Porous material, preparation method and application in fan blade noise reduction

Abstract

The invention belongs to the technical field of noise reduction materials, and relates to a porous material, a preparation method and application in fan blade noise reduction. The porosity of the porous material is 30 to 90 percent; the porous material comprises a first surface and a second surface, the thickness direction is the shortest normal direction from the first surface to the second surface, and the porosity of the porous material is reduced in a gradient manner along the thickness direction; and the porous material is made of a polymer. The porosity of the adopted porous material is reduced in a gradient mode in the thickness direction, the gradient change of the porosity is beneficial to increase of diffusion consumption of sound energy, reflection sound energy is reduced, and therefore noise caused by aerodynamics is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of noise reduction materials, and relates to a porous material, a preparation method and an application thereof in fan blade noise reduction. Background Art

[0002] With the high-performance development of industrial equipment and consumer electronic products, the noise problem of fans and turbomachinery (such as the fan blades of air conditioner outdoor units, engine turbine blades, blower fan blades, etc.) has become the core challenge restricting product performance and user experience. Noise can cause multi-dimensional negative impacts: 1. Obvious damage to user experience. For example, when the outdoor unit of a household air conditioner operates at night, if the noise exceeds a certain decibel, it will significantly affect the sleep quality. 2. Impact on the performance of professional equipment. For example, if the noise of the cooling fan of a medical CT machine exceeds a certain decibel, it may interfere with the signal-to-noise ratio of the imaging system, and an additional soundproof cover needs to be invested, increasing the cost. 3. Hidden threat to equipment reliability. Long-term high-frequency vibration will cause fretting wear, and cracks are likely to occur in the stress concentration area of the blade vibration (such as the root transition section), resulting in a reduction in the service life of the blade. 4. Excessive noise violates environmental protection regulations, such as the regulations on the noise limit of air conditioner outdoor units in EU EN 12102.

[0003] The noise generated by the rotation of the fan comes from multiple aspects. For example: the noise generated by the operation of the motor. When the motor is running, the internal electromagnetic field will change complexly. When the frequency of these electromagnetic forces is close to the natural frequency of the motor structure, resonance will be triggered, resulting in obvious electromagnetic noise. The noise generated by the dynamic balance problem of the fan blade. During the manufacturing process of the fan blade, if there is an uneven mass distribution, such as inconsistent material density in some areas, or during the installation process, there is a slight deviation in the connection position between the fan blade and the motor shaft, it will cause the center of gravity of the fan blade to shift when it rotates; when the fan blade rotates at high speed, this center of gravity shift will generate a centrifugal force, triggering the vibration of the fan blade and then generating noise. The smoothness of the fan blade surface affects the noise. The smoothness of the fan blade surface directly affects the frictional resistance between the air and the fan blade. When the fan blade surface is relatively rough, the air will form a turbulent air flow when flowing through the fan blade surface. This turbulent air flow will generate additional energy loss and be released in the form of noise. The curvature of the fan blade shape affects the wind tunnel vortex noise. The curvature of the fan blade determines the path and speed distribution of the air flow when flowing through the fan blade. When the curvature of the fan blade is not designed reasonably, the air flow on the fan blade surface will become uneven, and it is easy to have an air flow separation phenomenon in some parts of the fan blade, thus generating noise.

[0004] The current mainstream fan blade noise reduction technologies can be divided into structural optimization and material modification. Structural optimization: For example, Chinese invention patent CN116696860A discloses a noise reduction structure for an electric vehicle air conditioning fan impeller. The friction noise generated between the connecting bearing and the rotating shaft is isolated by a sound insulation cover, and the volume of the noise is buffered. With the arrangement of the sound insulation cotton on the outer side of the sound insulation cover, the noise is isolated in the sound insulation cover, and the sound insulation cotton and the impeller are tightly pressed together by a pressing component, avoiding the leakage of noise and improving the noise reduction effect. Another example is Chinese invention patent CN117469201A, which discloses a noise reduction fan blade, which includes a noise reduction device. The noise reduction device includes a silent ring that penetrates the middle part in the height direction of the blade and is connected to the distal end of the blade; a convex bump is also connected to the silent ring. Through the convex bump designed in the noise reduction device of the noise reduction fan blade of the present application, when working, the convex bump on the silent ring rotates with the blade, forming a nodular vortex inside the fan to increase the buoyancy of the blade and reduce the frictional resistance when the blade rotates, and the noise reduction effect is significantly improved. Material modification: Using carbon fiber composite materials to prepare the blade, which is lighter than aluminum alloy, and at the same time suppressing resonance through fiber orientation optimization, thereby reducing noise. Coating a nano-level noise reduction coating on the blade to play a role in sound absorption and insulation by reducing the transmitted sound wave energy.

[0005] However, there are still some deficiencies in the structural optimization of fan blade noise reduction. For example, the mold transformation cost is high. Structural optimization usually involves the re-design of the fan blade shape, and these changes require the adjustment of existing molds or the opening of new molds. Frequent adjustment of molds will increase the initial investment cost. It is difficult to balance performance. Some structural optimizations may affect other performances, such as reducing the air volume and air pressure at the same rotational speed. And due to the introduction of high-performance materials (carbon fiber composite materials), the material modification will significantly increase the raw material cost.

[0006] Therefore, how to effectively reduce the fan blade noise technology has become the key direction to improve product competitiveness. Summary of the Invention

[0007] The present invention aims at the deficiencies in the prior art and provides a porous material, a preparation method and its application in fan blade noise reduction.

[0008] One object of the present invention is achieved by the following technical solutions:

[0009] A porous material, characterized in that the porosity of the porous material is 30-90%;

[0010] The porous material includes a first surface and a second surface, and the thickness direction is the shortest normal direction from the first surface to the second surface. The porosity of the porous material decreases in a gradient along the thickness direction;

[0011] The material of the porous material is a polymer.

[0012] Preferably, when the porous material is placed horizontally, the porous material is cut along a horizontal plane perpendicular to the thickness direction to obtain a porous material 1 including a first surface and a porous material 2 including a second surface, and the horizontal plane passes through the midpoint of the shortest normal line from the first surface to the second surface;

[0013] The porosity of the porous material 1 including the first surface is 60-95%, the porosity of the porous material 2 including the second surface is 20-72%, and the porosity ratio of the porous material 1 including the first surface to the porous material 2 including the second surface is ≥1.2.

[0014] Preferably, the polymer is a thermoplastic polymer.

[0015] Preferably, the polymer is one or more of polyethylene, polypropylene, rigid polyurethane, polyvinyl chloride, polyvinylidene fluoride, polyamide or nylon, polyacrylate, polyacrylonitrile, ethylene vinyl acetate, polystyrene, polyethylene terephthalate, polymethyl methacrylate, polytetrafluoroethylene, polycarbonate, polyethersulfone, polyetherimide, polyetheretherketone, polysulfone.

[0016] Preferably, the porous material is formed by sintering polymer particle raw materials;

[0017] In the porous material, the average particle size of the polymer particle raw materials used decreases in a gradient along the thickness direction, and the decreasing direction is the same as the direction in which the porosity decreases.

[0018] The second object of the present invention is achieved by the following technical solutions:

[0019] A preparation method of the porous material includes the following steps:

[0020] Mix polymer particles of different particle sizes to obtain mixed particles;

[0021] Fill the mixed particles into the mold cavity, and use vibration to make the polymer particles with small particle sizes move downward;

[0022] Heat to soften and fuse adjacent polymer particles together, and obtain the porous material after cooling.

[0023] Preferably, the particle size range of the polymer particles is 0.05-8 mm, and includes at least two groups of particles with different particle sizes.

[0024] Preferably, the D50 of the largest particle size particle group is 0.2-5 mm, the D50 of the smallest particle size particle group is 0.05-2 mm, and the ratio of the D50 of the largest particle size particle group to the D50 of the smallest particle size particle group is ≥1.3;

[0025] And / or, in the polymer particles, the proportion of the smallest particle size group with a D50 of 0.05 to 2 mm is 10 to 30 wt%.

[0026] Preferably, the softening point of the polymer + 60°C ≥ the heating temperature ≥ the softening point of the polymer + 5°C.

[0027] The third object of the present invention is achieved by the following technical solution:

[0028] An application of a porous material in reducing the noise of a fan blade, wherein the above-mentioned porous material is fixedly connected in the fan blade, the second surface of the porous material corresponds to the windward surface of the fan blade, and the first surface corresponds to the leeward surface of the fan blade.

[0029] The fourth object of the present invention is achieved by the following technical solution:

[0030] A composite material, comprising a first porous material layer and a second porous material layer arranged overlapping up and down; the first porous material layer and the second porous material layer are made of the porous material described in claim 1, and the material hardness of the porous material in the first porous material layer < the material hardness of the porous material in the second porous material layer.

[0031] Preferably, the first surface and the second surface of the porous material respectively constitute the first surface and the second surface of the first porous material layer and the second porous material layer;

[0032] The first porous material layer and the second porous material layer are arranged overlapping up and down, and the second surface of the first porous material layer and the first surface of the second porous material layer are in direct contact.

[0033] Preferably, the thickness ratio of the first porous material layer to the second porous material layer is 1:0.1 to 1;

[0034] The polymer raw material in the first porous material layer is a polymer with a Shore hardness ≤ 60D, and the polymer raw material in the second porous material layer is a polymer with a Shore hardness > 60D.

[0035] The fifth object of the present invention is achieved by the following technical solution:

[0036] A preparation method of a composite material, comprising the following steps:

[0037] S1. Prepare the first porous material layer:

[0038] Mix first polymer particles with different particle sizes to obtain first mixed particles;

[0039] Fill the first mixed particles into the mold cavity, and use the vibration method to make the small-particle-size first polymer particles move downward;

[0040] Heat to soften and fuse adjacent first polymer particles together, and obtain a first porous material layer after cooling;

[0041] S2. Prepare a second porous material layer:

[0042] Mix second polymer particles with different particle sizes to obtain second mixed particles;

[0043] Fill the second mixed particles into the mold cavity, and use vibration to make the second polymer particles with small particle sizes move downward;

[0044] Heat to soften and fuse adjacent second polymer particles together, and obtain a second porous material layer after cooling;

[0045] S3. Consolidate the second porous material layer and the first porous material layer to form an integral structure;

[0046] The Shore hardness of the first polymer is less than that of the second polymer.

[0047] Preferably, the Shore hardness of the first polymer ≤ 60D, and the Shore hardness of the second polymer > 60D.

[0048] Preferably, the first surface of the second porous material layer is consolidated with the second surface of the first porous material layer.

[0049] The sixth object of the present invention is achieved by the following technical solutions:

[0050] Application of the composite material in the noise reduction of the fan blade, fix the composite material in the fan blade,

[0051] The second surface of the second porous material layer of the composite material corresponds to the windward surface of the fan blade, and the first surface of the first porous material layer of the composite material corresponds to the leeward surface of the fan blade.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] 1. The porosity of the porous material adopted in the present invention decreases in a gradient along the thickness direction. The gradient change of the porosity is beneficial to increasing the diffusion and consumption of sound energy, reducing the reflected sound energy, and thus reducing the noise caused by aerodynamics. When the porous material is applied in the fan blade, the surface with the largest porosity of the porous material corresponds to the leeward surface of the fan blade, and the surface with the smallest porosity corresponds to the windward surface of the fan blade. The surface with the smallest porosity as the windward surface, this design is more beneficial to improving the noise reduction effect.

[0054] 2. The composite material used in the present invention is composed of a hard and a soft porous material layer. The hard porous material layer can provide support for the soft material, so that the composite material will not deform when facing a large airflow. The soft porous material layer is conducive to absorbing more sound energy. Generally speaking, the noise reduction effect of using the composite material is better than that of a single layer.

[0055] 3. The present invention can realize the preparation of noise reduction porous materials and composite materials through vibration classification and sintering processes, and the whole preparation process is very simple and easy to implement.

[0056] 4. The structures of the porous materials and composite materials of the present invention are not fixed, and can be flexibly adapted to different fan blade shapes, with convenient installation and low maintenance costs.

[0057] 5. By providing a porous material, a composite material and their preparation methods, the present invention provides an efficient, economical and reliable solution for fan blade noise reduction, with significant technological progress and market application value. Description of the Drawings

[0058] Figure 1 It is a schematic diagram showing that the porosity of the porous material of the present invention decreases along the thickness direction;

[0059] Figure 2 It is a schematic diagram of the porous material installed in the fan blade;

[0060] Figure 3 It is a sheet structure diagram of the porous material;

[0061] Figure 4 It is a diagram of the sound wave transmission process;

[0062] Figure 5 It is the transmission and reflection paths of sound waves in the porous material with gradient porosity;

[0063] Figure 6 It is a schematic diagram of the structure of the composite material of the present invention;

[0064] Figure 7 It is a test schematic diagram of the noise reduction effect of the present invention. Detailed Embodiments

[0065] Hereinafter, the embodiments of the porous material of the present invention and its preparation method and application will be described in detail, and the embodiments of the composite material of the present invention and its preparation method and application will be described in detail. However, these embodiments are exemplary, and the disclosure of the present invention is not limited thereto. And the drawings used herein are only for better explaining the content disclosed by the present invention and do not limit the protection scope.

[0066] In some embodiments of the present invention, a porous material is provided, and the porosity of the porous material is 30-90%;

[0067] The porous material includes a first surface and a second surface, and the thickness direction is the shortest normal direction from the first surface to the second surface. The porosity of the porous material decreases in a gradient along the thickness direction;

[0068] The material of the porous material is a polymer.

[0069] Porosity is the ratio of the internal pore volume of the material to the total volume of the material. The porosity of the porous material is 30-90%; further, the porosity is 40-90%; still further, the porosity is 50-80%; still further, the porosity is 60-75%.

[0070] The higher the porosity of the porous material, the more air flow can pass through, the lower the back pressure borne by the porous material, and the better the noise reduction effect; if the porosity is too high, the absorption capacity for low-frequency sound waves will decrease, the overall noise reduction effect will be reduced, and as the porosity increases, the solid part in the material will decrease, resulting in a weakening of the overall structural strength. In actual use, due to changes in the material thickness or pore distribution, the stability of the noise reduction performance will be affected.

[0071] The calculation of porosity is as follows: First, immerse the porous material with a known mass and apparent volume in water. After the water has fully penetrated, take it out and measure the mass. From the measured mass, calculate the volume of water immersed in the porous material. Consider the volume of this water to be the same as the pore volume of the porous material, and calculate the porosity using the following formula (I).

[0072] Porosity % = (Volume of water) / (Apparent volume of porous material) × 100 (I).

[0073] The thickness direction is the shortest normal direction from the first surface to the second surface. The shortest normal direction can be understood as: find a point on the first surface such that the distance from this point to the second surface is the shortest, and the direction of this shortest distance is perpendicular to the first surface.

[0074] The porosity of the porous material decreases in a gradient along the thickness direction. The gradient decrease can be a linear decrease or a non-linear decrease, as long as it shows a decreasing trend in the thickness direction. The porosity decreasing in a gradient along the direction perpendicular to the first surface towards the second surface means that the porosity gradually decreases from the first surface to the second surface of the porous material. The first surface forms the surface with the largest porosity, and the second surface forms the surface with the smallest porosity, as Figure 1 shown (the white blank part represents the total pores. This figure is only a simple schematic diagram to show the trend of gradually decreasing porosity, and the actual pores are not like this).

[0075] Preferably, when the porous material is placed horizontally, the porous material is cut along a horizontal plane perpendicular to the thickness direction to obtain a porous material 1 including a first surface and a porous material 2 including a second surface. The "horizontal plane" is the plane perpendicular to the direction of the earth's gravity in the traditional sense, and this horizontal plane passes through the midpoint of the shortest normal line from the first surface to the second surface.

[0076] The porosity of the porous material 1 including the first surface is 60-95%, the porosity of the porous material 2 including the second surface is 20-72%, and the porosity ratio of the porous material 1 including the first surface to the porous material 2 including the second surface is ≥1.2. Further preferably, this ratio is 1.3-4. Even more preferably, this ratio is 1.5-3.0.

[0077] Preferably, the open-cell rate of the porous material is ≥80%. Further preferably, it is ≥90%. Most preferably, the open-cell rate is 100%. The open-cell rate refers to the percentage of the volume of interconnected pores in the total pore volume of the porous material. An open-cell rate of 100% means that all the pores are open pores.

[0078] The material of the porous material is a polymer, that is, the porous material is prepared from a polymer as a raw material. Preferably, the polymer is a thermoplastic polymer.

[0079] Further preferably, the polymer is one or more of polyethylene (PE), polypropylene (PP), rigid polyurethane (PU), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polyamide or nylon, polyacrylate (PA), polyacrylonitrile (PAN), ethylene vinyl acetate (EVA), polystyrene (PS), polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE), polycarbonate (PC), polyethersulfone (PES), polyetherimide (PEI), polyetheretherketone (PEEK), polysulfone (PSU). The polymers can be used alone or in combination.

[0080] The shape and size of the porous material are not particularly limited and are determined according to the application scenario.

[0081] Preferably, the porous material is formed from polymer particle raw materials through a sintering process. The "sintering process" refers to the process of heating to soften the surfaces of polymer particles and bond them together, ultimately forming a three-dimensional network with a pore structure. Sintering does not require the polymer particles to be completely melted, but rather achieves bonding through local softening. The unbonded areas between particles form pores, so local softening bonding can retain the pore structure between particles.

[0082] Preferably, in the porous material, the average particle size of the polymer particle raw materials used decreases in a gradient along the thickness direction. The decreasing direction is the same as the direction in which the porosity decreases. The average particle size of the polymer particle raw materials used on the first surface is the largest, and the average particle size of the polymer particle raw materials used on the second surface is the smallest.

[0083] The surface with a smaller porosity is composed of polymer particles with a small average particle size, while the surface with a larger porosity is composed of polymer particles with a large average particle size. The packing of small particles is denser than that of large particles, thus forming smaller gaps. And during the sintering process, the degree of softening and melting of small-sized polymer particles is more than that of large-sized polymer particles. When two adjacent melted particles touch, they will fuse together. After the fusion of small particles, the porosity is relatively small, while after the fusion of large particles, the porosity is relatively large. Therefore, if the average particle size of the polymer particle raw materials decreases in a gradient along the thickness direction, then the porosity of the formed porous material also decreases in a gradient.

[0084] In some embodiments of the present invention, a method for preparing the porous material is provided, including the following steps:

[0085] Mix polymer particles with different particle sizes to obtain mixed particles;

[0086] Fill the mixed particles into the mold cavity, and use vibration to make the small-sized polymer particles move downward;

[0087] Heat to make adjacent polymer particles soften and fuse together, and obtain the porous material after cooling.

[0088] During the preparation process of the present invention, the shape of the cavity of the mold used matches the shape of the required porous material. By filling the polymer particles into the mold cavity, heating and cooling, a porous material with a specific shape is obtained.

[0089] Preferably, the particle size range of the polymer particles is 0.05 - 8 mm, including at least two different particle size groups, and the number of particle size groups is selected from 2, 3 or more.

[0090] Preferably, the D50 of the largest particle size group is 0.2 - 5 mm, and the D50 of the smallest particle size group is 0.05 - 2 mm.

[0091] Preferably, the ratio of the D50 of the largest particle size group to the D50 of the smallest particle size group ≥ 1.3. Further, the ratio is 1.5 - 10; more preferably 2 - 5.

[0092] Preferably, in the polymer particles, the proportion of the smallest particle size group with D50 of 0.05 - 2 mm is 10 - 30 wt%.

[0093] During the vibration process, the vibration frequency and time depend on the polymer material and particle size. By way of example, the vibration frequency is controlled to be from 2000 / min to 50000 / min, and the vibration time is from 1 s to 10 min. Preferably, the vibration frequency is controlled to be from 6000 / min to 45000 / min, and the vibration time is from 5 s to 5 min.

[0094] This is a trial-and-error method. In the early stage, the material after vibration needs to be sintered and then tested. After the product reaches a certain performance, continue with this frequency and vibration time.

[0095] The heating temperature depends on the softening point of the polymer, and the heating temperature should be higher than the softening point of the polymer. Preferably, the softening point of the polymer + 60°C ≥ heating temperature ≥ softening point of the polymer + 5°C. Further preferably, the softening point of the polymer + 50°C ≥ heating temperature ≥ softening point of the polymer + 10°C. The heating time is... The softening point is expressed by the Vicat softening temperature.

[0096] The heating time is from 30 s to 10 min to ensure the fusion of polymer particles.

[0097] In some embodiments of the present invention, the application of the porous material in reducing noise of the fan blade is also provided. The porous material is fixedly connected in the fan blade, the second surface of the porous material corresponds to the windward side of the fan blade, and the first surface corresponds to the leeward side of the fan blade.

[0098] The windward side of the fan blade is the side that directly pushes the air flow and bears a higher air pressure when the fan blade rotates, also known as the pressure surface, and the other side of the fan blade is the leeward side.

[0099] The fan blade refers to a mechanical component composed of a hub and several blades (as shown in Figure 2 A), which drives the blades to rotate through a motor to generate an air flow. The fan blade includes, but is not limited to, electric fan blades, blower fan blades, turbine fan blades, air blower fan blades, engine fan blades, radiator fan blades, compressor fan blades, propeller fan blades, etc.

[0100] The porous material can be in a sheet shape, and the sheet shape shows two-dimensional planar ductility in the physical structure, that is, the length and width are greater than the thickness, as shown in Figure 3 shown. The schematic diagram of the installation of the sheet-shaped porous material on the fan blade is as shown in Figure 2 (A).

[0101] As shown in Figure 2 shown, the porous material is fixedly connected in the fan blade. Figure 2 (B) is Figure 2(A) In the cross-sectional view along AA, it can be seen that the second surface of the porous material corresponds to the windward side of the fan blade, and the first surface corresponds to the leeward side of the fan blade. This means that the second surface of the porous material, as the windward side, is subject to a higher air pressure; the first surface, as the leeward side, is subject to a lower air pressure. The porous material is set in the fan blade, and the second surface corresponds to the windward side of the fan blade to achieve the effect of silencing and reducing noise.

[0102] When preparing the fan blade, a position for the porous material is reserved, and then the porous material is fixed to the fan blade by welding (such as ultrasonic welding). The surface where the porous material contacts the fan blade is called the contact surface.

[0103] The porous material is installed on the fan blade, and its shape changes with the structural structure of the fan blade, so the porous material can have different shapes and sizes. The plane figure can be a rectangle, square, parallelogram, triangle, circle, rhombus, octagon, etc., and the three-dimensional shape can be a cuboid, cube, sphere, tetrahedron, octahedron, dodecahedron, etc. The number of porous materials installed in the fan blade can be one, two, or more. Multiple pieces of porous materials can be installed on the same fan blade or on different fan blades.

[0104] The porous material of the present invention can reduce the noise caused by aerodynamics. The noise caused by aerodynamics is the noise generated by the disturbance of airflow when rotating equipment such as fan blades is in operation. In the fan blade working scene, when the fan blade is started, the gas (or liquid) is pushed forward by the fan blade, which drives a certain amount of airflow, and noise is generated when the airflow hits the fan blade. The noise caused by aerodynamics can increase with the increase of rotation speed, and may be affected by several other factors, such as atmospheric turbulence, wind direction and wind speed. The present invention can reduce the noise generated by aerodynamics to a certain extent by fixing the porous material in the fan blade.

[0105] Figure 4 A shows the typical interaction process between sound waves and matter. In the figure, Ei is the emitted sound energy, Er is the reflected sound energy, Ea is the sound energy absorbed by the material, and Et is the transmitted sound energy, Ei = Er + Ea + Et.

[0106] The present invention utilizes the micropores of porous materials to absorb the emitted sound energy and reduce the reflected sound energy, thereby playing the role of silencing and reducing noise. The specific noise reduction mechanism is: when the sound wave hits the porous material, the emitted sound energy Ei passes through the irregular holes, hits the micropore wall and rebounds multiple times (such as Figure 4 B), in this case, the sound energy is converted into heat energy. Since the sound energy is converted into heat energy, the sound will be effectively absorbed, Ea will increase, and Er and Et will decrease.

[0107] As described above, the first surface has the largest porosity. Therefore, the surface with the smallest porosity of the porous material corresponds to the windward surface of the fan blade, the surface with the largest porosity corresponds to the leeward surface of the fan blade, and the surface with the smallest porosity, as the windward surface, bears a higher air pressure. When a sound wave is emitted, the sound wave first enters the surface with the smallest porosity of the porous material. After entering, as the porosity gradually increases, the reflection path of the sound wave becomes longer, and the sound energy rapidly diffuses and is consumed in the larger pores, resulting in a reduction in the reflected sound energy, as Figure 5 shown.

[0108] Therefore, for the noise caused by aerodynamics, the sound absorption and noise reduction effect of the porous material with a gradient decrease in porosity along the thickness direction is better than that of the porous material with a relatively uniform porosity distribution. Further, the setting where the surface with the smallest porosity corresponds to the windward surface of the fan blade and the surface with the largest porosity corresponds to the leeward surface of the fan blade has a better sound absorption and noise reduction effect than the setting where the surface with the smallest porosity is the leeward surface.

[0109] In some embodiments of the present invention, a composite material is provided. The composite material includes a first porous material layer and a second porous material layer which are stacked up and down; the first porous material layer and the second porous material layer are made of the above-mentioned porous material, and the material hardness of the porous material in the first porous material layer < the material hardness of the porous material in the second porous material layer.

[0110] The first surface and the second surface of the porous material respectively constitute the first surface and the second surface of the first porous material layer and the second porous material layer;

[0111] The first porous material layer and the second porous material layer are stacked up and down, and the second surface of the first porous material layer and the first surface of the second porous material layer are in direct contact, as Figure 6 shown.

[0112] Preferably, an interfacial bond is formed between the first porous material layer and the second porous material layer through sintering or a binder.

[0113] Preferably, the thickness ratio of the first porous material layer to the second porous material layer is 1:0.1 - 1.

[0114] Both the first porous material layer and the second porous material layer are made of the above-mentioned porous material. The porosity settings of the first porous material layer and the second porous material layer can be the same or different. The materials used for the two porous materials are different, and the material hardness of the porous material in the first porous material layer is less than that of the porous material in the second porous material layer. Therefore, the texture of the first porous material layer is softer than that of the second porous material layer.

[0115] Preferably, the polymer raw material in the first porous material layer is a polymer with a Shore hardness (measured according to ASTM D2240 standard) ≤ 60D, and the polymer raw material in the second porous material layer is a polymer with a Shore hardness (measured according to ASTM D2240 standard) > 60D.

[0116] More preferably, the polymer raw material in the first porous material layer is a polymer with a Shore hardness of 10 - 60D, and even more preferably 20 - 50D.

[0117] More preferably, the polymer raw material in the second porous material layer is a polymer with a Shore hardness of 61 - 100D, further preferably 65 - 90D, and even more preferably 70 - 80D.

[0118] In some embodiments of the present invention, a method for preparing the composite material is provided, including the following steps:

[0119] S1. Prepare the first porous material layer:

[0121] Mix first polymer particles with different particle sizes to obtain first mixed particles;

[0122] Fill the first mixed particles into the mold cavity, and use vibration to make the first polymer particles with smaller particle sizes move downward;

[0123] Heat to soften and fuse adjacent first polymer particles together, and obtain the first porous material layer after cooling;

[0124] S2. Prepare the second porous material layer:

[0125] Mix second polymer particles with different particle sizes to obtain second mixed particles;

[0126] Fill the second mixed particles into the mold cavity, and use vibration to make the second polymer particles with smaller particle sizes move downward;

[0127] Heat to soften and fuse adjacent second polymer particles together, and obtain the second porous material layer after cooling;

[0128] S3. Consolidate the second porous material layer and the first porous material layer to form an integral structure;

[0129] The Shore hardness of the first polymer is less than that of the second polymer.

[0130] The particle size ranges of the first polymer particles and the second polymer particles are the same as those of the polymer particles described above.

[0131] Preferably, the Shore hardness of the first polymer ≤ 60D, and the Shore hardness of the second polymer > 60D.

[0132] Further preferably, the Shore hardness of the first polymer is 10 to 60 D, and more preferably 20 to 50 D.

[0133] Further preferably, the Shore hardness of the second polymer is 61 to 100 D, more preferably 65 to 90 D, and still more preferably 70 to 80 D.

[0134] Preferably, the first surface of the second porous material layer is consolidated with the second surface of the first porous material layer. The method for consolidating the second porous material layer and the first porous material layer can be by using an adhesive, sintering, etc.

[0135] When consolidating with an adhesive, directly coat the adhesive on the first surface of the second porous material layer and / or the second surface of the first porous material layer, and then consolidate.

[0136] When consolidating by sintering, press the first surface of the second porous material layer onto the second surface of the first porous - 14 - material layer, and the first surface and the second surface are welded under heating conditions.

[0137] In some embodiments of the present invention, an application of the composite material in noise reduction of a fan blade is provided. The composite material is fixedly connected in the fan blade.

[0138] The second surface of the second porous material layer of the composite material corresponds to the windward side of the fan blade, and the first surface of the first porous material layer of the composite material corresponds to the leeward side of the fan blade.

[0139] The composite material is fixedly connected in the fan blade. The second surface of the second porous material layer of the composite material corresponds to the windward side of the fan blade, and the first surface of the first porous material layer of the composite material corresponds to the leeward side of the fan blade. This means that the second surface of the second porous material layer of the composite material serves as the windward side of the fan blade and bears a higher air pressure; the first surface of the first porous material layer of the composite material serves as the leeward side of the fan blade and bears a lower air pressure.

[0140] When preparing the fan blade, reserve a position for the composite material, and then fixedly connect the composite material in the fan blade by welding (such as ultrasonic welding).

[0141] The hard porous material layer can provide support to the soft material, so that the composite material will not deform when facing a large airflow. When sound waves pass through the soft porous material, the soft material will deform (although the deformation is very slight) due to the vibration of the sound waves, and this deformation can consume the energy of the sound waves to achieve the purpose of sound absorption; the soft porous material can trap the sound waves in the microscopic openings, and thus the energy of the sound waves will be converted into heat to achieve the purpose of sound absorption; and the transmission of sound waves in the soft porous material will slow down and there will be more reflections, so the sound absorption is stronger. Generally speaking, the noise reduction effect of using the composite material is better.

[0142] The technical solution of the present invention will be further described and illustrated below through specific embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only used to assist in understanding the present invention and are not used for specific limitations of the present invention. Moreover, the accompanying drawings used in this article are only for better illustrating the content disclosed by the present invention and do not have a limiting effect on the protection scope. If there is no special description, the raw materials used in the embodiments of the present invention are all common raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0143] The information of the polymer particles used in the following examples and comparative examples is shown in Table 1:

[0144] Table 1

[0145]

[0146] In the following examples and comparative examples, the porosity is calculated as follows: First, a porous material with a known mass and apparent volume is immersed in water. After the water has fully penetrated, it is taken out and the mass is measured. From the measured mass, the volume of the water immersed in the porous material is calculated. This volume of water is regarded as the same as the pore volume of the porous material, and the porosity is calculated by the following formula (I).

[0147] Porosity % = (Volume of water) / (Apparent volume of porous material) × 100 (I).

[0148] Example 1

[0149] This example provides a porous material, which is a sheet-shaped cuboid with a porosity of 74%; the porous material includes a first surface and a second surface, and the thickness direction is the shortest normal direction from the first surface to the second surface. The porosity of the porous material decreases gradiently along the thickness direction; the material of the porous material is Polymer 1. When the porous material is placed horizontally, the porous material is cut along a horizontal plane perpendicular to the thickness direction to obtain Porous Material 1 including the first surface and Porous Material 2 including the second surface. This horizontal plane passes through the midpoint of the shortest normal from the first surface to the second surface. The "horizontal plane" is the plane perpendicular to the direction of the earth's gravity in the traditional sense. The porosity of Porous Material 1 including the first surface is 83%, and the porosity of Porous Material 2 including the second surface is 63%.

[0150] The preparation method of the porous material includes the following steps:

[0151] Polymer 1 with a large particle size D50 of 0.5 mm and Polymer 1 with a small particle size D50 of 0.25 mm are mixed according to a mass percentage ratio of 80%:20% to obtain mixed particles;

[0152] Fill the mixed particles into the mold cavity, and use vibration (vibration frequency: 10,000 / min, vibration time: 1 min) to make the polymer particles with small particle size move downward;

[0153] Heat (at 135 °C for 10 minutes) to soften and fuse adjacent polymer particles together, and obtain the porous material after cooling.

[0154] Example 2

[0155] This example provides a porous material, which has the same shape and size as that in Example 1, and the porosity is 80%; the porous material includes a first surface and a second surface, and the thickness direction is the shortest normal direction from the first surface to the second surface. The porosity of the porous material decreases in a gradient along the thickness direction; the material of the porous material is Polymer 2. When the porous material is placed horizontally, cut the porous material along a horizontal plane perpendicular to the thickness direction to obtain Porous Material 1 including the first surface and Porous Material 2 including the second surface. This horizontal plane passes through the midpoint of the shortest normal line from the first surface to the second surface. The "horizontal plane" is the plane perpendicular to the direction of the earth's gravity in the traditional sense. The porosity of Porous Material 1 including the first surface is 92%, and the porosity of Porous Material 2 including the second surface is 67%.

[0156] The preparation method of the porous material includes the following steps:

[0157] Mix Polymer 2 with a large particle size D50 of 1.0 mm and Polymer 2 with a small particle size D50 of 0.5 mm according to a mass percentage ratio of 75%:25% to obtain mixed particles;

[0158] Fill the mixed particles into the mold cavity, and use vibration (vibration frequency: 20,000 / min, vibration time: 40 s) to make the polymer particles with small particle size move downward;

[0159] Heat (at 135 °C for 12 minutes) to soften and fuse adjacent polymer particles together, and obtain the porous material after cooling.

[0160] Example 3

[0161] This embodiment provides a porous material with the same shape and size as in Embodiment 1, and a porosity of 68%; the porous material includes a first surface and a second surface, and the thickness direction is the shortest normal direction from the first surface to the second surface. The porosity of the porous material decreases in a gradient along the thickness direction; the material of the porous material is Polymer 3. When the porous material is placed horizontally, it is cut along a horizontal plane perpendicular to the thickness direction to obtain Porous Material 1 including the first surface and Porous Material 2 including the second surface. This horizontal plane passes through the midpoint of the shortest normal from the first surface to the second surface. The "horizontal plane" is the plane perpendicular to the direction of the earth's gravity in the traditional sense. The porosity of Porous Material 1 including the first surface is 82%, and the porosity of Porous Material 2 including the second surface is 52%.

[0162] The preparation method of the porous material includes the following steps:

[0163] Mix Polymer 3 with a large particle size D50 of 0.6 mm and Polymer 3 with a small particle size D50 of 0.2 mm in a mass percentage ratio of 70%:30% to obtain mixed particles;

[0164] Fill the mixed particles into the mold cavity, and use vibration (vibration frequency: 10,000 / min, vibration time: 2 min) to make the small particle size polymer particles move downward;

[0165] Heat (140 °C, 8 minutes) to soften and fuse adjacent polymer particles together, and obtain the porous material after cooling.

[0166] Embodiment 4

[0167] This embodiment provides a porous material with the same shape and size as in Embodiment 1, and a porosity of 52%; the porous material includes a first surface and a second surface, and the thickness direction is the shortest normal direction from the first surface to the second surface. The porosity of the porous material decreases in a gradient along the thickness direction; the material of the porous material is Polymer 4. When the porous material is placed horizontally, it is cut along a horizontal plane perpendicular to the thickness direction to obtain Porous Material 1 including the first surface and Porous Material 2 including the second surface. This horizontal plane passes through the midpoint of the shortest normal from the first surface to the second surface. The "horizontal plane" is the plane perpendicular to the direction of the earth's gravity in the traditional sense. The porosity of Porous Material 1 including the first surface is 62%, and the porosity of Porous Material 2 including the second surface is 42%.

[0168] The preparation method of the porous material includes the following steps:

[0169] Mix Polymer 4 with a large particle size D50 of 0.25 mm and Polymer 4 with a small particle size D50 of 0.1 mm in a mass percentage ratio of 85%:15% to obtain mixed particles;

[0170] Fill the mixed particles into the mold cavity, and use vibration (vibration frequency is 15000 / min, vibration time is 90 s) to make the polymer particles with small particle size move downward;

[0171] Heat (at 165 °C for 10 minutes) to soften and fuse adjacent polymer particles together, and the porous material is obtained after cooling.

[0172] Example 5

[0173] This example provides a composite material, which includes a first porous material layer and a second porous material layer arranged in an overlapping manner up and down; the thickness ratio of the first porous material layer to the second porous material layer is 1:0.2. The first porous material layer is the same as the porous material in Example 1 and has the same size. The second porous material layer is the same as the porous material in Example 3, but the thickness is 0.2 times that of the porous material in Example 3.

[0174] The composite material is prepared by the following preparation method:

[0175] S1. Prepare the first porous material layer: The method for preparing the first porous material layer is the same as that in Example 1.

[0176] S2. Prepare the second porous material layer: The method for preparing the first porous material layer is the same as that in Example 3.

[0177] S3. Press the first surface of the second porous material layer on the second surface of the first porous material layer, and heat (at 145 °C for 5 minutes) to weld the first surface of the second porous material layer and the second surface of the first porous material layer to form an integral structure.

[0178] Example 6

[0179] This example provides a composite material, which includes a first porous material layer and a second porous material layer arranged in an overlapping manner up and down; the thickness ratio of the first porous material layer to the second porous material layer is 1:0.3. The first porous material layer is the same as the porous material in Example 2 and has the same size. The second porous material layer is the same as the porous material in Example 4, but the thickness is 0.3 times that of the porous material in Example 4.

[0180] The composite material is prepared by the following preparation method:

[0182] S1. Prepare the first porous material layer: The method for preparing the first porous material layer is the same as that in Example 2.

[0183] S2. Prepare the second porous material layer: The method for preparing the first porous material layer is the same as that in Example 4.

[0184] S3. Press the first surface of the second porous material layer against the second surface of the first porous material layer, and weld the first surface of the second porous material layer and the second surface of the first porous material layer under heating (170 °C, 6 minutes) to form an integral structure.

[0185] Comparative Example 1

[0186] The difference between Comparative Example 1 and Example 1 is that a porous material is prepared using Polymer 1 with a large particle size D50 of 0.5 mm. The porosity of the prepared porous material is 82%.

[0187] Comparative Example 2

[0188] The difference between Comparative Example 2 and Example 1 is that a porous material is prepared using Polymer 1 with a small particle size D50 of 0.25 mm. The porosity of the prepared porous material is 68%.

[0189] Perform noise reduction tests on the porous materials prepared in Examples 1-6 and Comparative Examples 1-2. The specific method of the noise reduction test is as follows: First, place a solid solid (not a porous material) 10 mm away from the air outlet, set the air flow rate to 5 m 3 / h, and the pressure is 0.17 Mpa. When the air flow blows towards the solid, record the volume (A). The noise generator is placed 400 mm away from the air outlet. Then replace the solid with a porous material and record the volume (B) of the porous material in the same way. The noise reduction value is the difference in volume, that is, the volume of the solid (A) - the volume of the porous material (B). The specific test schematic diagram is as Figure 7 shown.

[0190] In one test process, the placement direction of the porous material is: the second surface of the porous materials in Examples 1-4 faces the air flow, and the first surface faces away from the air flow. The placement direction of the composite material is: the second surface of the second porous material layer of the composite materials in Examples 5-6 faces the air flow, and the first surface of the first porous material layer faces away from the air flow. The noise test results (represented by the noise reduction value 1) are shown in Table 2.

[0191] In another test process, the placement direction of the porous material is: the second surface of the porous materials in Examples 1-4 faces away from the air flow, and the first surface faces the air flow. The placement direction of the composite material is: the second surface of the second porous material layer of the composite materials in Examples 5-6 faces away from the air flow, and the first surface of the first porous material layer faces the air flow. The noise test results (represented by the noise reduction value 2) are shown in Table 2.

[0192] Table 2

[0193]

[0194] As can be seen from Table 2, the noise reduction performance of the porous materials in Examples 1-6 is overall better than that in Comparative Examples 1-2. Among them, in Examples 5-6, due to the use of composite materials, the noise reduction effect is better. Also, for Examples 1-4, when the second surface of the porous material faces the airflow, that is, the surface with a smaller porosity faces the airflow, the noise reduction effect is better than when the first surface of the porous material faces the airflow. For Examples 5-6, when the harder side of the composite material faces the airflow, it also has a better noise reduction effect compared to when the softer side faces the airflow.

[0195] Application Example 1

[0196] Find the position with the maximum back pressure of the fan blade, reserve space, and fix the sheet-shaped porous material of Example 1 in the fan blade of the outdoor unit of the air conditioner by ultrasonic welding. Moreover, the second surface of the porous material corresponds to the windward side of the fan blade, and the first surface corresponds to the leeward side of the fan blade.

[0197] Application Example 2

[0198] Find the position with the maximum back pressure of the fan blade, reserve space, and fix the sheet-shaped composite material of Example 5 in the fan blade of the outdoor unit of the air conditioner by ultrasonic welding. Moreover, the second surface of the second porous material layer of the composite material corresponds to the windward side of the fan blade, playing a role in noise reduction; the first surface of the first porous material layer of the composite material corresponds to the leeward side of the fan blade.

[0199] All aspects, embodiments, and features of the present invention should be considered illustrative in all respects and do not limit the present invention. The scope of the present invention is only defined by the claims. Without departing from the spirit and scope of the claimed present invention, those skilled in the art will understand other embodiments, modifications, and uses.

[0200] In the preparation method of the present invention, the order of each step is not limited to the listed order. For those of ordinary skill in the art, without creative efforts, the sequential changes of each step are also within the protection scope of the present invention. In addition, two or more steps or actions can be carried out simultaneously.

[0201] Finally, it should be noted that the specific embodiments described herein are only examples of the present invention and do not limit the implementation manners of the present invention. Those skilled in the technical field to which the present invention belongs can make various modifications or supplements to the described specific embodiments or use similar methods for substitution. It is not necessary and impossible to list all implementation manners here. And these obvious changes or variations derived from the essential spirit of the present invention still belong to the protection scope of the present invention. Interpreting them as any additional limitations is contrary to the spirit of the present invention.

Claims

1. A porous material, characterized in that, The porosity of the porous material is 30-90%; The porous material includes a first surface and a second surface, and the thickness direction is the shortest normal direction from the first surface to the second surface. The porosity of the porous material decreases gradiently along the thickness direction; The material of the porous material is a polymer.

2. The porous material according to claim 1, characterized in that, When the porous material is placed horizontally, the porous material is cut along a horizontal plane perpendicular to the thickness direction to obtain a porous material 1 including the first surface and a porous material 2 including the second surface. This horizontal plane passes through the midpoint of the shortest normal from the first surface to the second surface; The porosity of the porous material 1 including the first surface is 60-95%, and the porosity of the porous material 2 including the second surface is 20-72%. And the porosity ratio of the porous material 1 including the first surface to the porous material 2 including the second surface is ≥1.2; 3. A porous material according to claim 1 or 2, characterized in that, The polymer is a thermoplastic polymer; And / or, the polymer is one or more of polyethylene, polypropylene, rigid polyurethane, polyvinyl chloride, polyvinylidene fluoride, polyamide or nylon, polyacrylate, polyacrylonitrile, ethylene vinyl acetate, polystyrene, polyethylene terephthalate, polymethyl methacrylate, polytetrafluoroethylene, polycarbonate, polyethersulfone, polyetherimide, polyetheretherketone, polysulfone; 4. A porous material according to claim 1, characterized in that, The porous material is formed from polymer particle raw materials through a sintering process; In the porous material, the average particle size of the polymer particle raw materials used decreases gradiently along the thickness direction, and the decreasing direction is the same as the direction in which the porosity decreases; 5. The preparation method of the porous material according to claim 1, wherein, It includes the following steps: Mix polymer particles of different particle sizes to obtain mixed particles; Fill the mixed particles into the mold cavity, and use vibration to make the small-particle-size polymer particles move downward; Heat to soften and fuse adjacent polymer particles together, and obtain the porous material after cooling.

6. The preparation method according to claim 5, characterized in that, The particle size range of the polymer particles is 0.05-8 mm, and it includes at least two different particle-size groups.

7. The preparation method according to claim 6, characterized in that, The D50 of the largest particle-size group is 0.2-5 mm, the D50 of the smallest particle-size group is 0.05-2 mm, and the ratio of the D50 of the largest particle-size group to the D50 of the smallest particle-size group is ≥1.3; And / or, in the polymer particles, the proportion of the smallest particle-size group with D50 of 0.05-2 mm is 10-30 wt%; 8. The preparation method according to claim 5, characterized in that, The softening point of the polymer + 60°C ≥ the heating temperature ≥ the softening point of the polymer + 5°C.

9. The application of the porous material in reducing the noise of a fan blade according to claim 1, wherein, The porous material is fixedly connected in the fan blade. The second surface of the porous material corresponds to the windward surface of the fan blade, and the first surface corresponds to the leeward surface of the fan blade.

10. A composite material, characterized in that, The composite material includes a first porous material layer and a second porous material layer arranged overlapping up and down; the first porous material layer and the second porous material layer are made of the porous material described in claim 1, and the material hardness of the porous material in the first porous material layer < the material hardness of the porous material in the second porous material layer.

11. A composite material according to claim 10, characterized in that, The first surface and the second surface of the porous material respectively constitute the first surface and the second surface of the first porous material layer and the second porous material layer; The first porous material layer and the second porous material layer are arranged overlapping up and down, and the second surface of the first porous material layer and the first surface of the second porous material layer are in direct contact.

12. A composite material according to claim 10, characterized in that, The thickness ratio of the first porous material layer to the second porous material layer is 1:0.1 - 1; The polymer raw material in the first porous material layer is a polymer with a Shore hardness ≤ 60D, and the polymer raw material in the second porous material layer is a polymer with a Shore hardness > 60D.

13. A method for preparing a composite material according to claim 10, characterized in that, It includes the following steps: S1. Prepare the first porous material layer: Mix first polymer particles with different particle sizes to obtain first mixed particles; Fill the first mixed particles into the mold cavity, and use vibration to make the first polymer particles with small particle sizes move downward; Heat to soften and fuse adjacent first polymer particles together, and obtain the first porous material layer after cooling; S2. Prepare the second porous material layer: Mix second polymer particles with different particle sizes to obtain second mixed particles; Fill the second mixed particles into the mold cavity, and use vibration to make the second polymer particles with small particle sizes move downward; Heat to soften and fuse adjacent second polymer particles together, and obtain the second porous material layer after cooling; S3. Consolidate the second porous material layer and the first porous material layer to form an integral structure; The Shore hardness of the first polymer is less than that of the second polymer.

14. The preparation method according to claim 13, wherein The Shore hardness of the first polymer ≤ 60D, and the Shore hardness of the second polymer > 60D.

15. The preparation method according to claim 13, wherein Consolidate the first surface of the second porous material layer and the second surface of the first porous material layer.

16. The application of the composite material according to claim 10 in the noise reduction of the fan blade, characterized in that, The composite material is fixedly connected in the fan blade, The second surface of the second porous material layer of the composite material corresponds to the windward surface of the fan blade, and the first surface of the first porous material layer of the composite material corresponds to the leeward surface of the fan blade.

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