Rapid repairing method for composite lightning stroke protection layer based on conductive coating

Abstract

The invention discloses a rapid repairing method for a composite lightning stroke protection layer based on a conductive coating, and belongs to the technical field of aircraft outer surface repairing. The method comprises the following steps: evaluating and calibrating a lightning stroke damage area, and determining a damage range; the lightning stroke damage area is cleaned, a repair area is defined, and a non-repair area is accurately covered with an isolation material; according to the repair area, determining the required conductive coating dosage, and preparing a conductive coating; and uniformly spraying a layer of the conductive coating on the repair area, measuring the surface resistance after normal-temperature curing, determining the number of layers needing to be sprayed according to a measurement result and a maintenance standard, and repeating the steps of spraying, curing and measuring until the surface resistance meets the maintenance standard, thereby finishing the repair. By removing residues in the damaged area and uniformly spraying the self-made conductive coating on the damaged area, the lightning stroke protection performance of the surface of the composite material structure is quickly recovered, the defects of a traditional repair method are overcome, and the method is particularly suitable for quick repair in the outfield station crossing period of a transport aircraft; and flight delay or parking maintenance risks caused by lightning stroke damage are obviously reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of aircraft outer surface repair, and in particular relates to a rapid repair method for a composite material lightning protection layer based on a conductive coating. Background Art

[0002] Composite materials have been widely used in the aerospace field due to their excellent specific strength, specific stiffness, chemical stability, corrosion resistance, fatigue resistance and design flexibility. Especially in the new generation of large civil airliners (such as B787 and A350), the proportion of composite materials used even exceeds 50%, of which carbon fiber composite materials are the main ones. The electrical conductivity of carbon fiber composite materials is poorer than that of metals, and it is difficult for the current to be quickly conducted away on the surface of the composite materials, thereby generating a large amount of resistive heat, so it is more susceptible to lightning damage. The strong current and high voltage carried by lightning will impact the composite materials, resulting in extremely high temperatures and huge shock waves, which will cause ablation, cracking or perforation, seriously endangering the flight safety of the aircraft.

[0003] According to statistics, civil aircraft are struck by lightning approximately once every 3,000 hours of flight or once a year. In thunderstorms, the probability of an aircraft being struck by lightning is high, and forced landings or crashes caused by lightning strikes also occur from time to time. Since an aircraft cannot be grounded when flying in the air, it is impossible to directly avoid lightning, so it can only be dealt with through lightning protection measures. The core of lightning protection is to enhance the conductivity of the aircraft surface so that lightning can be quickly diverted to the surrounding atmosphere, thereby reducing the electrothermal and mechanical effects caused by lightning strikes.

[0004] The current mainstream method of lightning protection for composite materials is to metalize the composite materials, such as laying metal guide strips on the surface, spraying a metal layer, or using a protective layer such as a lightning protection metal mesh, so that the lightning current can quickly pass through the protective layer into the atmosphere, thereby protecting the underlying composite materials from the impact of the lightning current.

[0005] The protective layer can effectively protect the aircraft from lightning strikes, but the repair process after a lightning strike is more complicated. According to the allowable damage limits specified in the Aircraft Structural Maintenance Manual, the damage needs to be evaluated and a repair method needs to be selected. For situations that do not exceed the damage limit, sealing can be used, and regular inspections can be carried out after recording, and the repair can be completed within the specified time. If the damage exceeds the allowable damage limit, it must be repaired in accordance with the manual requirements. Temporary repairs are usually performed during transit using conductive tape and patches for quick bonding, but the tape is easy to fall off and the covering effect is limited, and it is difficult to achieve perfect conductive overlap at the damaged edge. Permanent repairs require vacuum high-temperature curing of the resin. Although no subsequent inspection is required, the curing process involves vacuum bags and heating equipment, and it takes a long time.

[0006] Conductive coating is an adhesive with good electrical conductivity, usually made of a mixture of highly conductive fillers (such as silver powder, carbon nanotubes, graphene, etc.) and a resin matrix (such as epoxy resin, silicone resin, etc.). Its main feature is that it can achieve current conduction while maintaining good bonding properties. It is widely used in electronics, aerospace, automobile, communications and other industries. Conductive coating has the following characteristics: 1) The use of conductive coating is very simple. It can be applied by spraying, scraping, injection or coating, which is suitable for complex shapes and large-area repairs; 2) Many conductive coatings can be quickly cured at room temperature or low temperature, avoiding damage to the substrate by high-temperature treatment, and become an ideal material for rapid repairs; 3) The performance of conductive coatings can be optimized by adjusting the type, proportion and dispersibility of fillers to meet the needs of different usage scenarios; 4) Modern conductive coatings are increasingly tending to be environmentally friendly and harmless, and most of them use environmentally friendly solvents and resins to exert excellent performance while reducing the impact on the environment and human body.

[0007] In view of the shortcomings of existing aircraft lightning damage repair technology and the advantages of conductive coatings such as rapid curing and excellent conductivity, it is imperative to provide a rapid repair method for composite lightning protection layers based on conductive coatings. Summary of the invention

[0008] In view of the above technical problems, the present invention proposes a rapid repair method for composite lightning protection layer based on conductive coating, aiming to solve the problems of complex operation, high requirements for curing equipment, long curing time, etc. in the traditional repair process, so as to achieve the rapid repair effect of lightning damage, thereby significantly reducing the risk of flight delays or ground maintenance caused by lightning damage.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A method for quickly repairing a composite lightning protection layer based on a conductive coating comprises the following steps:

[0011] Evaluate and demarcate the lightning damage area and clarify the damage scope;

[0012] Clean the lightning damaged area, identify the repair area, and use isolation materials to accurately cover the non-repair area;

[0013] Determine the required amount of conductive coating according to the repair area and prepare the conductive coating;

[0014] A layer of the conductive coating is sprayed evenly on the repair area, and the surface resistance is measured after curing at room temperature. The number of layers required to be sprayed is determined based on the measurement results and the repair standard, and the "spraying-curing-measurement" steps are repeated until the surface resistance meets the repair standard and the repair is completed.

[0015] Furthermore, the lightning damage area that is evaluated and calibrated is a damage area that does not involve internal damage to the composite material structure.

[0016] Furthermore, the specific steps of the cleaning include: using sandpaper to grind the lightning damaged area and the surrounding area extending 5-10 mm outward along the damage contour; the lightning damaged area needs to be grinded to remove the residual metal protective layer on the surface of the composite material until the composite material matrix is ​​exposed; the surrounding area is grinded until the metal protective layer on the surface of the composite material is exposed, and the grinding process must not damage the composite material matrix and the surface metal protective layer; all grinded areas are cleaned with anhydrous ethanol to remove surface stains to form an area to be repaired.

[0017] Furthermore, the specific operating steps of using the isolation material to accurately cover the non-repair area include: using an easily removable material such as a film or protective paper as the isolation material, cutting out a contour and area corresponding to the repair area in the middle of the isolation material, and then fixing the cut isolation material to the surface of the composite material structure, leaving only the repair area exposed.

[0018] Furthermore, the standard for determining the amount of conductive coating is: determined according to the area of ​​the repair region and the mass of conductive coating required per unit area of ​​repair.

[0019] Furthermore, the specific preparation steps of the conductive coating include: weighing the selected conductive particles, polymers and solvents respectively, and then using ultrasonic dispersion method to fully mix the components, with the dispersion time being not less than 5 minutes, to obtain a uniformly dispersed conductive coating mixture; filling the conductive coating mixture into an air tank, spray gun or other easy-to-use spraying equipment to facilitate subsequent rapid repairs by spraying.

[0020] Furthermore, the conductive particles include metal conductive particles such as silver (Ag) and copper (Cu) and non-metal conductive particles such as carbon nanotubes and graphene;

[0021] The morphology of the conductive particles includes flake, spherical, dendritic or linear;

[0022] The size of the conductive particles may range from millimeter to micrometer and nanometer to nanometer.

[0023] Furthermore, the polymer should be a polymer having good adhesion to the conductive particles, such as one or more of polymethyl methacrylate, polyurethane, epoxy resin, polyamide, polystyrene, polyetheretherketone, polytetrafluoroethylene, polyethylene, acrylic acid, polyether, polyvinylpyrrolidone, polycarbonate, polylactic acid and polycaprolactone.

[0024] Furthermore, the solvent should be a solvent that has a good synergistic effect with the polymer and is easily volatile and solidified, such as one or more of anhydrous ethanol, toluene, dichloromethane, methyl ethyl ketone, cyclohexane, xylene, ethanol, N,N-dimethylacetamide, N-methylpyrrolidone, ethyl acetate and chloroform.

[0025] Furthermore, in the "spraying-curing-measurement" process, the curing time is 5-10 minutes.

[0026] Furthermore, in the "spraying-curing-measurement" process, the specific operation steps of the measurement are: taking any point on the conductive coating in the repair area and the metal protective layer in the non-repair area, and measuring the surface resistance between the two points.

[0027] Compared with the prior art, the present invention has the following advantages and technical effects:

[0028] The repair method of the present invention first evaluates and calibrates the lightning damage area of ​​the composite material, which is a damage area that does not involve internal damage to the composite material structure, and then removes the residual metal material in the damage area through surface treatment, clarifies the damage area, and uses isolation materials to accurately cover the non-repair area, and then determines the required amount of conductive coating, prepares the conductive coating, and finally evenly sprays a layer of conductive coating on the repair area, and measures the surface resistance after curing at room temperature. The number of layers required to be sprayed is determined according to the measurement results and the maintenance standard, and the "spraying-curing-measurement" steps are repeated until the surface resistance meets the maintenance standard, and the repair is completed. The present invention quickly restores the lightning protection performance of the surface of the composite structure by removing the residue in the damaged area and evenly spraying the homemade conductive coating on the damaged area, thereby solving the shortcomings of traditional repair methods. It is particularly suitable for rapid repairs during the field transit of transport aircraft, and significantly reduces the risk of flight delays or ground maintenance caused by lightning damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0030] Figure 1 The polishing method and cleaning effect diagram of the damaged area in Example 1;

[0031] Figure 2 The preparation and spraying method of the conductive coating in Example 1;

[0032] Figure 3 This is the repaired sample of the repaired area in Example 1;

[0033] Figure 4 This is a schematic diagram of the resistance measurement method in Example 1;

[0034] Figure 5 This is a comparison of the appearance of the damaged sample before and after repair in Example 2;

[0035] Figure 6 This is a schematic diagram of the resistance measurement of a 10cm×10cm rectangular repair area in Example 3;

[0036] Figure 7 is a graph showing the relationship between resistance and standing time in Example 4;

[0037] Figure 8 This is a graph showing the relationship between the resistance of the sample and the immersion time in Example 1;

[0038] Fig. 9 This is a graph showing the relationship between sample mass and immersion time in Example 1. DETAILED DESCRIPTION

[0039] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0040] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0041] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0042] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0043] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0044] The present invention provides a rapid repair method for a composite lightning protection layer based on a conductive coating. The method fully combines the advantages of the conductive coating in terms of conductivity and rapid curing, and innovatively proposes a room temperature rapid repair technology that does not rely on a vacuum high temperature curing process. It is particularly suitable for the rapid repair of flame sprayed metal layers on the surface of composite structures and lightning protection metal mesh lightning damage. The specific repair steps include: evaluating and calibrating the lightning damage area of ​​the composite material to clarify the damage range; removing the residual metal material in the damaged area by surface treatment, clarifying the repair area, and using isolation materials to accurately cover the non-repair area; determining the required amount of conductive coating and preparing the conductive coating; uniformly spraying a layer of conductive coating on the repair area, measuring the surface resistance after curing at room temperature, determining the number of layers to be sprayed according to the measurement results and maintenance standards, repeating the "spraying-curing-measurement" steps until the surface resistance meets the maintenance standards, and completing the repair. The method can quickly restore the lightning protection performance of the surface of the composite structure during the field transit of transport aviation aircraft, and significantly reduce the risk of flight delays or ground maintenance caused by lightning damage.

[0045] The embodiment of the present invention provides a method for quickly repairing a composite material lightning protection layer based on a conductive coating, comprising the following steps:

[0046] (1) Evaluate and demarcate the lightning damage area of ​​composite materials and clarify the damage scope;

[0047] (2) Clean the lightning damaged area, identify the repair area, and use isolation materials to accurately cover the non-repair area;

[0048] (3) determining the required amount of conductive coating according to the repair area and preparing the conductive coating;

[0049] (4) Spray a layer of the conductive coating evenly on the repair area, measure the surface resistance after curing at room temperature, determine the number of layers to be sprayed based on the measurement results and the repair standard, repeat the "spraying-curing-measurement" steps until the surface resistance meets the repair standard and the repair is completed.

[0050] As an implementation method of the present invention, the lightning damage area evaluated and marked in step (1) is a damage area that does not involve internal damage to the composite material structure, which complies with the maintenance requirements of the Aircraft Structural Maintenance Manual.

[0051] As an implementation method of the present invention, in order to better restore the conductive properties of the composite material surface and avoid the influence of residues on the conductive repair process, the present invention first uses sandpaper to polish the damaged area and its surrounding areas, then uses anhydrous ethanol to clean it to ensure that the area to be repaired is clean, and finally uses isolation materials to isolate the non-repaired area. The specific cleaning steps in step (2) include: S1, removing residual metal materials in the damaged area by surface treatment; S2, using sandpaper to polish the lightning damaged area and the surrounding area extending 5-10mm outward along the damaged contour; the lightning damaged area needs to be polished to remove the residual metal protective layer on the surface of the composite material until the composite material matrix is ​​exposed; the surrounding area is polished until the metal protective layer on the surface of the composite material is exposed, and the composite material matrix and the surface metal protective layer must not be damaged during the polishing process; S3, using anhydrous ethanol to clean all polished areas to remove surface stains to form an area to be repaired. The specific operation steps of using the isolation material to accurately cover the non-repair area include: using a film or protective paper or other easily removable material as the isolation material, cutting out the contour and area corresponding to the repair area in the middle of the isolation material, and then fixing the cut isolation material to the surface of the composite material structure, exposing only the repair area. In the following embodiments of the present invention, grinding the peripheral area extending 5 mm outward along the damaged contour is used as an example to verify the effect.

[0052] As an implementation method of the present invention, the amount of conductive coating used in step (3) is determined based on the area of ​​the repair region and the mass of conductive coating required per unit area of ​​the repair region.

[0053] As an embodiment of the present invention, the specific preparation steps of the conductive coating in step (3) include: weighing the selected conductive particles, polymer and solvent respectively, and then using ultrasonic dispersion method to fully mix the components for a dispersion time of not less than 5 minutes to obtain a uniformly dispersed conductive coating mixture; filling the conductive coating mixture into an air tank, spray gun and other easy-to-use spraying equipment to facilitate subsequent rapid repairs by spraying.

[0054] The conductive particles include metal conductive particles such as silver (Ag) and copper (Cu) and non-metal conductive particles such as carbon nanotubes and graphene; the morphology of the conductive particles includes flake, spherical, dendritic or linear; the size range of the conductive particles can cover millimeter, micron and nanometer levels. For example, in the following embodiments of the present invention, the conductive particles can be selected as flake silver particles with a size of 20 μm.

[0055] The polymer should be a polymer having good adhesion to the conductive particles, such as one or more of polymethyl methacrylate, polyurethane, epoxy resin, polyamide, polystyrene, polyetheretherketone, polytetrafluoroethylene, polyethylene, acrylic acid, polyether, polyvinyl pyrrolidone, polycarbonate, polylactic acid and polycaprolactone. Exemplarily, in the following embodiments of the present invention, the polymer can be selected from polymethyl methacrylate (PMMA).

[0056] The solvent should be a solvent that has good synergy with the polymer and is easy to volatilize and solidify, such as one or more of anhydrous ethanol, toluene, dichloromethane, methyl ethyl ketone, cyclohexane, xylene, ethanol, N,N-dimethylacetamide, N-methylpyrrolidone, ethyl acetate and chloroform. Exemplarily, in the following embodiments of the present invention, the solvent can be selected from ethyl acetate.

[0057] For example, if the conductive particles are 20 μm flaky silver particles, the polymer is polymethyl methacrylate, and the solvent is ethyl acetate, the required amount of conductive coating is 0.054 g / cm based on the amount of metal silver (Ag) particles required per unit area of ​​repair. 2 、Polymethyl methacrylate is 0.0105g / cm 2 , ethyl acetate: 0.18mL / cm 2 The spraying amount is the total amount and has nothing to do with the number of layers. For example, spraying one layer can be determined according to 0.054g / cm 2 Metallic silver (Ag) particles are sprayed, and three layers can also be sprayed at 0.054g / cm 2 Metallic silver (Ag) particles are sprayed.

[0058] As an embodiment of the present invention, in the process of "spraying-curing-measuring" described in step (4), the lightning protection layer on the surface of the composite material is repaired by spraying. The curing time is 5-10 minutes. After curing, it has better electrical conductivity. According to the repair standards in the "Aircraft Structure Maintenance Manual", the corresponding surface resistance is measured for evaluation. In the following embodiments of the present invention, the curing time can be selected as 5 minutes and 10 minutes as examples for effect verification.

[0059] As an embodiment of the present invention, in the "spraying-curing-measurement" process in step (4), the specific operation steps of the measurement are: take an arbitrary point on the conductive coating in the repair area and the metal protective layer in the non-repair area, and measure the surface resistance between the two points.

[0060] As an implementation method of the present invention, the maintenance standard in step (4) is that the surface resistance measurement result between any two points of the conductive coating in the repair area and the metal protective layer in the non-repair area is less than 0.1Ω. The present invention determines the number of spray layers of the conductive coating by the surface conductivity. According to the requirements of the Aircraft Structural Maintenance Manual, the surface resistance measurement result between any two points of the conductive coating in the repair area and the metal protective layer in the non-repair area should be less than 0.1Ω. If the resistance is higher than 0.1Ω, it is necessary to continue spraying the conductive coating and measuring the resistance until the resistance meets the maintenance standard, and then the repair can be ended.

[0061] The standard in the Aircraft Structure Maintenance Manual is: resistance ≤ 0.1Ω.

[0062] The "room temperature" in the present invention refers to 20-30°C unless otherwise specified.

[0063] The raw materials used in the present invention are all purchased from the market.

[0064] The technical solution of the present invention is further illustrated by the following embodiments.

[0065] Example 1

[0066] A method for quickly repairing a composite lightning protection layer based on a conductive coating comprises the following steps:

[0067] (1) Evaluate and calibrate the lightning damage area of ​​the composite material. The damage area refers to the lightning damage area that only involves the flame-sprayed metal layer or lightning protection metal mesh on the surface of the composite structure, and does not involve the internal damage area of ​​the composite structure;

[0068] (2) Remove the residual metal material in the damaged area through surface treatment, then use sandpaper to polish the lightning damaged area and the surrounding area extending 5 mm outward along the damaged contour, and then use anhydrous ethanol to clean all the polished areas to remove surface stains to form the area to be repaired; use isolation materials to accurately cover the non-repair area;

[0069] (3) selecting flaky silver particles with a size of 20 μm as conductive particles, polymethyl methacrylate as a polymer, and ethyl acetate as an organic solvent, and fully mixing them according to a ratio of 1.8 g of conductive particles, 0.35 g of polymethyl methacrylate, and 6 mL of ethyl acetate, and performing ultrasonic dispersion treatment for 5 min to form a uniformly dispersed conductive coating mixture; and filling the conductive coating mixture into an air tank to obtain a conductive coating;

[0070] (4) A composite material specimen containing a damaged metal mesh was prepared with a 5 cm × 5 cm damaged specimen as the reference and a circular area with a diameter of D = 1.67 cm as the damaged area. An air tank filled with conductive coating was used to evenly spray a layer of conductive coating on the repair area (the prepared conductive coating was deemed to be completely sprayed, the same below). After curing at room temperature for 10 minutes, the surface resistance between the conductive coating in the repair area and the metal protective layer in the non-repair area was measured using the needle probe of a DC low resistance meter in accordance with the requirements of the Aircraft Structural Maintenance Manual.

[0071] Figure 1 The polishing method and cleaning effect diagram of the damaged area in Example 1;

[0072] Figure 2 Preparation and spraying methods for conductive coatings;

[0073] Figure 3 This is the repaired sample of the repaired area in Example 1;

[0074] Figure 4 This is a schematic diagram of the resistance measurement method in Example 1;

[0075] Table 1 shows the resistance test results of the repaired samples in Example 1.

[0076] Table 1 Surface resistance measurement value of the repaired sample / Ω

[0077]

[0078] It can be seen from Table 1 that for the damaged specimens repaired with conductive coating, the resistance between the conductive coating in the repaired area and the metal protective layer in the unrepaired area, the resistance inside the repaired area, and the resistance between the unrepaired areas are all much smaller than the 0.1Ω required by the Aircraft Structural Maintenance Manual, which meets the standard requirements of the Aircraft Structural Maintenance Manual for lightning damage repair.

[0079] The surface resistance of the composite material sample containing the complete metal mesh was measured and compared with the composite material sample repaired with the conductive coating in Example 1. Figure 4 The measurement results are shown in Table 2.

[0080] Table 2 Resistance measurement values ​​of undamaged samples and damaged samples after repair / Ω

[0081]

[0082]

[0083] As can be seen from Table 2, the surface resistance of the sample repaired with the conductive coating is close to that of the undamaged sample, both showing excellent conductivity, and the resistance value is much lower than the 0.1Ω required by the Aircraft Structural Maintenance Manual. It can be concluded that the self-made conductive coating can effectively restore the conductive properties of the material surface, proving its feasibility as a new solution for rapid repair of lightning damage to composite materials.

[0084] The surface resistance of the composite material sample containing the damaged metal mesh and not repaired and the composite material sample repaired with the conductive coating in Example 1 were measured using the following method: Figure 4 The results obtained are shown in Table 3.

[0085] Table 3 Resistance measurement values ​​of damaged samples before and after repair / Ω

[0086]

[0087] It can be seen from Table 3 that the sample before repair is in an insulated and non-conductive state near the damaged area, and the resistance measurement value is infinite. The repaired sample obtained according to the conductive coating repair steps completely restored the conductive properties near the damaged area, and at the same time, the resistance between points not involving the damaged area also showed a significant decrease, and was far lower than the 0.1Ω required in the Aircraft Structural Maintenance Manual. It can be seen that the self-made conductive coating can restore the conductive properties of the material surface, as a new solution for the rapid repair of lightning damage to composite materials.

[0088] Example 2

[0089] A method for quickly repairing a composite lightning protection layer based on a conductive coating comprises the following steps:

[0090] Steps (1) to (3) are the same as in Example 1;

[0091] (4) Taking a rectangular area of ​​8cm×8cm as the repair area benchmark, the sample is laid with a truncated metal copper mesh on the surface of the composite material, and the surface resistance of the left and right areas is close to infinity. Use an air tank filled with conductive paint to evenly spray a layer of conductive paint on the repair area. After curing at room temperature for 10 minutes, use the needle probe of a DC low resistance meter to measure the surface resistance between the conductive coating in the repair area and the metal protective layer in the non-repair area according to the requirements of the "Aircraft Structure Maintenance Manual". After measurement, it was found that the resistance after spraying a layer of conductive coating on the damaged area could not meet the 0.1Ω standard required by the "Aircraft Structure Maintenance Manual". Therefore, the "spray-curing-measurement" operation was repeated, that is, a new batch of conductive paint in step (3) was re-prepared for spraying and curing, and the resistance of the sample containing two layers of conductive coating was measured. It was found that it still did not meet the standard. The "spraying-curing-measurement" process was repeated for the third time, i.e., a new batch of conductive coating from step (3) was prepared again for spraying and curing. After spraying three layers of conductive coating, the surface resistance between the conductive coating in the repaired area and the metal protective layer in the unrepaired area dropped to below 0.1Ω, which meets the standard requirements for lightning damage repair in the Aircraft Structural Maintenance Manual.

[0092] Figure 5 This is a comparison of the appearance of the damaged sample in Example 2 before and after repair.

[0093] Example 3

[0094] A method for quickly repairing a composite lightning protection layer based on a conductive coating comprises the following steps:

[0095] Steps (1) to (3) are the same as in Example 1;

[0096] (4) Using a rectangular area of ​​10 cm × 10 cm as the repair area reference (the sample is an undamaged ordinary sample), use an air tank filled with conductive paint to evenly spray a layer of conductive paint on the repair area. After curing at room temperature for 10 minutes, use the needle probe of a DC low resistance meter to measure the surface resistance between the conductive coating in the repair area and the metal protective layer in the non-repair area according to the requirements of the Aircraft Structural Maintenance Manual. Based on the measurement results of Example 2, this experiment also repeated "spraying-curing-measurement" three times.

[0097] Figure 6 This is a schematic diagram of the resistance measurement of the 10 cm×10 cm rectangular repair area in Example 3. The surface resistance measurement results of the sample after three sprayings are shown in Table 4.

[0098] Table 4 10cm×10cm rectangular area conductive coating internal resistance measurement value

[0099]

[0100] As can be seen from Table 4, for the repair of large rectangular specimens, more conductive coatings need to be sprayed to achieve the required conductivity. For this rectangular repair area, after spraying three layers of conductive coating, the conductivity in all directions reached the 0.1Ω requirement specified in the Aircraft Structural Maintenance Manual. At this time, the amount of conductive coating required per unit area is: 0.054g / cm2 of metallic silver (Ag) particles 2 、Polymethyl methacrylate (PMMA) 0.021g / cm 2 , ethyl acetate 0.375mL / cm 2 The amount is the total coating amount, which has nothing to do with the number of layers, such as one layer or three layers. Repairing the area to be repaired according to the coating standard can restore excellent conductive properties.

[0101] Example 4

[0102] The same as Example 3, except that the room temperature curing time in step (4) is set to 5 minutes. That is, a rectangular area of ​​10 cm × 10 cm is used as the repair area reference (the sample is an undamaged ordinary sample), and an air tank filled with conductive coating is used to evenly spray a layer of conductive coating on the repair area. After curing at room temperature for 5 minutes, the needle probe of a DC low resistance meter is used to measure the surface resistance between the conductive coating in the repair area and the metal protective layer in the non-repair area according to the requirements of the Aircraft Structure Maintenance Manual. According to the measurement results of Example 2, this experiment also adopts the repeated "spraying-curing-measurement" three times.

[0103] The sprayed coating was left to stand for 0 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min and 35 min respectively.

[0104] Select as Figure 6 The resistance between the two points 0-1 shown in the figure is used as a reference, and the resistance of Example 4 is measured under different standing times. The results are as follows Figure 7 As shown. Figure 7 It can be seen that the conductive coating prepared by the present invention has a fast curing speed. After multi-layer spraying, the resistance is close to 0.1Ω at 5 minutes and has dropped to below 0.1Ω at 10 minutes, which meets the maintenance standard requirements. As the curing time increases, the conductive performance is further improved and tends to be stable after 30 minutes, and the resistance value can reach 0.01Ω or lower.

[0105] Effect example

[0106] The samples repaired with the conductive coating in Example 1 were soaked in water to test the water absorption performance of the repaired samples. The soaking time was 24h, 48h, 72h, 96h, 120h, 144h, and 168h. The resistance test method of the repaired samples in each direction is as follows: Figure 4 The relationship between resistance and immersion time is shown in Figure 8 The relationship between the weight change of the sample and the immersion time is shown in Fig. 9 The intact specimen without damage was used as blank control and was subjected to the same immersion treatment.

[0107] Depend on Figure 8 It can be seen that the conductivity of the repaired sample decreased slightly under the condition of long-term immersion in water, and the conductivity is still far below the 0.1Ω required in the Aircraft Structural Maintenance Manual. This shows that the conductivity of the self-made conductive coating is not significantly affected even in a humid environment.

[0108] Depend on Fig. 9 It can be seen that the quality of the repaired sample does not change significantly under long-term water immersion conditions, and maintains the same water absorption as the intact sample. This shows that the homemade conductive coating can still maintain good structural stability in a humid environment.

[0109] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for quickly repairing a composite lightning protection layer based on a conductive coating, characterized in that: The following steps are involved: Evaluate and demarcate the lightning damage area and clarify the damage scope; Clean the lightning damaged area, identify the repair area, and use isolation materials to accurately cover the non-repair area; Determine the required amount of conductive coating according to the repair area and prepare the conductive coating; A layer of the conductive coating is sprayed evenly on the repair area, and the surface resistance is measured after curing at room temperature. The number of layers to be sprayed is determined based on the measurement results and the repair standard, and the "spraying-curing-measurement" steps are repeated until the surface resistance meets the repair standard and the repair is completed.

2. The rapid repair method of composite lightning protection layer based on conductive coating according to claim 1 is characterized in that: The evaluated and demarcated lightning damage area refers to a damage area that does not involve internal damage to the composite material structure.

3. The rapid repair method of composite lightning protection layer based on conductive coating according to claim 1 is characterized in that: The specific steps of the cleaning include: using sandpaper to polish the lightning damaged area and the surrounding area extending 5-10 mm outward along the damage contour; the lightning damaged area needs to be polished to remove the residual metal protective layer on the surface of the composite material until the composite material matrix is ​​exposed; the surrounding area needs to be polished until the metal protective layer on the surface of the composite material is exposed, and the polishing process must not damage the composite material matrix and the surface metal protective layer; using anhydrous ethanol to clean all polished areas to remove surface stains to form an area to be repaired.

4. The rapid repair method of composite lightning protection layer based on conductive coating according to claim 1 is characterized in that: The specific preparation steps of the conductive coating include: selecting conductive particles, polymers and solvents, mixing and ultrasonically treating to obtain a conductive coating mixed liquid; and loading the conductive coating mixed liquid into a spraying device.

5. The rapid repair method of composite lightning protection layer based on conductive coating according to claim 4 is characterized in that: The conductive particles include silver, copper, carbon nanotubes or graphene; The conductive particles may have a flake shape, a spherical shape, a dendrite shape or a linear shape.

6. The rapid repair method of composite lightning protection layer based on conductive coating according to claim 4 is characterized in that: The polymer includes one or more of polymethyl methacrylate, polyurethane, epoxy resin, polyamide, polystyrene, polyetheretherketone, polytetrafluoroethylene, polyethylene, acrylic acid, polyether, polyvinyl pyrrolidone, polycarbonate, polylactic acid and polycaprolactone.

7. The rapid repair method of composite lightning protection layer based on conductive coating according to claim 4 is characterized in that: The solvent includes one or more of anhydrous ethanol, toluene, dichloromethane, methyl ethyl ketone, cyclohexane, xylene, ethanol, N,N-dimethylacetamide, N-methylpyrrolidone, ethyl acetate and chloroform.

8. The method for rapid repair of composite lightning protection layer based on conductive coating according to claim 1, characterized in that: During the "spraying-curing-measurement" process, the curing time is 5-10 minutes.

9. The method for rapid repair of composite lightning protection layer based on conductive coating according to claim 1, characterized in that: In the "spraying-curing-measurement" process, the specific operation steps of the measurement are: taking a point at random on the conductive coating in the repair area and the metal protective layer in the non-repair area, and measuring the surface resistance between the two points.

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