A potting process for foam core boards

Abstract

This invention relates to a potting process for a foam core board, comprising the following steps: filling the potting holes with a curing adhesive, allowing the adhesive to solidify into a rigid body at room temperature while ensuring complete heat release during curing; heating the entire foam board to allow the rigid body to undergo secondary curing and the adhesive film to expand; the heating temperature is 120℃~190℃, the holding time is 90~120 minutes, and then the board is allowed to cool naturally. In this invention, the surface of the expanding adhesive film is non-smooth, allowing the fluid potting adhesive to fully contact the surface of the expanding adhesive film during injection, filling any uneven areas and further increasing the contact area at the bonding interface with the expanding adhesive film. This improves the adhesion between the potting adhesive and the expanding adhesive film, helping to reduce cracking at the bonding interface.

Description

Technical Field

[0001] This invention relates to the field of composite material foam core processing technology, and to a method for potting foam core boards. Background Technology

[0002] Composite foam sandwich structures possess unique advantages such as high specific strength, high specific modulus, high flexural strength, and high stiffness, and are currently widely used in the aerospace field. However, when foam sandwich composite structures are assembled within the foam area, the relatively low stiffness of the foam material results in weak support for the composite skin, failing to meet high load-bearing requirements. To prevent damage to the foam sandwich structure and improve its mechanical properties, it is necessary to open and seal the fastener assembly area on the foam. Due to the difference in thermal expansion coefficients between the potting compound and the foam, cracking is prone to occur at the adhesive interface between the potting compound and the foam during potting curing and subsequent co-curing of the foam and skin, affecting the internal quality of the foam sandwich structure and its subsequent assembly strength.

[0003] Recent inventions regarding methods to prevent potting cracking include:

[0004] 1) An internal plate for preventing cracking of potting compound in transformers (Authorization No. CN207752846U): This patent designs an internal plate to prevent cracking of potting compound in transformers. It works in conjunction with the outer casing containing the transformer coil, preventing cracking of the potting compound after potting when it cannot be replaced. However, placing the internal plate inside the potting compound increases its weight and does not meet the requirements for subsequent potting operations involving drilling holes for fasteners in the potting area.

[0005] 2) A capacitor structure to prevent potting compound cracking (Authorization No.: CN208834908U): This patent proposes a capacitor structure to prevent potting compound cracking, including a metal shell, a capacitor core, an insulating edging, and potting compound. The plastic insulating edging is fixed to the periphery of the opening end of the metal shell and covers the inner sidewall of the opening end of the metal shell. The small difference in the linear expansion coefficient between the plastic insulating edging and the potting compound prevents the metal shell and the potting compound from separating. This patent uses plastic insulating edging to solve the problem of cracking caused by the inconsistent expansion coefficients of the metal shell and the potting compound.

[0006] 3) A method for molding honeycomb sandwich parts with potting adhesive (application number: CN115352101A): potting adhesive is uniformly injected into the core cells of the honeycomb sandwich material, and after curing, it is processed into a filling module. According to the shape of the potting area, potting holes are opened on the honeycomb. The filling module is wrapped with a compensation adhesive layer and then placed into the honeycomb potting hole to realize the manufacturing of honeycomb potting parts. After the potting module is formed, cured, and processed, the compensation adhesive layer is used for bonding. The manufacturing cost is high, the efficiency is low, and there is a problem of incomplete filling of the compensation adhesive layer.

[0007] In addition, in the existing technology, the expansion film is laid first and then the parts are inserted. Since the gap is very small and the film is sticky, it is easy to squeeze or move the film, causing the film to accumulate, fall off or shift, resulting in incomplete bonding.

[0008] Furthermore, during machining, the material inside the filling hole has a different hardness than the material of the foam core board, and using the same milling parameters will also bring the risk of cracking.

[0009] In summary, while the aforementioned core material potting method can achieve foam potting, adding an internal plate or edge-wrapping material to the potting compound requires structural design changes and cannot meet the stiffness requirements of the potting area of ​​the foam sandwich structure. Furthermore, the method of manufacturing a potting block and then bonding it to the foam with an adhesive layer is not suitable for foam potting, as there may be incomplete filling of the adhesive film. Therefore, existing foam potting methods cannot meet the potting requirements of the assembly area of ​​the foam sandwich structure. Summary of the Invention

[0010] The purpose of this invention is to propose a method to prevent cracking in foam potting. This method effectively solves the problem of cracking between the potting compound and the foam during subsequent co-curing of the skin and the foam, as well as cracking during machining, caused by the different coefficients of thermal expansion and hardness of the foam and the potting compound during processing (including potting and machining). It can improve the bonding quality between the foam and the potting compound, achieve high-quality and efficient foam potting operations, and can be widely applied to the potting operations of foam pores of different sizes.

[0011] The technical solution of this invention is:

[0012] A method for potting a foam core board is provided, comprising the following steps:

[0013] Step 1: Obtain the foam core board, ensuring that the foam core board has a processing allowance in thickness, and open the filling holes on the foam core board;

[0014] Step 2: Apply an adhesive film to the inner wall of the potting hole. The adhesive film is a heat-expanding adhesive film.

[0015] Step 3: Fill the potting hole with curing adhesive to allow the curing adhesive to solidify into a rigid body at room temperature, and ensure that the heat generated during curing is completely released.

[0016] Step 4: Heat the entire foam board to allow the rigid body to undergo secondary curing and the adhesive film to expand. The heating temperature is 120℃~190℃, the holding time is 90~120 minutes, and then it is allowed to cool naturally.

[0017] Step 5: Mill both the upper and lower surfaces of the foam board to remove excess material, so that the solidified rigid body in the filling hole forms an integral plane with the foam board, thus obtaining the filled foam core board.

[0018] Furthermore, the foam core board is made of PMI foam.

[0019] Furthermore, the potting compound is a two-component epoxy resin adhesive. Preferably, the grade is CG1305A / B.

[0020] Furthermore, the expanding film is made of expanding foam. Preferred grades are FM490A, J-297B, or J-490B.

[0021] Furthermore, in step 3, the total time for the potting compound to cure at room temperature and dissipate heat is at least 24 hours.

[0022] Furthermore, during the room temperature curing process of the potting compound, curing is carried out under vacuum. Vacuum bag treatment is preferred.

[0023] Furthermore, the preferred heating temperature for the potting compound is 120°C, and the preferred heating time is 90 minutes;

[0024] Furthermore, the foam core board obtained in step 1 is a dried foam core board. Even further, the drying process parameters are a drying temperature of at least 180°C and a drying time of at least 180 minutes.

[0025] Furthermore, in step 5, the filling holes of the foam board after filling are first milled, and then the foam is milled outward from the filling holes. Preferably, when milling the filling holes, the milling cutter speed is not less than 6000 r / min. Preferably, when milling the foam core board outward from the filling holes, the milling cutter speed is not more than 4000 r / min.

[0026] The advantages of this invention are: the method for preventing foam potting cracking is applicable to foam potting operations of different sizes and shapes, and the potting operation is simple, the potting cost is low, the speed is fast, and it can solve the problem of foam and potting adhesive cracking.

[0027] Compared to the rigid parts and adhesive film in existing technologies, the surface of the expanding adhesive film in this invention is a non-smooth surface. When the fluid potting compound is injected and filled, it will make full contact with the surface of the expanding adhesive film, and fill the uneven parts of its surface, further increasing the contact area of ​​the bonding interface with the expanding adhesive film, improving the bonding force between the potting compound and the expanding adhesive film, and helping to reduce the cracking of the bonding interface.

[0028] The adhesive injection method of this invention will not damage or destroy the laid adhesive film, ensuring its integrity.

[0029] In this method, the machining is carried out in two ways, and the movement trajectory of the cutting head is planned to prevent machining cracks. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of foam potting.

[0031] Among them: 1-support tooling, 2-tape, 3-foam, 4-film, 5-potting compound. Detailed Implementation

[0032] The disclosed examples will be described more fully with reference to the accompanying drawings, in which some (but not all) of the disclosed examples are shown. In fact, many different examples may be described, and these examples should not be construed as limited to those set forth herein. Rather, these examples are described so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0033] A method for potting a foam core board is provided, comprising the following steps:

[0034] Step 1: Obtain the foam core board, ensuring that the foam core board has a processing allowance in thickness, and open the filling holes on the foam core board;

[0035] Step 2: Apply an adhesive film to the inner wall of the potting hole. The adhesive film is a heat-expanding adhesive film.

[0036] Step 3: Fill the potting hole with curing adhesive to allow the curing adhesive to solidify into a rigid body at room temperature, and ensure that the heat generated during curing is completely released.

[0037] Step 4: Heat the entire foam board to allow the rigid body to undergo secondary curing and the adhesive film to expand. The heating temperature is 120℃~190℃, the holding time is 90~120 minutes, and then it is allowed to cool naturally.

[0038] Step 5: Mill both the upper and lower surfaces of the foam board to remove excess material, so that the solidified rigid body in the filling hole forms an integral plane with the foam board, thus obtaining the filled foam core board.

[0039] The foam core board is made of PMI foam.

[0040] The potting compound is a two-component epoxy resin. Its brand name is CG1305A / B.

[0041] The expanding film is made of expanding foam. Its brand name is FM490A.

[0042] In step 3, the total time for the potting compound to cure at room temperature and dissipate heat is at least 24 hours.

[0043] During the room temperature curing process of the potting compound, curing is carried out under vacuum. Vacuum bags are used for treatment.

[0044] The potting compound is heated at 120℃ for 90 minutes.

[0045] The foam core board obtained in step 1 is a dried foam core board. The drying process parameters are: drying temperature at least 180°C and drying time at least 180 minutes.

[0046] In step 5, the filling holes of the foam board after filling are first milled, and then the foam is milled outward from the filling holes. When milling the filling holes, the milling cutter speed should not be less than 6000 r / min. When milling the foam core board outward from the filling holes, the milling cutter speed should not exceed 4000 r / min.

[0047] Descriptions of various advantageous arrangements have been shown for illustrative and descriptive purposes, but such descriptions are not intended to be exclusive or limited to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art. Furthermore, different advantageous examples may describe different advantages compared to other advantageous examples. One or more examples have been selected and described in order to best illustrate the principles and practical application of the examples, and to enable those skilled in the art to understand that this disclosure contains various examples with various modifications suitable for the particular intended use.

Claims

1. A method for potting a foam core board, characterized in that: The steps include: Step 1: Obtain the foam core board, ensuring that the foam core board has a processing allowance in thickness, and open the filling holes on the foam core board; Step 2: Apply an adhesive film to the inner wall of the potting hole. The adhesive film is a heat-expanding adhesive film. Step 3: Fill the potting hole with curing adhesive to allow the curing adhesive to solidify into a rigid body at room temperature, and ensure that the heat generated during curing is completely released. Step 4: Heat the entire foam board to allow the rigid body to undergo secondary curing and the adhesive film to expand. The heating temperature is 120℃~190℃, the holding time is 90~120 minutes, and then it is allowed to cool naturally. Step 5: Mill both the upper and lower surfaces of the foam board to remove excess material, so that the solidified rigid body in the filling hole forms an integral plane with the foam board, thus obtaining the filled foam core board.

2. The potting process for a foam core board as described in claim 1, characterized in that: The foam core board is made of PMI foam.

3. The potting process method for a foam core board as described in claim 1, characterized in that: The potting compound is a two-component epoxy resin adhesive.

4. The potting process method for a foam core board as described in claim 1, characterized in that: The expanding film is made of expanding foam.

5. The potting process method for a foam core board as described in claim 1, characterized in that: In step 3, the total time for the potting compound to cure at room temperature and dissipate heat is at least 24 hours.

6. The potting process method for a foam core board as described in claim 1, characterized in that: During the room temperature curing process of the potting compound, it is cured under vacuum and vacuum bags are used for treatment.

7. The potting process method for a foam core board as described in claim 1, characterized in that: The potting compound is heated to 120℃ for 90 minutes.

8. The potting process method for a foam core board as described in claim 1, characterized in that: The foam core board obtained in step 1 is a dried foam core board. The drying process parameters are a drying temperature of at least 180°C and a drying time of at least 180 minutes.

9. The potting process for a foam core board as described in claim 1, characterized in that: In step 5, the filling holes of the foam board after filling are first milled, and then the foam is milled outward from the filling holes.

10. The potting process for a foam core board as described in claim 1, characterized in that: When milling the filling hole, the milling cutter speed shall not be less than 6000 r / min; when milling the foam core board from the filling hole, the milling cutter speed shall not be greater than 4000 r / min.

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