Fat refining processing device for processing anti-wear agent

Abstract

The invention discloses a fat refining processing device for antiwear agent processing, and relates to the technical field of fat refinement, the fat refining processing device for antiwear agent processing comprises a distillation retort, the top of the distillation retort is connected with a first discharge pipe and a second discharge pipe, and the second discharge pipe is communicated with an adsorption tank; an adsorbent for adsorbing fatty acid is stored in the adsorption tank; the adsorption tank is connected with a discharge pipe for discharging fatty acid finished products, the bottom of the adsorption tank is connected with an air inlet pipe, and the air inlet pipe is communicated with a steam generation device for providing steam for the adsorption tank. Water vapor generated by the vapor generation device can flow back into the distillation retort through the gas inlet pipe, the adsorption tank and the second discharge pipe, and a guide assembly for guiding the backflow water vapor is mounted in the distillation retort. The distillation retort is heated and cleaned by heat energy of high-temperature water vapor, and corrosion of the high-temperature water vapor to a pipeline in the discharging process is avoided.

Description

Technical Field

[0001] This invention relates to the field of fat refining technology, specifically to a fat refining processing apparatus for processing anti-wear agents. Background Technology

[0002] Crude fatty acids obtained from the intermittent or continuous hydrolysis of animal and vegetable oils or vegetable oil soap residues require distillation refining before use. The purpose of distillation is to improve the color of the fatty acids, remove impurities such as undecomposed oils and unsaponifiables from the crude acid, and obtain high-purity fatty acid components from the mixed fatty acids through fractional distillation to meet industrial needs. Existing technologies include research on fatty acid distillation refining devices. For example, Chinese invention patent application CN118491126A discloses a fatty acid distillation system, including a distillation tank and a distillation tube, with the distillation tube positioned at the top of the tank and support feet located on the tank surface; and a stirring assembly, disposed within the tank, including a stirring element, an adjusting element, a driving element, a transmission element, and a scraping element, with the stirring element located inside the tank and the adjusting element located within the stirring element.

[0003] To further improve the quality of fatty acid products, adsorbents such as activated carbon are often used to treat the fractionated fatty acids to remove impurities such as pigments. Currently, the adsorption process first involves collecting the fatty acid fraction to be adsorbed from the distillation, then mixing the liquefied fatty acid fraction with the adsorbent, and finally obtaining the finished fatty acid product. Since the adsorption performance of the adsorbent decreases after use, it needs to be activated with high-temperature steam. However, the high-temperature steam after contact with the adsorbent still has residual heat; direct discharge not only wastes heat energy but also corrodes the discharge pipeline. Summary of the Invention

[0004] The purpose of this invention is to provide a fat refining apparatus for processing anti-wear agents, so as to overcome the above-mentioned shortcomings of the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a fat refining processing apparatus for anti-wear agent processing, comprising a distillation tank, a first discharge pipe and a second discharge pipe connected to the top of the distillation tank, the second discharge pipe being connected to an adsorption tank, the adsorption tank containing an adsorbent for adsorbing fatty acids; a discharge pipe for discharging the finished fatty acid product connected to the adsorption tank, and an air inlet pipe connected to the bottom of the adsorption tank, the air inlet pipe being connected to a steam generator for supplying water vapor to the adsorption tank.

[0006] The steam generated by the steam generator can flow back into the distillation tank through the inlet pipe, the adsorption tank, and the second outlet pipe. The distillation tank is equipped with a guide assembly for guiding the refluxed steam.

[0007] As a preferred embodiment of the present invention, a switch plate is rotatably mounted on the top of the distillation tank, and the switch plate is used to control the opening and closing of the first discharge pipe and the second discharge pipe.

[0008] As a preferred embodiment of the present invention, the guiding component includes a rotating shaft rotatably installed inside the distillation tank, the rotating shaft being vertical and coaxial with the distillation tank; a guide pipe corresponding to the position of the second discharge pipe is installed on the rotating shaft, and a plurality of hollow guide plates are uniformly installed on the circumferential surface of the guide pipe; the top end of the guide plate is connected to the guide pipe, and the bottom end of the guide plate faces the inner wall of the distillation tank.

[0009] As a preferred embodiment of the present invention, the guide tube and the rotating shaft are slidably fitted in the vertical direction, and the guide tube has a first state of being separated from the second discharge tube and a second state of being in contact with the second discharge tube.

[0010] As a preferred embodiment of the present invention, the bottom of the distillation tank is provided with a plurality of discharge holes evenly distributed around the rotating shaft. An annular receiving pipe is fixedly installed on the bottom surface of the distillation tank at the position corresponding to the discharge holes. An annular plate that fits against the bottom surface of the distillation tank is rotatably installed inside the receiving pipe. A through groove corresponding to each discharge hole is provided on the annular plate.

[0011] As a preferred embodiment of the present invention, a first magnetic plate is fixedly installed on the inner circumferential surface of the annular plate, a second magnetic plate corresponding to the position of the first magnetic plate is fixedly installed on the rotating shaft via a support arm, and two stops are fixedly installed in the receiving tube corresponding to the position of the first magnetic plate.

[0012] As a preferred embodiment of the present invention, a guide groove is provided on the outer wall of the guide tube. The guide groove includes a horizontal first annular groove and a second annular groove, which are connected by an arc groove. A ball that cooperates with the guide groove is installed in the distillation tank by a bracket.

[0013] As a preferred embodiment of the present invention, the ball is movably installed inside the ball sleeve, and an elastic element is connected between the ball sleeve and the bracket so that the ball is always in contact with the vertical surface of the guide groove.

[0014] As a preferred embodiment of the present invention, the first annular groove is located above the second annular groove. When the ball is in the first annular groove, the guide tube is in the first state; when the ball is in the second annular groove, the guide tube is in the second state.

[0015] As a preferred embodiment of the present invention, the depth of the first annular groove is gradually changing, and a step is formed at the location corresponding to the arc-shaped groove, with its edge aligned with one side of the arc-shaped groove; the depth of the second annular groove is gradually changing, and a step is formed at the location corresponding to the arc-shaped groove, with its edge aligned with the other side of the arc-shaped groove.

[0016] In the above technical solution, the present invention provides a fat refining processing device for anti-wear agent processing, which connects an adsorption tank and a distillation tank. The adsorbent in the adsorption tank comes into contact with the atomized fatty acids, improving the adsorption effect on impurities in the fatty acids. After the high-temperature steam generated by the steam generator activates the adsorbent, the still-warm steam enters the distillation tank and, under the action of the guiding component, contacts the inner wall of the distillation tank, cleaning the residual mother liquor on the inner wall of the distillation tank. Finally, the liquefied steam carries the impurities detached from the adsorbent and the residual mother liquor in the distillation tank out together. The present invention utilizes the thermal energy of high-temperature steam to heat and clean the distillation tank, avoiding corrosion of the pipeline by high-temperature steam during the discharge process. The guide plate in the present invention not only plays a role in stirring the mother liquor during the distillation process, but also plays a role in guiding the steam during the high-temperature steam reflux process. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0018] Figure 1 This is a three-dimensional structural schematic diagram of the fat refining processing apparatus for anti-wear agent processing in the embodiment;

[0019] Figure 2 This is a schematic diagram of the first three-dimensional structure of the distillation tank in the embodiment;

[0020] Figure 3 for Figure 2 Enlarged view of point A in the middle;

[0021] Figure 4 A partial structural diagram of the rolling ball, ball sleeve, and guide tube;

[0022] Figure 5 This is a schematic diagram of the second three-dimensional structure of the distillation tank in the embodiment;

[0023] Figure 6 for Figure 5 Enlarged view of point B in the middle;

[0024] Figure 7 This is a schematic diagram of the third three-dimensional structure of the distillation tank in the embodiment.

[0025] Explanation of reference numerals in the attached figures:

[0026] 1. Distillation tank; 101. Discharge port; 2. First discharge pipe; 3. Second discharge pipe; 4. Adsorption tank; 5. Discharge pipe; 6. Air inlet pipe; 7. Switch plate; 8. Rotating shaft; 9. Guide pipe; 901. First annular groove; 902. Second annular groove; 903. Arc groove; 10. Guide plate; 11. Receiving pipe; 12. Annular plate; 1201. Through groove; 13. First magnetic plate; 14. Second magnetic plate; 15. Stop block; 16. Rolling ball; 17. Ball sleeve. Detailed Implementation

[0027] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0028] like Figure 1 and Figure 5 As shown, this embodiment provides a fat refining processing apparatus for anti-wear agent processing, including a distillation tank 1. The bottom of the distillation tank 1 has a feed inlet, through which the mother liquor to be distilled enters the distillation tank 1. A first discharge pipe 2 and a second discharge pipe 3 are connected to the top of the distillation tank 1. A switch plate 7 is rotatably mounted on the top of the distillation tank 1, used to control the opening and closing of the first and second discharge pipes 2 and 3. During distillation, the switch plate 7 is first rotated by external force, blocking the second discharge pipe 3 and opening the first discharge pipe 2. Then, the distillation tank 1 is heated by an external heat source until a first temperature range is reached and maintained. The first fraction evaporates and is discharged through the first discharge pipe 2. Heating continues until a second temperature range is reached and maintained. The switch plate 7 is then adjusted by external force, blocking the first discharge pipe 2 and opening the second discharge pipe 3. The evaporated fatty acids are discharged from the distillation tank 1 through the second discharge pipe 3. Finally, the remaining mother liquor in the distillation tank 1 is discharged.

[0029] like Figure 1As shown, the second discharge pipe 3 is connected to the adsorption tank 4, which contains an adsorbent for adsorbing fatty acids. The adsorption tank 4 is connected to a discharge pipe 5 for discharging the finished fatty acid product. An inlet pipe 6 is connected to the bottom of the adsorption tank 4, and this inlet pipe 6 is connected to a steam generator that supplies steam to the adsorption tank 4. Both the discharge pipe 5 and the inlet pipe 6 are equipped with manually controllable switches. The steam generated by the steam generator can flow back to the distillation tank 1 through the inlet pipe 6, the adsorption tank 4, and the second discharge pipe 3. Specifically, during distillation, the inlet pipe 6 is closed, and the discharge pipe 5 is open. Gaseous fatty acids enter the adsorption tank 4 through the second discharge pipe 3 and come into contact with the adsorbent inside. The adsorbent adsorbs impurities such as pigments, and the adsorbed fatty acids are discharged through the discharge pipe 5. When activating the adsorbent, the inlet pipe 6 is opened, and the discharge pipe 5 is closed. The steam generated by the steam generator enters the adsorption tank 4 through the inlet pipe 6, activating the adsorbent in the adsorption tank 4. The impurities adsorbed on the adsorbent are separated from the adsorbent and leave the adsorption tank 4 together with the steam, and enter the distillation tank 1 through the second outlet pipe 3.

[0030] like Figure 2 As shown, a guide assembly for guiding the reflux steam is installed inside the distillation tank 1. The guide assembly includes a rotating shaft 8 rotatably mounted inside the distillation tank 1, the shaft 8 being vertical and coaxial with the distillation tank 1; a guide pipe 9 corresponding to the position of the second discharge pipe 3 is mounted on the rotating shaft 8, and the guide pipe 9 and the rotating shaft 8 are slidably engaged in the vertical direction. A plurality of hollow guide plates 10 are evenly installed on the circumferential surface of the guide pipe 9; the top end of the guide plate 10 is connected to the guide pipe 9, and the bottom end of the guide plate 10 faces the inner wall of the distillation tank 1. The guide pipe 9 has a first state of being separated from the second discharge pipe 3, and a second state of being in contact with the second discharge pipe 3.

[0031] During distillation, the guide tube 9 is in its first state, driven by an external motor to rotate the shaft 8. The shaft 8 then rotates the guide tube 9 and the guide plate 10, which agitates the mother liquor in the distillation tank 1, promoting its evaporation. During the steam backflow process, the guide tube 9 is in its second state. The external motor drives the shaft 8 to rotate, which in turn rotates the guide tube 9 and the guide plate 10. High-temperature steam returning from the second discharge pipe 3 can directly enter the guide tube 9 and be sprayed from the bottom of the guide plate 10 onto the inner wall of the distillation tank 1. The high-temperature steam liquefies on the inner wall of the distillation tank 1, cleaning the residual mother liquor. Thus, the steam mixed with impurities and mother liquor liquefies and collects at the bottom of the distillation tank 1. After activation, steam continues to be supplied for a period of time to further clean the inner wall of the distillation tank 1. Finally, the liquid collected at the bottom of the distillation tank 1 is discharged. It should be noted that by switching the state of the guide pipe 9, the fatty acid fraction can be smoothly discharged through the second discharge pipe 3 during the distillation process, and the water vapor can directly enter the guide plate 10 through the guide pipe 9 during the reflux process, instead of being randomly dispersed in the distillation tank 1, thereby improving the cleaning effect of water vapor on the inner wall of the distillation tank 1.

[0032] like Figure 6 and Figure 7 As shown, the bottom of the distillation tank 1 has several discharge holes 101 evenly distributed around the rotating shaft 8. A ring-shaped receiving pipe 11 is fixedly installed on the bottom surface of the distillation tank 1 at a position corresponding to each discharge hole 101. An annular plate 12, which is in contact with the bottom surface of the distillation tank 1, is rotatably installed inside the receiving pipe 11. The annular plate 12 has through grooves 1201 that correspond one-to-one with each discharge hole 101. During distillation, the through grooves 1201 and discharge holes 101 are staggered, preventing the mother liquor in the distillation tank 1 from being discharged through the discharge holes 101. After distillation, the remaining mother liquor needs to be discharged, and after the steam reflux has cleaned the inner wall of the distillation tank 1, the annular plate 12 is rotated by an external force at a certain angle, aligning the through grooves 1201 with the discharge holes 101, allowing the liquid at the bottom of the distillation tank 1 to be discharged through the discharge holes 101.

[0033] like Figure 6As shown, a first magnetic plate 13 is fixedly installed on the inner circumference of the annular plate 12. A second magnetic plate 14, corresponding to the position of the first magnetic plate 13, is fixedly installed on the rotating shaft 8 via a support arm. Two stops 15 are fixedly installed in the receiving pipe 11 at the position corresponding to the first magnetic plate 13. When the rotating shaft 8 rotates, it drives the second magnetic plate 14 to rotate synchronously via the support arm. The second magnetic plate 14, in turn, drives the first magnetic plate 13 and the annular plate 12 to rotate through the mutual attraction of their magnetic forces. Thus, the rotation of the rotating shaft 8 can control the opening and closing of the discharge hole 101. Specifically, during the distillation process, when the discharge hole 101 needs to be closed, an external motor drives the rotating shaft 8 to rotate forward. The rotating shaft 8 drives the second magnetic plate 14, the first magnetic plate 13, and the annular plate 12 to rotate synchronously forward until the first magnetic plate 13 comes into contact with one of the two corresponding stops 15. At this time, the through groove 1201 and the discharge hole 101 are misaligned, and the discharge hole 101 is in a closed state. As the rotating shaft 8 continues to rotate in the forward direction, the second magnetic plate 14 generates a magnetic force that attracts the first magnetic plate 13 whenever it rotates to the position corresponding to the first magnetic plate 13. However, the first magnetic plate 13 is blocked by the stop 15 that is in contact with it and always remains in its original position. The annular plate 12 also remains stationary relative to the distillation tank 1. When it is necessary to discharge the liquid at the bottom of the distillation tank 1, the motor drives the rotating shaft 8 to rotate in the reverse direction. The rotating shaft 8 drives the second magnetic plate 14, the first magnetic plate 13 and the annular plate 12 to rotate in the reverse direction synchronously until the first magnetic plate 13 is in contact with the other of the two corresponding stop blocks 15. At this time, the through groove 1201 and the discharge hole 101 are aligned, the discharge hole 101 is in the open state, and the liquid at the bottom of the distillation tank 1 can be discharged from the discharge hole 101 into the receiving pipe 11. Similarly, as the rotating shaft 8 continues to rotate in the opposite direction, the second magnetic plate 14 will generate a magnetic force that attracts each other when it rotates to the position corresponding to the first magnetic plate 13. However, the first magnetic plate 13 is blocked by the stop block 15 that is attached to it and always stays in the original position, so that the liquid at the bottom of the distillation tank 1 can be continuously discharged from the discharge hole 101.

[0034] like Figure 3 and Figure 4 As shown, a guide groove is formed on the outer wall of the guide pipe 9. The guide groove includes a horizontal first annular groove 901 and a second annular groove 902, which are connected by an arc-shaped groove 903. A ball 16 that cooperates with the guide groove is installed in the distillation tank 1 by a bracket. The ball 16 is movably installed in a ball sleeve 17. An elastic element connects the ball sleeve 17 and the bracket so that the ball 16 is always in contact with the vertical surface of the guide groove. The first annular groove 901 is located above the second annular groove 902. When the ball 16 is in the first annular groove 901, the guide pipe 9 is in a first state; when the ball 16 is in the second annular groove 902, the guide pipe 9 is in a second state. The groove depth of the first annular groove 901 is gradually changing, and a step is formed at the location corresponding to the arc-shaped groove 903, with its edge aligned with one side of the arc-shaped groove 903. The groove depth of the second annular groove 902 is gradually changing, and a step is formed at the location corresponding to the arc-shaped groove 903, with its edge aligned with the other side of the arc-shaped groove 903.

[0035] Specifically, when the guide tube 9 is in the first state, the ball 16 is in the first annular groove 901. At this time, the rotating shaft 8 drives the guide tube 9 to rotate in the forward direction. The ball 16 is always located in the first annular groove 901. Since the depth of the first annular groove 901 is changing, the ball 16 and the ball sleeve 17 also move relative to the support. The degree of compression of the elastic element is also constantly changing. When the rotating shaft 8 drives the guide tube 9 to rotate in the opposite direction, the ball 16 initially rolls along the first annular groove 901. When the ball 16 rolls to the position corresponding to the arc groove 903, due to the presence of a step, the ball 16 cannot cross the step to continue rolling along the first annular groove 901. Instead, it can only move towards the second annular groove 902 under the guidance of the arc groove 903. Since the height of the ball 16 relative to the distillation tank 1 is fixed, the interaction force between the ball 16 and the guide tube 9 causes the guide tube 9 to rise a certain distance, and the top of the guide tube 9 comes into contact with the bottom of the second discharge pipe 3, that is, the guide tube 9 switches from the first state to the second state. As the rotating shaft 8 drives the guide tube 9 to continue rotating in the opposite direction, the ball 16 always rolls along the second annular groove 902, and the height of the guide tube 9 remains constant, that is, the guide tube 9 always remains in the second state of being in contact with the second discharge pipe 3. When the rotating shaft 8 drives the guide tube 9 to rotate in the forward direction, the ball 16 initially rolls along the second annular groove 902. When the ball 16 rolls to the position corresponding to the arc groove 903, due to the presence of a step, the ball 16 cannot cross the step to continue rolling along the second annular groove 902. Instead, it can only move towards the first annular groove 901 under the guidance of the arc groove 903. Since the height of the ball 16 relative to the distillation tank 1 is fixed, the interaction force between the ball 16 and the guide tube 9 causes the guide tube 9 to descend a certain distance, separating the top of the guide tube 9 from the bottom of the second discharge pipe 3. That is, the guide tube 9 switches from the second state to the first state. As the rotating shaft 8 drives the guide tube 9 to continue rotating in the forward direction, the ball 16 always rolls along the first annular groove 901, and the height of the guide tube 9 remains constant. That is, the guide tube 9 always remains in the first state of being separated from the second discharge pipe 3.

[0036] In summary, the fat refining apparatus for anti-wear agent processing in this embodiment controls the rotation direction of the rotating shaft 8 via an external motor. This not only controls the opening and closing of the discharge hole 101 but also controls the connection and separation of the guide pipe 9 and the second discharge pipe 3. During distillation, the rotating shaft 8 rotates in the forward direction, the discharge hole 101 closes, and the guide pipe 9 separates from the second discharge pipe 3. During steam reflux, the rotating shaft 8 rotates in the reverse direction, the discharge hole 101 opens, and the guide pipe 9 comes into contact with the second discharge pipe 3.

[0037] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A fat refining processing device for anti-wear agent processing, comprising a distillation tank (1), a first discharge pipe (2) and a second discharge pipe (3) are connected at the top of the distillation tank (1), characterized in that, The second discharge pipe (3) is communicated with the adsorption tank (4), the adsorption tank (4) stores the adsorbent for adsorbing the fatty acid; the adsorption tank (4) is connected with the discharge pipe (5) for discharging the fatty acid product, the bottom of the adsorption tank (4) is connected with the air inlet pipe (6), the air inlet pipe (6) is communicated with the steam generating device for providing water vapor to the adsorption tank (4); The water vapor generated by the steam generating device can flow back to the distillation tank (1) through the air inlet pipe (6), the adsorption tank (4) and the second discharge pipe (3), and the distillation tank (1) is provided with a guide assembly for guiding the backflow water vapor.

2. The fat refining apparatus for anti-wear agent processing according to claim 1, characterized by, The distillation tank (1) is rotatably provided with a switch plate (7) at the top, and the switch plate (7) is used for switching control of the first discharge pipe (2) and the second discharge pipe (3).

3. The fat refining apparatus for anti-wear agent processing according to claim 3, characterized by, The guide assembly comprises a rotating shaft (8) rotatably installed in the distillation tank (1), the rotating shaft (8) is in a vertical state and coaxial with the distillation tank (1); the rotating shaft (8) is provided with a flow guide pipe (9) corresponding to the position of the second discharge pipe (3), a plurality of hollow flow guide plates (10) are uniformly arranged on the circumferential surface of the flow guide pipe (9); the top end of the flow guide plate (10) is communicated with the flow guide pipe (9), and the bottom end of the flow guide plate (10) faces the inner wall of the distillation tank (1).

4. The fat finishing apparatus for anti-wear agent processing according to claim 3, characterized by The flow guide pipe (9) and the rotating shaft (8) are slidingly fitted in the vertical direction, the flow guide pipe (9) has a first state separated from the second discharge pipe (3) and a second state abutting the second discharge pipe (3).

5. The fat finishing apparatus for anti-wear agent processing according to claim 3, characterized by A plurality of discharge holes (101) are uniformly arranged around the rotating shaft (8) at the bottom of the distillation tank (1), and an annular receiving pipe (11) is fixedly arranged at the position corresponding to the discharge hole (101) on the bottom surface of the distillation tank (1), a ring-shaped plate (12) is rotatably arranged in the receiving pipe (11) and abuts the bottom surface of the distillation tank (1), and a through slot (1201) corresponding to the discharge hole (101) is arranged on the ring-shaped plate (12).

6. The fat finishing apparatus for anti-wear agent processing according to claim 5, characterized by A first magnetic plate (13) is fixedly arranged on the inner circumferential surface of the ring-shaped plate (12), a second magnetic plate (14) corresponding to the position of the first magnetic plate (13) is fixedly arranged on the rotating shaft (8) through a support arm, and two stoppers (15) are fixedly arranged in the receiving pipe (11) corresponding to the position of the first magnetic plate (13).

7. The fat finishing apparatus for anti-wear agent processing according to claim 6, characterized by A guide groove is arranged on the outer wall of the flow guide pipe (9), the guide groove comprises a first annular groove (901) and a second annular groove (902), and the two are communicated through an arc-shaped groove (903), and a rolling ball (16) cooperating with the guide groove is arranged in the distillation tank (1) through a support.

8. The fat finishing apparatus for anti-wear agent processing according to claim 7, characterized by The rolling ball (16) is movably arranged in a ball sleeve (17), and an elastic member is arranged between the ball sleeve (17) and the support, so that the rolling ball (16) always abuts the vertical surface of the guide groove.

9. The fat finishing apparatus for anti-wear agent processing according to claim 8, characterized by The first annular groove (901) is located above the second annular groove (902), when the rolling ball (16) is in the first annular groove (901), the flow guide pipe (9) is in the first state; when the rolling ball (16) is in the second annular groove (902), the flow guide pipe (9) is in the second state.

10. The fat finishing apparatus for anti-wear agent processing according to claim 9, characterized by The first annular groove (901) has a gradually changed groove depth, and a step is formed at a position corresponding to the arc-shaped groove (903) and aligning with one side of the arc-shaped groove (903); the second annular groove (902) has a gradually changed groove depth, and a step is formed at a position corresponding to the arc-shaped groove (903) and aligning with the other side of the arc-shaped groove (903).

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