An anti-static gasket for a civil aviation passenger plane fuel tank cap

Abstract

The utility model discloses a kind of anti-static gaskets for civil aviation passenger plane fuel tank mouth cover, it is applicable to B737NG series aircraft.Gasket is made of annular base material skeleton (1) woven by aluminum alloy wire plain weave and the conductive polyurethane layer (2) completely covering its outside;Polyurethane layer continuously extends on the skeleton upper and lower surfaces and inner and outer edges, forms closed sealing body with wedge-shaped sealing lip, and sets up exposed ground contact at edge.The utility model is formed by vacuum auxiliary pouring once, without lubricating grease, can realize high reliable sealing and static dissipation, with the advantages of high sealing performance, anti-peeling, light weight, low cost, long life, etc., can replace traditional aviation rubber gasket.

Description

Technical Field

[0001] This utility model relates to the technical field of antistatic gaskets for fuel tank caps of civil aircraft, and in particular to an antistatic gasket for fuel tank caps of civil aircraft. Background Technology

[0002] For a long time, fuel tank cap gaskets on civil aircraft have used a combination of aerospace rubber and grease for sealing. However, rubber is prone to aging and cracking under high and low temperatures, fuel immersion, and alternating loads, while grease is prone to drying and loss, leading to micro-gaps on the cap mating surfaces, increasing the risk of fuel leakage and shortening maintenance cycles. Furthermore, the high resistivity of rubber gaskets means that static electricity cannot be quickly released, posing a potential hazard of igniting fuel vapors. While existing technologies attempt to coat the rubber surface with conductive coatings, the coatings have poor adhesion and are easily peeled off after installation, failing to meet continuous anti-static requirements. Therefore, there is an urgent need for a new type of gasket that simultaneously addresses the dual problems of "sealing failure" and "static electricity accumulation," and is maintenance-free throughout its entire lifespan. Utility Model Content

[0003] The purpose of this invention is to provide an antistatic gasket for the fuel tank cap of a civil aircraft, thereby solving the aforementioned problems in the prior art.

[0004] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0005] An antistatic gasket for a fuel tank cap on a civil aircraft includes an annular substrate skeleton formed by plain weaving aluminum alloy wires, and a conductive polyurethane layer that is cast in a mold to completely cover the substrate skeleton. The conductive polyurethane layer extends continuously between the upper and lower surfaces of the skeleton and forms rounded corners at the inner and outer edges of the skeleton, forming a closed seal that fits tightly against the mating surface of the fuel tank cap.

[0006] In some specific embodiments, the annular substrate skeleton is a single-layer annular woven mesh with a mesh count between 80 and 120 and a wire diameter between 0.08 mm and 0.12 mm.

[0007] In some specific embodiments, the substrate skeleton consists of 2 to 4 layers of annular woven mesh stacked together, with the layers sewn together at intervals by aluminum alloy stitching, and the stitching interval being 5 mm to 8 mm.

[0008] In some specific embodiments, the thickness of the conductive polyurethane layer is 0.5 mm to 1.0 mm on both the upper and lower surfaces of the skeleton, and gradually increases to 1.2 mm at the inner and outer edges to form a sealing lip.

[0009] In some specific embodiments, the sealing lip has a wedge-shaped cross-section with a wedge angle of 30° to 45° and the wedge tip facing the mating surface of the fuel tank cap.

[0010] In some specific embodiments, the conductive polyurethane layer has a continuous three-dimensional conductive path formed by overlapping conductive fillers, and its surface resistance is ≤10. 6 Ω, which meets the requirements for electrostatic dissipation.

[0011] In some specific embodiments, at least three anti-static grounding contacts are evenly distributed on the outer periphery of the gasket. The contacts are hemispherical micro-convexities with exposed conductive polyurethane layer surfaces, with a height of 0.1mm to 0.2mm, which directly contact the metal surface of the fuel tank cap to form grounding.

[0012] In some specific embodiments, there is no gap between the inner and outer edges of the substrate skeleton and the conductive polyurethane layer, and the polyurethane penetrates into the braided nodes to a depth of ≥0.05mm.

[0013] In some specific embodiments, the gasket is annular in shape, with an inner diameter of Φ160mm~Φ180mm, an outer diameter of Φ200mm~Φ220mm, and a thickness of 1.5mm~2.5mm. It has arc-shaped notches at the inner and outer edges that correspond to the bolt holes of the fuel tank cap, and the width of the notches is 1mm~2mm larger than the diameter of the bolt holes.

[0014] In some specific embodiments, the conductive polyurethane layer is formed in one step with the substrate skeleton by vacuum-assisted casting, and the peel strength between the two after curing is ≥5kN / m.

[0015] The beneficial effects of this utility model are:

[0016] Improved sealing reliability: The conductive polyurethane layer fully encapsulates the skeleton and forms a double wedge-shaped sealing lip, increasing the contact area by more than 30% compared to traditional rubber gaskets. After 1000 thermal cycles at -55℃ to +85℃, the fuel leakage is <0.1mL / min, meeting the requirements of CAAC / FAA Clause 25.963.

[0017] Durable antistatic properties: Conductive fillers form a three-dimensional network within the polyurethane, resulting in a stable surface resistivity of 10. 5 ~10 6 Ω; the outer peripheral grounding contact and the metal of the cap always maintain metal-polymer contact, and the resistance change after 5000h salt spray test is <10%, the electrostatic dissipation time is <0.1s, eliminating the risk of spark ignition.

[0018] Peel and displacement resistant: Polyurethane is infiltrated into the aluminum alloy braided joints, with a peel strength ≥5kN / m. After installation, there is no loosening or slippage under vibration, impact, and thermal expansion and contraction conditions. When replacing parts, they can be removed as a whole without any residue.

[0019] Lubrication-free throughout its entire lifespan: The coefficient of friction between the gasket and the mating surface is 0.25 to 0.30, which is lower than that of rubber gaskets after grease aging (0.45 to 0.60), achieving a "dry" seal and eliminating the need for regular grease changes and application, reducing line maintenance time by more than 50%.

[0020] Lightweight and low cost: Polyurethane has a density of 1.15g / cm³, which is only 84% of that of aviation rubber; the weight of gaskets of the same specification is reduced by 20%, the material cost is reduced by about 30%, the weight of a single aircraft is reduced by 0.3kg, and the annual fuel cost savings for airlines are significant.

[0021] Flexible molding and highly adaptable: The mesh count, number of layers, and outline of the skeleton can be quickly adjusted through laser cutting. The same set of molds can produce a variety of cap specifications. The development cycle is shortened from 45 days for traditional rubber molds to 7 days, meeting the needs of small batch and multi-model modification. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the antistatic gasket structure for the fuel tank cap of a civil aircraft according to this utility model;

[0023] Figure 2 This is a schematic diagram of the plain weave structure of the antistatic gasket of this utility model.

[0024] In the attached diagram, 1 is the substrate skeleton; 2 is the conductive polyurethane layer. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the scope of the present utility model.

[0026] Reference Figure 1 and Figure 2 The antistatic gasket shown is for a fuel tank cap of a civil aircraft. It includes an annular substrate skeleton 1 formed by plain weaving of aluminum alloy wires, and a conductive polyurethane layer 2 that is cast in a mold to completely cover the substrate skeleton 1. The conductive polyurethane layer 2 extends continuously between the upper surface and the lower surface of the skeleton, and forms rounded corner transitions at the inner edge and the outer edge of the skeleton, forming a closed seal that fits tightly with the mating surface of the fuel tank cap.

[0027] like Figure 1 and Figure 2 As shown, the antistatic gasket of this utility model is a closed ring, and its static structure consists of two parts: an inner ring-shaped substrate skeleton 1 and a conductive polyurethane layer 2 completely covering the skeleton. The two parts are formed in one step by a vacuum-assisted casting process, with no interface gap between them, forming an inseparable sealed-conductive integrated component.

[0028] I. Circular Substrate Skeleton 1

[0029] Material and weaving method

[0030] The skeleton is made of aerospace-grade rust-proof aluminum alloy wire with a single wire diameter of 0.08mm to 0.12mm, and is formed into a mesh prefabricated body through plain weave. The plain weave structure ensures that each interlacing of two adjacent warp and weft wires forms a locking node, guaranteeing that the mesh has stable dimensional retention capabilities during shearing, stretching, and circumferential expansion.

[0031] Number of layers and thickness

[0032] Depending on the rigidity and sealing requirements of the cap, the skeleton can be a single layer or 2 to 4 layers of the same size mesh blanks can be stacked concentrically. In the case of multiple layers, the layers are stitched together circumferentially with aluminum alloy thread of the same material at a stitch spacing of 5 mm to 8 mm to prevent slippage between layers during subsequent pouring. The thickness of a single-layer skeleton is 0.15 mm to 0.20 mm, and the maximum thickness after four layers are stacked does not exceed 0.80 mm.

[0033] Outline dimensions

[0034] The inner ring diameter of the skeleton is Φ160mm~Φ180mm, and the outer ring diameter is Φ200mm~Φ220mm, which is consistent with the bottom contour of the sealing groove of the B737NG series fuel tank cap. At the bolt hole positions on the inner and outer ring edges, arc-shaped notches are formed by laser cutting. The width of the notches is 1mm~2mm larger than the bolt hole diameter to ensure that there is no interference between the bolt rod and the skeleton during assembly.

[0035] II. Conductive polyurethane layer 2

[0036] Material composition

[0037] A two-component fuel-resistant polyurethane elastomer was selected as the matrix. Conductive fillers were added to the A component prepolymer: 10wt%–15wt% carbon black with a particle size of 20 nm–50 nm, 1wt%–3wt% nickel-plated carbon nanotubes with a length of 10 μm–30 μm, and 0.5wt%–1wt% organosilicon coupling agent. The fillers were uniformly dispersed by high-speed shearing to form a three-dimensional conductive network.

[0038] Encapsulation structure

[0039] The mold cavity and skeleton are contoured, with a gap of 1.0mm to 1.2mm. After casting, polyurethane forms a continuous skin layer of 0.5mm to 1.0mm thickness on the upper and lower surfaces of the skeleton. At the inner and outer edges of the skeleton, the molten material flows along the annular end face and wraps around the aluminum alloy wire, forming a rounded transition with a radius of about 0.5mm. The thickness of the rounded corner area increases to 1.2mm, forming a wedge-shaped sealing lip. The wedge angle of the wedge-shaped lip is 30° to 45°, with the wedge tip pointing towards the mating surface of the cap. Under the action of bolt preload, it can generate a three-stage progressive compression of surface-line-surface, improving the filling ability of micro-irregularities.

[0040] grounding contact

[0041] At least three hemispherical micro-protrusions are evenly distributed around the outer ring of the gasket, with a height of 0.1mm to 0.2mm and a diameter of 1mm to 2mm. They are brought out in one go by the same polyurethane material during casting, and the surface exposes a conductive network for direct contact with the metal surface of the cap to form a static discharge path.

[0042] Interface penetration

[0043] Vacuum-assisted casting pressure is maintained at -0.08MPa to -0.09MPa for 10 minutes to allow the adhesive with a viscosity of 800mPa·s to 1200mPa·s to fully penetrate into the gaps between the braided nodes, with a penetration depth of ≥0.05mm. After curing, a mechanical interlock between the aluminum alloy wire and the polyurethane is formed, with a peel strength of ≥5kN / m, preventing the polyurethane skin from separating from the skeleton during service.

[0044] Dimensions and tolerances

[0045] The total thickness of the finished gasket is 1.5mm to 2.5mm, and the thickness difference within the same circumference is ≤0.05mm; the inner and outer diameter tolerances are ±0.2mm, and the wedge-shaped sealing lip height symmetry is ≤0.02mm, ensuring that the compression rate is controlled at 15% to 25% under a cap bolt torque of 8 N·m to 12 N·m, achieving the best sealing-rebound balance.

[0046] III. Connections between Parts

[0047] The annular substrate skeleton 1 is located on the geometric mid-surface of the gasket, providing rigidity and dimensional reference for the entire component; the conductive polyurethane layer 2 wraps the skeleton in a fully enclosed manner with 360° full circumference, double sides and inner and outer edges, and there are no bubbles or delamination at the interface between the two; the wedge-shaped sealing lip and the grounding contact are different local geometric features of polyurethane material, which are complementary in function but continuous in material, without secondary bonding or mechanical connection.

[0048] With the above static structure, this gasket can achieve both "conductive continuity" and "zero leakage seal" with just one bolt tightening when installed, without the need for additional grease or conductive adhesive, thus meeting the requirements of long service life, maintenance-free operation, and anti-static properties for fuel tank caps on civil aircraft.

[0049] In some specific embodiments, the annular substrate skeleton 1 is a single-layer annular woven mesh with a mesh count between 80 and 120 meshes and a wire diameter between 0.08 mm and 0.12 mm.

[0050] In some specific embodiments, the substrate skeleton 1 is composed of 2 to 4 layers of annular woven mesh stacked together, with the layers sewn together at intervals by aluminum alloy stitching, and the stitching interval being 5 mm to 8 mm.

[0051] In some specific embodiments, the thickness of the conductive polyurethane layer 2 is 0.5 mm to 1.0 mm on both the upper and lower surfaces of the skeleton, and gradually increases to 1.2 mm at the inner and outer edges to form a sealing lip.

[0052] In some specific embodiments, the sealing lip has a wedge-shaped cross-section with a wedge angle of 30° to 45° and the wedge tip facing the mating surface of the fuel tank cap.

[0053] In some specific embodiments, the conductive polyurethane layer 2 has a continuous three-dimensional conductive path formed by overlapping conductive fillers, and its surface resistance is ≤10. 6 Ω, which meets the requirements for electrostatic dissipation.

[0054] In some specific embodiments, at least three anti-static grounding contacts are evenly distributed on the outer periphery of the gasket. The contacts are hemispherical micro-convexities exposed on the surface of the conductive polyurethane layer 2, with a height of 0.1mm to 0.2mm, which directly contact the metal surface of the fuel tank cap to form grounding.

[0055] In some specific embodiments, there is no gap between the inner and outer edges of the substrate skeleton 1 and the conductive polyurethane layer 2, and the polyurethane penetrates into the braided nodes to a depth of ≥0.05mm.

[0056] In some specific embodiments, the gasket is annular in shape, with an inner diameter of Φ160mm~Φ180mm, an outer diameter of Φ200mm~Φ220mm, and a thickness of 1.5mm~2.5mm. It has arc-shaped notches at the inner and outer edges that correspond to the bolt holes of the fuel tank cap, and the width of the notches is 1mm~2mm larger than the diameter of the bolt holes.

[0057] In some specific embodiments, the conductive polyurethane layer 2 is formed in one step with the substrate skeleton 1 by vacuum-assisted casting, and the peel strength between the two after curing is ≥5kN / m.

[0058] The working principle of this utility model can be summarized as a three-in-one system of "elastic compression sealing + three-dimensional conductive continuity + interface anchor bolt locking", and the specific process is as follows:

[0059] Elastic compression seal

[0060] When the fuel tank cap bolts are tightened, the axial load is uniformly transferred to the conductive polyurethane layer through the metal surface of the cap. The polyurethane layer generates 15%–25% compressive strain on the upper and lower surfaces of the skeleton.

[0061] The main body undergoes elastic deformation in the thickness direction to store rebound energy, forming the first-stage surface seal;

[0062] The inner and outer wedge-shaped sealing lips are thicker and have a wedge angle of 30° to 45°, which generate higher surface pressure under the same displacement. After the lip tip is squeezed, it fits against the micro-dents on the inlet cover mating surface, forming a second-stage line seal.

[0063] Due to the excess material volume in the rounded transition zone, it flows laterally to fill the gaps at the edges of the bolt holes and the bottom of the sealing groove, achieving a third-level point-to-surface seal.

[0064] The three-stage sealing works synergistically to create an "S"-shaped maze effect in the fuel molecule penetration path, increasing the penetration length by more than three times compared to traditional rubber gaskets. This ensures that the leakage rate remains <0.1 mL / min under fuel pulse cycles of -55℃ to +85℃ and 0.3MPa.

[0065] Three-dimensional conductive continuity

[0066] When the gasket is compressed, the density of the carbon black-carbon nanotube network within the conductive polyurethane layer increases, and the node contact resistance decreases. Simultaneously, the outer hemispherical grounding contact is flattened, forming a parallel conductive path of metal-conductive polymer-metal with the aluminum alloy of the tank cap and the fuel tank frame. Electrostatic charge travels from the inner surface of the fuel tank → tank cap → grounding contact → conductive polyurethane three-dimensional network → fuel tank frame → fuselage grounding stake, with the resistance remaining stable at 10 ohms throughout the entire process. 5 ~10 6 Ω, electrostatic dissipation time constant τ < 0.1s, to avoid charge accumulation to the point where the 0.2 mJ ignition energy is sufficient to break down fuel vapor.

[0067] Interface anchor bolt locking

[0068] During the vacuum casting stage, the polyurethane melt penetrates the aluminum alloy braided joints by ≥0.05mm under a negative pressure of -0.08MPa to -0.09MPa, forming "anchor" micropillars after curing. When the gasket is subjected to airborne vibration, thermal cycling, or pressure pulsation, these micropillars transfer the shear load from the polyurethane skin to the metal skeleton, preventing relative slippage between the skin and the skeleton. Peel tests show that the failure occurs in the polyurethane bulk rather than at the interface. Even after 30,000 cycles of 15g vibration after actual installation, the permanent compression deformation is <5%, and there is no decrease in sealing height or grounding resistance.

[0069] In summary, this utility model can simultaneously complete three functions—"high elastic rebound sealing," "low resistance electrostatic discharge," and "high peel strength interface retention"—with just one bolt tightening, achieving maintenance-free, lubrication-free, loosening-free, leakage-free, and electrostatic accumulation-free operation throughout its entire life cycle.

[0070] By adopting the above-disclosed technical solution of this utility model, the following beneficial effects are obtained:

[0071] Excellent sealing performance: By fully encapsulating the substrate skeleton with polyurethane casting, the contact area of ​​the mating surfaces is increased, further improving the sealing performance;

[0072] Excellent anti-peel properties: The polyurethane material in this invention has excellent adhesion, making it less likely to fall off when replacing gaskets and less likely to shift during aircraft airworthiness testing.

[0073] Good economic performance: Compared with the existing aviation rubber materials for gaskets, polyurethane materials have a price advantage;

[0074] Highly adaptable: The diameter, aperture, mesh count, and number of layers of aluminum alloy wire can be adjusted according to actual application needs. It can be made into various shapes through cutting and other processing methods to meet the needs of different scenarios.

[0075] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. An antistatic gasket for a fuel tank cap on a civil aircraft, characterized in that, It includes an annular substrate skeleton (1) formed by plain weaving of aluminum alloy wires, and a conductive polyurethane layer (2) that completely covers the substrate skeleton (1) by casting through a mold; the conductive polyurethane layer (2) extends continuously between the upper surface and the lower surface of the skeleton, and forms a rounded transition at the inner edge and the outer edge of the skeleton, forming a closed seal that fits tightly with the mating surface of the fuel tank cap.

2. The antistatic pad according to claim 1, characterized in that: The annular substrate skeleton (1) is a single-layer annular woven mesh with a mesh count between 80 and 120 and a wire diameter between 0.08 mm and 0.12 mm.

3. The antistatic pad according to claim 1, characterized in that: The substrate skeleton (1) consists of 2 to 4 layers of annular woven mesh stacked together, with the layers sewn together at intervals by aluminum alloy stitching, and the stitching interval is 5 mm to 8 mm.

4. The antistatic pad according to claim 3, characterized in that: The thickness of the conductive polyurethane layer (2) is 0.5 mm to 1.0 mm on both the upper and lower surfaces of the skeleton, and gradually increases to 1.2 mm at the inner and outer edges to form a sealing lip.

5. The antistatic pad according to claim 4, characterized in that: The sealing lip has a wedge-shaped cross-section with a wedge angle of 30° to 45°, and the wedge tip faces the mating surface of the fuel tank cap.

6. The antistatic pad according to claim 5, characterized in that: The conductive polyurethane layer (2) has a continuous three-dimensional conductive path formed by overlapping conductive fillers, and its surface resistance is ≤10. 6 Ω, which meets the requirements for electrostatic dissipation.

7. The antistatic pad according to claim 6, characterized in that: At least three anti-static grounding contacts are evenly distributed around the outer periphery of the gasket. The contacts are hemispherical micro-convexities exposed on the surface of the conductive polyurethane layer (2), with a height of 0.1mm to 0.2mm, which directly contact the metal surface of the fuel tank cap to form grounding.

8. The antistatic pad according to claim 1, characterized in that: There is no gap between the inner and outer edges of the substrate skeleton (1) and the conductive polyurethane layer (2), and the polyurethane penetrates into the braided node to a depth of ≥0.05mm.

9. The antistatic pad according to claim 1, characterized in that: The gasket is annular in shape, with an inner diameter of Φ160mm~Φ180mm, an outer diameter of Φ200mm~Φ220mm, and a thickness of 1.5mm~2.5mm. It has arc-shaped notches at the inner and outer edges that correspond to the bolt holes of the fuel tank cap, and the width of the notches is 1mm~2mm larger than the diameter of the bolt holes.

10. The antistatic pad according to any one of claims 1-9, characterized in that: The conductive polyurethane layer (2) is formed in one step with the substrate skeleton (1) by vacuum-assisted casting, and the peel strength between the two after curing is ≥5kN / m.

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