A method for repairing a polyimide high temperature cured vacuum bag

Abstract

The application is a kind of polyimide high-temperature curing vacuum bag repairing method, which comprises the following steps: 1) vacuuming the damaged vacuum bag to find out the damaged part; 2) releasing the vacuum to flatten and compact the damaged part, then using polyimide high-temperature adhesive tape to block and vacuum again to pre-shape the vacuum bag; 3) covering the high-temperature sealing strip on it and paying attention to fill the joint around the high-temperature adhesive tape; 4) covering a small piece of polyimide high-temperature vacuum bag on the high-temperature sealing strip and compacting it; 5) filling the high-temperature organic silicon sealant around the sealing strip, compacting the small piece of vacuum bag again, discharging the air to make it tightly fit with the high-temperature sealing strip and the organic silicon sealant; 6) trimming the small piece of vacuum bag to be slightly larger than the organic silicon sealant, heating the organic silicon sealant with a hot hair dryer to make it slightly solidify. The application provides a method which can effectively repair the damaged part of the polyimide high-temperature curing vacuum bag and restore its use function.

Description

Technical Field

[0001] This invention relates to a repair method for high-temperature curing vacuum bags made of polyimide, belonging to the technical field of bag pressure curing molding process for composite materials. Background Technology

[0002] Bag compression molding is a method that uses an elastic bag to accept fluid pressure, allowing the composite material between a rigid mold and the elastic bag to be uniformly compressed and formed into a part. It is widely used in the fabrication and molding processes of thermosetting materials and large composite devices. Based on the fluid pressure, it can be divided into pressurized bag molding, vacuum bag compression molding, and autoclave molding. Among these, vacuum bag-autoclave molding is the main method for producing high-strength components of high-fiber reinforced thermosetting plastics for aerospace applications. The basic process involves combining prepreg layers with other process auxiliary materials to form a vacuum bag assembly system, which is then cured in an autoclave under specific pressure (including the vacuum negative pressure inside the bag and the positive pressure outside) and temperature to produce parts of various shapes. The process is divided into five stages: 1) Heating stage: Select an appropriate heating rate according to the part to ensure uniform heating. Vacuum pressure is mainly used in this stage; 2) Adhesive absorption stage: Essentially an intermediate heat preservation stage, the purpose is to melt the resin, impregnate the fiber and remove volatiles. At the same time, the resin will solidify to a gel state. The pressure in this stage is 1 / 3 to 1 / 2 of the total pressure; 3) Second heating stage: After the adhesive absorption stage, the resin matrix is ​​in a semi-cured state and the volatiles have been fully discharged. The temperature can be gradually raised to the curing temperature. The heating rate needs to be controlled in this stage to prevent explosive polymerization; 4) Heat preservation and hot pressing stage: The temperature has been raised to the curing temperature. Full pressure needs to be applied in this stage to ensure that the resin layers can be fully compacted during the curing process. The process parameters such as temperature, pressure and time must be strictly controlled according to the resin matrix formula; 5) Cooling stage: Under a certain pressure, natural cooling or other cooling methods are used to cool the part to a certain temperature or near room temperature. After that, the pressure can be released to obtain the part.

[0003] For composite materials with resin matrices such as polyimide that have a curing temperature higher than 300℃, polyimide high-temperature vacuum bags are required for the bag pressing process. However, these bags typically have low toughness. If wrinkles or bridging occur during the sealing stage, the air inside the bag cannot be completely expelled. Under the pressure during the adhesive absorption and hot pressing stages, the bags are prone to rupture, leading to air leakage, a decrease in vacuum level, and affecting the molding of the parts. Cracks are also very easy to extend and difficult to repair, often requiring the vacuum bags to be remade, increasing manpower, material resources, and time costs.

[0004] Over the years, domestic and foreign companies, including Boeing, have made great progress in the field of vacuum bag compression molding technology and have proposed some relatively mature vacuum bag sealing methods, which can effectively reduce the occurrence of vacuum bag leakage and damage, and are of great significance for reducing various costs. However, no simple and efficient vacuum bag repair method has been proposed yet. For the occurrence of damage, it is usually necessary to spend a lot of money to make a new vacuum bag sealing structure. Summary of the Invention

[0005] This invention addresses the aforementioned existing technical situation by providing a method for repairing high-temperature curing vacuum bags made of polyimide. The purpose of this method is to effectively repair damaged areas of high-temperature vacuum bags, enabling the damaged vacuum bags to be reused without affecting the molding quality of components and saving time and costs.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] The repair method for polyimide high-temperature curing vacuum bags described in this invention involves first evacuating the damaged vacuum bag 2 to identify the damaged area 3. Then, the vacuum inside the vacuum bag 2 is released, and the damaged area 3 is flattened and compacted. Next, polyimide high-temperature tape 4 is used to seal around the damaged area 3, and the vacuum bag 2 is evacuated again. Atmospheric pressure is used to pre-shape the polyimide high-temperature tape 4 around the damaged area 3. Finally, a high-temperature resistant sealing strip 5 is applied to the polyimide high-temperature tape 4 surrounding the damaged area 3. Cover the high-temperature resistant sealing strip 5 with a piece of polyimide high-temperature vacuum bag material 7 and press it firmly. Then fill the lower surface of the flange around the polyimide high-temperature vacuum bag material 7 with high-temperature resistant silicone sealant 6. Press the polyimide high-temperature vacuum bag material 7 firmly again and remove the air so that it is tightly bonded to the high-temperature resistant sealing strip 5 and the high-temperature resistant silicone sealant 6. Finally, use a hot air blower to heat the high-temperature resistant silicone sealant 6 to cure it and prevent it from flowing and causing poor sealing. Then continue the curing process that has not been carried out.

[0008] The high temperature resistance mentioned in the above method refers to a maximum operating temperature of 427℃.

[0009] In one embodiment, the polyimide high-temperature vacuum bag material 7 is designated Thermalimide, with a maximum service temperature of 426°C and an elongation at break of 95%.

[0010] In one embodiment, the polyimide high-temperature tape 4 is designated as AIRKAP236.

[0011] In one embodiment, the high-temperature resistant sealing strip 5 is grade A-800-3G, with a maximum operating temperature of 427°C.

[0012] In one embodiment, the high-temperature resistant silicone sealant 6 is designated as HM306.

[0013] During implementation, the distance between the adjacent edges of the polyimide high-temperature tape 4 and the damaged area 3 should exceed 10mm.

[0014] During implementation, after the polyimide high-temperature vacuum bag material 7 is tightly bonded to the high-temperature resistant sealing strip 5 and the high-temperature resistant silicone sealant 6, the periphery of the polyimide high-temperature vacuum bag material 7 is trimmed so that the distance between the adjacent edges of the polyimide high-temperature vacuum bag material 7 and the high-temperature resistant silicone sealant 6 reaches 5-10mm, in order to prevent the edges from causing friction between the vacuum bags and thus causing new damage.

[0015] During implementation, the final curing process includes a heat preservation period of 2 hours at 90°C.

[0016] The beneficial effects of the technical solution of this invention are:

[0017] Because of the pre-vacuuming process, the vacuum bag has already achieved a shaping effect, preventing the risk of new ruptures in areas other than the damaged area. The damaged area is compacted before being sealed, which avoids the extension of cracks around the damaged area due to insufficient displacement after repressurization. The high-temperature tape can also prevent the cracks from spreading to some extent. The double protection of high-temperature resistant sealing strips and silicone sealant can tightly adhere the small piece of vacuum bag to the damaged area, ensuring the vacuum level is maintained after repair and restoring the function of the vacuum bag. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the repair of a damaged area in the vacuum bag according to the present invention; Detailed Implementation

[0019] The present invention will be further described below with reference to embodiments:

[0020] like Figure 1 As shown, the repair method described in this invention comprises the following steps:

[0021] Step 1: Determine the location of the damage

[0022] First, vacuum the damaged vacuum bag 2 and locate the damaged point 3 by listening for the sound of air leakage.

[0023] Step 2: Seal the damaged area

[0024] After releasing the vacuum, flatten and compact the damaged area 3 using component 1, and then attach a piece of polyimide high-temperature tape 4 slightly larger than the damaged area 3. Note that the tape in the direction of the crack should be at least 10mm larger than the edge of the crack to prevent the crack from extending. Then, vacuum again to pre-shape the vacuum bag 2.

[0025] Step 3: Repair the edges

[0026] Use a high-temperature resistant sealing strip 5 to cover the polyimide high-temperature tape 4, and make sure to cover the edges of the polyimide high-temperature tape 4 to block the air passage;

[0027] Step 4: Assemble the new vacuum bag

[0028] A small piece of polyimide high-temperature vacuum bag material 7 is then placed on top of the high-temperature resistant sealing strip 5 and pressed to expel the air and compact it.

[0029] Step 5: Seal the edges

[0030] Fill the high-temperature resistant silicone sealant 6 around the high-temperature resistant sealing strip 5 and the gap between the two vacuum bags with the pre-mixed high-temperature resistant silicone sealant 6. Then, press the polyimide high-temperature vacuum bag material 7 again to remove air and make it fit tightly with the high-temperature resistant sealing strip 5 and the high-temperature resistant silicone sealant 6, thus completing the vacuum bag repair with multiple layers of protection.

[0031] Step Six: Post-processing

[0032] Trim small pieces of polyimide high-temperature vacuum bag material 7, making its edges 5-10mm larger than the edges of the high-temperature resistant silicone sealant 6, to prevent the excessively large edges from rubbing against the original vacuum bag and causing new damage. Finally, use a hot air blower to slightly heat the silicone sealant to slightly cure it, preventing it from leaking and causing gaps. Then, continue the unfinished curing process, adding a heat preservation time during the heating process, holding it at 90℃ for about 2 hours, so that the silicone sealant can be more fully cured and set.

Claims

1. A method for repairing a high-temperature curing polyimide vacuum bag, the method first involves evacuating the damaged vacuum bag (2), identifying the damaged area (3), releasing the vacuum in the vacuum bag (2), flattening and compacting the damaged area (3), then sealing the area around the damaged area (3) with high-temperature polyimide tape (4), and evacuating the vacuum bag (2) again. Atmospheric pressure is used to pre-shape the high-temperature polyimide tape (4) around the damaged area (3), and then high-temperature resistant sealing strips (5) are applied to the polyimide high-temperature tape around the damaged area (3). 4) On top of the high-temperature resistant sealing strip (5), cover it with a piece of polyimide high-temperature vacuum bag material (7) and press it firmly. Then fill the lower surface of the flange around the polyimide high-temperature vacuum bag material (7) with high-temperature resistant silicone sealant (6). Press the polyimide high-temperature vacuum bag material (7) firmly again and remove the air so that it is tightly bonded to the high-temperature resistant sealing strip (5) and the high-temperature resistant silicone sealant (6). Finally, use a hot air blower to heat the high-temperature resistant silicone sealant (6) to make it solidify to prevent flow and poor sealing. Then continue the curing process that has not been carried out. The high temperature resistance mentioned in the above method refers to a maximum operating temperature of 427℃.

2. The repair method for polyimide high-temperature curing vacuum bags according to claim 1, characterized in that: The polyimide high-temperature vacuum bag material (7) is designated Thermalimide, with a maximum service temperature of 426°C and an elongation at break of 95%.

3. The repair method for polyimide high-temperature curing vacuum bags according to claim 1, characterized in that: The polyimide high-temperature tape (4) is grade AIRKAP236.

4. The repair method for polyimide high-temperature curing vacuum bags according to claim 1, characterized in that: The high-temperature resistant sealing strip (5) is grade A-800-3G and has a maximum operating temperature of 427℃.

5. The repair method for polyimide high-temperature curing vacuum bags according to claim 1, characterized in that: The high-temperature resistant silicone sealant (6) is grade HM306.

6. The repair method for polyimide high-temperature curing vacuum bags according to claim 1, characterized in that: The distance between the adjacent edges of the polyimide high-temperature tape (4) and the damaged area (3) should exceed 10 mm.

7. The repair method for polyimide high-temperature curing vacuum bags according to claim 1, characterized in that: After the polyimide high-temperature vacuum bag material (7) is tightly bonded to the high-temperature resistant sealing strip (5) and the high-temperature resistant silicone sealant (6), the periphery of the polyimide high-temperature vacuum bag material (7) is trimmed so that the distance between the adjacent edges of the polyimide high-temperature vacuum bag material (7) and the high-temperature resistant silicone sealant (6) reaches 5-10mm, so as to prevent the edges from causing friction between the vacuum bags and thus causing new damage.

8. The repair method for polyimide high-temperature curing vacuum bags according to claim 1, characterized in that: The final curing process includes a heat preservation period of 2 hours at 90°C.

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