Crack defect repairing method for large rubber-fabric composite flexible sealing ring

Abstract

The invention provides a crack defect repairing method for a large rubber-fabric composite flexible sealing ring. The crack defect repairing method comprises the following steps: a) detecting and recording the hardness of the sealing ring in a plane area around a crack defect; b) polishing the crack part to form a repairing area which is tidy in edge and is flush with the original sealing surface, and measuring the size of the repairing area; c) selecting an unvulcanized rubber repair film matched with the hardness of the sealing ring; d) sequentially carrying out sand blasting, solvent cleaning and rubber cement impregnation pretreatment on the repairing fabric; e) cutting rubber repairing films and repairing fabrics according to the types of the crack defects, and alternately arranging and filling the repairing area with the rubber repairing films and the repairing fabrics to form a repairing layer; (f) placing the sealing ring filled with the repairing layer into a heating mold matched with the section of the original sealing ring, heating, pressurizing and vulcanizing to finish repairing; layered repairing and heat vulcanization reinforcing are adopted according to the crack type, on-site rapid repairing of the flexible sealing ring is achieved, the strength and the air tightness are remarkably recovered, meanwhile, the downtime is effectively shortened, and the maintenance cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of rubber repair, and in particular relates to a method for repairing crack defects of a large rubber-fabric composite flexible sealing ring. Background Art

[0002] Existing large flexible sealing rings generally utilize layers of rubber and curved fabric alternating at predetermined thicknesses, then vulcanized to create a ring-shaped compensating element. During installation, these rings are secured between pipeline or turbine flanges using metal pressure plates or clamps. They can simultaneously absorb axial, radial, and angular displacement, ensuring airtightness in high-temperature, dust-laden, or corrosive media. Commonly used rubber matrices include EPDM, chloroprene rubber, hydrogenated nitrile rubber, and fluororubber. Fabric layers are often constructed from aramid or glass fiber to enhance heat and tear resistance. Designed for a service life exceeding ten years.

[0003] During operation, thermal expansion and contraction, pressure fluctuations, and vibrations cause the sealing ring to undergo cyclical stretching and bending. The inner rubber lining first ages and cracks, followed by radial or circumferential cracks at the interface with the fabric. Common repair practices involve shutting down the machine, disassembling, and replacing the entire sealing ring, or shipping it back to the manufacturer for re-patching and reinstallation using large-scale plate vulcanization equipment. While these methods can restore performance, they require limited space for disassembly and assembly, are cumbersome, and require significant downtime, resulting in significant economic losses for the power generation side.

[0004] To minimize downtime, some on-site quick-repair solutions employ room-temperature self-vulcanizing adhesive or two-component cold-bonding adhesive to sand, clean, gluing, and compact the cracked area, supplemented by a single layer of fabric reinforcement when necessary. Other solutions utilize portable electrically heated press dies, filling the defective area with unvulcanized adhesive sheets and fabric before hot-vulcanizing and forming the part in situ. However, cold-bonding methods are affected by ambient temperature and medium penetration, resulting in limited interfacial bonding between the adhesive layer and the original adhesive, making it difficult to restore the circumferential and radial strength of the cracked area. On-site hot vulcanization, on the other hand, is limited by mold fit and temperature uniformity, often resulting in localized under-vulcanization or insufficient rubber flow, which can easily lead to secondary leaks.

[0005] In summary, existing crack repair technologies still have shortcomings in terms of structural compatibility, mechanical recovery, and ease of construction: Overall replacement costs are high and the construction period is long; cold-bonded patches lack sufficient bond strength and heat resistance; and on-site hot vulcanization is limited by equipment conditions, making it difficult to ensure uniform vulcanization and coordinated load-bearing between the fabric and adhesive layers. To address these challenges, on-site repair of cracks in flexible sealing rings still needs improvement. Summary of the Invention

[0006] The invention provides a method for repairing crack defects of a large rubber-fabric composite flexible sealing ring, which solves the problems in the prior art.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] A method for repairing crack defects in a large rubber-fabric composite flexible sealing ring includes:

[0009] a) Use a Shore A hardness tester to test and record the hardness of the sealing ring in the plane area around the crack defect;

[0010] b) Grind the cracked area to form a repair area with neat edges that is flush with the original sealing surface, and measure the length, width, and depth of the repair area;

[0011] c) Select an unvulcanized rubber repair sheet that matches the hardness of the sealing ring;

[0012] d) Pre-treating the repaired fabric by sandblasting, solvent cleaning and rubber mortar dipping;

[0013] e) Cutting the rubber repair sheets and the repair fabric according to the type of crack defects and arranging them alternately to fill the repair area to form a repair layer;

[0014] f) Place the sealing ring filled with the repair layer into a heated mold that matches the cross-section of the original sealing ring, and vulcanize it under pressure at a temperature of 120-150°C for 0.5-4 hours to vulcanize and form the repair layer and the original sealing ring as a whole.

[0015] Furthermore, in step e), when the crack defect is a surface rubber crack, the repair area is only filled with a single-layer rubber repair film.

[0016] Furthermore, in step e), when the crack defect is a fabric break, the repair layer filled in the repair area includes at least one layer of repair fabric and rubber repair films sandwiched between the upper and lower layers of the repair fabric.

[0017] Furthermore, in step e), when the crack defect is a through fracture, the repair layer filled in the repair area includes multiple layers of rubber repair films and repair fabrics, the repair films and repair fabrics are alternately stacked, and the outermost layer of the repair layer is the rubber repair film.

[0018] Furthermore, it is characterized in that: in step e), the repairing fabric is fixed to the same fabric layer of the original sealing ring by sewing.

[0019] Furthermore, the thickness of a single piece of the rubber repair film is 1 mm to 3 mm.

[0020] Furthermore, the rubber repair film is made of EPDM rubber or chloroprene rubber, and its Shore A hardness is 70-80.

[0021] Furthermore, the repair fabric is aramid cloth or glass fiber cloth.

[0022] Furthermore, the sandblasting uses 20-40 mesh brown corundum, and the sandblasting pressure is 0.1-0.2 MPa; the solvent cleaning uses ethyl acetate or anhydrous ethanol.

[0023] Furthermore, the thickness of the rubber mortar-impregnated fabric impregnated layer is 0.1 mm to 0.3 mm.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] First, the method of the present invention significantly improves the bonding uniformity and vulcanization adequacy between the repair layer and the original rubber-fabric interface by precisely arranging the rubber film and fabric layer according to the crack type in the repair area and using a heated mold with the same cross-section as the sealing ring. The peel strength and tensile strength are on par with the bulk strength. Second, by selecting unvulcanized film based on the hardness matching principle and controlling the thickness of the single film, the circumferential and radial bearing stiffness of the cracked section can be restored. After 1×10 6 After the first cycle compression fatigue test, no secondary cracking was observed in the repaired area. Furthermore, the integrated sandblasting-cleaning-impregnation fabric pretreatment process improved the wettability of the fabric and the adhesive, enabling the multi-layer stacked structure to maintain a stable seal under high-temperature vibration conditions. The on-site construction time was shortened to about 30% of the original plan, effectively reducing downtime losses.

[0026] Of course, the implementation of the various technical solutions of the present invention does not necessarily require achieving all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, they can also obtain drawings of other embodiments based on these drawings.

[0028] Figure 1 This is a schematic diagram of a defective cross-sectional structure of a flexible sealing ring in Example 1 of the present invention;

[0029] Figure 2 Schematic diagram of a defective cross-sectional structure of a flexible sealing ring according to Example 2 of the present invention;

[0030] Figure 3 This is a schematic diagram of a defective cross-sectional structure of a flexible sealing ring in Example 3 of the present invention;

[0031] Figure 4 Schematic diagram of a defective cross-sectional structure of a flexible sealing ring according to Example 4 of the present invention;

[0032] Figure 5Schematic diagram of a defective cross-sectional structure of a flexible sealing ring in Example 5 of the present invention;

[0033] Figure 6 This is a schematic diagram of the cross-sectional structure of the repaired flexible sealing ring according to Example 1 of the present invention;

[0034] Figure 7 This is a schematic diagram of the cross-sectional structure of the repaired flexible sealing ring according to Example 2 of the present invention;

[0035] Figure 8 This is a schematic diagram of the cross-sectional structure of the repaired flexible sealing ring according to Example 3 of the present invention;

[0036] Figure 9 This is a schematic diagram of the cross-sectional structure of the repaired flexible sealing ring according to Example 4 of the present invention;

[0037] Figure 10 This is a schematic diagram of the cross-sectional structure of the repaired flexible sealing ring according to Example 5 of the present invention. DETAILED DESCRIPTION

[0038] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0039] In the description of this patent, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings. They are only for the convenience of describing this patent and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they should not be understood as limitations on this patent.

[0040] In the description of this patent, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," "connected," and "set" should be understood in a broad sense. For example, they can refer to fixed connection or set, detachable connection or set, or integral connection or set. Those skilled in the art can understand the specific meanings of the above terms in this patent based on the specific circumstances. The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0041] Example 1:

[0042] like Figure 1The Type I defect shown is a surface rubber crack, which is characterized by cracks limited to the outermost covering rubber, appearing as small, sharp-angled openings on the surface of the rubber layer, while the internal fabric reinforcement layers remain continuous. This defect is usually caused by UV aging or high-temperature oxidation. It does not damage the load-bearing skeleton of the composite layer in the early stage, but if not treated in time, the crack can expand circumferentially under thermal-mechanical cycles and further invade the fabric layer.

[0043] See also Figure 6 In view of the above defects, the crack defect repair method of the large rubber-fabric composite flexible sealing ring includes:

[0044] Step a), using a Shore A hardness tester to test and record the hardness of the sealing ring in the plane area around the crack;

[0045] Step b) using P80 emery cloth or tungsten steel grinding disc to grind the crack into a repair area with neat edges and appropriate depth, and using a vernier caliper to measure the length, width and depth;

[0046] Step c), selecting an unvulcanized EPDM or chloroprene rubber repair film with a single thickness of 3 mm that matches the original hardness;

[0047] Step d), cutting the film into a single layer according to size and filling it in the repair area;

[0048] Step e): Place the filled sealing ring into an electrically heated mold that matches its cross section, and vulcanize it under pressure at 120° C.-150° C. and 0.5-1.0 MPa for 0.5-1 hour to complete the defect repair.

[0049] The sealing ring repair area after cooling and demoulding was subjected to an airtight test at 0.6 MPa for 30 min, with a pressure drop of ≤0.1 MPa. 6 Dynamic fatigue testing with a frequency of 25Hz and an amplitude of 0.5mm revealed no bulging, debonding, or cracking in the repaired area. Peel strength and radial tensile strength tests were also conducted on the repaired seal ring, and the results were consistent with those of the original seal ring. After the flexible seal ring was fully assembled and started up, the turbine maintained a vacuum pressure of -4 to -6 kPa for 48-72 hours and operated normally.

[0050] Example 2:

[0051] like Figure 2 The first type of Class II defect shown is a single-layer fabric fracture. The crack continues from the outer rubber layer into the first fabric reinforcement layer, causing it to break, while the layers below remain intact. This type of damage is common after local excessive bending or foreign object impact, causing the outermost stress-bearing fibers to be pulled apart, thereby weakening the local radial stiffness.

[0052] See also Figure 7In view of the above defects, the crack defect repair method of the large rubber-fabric composite flexible sealing ring includes:

[0053] Step a), using a Shore A hardness tester to test and record the hardness of the sealing ring in the plane area around the crack;

[0054] Step b) using P80 emery cloth or tungsten steel grinding disc to grind the crack into a repair area with neat edges and appropriate depth, and using a vernier caliper to measure the length, width and depth;

[0055] Step c), prepare one piece of unvulcanized EPDM rubber or chloroprene rubber repair film with a thickness of 1 mm and 3 mm respectively;

[0056] Step d), sandblasting the plain aramid cloth with 40 mesh brown corundum at 0.2 MPa, cleaning with ethyl acetate, and then dipping the cloth in 0.1-0.2 mm thick EPDM rubber mortar or chloroprene rubber mortar;

[0057] Step e) Cut and fill the patch area in the order of "film 1mm / fabric / film 3mm", and sew the fabric layer to the original fabric layer with aramid thread with a 10mm stitch length during the filling process;

[0058] Step f), vulcanizing at 120-150° C. and 0.5-1.0 MPa for 1-2 hours to complete the defect repair.

[0059] The sealing ring repair area after cooling and demoulding was subjected to an airtight test at 0.6 MPa for 30 min, with a pressure drop of ≤0.1 MPa. 6 Dynamic fatigue testing with a frequency of 25Hz and an amplitude of 0.5mm revealed no bulging, debonding, or cracking in the repaired area. Peel strength and radial tensile strength tests were also conducted on the repaired seal ring, and the results were consistent with those of the original seal ring. After the flexible seal ring was fully assembled and started up, the turbine maintained a vacuum pressure of -4 to -6 kPa for 48-72 hours and operated normally.

[0060] Example 3:

[0061] like Figure 3 The second type of Class II defect shown is a fracture between two fabric layers. The crack depth has penetrated the two outer fabric layers, accompanied by cracking of the corresponding adhesive layer, and the damage range has expanded one layer inward. This situation is more common under the combined effects of thermal expansion and contraction and pressure pulsation. If it continues to deteriorate, it will cause local buckling of the sealing ring.

[0062] See also Figure 8 In view of the above defects, the crack defect repair method of the large rubber-fabric composite flexible sealing ring includes:

[0063] Step a), using a Shore A hardness tester to test and record the hardness of the sealing ring in the plane area around the crack;

[0064] Step b) using P80 emery cloth or tungsten steel grinding disc to grind the crack into a repair area with neat edges and appropriate depth, and using a vernier caliper to measure the length, width and depth;

[0065] Step c), prepare one piece of unvulcanized EPDM rubber or chloroprene rubber repair film with a thickness of 1 mm and 3 mm respectively;

[0066] Step d), sandblasting the plain aramid cloth with 40 mesh brown corundum at 0.2 MPa, cleaning with ethyl acetate, and then dipping the cloth in 0.1-0.2 mm thick EPDM rubber mortar or chloroprene rubber mortar;

[0067] Step e) stacking the film and fabric alternately in the order of film 1 mm / fabric / film 2 mm / fabric / film 3 mm and sewing them in place;

[0068] Step f), placing the mold and vulcanizing at 120-150°C and 0.5-1.0 MPa for 1-2 hours to complete the defect repair.

[0069] The sealing ring repair area after cooling and demoulding was subjected to an airtight test at 0.6 MPa for 30 min, with a pressure drop of ≤0.1 MPa. 6 Dynamic fatigue testing with a frequency of 25Hz and an amplitude of 0.5mm revealed no bulging, debonding, or cracking in the repaired area. Peel strength and radial tensile strength tests were also conducted on the repaired seal ring, and the results were consistent with those of the original seal ring. After the flexible seal ring was fully assembled and started up, the turbine maintained a vacuum pressure of -4 to -6 kPa for 48-72 hours and operated normally.

[0070] Example 4:

[0071] like Figure 4 The third type of Class II defect shown is a three-layer fabric fracture. The crack penetrates all three fabric layers and forms a clear wedge-shaped rupture. The inner cavity may show signs of medium infiltration. At this time, the coordinated load-bearing of the rubber-fabric laminate is significantly weakened, and multi-layer alternating reinforcement is necessary to restore strength.

[0072] See also Figure 9 In view of the above defects, the crack defect repair method of the large rubber-fabric composite flexible sealing ring includes:

[0073] Step a), using a Shore A hardness tester to test and record the hardness of the sealing ring in the plane area around the crack;

[0074] Step b) using P80 emery cloth or tungsten steel grinding disc to grind the crack into a repair area with neat edges and appropriate depth, and using a vernier caliper to measure the length, width and depth;

[0075] Step c), prepare one piece of unvulcanized EPDM rubber or chloroprene rubber repair film with a thickness of 1 mm and 3 mm respectively;

[0076] Step d), sandblasting the plain aramid cloth with 40 mesh brown corundum at 0.2 MPa, cleaning with ethyl acetate, and then dipping the cloth in 0.1-0.2 mm thick EPDM rubber mortar or chloroprene rubber mortar;

[0077] Step e) filling the repair area in a structure of film 1mm / fabric / film 2mm / fabric / film 2mm / fabric / film 3mm, and sewing and fixing each fabric layer;

[0078] Step f), vulcanizing at 120-150° C. and 0.5-1.0 MPa for 2-3 hours to complete the defect repair.

[0079] The sealing ring repair area after cooling and demoulding was subjected to an airtight test at 0.6 MPa for 30 min, with a pressure drop of ≤0.1 MPa. 6 Dynamic fatigue testing with a frequency of 25Hz and an amplitude of 0.5mm revealed no bulging, debonding, or cracking in the repaired area. Peel strength and radial tensile strength tests were also conducted on the repaired seal ring, and the results were consistent with those of the original seal ring. After the flexible seal ring was fully assembled and started up, the turbine maintained a vacuum pressure of -4 to -6 kPa for 48-72 hours and operated normally.

[0080] Example 5:

[0081] like Figure 5 The Type III defect shown is a through-fracture. The crack has cut through all rubber and fabric layers, separating the sealing ring cross section into two sections, with obvious dislocation or gap. This defect is mostly caused by extreme impact or long-term fatigue accumulation. Once it occurs, the sealing and compensation functions will be completely lost, requiring a structural repair with multiple layers alternating and extending to the complete cross section.

[0082] See also Figure 10 In view of the above defects, the crack defect repair method of the large rubber-fabric composite flexible sealing ring includes:

[0083] Step a), using a Shore A hardness tester to test and record the hardness of the sealing ring in the plane area around the crack;

[0084] Step b) using P80 emery cloth or tungsten steel grinding disc to grind the crack into a repair area with neat edges and appropriate depth, and using a vernier caliper to measure the length, width and depth;

[0085] Step c), prepare one piece of unvulcanized EPDM rubber or chloroprene rubber repair film with a thickness of 1 mm and 3 mm respectively;

[0086] Step d), sandblasting the plain aramid cloth with 40 mesh brown corundum at 0.2 MPa, cleaning with ethyl acetate, and then dipping the cloth in 0.1-0.2 mm thick EPDM rubber mortar or chloroprene rubber mortar;

[0087] Step e), according to the crack depth, 3mm and 2mm thick films are alternately stacked with multiple layers of impregnated aramid cloth, with the outermost layer being a 3mm film, and sewn layer by layer;

[0088] Step f), vulcanizing at 120-150° C. and 0.5-1.0 MPa for 3-4 hours to complete the defect repair.

[0089] The sealing ring repair area after cooling and demoulding was subjected to an airtight test at 0.6 MPa for 30 min, with a pressure drop of ≤0.1 MPa. 6 Dynamic fatigue testing with a frequency of 25Hz and an amplitude of 0.5mm revealed no bulging, debonding, or cracking in the repaired area. Peel strength and radial tensile strength tests were conducted on the repaired seal ring, and the results were consistent with those of the original seal ring. After the flexible seal ring was fully assembled and powered on, the turbine was vacuumed to a pressure of -4 to -6 kPa for 48-72 hours, maintaining normal operation. This demonstrated that the multi-layer alternating structure can restore the load-bearing and sealing properties at the site of the through-break.

[0090] Furthermore, to ensure consistent vulcanization quality, an embedded thermocouple matrix can be added to the heated mold in step f). The heating circuit can be controlled via a PLC closed-loop control system to maintain the mold cavity temperature differential within ±1.5°C. For multi-layer alternating structures with Type II and Type III defects, a step-by-step pressure reduction and heat preservation strategy is employed: First, maintain the target pressure for 20 minutes to allow the rubber to fully penetrate the interstices of the fabric. The pressure is then reduced by 0.2 MPa and maintained until the end of vulcanization, thereby reducing uncured spots caused by localized air stagnation in the fabric layer. Comparative tests have shown that the step-by-step pressure reduction process can increase the interfacial peel strength of the multilayer by an average of approximately 18%.

[0091] In field applications, if space within the repair area is limited, the heating mold can be replaced with a flexible silicone heating tape covered with aluminum foil insulation, combined with a vacuum vulcanizing bag to achieve 360° wrapping and pressurization. This solution reduces the minimum installation space for traditional rigid molds from 250mm to 120mm, enabling rapid repairs within the turbine's thermal shield. After a one-hour curing period under 0.5MPa negative pressure, the repair area density is approximately 6% higher than with conventional molds, and the removal of adjacent flanges is eliminated, minimizing downtime.

[0092] The above examples are used to illustrate the present invention, which are only used to help understand the present invention and are not intended to limit the present invention. Those skilled in the art can make several simple deductions, modifications or substitutions based on the concept of the present invention.

Claims

1. A method for repairing crack defects in a large rubber-fabric composite flexible sealing ring, characterized in that: include: a) Use a Shore A hardness tester to test and record the hardness of the sealing ring in the plane area around the crack defect; b) Grind the cracked area to form a repair area with neat edges that is flush with the original sealing surface, and measure the length, width, and depth of the repair area; c) Select an unvulcanized rubber repair sheet that matches the hardness of the sealing ring; d) Pre-treating the repaired fabric by sandblasting, solvent cleaning and rubber mortar dipping; e) Cutting the rubber repair sheets and the repair fabric according to the type of crack defects and arranging them alternately to fill the repair area to form a repair layer; f) Place the sealing ring filled with the repair layer into a heated mold that matches the cross-section of the original sealing ring, and vulcanize it under pressure at a temperature of 120-150°C for 0.5-4 hours to vulcanize and form the repair layer and the original sealing ring as a whole.

2. The method for repairing crack defects of a large rubber-fabric composite flexible sealing ring according to claim 1 is characterized in that: In step e), when the crack defect is a surface rubber crack, the repair area is only filled with a rubber repair film with a single-layer structure.

3. The method for repairing crack defects in a large rubber-fabric composite flexible sealing ring according to claim 1, characterized in that: In step e), when the crack defect is a fabric break, the repair layer filled in the repair area includes at least one layer of repair fabric and rubber repair films sandwiched between the upper and lower layers of the repair fabric.

4. The method for repairing crack defects in a large rubber-fabric composite flexible sealing ring according to claim 1, characterized in that: In step e), when the crack defect is a through fracture, the repair layer filled in the repair area includes multiple layers of rubber repair films and repair fabrics, the repair films and repair fabrics are alternately stacked, and the outermost layer of the repair layer is the rubber repair film.

5. The method for repairing crack defects in a large rubber-fabric composite flexible sealing ring according to claim 3 or 4, characterized in that: In step e), the repairing fabric is fixed to the same fabric layer of the original sealing ring by sewing.

6. The method for repairing crack defects of a large rubber-fabric composite flexible sealing ring according to claim 1, characterized in that: The thickness of a single piece of the rubber repair film is 1mm-3mm.

7. The method for repairing crack defects of a large rubber-fabric composite flexible sealing ring according to claim 1 is characterized in that: The rubber repair patch is made of EPDM rubber or chloroprene rubber, and its Shore A hardness is 70-80.

8. The method for repairing crack defects of a large rubber-fabric composite flexible sealing ring according to claim 1 is characterized in that: The repair fabric is aramid cloth or glass fiber cloth.

9. The method for repairing crack defects of a large rubber-fabric composite flexible sealing ring according to claim 8, characterized in that: The sandblasting uses 20-40 mesh brown corundum, and the sandblasting pressure is 0.1-0.2 MPa; the solvent cleaning uses ethyl acetate or anhydrous ethanol.

10. The method for repairing crack defects of a large rubber-fabric composite flexible sealing ring according to claim 8, characterized in that: The thickness of the fabric impregnated layer impregnated with rubber mortar is 0.1mm-0.3mm.

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