Preparation method of semi-cured flexible aramid honeycomb core material

Abstract

The present application relates to aramid honeycomb core material technical field, specifically a kind of preparation method of semi-cured flexible aramid honeycomb core material, including aramid honeycomb sheet without impregnating phenolic resin, impregnated phenolic resin and semi-cured process, mold lay-up solidification with shape, different thickness aramid honeycomb sheet without impregnating phenolic resin is obtained by sheet cutting, semi-cured in low temperature oven after impregnating phenolic resin, high-temperature solidification after mold lay-up with shape.The present application compared with prior art, its advantages are: using phenolic resin gradient solidification scheme, make a kind of semi-cured flexible aramid honeycomb core material, solve the whole solidification conventional honeycomb due to saddle effect, easy delamination, irregular whole solidification flexible honeycomb due to high difficulty, low efficiency, high application cost, semi-cured honeycomb resin easy to gather and produce bubble problem with shape;Manufacturing process is small in difficulty, preparation efficiency is high, application process is easy to realize, preparation process is simple and easy to control, and stability is high.

Description

Technical Field

[0001] This invention relates to the field of aramid honeycomb core material technology, specifically a method for preparing a semi-cured flexible aramid honeycomb core material. Background Technology

[0002] Aramid honeycomb core materials, due to their high strength, light weight, corrosion resistance, fatigue resistance, and low dielectric constant, are widely used in aerospace, rail transportation, and other applications requiring high strength and low weight. They are suitable for high-end aerospace fields such as airborne, shipborne, and spaceborne radar, and antenna support structures. The conventional manufacturing process for aramid honeycomb core materials includes steps such as adhesive application, lamination, hot pressing, edge trimming, stretching, shaping, impregnation, curing, edge trimming, sheet cutting, and inspection. Aramid honeycombs produced according to this process are in a fully cured state, resulting in high honeycomb hardness. When manufacturing irregularly shaped, multi-curved structures, a saddle effect occurs, leading to high resilience and a tendency for delamination. Alternatively, after forced molding, the honeycomb is subjected to compression, significantly reducing its strength and rigidity.

[0003] Based on overseas examples, some manufacturers have developed irregularly shaped, fully cured flexible aramid honeycomb core materials with varying free edges. The manufacturing process of this fully cured product requires high-temperature setting of the aramid paper before adhesive application. Furthermore, the stacking process necessitates non-equidistant, centered alignment, maintaining a certain offset. This results in high manufacturing difficulty, a high error rate, a low pass rate, and high overall cost. Additionally, some semi-cured honeycomb cores exhibit resin surface aggregation and bubbles during conformal curing, affecting the bonding strength with the face material.

[0004] Chinese Patent No. 202210344469.1 discloses a microwave absorbing honeycomb structure for preventing surface cracking and its preparation method. The method includes the fabrication of a semi-cured honeycomb and the fabrication of a microwave absorbing honeycomb. The fabrication of the microwave absorbing honeycomb includes: slicing the semi-cured honeycomb block into sheets of suitable thickness; immersing the semi-cured honeycomb sheets in a microwave absorbing coating and drying them; repeating this process multiple times until the density of the honeycomb sheets reaches the required level; and then co-curing the honeycomb sheets to obtain the microwave absorbing honeycomb sheet. The purpose of the aforementioned patented semi-cured honeycomb is to increase bonding strength and prevent surface cracking. By first completing the semi-curing, then impregnating with the microwave absorbing material, and finally performing the final curing, the bonding strength between the microwave absorbing material and the substrate surface is relatively good, which can prevent surface cracking. However, the material lacks flexibility and may produce a saddle effect. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a flexible aramid honeycomb core material that avoids the saddle effect caused by laying irregular curved surfaces and has low product resilience.

[0006] To achieve the above objectives, a method for preparing a semi-cured flexible aramid honeycomb core material is designed, and the steps of the method are as follows:

[0007] S1: Aramid honeycomb sheets cut without impregnation of phenolic resin;

[0008] S2: After impregnating the aramid honeycomb sheet with phenolic resin, it is semi-cured at low temperature in an oven. The density of the semi-cured honeycomb sheet is measured. The above process is repeated multiple times to measure the density of the semi-cured honeycomb sheet, so that the honeycomb reaches the target density and maintains flexibility.

[0009] S3: Select a set of molds, lay out the honeycomb profiles, and then cure them at high temperature in an oven.

[0010] Preferably, in step S2, the impregnation process involves immersing the honeycomb sheets in a phenolic resin bath for 5-6 minutes to ensure thorough saturation. The sheets are then lifted vertically, and excess resin is blown away using an air knife after removal. The curing process involves maintaining a horizontal state for the sheets, allowing circulating air to pass through them, and placing them in an oven. The heating rate is 3℃-5℃ / min. Except for the final semi-curing, the constant temperature is 120℃±2℃. During the final semi-curing, the constant temperature is 100℃±2℃, and the constant temperature holding time is consistently 30min±3min.

[0011] Preferably, the impregnation and semi-curing process in step S2 includes multiple steps to achieve uniform distribution of phenolic resin. The final constant temperature holding temperature is 100℃±2℃, and the other constant temperature holding temperatures are 120℃±2℃. The constant temperature holding time is 30min±3min for each step. After each constant temperature holding, the temperature is reduced to room temperature for 30min-45min.

[0012] Preferably, the aramid honeycomb sheet in step S1 is prepared by high-speed slicing of shaped, unimpregnated aramid honeycomb blocks using a high-precision horizontal band saw.

[0013] Preferably, the thickness of the aramid honeycomb sheet in step S1 is 3-50mm, the nominal cell side length is 1.83mm, 2.75mm, 4.80mm, 5.70mm and 7.20mm, and the nominal density is 18kg / m³-48kg / m³.

[0014] Preferably, in step S3, the core material is cured separately according to the mold shape. The laying method is to lay a non-stick release material on the mold surface, lay the semi-cured flexible aramid honeycomb core material, lay a non-stick release material, lay a high-temperature vacuum film, and after vacuuming, make the honeycomb core material fit tightly with the mold to maintain the target shape. The vacuum degree is -0.03MPa to -0.05MPa.

[0015] Preferably, the heating rate in step S3 includes two types: 2℃-3℃ / min and 5℃-7℃ / min, and the constant temperature holding temperature includes two stages: 120℃±2℃ and 175℃±5℃. The curing process is as follows: in the first stage, the temperature is increased from room temperature to 120℃±2℃ at a rate of 2℃-3℃ / min, and the temperature is held at a constant temperature for 120min±5min; in the second stage, the temperature is increased from 120℃ to 175℃±3℃ at a rate of 5℃-7℃ / min, and the temperature is held at a constant temperature for 45min±3min; after the constant temperature holding period, the temperature is reduced to room temperature for 60min-90min.

[0016] Compared with the prior art, the advantages of this invention are as follows: This invention utilizes a phenolic resin gradient curing scheme to produce a semi-cured flexible aramid honeycomb core material and corresponding application process, which solves the problems of conventional fully cured honeycomb being prone to delamination due to the saddle effect, irregular fully cured flexible honeycomb being difficult to manufacture, inefficient, and costly to apply, and semi-cured honeycomb being prone to resin aggregation and bubble formation. This method has a simple manufacturing process, high preparation efficiency, easy application process, simple and easy-to-control preparation process, and high stability. Detailed Implementation

[0017] Based on the technical solution of this invention, a semi-cured flexible aramid honeycomb core material with a side length of 2.75 mm and a nominal density of 64 kg / m³ is prepared. An unimpregnated aramid honeycomb block with a side length of 2.75 mm, approximately hexagonal pores, a density of 22 kg / m³, and dimensions of 1.25*2.50*0.85 m is selected, fixed on a high-speed, high-precision horizontal band saw, and cut into 15 mm thick unimpregnated aramid honeycomb sheets by setting the thickness.

[0018] Unimpregnated aramid honeycomb sheets were placed in a high-temperature resistant phenolic resin bath and soaked for 5 minutes. The resin was then removed while the cells were vertical. After the resin was removed, the honeycomb sheets were cleaned with an air knife to remove excess resin. The sheets were then placed in an oven with the cells horizontal and the temperature increased to 120°C at a rate of 4°C / min. The temperature was maintained at 120°C for 30 minutes, followed by a 45-minute cooling to room temperature. The honeycomb sheets were then removed, and the density was measured to be 44 kg / m³, completing the first impregnation and semi-curing process.

[0019] The honeycomb sheets that have undergone the first impregnation and semi-curing are placed in a high-temperature phenolic resin bath and soaked for 5 minutes. The resin is then removed while the cells are vertical. After the aramid honeycomb sheets are removed, they are blew clean with an air knife to remove excess resin. The sheets are then placed in an oven while the cells are horizontal, and the temperature is increased to 100°C at a rate of 4°C / min, held at 100°C for 30 minutes, and then cooled to room temperature for the next 30 minutes. The honeycomb sheets are then removed, and the density is measured to be 65 kg / m³. This completes the final impregnation and semi-curing, resulting in a semi-cured flexible aramid honeycomb core material with a side length of 2.75 mm and a density of 65 kg / m³. Some honeycomb sheets require more impregnation and semi-curing cycles. In these cases, the final cycle should be held at 100°C, and the other cycles at 120°C.

[0020] The semi-cured flexible aramid honeycomb core material with a side length of 2.75 mm and a density of 65 kg / m³ prepared by the above method is soft and uniform in state, can be bent into multiple curved surfaces, and the preparation process is simple and controllable.

[0021] A hemispherical mold was selected. After cleaning the mold surface, a layer of cut Teflon cloth was first laid on top, ensuring a tight fit with the mold. The semi-cured flexible aramid honeycomb core material with a side length of 2.75 mm and a density of 65 kg / m³ was then laid on the Teflon cloth, and the edges were fixed with high-temperature adhesive. Another layer of cut Teflon cloth was then laid on the upper surface of the honeycomb core material, followed by a high-temperature vacuum film. The entire structure was evacuated to -0.04 MPa. Maintaining the vacuum, the entire structure was placed in an oven, and the temperature was increased from room temperature to 120°C at a rate of 2°C / min, held at this temperature for 120 minutes, and then increased from 120°C to 175°C at a rate of 6°C / min, held at this temperature for 45 minutes. After the holding period, the temperature was lowered to room temperature for 90 minutes. The cured honeycomb core material was removed; the surface of the honeycomb core material showed no bubbles, and resin aggregation was minimal, indicating minimal impact on the adhesion to the surface material.

[0022] The above description is merely one specific embodiment of this invention, but the scope of protection of this invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in this invention, based on the technical solution and novel concept of this invention, should be covered within the scope of protection of this invention.

Claims

1. A method for preparing a semi-cured flexible aramid honeycomb core material, characterized in that: The steps of the method are as follows: S1: Aramid honeycomb sheets cut without impregnation of phenolic resin; S2: After impregnating the aramid honeycomb sheet with phenolic resin, it is semi-cured at low temperature in an oven. The density of the semi-cured honeycomb sheet is measured. The above process is repeated multiple times to measure the density of the semi-cured honeycomb sheet to achieve the target density while maintaining flexibility. The impregnation process involves immersing the honeycomb sheet in a glue tank containing phenolic resin for 5-6 minutes to ensure full wetting. Then, the glue is removed while keeping the cells vertical. After removing the aramid honeycomb sheet, an air knife is used to blow away excess glue. The curing process involves keeping the cells horizontal, circulating air through the cells, and placing it in an oven. The heating rate is 3℃-5℃ / min. Except for the final semi-curing, the constant temperature is 120℃±2℃. During the final semi-curing, the constant temperature is 100℃±2℃, and the constant temperature holding time is always 30min±3min. S3: Select a set of molds, lay out the honeycomb profiles, and then cure them at high temperature in an oven.

2. The method for preparing a semi-cured flexible aramid honeycomb core material as described in claim 1, characterized in that... The impregnation and semi-curing process in step S2 includes multiple steps to achieve uniform distribution of phenolic resin. The final constant temperature holding temperature is 100℃±2℃, and the other constant temperature holding temperatures are 120℃±2℃. The constant temperature holding time is 30min±3min for each step. After each constant temperature holding, the temperature is reduced to room temperature for 30min-45min.

3. The method for preparing a semi-cured flexible aramid honeycomb core material as described in claim 1, characterized in that... The aramid honeycomb sheet in step S1 is prepared by high-speed cutting of shaped, unimpregnated aramid honeycomb blocks using a high-precision horizontal band saw.

4. The method for preparing a semi-cured flexible aramid honeycomb core material as described in claim 1, characterized in that... The aramid honeycomb sheet in step S1 has a thickness of 3-50mm, nominal cell side lengths of 1.83mm, 2.75mm, 4.80mm, 5.70mm and 7.20mm, and a nominal density of 18kg / m³-48kg / m³.

5. The method for preparing a semi-cured flexible aramid honeycomb core material as described in claim 1, characterized in that... In step S3, the core material is cured separately according to the shape. The laying method is to lay a non-stick release material on the mold surface, lay the semi-cured flexible aramid honeycomb core material, lay a non-stick release material, lay a high-temperature vacuum film, and after vacuuming, make the honeycomb core material fit tightly with the mold to maintain the target shape. The vacuum degree is -0.03MPa to -0.05MPa.

6. The method for preparing a semi-cured flexible aramid honeycomb core material as described in claim 1, characterized in that... The heating rate in step S3 includes two types: 2℃-3℃ / min and 5℃-7℃ / min. The constant temperature holding temperature includes two stages: 120℃±2℃ and 175℃±5℃. The curing process is as follows: in the first stage, the temperature is increased from room temperature to 120℃±2℃ at a rate of 2℃-3℃ / min, and the temperature is held at a constant temperature for 120min±5min. In the second stage, the temperature is increased from 120℃ to 175℃±3℃ at a rate of 5℃-7℃ / min, and the temperature is held at a constant temperature for 45min±3min. After the constant temperature holding is completed, the temperature is reduced to room temperature for 60min-90min.