Anti-blocking grinding cavity structure of spherical graphite vibration mill

Abstract

The utility model provides a kind of anti-blocking grinding cavity structure of spherical graphite vibration mill, belong to spherical graphite vibration mill technical field, the anti-blocking grinding cavity structure of this spherical graphite vibration mill includes grinding cavity, dispersing flow guide piece and vibration grinding assembly, the grinding cavity is hollow cylinder structure, the inner wall surface of the grinding cavity is provided with multiple annular ridges distributed along the axial direction, the dispersing flow guide piece is fixedly installed in the inner side of the feed end of the grinding cavity, the dispersing flow guide piece is in the structure of cone frustum, the large end of the dispersing flow guide piece is towards the feed direction of the grinding cavity, annular gap passage is formed between the small end of the dispersing flow guide piece and the inner wall surface of the grinding cavity;It can solve the existing spherical graphite vibration mill grinding cavity's feed area and internal grinding area will occur accumulation and hardening, leading to grinding efficiency decline, equipment needs frequent shutdown cleaning, seriously affect the continuity of production and economic benefit's technical problem.

Description

Technical Field

[0001] This utility model belongs to the technical field of spherical graphite vibratory mills, specifically, it relates to an anti-clogging grinding chamber structure for a spherical graphite vibratory mill. Background Technology

[0002] Spherical graphite is an important component of lithium-ion battery anode materials. Its preparation requires spheroidizing natural or artificial graphite using a vibratory mill. Traditional spherical graphite vibratory mills mainly consist of a vibratory motor, grinding chamber, and feeding / discharging devices. After the material enters the grinding chamber through the feed inlet, it collides and rubs against the grinding media under the action of vibration, gradually achieving spheroidization and particle size refinement. However, in actual production applications, due to the numerous lamellar structures and irregular morphologies on the surface of spherical graphite particles, the particles are prone to interlocking and... Overlapping, coupled with the strong cohesive force of the material itself, easily leads to bridging and arching effects inside the grinding chamber, causing obstruction of material flow. Existing technologies typically use methods such as increasing vibration intensity, improving the precision of feed speed control, or periodic shutdown for cleaning to alleviate the material blockage problem. However, increasing vibration intensity will exacerbate equipment wear and energy consumption, and precise control of feed speed requires a complex automation system, which increases equipment costs. Periodic shutdown for cleaning directly affects production efficiency. Therefore, there is an urgent need to develop a grinding chamber structure that is simple in structure, low in cost, and can fundamentally prevent material blockage. Utility Model Content

[0003] In view of this, the present invention provides an anti-clogging grinding chamber structure for a spherical graphite vibratory mill, which can solve the technical problem that, during long-term continuous operation of existing spherical graphite vibratory mills, due to the strong self-aggregation and poor flowability of spherical graphite materials, the material is prone to accumulation and caking in the feeding area and internal grinding area of ​​the grinding chamber, resulting in material blockage, which leads to a decrease in grinding efficiency, frequent equipment shutdowns for cleaning, and seriously affects production continuity and economic benefits.

[0004] This utility model is implemented as follows:

[0005] This utility model provides an anti-clogging grinding chamber structure for a spherical graphite vibratory mill, comprising a grinding chamber, a dispersing guide, and a vibratory grinding assembly. The grinding chamber is a hollow cylindrical structure, and its inner wall surface is provided with multiple axially distributed annular ridges. The dispersing guide is fixedly installed on the inner side of the feed end of the grinding chamber. The dispersing guide has a frustoconical structure, with its large end facing the feed direction of the grinding chamber, and its small end forming an annular gap channel with the inner wall surface of the grinding chamber. The vibratory grinding assembly is disposed on the bottom outer side of the grinding chamber and is used to drive the grinding chamber to generate vibration.

[0006] The technical effects of the anti-clogging grinding chamber structure of the spherical graphite vibratory mill provided by this utility model are as follows: By setting multiple axially distributed annular ridges on the inner wall of the grinding chamber, the spherical graphite material can fall and roll step by step along the stepped structure formed by the annular ridges during the vibratory grinding process, avoiding the formation of a dense accumulation layer of material in the chamber. At the same time, the frustum-shaped structure of the dispersing guide can evenly disperse the material entering the grinding chamber to the surrounding area, allowing the material to enter the grinding area through the annular gap channel, effectively preventing the material from clogging at the feed inlet, and ensuring the continuity and uniformity of material flow in the grinding chamber.

[0007] Based on the above technical solution, the anti-clogging grinding chamber structure of the spherical graphite vibratory mill of this utility model can be further improved as follows:

[0008] The annular ridge has a triangular cross-section, and its inclined surface faces the discharge end of the grinding chamber.

[0009] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: the annular ridge adopts a triangular cross-sectional structure with the inclined surface facing the discharge end, so that when the material slides along the inclined surface under vibration, it is subjected to a downward thrust component, which promotes the material to move towards the discharge end. At the same time, the triangular ridge can crush and loosen the accumulated material, further reducing the risk of material blockage in the grinding chamber and improving the flow performance of the material in the chamber.

[0010] Furthermore, the axial distance between two adjacent annular ridges is 2 to 5 times the axial height of the annular ridge.

[0011] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: maintaining a reasonable axial spacing between adjacent annular ridges allows sufficient space for the material to tumble and grind in the groove area formed between adjacent ridges, avoiding the blockage caused by the material movement being restricted due to the spacing being too small. At the same time, the ratio between the spacing and the height of the ridges ensures that the material can smoothly transition from one groove area to the next, maintaining the continuous flow of the material in the entire grinding chamber.

[0012] Furthermore, the cone-shaped side surface of the dispersing guide is uniformly distributed with multiple spiral grooves, and the spiral direction of the spiral grooves is consistent with the vibration rotation direction of the grinding chamber.

[0013] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: a spiral groove is set on the side of the cone of the dispersing guide, so that the material is guided by the spiral groove when passing through the surface of the dispersing guide and generates a rotational motion. This rotational motion is consistent with the vibration rotation direction of the grinding chamber, which can enhance the dispersion effect of the material and make the material more evenly distributed in the circumferential range of the annular gap channel, avoiding the material from accumulating in a certain local area and causing material blockage.

[0014] Furthermore, the small end face of the dispersing guide is in the shape of a concave spherical surface, and the radius of curvature of the concave spherical surface is greater than half the diameter of the small end of the dispersing guide.

[0015] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: the small end face of the dispersing guide is a concave spherical shape. When the material hits the concave spherical surface, it will be subjected to an outward reflection force, causing the material to naturally disperse towards the annular gap channel. The curvature radius design of the concave spherical surface ensures that the angle and direction of the material reflection can effectively match the position of the annular gap channel, improving the efficiency of material transfer from the central area to the peripheral area and reducing the retention and accumulation of material at the end of the dispersing guide.

[0016] Furthermore, the radial width of the annular gap channel gradually increases along the axial direction of the grinding cavity, and the minimum radial width of the annular gap channel at the feed end is 1 / 10 to 1 / 5 of the inner diameter of the grinding cavity.

[0017] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: the design of the radial width of the annular gap channel gradually increasing along the axial direction allows the material to gradually obtain a larger movement space after entering the grinding chamber. This gradual channel structure avoids eddies and accumulation caused by sudden changes in material flow rate. At the same time, maintaining an appropriate minimum radial width at the feed end can reasonably control the material flow rate and prevent excessive material from rushing in at the same time and causing blockage inside the grinding chamber.

[0018] Furthermore, the bottom surface of the groove formed between the inner wall surface of the grinding cavity and the annular ridge has an arc-shaped curved surface structure.

[0019] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: the bottom surface of the groove formed between the inner wall of the grinding chamber and the annular ridge adopts an arc-shaped curved surface structure, which eliminates sharp edges and dead corner areas, making it less likely for materials to stagnate and adhere at the bottom of the groove during vibration. The arc-shaped curved surface can guide the material to move along a smooth curved trajectory, reduce the frictional resistance between the material and the inner wall of the chamber, promote the continuous flow and tumbling of the material, and reduce the probability of material blockage.

[0020] Furthermore, the dispersing guide is connected to the feed end flange of the grinding chamber by multiple fixing bolts, which are evenly distributed along the circumference of the feed end flange.

[0021] The beneficial effects of adopting the above-mentioned improved scheme are as follows: the use of fixing bolts to connect the dispersing guide to the feed end flange facilitates the installation and disassembly of the dispersing guide, and makes it convenient to clean and maintain the inside of the grinding chamber. The uniform circumferential distribution of the bolts ensures the installation stability of the dispersing guide under vibration environment, and avoids the position displacement of the dispersing guide due to loose fixing, which affects its dispersing and guiding function. At the same time, it is convenient to replace the dispersing guide with different structural parameters according to different material characteristics.

[0022] Furthermore, the grinding chamber is made of wear-resistant alloy steel, and the dispersing guide is made of stainless steel.

[0023] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: the grinding chamber is made of wear-resistant alloy steel, which can withstand the wear and impact generated by long-term grinding of spherical graphite materials, and maintain the structural integrity of the inner wall and annular ridge of the grinding chamber. The dispersion guide is made of stainless steel, which has good corrosion resistance and surface smoothness, and reduces the adhesion of materials on the surface of the dispersion guide. The reasonable selection of the two materials takes into account the service life and functional requirements of each component.

[0024] Furthermore, the top edge of the annular ridge is a circular arc transition structure, and the radius of the circular arc transition structure is 1 / 5 to 1 / 3 of the height of the annular ridge.

[0025] The beneficial effects of adopting the above-mentioned improvement scheme are as follows: the top edge of the annular ridge adopts a rounded transition structure, which avoids the cutting and crushing effect of sharp edges on the material, so that the material can smoothly roll over when passing the top of the ridge without being stuck or excessively crushed. The rounded transition structure can also reduce the collision stress between the material and the ridge, reduce the wear rate of the ridge edge, extend the service life of the annular ridge, and maintain the continuity of material flow in the grinding chamber.

[0026] Compared with existing technologies, the beneficial effects of the anti-clogging grinding chamber structure of the spherical graphite vibratory mill provided by this utility model are as follows: This utility model constructs a grinding chamber structure that can effectively prevent material blockage by setting multiple axially distributed annular ridges on the inner wall of the grinding chamber and cooperating with a frustum-shaped dispersing guide installed at the feed end. The stepped structure formed by the annular ridges forces the material to continuously roll and fall during vibration, destroying the dense accumulation state of the material. The dispersing guide evenly disperses the feed material into the annular gap channel, avoiding concentrated accumulation of material at the feed inlet. The synergistic effect of the two ensures that the material always maintains a loose flow state in the grinding chamber, effectively solving the material blockage problem of the spherical graphite vibratory mill. Compared with existing technologies, this utility model does not require additional power devices or complex control systems. It achieves the anti-clogging function simply by optimizing the internal structure of the grinding chamber and adding dispersing guides. The structure is simple and reliable, easy to maintain, significantly improves the continuous running time and grinding efficiency of the equipment, and reduces production costs. It is particularly suitable for the vibration grinding of powder materials with poor flowability, such as spherical graphite. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments of this utility model will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the anti-clogging grinding chamber structure of a spherical graphite vibratory mill;

[0029] Figure 2 This is a schematic diagram of the structure of the flow-dispersing guide component;

[0030] Figure 3 This is a schematic diagram of the structure of a ring-shaped ridge;

[0031] The attached diagram lists the components represented by each number as follows:

[0032] 10. Grinding chamber; 20. Dispersing guide; 30. Vibration grinding assembly. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of this utility model clearer, the technical solutions of the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings.

[0034] like Figure 1-3The figure shows a schematic diagram of the anti-clogging grinding chamber structure of a spherical graphite vibratory mill provided by this utility model. The figure includes a grinding chamber 10, a dispersing guide 20, and a vibratory grinding assembly 30. The grinding chamber is a hollow cylindrical structure. The inner wall of the grinding chamber is provided with multiple annular ridges distributed along the axial direction. The dispersing guide is fixedly installed on the inner side of the feed end of the grinding chamber. The dispersing guide has a frustoconical structure. The large end of the dispersing guide faces the feed direction of the grinding chamber. The small end of the dispersing guide forms an annular gap channel with the inner wall of the grinding chamber. The vibratory grinding assembly is located on the bottom outer side of the grinding chamber and is used to drive the grinding chamber to generate vibration.

[0035] In the above technical solution, the cross-section of the annular ridge is triangular, and the inclined surface of the annular ridge faces the discharge end of the grinding chamber.

[0036] Furthermore, in the above technical solution, the axial distance between two adjacent annular ridges is 2 to 5 times the axial height of the annular ridge.

[0037] Furthermore, in the above technical solution, multiple spiral grooves are evenly distributed on the side of the cone of the dispersing guide, and the spiral direction of the spiral grooves is consistent with the vibration rotation direction of the grinding chamber.

[0038] Furthermore, in the above technical solution, the small end face of the dispersing guide is in the shape of a concave spherical surface, and the radius of curvature of the concave spherical surface is greater than half the diameter of the small end of the dispersing guide.

[0039] Furthermore, in the above technical solution, the radial width of the annular gap channel gradually increases along the axial direction of the grinding cavity, and the minimum radial width of the annular gap channel at the feed end is 1 / 10 to 1 / 5 of the inner diameter of the grinding cavity.

[0040] Furthermore, in the above technical solution, the bottom surface of the groove formed between the inner wall surface of the grinding cavity and the annular ridge has an arc-shaped curved surface structure.

[0041] Furthermore, in the above technical solution, the dispersing guide is connected to the feed end flange of the grinding chamber by multiple fixing bolts, and the fixing bolts are evenly distributed along the circumference of the feed end flange.

[0042] Furthermore, in the above technical solution, the grinding chamber is made of wear-resistant alloy steel, and the dispersing guide is made of stainless steel.

[0043] Furthermore, in the above technical solution, the top edge of the annular ridge is a circular arc transition structure, and the radius of the circular arc transition structure is 1 / 5 to 1 / 3 of the height of the annular ridge.

[0044] The following is a specific embodiment 1 of this utility model: In this embodiment, the grinding chamber adopts a cylindrical structure with an outer diameter of 600mm, an inner diameter of 550mm, and a total length of 1200mm. The material of the grinding chamber is chromium-molybdenum alloy steel, which has a Rockwell hardness of HRC55 to HRC60 and excellent wear resistance. Eight annular ridges are evenly distributed along the axial direction on the inner wall of the grinding chamber. Each annular ridge has a height of 15mm and a bottom width of 25mm. The cross-section of the annular ridge is an isosceles triangle structure, and the angle between the inclined surface and the axis of the chamber is 30°. The inclined surface faces the discharge end. The distance between two adjacent annular ridges is... The axial spacing is 45mm. The top edge of the annular ridge adopts a 3mm radius arc transition. The bottom surface of the groove formed between the annular ridge and the inner wall surface adopts an arc-shaped curved surface structure with a radius of 18mm. The dispersing guide is made of 304 stainless steel and has a truncated cone shape. The large end diameter is 280mm, the small end diameter is 120mm, the truncated cone height is 180mm, and the cone angle is 55°. Six spiral grooves are evenly distributed on the side of the truncated cone. Each spiral groove is 8mm wide and 4mm deep, with a spiral helix angle of 25°. The spiral grooves rotate in a right-hand direction, consistent with the vibration rotation direction of the grinding chamber. The small end face of the dispersing guide... The structure is a concave spherical surface with a radius of curvature of 80mm. The center of the sphere is located 30mm from the small end face on the axis of the dispersing guide. The dispersing guide is connected to the flange at the feed end of the grinding chamber by six M12 bolts. The bolts are evenly distributed around the flange circumference, with a central angle of 60° between adjacent bolts. The annular gap channel formed between the small end of the dispersing guide and the inner wall of the grinding chamber has a minimum radial width of 55mm at the feed end. This width gradually increases along the axial direction, reaching 85mm at a distance of 120mm from the feed end. The vibratory grinding assembly is installed on the outer bottom of the grinding chamber and includes two vibratory motors. The motor has an excitation force of 30kN and a working frequency of 20Hz. During use, zirconia ceramic balls are first filled into the grinding chamber as grinding media, filling it to 50% of the effective volume. Then, the vibratory grinding assembly is started, and the spherical graphite material to be processed is continuously fed into the feed end at a rate of 80 kg per hour. After passing through the dispersing guide, the material is evenly dispersed into the grinding area. Under the action of vibration, the material continuously rolls and falls along the stepped structure formed by the annular ridge, maintaining good fluidity. After 4 to 6 hours of continuous grinding, spherical graphite products with uniform particle size distribution are obtained from the discharge end. No material blockage occurs in the grinding chamber during the entire process, and the equipment operates stably.

[0045] The following is another specific embodiment 2 of this utility model: This embodiment 2 is based on embodiment 1, with the number of annular ridges increased to 12, the axial distance between adjacent annular ridges reduced to 30mm, and the height of the annular ridges kept unchanged at 15mm. This denser arrangement of annular ridges further enhances the disturbance effect on the material flow, increasing the tumbling frequency of the material in the grinding chamber. It is particularly suitable for spherical graphite raw materials with high viscosity or more irregular particle shape. At the same time, the number of spiral grooves on the side of the cone of the dispersing guide is increased to 8, and the depth of the spiral grooves is increased to 6mm, which enhances the rotational dispersion effect of the material and makes the distribution of the material in the annular gap channel more uniform. After actual use verification, this improved structure has a more significant anti-clogging effect when processing high viscosity spherical graphite raw materials, and the continuous running time can reach more than 8 hours without stopping for cleaning.

[0046] The following is another specific embodiment 3 of this utility model: This embodiment 3 is based on embodiment 1, and the structure of the dispersing guide is improved. The cone angle of the frustum is reduced from 55° to 45°, making the frustum more slender. This design extends the residence time of the material on the side of the frustum, and the guiding effect of the spiral groove on the material is more sufficient. At the same time, the radius of curvature of the concave spherical surface at the small end is increased to 100mm, making the curvature of the concave spherical surface smoother. The reflection angle of the material after hitting the concave spherical surface is more horizontal, which is more conducive to the transfer of the material to the annular gap channel. In addition, the minimum radial width of the annular gap channel at the feed end is reduced to 45mm, which allows for stricter control of the material flow rate entering the grinding chamber and avoids local accumulation caused by excessive instantaneous material volume. This improved structure is particularly suitable for production conditions with large fluctuations in feed rate, and can effectively buffer changes in feed volume and maintain the stability of material distribution in the grinding chamber.

[0047] Specifically, the principle of this invention is as follows: The anti-clogging grinding chamber structure of this invention is mainly based on the principles of material flow dynamics and vibration dynamics. By setting an annular ridge on the inner wall of the grinding chamber, the originally smooth inner wall of the chamber is transformed into a multi-step structure. When the material moves downward along the inner wall of the chamber under the action of vibration, the presence of the annular ridge prevents the material from forming a continuous dense layer, but instead divides it into multiple independent flow layers. The material in each flow layer undergoes a falling and tumbling process when passing through the annular ridge. This repeated falling and tumbling motion forces the interlocking structure between material particles to be continuously destroyed and reorganized, maintaining the loose state of the material. At the same time, the triangular cross-section and inclined surface design of the annular ridge cause the material to be pushed downward during vibration, accelerating the movement of the material towards the discharge end, further reducing the risk of clogging and dispersing the material. The frustum-shaped structure of the guide component utilizes the diffusion principle in fluid mechanics. After the material enters from the feed inlet, it first impacts the large end surface of the frustum. Under the action of the impact force, the material diffuses in all directions. The spiral grooves on the side of the frustum further guide the material to generate rotational motion, so that the material is evenly distributed throughout the entire circumferential range of the annular gap channel, avoiding excessive concentration of material in a certain local area. The concave spherical design at the small end utilizes the reflection principle, so that the material impacting the central area can be effectively reflected to the periphery. Combined with the gradual width design of the annular gap channel, a smooth transition of material from the feed area to the grinding area is achieved. Through reasonable geometric shape matching and size matching, the entire structure can achieve effective dispersion and continuous flow of material using the vibration energy of the vibratory mill itself without increasing external power, thus eliminating the conditions for material blockage from a mechanistic perspective.

[0048] In use, spherical graphite raw materials and grinding media are first added to the grinding chamber according to a set ratio. The filling amount of grinding media is usually 40% to 60% of the effective volume of the grinding chamber. Then, the vibratory grinding component is activated to cause the grinding chamber to generate three-dimensional vibration. The vibration frequency is set between 15Hz and 25Hz, and the amplitude is controlled within the range of 3mm to 8mm. The spherical graphite material to be processed is continuously fed into the feed end of the grinding chamber through the feeding device. The material is first dispersed by the dispersing and guiding components and enters the internal grinding area of ​​the grinding chamber from the annular gap channel. Within the grinding chamber, the material and grinding media undergo thorough collision and friction under vibration, achieving spheroidization and particle size refinement. As the material moves downward, it continuously passes through the stepped structure formed by the annular ridges, maintaining a loose flow state. The fully ground material is discharged from the discharge end of the grinding chamber. No machine shutdown is required for cleaning during the entire processing, enabling continuous and stable operation. When maintenance or replacement of different specifications of dispersing guides is needed inside the grinding chamber, the dispersing guides can be removed from the feed end flange by loosening the fixing bolts. After maintenance, they can be reinstalled and the bolts tightened in reverse order.

Claims

1. A clog-resistant grinding chamber structure for a spherical graphite vibratory mill, characterized in that, The device includes a grinding chamber, a dispersing guide, and a vibratory grinding assembly. The grinding chamber is a hollow cylindrical structure with multiple axially distributed annular ridges on its inner wall. The dispersing guide is fixedly installed inside the feed end of the grinding chamber and has a frustoconical structure. The large end of the dispersing guide faces the feed direction of the grinding chamber, and the small end of the dispersing guide forms an annular gap channel with the inner wall of the grinding chamber. The vibratory grinding assembly is located on the bottom outer side of the grinding chamber and is used to drive the grinding chamber to vibrate.

2. The anti-clogging grinding chamber structure of a spherical graphite vibratory mill according to claim 1, characterized in that, The cross-section of the annular ridge is triangular, and the inclined surface of the annular ridge faces the discharge end of the grinding chamber.

3. The anti-clogging grinding chamber structure of a spherical graphite vibratory mill according to claim 2, characterized in that, The axial distance between two adjacent annular ridges is 2 to 5 times the axial height of the annular ridge.

4. The anti-clogging grinding chamber structure of a spherical graphite vibratory mill according to claim 3, characterized in that, The cone-shaped side surface of the dispersing guide has multiple spiral grooves evenly distributed, and the spiral direction of the spiral grooves is consistent with the vibration rotation direction of the grinding chamber.

5. The anti-clogging grinding chamber structure of a spherical graphite vibratory mill according to claim 4, characterized in that, The small end face of the dispersing guide is in the shape of a concave spherical surface, and the radius of curvature of the concave spherical surface is greater than half the diameter of the small end of the dispersing guide.

6. The anti-clogging grinding chamber structure of a spherical graphite vibratory mill according to claim 5, characterized in that, The radial width of the annular gap channel gradually increases along the axial direction of the grinding cavity, and the minimum radial width of the annular gap channel at the feed end is 1 / 10 to 1 / 5 of the inner diameter of the grinding cavity.

7. The anti-clogging grinding chamber structure of a spherical graphite vibratory mill according to claim 6, characterized in that, The bottom surface of the groove formed between the inner wall of the grinding cavity and the annular ridge has an arc-shaped curved surface structure.

8. The anti-clogging grinding chamber structure of a spherical graphite vibratory mill according to claim 7, characterized in that, The dispersing guide is connected to the feed end flange of the grinding chamber by multiple fixing bolts, which are evenly distributed along the circumference of the feed end flange.

9. The anti-clogging grinding chamber structure of a spherical graphite vibratory mill according to claim 8, characterized in that, The grinding chamber is made of wear-resistant alloy steel, and the dispersing guide is made of stainless steel.

10. The anti-clogging grinding chamber structure of a spherical graphite vibratory mill according to claim 9, characterized in that, The top edge of the annular ridge is a circular arc transition structure, and the radius of the circular arc transition structure is 1 / 5 to 1 / 3 of the height of the annular ridge.

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