A cushioning structure for a mold

Abstract

The application provides a buffer structure of a mold, and belongs to the technical field of injection molds. The buffer structure of the mold can avoid noise and vibration, and the overall reliability is higher.

Description

Technical Field

[0001] The invention belongs to the technical field of injection molds and relates to a buffer structure of a mold. Background Art

[0002] Injection molding, also known as injection molding, is a molding process that combines injection and molding. It boasts high production speed, high efficiency, and the ability to be automated, making it suitable for mass production and complex-shaped products. At a certain temperature, completely molten plastic material is stirred by a screw and injected into the mold cavity under high pressure. After cooling and solidification, the resulting molded product is obtained. After the product is formed, the mold opens, and the injection molding machine pushes the ejector plate, compressing the spring toward the movable mold. Ejectors on the ejector plate eject the product, achieving demolding. The injection molding machine then releases the ejector, and the spring forces the ejector plate to quickly return to rest against the base plate. Because the space between the ejector plate and the base plate is large when ejected, if a hard object falls on the base plate, the ejector plate will impact the hard object during its return, damaging the ejector plate, the base plate, and its guide components. Furthermore, due to the strong spring force, the ejector plate will strike the base plate at a high speed, generating loud noise and vibration. Long-term use can lead to instability, such as loose bolts and component deformation, affecting mold reliability.

[0003] In response to the above problems, the patent document (application number: 201220079534.4) discloses an injection mold reset rod anti-collision gasket, which includes an upper mold plate and a lower mold plate, the upper mold plate is connected to the mold cavity, the mold foot is installed on the lower mold plate, a lower top plate and an upper top plate are set between the mold feet, the upper top plate is connected to the reset rod, a groove is formed on the mold parting surface of the mold cavity, an anti-collision gasket is installed in the groove, the anti-collision gasket is fixed by screws, the reset rod passes through the mold core to prevent contact with the gasket, and the hardness of the anti-collision gasket is processed to HRC55, which is high in hardness and wear-resistant, and can prevent the reset rod from damaging the mold during reset. However, due to the high hardness of the anti-collision gasket, when it is hit by the ejector plate, the impact force will still be transmitted to the bottom plate, and a large noise will be generated.

[0004] In this regard, the patent document (application number: 201920099577.0) discloses a reset and buffer mechanism for the ejector plate of an injection mold, comprising an upper and lower compound plate of the mold, a cavity plate installed under the upper compound plate, two mold feet installed on the lower compound plate, an ejector base plate and an ejector panel arranged between the two mold feet, the ejector panel is connected to the reset rod, the reset rod passes through the core plate, a gasket is arranged on the cavity plate corresponding to the reset rod, when the mold is closed, the gasket contacts the reset rod, a buffer pad is arranged on the lower compound plate, the buffer pad is fixed by a plug screw, and a gap is set between the plug screw and the buffer pad. The buffer pad is made of polyurethane material and can have a certain buffering effect, but the ejector plate directly hits the buffer pad for a long time, and its impact force is all concentrated on the buffer pad, which can easily damage the buffer pad, resulting in a low service life and reliability of the buffer pad. Summary of the Invention

[0005] The purpose of the present invention is to address the above-mentioned problems in the existing technology and propose a mold buffer structure to solve the problems of high noise and vibration when the existing ejector plate is reset and low reliability.

[0006] The objectives of the present invention can be achieved through the following technical solutions: a buffer structure of a mold, the mold includes a base plate and an ejector plate arranged relatively to each other, the buffer structure includes a limit column fixed on the side surface of the base plate and arranged toward the ejector plate, characterized in that the outer circumferential surface of the limit column has a limit convex edge in the circumferential direction, the sliding sleeve on the limit convex edge is provided with a buffer sleeve, the inner circumferential surface of the buffer sleeve has a damping convex edge located below the limit convex edge in the circumferential direction, and an elastic sealing ring is also pressed between the lower end of the buffer sleeve and the bottom plate, and under the elastic action of the elastic sealing ring, the upper end surface of the damping convex edge is upwardly pressed against the lower end surface of the limit convex edge, so that the upper end surface of the buffer sleeve is higher than the upper end surface of the limit column, and an oil storage cavity located inside the elastic sealing ring is formed between the lower end surface of the buffer sleeve and the bottom plate, and an oil flow gap connected to the oil storage cavity is provided between the inner circumferential surface of the damping convex edge and the outer circumferential surface of the limit column.

[0007] A number of ejectors are vertically fixed on the side surface of the ejector plate, which are used to eject the product when the ejector plate rises. The limiting column is fixed on the side surface of the bottom plate. Under the elastic force of the elastic sealing ring, the damping convex edge presses upward against the limiting convex edge to form a limit. At this time, the upper end surface of the buffer sleeve is higher than the upper end surface of the limiting column, and an oil storage cavity is formed below the lower end surface of the buffer sleeve. The oil storage cavity is filled with grease, and the elastic sealing ring on the outside plays a sealing role to prevent the grease from leaking outward. When the ejector plate moves downward to reset, the lower side surface first presses against the upper end surface of the buffer sleeve, and the buffer sleeve compresses the elastic sealing ring to move downward. At the same time, the lower end of the buffer sleeve The surface and the side surface of the bottom plate are gradually approached, so that the oil storage cavity becomes smaller, and the upper end surface of the damping convex edge and the lower end surface of the limiting convex edge are separated and the gap between the two gradually becomes larger. The grease in the oil storage cavity passes through the oil gap and gradually squeezes into the gap between the upper end surface of the damping convex edge and the lower end surface of the limiting convex edge. That is, the flow of grease can produce greater damping. Combined with the elastic force of the elastic sealing ring, it buffers the descent of the buffer sleeve, and the buffer sleeve buffers the reset of the ejector plate, avoiding direct hard impact to generate noise and vibration, making other components on the mold more stable and the overall reliability higher. At the same time, the damping generated by the flow of grease can also prevent the instantaneous impact force from being fully applied to the elastic sealing ring, thereby protecting the elastic sealing ring, increasing its service life, and further improving the reliability of the mold. The elastic sealing ring is tightened between the buffer sleeve and the base plate to seal the grease. In particular, when the buffer sleeve descends and the oil pressure in the oil storage chamber gradually increases, the elastic sealing ring is gradually compressed, and its tightening force also gradually increases. That is, the sealing ability of the elastic sealing ring is proportional to the oil pressure in the oil storage chamber, thereby preventing grease leakage and improving stability. That is, the elastic sealing ring not only plays the role of elastically supporting the buffer sleeve and providing buffering elastic force, but also plays the role of sealing grease. When the ejector plate is in place, it rests on the upper end face of the limit column to prevent the elastic sealing ring from being over-extruded. When the ejector plate moves upward to eject the product, the buffer sleeve is released and gradually moves upward under the elastic force of the elastic sealing ring, while the grease between the damping ridge and the limit ridge returns to the oil storage chamber through the oil gap.

[0008] In the aforementioned mold's cushioning structure, the oil reservoir is formed by the lower end of the cushion sleeve, the upper side of the base plate, the inner circumference of the elastic sealing ring, and the outer circumference of the limiting post. When the cushion sleeve descends, a cushioning cavity is formed between the upper end surface of the damping ridge and the lower end surface of the limiting ridge. The cushioning cavity communicates with the oil reservoir via an oil-passing gap. When the cushion sleeve descends, the volume of the oil reservoir decreases by an equal amount to the volume of the cushioning cavity. This prevents grease leakage from the elastic sealing ring and allows air to enter the cushioning cavity from outside the limiting ridge.

[0009] In the buffer structure of the above-mentioned mold, the inner circumference of the damping ridge is a conical surface, and the diameter of the inner circumference of the damping ridge gradually decreases from bottom to top, and the minimum inner diameter of the damping ridge is larger than the outer diameter of the limit column. When the buffer sleeve just starts to descend, the sealing ability of the elastic sealing ring is still relatively low. For this reason, the inner circumference of the damping ridge is set to a conical surface, and the inner diameter of the lower end is larger, so that the width of the lower end of the oil gap is larger, and grease can enter more easily, reducing the initial increase rate of the oil pressure in the oil storage chamber and avoiding leakage from the elastic sealing ring. As the buffer sleeve descends, the elastic sealing ring is compressed and gradually generates a greater sealing ability, and the grease reaches upward and passes through the narrow oil gap, gradually increasing through damping, thereby generating a greater buffering force when the elastic sealing ring has a higher sealing ability, reducing noise and vibration.

[0010] In the above-mentioned mold buffer structure, the inner circumference of the damping convex edge has a plurality of damping convex portions, each of which is hemispherical and has a diameter that gradually decreases from bottom to top. The damping convex portions can generate greater resistance to the passage of grease, thereby increasing damping.

[0011] In the aforementioned mold buffer structure, the elastic sealing ring is made of polyurethane material and has a flat lower end surface. The lower end surface of the elastic sealing ring is pressed tightly against the side surface of the base plate. A mounting groove is circumferentially formed at the outer edge of the lower end surface of the buffer sleeve. The upper end surface of the elastic sealing ring has an annular mounting flange circumferentially formed thereon, and the mounting flange is snapped into the mounting groove. The flat lower end surface of the elastic sealing ring can be tightly attached to the side surface of the base plate, which not only provides good sealing performance but also prevents the lower end of the elastic sealing ring from moving relative to the base plate during compression, thereby causing more axial compression of the elastic sealing ring and increasing the elastic force. The mounting flange cooperates with the mounting groove to ensure the positional stability of the elastic sealing ring.

[0012] In the aforementioned mold's buffer structure, the inner circumference of the elastic sealing ring is a radially inwardly convex curved surface, while the outer circumference of the elastic sealing ring is a radially inwardly concave curved surface. The convex curvature of the convex curved surface is greater than the concave curvature of the concave curved surface. The convex and concave curved surfaces guide the elastic sealing ring when compressed, causing it to arch radially inward rather than deform outward, thereby compressing the oil reservoir and creating resistance to oil flow. The concave curved surface has a relatively small curvature, so that when compressed, the inner side of the elastic sealing ring arches radially inward, while the outer side minimizes bending deformation. Even if bending occurs, it is radially concave inward rather than bulging outward.

[0013] In the aforementioned mold buffer structure, the lower end surface of the buffer sleeve has an annular limiting groove circumferentially located near the mounting groove. The limiting groove wall has an arcuate cross-section. The inner edge of the upper end of the elastic sealing ring is engaged within the limiting groove, and the arcuate convex surface is in contact with the limiting groove wall. The limiting groove wall abuts against the upper end of the arcuate convex surface, thereby limiting the upper end of the arcuate convex surface when it is compressed and deforms inwardly. This prevents tearing at the connection between the upper end surface of the elastic sealing ring and the mounting convex edge, thereby increasing the service life of the elastic sealing ring.

[0014] In the above mold buffer structure, an annular groove is formed circumferentially on the arc-shaped concave surface of the elastic sealing ring, and an annular steel wire is sleeved in the annular groove. The annular steel wire can constrain the elastic sealing ring in the radial direction to prevent it from deforming outward when compressed.

[0015] In the aforementioned mold buffer structure, the axial length of the buffer sleeve is shorter than the axial length of the limiting post, and the vertical distance from the upper end surface of the damping ridge to the upper end surface of the buffer sleeve is greater than the axial length of the limiting ridge. This ensures that when the buffer sleeve moves downward, its upper end surface is flush with the upper end surface of the limiting post. When the ejector plate abuts the limiting post, a gap remains between the lower end surface of the buffer sleeve and the upper side surface of the base plate, thereby preventing excessive compression of the elastic sealing ring and increasing its service life.

[0016] In the above-mentioned mold buffer structure, the outer circumference of the limiting convex edge is slidably matched with the inner circumference of the buffer sleeve, and a sealing ring is provided between the outer circumference of the limiting convex edge and the inner circumference of the buffer sleeve, forming a seal between the two to prevent external air from entering the buffer cavity.

[0017] Compared with the existing technology, the cushioning structure of this mold has the following advantages:

[0018] 1. When the ejector plate moves downward to reset, the buffer sleeve compresses the elastic sealing ring and moves downward. At the same time, the grease in the oil storage cavity passes through the oil gap and gradually squeezes into the buffer cavity. That is, the flow of grease can produce greater damping. Combined with the elastic force of the elastic sealing ring, it cushions the descent of the buffer sleeve. The buffer sleeve also cushions the reset of the ejector plate, avoiding noise and vibration caused by direct hard impact, making other components on the mold more stable and the overall reliability higher.

[0019] 2. Since the elastic sealing ring is tightened between the buffer sleeve and the base plate, it seals the grease. In particular, when the buffer sleeve descends and the oil pressure in the oil storage chamber gradually increases, the elastic sealing ring is gradually compressed, and its tightening force also gradually increases. That is, the sealing ability of the elastic sealing ring is proportional to the oil pressure in the oil storage chamber, thereby avoiding grease leakage and improving stability. That is, the elastic sealing ring not only plays the role of elastically supporting the buffer sleeve and providing buffering elastic force, but also plays the role of sealing grease.

[0020] 3. Since the inner peripheral surface of the damping convex edge is set to a conical surface and the inner diameter of the lower end is larger, the width of the lower end of the oil gap is larger, which reduces the increase rate of the oil pressure in the oil storage chamber in the early stage and avoids leakage from the elastic sealing ring. As the buffer sleeve descends, the elastic sealing ring is compressed and gradually produces a greater sealing ability, and the grease reaches upward and passes through the smaller oil gap, gradually increasing through damping, thereby generating a greater buffering force when the elastic sealing ring has a higher sealing ability, reducing noise and vibration.

[0021] 4. Since the wall of the limiting groove is in contact with the upper end of the arc-shaped convex surface, it limits the upper end of the arc-shaped convex surface when the arc-shaped convex surface is deformed inward due to compression, thereby avoiding tearing at the connection position between the upper end face of the elastic sealing ring and the mounting convex edge, thereby improving the service life of the elastic sealing ring. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a cross-sectional view of the local structure of the mold when it is in the open state.

[0023] Figure 2 yes Figure 1 A magnified view of the structure at point A.

[0024] Figure 3 It is a schematic diagram of the three-dimensional structure of the buffer sleeve.

[0025] Figure 4 It is a cross-sectional view of the local structure of the mold in the closed state.

[0026] Figure 5 yes Figure 4 A magnified view of the structure at point B.

[0027] In the figure, 1. fixed mold; 2. movable mold; 21. cavity; 3. bottom plate; 4. ejector plate; 41. ejector pin; 42. spring; 5. limiting column; 51. limiting ridge; 52. sealing ring; 53. screw; 6. buffer sleeve; 61. damping ridge; 611. damping ridge; 62. mounting groove; 63. limiting groove; 7. elastic sealing ring; 71. mounting ridge; 72. arc-shaped convex surface; 73. arc-shaped concave surface; 74. annular groove; 75. annular steel wire; 8. oil storage chamber; 9. oil gap; 10. buffer chamber. DETAILED DESCRIPTION

[0028] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0029] like Figure 1As shown, a buffer structure of a mold, the mold includes a fixed mold 1 and a movable mold 2. The movable mold 2 can be moved relative to the fixed mold 1 by the drive of the injection molding machine, and a cavity 21 can be formed when the two are closed. An ejector plate 4 and a bottom plate 3 are also provided on the side of the movable mold 2. The movable mold 2 is fixed on the bottom plate 3, and there is a space between the movable mold 2 and the bottom plate 3. The ejector plate 4 is arranged between the movable mold 2 and the bottom plate 3. A number of ejectors 41 are vertically fixed on the upper side surface of the ejector plate 4. The ejector 41 passes through the movable mold 2 and is opposite to the product in the cavity 21. A spring 42 is also sleeved on the ejector 41. The spring 42 acts between the movable mold 2 and the ejector plate 4. When the movable mold 2 is opened relative to the fixed mold 1 under the driving force of the injection molding machine, the injection molding machine can also push the ejector plate 4 to move relative to the movable mold 2, so that the ejector 41 ejects the product. Then the injection molding machine releases the ejector plate 4, and the ejector plate 4 is reset to the bottom plate 3 under the action of the spring 42. Combined with Figure 2 、 Figure 3 As shown, the buffer structure includes a limiting column 5, which is fixed on the upper side of the base plate 3 and faces the lower side of the ejection plate 4 by a screw 53. The outer circumference of the upper end of the limiting column 5 is circumferentially provided with an annular limiting ridge 51. The upper end face of the limiting ridge 51 is flush with the upper end face of the limiting column 5. A buffer sleeve 6 is slidingly sleeved on the limiting ridge 51. The inner circumference of the buffer sleeve 6 is slidably matched with the outer circumference of the limiting ridge 51. A sealing groove is circumferentially provided on the outer circumference of the limiting ridge 51. A sealing ring 52 is sleeved in the sealing groove. The sealing ring 52 is tightened between the buffer sleeve 6 and the limiting ridge 51. The inner circumference of the buffer sleeve 6 is circumferentially provided with an annular damping ridge 61. The damping ridge 61 is located below the limiting ridge 51. The axial length of the buffer sleeve 6 is less than the axial length of the limiting column 5, and the vertical distance from the upper end face of the damping ridge 61 to the upper end face of the buffer sleeve 6 is greater than the axial length of the limiting ridge 51. Combined with Figure 4 、 Figure 5 As shown, an elastic sealing ring 7 is also pressed between the lower end of the buffer sleeve 6 and the base plate 3. Under the elastic action of the elastic sealing ring 7, the upper end surface of the damping ridge 61 presses upward against the lower end surface of the limiting ridge 51, so that the upper end surface of the buffer sleeve 6 is higher than the upper end surface of the limiting column 5, and the lower end of the buffer sleeve 6, the upper side surface of the base plate 3, the inner circumference of the elastic sealing ring 7 and the outer circumference of the limiting column 5 are surrounded to form an oil storage chamber 8, and there is an oil gap 9 between the inner circumference of the damping ridge 61 and the outer circumference of the limiting column 5, and the lower end of the oil gap 9 is connected with the oil storage chamber 8. When the buffer sleeve 6 descends, a buffer chamber 10 can be formed between the upper end surface of the damping ridge 61 and the lower end surface of the limiting ridge 51, and the buffer chamber 10 is connected with the upper end of the oil gap 9.

[0030] Specifically, the inner circumference of the damping ridge 61 is a conical surface, and the diameter of the inner circumference of the damping ridge 61 gradually decreases from bottom to top. The maximum radial width of the damping ridge 61 is smaller than the radial width of the limiting ridge 51. The minimum inner diameter of the damping ridge 61 is larger than the outer diameter of the limiting column 5. Damping protrusions 611 are evenly distributed on the inner circumference of the damping ridge 61. The damping protrusions 611 are hemispherical, and the diameter of the damping protrusions 611 gradually decreases from bottom to top. The elastic sealing ring 7 is made of polyurethane material and has a flat lower end face. The lower end face of the elastic sealing ring 7 is pressed tightly against the upper side face of the base plate 3. A mounting groove 62 is circumferentially provided at the outer edge of the lower end face of the buffer sleeve 6. An annular mounting ridge 71 is circumferentially provided on the upper end face of the elastic sealing ring 7. The mounting ridge 71 is snapped into the mounting groove 62. The inner circumference of the elastic sealing ring 7 is a radially inwardly convex arc-shaped convex surface 72, and the outer circumference of the elastic sealing ring 7 is a radially inwardly concave arc-shaped concave surface 73. The convex arc of the convex arc 72 is greater than the concave arc of the concave arc 73. The lower end surface of the buffer sleeve 6 has an annular limit groove 63 circumferentially near the mounting groove 62. The cross-section of the groove wall of the limit groove 63 is arc-shaped. The inner edge of the upper end of the elastic sealing ring 7 is clamped in the limit groove 63, and the convex arc 72 is in contact with the groove wall of the limit groove 63. An annular groove 74 is circumferentially formed on the arc-shaped concave surface 73 of the elastic sealing ring 7, and an annular steel wire 75 is sleeved in the annular groove 74.

[0031] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

[0032] Although this document frequently uses terms such as fixed mold 1, movable mold 2, and cavity 21, the use of other terms is not excluded. These terms are used solely to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitations is contrary to the spirit of the present invention.

Claims

1. A mold buffer structure, the mold comprising a bottom plate (3) and an ejector plate (4) arranged opposite to each other, the buffer structure comprising a limiting column (5) fixed on the side of the bottom plate (3) and arranged toward the ejector plate (4), characterized in that: The outer circumference of the limiting column (5) is provided with a limiting convex edge (51) in the circumferential direction, and the sliding sleeve of the limiting convex edge (51) is provided with a buffer sleeve (6), and the inner circumferential surface of the buffer sleeve (6) is provided with a damping convex edge (61) located below the limiting convex edge (51) in the circumferential direction. An elastic sealing ring (7) is also pressed between the lower end of the buffer sleeve (6) and the bottom plate (3). Under the elastic action of the elastic sealing ring (7), the upper end surface of the damping convex edge (61) is pressed upward against the lower end surface of the limiting convex edge (51), so that the upper end surface of the buffer sleeve (6) is higher than the upper end surface of the limiting column (5), and an oil storage cavity (8) located inside the elastic sealing ring (7) is formed between the lower end surface of the buffer sleeve (6) and the bottom plate (3). The inner circumferential surface of the damping convex edge (61) and the outer circumferential surface of the limiting column (5) are connected. The oil storage chamber (8) is connected to the oil storage chamber (9); the lower end of the buffer sleeve (6), the upper side surface of the bottom plate (3), the inner peripheral surface of the elastic sealing ring (7) and the outer peripheral surface of the limiting column (5) are surrounded to form the above-mentioned oil storage chamber (8); when the buffer sleeve (6) descends, a buffer chamber (10) can be formed between the upper end surface of the damping convex edge (61) and the lower end surface of the limiting convex edge (51), and the buffer chamber (10) is connected to the oil storage chamber (8) through the oil storage chamber (9); the inner peripheral surface of the elastic sealing ring (7) is a radially inward arc-shaped convex surface (72), and the outer peripheral surface of the elastic sealing ring (7) is a radially inward arc-shaped concave surface (73), and the convex curvature of the arc-shaped convex surface (72) is greater than the concave curvature of the arc-shaped concave surface (73).

2. The mold buffer structure according to claim 1, characterized in that: The inner circumference of the damping convex edge (61) is a conical surface, and the diameter of the inner circumference of the damping convex edge (61) gradually decreases from bottom to top. The minimum inner diameter of the damping convex edge (61) is greater than the outer diameter of the limiting column (5).

3. The mold buffer structure according to claim 2, characterized in that: The inner peripheral surface of the damping convex edge (61) is provided with a plurality of damping convex portions (611), the damping convex portions (611) are hemispherical, and the diameter of the damping convex portions (611) gradually decreases from bottom to top.

4. The mold buffer structure according to any one of claims 1 to 3, characterized in that: The elastic sealing ring (7) is made of polyurethane material and has a flat lower end surface. The lower end surface of the elastic sealing ring (7) is pressed tightly against the upper side surface of the base plate (3). A mounting groove (62) is circumferentially provided at the outer edge of the lower end surface of the buffer sleeve (6). An annular mounting ridge (71) is circumferentially provided on the upper end surface of the elastic sealing ring (7), and the mounting ridge (71) is snap-fitted into the mounting groove (62).

5. The mold buffer structure according to claim 4, characterized in that: The lower end surface of the buffer sleeve (6) is provided with an annular limiting groove (63) in the circumferential direction near the mounting groove (62), and the cross section of the groove wall of the limiting groove (63) is arc-shaped. The inner edge of the upper end of the elastic sealing ring (7) is clamped in the limiting groove (63), and the arc-shaped convex surface (72) is in contact with the groove wall of the limiting groove (63).

6. The mold buffer structure according to claim 4, characterized in that: An annular groove (74) is formed circumferentially on the arc-shaped concave surface (73) of the elastic sealing ring (7), and an annular steel wire (75) is sleeved in the annular groove (74).

7. The mold buffer structure according to any one of claims 1 to 3, characterized in that: The axial length of the buffer sleeve (6) is smaller than the axial length of the limiting column (5), and the vertical distance from the upper end surface of the damping convex edge (61) to the upper end surface of the buffer sleeve (6) is greater than the axial length of the limiting convex edge (51).

8. The mold buffer structure according to any one of claims 1 to 3, characterized in that: The outer circumferential surface of the limiting convex edge (51) is slidably matched with the inner circumferential surface of the buffer sleeve (6), and a sealing ring (52) is further provided between the outer circumferential surface of the limiting convex edge (51) and the inner circumferential surface of the buffer sleeve (6).

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