Vortex air classifier double-layer rotating cage suitable for superfine powder separation

Abstract

The invention discloses a vortex air classifier double-layer rotating cage for sorting superfine powder, and belongs to the technical field of powder preparation. A double-layer rotating cage structure is designed on the basis of centrifugal separation and the sedimentation velocity difference of coarse and fine particles. The specific implementation method is as follows: the outer layer of the rotating cage consists of rotating cage blades which are uniformly distributed in the circumferential direction and is vertically fixed between an upper wheel carrier and a lower wheel carrier, and coarse and fine particles are subjected to centrifugal separation at the rotating cage blades to finish primary grading; the rotating cage inner layer is composed of a drainage cone and a triangular connecting support, the triangular connecting support and the lower wheel carrier are connected and fixed through threads, and the outer edges of the three arc-shaped faces of the drainage cone are attached to the inner edge of the upper wheel carrier. The taper angle of the drainage cone ranges from 5 degrees to 15 degrees, and the axial length of the drainage cone ranges from 1 / 8 to 1 time of the axial length of the rotating cage blade. And coarse and fine particles at the tail end of the drainage cone are separated for the second time due to settling velocity difference. The longer the drainage cone is, the smaller the particle size of the obtained fine powder product is and the narrower the particle size distribution is.

Description

Technical Field

[0001] The present invention relates to a double-layer rotating cage for ultrafine powder separation in a vortex air classifier, belonging to the technical field of powder preparation. Background Art

[0002] Due to their special physical and chemical properties, ultrafine powders are widely used in related fields such as pharmaceuticals, 3D printing, and fine chemicals. Since the particle size and particle size distribution of ultrafine powders will directly affect the product performance and quality, achieving finer and narrower-distributed ultrafine powders has become the demand for industry development. The vortex air classifier is a pneumatic classification device commonly used in the mechanical preparation of ultrafine powders. It has the advantages of high classification efficiency, adjustable particle size, and large output. It uses the different forces of coarse and fine particles in the air flow field to classify materials and obtain fine particles that meet the particle size requirements. A common method for the vortex air classifier to obtain fine powder products with small particle sizes is to increase the rotating speed of the rotating cage. As the rotating speed of the rotating cage increases, the centrifugal force exerted by the particles in the classification force field also increases. Larger particles are thrown towards the cylinder wall and it is difficult for them to enter the interior. Therefore, the collected particles are finer and the classification particle size decreases. However, increasing the rotating speed of the rotating cage will increase the equipment energy consumption and load. In addition, since the maximum rotating speed of the rotating cage is limited by performance such as motor power, torque, cooling performance, control accuracy, material strength, and mechanical balance, it is a practical method to improve the structure of the rotating cage to change the movement trajectories of coarse and fine particles, reduce the classification particle size, and obtain powders with narrow and fine particle size distributions. Summary of the Invention

[0003] The present invention proposes a double-layer rotating cage for a vortex air classifier suitable for ultrafine powder separation. By using the inner layer (drainage cone) of the rotating cage to change the movement trajectory of the fine powder that has passed through the outer layer (blade channel) of the rotating cage, the ultrafine powder in the fine powder can be separated out, achieving the purpose of reducing the classification particle size and obtaining ultrafine powder.

[0004] A double-layer rotating cage for a vortex air classifier suitable for ultrafine powder separation, characterized in that: the outer layer of the rotating cage is composed of rotating cage blades (2), and the rotating cage blades are evenly distributed circumferentially and are vertically fixed between the upper wheel frame (3) and the lower wheel frame (1) to form an air flow channel; the inner layer of the rotating cage is composed of a drainage cone (4), and the drainage cone and the triangular connecting bracket (5) are connected and fixed by threads. The triangular connecting bracket is connected and fixed to the lower wheel frame by threads. The outer edges of the three arc-shaped surfaces of the drainage cone are fitted with the inner edge of the upper wheel frame to ensure the sealing between the inner and outer layers of the rotating cage. The cone angle range of the drainage cone is 5-15°, and the axial length range of the drainage cone is between 1 / 8 and 1 times the axial length of the rotating cage blades. By adjusting the length of the drainage cone, the fineness of the fine powder product can be adjusted. The fineness of the fine powder product becomes smaller and the distribution becomes narrower as the drainage cone grows.

[0005] The working principle of the eddy current air classifier is mainly to form a strong eddy current field in the classifier through the diversion structure when the air flow enters the classifier. At the same time, the moving part, the rotating cage, makes a rotational motion. The particle size classification is realized by using the dynamic balance of the centrifugal force and the air flow drag force received by the particles. Among them, the fine particles flow through the channels between the blades of the rotating cage with the air flow, enter the center of the rotating cage and are discharged from the fine powder outlet; the coarse particles are thrown to the cavity wall under the action of the centrifugal force and settle. After being collected by the conical aggregate bucket, they are discharged from the coarse powder outlet. To analyze the action mechanism of the double-layer rotating cage, under the condition of a certain cone angle (12°), numerical simulations of gas phase and gas-solid two-phase were carried out on double-layer rotating cages with different lengths of the diversion cones respectively, and a comparative analysis was carried out with the rotating cage only equipped with radial blades. Through the gas phase simulation, it was found that the air flow of the double-layer rotating cage was blocked by the inner diversion cone of the rotating cage, and the air flow formed a certain angle at the bottom of the diversion cone and then entered the center of the rotating cage. Moreover, as the length of the diversion cone increased, the included angle between the streamline and the horizontal line gradually increased. The increase of the included angle hindered the radial movement of the air flow towards the central body, thus more effectively preventing larger particles from entering the fine powder area, and only finer particles could enter the fine powder outlet with the air flow. Through the gas-solid two-phase numerical simulation, it can be seen that the coarse and fine powders are first centrifugally classified at the outer edge of the rotating cage. The channels of the rotating cage blades play the role of a sieve. The finer particles pass through the channels between the blades under the action of centrifugal separation with the air flow to complete the first classification. Since the double-layer rotating cage adds a diversion cone as the inner layer of the rotating cage, the fine powder that enters the inside of the rotating cage after centrifugal classification undergoes a secondary separation. Among them, the ultrafine powder will follow the air flow and move upward to the center of the rotating cage to be collected as fine powder, while the coarser particles in the fine particles are blocked by the diversion cone and settle under the action of gravity to complete the second classification. The longer the length of the diversion cone, the finer the particle size of the fine powder product.

[0006] The beneficial effects of the present invention are as follows: The outer layer and the inner layer of the double-layer rotating cage respectively realize the two-stage separation of coarse and fine particles. Among them, the channels of the rotating cage blades, that is, the outer layer of the rotating cage, carry out centrifugal classification on the coarse and fine particles. The diversion cone, that is, the inner layer of the rotating cage, uses the principle of gravity sedimentation to realize the secondary separation of finer powders. The outer layer of the rotating cage completes the forced separation of coarse particles, and the inner layer of the rotating cage implements the precise capture of ultrafine particles. Through the optimization of the flow field, the secondary regulation of the particle size distribution is realized. The schematic diagrams of the movement trajectories of coarse and fine particles are as Figure 2 shown.

[0007] The present invention is suitable for the dry classification of various powders. Brief Description of the Drawings

[0008] Figure 1 It is the structure diagram of the double-layer rotating cage;

[0009] Figure 2 It is the schematic diagram of the particle trajectory of the double-layer rotating cage;

[0010] In the figure: 1. Lower wheel frame; 2. Rotating cage blade; 3. Upper wheel frame; 4. Diversion cone; 5. Triangular support Detailed Embodiments

[0011] This invention patent proposes a double-layer rotating cage for a vortex air classifier applicable to the separation of ultra-fine powders, as Figure 1 shown. The outer layer of the rotating cage is composed of rotating cage blades (2), which are evenly distributed circumferentially and vertically fixed between the upper wheel frame (3) and the lower wheel frame (1) to form an air flow channel; the inner layer of the rotating cage is composed of a drainage cone (4), and the drainage cone and the triangular connection bracket (5) are connected and fixed by threads. The triangular connection bracket is connected and fixed to the lower wheel frame by threads. The outer edges of the three arc-shaped surfaces of the drainage cone fit with the inner edge of the upper wheel frame to ensure the sealing between the inner and outer layers of the rotating cage. Among them, the cone angle range of the drainage cone is 5-15°, and the axial length range of the drainage cone is between 1 / 8 and 1 times the axial length of the rotating cage blades. By adjusting the length of the drainage cone, the particle size control of the required ultra-fine powder can be achieved.

[0012] In this invention, with the operating parameters and other structural parameters unchanged, a classification comparison test is respectively carried out using a radial straight blade rotating cage and the double-layer rotating cage designed in this invention. The experimental results show that compared with the radial straight blade rotating cage, the classification particle size can be reduced by up to 62.5% and the classification accuracy can be improved by up to 51.3% when using the double-layer rotating cage designed in this invention; the average particle size of the obtained fine powder product is reduced by 43.2% and the particle size distribution index is reduced by 8%. It shows that the double-layer rotating cage in this invention changes the particle motion characteristics, reduces the equipment classification particle size and improves the classification accuracy, and can obtain ultra-fine powders with a narrow and fine particle size distribution.

[0013] The description of the above embodiments is only used to help understand the method and core idea of this invention. It should be pointed out that for those of ordinary skill in the art in this technical field, without departing from the principle of this invention, several improvements and modifications can still be made to this invention, and these improvements and modifications also fall within the protection scope of the invention claims.

[0014] Three implementation cases of this invention patent adopt double-layer rotating cages with drainage cones of three axial lengths (1 / 2 times, 3 / 4 times, 1 time the axial length of the rotating cage blades), and calcium carbonate is selected as the raw material to be classified for material classification. Its particle size composition is shown in Table 1:

[0015] Table 1 Particle size differential distribution of calcium carbonate raw materials

[0016]

[0017] For simplicity of expression, the commonly used radial straight vane rotor is denoted as rotor A, and the double-layer rotors with axial lengths of 1 / 2 times, 3 / 4 times, and 1 times the drainage cone are denoted as: rotor B0.5, rotor B0.75, and rotor B1 respectively. Compared with rotor A, the classified particle sizes of the three double-layer rotors are reduced by 24.3%, 50.2%, and 62.5% respectively compared to the prototype rotor, and the classification accuracies are improved by 38.7%, 44.1%, and 51.3% respectively. Under the working conditions of a wind speed of 9 m / s, a rotor speed of 1200 rpm, and a feeding speed of 12 kg / h, the average particle size of the fine powder product obtained by rotor A is 10.5 μm, and the average particle sizes of the fine powder products obtained by rotor B0.5, rotor B0.75, and rotor B1 are 9.1 μm, 7.3 μm, and 5.9 μm respectively; the particle size distribution index of the fine powder product obtained by rotor A is 1.13, and the particle size distribution indexes of the fine powder products obtained by rotor B0.5, rotor B0.75, and rotor B1 are 1.15, 1.17, and 1.23 respectively (note: the larger the particle size distribution index, the narrower the particle distribution). It shows that the double-layer rotor designed by the present invention can reduce the classified particle size of the vortex air classifier and improve the classification accuracy, which is beneficial to obtaining high-quality fine powder with a narrow particle size distribution. At the same time, the longer the drainage cone, the finer and narrower the obtained product.

Claims

1. A double-layer cage of an eddy current air classifier suitable for ultrafine powder sorting, characterized by: The outer layer of the rotating cage is composed of rotating cage blades (2), which are evenly distributed in the circumference and vertically fixed between the upper wheel frame (3) and the lower wheel frame (1) to form an air flow channel; the inner layer of the rotating cage is composed of a drainage cone (4), and the drainage cone (4) and the triangular connecting bracket (5) are connected and fixed by threads. The triangular connecting bracket is connected and fixed to the lower wheel frame by threads. The outer edge of the three-section arc surface of the drainage cone fits with the inner edge of the upper wheel frame to ensure the sealing between the inner and outer layers of the cage. The drainage cone angle ranges from 5 to 15 degrees, and the axial length of the drainage cone ranges from 1 / 8 to 1 times the axial length of the cage blade. The fineness of the fine powder product can be adjusted by adjusting the length of the drainage cone. The particle size of the fine powder product becomes smaller and the distribution becomes narrower as the drainage cone grows.

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