Freezing mechanical crushing device suitable for preparing laser printer developing agent

Abstract

The utility model discloses a freezing mechanical crushing device suitable for preparing a laser printer developer, which comprises a crushing cavity, a feeding pipeline, a freezing airflow pipeline and a grading unit, wherein a feeding hole and a discharging hole are formed at two ends of the crushing cavity, and the feeding pipeline and the freezing airflow pipeline are respectively communicated with the feeding hole; the grading unit comprises a grading cavity, a material conveying pipeline and a material returning pipeline, the grading cavity is provided with a material conveying opening, a material discharging opening and a material returning opening, the material conveying pipeline is communicated with the material feeding opening and the material conveying opening, and the material returning pipeline is communicated with the material returning opening and the material supplying pipeline and / or the material feeding opening. On one hand, based on mixing of materials and freezing airflow, crushing is performed by improving material brittleness, the material crushing quality is effectively improved, and the sphericity of material particles is greatly improved; and on the other hand, crushing and grading are combined, materials can be continuously crushed and recovered in a grading manner, remaining materials can be circularly crushed, continuous production is achieved, energy consumption is low, production efficiency is high, and in addition, the structure is simple, operation is convenient, and input cost is low.

Description

Technical Field

[0001] This utility model belongs to the field of pulverizing devices, specifically relating to a cryogenic mechanical pulverizing device suitable for the preparation of laser printer developer. Background Technology

[0002] Laser printing developer, a key component in the laser printing process, mainly consists of resin, magnetic powder, charge control agent, pigment, additives, and other additives. Its particle size is generally around 10 μm, and it exhibits some heat sensitivity. Preparation methods are divided into pulverization and polymerization. Pulverization is widely used due to its simple preparation principle and low environmental pollution. The pulverization method for preparing laser printing developer mainly involves the following steps: ingredient preparation → premixing → mixing → coarse pulverization → ultrafine pulverization → grading → modification → homogenization → sieving → packaging. Ultrafine pulverization, as a crucial step in particle formation, plays a decisive role in the particle size distribution and microstructure. The uniformity and microstructure of the particles significantly affect the test results of printing performance.

[0003] Existing ultrafine grinding methods for developer preparation mainly involve air jet milling, which uses the energy of a high-speed airflow (300-500 m / s) to cause particles to impact, collide, and undergo frictional shearing, thus achieving ultrafine particle grinding. However, in actual production, existing technologies have the following drawbacks:

[0004] 1. Air jet mills for developers require high gas flow rates due to their low particle size, resulting in significant investment in equipment such as air compressors, air jet mills, and induced draft fans. They also consume a lot of energy during operation, leading to high costs.

[0005] 2. The finished product after air jet milling is often prone to over-grinding, with the overall particle size being too small and a large number of excessively small particles (<3μm), which affects the effective output. Furthermore, after impact and collision, the microscopic morphology of the particles often has many sharp corners and protrusions, which affects the electrical and magnetic properties of the developer. In addition, traditional mechanical milling generally has a low spindle speed, and the particle size of the material does not meet the requirements of the laser printer developer. Summary of the Invention

[0006] The technical problem to be solved by this utility model is to overcome the shortcomings of the prior art and provide a brand-new cryogenic mechanical pulverizing device suitable for the preparation of laser printer developer.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows:

[0008] A cryogenic mechanical pulverizing device suitable for preparing laser printer developers includes a pulverizing chamber with an inlet and an outlet at both ends, a feeding pipe, a cryogenic airflow pipe, and a grading unit. The feeding pipe and the cryogenic airflow pipe are respectively connected to the inlet. The grading unit includes a grading chamber, a conveying pipe, and a return pipe. The grading chamber has a conveying port, a discharge port, and a return port. The conveying pipe connects the discharge port and the conveying port. The return pipe connects the return port to the feeding pipe and / or the inlet. During pulverization, the material is mixed with the cryogenic airflow and enters the pulverizing chamber from the inlet. After pulverization, it enters the grading chamber from the discharge port through the conveying pipe. The finished material particles are discharged through the discharge port, and the remaining material enters the pulverizing chamber and / or the feeding pipe through the return pipe for cyclic pulverization.

[0009] According to a specific embodiment and preferred aspect of this utility model, the feeding pipe is connected to the refrigerated airflow pipe. The material enters the refrigerated airflow pipe from the feeding pipe and flows into the grinding chamber with the refrigerated airflow. Here, the material can be fully mixed with the refrigerated airflow before entering the grinding chamber to ensure that the material is fully frozen to improve its brittleness, thereby improving the grinding effect.

[0010] According to another specific embodiment and preferred aspect of this utility model, the temperature of the freezing airflow is -15 to -20°C; and / or, the flow velocity of the freezing airflow is 3-50 m / s. Here, based on the arrangement of the freezing airflow velocity, the material is pulverized at a low speed (compared to the speed of traditional airflow pulverization) under freezing conditions, which greatly increases the residence time of the material when passing through the pulverization chamber, increases the number of collisions, and improves the pulverization quality.

[0011] According to another specific embodiment and preferred aspect of this utility model, the pulverizing chamber includes a chamber body having an inlet and an outlet, and a pulverizing module disposed inside the chamber body. A cooling channel with a cooling medium is formed on the chamber body, and during pulverization, the chamber body simultaneously exchanges heat with the cooling medium. In this application, a chilled airflow is introduced into the cooling channel. The purpose of this arrangement is to ensure the stability of the temperature inside the pulverizing chamber, and to keep the temperature inside the pulverizing chamber close to the temperature of the mixture of material and chilled airflow. This avoids temperature changes caused by heat exchange between the material and the chamber wall during pulverization, thereby ensuring stable pulverization quality.

[0012] In some specific embodiments, the cooling channel extends spirally from one end of the cavity body to the other end around the centerline of the cavity body. This achieves a uniform temperature distribution within the cavity body.

[0013] Furthermore, the inlet of the cooling channel is located at the end of the cavity body near the feed port, and the outlet is located at the end of the cavity body near the discharge port. Here, the flow direction of the cooling medium in the cooling channel is the same as the flow direction of the mixture of material and frozen airflow in the crushing chamber. In this way, the mixture of material and frozen airflow can be kept in a stable low-temperature environment no matter where it flows.

[0014] Preferably, the crushing module includes a crushing roller shaft, an inner ring body sleeved on the crushing roller shaft, and an outer ring body fixed to the inner wall of the cavity body. The outer wall of the inner ring body is provided with multiple moving crushing blades arranged in a ring at intervals around its own center line, and the inner wall of the outer ring body is provided with multiple stationary crushing blades arranged in a ring at intervals around its own center line. The crushing surfaces formed by the multiple moving crushing blades and the multiple stationary crushing blades are spaced 1-2 mm apart. Here, based on the cooperation of the multiple moving and stationary crushing blades, the material undergoes impact, collision, friction, and shearing when it enters between them, and the particle size after crushing reaches Dv90 < 11 μm.

[0015] Specifically, the distance between two adjacent stationary crushing blades is greater than the distance between two adjacent moving crushing blades.

[0016] Preferably, both ends of the crushing roller shaft extend out of the cavity body, and each end of the crushing roller shaft is provided with a bearing seat and a cooling water circulation pipe mounted on the bearing seat and forming a heat exchange with the crushing roller shaft. Here, the crushing roller shaft is set independently and cooled by circulating water, thereby improving the bearing life.

[0017] In addition, the grading cavity includes a grading cavity body and a grading wheel disposed inside the grading cavity body. The top of the grading cavity body forms a discharge port, the bottom forms a return port, and one side forms a conveying port. The inner cavity of the grading cavity body gradually narrows from top to bottom, and the return port is connected to the feeding pipe.

[0018] Due to the implementation of the above technical solution, this utility model has the following advantages compared with the prior art:

[0019] Existing air jet mills for developers require high gas flow rates and have low particle sizes, resulting in significant investment in equipment such as air compressors, air jet mills, and induced draft fans, as well as high energy consumption and costs. Furthermore, the finished product often exhibits over-grinding, with an overall smaller particle size and a higher proportion of excessively small particles (<3μm), impacting effective yield. Additionally, the impact and collision effects on the particles often result in numerous sharp corners and protrusions, affecting the electrical and magnetic properties of the developer. Moreover, traditional mechanical milling generally has low spindle speeds, failing to meet the particle size requirements for laser printer developers. This application addresses the issue of cryogenic mechanical milling suitable for preparing laser printer developers. The device features an integrated structural design that cleverly addresses the shortcomings and defects of existing technologies. This pulverizing device mixes materials with a chilled airflow before pulverizing them in the pulverizing chamber. The mixing with the chilled airflow increases the brittleness of the materials, resulting in better particle morphology, exhibiting an elliptical shape. Compared to traditional airflow pulverization, the sphericity of the particles is improved from approximately 60% to 85%. The pulverized particles are then carried by the airflow through a conveying pipe into a grading chamber. The finished particles that meet the requirements are discharged through the discharge port, while the remaining material is returned to the pulverizing chamber and / or the feeding pipe via a return pipe for further cyclic pulverization and re-grading. Therefore, compared to existing technologies, this invention, on the one hand, improves the pulverization quality and significantly enhances particle sphericity by increasing the brittleness of the materials through mixing with chilled airflow; on the other hand, it combines pulverization and grading, enabling continuous pulverization and graded recovery of materials, with the remaining material being recycled for further pulverization, achieving continuous production with low energy consumption and high production efficiency. Furthermore, it features a simple structure, convenient operation, and low investment cost. Attached Figure Description

[0020] Figure 1 This is a front view schematic diagram of the cryogenic mechanical pulverizing device for preparing laser printer developer according to the present invention;

[0021] Figure 2 for Figure 1 A half-sectional view of the grinding chamber;

[0022] Wherein: 1. Crushing chamber; 10. Chamber body; k0. Feed inlet; k1. Discharge outlet; t. Cooling channel; 11. Crushing module; 110. Crushing roller shaft; a0. Bearing seat; a1. Cooling water circulation pipe; 111. Inner ring body; p1. Moving crushing blade; 112. Outer ring body; p2. Fixed crushing blade;

[0023] 2. Material supply pipeline;

[0024] 3. Refrigeration airflow duct;

[0025] 4. Grading unit; 40. Grading cavity; 400. Grading cavity body; 401. Grading wheel; k2. Feeding port; k3. Discharge port; k4. Return port; 41. Feeding pipe; 42. Return pipe. Detailed Implementation

[0026] To make the above-mentioned objects, features, and advantages of this utility model more apparent and understandable, the present utility model will be described in detail below with reference to the accompanying drawings and specific embodiments. Many specific details are set forth in the following description to provide a full understanding of the present utility model. However, the present utility model can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present utility model. Therefore, the present utility model is not limited to the specific embodiments disclosed below.

[0027] In the description of this utility model, it should be understood that the terms "center," "longitudinal," "transverse," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0028] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0029] In this utility model, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0030] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0031] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0032] like Figure 1 and Figure 2 As shown, the cryogenic mechanical pulverizing device for preparing laser printer developer involved in this embodiment includes a pulverizing chamber 1, a feeding pipe 2, a cryogenic airflow pipe 3, and a grading unit 4.

[0033] Specifically, the crushing chamber 1 includes a chamber body 10 with an inlet k0 and an outlet k1 formed at both ends, and a crushing module 11 disposed inside the chamber body 10. The chamber body 10 has a cooling channel t connected to a cooling medium. During crushing, the chamber body 10 simultaneously exchanges heat with the cooling medium. In this application, a chilled airflow is introduced into the cooling channel. This arrangement aims to ensure the stability of the temperature within the crushing chamber and to keep the temperature within the crushing chamber close to the temperature of the mixture of material and chilled airflow. This prevents the material from exchanging heat with the chamber wall during crushing, thus ensuring stable crushing quality.

[0034] For ease of implementation, the cooling channel t extends spirally from one end of the cavity body 10 around the centerline of the cavity body 10 to the other end. This achieves a uniform temperature distribution within the cavity body.

[0035] Meanwhile, the inlet of the cooling channel t is located on the cavity body near the feed port k0, and the outlet is located on the cavity body 10 near the discharge port k1. Here, the flow direction of the cooling medium in the cooling channel is the same as the flow direction of the mixture of material and frozen airflow in the crushing chamber. In this way, the mixture of material and frozen airflow can be in a stable low-temperature environment no matter where it flows.

[0036] The pulverizing module 11 includes a pulverizing roller shaft 110, an inner ring body 111 sleeved on the pulverizing roller shaft 110, and an outer ring body 112 fixed to the inner wall of the cavity body 10. The outer wall of the inner ring body 111 is provided with multiple moving pulverizing blades p1 arranged in a ring-like interval around its own center line. The inner wall of the outer ring body 112 is provided with multiple fixed pulverizing blades p2 arranged in a ring-like interval around its own center line. Each moving pulverizing blade p1 and each fixed pulverizing blade p2 extends axially along the pulverizing roller shaft 110. The pulverizing surfaces formed by the multiple moving pulverizing blades p1 and the multiple fixed pulverizing blades p2 are spaced 1-2 mm apart, forming a ring-shaped pulverizing channel. During pulverization, the material and the chilled airflow mixture are pulverized through the pulverizing channel. Here, based on the cooperation of the multiple moving and fixed pulverizing blades, the material undergoes impact, collision, friction, and shearing when entering between them, and the particle size after pulverization reaches Dv90 < 11 μm.

[0037] Specifically, the distance between two adjacent stationary crushing blades p2 is greater than the distance between two adjacent moving crushing blades p1; both ends of the crushing roller shaft 110 extend out of the cavity body 10, and each end of the crushing roller shaft 110 is provided with a bearing seat a0 and a cooling water circulation pipe a1 disposed on the bearing seat a0 and forming heat exchange with the crushing roller shaft 110. The layout of the cooling water circulation pipe a1 is a conventional design and will not be described in detail here. Here, the crushing roller shaft is independently set and cooled by circulating water, which improves the bearing life. The linear speed of the crushing roller shaft 110 is adjustable, which can reduce the over-crushing of particles, increase the effective output by 20%, and is more energy-efficient in continuous production. The energy consumption per unit output of airflow crushing is about 4000 kW·h / t, while the energy consumption per unit output of this utility model is about 2000 kW·h / t.

[0038] In this example, the feeding pipe 2 and the refrigerated airflow pipe 3 are respectively connected to the feed inlet k0. During crushing, the material is mixed with the refrigerated airflow and enters the crushing chamber 1 from the feed inlet k0.

[0039] In some specific embodiments, the feeding pipe 2 and the refrigerated airflow pipe 3 are connected. The material enters the refrigerated airflow pipe 3 from the feeding pipe 2 and flows into the grinding chamber 1 with the refrigerated airflow. Here, the material can be fully mixed with the refrigerated airflow before entering the grinding chamber to ensure that the material is fully frozen to improve its brittleness, thereby improving the grinding effect.

[0040] For further ease of implementation, the temperature of the freezing airflow is -15 to -20°C; and / or, the flow rate of the freezing airflow is 3-50 m / s. Here, based on the arrangement of the freezing airflow velocity, materials are pulverized at a low speed (compared to the speed of traditional airflow pulverization) under freezing conditions, significantly increasing the residence time of the material in the pulverizing chamber, increasing the number of collisions, and improving the pulverization quality.

[0041] In this example, the grading unit 4 includes a grading chamber 40, a conveying pipe 41, and a return pipe 42. The grading chamber 40 has a conveying port k2, a discharge port k3, and a return port k4. The conveying pipe 41 connects the discharge port k1 and the conveying port k2. The return pipe 42 connects the return port k4 with the feeding pipe 2 and / or the inlet port k0. The crushed material particles are driven by the airflow and enter the grading chamber 40 from the discharge port k1 through the conveying pipe 41. The finished material particles are discharged through the discharge port k0, and the remaining material enters the crushing chamber 1 and / or the feeding pipe 2 through the return pipe 42 for cyclic crushing.

[0042] In some specific embodiments, the grading cavity 40 includes a grading cavity body 400 and a grading wheel 401 disposed within the grading cavity body 400. The top of the grading cavity body 400 forms a discharge port k3, the bottom forms a return port k4, and one side forms a conveying port k2. The inner cavity of the grading cavity body 400 gradually narrows from top to bottom, and the return port k4 is connected to the feeding pipe 2. The grading wheel 401 is a prior art technology. Particles of the required particle size are carried out by the induced draft fan to enter the next process, while oversized particles larger than 20μm are retained by the grading wheel and re-crushed.

[0043] In summary, after adopting this pulverizing device, the material is mixed with the chilled airflow and then enters the pulverizing chamber for pulverization. The brittleness of the material increases after mixing with the chilled airflow, and the pulverized material particles have a better morphology, exhibiting an elliptical shape. Compared with traditional airflow pulverization, the sphericity of the material particles is basically increased from 60% to 85%. Then, the pulverized material particles continue to enter the grading chamber through the conveying pipe under the drive of the airflow. The finished material particles that meet the requirements are discharged through the discharge port, while the remaining material is returned to the pulverizing chamber and / or the feeding pipe through the return pipe to participate in cyclic pulverization and re-grading. Therefore, compared with the prior art, this utility model has several advantages. First, it improves the pulverization quality of materials by increasing their brittleness through the mixing of materials and chilled airflow, thereby significantly enhancing the sphericity of the material particles. Second, it combines pulverization with grading, enabling continuous pulverization and graded recycling of materials, with residual materials being recycled for further pulverization, achieving continuous production with low energy consumption and high production efficiency. Furthermore, it features a simple structure, convenient operation, and low investment cost. Third, the materials are fully mixed with the chilled airflow before entering the pulverization chamber to ensure thorough freezing and improve brittleness, thus enhancing the pulverization effect. Fourth, based on the layout of the chilled airflow velocity, the materials are pulverized at a low speed (compared to the speed of traditional airflow pulverization) under freezing conditions, significantly increasing the residence time of the materials in the pulverization chamber, increasing the number of collisions, and improving the pulverization quality. Fifthly, a chilled airflow is introduced into the cooling channel. This design aims to ensure a stable temperature within the crushing chamber, maintaining a temperature close to that of the material and the chilled airflow mixture. This prevents heat exchange between the material and the chamber wall during crushing, thus ensuring stable crushing quality. Sixthly, the flow direction of the cooling medium in the cooling channel is the same as the flow direction of the material and chilled airflow mixture within the crushing chamber. This ensures that the material and chilled airflow mixture remain in a stable low-temperature environment regardless of their position. Seventhly, based on the coordination of multiple moving and stationary crushing blades, the material undergoes impact, collision, friction, and shearing when entering the space between them, resulting in a crushed particle size of Dv90 < 11 μm. Eighthly, the crushing roller shaft is independently designed and cooled by circulating water, improving bearing life.

[0044] The present utility model has been described in detail above, with the aim of enabling those skilled in the art to understand its contents and implement it. However, this description should not be construed as limiting the scope of protection of the present utility model. All equivalent changes or modifications made in accordance with the spirit and essence of the present utility model should be included within the scope of protection of the present utility model.

Claims

1. A cryogenic mechanical pulverizing device suitable for preparing laser printer developer, characterized in that, It includes a crushing chamber with an inlet and an outlet at both ends, a feeding pipe, a chilled airflow pipe, and a grading unit, wherein the feeding pipe and the chilled airflow pipe are respectively connected to the inlet; the grading unit includes a grading chamber, a conveying pipe, and a return pipe, wherein the grading chamber has a conveying port, a discharge port, and a return port, the conveying pipe connects the discharge port and the conveying port, and the return pipe connects the return port to the feeding pipe and / or the inlet. During crushing, the material is mixed with the chilled airflow and enters the crushing chamber from the inlet, and after crushing, it enters the grading chamber from the discharge port through the conveying pipe. The finished material particles are discharged through the discharge port, and the remaining material enters the crushing chamber and / or the feeding pipe through the return pipe for cyclic crushing.

2. The cryogenic mechanical pulverizing apparatus for preparing laser printer developer according to claim 1, characterized in that, The feeding pipe is connected to the refrigerated airflow pipe. The material enters the refrigerated airflow pipe from the feeding pipe and flows into the crushing chamber with the refrigerated airflow.

3. The cryogenic mechanical pulverizing apparatus for preparing laser printer developer according to claim 1, characterized in that, The temperature of the chilled gas flow is -15 to -20°C; and / or the flow velocity of the chilled gas flow is 3-50 m / s.

4. The cryogenic mechanical pulverizing apparatus for preparing laser printer developer according to claim 1, characterized in that, The crushing chamber includes a chamber body with the feed inlet and the discharge outlet, and a crushing module disposed inside the chamber body. The chamber body has a cooling channel connected to a cooling medium. During crushing, the chamber body exchanges heat with the cooling medium simultaneously.

5. The cryogenic mechanical pulverizing apparatus for preparing laser printer developer according to claim 4, characterized in that, The cooling channel extends spirally from one end of the cavity body to the other end, around the centerline of the cavity body.

6. The cryogenic mechanical pulverizing apparatus for preparing laser printer developers according to claim 5, characterized in that, The inlet of the cooling channel is located on the cavity body near the feed port, and the outlet is located on the cavity body near the discharge port.

7. The cryogenic mechanical pulverizing apparatus for preparing laser printer developer according to claim 4, characterized in that, The pulverizing module includes a pulverizing roller shaft, an inner ring body sleeved on the pulverizing roller shaft, and an outer ring body fixed on the inner wall of the cavity body. The outer wall of the inner ring body is provided with a plurality of moving pulverizing blades arranged in a ring at intervals around its own center line. The inner wall of the outer ring body is provided with a plurality of fixed pulverizing blades arranged in a ring at intervals around its own center line. The pulverizing surface formed by the plurality of moving pulverizing blades and the pulverizing surface formed by the plurality of fixed pulverizing blades are spaced 1 to 2 mm apart.

8. The cryogenic mechanical pulverizing apparatus for preparing laser printer developer according to claim 7, characterized in that, The distance between two adjacent stationary crushing blades is greater than the distance between two adjacent moving crushing blades.

9. The cryogenic mechanical pulverizing apparatus for preparing laser printer developer according to claim 7, characterized in that, Both ends of the crushing roller shaft extend out of the cavity body, wherein each end of the crushing roller shaft is provided with a bearing seat and a cooling water circulation pipe disposed on the bearing seat and forming a heat exchange with the crushing roller shaft.

10. The cryogenic mechanical pulverizing apparatus for preparing laser printer developer according to claim 1, characterized in that, The grading cavity includes a grading cavity body and a grading wheel disposed within the grading cavity body. The top of the grading cavity body forms the discharge port, the bottom forms the return port, and one side forms the conveying port. The inner cavity of the grading cavity body gradually narrows from top to bottom, and the return port is connected to the feeding pipe.

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