Recycling method of aircraft surface stealth coating and reutilization system of wave-absorbing agent filler

Abstract

The invention discloses a recycling method of an aircraft surface stealth coating and a reutilization system of a wave-absorbing agent filler, and belongs to the technical field of aviation material recycling. Shot blasting and directional stripping of the coating; burning to decompose the resin at 600-800 DEG C; purifying the wave-absorbing agent through airflow screening; citric acid is used for corrosion inhibition and rust removal; and mixing with new resin, and grinding until the particle size is 500nm. The system is composed of a pretreatment module, a shot peening stripping module, an incineration module, an airflow screening module, a rust removal module and a mixed grinding module. The invention solves the problems of difficult separation and purification and large performance loss in the wave-absorbing agent recovery, realizes the efficient recovery of ferrite and rare metal wave-absorbing agents, and has the purity of more than or equal to 85%. The recycled wave-absorbing agent can be reused for preparation of a stealth coating, the cost of raw materials is reduced by 40% or above, resource waste and environmental pollution are reduced, and the green manufacturing requirement is met.

Description

Technical Field

[0001] This invention belongs to the field of aviation material recycling technology, specifically relating to a method for recycling stealth coatings on aircraft surfaces and a system for reusing radar absorber fillers. Background Technology

[0002] In the aerospace field, stealth coatings are one of the key materials for achieving aircraft stealth performance. Aircraft stealth coatings typically consist of a resin matrix and various radar-absorbing fillers, such as ferrites and rare metals (e.g., neodymium, cobalt). These radar-absorbing fillers possess unique electromagnetic properties, effectively absorbing radar waves, thus enabling the aircraft to achieve stealth capabilities. However, current aircraft stealth coatings suffer from high costs. On one hand, the preparation and processing of the coating matrix resin are complex; on the other hand, the rare metals and other materials involved in the radar-absorbing fillers are themselves expensive and difficult to obtain. Furthermore, during aircraft maintenance or retirement, the old stealth coating is removed; direct disposal not only wastes significant resources but also creates environmental pressure.

[0003] Current technologies mainly involve coating removal, not material recycling. Furthermore, for materials like aircraft stealth coatings that contain multiple high-performance absorbers, there are problems such as high difficulty in separation and purification, high recycling costs, and significant performance loss of the absorbers during recycling, making it difficult to achieve efficient reuse of the absorbers. Summary of the Invention

[0004] The purpose of this invention is to design a method for recycling stealth coatings on aircraft surfaces and a system for reusing radar absorbers and fillers, so as to reduce the cost of using stealth coatings, achieve efficient recycling and reuse of radar absorbers such as ferrites and rare metals in the coating, improve resource recycling rate, and reduce environmental problems caused by coating waste.

[0005] The technical solution of the present invention is as follows:

[0006] A method for recycling stealth coatings on aircraft surfaces includes the following steps:

[0007] (1) Pretreatment: Remove impurities from the coating surface by purging with compressed air and using RJ-1 solvent-based cleaning agent;

[0008] (2) Coating directional peeling: Wet shot peening equipment is used, with ceramic shot peening as the medium, and the paint layer and coating are peeled off under the conditions of pressure 0.4-0.6MPa, shot peening angle 30-45° and shot peening distance 150-200mm.

[0009] (3) Incineration treatment: The coating mixture is incinerated in stages at 600-800℃ for 2-3 hours with an oxygen content of 8-12% to obtain crude microwave absorber;

[0010] (4) Airflow sieving: Sieving is performed by a vertical airflow sieve with an airflow velocity of 15-20 m / s and a sieve mesh size of 25-30 μm;

[0011] (5) Rust removal treatment: Immerse in a 5-10% citric acid solution with 0.1-0.2% LAN-826 corrosion inhibitor for 1-2 hours;

[0012] (6) Mixing and grinding: Mix the regenerated microwave absorber and the freshly made resin at a mass ratio of 65:35 and grind them in a sand mill until the particle size is ≤500nm.

[0013] In the above technical solution, the ceramic shot peening particle size in step (2) is 0.2-0.5mm, hardness HRC45-50, roundness ≥90%, and shot peening path overlap rate ≥30%.

[0014] In the above technical solution, the incineration temperature in step (3) is selected according to the type of microwave absorber: 600-700℃ for ferrite and 700-800℃ for rare metal.

[0015] In the above technical solution, the screening parameters in step (4) are: 500 mesh screen for ferrite microwave absorber and 600 mesh screen for rare metal microwave absorber.

[0016] In the above technical solution, the rust removal liquid to solid ratio in step (5) is 5:1 (L / kg), and then it is rinsed three times with deionized water until the pH is 6.5-7.5.

[0017] A microwave absorbing filler recycling system, comprising:

[0018] Pretreatment module: includes a compressed air system and an RJ-1 cleaning agent treatment unit;

[0019] Shot peening and stripping module: equipped with YT0-1308 liquid sandblasting machine, pulse bag dust collection system and collection bin;

[0020] Incineration module: WFS-50 incinerator with exhaust gas treatment system;

[0021] Airflow screening module: QS-1000 vertical airflow screen;

[0022] Rust removal module: PP material reactor;

[0023] Mixing and grinding modules: SXJ-500 double planetary disperser and PHE-500 horizontal sand mill.

[0024] In the above technical solution, the exhaust gas treatment system includes a cyclone dust collector, an activated carbon adsorption tower, and a Pt-Rh catalytic combustion device.

[0025] In the above technical solution, the shot peening stripping module is equipped with an industrial camera monitoring system with a resolution of 1920×1080 and a frame rate of 30fps.

[0026] In the above technical solution, the hybrid grinding module uses 0.1-0.3mm zirconia beads as grinding media with a filling rate of 70-75%.

[0027] A regenerated stealth coating is made from a microwave absorbing agent recovered by the above method and E-51 epoxy resin at a mass ratio of 65:35, wherein the microwave absorbing agent has a dispersed particle size of ≤500nm.

[0028] Beneficial effects:

[0029] By recycling and reusing the microwave absorbing agents in stealth coatings, the raw material costs of new stealth coatings have been significantly reduced. This enables the recycling of expensive microwave absorbing agents such as ferrites and rare metals, improving resource utilization and alleviating the pressure of rare metal resource shortages. It also avoids the direct disposal of stealth coatings, reducing resource waste and environmental pollution, and aligns with the development concepts of green manufacturing and a circular economy. Attached Figure Description

[0030] Figure 1 This is a flowchart of a method for recycling stealth coatings on aircraft surfaces and a system for reusing radar-absorbing fillers according to the present invention.

[0031] Figure 2 This is a structural diagram of an aircraft component containing a stealth coating. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0033] Example:

[0034] This embodiment discloses a method for recycling stealth coatings on aircraft surfaces and a system for reusing radar-absorbing fillers. The process is as follows: Figure 1 As shown.

[0035] 1. Preprocessing:

[0036] Loose impurities such as dust and oil stains on the surface of the coating to be treated are removed by air purging and cleaning agents.

[0037] The specific operation is as follows: Select retired or maintenance-needed aircraft stealth coating components (such as wing skin and fuselage side panels, made of aviation aluminum alloy 2A12) and fix them using customized chemical fixtures. The fixtures are made of high-strength alloy steel with a polyurethane buffer layer (5mm thick) to prevent direct contact between the fixtures and the aircraft component surface, which could cause scratches. During fixing, control the clamping force of the fixtures to 0.3-0.5MPa to ensure that the components do not shift during subsequent processing, while avoiding excessive pressure that could cause deformation. Use compressed air to blow away loose impurities such as dust and oil stains from the surface of the aircraft components (pressure 0.2-0.3MPa, airflow temperature 25±5℃). For stubborn oil stains, use RJ-1 solvent-based cleaner (phenol and chlorine-free, non-toxic, non-polluting, and environmentally friendly) to wipe them. After wiping, blow them clean again with compressed air to ensure that there is no oil residue on the coating surface.

[0038] 2. Directional peeling of coating:

[0039] The paint layer on the coating surface is first removed using shot peening equipment, and then the coating is further peeled off.

[0040] Aircraft components with stealth coatings generally consist of four parts: the substrate, the interface, the coating, and the paint layer. Figure 2 As shown, coatings and paint layers adhere to the substrate surface through intermolecular forces. In wet shot peening, the erosion effect of the shot is generally considered the primary form of material removal, while the water jet mainly accelerates the shot peening process. However, some studies have shown that when the jet pressure is relatively high and the processed material has low strength, the water jet can also remove the coating through a "water wedge" effect. Wet shot peening pressures are generally relatively low, at most a few megapascals; therefore, during wet shot peening, the erosion effect of the shot is the primary form of dirt removal, and the "water wedge" effect can be ignored. The removal of the coating from the substrate surface is achieved by the fracture of the coating after being impacted by the shot. When the coating is thick or the shot peening energy is low, fracture mainly occurs inside the coating. In this case, the coating removal process is similar to abrasive waterjet processing, and the substrate surface is exposed as the coating is continuously removed. When the coating thickness is small or the shot peening energy is high, fracture occurs inside the coating and at the interface between the coating and the substrate, directly achieving single-particle removal of the coating. When the coating thickness is small or the shot peening energy is too high, single-particle removal of the coating can be achieved directly, but it will damage the substrate.

[0041] Shot peening equipment commissioning: A liquid sandblasting machine (model YT0-1308) is selected, and ceramic shot peening medium (mainly composed of SiO2 and ZrO) is selected. Its particle size is controlled by sieving to 0.2-0.5mm (of which 0.3-0.4mm particle size accounts for ≥70%). The hardness of ceramic shot peening is HRC45-50, and the roundness is ≥90% to avoid sharp particles scratching the aircraft substrate. Adjust the shot peening system parameters: The shot peening pressure is precisely controlled to 0.4-0.6MPa via a pressure regulating valve (each 0.1MPa increment is an adjustment level), the shot peening angle is set to 30-45° via a robotic arm adjustment mechanism (can be finely adjusted in real time according to the surface curvature of the component; 30° is used when the radius of curvature is ≤500mm, and 45° is used when the radius of curvature is >500mm), the shot peening distance (distance between the nozzle and the coating surface) is 150-200mm, the nozzle diameter is 6mm, the nozzle length is 80mm, the nozzle moving speed is 50-80mm / s, a reciprocating shot peening path is adopted, and the overlap rate of adjacent shot peening trajectories is ≥30%.

[0042] Targeted peeling operation: The shot peening chamber is started, and the pulse bag dust collection system (dust collection efficiency ≥99.5%) is activated simultaneously. High-speed ceramic shot peening impacts the stealth coating, causing the paint layer and coating to peel off sequentially from the substrate surface. During the peeling process, the paint layer peeling is monitored in real time using a high-definition industrial camera (1920×1080 resolution, 30fps). Shot peening is paused when the paint color on the substrate surface disappears, revealing the gloss of the coating surface (no residual paint area ≥95%). High-pressure water jets are used to wash away the paint debris. The shot peening equipment is restarted, and the coating peeling is monitored again using the camera. Shot peening is paused when the coating on the substrate surface disappears, revealing the gloss of the metal substrate surface (no residual coating area ≥95%). The coating debris generated during peeling is collected by the dust collection system and falls into a closed collection silo, resulting in a coating mixture to be processed (moisture content ≤1%, particle size ≤10mm).

[0043] Substrate Surface Inspection: After the coating is peeled off, clean the substrate surface as soon as possible. Use a surface roughness tester (model TR200) ​​to check the surface roughness of the aircraft component substrate, requiring Ra≤1.6μm; at the same time, use penetrant testing (PT) to check for defects such as cracks on the substrate surface to ensure that the substrate is undamaged and can be used for subsequent recoating.

[0044] 3. Incineration treatment of coating mixture:

[0045] The coating material, which is a mixture of microwave absorber and resin, is decomposed at high temperature in an incinerator. The base resin is completely burned and decomposed. After incineration, the solid residue is collected, which is the crude microwave absorber.

[0046] Incineration equipment preparation: An intermittent industrial incinerator (model WFS-50) is selected, with the furnace chamber made of high-temperature resistant corundum bricks and lined with a ceramic fiber insulation layer (100mm thick) to ensure the furnace chamber's insulation performance. The incinerator is equipped with a preheating system, a temperature control system, and a tail gas treatment system. The preheating system preheats the furnace temperature to 300℃ to prevent incomplete combustion of the coating mixture due to direct combustion in a cold furnace.

[0047] Feeding and Incineration Parameter Control: The coating mixture in the collection bin is uniformly fed into the incinerator at a rate of 5-8 kg / h (based on a furnace volume of 50L). The coating mixture is spread evenly in the furnace to a thickness of 50-80 mm. The incineration program is started, and the furnace temperature is controlled in stages: In the first stage (0-30 minutes), the temperature is raised to 400℃ to volatilize low-boiling-point organic impurities in the coating; in the second stage (30-90 minutes), the temperature is raised to 600-800℃ (600-700℃ for ferrite microwave absorbers, and 700-800℃ for rare metal microwave absorbers), and held for 2-3 hours to ensure complete combustion and decomposition of the base resin (such as epoxy resin and polyurethane resin) (organic matter removal rate ≥99%). During incineration, the oxygen content in the furnace is controlled at 8-12% (monitored in real time by an oxygen analyzer, and the air intake is adjusted) to avoid incomplete combustion and the generation of harmful gases due to oxygen deficiency.

[0048] Exhaust Gas Treatment: The waste gas generated from incineration (mainly containing CO2, a small amount of CO, dust, and volatile organic compounds) enters the exhaust gas treatment system through the flue. First, large dust particles (particle size ≥ 10 μm) are removed by a cyclone dust collector, and then the gas enters an activated carbon adsorption tower (activated carbon filling amount 50 kg, specific surface area ≥ 1000 m²). 2 The system adsorbs volatile organic compounds (VOCs) and then oxidizes residual CO and other harmful gases into CO2 through a catalytic combustion device (the catalyst is a Pt-Rh honeycomb ceramic catalyst, and the reaction temperature is 300-350℃). The treated exhaust gas meets the requirements of the "Integrated Emission Standard of Air Pollutants" (GB 16297-1996) and is discharged through a 15m high exhaust stack.

[0049] Residue collection: After incineration, wait for the furnace to cool naturally to below 100℃, open the discharge port, and collect the solid residue (i.e., the crude product containing the microwave absorber) in the furnace. The moisture content of the residue is ≤0.5%, and the particle size is ≤5mm.

[0050] 4. Airflow sieving of crude microwave absorber:

[0051] Light impurities (mainly unburned organic debris and dust) in the residue are removed by air sieving, thus preserving and improving the purity of the microwave absorber.

[0052] Airflow screen commissioning: A vertical airflow screen (model QS-1000) is selected, with the screen material being 316L stainless steel. The screen mesh size is set according to the particle size of the microwave absorber: 500 mesh (approximately 30μm aperture) corresponds to ferrite microwave absorbers, and 600 mesh (approximately 25μm aperture) corresponds to rare metal microwave absorbers. Adjust the airflow screen parameters: the fan frequency is 45-55Hz, corresponding to an airflow velocity of 15-20m / s (monitored in real-time by an anemometer, with each 1m / s increment representing an adjustment level), the screening time is set to 10-15 minutes, and the feed rate is 2-3kg / min (controlled by a frequency converter).

[0053] Screening operation: The incinerated solid residue is fed into an air classifier through a closed feed pipe. Under the action of high-speed airflow, light impurities in the residue (such as incompletely burned organic debris and dust, with a density ≤1.5g / cm³) are screened. 3 The airflow passes through the screen and enters the dust collection bag; while the crude absorbent (ferrite density 4.8-5.2 g / cm³)... 3 Rare metal microwave absorbers have a density of 6.0-7.5 g / cm³. 3 Due to their high density, they cannot pass through the screen and accumulate on the screen surface, eventually falling into the finished product collection hopper.

[0054] Post-screening treatment: After screening, the collected crude microwave absorber is sampled and tested, requiring a purity ≥85% (by gravimetric analysis, the content of light impurities ≤15%). If the purity does not meet the standard, screening must be repeated (adjusting the airflow speed to increase by 0.5-1 m / s and extending the screening time by 3-5 minutes). The screened light impurities are collected and handed over to a professional hazardous waste treatment facility for disposal.

[0055] 5. Rust removal treatment with microwave absorber:

[0056] Soak the ferrite microwave absorber in a weak acid of appropriate concentration and add a corrosion inhibitor to remove the rust components on the surface, while ensuring that the absorber itself is not corroded as much as possible.

[0057] Rust remover preparation: Citric acid is selected as the main component of the rust remover. A 5-10% (w / w) citric acid aqueous solution is prepared (adjusted according to the degree of rust on the microwave absorber surface: 5% for light rust, 10% for heavy rust). During preparation, 0.1-0.2% (w / w) of corrosion inhibitor (LAN-826, mainly composed of organic nitrogen compounds and alcohol isomers) is added to prevent corrosion of the microwave absorber itself during rust removal. The prepared rust remover is poured into a corrosion-resistant reactor (PP material, 50L capacity) and stirred evenly (stirring speed 100 rpm, stirring time 5 minutes), controlling the temperature of the rust remover at 25±5℃.

[0058] Rust removal by weak acid immersion: Slowly add the crude microwave absorber (after air sieving) to the reaction vessel. The liquid-to-solid ratio of the microwave absorber to the rust remover is 5:1 (volume-to-mass ratio, unit: L / kg), ensuring the microwave absorber is completely submerged in the rust remover. Immerse at room temperature for 1-2 hours, stirring for 5 minutes every 15 minutes (stirring speed 150 rpm) to promote the complexation reaction between the rust on the surface of the microwave absorber and citric acid. The reaction that occurs is as follows:

[0059] ;

[0060] Washing and Drying: After soaking, open the valve at the bottom of the reactor to discharge the rust removal waste liquid (the waste liquid is discharged after neutralization treatment to meet standards). Then, rinse the microwave absorber with deionized water, using 3 times the mass of the microwave absorber for each rinse. Stir for 5 minutes during rinsing, and repeat rinsing 3-4 times until the pH value of the rinsing solution is 6.5-7.5 (detected in real time using a precision pH meter). Place the rinsed microwave absorber into a vacuum drying oven (model DZF-6050), set the drying temperature to 80-100℃, the vacuum degree to -0.08~-0.09MPa, and the drying time to 2-3 hours, until the moisture content of the microwave absorber is ≤0.3%. After drying, remove the microwave absorber and store it in a sealed recycling box (made of 304 stainless steel with built-in moisture-proof silicone) for later use.

[0061] Rust removal effect test: Samples of the rust-removing absorber were taken and the surface morphology was observed using a scanning electron microscope (SEM). The surface of the absorber was required to be free of obvious rust residue and have intact particle morphology. At the same time, the phase of the absorber was analyzed by X-ray diffraction (XRD) to ensure that its main phases had not changed (phase purity ≥ 98%).

[0062] 6. Grinding and mixing of microwave absorber and resin:

[0063] The microwave absorber is remixed and ground with the freshly prepared resin matrix in a certain proportion to ensure that the microwave absorber is evenly dispersed in the resin matrix and has a small particle size.

[0064] Raw material preparation: Select freshly prepared matrix resin (epoxy resin, brand name E-51) and regenerated microwave absorbing agent and mix them in a preset ratio (the mass ratio of microwave absorbing agent to resin is 65:35, which can be adjusted according to the stealth performance of the target). At the same time, add 0.5-1% by mass of dispersant (model BYK-163) to improve the dispersibility of microwave absorbing agent in resin.

[0065] Preliminary mixing: Add the above raw materials to a dual planetary dispersion mixer (model SXJ-500), set the stirring speed to 300 rpm, the stirring time to 1-2 hours, and the mixing temperature to 30-40℃, so that the microwave absorber, resin and dispersant are initially mixed evenly to obtain a preliminary mixture (no obvious lumps, microwave absorber dispersion uniformity ≥70%).

[0066] Nanoscale grinding: The initial mixture is fed into a horizontal sand mill (model PHE-500). Zirconia beads (0.1-0.3mm particle size, with ≥80% of the particles being 0.2mm) are used as the grinding media, with a media filling rate of 70-75%. A series of grinding parameters are set. The spindle speed is 2000-2500 rpm, the grinding temperature is controlled at 30-40℃ (cooled by a cooling water circulation system), and the grinding time is 3-5 hours. Samples are taken every hour during this period, and the particle size is measured using a laser particle size analyzer (model S3500). The required dispersion particle size of the microwave absorber in the resin is ≤500nm. After the grinding meets the standard, grinding is stopped, resulting in a uniform coating slurry.

[0067] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for recycling stealth coatings on aircraft surfaces, characterized in that, Includes the following steps: (1) Pretreatment: Remove impurities from the coating surface by purging with compressed air and using RJ-1 solvent-based cleaning agent; (2) Coating directional peeling: Wet shot peening equipment is used, with ceramic shot peening as the medium, and the paint layer and coating are peeled off under the conditions of pressure 0.4-0.6MPa, shot peening angle 30-45° and shot peening distance 150-200mm. (3) Incineration treatment: The coating mixture is incinerated in stages at 600-800℃ for 2-3 hours with an oxygen content of 8-12% to obtain crude microwave absorber; (4) Airflow sieving: Sieving is performed by a vertical airflow sieve with an airflow velocity of 15-20 m / s and a sieve mesh size of 25-30 μm; (5) Rust removal treatment: Immerse in a 5-10% citric acid solution with 0.1-0.2% LAN-826 corrosion inhibitor for 1-2 hours; (6) Mixing and grinding: Mix the regenerated microwave absorber and the freshly made resin at a mass ratio of 65:35 and grind them in a sand mill until the particle size is ≤500nm.

2. The method according to claim 1, characterized in that, The ceramic shot peening particle size in step (2) is 0.2-0.5mm, hardness HRC45-50, roundness ≥90%, and shot peening path overlap rate ≥30%.

3. The method according to claim 1, characterized in that, In step (3), the incineration temperature is selected according to the type of microwave absorber: 600-700℃ for ferrite and 700-800℃ for rare metals.

4. The method according to claim 1, characterized in that, The sieving parameters in step (4) are as follows: 500 mesh screen for ferrite microwave absorber and 600 mesh screen for rare metal microwave absorber.

5. The method according to claim 1, characterized in that, In step (5), the rust removal liquid has a solid ratio of 5:1 (L / kg), and is subsequently rinsed three times with deionized water until the pH reaches 6.5-7.

5.

6. A system for reusing microwave absorbing fillers, characterized in that, include: Pretreatment module: includes a compressed air system and an RJ-1 cleaning agent treatment unit; Shot peening and stripping module: equipped with YT0-1308 liquid sandblasting machine, pulse bag dust collection system and collection bin; Incineration module: WFS-50 incinerator with exhaust gas treatment system; Airflow screening module: QS-1000 vertical airflow screen; Rust removal module: PP material reactor; Mixing and grinding modules: SXJ-500 double planetary disperser and PHE-500 horizontal sand mill.

7. The system according to claim 6, characterized in that, The exhaust gas treatment system includes a cyclone dust collector, an activated carbon adsorption tower, and a Pt-Rh catalytic combustion device.

8. The system according to claim 6, characterized in that, The shot peening stripping module is equipped with an industrial camera monitoring system with a resolution of 1920×1080 and a frame rate of 30fps.

9. The system according to claim 6, characterized in that, The hybrid grinding module uses 0.1-0.3mm zirconia beads as grinding media with a filling rate of 70-75%.

10. A regenerated stealth coating, characterized in that, The microwave absorbing agent recovered by the method of any one of claims 1-5 is prepared by mixing E-51 epoxy resin at a mass ratio of 65:35, and the dispersed particle size of the microwave absorbing agent is ≤500nm.

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