Composite noise reduction structure based on local resonance principle and preparation method thereof

Abstract

The invention discloses a composite noise reduction structure based on a local resonance principle and a preparation method thereof, and belongs to the field of design and processing of composite noise reduction structures. The structure comprises an epoxy resin supporting panel, a metal ring-elastomer local resonance unit and a porous material, and efficient suppression of broadband noise is achieved through combination of the local resonance effect and the porous sound absorption characteristic. The resonance unit is of a structure in which a metal ring and an elastic body are mechanically embedded and are in mirror distribution; the elastic body is of a stepped cylinder structure, the metal ring is nested on a small-diameter cylinder, and the metal ring is a double-layer elastic supporting body with radial rigidity gradient after mirroring; the epoxy resin supporting panel is poured and formed through a steel mold, the elastic body is poured through a split mold, a metal ring cutting process and a porous material are processed and prepared according to requirements, and all the components are assembled into a whole through an adhesive. The invention has the advantages of obvious noise reduction effect, light weight, strong durability, simple preparation process and the like, and is suitable for noise control in various different application scenes.

Description

Technical Field

[0001] This invention relates to the field of composite noise reduction structure design and fabrication, specifically to a composite noise reduction structure based on the principle of local resonance and its fabrication method. Background Technology

[0002] In many fields requiring a safe acoustic environment, such as high-speed transportation, rail transit, and industrial equipment, noise issues related to high-speed rail pantographs (or similar current collection and power transmission components) have become a key bottleneck restricting the improvement of equipment performance and environmentally friendly development. As a core component connecting the equipment to the power supply and transmission systems, the pantograph generates strong aerodynamic interactions with the surrounding complex flow field during high-speed operation, resulting in a wide frequency range of aerodynamic noise. The low-frequency components, due to their high energy content and prominent propagation characteristics, have a significant impact on the acoustic environment. Simultaneously, structural noise caused by the vibration transmission of the pantograph support and the frictional vibration of the contact friction pairs further exacerbates the complexity of noise pollution. This type of noise not only deteriorates the internal acoustic environment of the equipment, reducing the experience and working environment quality for drivers and operators, but also adversely affects surrounding residential areas, educational areas, and other sound-sensitive environments, conflicting with increasingly stringent environmental noise standards.

[0003] Current noise reduction methods used in the industry have significant limitations: while traditional sound-absorbing materials can dissipate some energy from mid-to-high frequency noise, their attenuation effect on low-frequency noise is extremely poor, making it difficult to effectively solve the problem of low-frequency-dominated noise. Metal soundproof enclosures, although able to block noise propagation paths to some extent, significantly increase component load, adversely affecting equipment energy consumption and operational safety. Furthermore, after long-term service, they are prone to structural gaps due to vibration fatigue, leading to a decrease in noise reduction efficiency. In addition, existing composite noise reduction structures often employ complex multi-layered designs, resulting in cumbersome installation procedures, high maintenance costs, and susceptibility to material aging and interlayer debonding in harsh environments such as rain, dust, and oil contamination. Their service life is typically less than 3 years, failing to meet the requirements for long-term stable service.

[0004] In existing technologies, based on the principle of local resonance, sound absorption in the low-frequency band is achieved by constructing elastic-mass resonant units. However, current research is mostly in the laboratory exploration stage. The core challenges are: First, there is a lack of unit array design methods adapted to complex spatial structures. The rigid or strong shear coupling between the mass block and the elastic matrix often inhibits its lateral motion degree of freedom, causing the system dynamics to be dominated by vertical compression mode. This not only limits the intensity of the negative effective mass effect, but also restricts the dynamic mass ratio of the system due to the limited elastic energy storage volume, resulting in a narrow band gap and insufficient attenuation efficiency. The resonant frequency is easily affected by installation conditions, making it difficult to achieve stable and precise low-frequency noise reduction control. Second, the molding precision control of elastomers (such as silicone rubber) is difficult, resulting in poor consistency of unit performance. The pass rate during mass production is less than 70%, which restricts engineering applications. Third, the connection process of each layer structure has not formed a standardized system, making it difficult to meet the stringent requirements of equipment components for vibration fatigue strength and long-term reliability. Therefore, developing a noise reduction structure that balances wideband noise reduction performance, lightweight structure, and process stability is of great engineering application value and scientific research significance for promoting the green, comfortable, and intelligent development of transportation equipment and industrial equipment. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a composite noise reduction structure based on the principle of local resonance and its fabrication method. By optimizing the structural design and fabrication process, efficient noise control can be achieved.

[0006] This invention provides a composite noise reduction structure based on the principle of local resonance, comprising a metal ring-elastomer local resonance unit, a porous material, and an epoxy resin support panel;

[0007] The metal ring-elastic body local resonant unit is a structure in which the metal ring and the elastomer are mechanically interlocked and mirror-distributed; the elastomer is a stepped cylindrical structure formed by two cylinders of different diameters coaxially connected, with the metal ring nested on the smaller diameter cylinder;

[0008] The porous material is a perforated cube made of high-density porous material through perforation processing, and the metal ring-elastic local resonant unit is placed at the perforation position;

[0009] The epoxy resin support panel is a rectangular plate with a fixing post in the middle, and the fixing post is inserted into the round hole at the bottom of the large-diameter cylinder of the elastomer.

[0010] Furthermore, the epoxy resin support panel is formed by injection molding of epoxy resin and curing agent mixed together.

[0011] Furthermore, the density of the porous material is 100~200g / m³; the porous material is selected from high-density rock wool boards.

[0012] Furthermore, the Young's modulus of the elastomer is 0.5~5MPa; the elastomer is made of silicone rubber material that is cured at room temperature or by heating; the diameter of the large-diameter cylinder of the elastomer is the same as the outer diameter of the metal ring, and the diameter of the small-diameter cylinder is 0.1~0.2mm smaller than the inner diameter of the metal ring.

[0013] Furthermore, the metal ring is made of iron, aluminum, or silver; the metal ring and the elastomer are coaxially fitted together and have the same outer diameter, and a gap of 0.1~0.2mm is provided between the metal ring and the small-diameter cylinder of the elastomer.

[0014] The present invention provides a mold for preparing the above-mentioned composite noise reduction structure, including an epoxy resin injection mold, an epoxy resin injection cover plate mold, an elastomer injection groove mold, and a cover plate mold with a fixing column.

[0015] The epoxy resin injection mold is a steel plate with rectangular grooves on its surface. There are n×n cylindrical grooves arranged in the rectangular grooves, and the steel plate is surrounded by support columns.

[0016] The epoxy resin injection cover plate mold is a steel plate with round holes on its surface, and the steel plate has round holes around its perimeter that match the positions of the epoxy resin injection mold support columns.

[0017] The elastomer injection groove mold is a steel plate with n×n stepped cylindrical grooves on its surface, and the steel plate is surrounded by support columns.

[0018] The cover plate mold with fixed columns is a steel plate with n×n cylinders on its surface. The cylinders are surrounded by circular holes to ensure that the elastomer overflows. The steel plate is surrounded by circular holes that match the positions of the support columns of the elastomer injection groove mold. When the cover plate mold with fixed columns is placed on the elastomer injection groove mold, the cylinders of the cover plate mold with fixed columns are located in the middle of the stepped cylindrical groove of the elastomer injection groove mold.

[0019] Furthermore, the rectangular groove of the epoxy resin injection mold has the same thickness as the epoxy resin support panel, and the cylindrical groove of the epoxy resin injection mold has the same diameter and height as the fixing post of the epoxy resin support panel; the stepped cylindrical groove of the elastomer injection groove mold has the same diameter and height as the stepped cylinder of the elastomer; and the cylinder of the cover plate mold with fixing post has the same diameter and height as the circular hole at the bottom of the large-diameter cylinder of the elastomer.

[0020] The present invention also provides a method for preparing a composite noise reduction structure using the above-mentioned mold, comprising:

[0021] Step 1: Cut the porous material according to the installation dimensions of the noise reduction structure, use a perforation device to process through holes in the porous material, and grind the edges to remove burrs;

[0022] Step 2: Cut the metal plate into a circular metal sheet according to the design dimensions using laser cutting, and then punch the inner hole and grind the edge of the metal sheet to ensure that the surface is smooth and the dimensional accuracy meets the requirements;

[0023] Step 3: Clean the elastomer injection groove mold and the cover plate mold with fixing posts. Apply release agent to the inner surface and repeat 2-3 times after surface evaporation to ensure demolding effect. Mix the elastomer raw material and crosslinking agent, stir evenly, and then vacuum degas to obtain elastomer solution. Pour the elastomer solution into the stepped cylindrical groove of the elastomer injection groove mold and cover it with the cover plate mold with fixing posts. The cylinder of the cover plate mold with fixing posts is located in the middle of the stepped cylindrical groove. Combine and fix the elastomer injection groove mold and the cover plate mold with fixing posts, cure, and inspect and repair the surface of the cylinder after demolding.

[0024] Step 4: Clean the epoxy resin injection mold and epoxy resin injection cover mold. Apply release agent to the inner surface and repeat 2-3 times after surface evaporation to ensure demolding effect. Mix epoxy resin and curing agent at a mass ratio of 3-7:1, stir evenly, and then degas under vacuum to obtain epoxy resin solution. Pour the epoxy resin solution into the cylindrical and rectangular grooves of the epoxy resin injection mold, and cover with the epoxy resin injection cover mold. Combine and fix the epoxy resin injection mold and epoxy resin injection cover mold, cure, and after demolding, sand the panel surface until smooth.

[0025] Step 5: Apply epoxy resin adhesive to the surface of the epoxy resin support panel, and attach and fix the elastomer. After the adhesive has cured, fit the metal ring around the small-diameter cylinder of the elastomer to form a metal ring-elastomer-epoxy resin panel unit cell structure.

[0026] Step 6: Symmetrically splice the unit cell structure of the metal ring-elastomer and the epoxy resin panel with adhesive, with the contact surfaces being the upper surfaces of the metal ring and the elastomer; then apply adhesive to the outer surface of the metal ring-elastomer local resonance unit layer to attach and fix the porous material, which then wraps the entire metal ring-elastomer unit layer. Pressurize and cure for 24 hours to complete the overall assembly.

[0027] Furthermore, in step 3, the curing process involves curing at room temperature for 24-48 hours or curing at 40-50°C for 6-12 hours.

[0028] The beneficial effects of this invention are as follows:

[0029] (1) The present invention designs a composite noise reduction structure based on the principle of local resonance. A metal ring is nested within a composite unit composed of two layers of cylindrical elastic bodies with different diameters. Compared with the traditional homogeneous unit of "mass block-spring", this structure achieves significant physical mechanism enhancement in both promoting lateral slip and optimizing resonance quality, thus showing excellent advantages in low-frequency broadband sound insulation performance. This innovative structure constructs a more efficient coupled dynamic system by introducing a double-layer elastic support with radial stiffness gradient: the outer elastic sleeve with lower stiffness preferentially undergoes shear deformation under acoustic excitation, effectively driving the metal ring to generate a large-scale lateral slip and fully releasing its inertial motion capability; the inner elastic column with higher stiffness provides the necessary restoring force and stability, ensuring the system's definite resonance frequency. This gradient design not only promotes the participation of a larger volume of elastic material in resonance through multi-interface stress transfer, significantly improving the equivalent resonance quality of the system, but also optimizes the vibration modes by guiding the redistribution of energy in the elastic body. As a result, this unit can excite a stronger and wider-bandwidth negative effective mass effect in the target low-frequency band, thus providing a key theoretical basis and unit design paradigm for constructing a periodic sound insulation system with wide bandwidth, strong attenuation, and tunable characteristics. This invention, through the combination of local resonance and porous sound absorption, achieves a noise reduction of up to 47.7 dB (50~6300 Hz band), while significantly reducing the overall weight compared to traditional structures, making it suitable for various complex sound insulation and noise reduction applications. Furthermore, the introduction of a radial stiffness gradient double-layer elastic support in this invention not only enhances the load-bearing capacity of the composite noise reduction structure but also improves its application in high-speed transportation, rail transportation, and industrial equipment.

[0030] (2) The present invention provides a mold suitable for the industrial mass production of the composite noise reduction structure of the present invention. The epoxy resin support panel is cast using a steel mold to ensure dimensional accuracy and structural strength. The elastomer column is made using a combination mold (n×n column elastomer injection groove mold + mold with n×n fixed column cover plate) to ensure array consistency and molding quality. The metal ring and porous material are processed using standardized processing technology to ensure dimensional accuracy. All components are assembled into one piece using high-strength adhesive, making the composite noise reduction structure of the present invention have important engineering application value and scientific research significance. Attached Figure Description

[0031] Figure 1 This is a single-cell cross-sectional view of the composite noise reduction structure of the method of the present invention;

[0032] Figure 2 This is an exploded view of the composite noise reduction structure assembled according to the method of the present invention;

[0033] Figure 3 The epoxy resin injection mold is the method of the present invention.

[0034] Figure 4This is the epoxy resin injection cover plate mold for the method of the present invention;

[0035] Figure 5 This is an elastomer injection groove mold for the method of the present invention;

[0036] Figure 6 This invention relates to a cover plate mold for elastomer injection with fixing columns;

[0037] Figure 7 This is a schematic diagram of a metal ring-elastic resonant unit array.

[0038] In the diagram, 1 is a metal ring, 2 is a porous material, 3 is an elastomer, and 4 is an epoxy resin board. Detailed Implementation

[0039] The present invention will now be further described with reference to the accompanying drawings.

[0040] This invention discloses a composite noise reduction structure based on the principle of local resonance, comprising: an epoxy resin support panel, a metal ring-elastomer local resonance unit layer, and a porous material layer.

[0041] The metal ring-elastic body local resonant unit layer consists of local resonant units that are mechanically interlocked and mirror-distributed between metal rings and elastomers. Each unit includes a metal ring (mass block) and an elastomer (stepped column). The metal ring and the elastomer (stepped column) are coaxially interlocked and have the same outer diameter.

[0042] The porous material layer is a perforated cube made of high-density porous material plate through a perforation process. The perforations are used to place the metal ring-elastomer local resonant unit. The density of the porous material used is controlled between 100 and 160 kg / m³. For special scenarios requiring high pressure resistance or high sound insulation, the density of the porous material can be optimized by selecting an ultra-high-density porous material with a density of ≥160 kg / m³ to achieve the target requirements.

[0043] The elastomer material is a room temperature or heat-cured elastomer material; for the selection of elastomer material, taking silicone rubber as an example, silicone rubber with a Young's modulus in the range of 0.5~5MPa can be selected, which, according to the empirical formula, translates to a Shore hardness of approximately 5~90 ​​(error ±2).

[0044] In the metal ring-elastomer localized resonant unit, a pre-set micro-gap of 0.1~0.2mm between the metal ring and the double-layer cylindrical elastomer is not a manufacturing tolerance, but a key design feature. Mechanically, this gap is equivalent to introducing a micro-amplitude pre-slip region and a weakened contact interface. Its core advantages are twofold: firstly, it significantly reduces the static friction constraint between the metal ring and the elastomer surface, allowing the mass ring to slide more freely laterally under small excitations, thereby more efficiently exciting its inertial motion and enhancing the negative effective mass effect. Secondly, the gap provides an additional nonlinear stiffness adjustment mechanism. In the small amplitude vibration stage, the system behaves approximately linearly. As the amplitude increases to the contact interface, the stiffness increases nonlinearly. This characteristic helps to broaden the effective frequency band of the resonant response and may dissipate some vibrational energy through contact friction. Therefore, this micro-gap design synergistically optimizes the unit's start-up sensitivity, dynamic range, and energy dissipation capability, ultimately contributing to improved robustness of the overall sound insulation structure over a wide frequency range.

[0045] The epoxy resin support panel has a fixing column, which is made by mixing epoxy resin and curing agent in a certain mass ratio and then pouring it into the mold, resulting in high strength and rigidity.

[0046] A mold for preparing a composite noise reduction structure includes a steel mold for injecting epoxy resin to support the panel, the shape of which is consistent with the panel size; and a modular mold for injecting elastomer columns, which consists of an n×n column elastomer injection groove mold (the diameter of the column groove matches the elastomer column, and the depth is the column height) and a steel cover plate mold with n×n fixed columns (the diameter of the fixed columns is smaller than that of the column groove).

[0047] A method for preparing a composite noise reduction structure, requiring equipment including an epoxy resin injection steel mold (for epoxy resin), an epoxy resin injection cover plate mold, an n×n cylindrical elastomer injection groove mold, a steel cover plate mold with n×n fixed columns, cutting equipment, perforation equipment, a vacuum pump, vacuum bags, adhesives, etc., and the preparation steps are as follows:

[0048] Step 1: Cut the porous material board into the corresponding shape according to the installation dimensions of the noise reduction structure, use a perforation device to process through holes in the porous material board, and grind the edges to remove burrs;

[0049] Step 2: Cut the metal plate into a circular metal sheet according to the design dimensions using laser cutting, and then punch the inner hole and grind the edge of the metal sheet to ensure that the surface is smooth and the dimensional accuracy meets the requirements;

[0050] Step 3: Clean the column groove mold and the steel cover plate with the fixing column. Apply release agent to the inner surface and repeat 2-3 times after the surface evaporates to ensure the demolding effect.

[0051] Step 4: Mix the elastomer raw materials and curing agents according to different application scenarios and usage requirements, stir evenly, and then degas under vacuum. (For example, a two-component system of silicone rubber is usually described as: Component A (base rubber compound) and Component B (curing agent or crosslinking agent). The required ratio depends on the specific system. In common addition-curing silicone rubbers, the weight ratio of Component A to Component B is usually between 1:1 and 10:1. The optimal ratio needs to be determined experimentally to ensure the best balance between catalyst activity and crosslinking density, thereby obtaining the ideal vulcanization rate and final material properties. The accuracy of the ratio is crucial to ensuring complete curing of the material and obtaining the expected physicochemical properties.)

[0052] Step 5: Pour the degassed elastomer solution into the cylindrical groove, and fix the cylindrical mold and cover plate together (the fixed column is inserted into the cylindrical groove). Cure at room temperature for 24~48h (or in an oven at 40~50℃ for 6~12h). After demolding, check and trim the surface of the column.

[0053] Step 6: Clean the steel mold, evenly apply release agent to the inner surface, and let it dry. Mix epoxy resin and curing agent at a mass ratio of 4:1 (the core of epoxy resin system formulation lies in the precise chemical equivalence between curing agent and resin, the specific ratio of which is determined by the molecular structure and reaction mechanism of the selected curing agent. Optimizing the formulation aims to ensure the full action of reactive groups to build a complete cross-linking network, thereby obtaining the thermomechanical properties and long-term stability required by the design. Slight deviations in the formulation will directly affect the degree of curing, residual stress, and final application performance. Common curing agents include amines such as ethylenediamine, m-phenylenediamine, or dicyandiamide, with a weight ratio typically ranging from 3:1 to 7:1. In addition, there are acid anhydrides such as methyltetrahydrophthalic anhydride, with a formulation typically based on an equivalence ratio of epoxy groups to acid anhydride groups of 1:0.8 to 1:1.1). After vacuum degassing, slowly pour the mixture into the epoxy resin casting mold and cover it with an epoxy resin casting cover plate. Cure at room temperature for 12-24 hours. After demolding, sand the panel surface until smooth.

[0054] Step 7: Apply epoxy resin adhesive to the surface of the epoxy resin support panel, and attach and fix the elastomer column array. After the adhesive has cured, put the metal rings on the outside of the small diameter elastomer cylinders one by one.

[0055] Step 8: Apply adhesive (such as 3M90 spray adhesive) to the surface of the metal ring-elastomer unit layer and between the resonant units on both sides to attach and fix the porous material layer, and cure under pressure for 24 hours to complete the overall assembly.

[0056] In step 5, the modular mold used for elastomer injection must ensure precise fit between the fixed column and the cylindrical groove to avoid leakage during the injection process; in step 6, the epoxy resin solution must undergo vacuum degassing to prevent bubble defects after curing.

[0057] The epoxy resin support panel provides structural strength, the metal ring-elastomer unit suppresses low-frequency noise through localized resonance, and the porous material layer absorbs mid-to-high-frequency noise through porous sound absorption. These three elements work together to achieve broadband noise reduction. Because of the large mass of the metal ring, it plays a major resonant role in the entire structure. Different performance indicators can be achieved by adjusting the size of the metal ring, thereby controlling the mass of the composite structure and meeting various engineering application scenarios.

[0058] Example 1

[0059] like Figure 1 As shown, the overall size design of the composite noise reduction structure based on the principle of local resonance (unit cell length 25mm × width 25mm × height 24mm) consists of an epoxy resin support panel (thickness 2mm), a metal ring-elastomer unit layer (height 20mm), and a porous material layer (thickness 20mm) from bottom to top.

[0060] like Figure 3 , Figure 4 As shown, the epoxy resin injection mold (rectangular groove 2mm deep, 25mm long, 2mm wide, 10×10 cylindrical groove, 4mm in diameter, 4mm in height) and the epoxy resin injection cover plate mold.

[0061] like Figure 4 , 5 As shown, the elastomer injection mold includes a 10×10 cylindrical elastomer injection groove mold (stepped cylindrical groove with an upper diameter of 12mm, a lower diameter of 8mm, and a depth of 10mm) and a steel cover plate with a fixing post (the fixing post has a diameter of 4mm and a height of 4mm, but can actually be slightly larger to match the epoxy resin support panel). After assembly, the gap between the fixing post and the groove wall is 0.1mm to prevent leakage and ensure the verticality of the column.

[0062] The noise reduction structure is fabricated through the following process:

[0063] 1. Preparation of porous material layers:

[0064] High-density rock wool boards are cut into 25mm × 25mm × 20mm cuboids using high-precision cutting equipment. During cutting, ensure the cut surfaces are flat, with an error controlled within ±0.5mm, to guarantee good bonding with other structures later. CNC drilling equipment is used to drill holes in the cut perforated material boards. During drilling, the drill bit must be kept sharp to prevent cracking or chipping of the perforated material boards. The edges of the perforated material boards are carefully sanded with sandpaper to remove all burrs and sharp corners, preventing injury to operators during subsequent installation and use, and also avoiding scratching damage to other components. After sanding, the surface of the high-density rock wool boards is cleaned of dust using compressed air and set aside for later use.

[0065] 2. Preparation of metal rings:

[0066] Aluminum plates with a thickness of 8mm and a density of 2700kg / m³ were selected as raw materials, possessing good ductility and processing performance to meet the dimensional accuracy requirements of the metal ring. The metal plates were cut using laser cutting equipment to produce circular aluminum sheets with an outer diameter of 12mm. Laser cutting is characterized by high precision and speed, ensuring that the diameter error of the circular aluminum sheet is controlled within ±0.05mm, and the cut surface is smooth and burr-free. A high-precision punch press was used to punch an inner hole at the center of the circular aluminum sheet, with an inner hole diameter set at 8mm. The punch head of the punch press underwent special treatment to ensure that the punched inner hole edges were smooth and free from deformation. After punching, the aluminum sheet was placed in specialized grinding equipment for grinding of the inner and outer edges and surface. 400-grit sandpaper was used for rough grinding to remove obvious processing marks, followed by fine grinding with 600-grit sandpaper to reduce the surface roughness of the aluminum ring. After polishing, the aluminum sheet is cleaned with alcohol to remove surface oil and impurities, and then placed in a drying oven at 60℃ for 30 minutes for later use. The final dimensional accuracy of the aluminum sheet must be strictly controlled within ±0.05mm.

[0067] 3. Preparation of elastomer cylinders:

[0068] Thoroughly clean the 10×10 cylindrical elastomer injection groove mold and the steel cover plate mold with fixing columns using mold cleaner, and wipe repeatedly with a lint-free cloth to ensure that the inner surface of the mold is free of any oil, dust, and impurities. Then, place them in a ventilated place to dry. Next, evenly apply a layer of release agent to the inner surface of the mold. Let it stand for 10 minutes to allow the release agent to evaporate and dry on the surface, then repeat the application once more. Apply a total of 2-3 times to ensure good demolding results.

[0069] Prepare the silicone rubber material and crosslinking agent at a 1:1 mass ratio. Pour the silicone rubber material into a clean mixing container, then slowly add the crosslinking agent and stir using an electric stirrer for approximately 5 minutes to ensure uniform mixing. After stirring, place the mixed silicone rubber material into a vacuum degassing device for degassing treatment to ensure complete removal of air bubbles. Slowly pour the degassed elastomer material into the cylindrical grooves of the cylindrical mold. During pouring, use a funnel to guide the material slowly along the groove wall to avoid generating new air bubbles. Each cylindrical groove should be filled completely, with the liquid level flush with the upper surface of the mold, with an error not exceeding ±0.5mm. After pouring, scrape off any excess material from the mold surface with a scraper to keep the mold surface clean. Cover the elastomer pouring groove mold with a steel cover plate mold containing fixing posts, ensuring that each fixing post is accurately inserted into its corresponding cylindrical groove. Securely fasten the elastomer injection groove mold and the steel cover plate mold with fixing posts using specialized clamps. The pressure of the clamps should be evenly distributed to prevent mold deformation. During the fixing process, check the mold's seal to prevent leakage during injection. Place the mold filled with silicone rubber in a temperature and humidity controlled curing chamber for curing. Set the curing temperature to room temperature (25℃), relative humidity to 50%, and curing time to 24 hours. During curing, avoid vibration and impact on the mold, and maintain a stable curing environment.

[0070] 4. Preparation of epoxy resin panels:

[0071] First, thoroughly clean the epoxy resin injection mold and epoxy resin cover mold. Then, wipe them clean with alcohol and let them dry. Apply a layer of release agent evenly to the inner surface of the mold, using a layered application method. After applying the first thin layer, let it stand for 15 minutes to allow it to initially dry and form a film before applying the second layer. Ensure the release agent evenly covers all areas, creating a good release effect and preventing the epoxy resin from sticking to the mold after curing. Mix epoxy resin and hardener at a 4:1 mass ratio, stir thoroughly, and then degas under vacuum. Slowly pour the mixture into the epoxy resin injection mold, and then cover it with the epoxy resin cover mold. Use specialized clamps to firmly fix the epoxy resin injection mold and epoxy resin cover mold, ensuring even pressure to prevent mold deformation. During the fixing process, check the mold's seal to prevent leakage during injection. After curing at room temperature for 18 hours, demold and sand the panel surface until smooth.

[0072] 5. Overall structural assembly:

[0073] Apply epoxy resin adhesive evenly to the surface of the epoxy resin support panel, then attach the silicone rubber cylinders to the epoxy resin support panel fixing posts, ensuring accurate positioning. Next, slip the metal rings onto the outside of the small-diameter cylinders on the upper part of the silicone rubber cylinders one by one, pressing gently to secure them firmly. Apply adhesive to the upper and outer surfaces of the metal rings and elastomers, symmetrically splicing them with the upper surfaces of the metal rings and elastomers as the contact surfaces. Align and adhere the high-density rock wool layer to the surface of the spliced ​​metal ring-elastomer unit layer to complete the overall assembly.

[0074] In summary, the composite noise reduction structure of this invention integrates a stepped elastic-mass resonant unit into the structure to construct an acoustic bandgap in a specific low-frequency band, thereby significantly dissipating noise energy in that band; and coupled with porous sound-absorbing materials, it achieves efficient control of broadband noise from 50 to 6300 Hz.

[0075] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0076] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A composite noise reduction structure based on the principle of local resonance, characterized in that, The metal ring-elastic body local resonance unit, the porous material, and the epoxy resin support panel are provided. The metal ring-elastic body local resonance unit is a structure in which a metal ring and an elastic body are mechanically embedded and mirror-distributed. The porous material is a perforated cube made of high-density porous material by perforation processing, and the metal ring-elastic body local resonance unit is placed at the perforated position. The epoxy resin support panel is a rectangular panel with a fixed column in the middle, and the fixed column is inserted into the circular hole at the bottom of the large-diameter cylinder of the elastic body.

2. The composite noise reduction structure based on the principle of local resonance according to claim 1, characterized in that, The epoxy resin support panel is formed by mixing and pouring epoxy resin with a curing agent.

3. The composite noise reduction structure based on the principle of local resonance according to claim 1, characterized in that, The density of the porous material is 100-200 g / m³, and the porous material is selected from high-density rock wool boards.

4. The composite noise reduction structure based on the principle of local resonance according to claim 1, characterized in that, The Young's modulus of the elastic body is 0.5-5 MPa, and the elastic body is made of room temperature or heated curing silicone rubber material.

5. The composite noise reduction structure based on the principle of local resonance according to claim 1, characterized in that, The diameter of the large-diameter cylinder of the elastic body is the same as the outer diameter of the metal ring, and the diameter of the small-diameter cylinder is smaller than the inner diameter of the metal ring by 0.1-0.2 mm.

6. A mold for preparing the composite noise-reducing structure according to any one of claims 1 to 5, characterized by, The metal ring is made of iron, aluminum, or silver. The metal ring and the elastic body are coaxially embedded and have the same outer diameter, and a gap of 0.1-0.2 mm is provided between the metal ring and the small-diameter cylinder of the elastic body. The epoxy resin pouring mold, the epoxy resin pouring cover plate mold, the elastic body pouring groove mold, and the cover plate mold with a fixed column are provided. The epoxy resin pouring mold is a steel plate with a rectangular groove on the surface, and n×n cylindrical grooves are arranged in the rectangular groove. The epoxy resin pouring cover plate mold is a steel plate with a circular hole on the surface, and the circular holes around the steel plate match the positions of the support columns of the epoxy resin pouring mold.

7. The mold for the composite noise-reducing structure of claim 6, wherein, The elastic body pouring groove mold is a steel plate with n×n stepped cylindrical groove on the surface, and support columns are arranged around the steel plate.

8. The method for preparing a composite noise reduction structure using a mold as described in claims 6-7, characterized in that, The cover plate mold with a fixed column is a steel plate with n×n cylinders on the surface, and circular holes are arranged around the cylinders. When the cover plate mold with a fixed column covers the elastic body pouring groove mold, the cylinders of the cover plate mold with a fixed column are located in the middle of the stepped cylindrical groove of the elastic body pouring groove mold. The thickness of the rectangular groove of the epoxy resin pouring mold is the same as the thickness of the epoxy resin support panel, and the cylindrical groove of the epoxy resin pouring mold has the same diameter and height as the fixed column of the epoxy resin support panel. The stepped cylindrical groove of the elastic body pouring groove mold has the same diameter and height as the stepped cylindrical body of the elastic body. The steps include: Step 1: Cut the porous material according to the installation size of the noise reduction structure, use a perforation device to process through holes on the porous material, and polish the edges to remove burrs; Step 2: Cut a metal plate into a circular metal sheet by laser cutting according to the designed size, and perform inner hole stamping and edge polishing on the metal sheet to ensure a smooth surface and meet the size accuracy requirements; Step 3: clean the elastomer perfusion groove mold and the cover plate mold with fixed columns, and apply release agent to the inner surface, repeat 2-3 times after the surface volatilizes to ensure the release effect; mix the elastomer raw material and the crosslinking agent, stir uniformly, and vacuum degassing to obtain an elastomer solution; pour the elastomer solution into the stepped cylinder groove of the elastomer perfusion groove mold, and cover the cover plate mold with fixed columns; the cylinder of the cover plate mold with fixed columns is located in the middle of the stepped cylinder groove; combine and fix the elastomer perfusion groove mold and the cover plate mold with fixed columns, cure, and check and trim the surface of the column after demolding; Step 4: clean the epoxy resin perfusion mold and the epoxy resin perfusion cover plate mold, and apply release agent to the inner surface, repeat 2-3 times after the surface volatilizes to ensure the release effect; mix the epoxy resin and the curing agent according to the mass ratio of 3-7:1, stir uniformly, and vacuum degassing to obtain an epoxy resin solution; pour the epoxy resin solution into the cylindrical groove and the rectangular groove of the epoxy resin perfusion mold, and cover the epoxy resin perfusion cover plate mold; combine and fix the epoxy resin perfusion mold and the epoxy resin perfusion cover plate mold, cure, and polish the surface of the panel to be smooth after demolding; Step 5: apply epoxy resin adhesive to the surface of the epoxy resin support panel, and paste and fix the elastomer, then put the metal ring outside the elastomer small-diameter cylinder to form a metal ring-elastomer and epoxy resin panel unit cell structure; Step 6: symmetrically splice the metal ring-elastomer and epoxy resin panel unit cell structure using adhesive, and the contact surface is the upper surface of the metal ring and the elastomer; then apply adhesive to the outer surface of the metal ring-elastomer local resonance unit layer, paste and fix the porous material, and pressurize and cure for 24h to complete the overall assembly.

9. The method of claim 8, wherein the mold is prepared by, In step 3, the curing is 24-48h at room temperature or 40-50℃ for 6-12h.

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