickness of the high crosslinking density layer (2) is less than the thickness of the low crosslinking density layer (3) along the compression direction; in the total thickness of the sealing ring body (1) cross section along the compression direction, the combined thickness of the low crosslinking density layer (3) and the crosslinking density gradient transition layer (4) is greater than the wall thickness of the high crosslinking density layer (2).

10. The sealing ring for a strong alkali-resistant electrolytic cell according to claim 1, characterized in that, At the interface between the high crosslinking density layer (2) and the low crosslinking density layer (3), the EPDM rubber molecular chains in the two rubber compounds participate in a co-crosslinking reaction during vulcanization, forming a co-crosslinking network across the two layers at the interface, thus connecting the high crosslinking density layer (2) and the low crosslinking density layer (3) into one unit by chemical bonding.

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