Powder hollowness grading device and method based on terminal settling velocity difference

Abstract

The invention relates to the field of powder grading, in particular to a powder hollowness grading device and method based on terminal settling velocity difference. The device comprises a feeding unit used for supplying powder; the dispersion conveying unit comprises a conveying channel and two fan blade rotating devices, the conveying channel is obliquely arranged downwards from left to right and used for receiving the powder supplied by the feeding unit and allowing the powder to slide down along the conveying channel, and fan blades of the two fan blade rotating devices are embedded in the conveying channel side by side in the front-back direction; the airflow grading unit comprises an air cavity and an air outlet device, the air cavity is obliquely arranged upwards from left to right, an air outlet is formed in the upper end of the air cavity, an air inlet is formed in the lower end of the air cavity, the air outlet directly faces an outlet in the lower end of the conveying channel, and the air outlet device is used for blowing air to the air inlet of the air cavity; and the collecting unit is used for collecting the powder graded by the airflow grading unit. Accurate grading of the hollowness degree of the powder can be achieved based on the density difference, and the purity of the target solid powder is improved.

Description

Technical Field

[0001] This invention relates to the field of powder classification, and specifically to a powder hollowness classification device and method based on the difference in terminal settling velocity. Background Technology

[0002] In the preparation and downstream applications of powder materials, high-performance metal powders such as nickel-based alloy powders, stainless steel powders, and titanium alloy powders, as well as some ceramic and food powders, are often produced using technologies such as water vapor atomization, plasma atomization, and centrifugal atomization. During these processes, due to factors such as melt breakage, gas entrainment, and solidification shrinkage, a certain proportion of hollow powder inevitably mixes into the finished powder. The closed or semi-closed pore structure inside hollow powder particles results in a significantly lower apparent density than solid powders with the same composition and similar particle size.

[0003] The presence of hollow pasta poses a serious challenge to powder performance and subsequent applications. For example, in applications such as powder spraying and molding, the presence of hollow pasta can lead to decreased powder flowability and uneven molding density, which in turn affects the mechanical properties, density and surface quality of the final product. In the food processing field, the mixing of hollow pasta and solid pasta can lead to inconsistent cooking and maturation times, affecting the stability of product quality.

[0004] For powder classification based on density differences, the most traditional and widely used method is gravity sedimentation. Its basic principle is that in a horizontal airflow field, the ratio of drag force to gravity is higher for lower-density powders (hollow powders), thus they are blown to greater distances or different collection areas, achieving separation from higher-density powders (solid powders). However, this method relies heavily on horizontal airflow, making it difficult to guarantee separation accuracy. Furthermore, factors such as particle agglomeration further exacerbate the difficulty and accuracy of separation.

[0005] Therefore, it is urgent to solve the problems of insufficient accuracy and high difficulty in existing separation (grading) methods. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a powder hollowness classification device based on the difference in terminal settling velocity. It can achieve accurate classification of powder hollowness based on density difference and improve the purity of target solid powder.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is: a powder hollowness classification device based on the difference in terminal settling velocity, comprising: The feeding unit is used to supply powder; The dispersed conveying unit includes a conveying channel and two fan-blade rotating devices. The conveying channel is inclined downward from left to right to receive the powder supplied by the feeding unit and allow the powder to slide down along it. The fan blades of the two fan-blade rotating devices are embedded side by side in the conveying channel in the front-to-back direction. The airflow grading unit includes an air chamber and an air outlet device. The air chamber is inclined upward from left to right, with an air outlet at the upper end and an air inlet at the lower end. The air outlet is directly opposite the lower outlet of the conveying channel. The air outlet device is used to blow air into the air inlet of the air chamber. A collection unit is used to collect the powder that has been classified by the airflow classification unit.

[0008] Furthermore, the airflow classification unit also includes several airflow distribution plates, which are arranged at intervals in the front-to-back direction within the air cavity.

[0009] Furthermore, the powder hollowness classification device based on the difference in terminal settling velocity also includes a flow stabilization unit, which includes an airflow buffer chamber and an airflow regulating valve. The air outlet device is connected to the air inlet of the air chamber through the airflow buffer chamber, and the airflow regulating valve is located at the air inlet of the air chamber.

[0010] Furthermore, the feeding unit includes a screw conveyor.

[0011] Furthermore, the feeding unit also includes a quantitative feeding device for quantitatively feeding the screw conveyor.

[0012] Furthermore, the quantitative feeding device includes a feeding bin located on the side of the screw conveyor, and the screw of the screw conveyor extends into the feeding bin.

[0013] Furthermore, the collection unit includes a collection tank having at least two collection cavities arranged from left to right for receiving falling powder.

[0014] Furthermore, the top view of the collection tank is radiating from left to right.

[0015] Furthermore, an arc-shaped baffle is provided on the right edge of each collection chamber, and in any two adjacent arc-shaped baffles, the right arc-shaped baffle is higher than the left arc-shaped baffle.

[0016] Furthermore, the collection unit also includes a collection tank corresponding to the collection chamber, with each collection tank connected to the corresponding collection chamber.

[0017] This invention also relates to a powder hollowness classification method based on the aforementioned powder hollowness classification device based on terminal settling velocity differences, comprising: After the powder to be classified is pre-treated by sieving, the powder is supplied to the conveying channel of the dispersing and conveying unit through the feeding unit; The powder slides down the conveyor channel and is dispersed by two fan-bladed rotating devices that are rotating in opposite directions. The air outlet blows air into the air chamber, which guides the air to blow air upwards at an angle onto the powder that has been dispersed and has slid down to the lower end of the conveying channel, thereby achieving the classification of the hollowness of the powder. The collection unit collects the powder after hollowness classification.

[0018] By adopting the above technical solution, the present invention has the following beneficial effects: This invention utilizes two fan blades arranged side-by-side in the front-to-back direction, rotating in opposite directions on the receiving side, to break up agglomerated particles generated during the feeding process as the powder slides down the conveying channel. This eliminates particle agglomeration, ensuring the powder enters the grading stage in a monodisperse state. This avoids insufficient airflow contact caused by particle agglomeration, improving grading accuracy. It also evenly disperses the powder at the air outlet, preventing it from entering the airflow field as a stream and ensuring consistent airflow force on each powder particle. Furthermore, the air chamber of this invention is designed with an upward tilt, causing the powder to be simultaneously subjected to forward thrust and upward lift from the gas. Based on the density difference between hollow and solid powder, it achieves precise differentiation of their trajectories. Hollow powder, aided by bidirectional airflow, achieves higher flight altitude and a longer flight trajectory, forming a full arc motion. Solid powder, due to its higher density, settles rapidly under gravity, thus achieving undisturbed and precise powder grading, significantly improving grading purity. This invention makes synergistic improvements to both the powder outflow state and the gas outflow state, which not only improves the classification accuracy and product purity, but also fundamentally enhances the stability, reliability and processing capacity of the equipment for real industrial materials. The entire device is suitable for classifying various powder materials that require the removal of hollow powder, such as metal-based powders, water vapor atomized powders, starch-based powders, lithium battery cathode material powders and pharmaceutical microsphere powders. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the powder hollowness classification device based on the difference in terminal settling velocity of the present invention. Figure 2 for Figure 1 The main view; Figure 3 This is a schematic diagram of the feeding unit, the dispersing and conveying unit, and the airflow classification unit of the present invention; Figure 4 This is a schematic diagram of the collection unit of the present invention; Figure 5 This is a schematic diagram of the feeding unit of the present invention; Figure 6 This is a schematic diagram of the structure of the powder hollowness classification device based on the difference in terminal settling velocity of the present invention after the protective cover is installed. Figure 7 The images show the experimental powder used in the examples and the powder collected in each collection chamber. Figure 8 This is a diagram showing the powder collected in each collection chamber in the comparative example; In the diagram, 1. Feeding unit; 11. Screw conveyor; 12. Quantitative feeding device; 2. Distributed conveying unit; 21. Conveying channel; 22. Fan blade rotating device; 3. Airflow classification unit; 31. Air chamber; 32. Air outlet device; 33. Airflow distribution plate; 4. Collection unit; 41. Collection trough; 42. Collection cavity; 43. Arc-shaped baffle; 44. Collection tank; 51. Feeding protective cover; 52. Conveying protective cover; 53. Collection protective cover; Figure 7 In the figures, (a) to (e) are images of the experimental powder and the powder collected in the first to fourth stage collection chambers, respectively, in the examples. Figure 8 In the images, (a) to (d) are pictures of the experimental powder in the comparative example and the powder collected in the first to fourth stage collection chambers, respectively. Detailed Implementation

[0020] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0021] like Figures 1 to 6 As shown, a powder hollowness classification device based on terminal settling velocity differences includes: Feeding unit 1 is used to supply powder; The dispersive conveying unit 2 includes a conveying channel 21 and two fan blade rotating devices 22. The conveying channel 21 is inclined downward from left to right to receive the powder supplied by the feeding unit 1 and allow the powder to slide down along it. The fan blades of the two fan blade rotating devices 22 are embedded side by side in the conveying channel 21 in the front-to-back direction. The airflow classification unit 3 includes an air chamber 31 and an air outlet device 32. The air chamber 31 is inclined upward from left to right, with an air outlet at the upper end and an air inlet at the lower end. The air outlet is directly opposite the lower outlet of the conveying channel 21. The air outlet device 32 is used to blow air into the air inlet of the air chamber 31. Collection unit 4 is used to collect powders that have been classified by airflow classification unit 3.

[0022] The airflow classification unit 3 has both conveying and dispersing functions, ensuring that the powder slides down naturally under gravity while avoiding particle agglomeration caused by excessive downward speed. The angle between the conveying channel 21 and the horizontal plane is preferably 30-45°; the inner wall is preferably coated with a polytetrafluoroethylene non-stick coating; the air chamber 31 is preferably a sealed, one-piece stainless steel classification chamber.

[0023] The blade angle of the fan blades is preferably 30°-45°, and the fan blades are preferably driven by a micro-speed-regulating motor with a rotation speed of 0-1000 r / min. For easily agglomerated powders, the rotation speed is preferably set to 0-800 r / min; for brittle powders, the rotation speed is preferably controlled at 0-500 r / min. The two fan blade rotating devices 22 rotate in opposite directions on the material-facing side (the front fan blade rotates counterclockwise, and the rear fan blade rotates clockwise, with the two fan blades covering the middle area of ​​the conveying channel 21 in the width direction, so that most of the powder falls on the fan blades and is dispersed to both sides by the two fan blades rotating in opposite directions on the material-facing side). This has a dual function: on the one hand, it can disperse the agglomerated particles generated during the feeding process, break up the particle agglomeration, and ensure that the powder enters the classification stage in a monodisperse state, avoiding the agglomerated particles from affecting the classification effect; on the other hand, it can evenly disperse the powder to the air outlet position, preventing the powder from entering the airflow field in the form of a stream, ensuring the consistency of the force of the airflow on each powder particle, maintaining the stability and reliability of the classification process, and further improving the classification accuracy.

[0024] The air chamber 31 is designed with an upward tilt, which allows the powder to be simultaneously subjected to the forward thrust and upward lift of the gas. Based on the density difference between hollow and solid powder, the movement trajectories of the two can be accurately distinguished. Hollow powder, with the help of bidirectional wind force, can achieve a higher flight altitude and a longer flight trajectory, forming a full arc motion, which facilitates accurate collection to the corresponding collection area of ​​collection unit 4. Solid powder, due to its higher density, settles rapidly under the action of gravity and can fall efficiently into the corresponding collection area of ​​collection unit 4, achieving undisturbed and accurate classification of powder and significantly improving the purity of the classification.

[0025] In some examples, the air outlet device 32 can be a fan, an airflow motor, etc. Preferably, it is a variable frequency speed control type airflow motor, which preferably provides a stable air pressure of 0.1-0.3 MPa.

[0026] In some examples, such as Figure 1 and Figure 3 As shown, the airflow classification unit 3 also includes several airflow distribution plates 33, which are arranged at intervals along the front-to-back direction within the air cavity 31. The airflow distribution plates 33 are preferably evenly distributed to ensure that the airflow is converted into a stable laminar flow. The interval between adjacent airflow distribution plates 33 is preferably 2-5 mm.

[0027] Specifically, the air chamber 31 is divided into multiple small air channels by the airflow distribution plate 33, which can effectively guide and divert the airflow to ensure that the airflow is evenly distributed in each part when it reaches the air outlet. This provides a uniform airflow dynamic basis for the stable classification of powders and avoids classification deviations caused by uneven airflow.

[0028] In some examples, the powder hollowness classification device based on the difference in terminal settling velocity also includes a flow stabilization unit, which includes an airflow buffer chamber and an airflow regulating valve. The air outlet device 32 is connected to the air inlet of the air chamber 31 through the airflow buffer chamber, and the airflow regulating valve is configured at the air inlet of the air chamber 31.

[0029] The airflow buffer chamber, made of carbon steel with a rust-proof coating, has a volume of 5-10 L and effectively buffers the pulsed airflow output from the airflow motor, ensuring airflow pressure fluctuations are ≤±0.005 MPa. The airflow regulating valve is a precision electronic regulating structure with an adjustment accuracy of ±0.01 m / s. It can precisely control the airflow velocity based on powder density parameters (calculated using Stokes' law), ensuring the airflow velocity remains stable between the "settling velocity at the terminal of hollow powder" and the "settling velocity at the terminal of solid powder," a key guarantee for accurate classification. This unit can also be linked with a PLC control system, enabling real-time monitoring and adjustment of airflow parameters with a response time ≤0.5 s.

[0030] Specifically, the airflow buffer chamber is used to stabilize the airflow pressure, and the airflow regulating valve is used to precisely control the airflow speed, thereby minimizing airflow fluctuations and reducing the impact of airflow fluctuations on powder classification.

[0031] In some examples, such as Figure 5 As shown, the feeding unit 1 includes a screw conveyor 11.

[0032] Specifically, the use of a screw conveyor 11 can perform initial shearing of the powder, reduce powder agglomeration, and achieve stable and reliable feeding.

[0033] Among them, a sealing gasket can be installed at the connection between the outlet of the screw conveyor 11 and the inlet of the dispersed conveying unit 2 to prevent powder dust from being emitted, which meets environmental protection requirements.

[0034] Preferably, such as Figure 5 As shown, the feeding unit 1 also includes a quantitative feeding device 12 for quantitatively feeding the screw conveyor 11.

[0035] Specifically, by cooperating with the quantitative feeding device 12 and the screw conveyor 11, the feeding rate can be precisely controlled to ensure that the powder enters the subsequent dispersion and conveying unit 2 evenly, and to avoid the grading effect being affected by feeding fluctuations.

[0036] More preferably, such as Figure 5As shown, the quantitative feeding device 12 includes a feeding bin located on the side of the screw conveyor 11. The feeding bin can be connected to the housing of the screw conveyor 11, and the side wall connected to the housing has a through hole. The screw of the screw conveyor 11 extends into the feeding bin through the through hole and can extend to a position near the side wall opposite the through hole of the feeding bin. After the powder is put into the feeding bin, quantitative feeding is achieved by rotating the screw of the screw conveyor 11. The feeding speed is controlled by setting the parameters of the screw. This quantitative feeding device 12 does not require the introduction of additional power and has a simple structure.

[0037] In some examples, such as Figure 1 , Figure 2 and Figure 4 As shown, the collection unit 4 includes a collection tank 41, which has at least two collection cavities 42 arranged from left to right for receiving falling powder.

[0038] In some examples, such as Figure 1 and Figure 4 As shown, the top view of the collection tank 41 is radiating from left to right.

[0039] The divergent shape is similar to a fan-shaped structure, which precisely matches the dispersion pattern of gas after passing through the air outlet: when the gas disperses, the two sides are the main directions, and the fan-shaped structure can cover the dispersion range of the airflow in all directions, realizing the collection of powder without dead angles. This design can effectively avoid powder waste caused by airflow dispersion and significantly improve the overall powder collection rate while being both practical and economical.

[0040] In some examples, such as Figure 1 , Figure 2 and Figure 4 As shown, each collection chamber 42 is provided with an arc-shaped baffle 43 on its right side edge. In any two adjacent arc-shaped baffles 43, the right arc-shaped baffle 43 is higher than the left arc-shaped baffle 43.

[0041] Specifically, particles with different terminal velocities exhibit parabolic motion. Solid powder has a steep trajectory and falls quickly, while hollow powder has a gentle trajectory and travels a long distance. The low, curved baffle 43 is placed closer to the air outlet because the landing point of heavy particles is already close, and the low curved baffle 43 is sufficient to intercept them along their falling path, while also preventing them from being accidentally hit by mid-section particles due to the curved baffle 43 being too high. The higher curved baffle 43 on the right is for light particles with gentle trajectories. The higher curved baffle 43 can "wait" and intercept particles that fly far but fall at a small angle from a relatively left position (if the curved baffle 43 is too low here, light particles may fly over the curved baffle 43 and not be collected). By employing this "lower left, higher right; closer left, farther right" matching, the starting point of the entire collection array can be significantly moved forward, and the array's length (left-right span) can be shortened. This allows for a more compact equipment layout while maintaining or even improving collection efficiency, resolving the "overall length problem" inherent in equal-height baffle schemes and saving floor space. Furthermore, the compact collection area reduces the space behind the device, potentially helping to weaken large-scale eddies and backflows, making the airflow field in the working area more stable and controllable, which is beneficial for improving the repeatability of the grading process.

[0042] In addition, this design allows for a higher degree of matching between the baffle height and the expected particle trajectory, enabling more precise delivery of particles with different flight distances into the target collection chamber 42.

[0043] In some examples, such as Figure 1 , Figure 2 and Figure 4 As shown, the collection unit 4 also includes a collection tank 44 corresponding to each collection chamber 42, and the collection tank 44 is connected to the corresponding collection chamber 42. Multiple collection chambers 42 are arranged in sequence, and the downward tilt angle of the bottom is preferably 15-20°.

[0044] Four collection chambers 42 can be provided. The first-stage collection chamber 42 is located adjacent to the outlet of the dispersion conveying unit 2. Because the airflow velocity in this area is insufficient to support the solid powder, the solid powder directly settles to the bottom of the first-stage collection chamber 42 and enters the first-stage collection tank 44 through the bottom interface. As the airflow advances to the fourth-stage collection chamber 42, the hollow powder is continuously carried and eventually gathers in the fourth-stage collection chamber 42 and falls into the fourth-stage collection tank 44. Each collection tank 44 is connected to the corresponding collection chamber 42 by a threaded seal. The tank opening has a built-in filter membrane with a pore size of 0.1 μm to prevent powder leakage without obstructing airflow. The volume of the collection tank 44 can be 2-5 L, and it can be quickly disassembled and replaced to adapt to continuous production.

[0045] A powder hollowness classification method using the aforementioned powder hollowness classification device based on terminal settling velocity differences, based on Stokes' law, includes the following steps: The first step is pretreatment: the powder to be graded is pre-screened, and powder with uniform particle size is screened out through a standard sieve (to ensure that the particle size of hollow powder and solid powder is consistent) to remove oversized impurities. The second step is to disperse the feeding: the feeding unit 1 (the quantitative feeding device 12 feeds the screw conveyor 11 in a quantitative manner, and the screw conveyor 11 conveys the material in a screw conveyor) supplies powder to the conveying channel 21 of the dispersing conveying unit 2. The powder slides down the conveying channel 21 and is dispersed by the two fan blades rotating on the opposite side of the material receiving side. The powder comes out of the outlet of the conveying channel 21 in a uniform single-particle state. The third step is airflow classification: the air outlet device 32 blows air into the air chamber 31 through the flow stabilization unit. The airflow is guided and diverted into multiple small air channels by the airflow distribution plate 33 within the air chamber 31. This upward airflow is directed at the powder that has been dispersed and descended to the lower end of the conveying channel 21, with an airflow velocity v. 气 "Hollow powder terminal settling velocity v" t（空） "and "solid powder terminal settling velocity v" t（实） "between (i.e. v) t（空） <v 气 < v t（实） At this time: because hollow powder has a low density and a low terminal settling velocity, it is blown by the airflow to the right collection chamber 42 and finally enters the hollow powder collection tank 44 from the fine powder outlet; because solid powder has a high density and a high terminal settling velocity, it cannot be blown by the airflow and settles to the left collection chamber 42 and enters the solid powder collection tank 44 from the coarse powder outlet. The fourth step is collection and testing: the solid powder and hollow powder after separation are collected separately, and the separation effect is verified by powder spraying spark detection or microscopic morphology analysis.

[0046] It is important to note that in actual use, to prevent the spread of powder dust and meet environmental and safety requirements, the entire powder hollowness classification device is equipped with a removable protective cover. This cover can be connected with bolts for easy removal and maintenance. Figure 6 As shown, the top of the screw conveyor 11 of the feeding unit 1 is equipped with a feeding protective cover 51, the top of the conveying channel 21 is equipped with a conveying protective cover 52, and the top of the collecting trough 41 is equipped with a collecting protective cover 53.

[0047] By cooperating with the quantitative feeding device 12 and the screw conveyor 11, the feeding rate can be precisely controlled to ensure that the powder enters the subsequent dispersion conveying unit 2 evenly, avoiding the impact of feeding fluctuations on the classification effect. In addition, the screw conveyor 11 performs preliminary shearing on the powder to reduce powder agglomeration.

[0048] The powder slides down the conveying channel 21 by its own weight. The two impellers rotating in opposite directions disperse the agglomerated particles a second time, further breaking up the particle agglomeration and ensuring that the powder enters the classification stage in a monodisperse state. On the other hand, they can disperse the powder evenly, preventing the powder from entering the airflow field in the form of a stream, ensuring the consistency of the force exerted by the airflow on each powder particle, maintaining the stability and reliability of the classification process, and further improving the classification accuracy.

[0049] The air coming out of the air outlet 32 ​​is buffered by the airflow buffer chamber and regulated by the airflow regulating valve, and then enters the air chamber 31 at a uniform speed. The air chamber 31 is divided into multiple small air channels by the airflow distribution plate 33, which can effectively guide and divert the airflow to ensure that the air force is evenly distributed in all parts when the airflow reaches the air outlet, forming laminar flow. This provides a uniform airflow dynamic basis for the stable classification of powders and avoids classification deviation caused by uneven air force.

[0050] A uniform laminar flow is used to blow single-particle, laminar powder upwards at an angle. The upward-sloping airflow causes the powder to be simultaneously subjected to forward thrust and upward lift. Based on the density difference between hollow and solid powder, the movement trajectories of the two are accurately distinguished. Hollow powder, aided by the bidirectional airflow, can achieve a higher flight altitude and a longer flight trajectory, forming a full arc motion, which facilitates precise collection to the collection area far from collection unit 4. Solid powder, due to its higher density, settles rapidly under gravity and can efficiently fall to the collection area near collection unit 4, achieving undisturbed and precise powder classification, and significantly improving the purity of the classification.

[0051] By matching the left low and right high, and the left near and right far, the starting point of the entire collection array can be moved forward significantly through the matching of the collection unit 4, and the length of the array (left and right span) can be shortened. This makes the equipment layout more compact while ensuring or even improving the collection efficiency, solving the problem of "overall length" in the equal height baffle scheme and saving space.

[0052] In addition, for various powder materials that require the removal of hollow powder, such as metal-based powders, water vapor atomized powders, starch-based powders, lithium battery cathode material powders, and pharmaceutical microsphere powders, the density characteristics of different powders can be adapted by adjusting key parameters such as airflow speed, thus solving the problem of limited application scenarios of existing technologies.

[0053] Example: The powder is classified using the above-mentioned powder hollowness classification method.

[0054] I. Specific procedures.

[0055] (1) Screening the powder, controlling the particle size of the metal powder (71-106 µm), the screened powder is as follows Figure 7 As shown in (a), the void fraction is approximately 6.5%; (2) Clean feeding unit 1, decentralized conveying unit 2 and collection unit 4; (3) Start the air outlet device 32 (fan). After the wind speed stabilizes, pour an appropriate amount of metal powder into the quantitative feeding device 12 so that the metal powder rolls into the airflow area. (4) The powder is blown into the collection chambers 42 in different areas.

[0056] (5) Turn off the air outlet device 32 (fan).

[0057] (6) Carefully collect the powder at each stage and record the data. The powder collected in the first to fourth stage collection chambers 42 is as follows: Figure 7 As shown in (b) to 7(e).

[0058] II. Experimental Results.

[0059] Through experiments, we discovered the following phenomena: most of the powder is concentrated in the second and third stage collection chambers 42, with the second stage collection chamber 42 having the most powder; less powder falls into the first and fourth stage collection chambers 42, with the fourth stage having the least metal powder.

[0060] The metal powder collected in the first-stage collection chamber 42, such as Figure 7 As shown in (b), the number of powder pieces is approximately 848; the number of hollow pasta pieces is 32; and the percentage of hollow pasta pieces is approximately 3.77%. The metal powder collected in the second-stage collection chamber 42, such as Figure 7 As shown in (c), the number of powder pieces is approximately 920; the number of hollow pasta pieces is 56; and the percentage of hollow pasta pieces is approximately 6.08%. The metal powder collected in the third-stage collection chamber 42, such as Figure 7 As shown in (d), the number of powder pieces is approximately 980; the number of hollow pasta pieces is 72; and the percentage of hollow pasta pieces is approximately 7.34%. The metal powder collected in the fourth-stage collection chamber 42, such as Figure 7 As shown in (e), the number of powder pieces is approximately 1120; the number of hollow pasta pieces is 96; and the percentage of hollow pasta pieces is approximately 8.57%.

[0061] By analyzing the graded metal powder, we obtained: Primary powder flowability: 15.85 Loose packing density of Grade 1 powder: (204.08-100.663) / 25=4.13668 Secondary powder flowability: 16.85 The loose density of the secondary powder is: (203.378-100.663) / 25=4.1086 Grade 3 powder flowability: 17.03 The loose density of the third-grade powder is: (202.185-100.663) / 25=4.06088 Grade 4 powder flowability: 17.28 The loose density of the fourth-grade powder is: (196.904-100.663) / 25=3.84964 The summary is as follows:

[0062] III. Results Analysis.

[0063] (1) Fluidity variation pattern: Data shows that as the powder grade is upgraded from level 1 to level 4, the fluidity value gradually increases from 15.85 s to 17.28 s, and the powder fluidity performance shows a continuous downward trend. Among them, level 1 powder has the best fluidity and level 4 powder has the worst fluidity.

[0064] (2) Correlation between loose packing density and hollow powder ratio: The lower the loose packing density, the higher the proportion of hollow powder in the powder. Data shows that the loose packing density decreases significantly with the increase of powder grade, from 4.1367 g / cm3 for grade 1 to 3.8496 g / cm3 for grade 4. This indicates that the proportion of hollow powder gradually increases with the increase of powder grade. Grade 4 powder has the highest proportion of hollow powder, while grade 1 powder has the lowest proportion of hollow powder. This is consistent with the statistical data of microscopic morphology detection.

[0065] (3) According to the experimental data, the void ratio of the collected powders after separation is lower than that of the test powder. The void ratio of the first-level powder is about 42% lower than that of the test powder. The void ratio of the powder in the collection area farthest from the air outlet is about 32% higher than that of the test powder. This proves that the separation effect of the separation device is obvious and can be applied to actual production.

[0066] Comparative example: The gravity sedimentation method mentioned in the background technology was used to classify metal powder with a hollow powder ratio of about 18%.

[0067] Among them, the powder collected in the first to fourth stage collection chambers 42 is as follows Figure 8 As shown in (a) to 8(d).

[0068] The hollow rate of the metal powder collected in the first-stage collection chamber 42 is 14.55%, the hollow rate of the metal powder collected in the second-stage collection chamber 42 is 16.92%, the hollow rate of the metal powder collected in the first-stage collection chamber 42 is 19.71%, and the hollow rate of the fourth-stage powder is 20.74%. According to experimental data, after separation, the void ratio of the metal powder collected in the first and second stage collection chambers 42 was lower than that of the benchmark test powder. The void ratio of the first stage powder decreased by only 19% compared to that of the benchmark test powder, and the void ratio of the powder in the collection area farthest from the air outlet increased by only 15% compared to that of the benchmark test powder. The powder separation efficiency was not high, and the separation effect was far worse than that of the example.

[0069] Furthermore, when the hollow powder ratio is low, the separation difficulty of the powder usually increases significantly. The metal powder processed in the example has a hollow ratio of only 6.5%, which belongs to the category of low-hollow powder with relatively high separation difficulty, while the comparative example processes high-hollow powder with a hollow ratio as high as 18%, which is relatively easy to separate. Although the separation conditions faced by the example are more stringent, its classification effect is still far superior to that of the comparative example, fully demonstrating that the method of the present invention can still achieve superior separation performance than the prior art when processing high-hollow powder, even in the more difficult-to-separate low-hollow powder.

[0070] The feasibility of the above embodiments will be explained below with reference to specific principles and formulas.

[0071] 1. Core formula: Stokes' law (applicable to fine particles, Reynolds number Re < 1).

[0072] When particles settle at a constant velocity in an airflow, gravity, buoyancy, and air resistance reach equilibrium; the settling velocity at this point is called the "terminal settling velocity" (v). t The formula is as follows: ; d p Particle diameter (assuming hollow and solid flour have the same particle size, this value cancels out). ρ p Particle density (ρ of hollow flour) 空 < Solid flour ρ 实 (Core differences) ρ g Air density (approximately 1.2 kg / m³) 3 (The density is much smaller than the particle density and can be approximately ignored). g: acceleration due to gravity (9.81 m / s²) 2 ); μ: Aerodynamic viscosity (approximately 1.81 × 10⁻⁶ at 20 °C) -5 ).

[0073] 2. Key conclusion: Hollow powder has a lower terminal settling velocity.

[0074] Because ρ 空 <ρ 实 Substituting into the formula, we get: vt（空） <v t（实）； This means that, at the same airflow speed, hollow powder is more easily carried away by the airflow (entering the fine powder collection area), while solid powder, due to its higher settling speed, is more likely to settle (entering the coarse / heavy powder collection area), thus achieving separation (grading).

[0075] Assuming that hollow and solid powders have the same particle size (excluding particle size interference) and only differ in density, the terminal settling velocity is calculated by substituting the parameters to verify the feasibility of separation.

[0076] 3. Known parameter settings.

[0077]

[0078] 4. Calculation of terminal settlement velocity.

[0079] Ignoring air density ρ g The formula simplifies to: ; Solid flour terminal settling velocity : ; Hollow powder terminal settling velocity : .

[0080] 5. Derivation of separation conditions.

[0081] If the airflow velocity is controlled between the two terminal settling velocities, i.e., 0.61 m / s <v 气 <1.06 m / s; Hollow pasta: due to v 气 >v t（空） They are carried by the airflow to a distant collection area; Solid pasta: due to v 气 <v t（实） Unable to be lifted by the airflow, they settle into the nearby collection area; at this point, effective separation of the two types of particles can be achieved. Airflow velocity: Based on the density parameters of the powders to be separated, the terminal settling velocities of hollow and solid powders are calculated using Stokes' law, determining the airflow velocity adjustment range to be 0.61 m / s to 1.06 m / s (based on a density of 800 kg / m³). 3 Hollow pasta and 1400 kg / m 3 (For example, solid pasta). Particle size pretreatment standard: Ensure the uniformity of particle size of the powder to be separated by sieving, with the particle size fluctuation range not exceeding ±5 μm.

[0082] 6. Separation device setup.

[0083] To completely solve the problems of existing powder separation technologies, such as the inability to accurately distinguish between hollow and solid powders of the same particle size but different densities, low separation efficiency, high energy consumption, and limited applicability, this invention provides an innovative and efficient new process for separating hollow powders. This process can significantly improve the separation accuracy and efficiency of hollow and solid powders, which is crucial for improving the purity of the target solid powder and ensuring product quality in subsequent powder applications (such as powder welding, material forming, etc.).

[0084] Specifically, the key to this invention lies in its core theoretical basis: Stokes' Law. Through an integrated process of "pre-treatment sieving – airflow dispersion – steady-flow classification – precise collection," it utilizes the difference in terminal settling velocities between hollow powder (low density) and solid powder (high density) to achieve efficient classification of the two within a specific airflow field. Specifically, the airflow classification unit precisely controls the airflow velocity (between the terminal settling velocities of hollow and solid powders), causing the hollow powder to be carried by the airflow to the fine powder collection area, while the solid powder, unable to be lifted by the airflow, settles to the coarse powder collection area.

[0085] This novel hollow powder separation process allows for the directional removal of hollow powder and the efficient purification of solid powder from mixed powders without damaging the original physical properties of the powder or introducing impurities. Furthermore, the process design fully considers both economic efficiency and environmental friendliness: on the one hand, the equipment has a simple structure and is easy to operate, requiring no complex mechanical transmissions or high-energy-consuming separation components, significantly reducing equipment purchase costs and operating energy consumption; on the other hand, the separation process generates no wastewater, waste gas, or waste residue, and by optimizing airflow parameters and feed rate, continuous batch processing can be achieved, adapting to the needs of industrial production.

[0086] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A powder hollowness classification device based on terminal settling velocity differences, characterized in that, include: Feeding unit (1) is used to supply powder; The dispersed conveying unit (2) includes a conveying channel (21) and two fan blade rotating devices (22). The conveying channel (21) is inclined downward from left to right to receive the powder supplied by the feeding unit (1) and allow the powder to slide down along it. The fan blades of the two fan blade rotating devices (22) are embedded side by side in the conveying channel (21) in the front-to-back direction. The airflow classification unit (3) includes an air chamber (31), an air outlet device (32), and several airflow distribution plates (33). The air chamber (31) is inclined upward from left to right, with an air outlet at the upper end and an air inlet at the lower end. The air outlet is directly opposite the lower outlet of the conveying channel (21). The air outlet device (32) is used to blow air into the air inlet of the air chamber (31). Several airflow distribution plates (33) are arranged at intervals in the front-back direction inside the air chamber (31). The collection unit (4) is used to collect the powder that has been classified by the airflow classification unit (3).

2. The powder hollowness classification device based on terminal settling velocity difference according to claim 1, characterized in that, It also includes a flow stabilizing unit, which includes an airflow buffer chamber and an airflow regulating valve. The air outlet device (32) is connected to the air inlet of the air chamber (31) through the airflow buffer chamber, and the airflow regulating valve is located at the air inlet of the air chamber (31).

3. The powder hollowness classification device based on terminal settling velocity difference according to claim 1, characterized in that, The feeding unit (1) includes a screw conveyor (11).

4. The powder hollowness classification device based on terminal settling velocity difference according to claim 3, characterized in that, The feeding unit (1) also includes a quantitative feeding device (12) for quantitatively feeding the screw conveyor (11).

5. The powder hollowness classification device based on terminal settling velocity difference according to claim 4, characterized in that, The quantitative feeding device (12) includes a feeding bin located on the side of the screw conveyor (11), and the screw of the screw conveyor (11) extends into the feeding bin.

6. The powder hollowness classification device based on terminal settling velocity difference according to claim 1, characterized in that, The collection unit (4) includes a collection tank (41), which has at least two collection cavities (42) arranged from left to right for receiving falling powder.

7. The powder hollowness classification device based on terminal settling velocity difference according to claim 6, characterized in that, The top view of the collection tank (41) is radiating from left to right.

8. The powder hollowness classification device based on terminal settling velocity difference according to claim 6, characterized in that, Each collection chamber (42) has an arc-shaped baffle (43) on its right side. In any two adjacent arc-shaped baffles (43), the right arc-shaped baffle (43) is higher than the left arc-shaped baffle (43).

9. The powder hollowness classification device based on terminal settling velocity difference according to claim 6, characterized in that, The collection unit (4) also includes a collection tank (44) corresponding to the collection cavity (42), and each collection tank (44) is connected to the corresponding collection cavity (42).

10. A powder hollowness classification method based on the powder hollowness classification device based on the terminal settling velocity difference as described in any one of claims 1-9, characterized in that, include: After the powder to be graded is pre-treated by sieving, the powder is supplied to the conveying channel (21) of the dispersing and conveying unit (2) through the feeding unit (1); The powder slides down the conveying channel (21) and is dispersed by two fan-bladed rotating devices (22) that rotate in opposite directions; The air outlet device (32) blows air into the air chamber (31). Guided by the air chamber (31), the air is blown upward at an angle to the powder that has been dispersed and has slid down to the lower end of the conveying channel (21), thereby achieving the classification of the hollowness of the powder. Collection unit (4) collects the powder after hollowness classification.

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