Double-layer filter element structure and air permeability detection method

Abstract

The application provides a double-layer filter core structure, a preparation method and a gas permeability detection method, belongs to the technical field of filtration, and comprises a double-layer filter main body and an outer cladding layer; the outer cladding layer is arranged around the outer periphery of the double-layer filter main body, a plurality of first combination parts are arranged between the double-layer filter main body and the outer cladding layer and are embedded with each other; the double-layer filter main body comprises a filter layer and a support layer, the filter layer and the support layer are arranged in sequence from top to bottom, and the second combination parts are arranged between the filter layer and the support layer and are embedded with each other. The double-layer filter core structure can avoid the edge of the double-layer filter main body from falling off or cracking. The structural strength of the double-layer filter main body and the outer cladding layer can be increased, and the outer cladding layer and the double-layer filter main body can be prevented from being separated. The combination strength between the filter layer and the support layer can be improved, and the combination surface of the double-layer filter core can be prevented from being separated.

Description

Technical Field

[0001] This invention belongs to the field of filtration technology, and more specifically, relates to a double-layer filter structure and a method for testing air permeability. Background Technology

[0002] Currently, in the microelectronics and semiconductor industry, everything from large-scale equipment, raw materials, and chemicals to smaller components like pipes, valves, and filter elements is primarily imported. Because these industries have stringent requirements for material purity and cleanliness, generally requiring at least 9N purity (i.e., 99.9999999%), this poses a challenge to domestically produced filter elements.

[0003] In the semiconductor industry, many specialty gases are used, such as F2, Cl2, AsH3, CF4, NH3, SiF4, and NOx. These gases must pass through filter elements before reaching the reaction chamber to intercept particles that detach due to vibration or airflow impact. These filters are typically composed of gasket filters and point-of-use (POU) filters. Because of the stability, corrosion resistance, and ease of installation with metal pipelines, these filter elements are all made of metal, commonly 316L stainless steel, pure nickel, and Hastelloy.

[0004] The semiconductor industry typically requires filter elements to achieve an LRV9 filtration efficiency. Currently, foreign filter element products can achieve LRV9 filtration efficiency for 3nm particles while maintaining a high flow rate under operating conditions. However, due to limitations in raw materials and manufacturing processes, domestically produced conventional filter elements and membrane filtration products cannot achieve 3nm filtration accuracy at the same flow rate, thus failing to meet the LRV9 filtration efficiency requirement. Some conventional filter cartridges can achieve 3nm filtration accuracy but cannot meet the required flow rate.

[0005] Dual-layer filter elements offer high filtration accuracy and good air permeability, while the thickness of the support layer can be adjusted to ensure mechanical strength, thus meeting both filtration accuracy and high flow rate requirements. However, the significant difference in particle size between the filter layer and the support layer in a dual-layer filter element can easily lead to defects such as cracking, edge chipping, and insufficient bonding strength at the interface between the two layers during sintering. To prevent filter element failure and ensure strength under high-pressure conditions, this patent employs a special method to manufacture the dual-layer filter and proposes a method for characterizing the bonding strength between the filter layer and the support layer by testing the air permeability of the filter. Summary of the Invention

[0006] The purpose of this invention is to provide a double-layer filter structure that avoids defects such as cracking, edge chipping, and insufficient strength of the bonding surface between the two layers during sintering, thereby preventing double-layer filter failure and ensuring strength under high pressure conditions.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: to provide a double-layer filter element structure, comprising a double-layer filter body and an outer layer;

[0008] The outer layer surrounds the outer periphery of the double-layer filter body, and a plurality of first joints are interlocked between the double-layer filter body and the outer layer.

[0009] The dual-layer filter body includes a filter layer and a support layer, which are arranged sequentially from top to bottom, and a second joint is provided between the filter layer and the support layer for mutual embedding.

[0010] In one possible implementation, the first joint includes a protruding rib extending outward along the double-layer filter body. The width of the cross-section of the protruding rib decreases sequentially from the inside to the outside. The outer end of the protruding rib has an arc-shaped outer angle, and the two sides of the inner end of the protruding rib are respectively provided with arc-shaped inner angles. The diameter of the arc-shaped inner angle is larger than the diameter of the arc-shaped outer angle.

[0011] In one possible implementation, the second joint includes a first wavy surface disposed on the lower end face of the filter layer and a second wavy surface disposed on the upper end face of the support layer, wherein the first wavy surface and the second wavy surface are adapted to fit each other.

[0012] In one possible implementation, the second joint includes a plurality of straight through grooves sequentially and parallelly formed on the upper end face of the support layer and a plurality of straight protrusions sequentially and parallelly formed on the lower end face of the filter layer, wherein the plurality of straight protrusions are fitted one-to-one into the plurality of straight through grooves.

[0013] The beneficial effects of the dual-layer filter element structure provided by this invention are as follows: Compared with the prior art, by providing an outer cladding layer around the periphery of the dual-layer filter body, the structural strength of the edge of the dual-layer filter body can be increased, preventing edge chipping or cracking. The edge of the dual-layer filter body is typically a welding area or a press-fit area, and does not affect the overall filtration effect of the dual-layer filter element. Multiple interlocking first joints are provided between the dual-layer filter body and the outer cladding layer, which increase the structural strength of both and prevent the outer cladding layer from detaching from the dual-layer filter body. Furthermore, interlocking second joints are provided between the filter layer and the support layer constituting the dual-layer filter body, which enhances the bonding strength between the filter layer and the support layer, preventing separation of the bonding surfaces of the dual-layer filter element.

[0014] This invention also provides a method for preparing a double-layer filter element, comprising the following steps:

[0015] S1: Pressing support layer: First, the annular middle mold is fitted onto the lower mold, and then the metal powder of the first particle size is added to the bottom layer of the inner cavity of the annular middle mold. The upper mold head is driven by a hydraulic press to press the metal powder of the first particle size. During pressing, the forming pressure is controlled to be 20MPa~100MPa, and the holding time is 1s~10s.

[0016] Among them, the inner circumferential of the middle mold has a cavity structure for forming multiple first joints, and the mold head of the upper mold has a cavity structure for forming second joints.

[0017] S2: Pressing the filter layer: After the upper mold is raised, replace the mold head with a horizontal surface, and then add the metal powder of the second particle size into the inner cavity of the annular middle mold and place it on the support layer of the pressing. The upper mold head is driven by the hydraulic press to press the metal powder of the second particle size. During pressing, the forming pressure is controlled at 150MPa~300MPa and the holding time is 5s~15s.

[0018] S3: Pressing the outer coating: After the upper mold is raised, replace it with a stepped mold head with the same cross-sectional shape as the annular middle mold, remove the annular middle mold, add metal powder of the third particle size into the space originally occupied by the annular middle mold, and press the metal powder of the third particle size by driving the upper mold head through the hydraulic press. During pressing, control the forming pressure to 150MPa~200MPa and the holding time to 10s~20s.

[0019] S4: The double-layer filter sheet is placed in a vacuum furnace under clamping conditions for sintering at a temperature of 900℃~1200℃ and a holding time of 3h~5h to produce the double-layer filter element structure.

[0020] Among them, the first particle size > the second particle size > the third particle size.

[0021] The beneficial effects of the dual-layer filter element preparation method provided by this invention are as follows: Compared with the prior art, the method sequentially completes the pressing of the support layer, the pressing of the filter layer, and the pressing of the outer layer, and finally completes the preparation of the dual-layer filter element through overall sintering. Specifically, the particle size of the support layer, the filter layer, and the outer layer decreases sequentially; that is, the porosity of the support layer, the filter layer, and the outer layer decreases sequentially, resulting in a sequential decrease in air permeability. In principle, the air permeability of the outer layer can approach zero, allowing gas to pass only through the filter layer and the support layer, thereby completing gas filtration. This invention provides a dual-layer filter element preparation method that can prepare dual-layer filter elements with a support layer, a filter layer, and an outer layer, avoiding defects such as cracking, edge chipping, and insufficient strength at the bonding surface between the support layer and the filter layer during sintering, thus preventing dual-layer filter element failure and ensuring strength under high-pressure conditions.

[0022] This invention also provides a method for testing the air permeability of a double-layer filter element, used to test the structure of the double-layer filter element, comprising the following steps:

[0023] a: Select an inlet pipe and an outlet pipe with a diameter of D, press the double-layer filter element between the inlet pipe and the outlet pipe, introduce clean nitrogen gas at constant pressure into the inlet pipe, record the gas flow rate as P1, and detect the pressure difference between the inlet pipe and the outlet pipe as S1.

[0024] b: After maintaining ventilation for at least 5 minutes and keeping the gas flow rate P1 and pressure difference S1 constant, calculate the forward permeability K. 正 K 正 =P1 / [S1*π*(D / 2) 2 ];

[0025] c: Stop introducing clean nitrogen into the intake pipe, then introduce clean nitrogen at constant pressure into the exhaust pipe, record the gas flow rate P2, and detect the pressure difference between the exhaust pipe and the outlet pipe as S2.

[0026] d: After maintaining ventilation for at least 5 minutes, and keeping the gas flow rate P2 and pressure difference S2 constant, calculate the reverse permeability K. 反 K 反 =P2 / [S2*π*(D / 2) 2 ];

[0027] Where, △K=|K 正 -K 反 |, if △K=0, or △K≤5%K 正 / 5%K 反 If the air permeability test result of the double-layer filter element is qualified, it means that the air permeability test result is qualified; if ΔK > 5%K 正 / 5%K 反 If the result is negative, it indicates that the air permeability of the double-layer filter element is not up to standard.

[0028] In one possible implementation, after step d, the double-layer filter element that has passed the air permeability test is longitudinally cut for re-inspection. The thickness of the bonding layer between the filter layer and the support layer is measured as h. If 0.2mm≤h≤0.5mm, it indicates that the double-layer filter element initially meets the bonding strength requirements; if h<0.2mm, it indicates that the double-layer filter element does not meet the bonding strength requirements; if h>0.5mm, it indicates that the filtration accuracy of the double-layer filter element is insufficient or the air permeability is inadequate.

[0029] In one possible implementation, the number of double-layer filter elements that pass the air permeability test is not less than one for every ten. Each double-layer filter element is cut at least twice in parallel longitudinal direction using a wire cutting method to divide it into at least three test segments, and at least one cut passes through the axis of the double-layer filter element.

[0030] In one possible implementation, a pull-out test is performed on the double-layer filter element that initially meets the bonding strength requirements, according to the method of ASTM D4541. If the filter layer and the support layer are not pulled apart, it indicates that the double-layer filter element meets the bonding strength requirements; if the filter layer is pulled apart, it indicates that the double-layer filter element does not meet the bonding strength requirements.

[0031] In one possible implementation, the double-layer filter element that initially meets the bonding strength requirements is bent, and the bending radius is set to S, where S takes the value of π / 3 to π / 2. If the filter layer and support layer in the middle area of ​​the double-layer filter element do not separate or the separation width is less than 1 / 5 of the diameter, it indicates that the double-layer filter element meets the bonding strength requirements; if the separation width of the filter layer and support layer in the middle area of ​​the double-layer filter element is greater than or equal to 1 / 5 of the diameter, it indicates that the double-layer filter element does not meet the bonding strength requirements.

[0032] The beneficial effect of the air permeability testing method for a double-layer filter element provided by this invention is that, compared with the prior art, by pressing the double-layer filter element between the inlet and outlet pipes and passing clean nitrogen gas at constant pressure in both the forward and reverse directions, the forward air permeability K is calculated. 正 And the reverse air permeability K 反 Using K 正 and K 反 The obtained absolute difference ΔK, ΔK is compared with K respectively. 正 and K 反 The air permeability of the double-layer filter element is compared to determine whether it meets the requirements. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a top view of a double-layer filter structure provided in the first embodiment of the present invention;

[0035] Figure 2 This is a cross-sectional view of a double-layer filter structure provided in the first embodiment of the present invention;

[0036] Figure 3 This is a top view of a double-layer filter structure provided in a second embodiment of the present invention;

[0037] Figure 4 This is a cross-sectional view of a double-layer filter structure provided in a second embodiment of the present invention;

[0038] Figure 5A flowchart of a method for preparing a double-layer filter element provided by the present invention;

[0039] Figure 6 The flowchart illustrates a method for testing the air permeability of a double-layer filter element provided by this invention.

[0040] Explanation of reference numerals in the attached figures:

[0041] 1. Filter layer; 2. Support layer; 3. Outer layer; 4. First joint; 5. Second joint. Detailed Implementation

[0042] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0043] Unless otherwise expressly defined, the use of terms such as "first," "second," or "third" in the claims, description, and accompanying drawings of this invention is for distinguishing different objects and not for describing a specific order.

[0044] Unless otherwise expressly defined, in the claims, description, and accompanying drawings of this invention, the use of directional terms such as "center," "lateral," "longitudinal," "horizontal," "vertical," "top," "bottom," "inner," "outer," "upper," "lower," "front," "rear," "left," "right," "clockwise," "counterclockwise," "high," and "low" to indicate orientation or positional relationships is based on the orientation and positional relationships shown in the accompanying drawings and is only for the convenience of describing the invention and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the specific scope of protection of this invention.

[0045] Please see Figure 1 and Figure 4 The present invention will now describe a dual-layer filter element structure. A dual-layer filter element structure includes a dual-layer filter body and an outer layer 3; the outer layer 3 surrounds the outer periphery of the dual-layer filter body, and a plurality of mutually embedded first connecting portions 4 are provided between the dual-layer filter body and the outer layer 3; the dual-layer filter body includes a filter layer 1 and a support layer 2, which are arranged sequentially from top to bottom, and mutually embedded second connecting portions 5 are provided between the filter layer 1 and the support layer 2.

[0046] This invention provides a dual-layer filter element structure. Compared with existing technologies, by providing an outer cladding layer 3 around the periphery of the dual-layer filter body, the structural strength of the edges of the dual-layer filter body can be increased, preventing edge chipping or cracking. The edges of the dual-layer filter body are typically welding or press-fit areas, and do not affect the overall filtration effect of the dual-layer filter element. Multiple interlocking first joints 4 are provided between the dual-layer filter body and the outer cladding layer 3, increasing the structural strength of both and preventing the outer cladding layer 3 from detaching from the dual-layer filter body. Furthermore, interlocking second joints 5 are provided between the filter layer 1 and the support layer 2 constituting the dual-layer filter body, enhancing the bonding strength between the filter layer 1 and the support layer 2 and preventing separation of the bonding surfaces of the dual-layer filter element.

[0047] Please see Figure 1 and Figure 3 The first joint 4 includes a protruding ridge extending outward along the double-layer filter body. The width of the cross-section of the ridge decreases gradually from the inside to the outside. The outer end of the ridge has an arc-shaped outer angle, and the inner ends of the ridge each have an arc-shaped inner angle. The diameter of the arc-shaped inner angle is larger than the diameter of the arc-shaped outer angle. The depth to which the ridge extends into the outer cladding layer 3 is greater than half the thickness of the outer cladding layer 3. Multiple ridges are evenly distributed circumferentially around the outer periphery of the double-layer filter body, which can comprehensively improve the bonding strength between the double-layer filter body and the outer cladding layer 3. The ridge with an arc-shaped outer angle at the outer end and an arc-shaped inner angle at the inner end makes it easier for the double-layer filter body and the outer cladding layer 3 to bond, minimizing the occurrence of bonding gaps.

[0048] In the first embodiment, please refer to Figure 2 The second joint 5 includes a first wavy surface disposed on the lower end face of the filter layer 1 and a second wavy surface disposed on the upper end face of the support layer 2. The first and second wavy surfaces are adapted to fit together. The mutual adaptation of the first and second wavy surfaces can increase the bonding strength between the filter layer 1 and the support layer 2. At the same time, when the airflow passes through the joint surface of the filter layer 1 and the support layer 2, the airflow direction can be transmitted radially along the wavy surface, forming a transmission path that combines dispersion and convergence. The airflow can be disturbed when passing through the joint surface of the filter layer 1 and the support layer 2, reducing the possibility of particulate matter clogging the filter layer 1 and the support layer 2.

[0049] In the second embodiment, please refer to Figure 4The second connecting part 5 includes a plurality of straight through grooves sequentially and parallelly formed on the upper end face of the support layer 2 and a plurality of straight protrusions sequentially and parallelly formed on the lower end face of the filter layer 1. The multiple straight protrusions are fitted one-to-one into the multiple straight through grooves. Compared to the first embodiment, the method of using straight protrusions and straight through grooves in the second embodiment provides a better effect in preventing lateral misalignment and delamination. Preferably, the width of the straight through grooves is 0.5mm to 2mm, the depth is 0.1mm to 1mm, and the spacing is 2mm to 5mm. The specific dimensions are adjusted according to the thickness and diameter of the filter layer 1 and the support layer 2, and will not be elaborated further here.

[0050] This invention also provides a method for preparing a double-layer filter element, comprising the following steps:

[0051] S1: Pressing support layer 2: First, the annular middle mold is fitted onto the lower mold, and then the metal powder of the first particle size is added to the bottom layer of the inner cavity of the annular middle mold. The upper mold head is driven by a hydraulic press to press the metal powder of the first particle size. During pressing, the forming pressure is controlled to be 20MPa~100MPa, and the holding time is 1s~10s.

[0052] Among them, the inner circumferential of the middle mold has a cavity structure for forming multiple first joints 4, and the mold head of the upper mold has a cavity structure for forming second joints 5.

[0053] S2: Pressing filter layer 1: After the upper mold is raised, replace the mold head with a horizontal surface, and then add the metal powder of the second particle size into the inner cavity of the annular middle mold and place it on the support layer 2 of the pressing. The upper mold head is driven by the hydraulic press to press the metal powder of the second particle size. During pressing, the forming pressure is controlled to be 150MPa~300MPa and the holding time is 5s~15s.

[0054] S3: Pressing the outer layer 3: After the upper mold is raised, replace it with a stepped mold head with the same cross-sectional shape as the annular middle mold, remove the annular middle mold, add metal powder of the third particle size into the space originally occupied by the annular middle mold, and press the metal powder of the third particle size by driving the upper mold head through the hydraulic press. During pressing, control the forming pressure to be 150MPa~200MPa and the holding time to be 10s~20s.

[0055] S4: The double-layer filter sheet is placed in a vacuum furnace under clamping conditions for sintering at a temperature of 900℃~1200℃ and a holding time of 3h~5h, to produce a double-layer filter element structure as described in any one of claims 1-4.

[0056] Among them, the first particle size > the second particle size > the third particle size.

[0057] This invention provides a method for preparing a double-layer filter element. Compared with existing technologies, this method sequentially presses the support layer 2, the filter layer 1, and the outer layer 3, and finally completes the preparation of the double-layer filter element through overall sintering. The particle size of the support layer 2, the filter layer 1, and the outer layer 3 decreases sequentially. In other words, the porosity of the support layer 2, the filter layer 1, and the outer layer 3 decreases sequentially, resulting in a sequential decrease in air permeability. In principle, the air permeability of the outer layer 3 can approach zero, allowing gas to pass only through the filter layer 1 and the support layer 2, thus completing gas filtration. This invention provides a method for preparing a double-layer filter element that can produce a double-layer filter element with a support layer 2, a filter layer 1, and an outer layer 3. It avoids defects such as cracking, edge chipping, and insufficient strength at the bonding surface between the support layer 2 and the filter layer 1 during sintering, preventing double-layer filter element failure and ensuring strength under high-pressure conditions.

[0058] This invention further provides a method for testing the air permeability of a double-layer filter element, used to test the double-layer filter element structure as described in any one of claims 1-4, characterized by comprising the following steps:

[0059] a: Select an inlet pipe and an outlet pipe with a diameter of D, press the double-layer filter element between the inlet pipe and the outlet pipe, introduce clean nitrogen gas at constant pressure into the inlet pipe, record the gas flow rate as P1, and detect the pressure difference between the inlet pipe and the outlet pipe as S1.

[0060] b: After maintaining ventilation for at least 5 minutes and keeping the gas flow rate P1 and pressure difference S1 constant, calculate the forward permeability K. 正 K 正 =P1 / [S1*π*(D / 2) 2 ];

[0061] c: Stop introducing clean nitrogen into the intake pipe, then introduce clean nitrogen at constant pressure into the exhaust pipe, record the gas flow rate P2, and detect the pressure difference between the exhaust pipe and the outlet pipe as S2.

[0062] d: After maintaining ventilation for at least 5 minutes, and keeping the gas flow rate P2 and pressure difference S2 constant, calculate the reverse permeability K. 反 K 反 =P2 / [S2*π*(D / 2) 2 ];

[0063] Where, △K=|K 正 -K 反 |, if △K=0, or △K≤5%K 正 / 5%K 反 If the air permeability test result of the double-layer filter element is qualified, it means that the air permeability test result is qualified; if ΔK > 5%K 正 / 5%K 反If the result is negative, it indicates that the air permeability of the double-layer filter element is not up to standard.

[0064] This invention provides a method for testing the air permeability of a double-layer filter element. Compared with existing technologies, this method involves pressing the double-layer filter element between the inlet and outlet pipes, and then passing clean nitrogen gas at constant pressure in both forward and reverse directions to calculate the forward air permeability K. 正 And the reverse air permeability K 反 The absolute difference ΔK obtained using Kpositive and Knegative is compared with Kpositive. 正 and K 反 The air permeability of the double-layer filter element is compared to determine whether it meets the requirements.

[0065] After step d, for double-layer filter elements that pass the air permeability test, a longitudinal cut is performed for re-inspection. The thickness h of the bonding layer between filter layer 1 and support layer 2 is measured. If 0.2mm ≤ h ≤ 0.5mm, it indicates that the initial double-layer filter element meets the bonding strength requirements; if h < 0.2mm, it indicates that the double-layer filter element does not meet the bonding strength requirements; if h > 0.5mm, it indicates that the filtration accuracy or air permeability of the double-layer filter element is insufficient. By detecting the thickness h of the bonding layer between filter layer 1 and support layer 2, the bonding strength of double-layer filter elements that pass the air permeability test is re-inspected to ensure that they meet the requirements. At the same time, the filtration accuracy and air permeability of the double-layer filter element are further confirmed to ensure that its air permeability meets the requirements and its lifespan meets the usage requirements.

[0066] Specifically, for every ten double-layer filter elements that pass the air permeability test, at least one should be randomly selected for inspection to ensure that the sampled products cover as many products as possible. Each inspected double-layer filter element should be cut at least twice in parallel longitudinal direction using a wire cutting method to divide it into at least three test segments, with at least one cut passing through the axis of the double-layer filter element. This regional testing method ensures more accurate and effective test results.

[0067] The first verification method involves conducting a pull-out test on the double-layer filter element that initially meets the bonding strength requirements, according to ASTM D4541. If the filter layer and support layer are not pulled apart, the double-layer filter element meets the bonding strength requirements; if the filter layer is pulled apart, the double-layer filter element does not meet the bonding strength requirements. Furthermore, based on the first verification method, the bonding strength between the support layer and filter layer is further verified by checking their lateral bonding strength. The pull-out force is set to N, and the thickness of the smaller of the support layer and filter layer is set to L. N = k * L, where k is the pull-out coefficient. Generally, the value of k is affected by the material and particle size of the metal powder, and is typically between 0.2 and 0.5. With the support layer fixed, the filter layer is pulled laterally. If there is no lateral relative displacement between the filter layer and support layer, the double-layer filter element meets the bonding strength requirements; if the filter layer shifts laterally relative to the support layer, the double-layer filter element does not meet the bonding strength requirements.

[0068] The second verification method is as follows: The double-layer filter element that initially meets the bonding strength requirements is bent. The bending radius is set to S, with S ranging from π / 3 to π / 2. When bending the double-layer filter element, the bending should be slow and gentle. If the filter layer and support layer near the middle of the double-layer filter element do not separate or the separation width is less than 1 / 5 of the diameter, then the double-layer filter element meets the bonding strength requirements. If the separation width of the filter layer and support layer near the middle of the double-layer filter element is greater than or equal to 1 / 5 of the diameter, then the double-layer filter element does not meet the bonding strength requirements.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A double-layer filter element structure, characterized in that, It includes a dual-layer filter body and an outer layer (3); The outer layer (3) surrounds the outer periphery of the double-layer filter body, and a plurality of first joints (4) are provided between the double-layer filter body and the outer layer (3). The dual-layer filter body includes a filter layer (1) and a support layer (2), the filter layer (1) and the support layer (2) are arranged sequentially from top to bottom, and a second joint (5) is provided between the filter layer (1) and the support layer (2) for mutual embedding; A method for preparing a dual-layer filter element structure includes the following steps: S1: Pressing support layer (2): First, the annular middle mold is fitted onto the lower mold, and then the metal powder of the first particle size is added to the bottom layer of the inner cavity of the annular middle mold. The upper mold head is driven by the hydraulic press to press the metal powder of the first particle size. During pressing, the forming pressure is controlled to be 20MPa~100MPa, and the holding time is 1s~10s. Among them, the inner circumferential of the middle mold has a cavity structure for forming multiple first joints (4), and the mold head of the upper mold has a cavity structure for forming second joints (5). S2: Pressing the filter layer (1): After the upper mold is raised, replace the mold head with a horizontal surface, and then add the metal powder of the second particle size into the inner cavity of the annular middle mold and place it on the support layer (2) of the pressing. The upper mold head is driven by the hydraulic press to press the metal powder of the second particle size. During pressing, the forming pressure is controlled to be 150MPa~300MPa and the holding time is 5s~15s. S3: Pressing the outer layer (3): After the upper mold is raised, replace it with a stepped mold head with the same cross-sectional shape as the annular middle mold, remove the annular middle mold, add metal powder of the third particle size into the space originally occupied by the annular middle mold, and press the metal powder of the third particle size by driving the upper mold head through the hydraulic press. During pressing, control the molding pressure to be 150MPa~200MPa and the holding time to be 10s~20s. S4: The double-layer filter sheet is placed in a vacuum furnace under clamping conditions for sintering at a temperature of 900℃~1200℃ and a holding time of 3h~5h to form a double-layer filter element structure. Among them, the first particle size > the second particle size > the third particle size.

2. The double-layer filter structure as described in claim 1, characterized in that, The first joint (4) includes a protruding rib extending outward along the double-layer filter body. The width of the cross-section of the protruding rib decreases from the inside to the outside. The outer end of the protruding rib has an arc-shaped outer angle. Arc-shaped inner angles are respectively provided on both sides of the inner end of the protruding rib. The diameter of the arc-shaped inner angle is greater than the diameter of the arc-shaped outer angle.

3. The double-layer filter structure as described in claim 1, characterized in that, The second joint (5) includes a first wave surface disposed on the lower end face of the filter layer (1) and a second wave surface disposed on the upper end face of the support layer (2), wherein the first wave surface and the second wave surface are adapted to fit each other.

4. The double-layer filter structure as described in claim 1, characterized in that, The second connecting part (5) includes a plurality of straight through grooves that are sequentially and parallelly opened on the upper end face of the support layer (2) and a plurality of straight protrusions that are sequentially and parallelly arranged on the lower end face of the filter layer (1). The plurality of straight protrusions are fitted into the plurality of straight through grooves one by one.

5. A method for preparing a double-layer filter element, characterized in that, Includes the following steps: S1: Pressing support layer (2): First, the annular middle mold is fitted onto the lower mold, and then the metal powder of the first particle size is added to the bottom layer of the inner cavity of the annular middle mold. The upper mold head is driven by the hydraulic press to press the metal powder of the first particle size. During pressing, the forming pressure is controlled to be 20MPa~100MPa, and the holding time is 1s~10s. Among them, the inner circumferential of the middle mold has a cavity structure for forming multiple first joints (4), and the mold head of the upper mold has a cavity structure for forming second joints (5). S2: Pressing the filter layer (1): After the upper mold is raised, replace the mold head with a horizontal surface, and then add the metal powder of the second particle size into the inner cavity of the annular middle mold and place it on the support layer (2) of the pressing. The upper mold head is driven by the hydraulic press to press the metal powder of the second particle size. During pressing, the forming pressure is controlled to be 150MPa~300MPa and the holding time is 5s~15s. S3: Pressing the outer layer (3): After the upper mold is raised, replace it with a stepped mold head with the same cross-sectional shape as the annular middle mold, remove the annular middle mold, add metal powder of the third particle size into the space originally occupied by the annular middle mold, and press the metal powder of the third particle size by driving the upper mold head through the hydraulic press. During pressing, control the molding pressure to be 150MPa~200MPa and the holding time to be 10s~20s. S4: The double-layer filter sheet is placed in a vacuum furnace under clamping conditions for sintering at a temperature of 900℃~1200℃ and a holding time of 3h~5h to produce the double-layer filter element structure as described in claim 1. Among them, the first particle size > the second particle size > the third particle size.

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