Method for filling pinhole recesses on carbon fiber composite honeycomb surface and verification method therefor

Abstract

The present application provides a method for filling pinhole recesses on a carbon fiber composite honeycomb surface. The method comprises: preparing a repair adhesive for a composite structure; pouring an organic solvent into a spray bottle for spraying the organic solvent onto the marked areas of the pinholes and small recesses, wherein the spraying time of the organic solvent does not exceed 10 s each time, and finishing blade coating of the repair adhesive within 30 s after spraying; by means of the volatilization effect of volatile matter in the organic solvent, dripping the adhesive solution into the pinholes and the small recess areas for filling, so as to obtain a smooth and continuous part surface; after the blade coating of the repair adhesive is finished, placing the composite honeycomb part that has been subjected to blade coating in a curing furnace for curing; and after curing is finished, polishing the blade-coated area by using alumina water-resistant sandpaper to remove excessive adhesive solution on the surface of the part. Moreover, the present application further provides a verification method for the carbon fiber composite honeycomb surface. In the present application, pinholes and small recesses on the surface of the carbon fiber composite honeycomb part can be filled, and the composite honeycomb part meets the primer spraying requirement after an adhesive spraying method is adopted.

Description

Carbon fiber composite honeycomb surface pinhole depression filling and verification method thereof TECHNICAL FIELD

[0001] The application belongs to the technical field of resin-based carbon fiber composite materials, and particularly relates to a carbon fiber composite honeycomb surface pinhole depression filling and verification method thereof. BACKGROUND

[0002] Carbon fiber composite materials have excellent properties such as specific stiffness, specific strength and the like, and are widely used in aerospace equipment manufacturing. Honeycomb joint part manufacturing is an effective means to realize lightweight of high-performance composite materials. Resin-based carbon fiber composite honeycomb sandwich joint parts are widely used in helicopter and fixed-wing aircraft fuselage structures, and safety is an important index of aerospace equipment. The glass fiber prepreg used for corrosion protection of different potentials is generally used as the first ply on the outer surface of the part, which is a functional material and mainly used for flame retardation. At the same time, in order to meet the lightweight design requirements of the aircraft, the surface film of the first ply at the position of the honeycomb core is generally removed to meet the weight reduction requirements, as shown in the following FIG. 1.

[0003] At present, in the part forming process of the honeycomb structure, the wall plate honeycomb core mainly transmits pressure to the lower skin during the curing process. However, the honeycomb core is a weak stiffness material, and when the external pressure is too large, it is easy to cause defects such as honeycomb core collapse, honeycomb chamfer shrinkage, and honeycomb shape change.

[0004] During the curing process, the upper and lower panels of the honeycomb core are bonded by the adhesive film to form a sealed cavity. Vacuum pumping can discharge the air trapped in the skin. Therefore, for air exhaust, the greater the pressure, the better. However, due to the sealed cavity formed by the adhesive film bonding the upper and lower panels of the honeycomb core, under the action of external pressure, negative pressure is easily formed in the cavity, causing the resin in the prepreg in the lower skin of the honeycomb to rise to the honeycomb core grid wall, as shown in FIG. 2. The part shows that the film surface appears vacuum, which is characterized by a large porosity. The composite material part forms a pinhole, a small depression, a dimple and other surface defects. The existence of surface defects makes it difficult for the composite honeycomb part to obtain a smooth and uniform surface, and it is difficult to meet the requirements of subsequent honeycomb part painting.

[0005] Among them, the pinhole refers to a small hole, a micro-porous surface defect that penetrates the surface of the cured composite material part, and the diameter is generally 0.25 mm (or smaller). The small depression is a surface defect that can be filled with a surface leveling agent or a dimple filling material, and the depth is generally not more than 0.05 mm.

[0006] In the process of forming a composite honeycomb part, part surface pinholes and small depressions are inevitable, but the surface quality of the composite material is extremely high, and the surface with surface pinholes and small depressions needs to be repaired to meet the subsequent primer (paint) and topcoat spraying. The method for repairing surface pinholes and small depressions is to scrape the hole putty on the surface of the part. The role is a colored paste used to fill pinholes before painting to obtain a smooth and uniform surface. Since the filling putty is granular, it is not easy to fill into the pinhole. This method is not ideal and cannot meet the surface quality requirements of the composite part, affecting the subsequent primer spraying, and the cycle is long. It often needs to be repeated 2-3 times of scraping, drying to meet the surface quality requirements of the part, and at the same time, the primer (paint) spraying can meet the requirements of the part paint layer adhesion. SUMMARY

[0007] The purpose of the application is to solve the surface defects (pores, pits, small depressions and poor glue area) of the composite part surface pinholes and small depressions, and to fill the pinholes before painting to obtain a smooth and uniform surface.

[0008] In a first aspect, the application provides a method for filling carbon fiber composite honeycomb surface pinholes and depressions, the method comprising:

[0009] Configuring a glue for repairing the composite structure;

[0010] Pouring an organic solvent into a spray bottle for spraying on the marked area of the pinhole and small depression;

[0011] The organic solvent is sprayed for no more than 10s at a time, and the scraping of the repair glue is completed within 30s after spraying; by using the volatilization effect of the volatile components in the organic solvent, the glue droplets are filled into the pinhole and small depression area to obtain a smooth and continuous part surface;

[0012] After the scraping of the repair glue is completed, the scraped composite honeycomb part is placed in a curing oven for curing;

[0013] After curing is completed, the scraped area is polished with an alumina water-resistant sandpaper to remove excess glue on the surface of the part.

[0014] Preferably, before the configuration of the glue for repairing the composite structure, it further comprises:

[0015] After the cloth is soaked in water and wrung out without water droplets, it is used to wipe the polished composite part, wherein the wiping method is horizontal and vertical cross wiping.

[0016] Preferably, before the cloth is soaked in water and wrung out without water droplets, it is used to wipe the polished composite part, wherein the wiping method is horizontal and vertical cross wiping, it further comprises:

[0017] Polish the surface to be smooth with a water sandpaper.

[0018] Preferably, before the surface is polished smooth with water sandpaper, the method further comprises:

[0019] Marking the areas of pinholes and small depressions on the surface of the composite honeycomb part.

[0020] Preferably, after the curing is completed, the method further comprises:

[0021] After the surface of the composite part is polished with water, performing a water film inspection.

[0022] Preferably, after the surface of the composite part is polished with water, performing a water film inspection, the method further comprises:

[0023] After drying, performing primer spraying.

[0024] Preferably, the method of spreading is vertical and horizontal cross spreading, and the spreading is performed according to the marked areas in sequence.

[0025] In a second aspect, the present application further provides a method for verifying the surface of a carbon fiber composite honeycomb, the method comprising:

[0026] Completely fixing the wet backing pad with pressure-sensitive protective tape, and the backing pad must be kept soaked with water during the whole period of 20h-24h;

[0027] After 24h, removing the backing pad soaked with water and absorbing the water on the surface, and immediately after the water is absorbed, testing the bonding force according to the following method:

[0028] Leaving the tape on the surface for at least 30s, lifting one end of the protective tape of the flat backing, and making it about 45°-90° to the test surface, and tightly pinching the end of the protective tape of the flat backing with fingers, and in a quick and sudden action, pulling off the remaining protective tape of the flat backing adhered to the surface of the sample;

[0029] If there is no peeling of the primer film, it is qualified.

[0030] Preferably, before the wet backing pad is completely fixed with the pressure-sensitive protective tape, the method further comprises:

[0031] Wiping the test area with a cleaning rag dipped with acetone, and the solvent is not allowed to dry naturally on the surface, and the cleaning rag is wiped dry;

[0032] Making a backing pad with cotton material, 5mm square or minimum diameter of 5mm, and thickness greater than 3mm; completely soaking the backing pad with deionized water, and placing it on the test surface;

[0033] Covering the wet pad with a piece of polyethylene transparent film, and the polyethylene-coated side of the film faces the wet pad.

[0034] The beneficial technical effects of the present application are as follows:

[0035] Through the method described in the present application, the surface pinholes (generally with a diameter of 0.25 mm or less) and small depressions (generally with a depth of not more than 0.05 mm) of the carbon fiber composite honeycomb part can be filled. After the glue spraying, the composite honeycomb part meets the requirements of primer spraying (the paint layer adhesion meets the requirements: when the test is performed after the wet cloth is retained on the coated surface for 20-24 h, there should be no primer film falling off). BRIEF DESCRIPTION OF DRAWINGS

[0036] Fig. 1 is a typical honeycomb sandwich part layup provided by the embodiment of the present application;

[0037] Fig. 2 is a schematic diagram of a honeycomb inner cavity negative pressure theoretical model provided by the embodiment of the present application;

[0038] Fig. 3 is a schematic diagram of water droplet effect provided by the embodiment of the present application;

[0039] Fig. 4 is a process flow diagram provided by the embodiment of the present application;

[0040] Fig. 5 is a schematic diagram of wet pad placement provided by the embodiment of the present application;

[0041] Fig. 6 is a schematic diagram of a typical flat substrate protection tape test provided by the embodiment of the present application. DETAILED DESCRIPTION

[0042] The present application mainly describes a method for filling the surface pinholes and small depressions of the carbon fiber composite honeycomb part. The technical solution is as follows: using the "water droplet" principle, spraying organic solvent (optionally ethanol or acetone) on the surface pinholes and small depression areas of the polished composite honeycomb sandwich part, quickly scraping the glue solution, using the volatilization effect of the volatile components in the organic solvent, the glue solution drops into the pinholes and small depression areas, and fills them to obtain a smooth and continuous part surface. The water droplet effect is shown in Fig. 3.

[0043] Referring to Fig. 4, the specific implementation steps provided by the present application are as follows:

[0044] 1. Mark the surface pinholes and small depression areas of the composite honeycomb part. To ensure the completeness of the surface pinhole and small depression filling, the size of the marked area should not exceed 300 mm x 300 mm, and the scraping of the glue should be completed within 1 min for one area.

[0045] 2. Polish the surface with a water sandpaper of 180 or more.

[0046] 3. Soak a clean cloth in water, wring it until no water droplets fall, and use it to wipe the polished composite part. The wiping method is cross wiping in the horizontal-wiping-vertical-wiping-horizontal-wiping manner.

[0047] 4. The adhesive is configured to repair the composite structure.

[0048] 5. Pour the acetone into a clean spray bottle for spraying on the surface of the pinhole and small concave area. The present application requires a fine atomizing high pressure spray bottle. The atomized acetone is sprayed on the surface of the pinhole and small concave area marked area from the high pressure spray.

[0049] 6. The acetone is sprayed for no more than 10s, and the repair adhesive is applied within 30s after spraying. The application method is: vertical scraping-horizontal scraping-vertical scraping cross scraping, and the marked area is scraped in turn.

[0050] 7. After the repair adhesive is applied, the scraped composite honeycomb part is placed in a curing oven for curing.

[0051] 8. After curing, the scraped area is polished with 180 grit aluminum oxide water-resistant sandpaper to remove excess glue on the surface of the part. After polishing the surface of the composite part with water, water film inspection is performed.

[0052] 9. After drying, primer spraying is performed for inspection of the filling effect of pinholes and small pits (a bright colored primer is selected to facilitate the inspection of pinhole and small pit filling).

[0053] 10. The primer is sprayed and cured.

[0054] 11. The paint adhesion test method is as follows: a clean wiping cloth dipped in acetone is used to scrub the test area. The solvent is not allowed to dry naturally on the surface, but is wiped dry with a clean wiping cloth; a cotton material is used to make a pad, 5mm square or minimum diameter 5mm, and greater than 3mm thick; the pad is completely soaked with deionized water and placed on the test surface; a piece of polyethylene transparent film is placed on the wet pad, with the polyethylene side facing the wet pad. The wet pad package is completely fixed with pressure-sensitive protective tape. The pad must remain soaked with water for the entire 20h-24h period, as shown in Figure 5.

[0055] After 24h, the water-soaked pad is removed and the water on the surface is absorbed. Immediately after the water is absorbed (within 2min), the adhesion is tested as follows:

[0056] The tape is left on the surface for at least 30s, the end of the flat substrate protective tape is lifted at an angle of about 45°-90° to the test surface, and the end of the flat substrate protective tape is pinched with the fingers, and the remaining flat substrate protective tape on the sample surface is pulled off with a quick and sudden motion, as shown in Figure 6.

[0057] 12. The paint adhesion test is carried out, and the test standard is that there should be no primer film peeling.

Claims

1. A method for filling surface pinhole depressions of a carbon fiber composite honeycomb, characterized by, The method includes: Develop adhesives for repairing composite material structures; Pour the organic solvent into a spray bottle and spray it onto the marked areas of pinholes and small depressions; The organic solvent spraying should not exceed 10 seconds, and the repair adhesive should be scraped off within 30 seconds after spraying. Utilizing the evaporation effect of the volatile components in the organic solvent, the adhesive is dripped into pinholes and small depressions to fill them and obtain a smooth and continuous part surface. After the repair adhesive is applied, the composite honeycomb parts are placed in a curing oven to cure. After curing, use alumina water-resistant sandpaper to sand and scrape the coated area to remove excess adhesive from the surface of the parts.

2. The method of claim 1, wherein, Before preparing the adhesive for repairing composite material structures, the following steps are also included: Soak a cloth in water, wring it until no water drips, and then use it to wipe the composite parts being polished. The wiping method is to wipe horizontally and vertically.

3. The method of claim 2, wherein, The process of soaking a wiping cloth in water, wringing it until no water drips, and then using it to wipe and polish composite parts, wherein the wiping method involves wiping in a crisscross pattern before the following steps are also included: Sand the surface with wet sandpaper until smooth.

4. The method of claim 3, wherein, Before sanding the surface with water sandpaper until it is smooth, the process also includes: Mark the pinholes and small depressions on the surface of the composite honeycomb parts.

5. The method of claim 1, wherein, After curing is complete, the coated area is sanded with alumina water-resistant sandpaper to remove excess adhesive from the surface of the parts. The process also includes: After water-polishing the surface of composite material parts, a water film inspection is performed.

6. The method of claim 5, wherein, After the water-polishing of the composite material parts surface and the subsequent water film inspection, the process also includes: After drying, apply the primer.

7. The method of claim 1, wherein, The scraping method is to scrape vertically and horizontally, and to scrape sequentially according to the marked areas.

8. A method of verifying the surface of a carbon fiber composite honeycomb, comprising: The method includes: Secure the wet liner package completely with pressure-sensitive protective tape. The liner must remain soaked in water throughout the 20-24 hour cycle. After 24 hours, remove the water-soaked pad and absorb the water from the surface. Immediately after absorbing the water, test the bonding strength as follows: Let the tape remain on the surface for at least 30 seconds. Lift one end of the flat substrate protective tape at approximately 45° to 90° to the test surface and pinch this end of the flat substrate protective tape firmly with your fingers. With a quick and sudden movement, tear off the remaining flat substrate protective tape that is attached to the sample surface. If no primer film peels off, it is acceptable.

9. The method of claim 8, wherein, Before completely securing the wet pad package with pressure-sensitive protective tape, the procedure also includes: Wipe the test area with a cleaning cloth dampened with acetone. Do not allow the solvent to air dry on the surface. Wipe it dry with a cleaning cloth. Make a pad using cotton material, 5mm square or with a minimum diameter of 5mm and a thickness greater than 3mm; completely saturate the pad with deionized water and place it on the test surface; Cover the wet pad with a piece of transparent polyethylene film, with the polyethylene-coated side facing the wet pad.

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