Seal, closure and device for making a seal for a closure, in particular for a bottle

Abstract

A seal for a closure cap of a container, in particular a bottle, is described, comprising a central deformable sealing disc (2) having a single circular lip (4) positioned on the sealing disc (2) so as to extend towards the open bottom (17) of the cap (14) when the seal (1) is inserted inside the cap (14) and the lip has an inclined side (5) facing outwards so as to rest on the inner edge (11) of the opening (13) of the bottle (12) when the cap (14) is applied thereto. The peripheral edge (3) of the deformable sealing disc (2) outside the lip (4) has a thickness (M, X) greater than the thickness (P) of the deformable sealing disc (2) in the portion inside the lip (4). The diameter (D) of the deformable sealing disc (2) is smaller than the diameter (T) of the flat circular portion (15) of the cap (14) to which the seal is applied, to the extent of not corresponding to the curved section (19) which links the flat circular portion (15) to the peripheral annular portion (16) fitted and fixed to the opening (13) of the bottle (12).

Description

Technical Field

[0001] This invention relates to a seal for sealing bottles, and more particularly to a seal installed in a cap, typically but not limited to the scope of the invention, made of metal, for sealing the opening of a bottle (or more generally, a container). Background Technology

[0002] As is well known, different types of caps—screw-on, crown-on, or pull-out, and others of similar type—are commonly used to seal bottles or other similar containers, which are typically made of glass and are intended for packaging liquid products intended for food use, such as beverages, pharmaceuticals, supplements, kitchenware, etc., or for more general purposes that differ from food supply.

[0003] More specifically, the present invention actually relates to a seal applied between a cap and an opening of a bottle or other similar container, the seal being prepared to adhere to the flat inner surface of the cap before being applied to the bottle.

[0004] Although the present invention is applicable to caps intended to be applied to bottles and similar containers (jars, vials, etc.), for convenience and brevity, only bottles are mentioned below, that is, all of the above-mentioned containers are included, and the scope of the invention is not limited in any way.

[0005] Currently, caps, such as those made of metal, are constructed from laminates having a flat, circular portion with an inner and outer surface, a perimeter annular portion extending from the edge of the circular portion, designed to be fitted and secured to the opening of a bottle in different ways depending on the cap type, and a seal secured to the inner surface of the flat, circular portion of the cap.

[0006] When the metal cap is positioned over the opening of the glass bottle, the descending annular portion undergoes a plastic forming process to attach to the outer contour of the bottle opening. For screw caps, this replicates the external threads of the glass bottle opening, or for crown caps or pull-out caps, a more regular curved shape.

[0007] This allows for the connection between the sealing surface of the glass bottle opening and the seal. Specifically, the outermost annular region of the seal contacts the sealing surface of the glass bottle opening.

[0008] In order for seals to properly seal bottled liquids, including pressurized liquids such as carbonated water and beverages, beer and other similar drinks, the material and thickness of these seals must allow them to be compressed when the cap is applied to the bottle and then tend to re-expand after the cap is applied, thus achieving a seal.

[0009] This effect is especially important for crown caps, which are secured to the bottle by clamping edges that attach to the bottle opening and press the seal firmly over the opening.

[0010] Therefore, the materials commonly used for seals are flexible plastic materials, such as polyethylene, polypropylene, elastomer copolymers, ethylene-vinyl acetate copolymers, polyethylene-polypropylene alloys, and other similar materials.

[0011] However, in order to optimize the seal (which may be partially damaged due to the elastic return of the material after the crown cap is folded over the bottle opening, resulting in a slight release of the clamping edge, but is generally optimized for all types of caps), the prior art teaches to provide a pair of lips that extend from the seal toward the open bottom of the cap to which it is applied.

[0012] One of the two lips extends along the outer perimeter of the seal and is designed to rest on the upper outer portion of the bottle opening, at an angle or rounded corner that is usually made to avoid sharp edges.

[0013] Another lip extends toward the open bottom of the cap, but along the circumference of the seal more inward, so that it inserts into the hole of the bottle opening with slight interference when the cap is applied to the bottle.

[0014] Known types of seals have some features that can withstand various improvements.

[0015] For example, providing two lips involves a significant amount of material consumption, and these lips also extend along their respective entire circumference, taking into account the limited thickness of the flat central portion relative to the lips.

[0016] Another feature that could be improved is that the geometry of the seal with two lips is complex and requires equally complex equipment or manufacturing processes.

[0017] Generally speaking, the geometry of a seal, which is actually the profile of its axial cross-section, can be optimized to reduce complexity and potentially improve sealing performance.

[0018] Furthermore, the complexity of the shape promotes production defects, resulting in a higher number of scrapped finished seals.

[0019] Another problem is that the presence of the outermost lip can cause damage to the seal when the cap is applied to the bottle, especially for crown caps. The damage is due to the possible stretching of the outermost portion, which is determined by the folding of the corresponding area of ​​the cap, when the cap is rolled up at the bottle opening. Summary of the Invention

[0020] The purpose of this invention is to provide a seal for bottle caps that does not have the aforementioned problems compared to prior art seals, and in particular has a simpler cross-sectional profile, making its production simpler and more economical, helping to save materials, while improving sealing properties.

[0021] Another object of the present invention is to provide, based on the above-mentioned object, a tool designed for producing the proposed seal, in order to help achieve the above-mentioned object.

[0022] Another object of the present invention is to provide a cap-seal assembly that includes features that facilitate obtaining or achieving the above-mentioned object.

[0023] These and other objectives are achieved by the seals formed and designed to the dimensions as described in claim 1, and will become clearer from the following description.

[0024] The apparatus for producing the seal according to the invention as described in claim 13, and the assembly consisting of a cap and a corresponding seal as described in claim 11, also contribute to achieving the above-mentioned objectives and other objectives that will become apparent to those skilled in the art.

[0025] To achieve the above objectives, the structural and functional features of the present invention are described in the independent claims mentioned above and described below, while the dependent claims describe further features and variations of the corresponding embodiments. Attached Figure Description

[0026] These structural and functional features, variations, and advantages derived from the invention will become more apparent from the following detailed description, which refers to the accompanying drawings, which illustrate preferred, non-limiting exemplary embodiments thereof, in which: - Figures 1A to 1E Different views of the seals obtained by employing the present invention are shown, some of which are cross-sectional views; - Figures 2A to 2D An assembly consisting of a cap and a seal obtained by employing the present invention, according to different embodiments, is shown, ready to be applied to a bottle; Figure 3A and Figure 3B A punch, which constitutes a major part of an apparatus for producing a seal according to the invention, is shown in cross-sectional view to highlight the mutual positioning of its components; Figure 4A and Figure 4B The same punch, broken down into its main components, is shown; Figure 5A and Figure 5B It is a three-dimensional diagram of the punch broken down into its main components under disassembled structure; Figure 6A and Figure 6B It is a 3D view of the assembled punch; Figure 7 The cross-sectional details of the seal are shown; and Figure 8 The cross-sectional details of the punch used to produce the seal are shown; Figure 9A and Figure 9B The results of a first experimental test performed using the seal according to the foregoing figures are shown; Figure 10A and Figure 10B The diagram shows the use of the following according to Figure 1 to... Figure 8 The results of the second experimental test performed on the seal. Detailed Implementation

[0027] Figure 1 to Figure 8 A seal 1 is described, which is installed in a lid 14, which is typically but not necessarily made of metal, for sealing the opening of a container 12, particularly a container made of glass (but not necessarily), such as, but not exclusively, a bottle.

[0028] It should be noted that, as stated in the introduction, the container can be, for example, composed of bottle 12, such as Figure 2A As specifically shown in the figure, the diagram shows a portion of the opening 13 of the bottle, because the type of container is not crucial for understanding the purpose of this invention.

[0029] Therefore, any container such as a jar or bottle, as long as it has suitable features, especially those concerning the opening, can be the object of this invention.

[0030] As mentioned above, for convenience and brevity, only bottles will be mentioned below, that is, all the containers mentioned above are included, and the scope of the invention is not limited in any way.

[0031] Figures 1A to 1E The seal 1 shown is provided for sealing the cover 14, as shown in the figure. Figure 2A and Figure 2B The illustration is intended to seal containers, especially bottles.

[0032] The lid 14 can be of any type, but in this case, the crown-style lid 14C will be preferred. Figure 2C ) or pull out the opening cover 14B ( Figure 2B ) or 14C ( Figure 2D ), or more generally, metal cap 14A ( Figure 2A ).

[0033] These caps 14 include a flat, circular portion 15 from which a peripheral annular portion 16 extends, designed to fit and secure to the opening 13 of the bottle 12.

[0034] The shape formed by the flat circular portion 15 of the lid and the peripheral annular portion 16 defines the inner surface 18 and the outer surface of the flat circular portion 15 of the lid 14.

[0035] The seal 1 is designed to be positioned between the upper part of the opening 13 of the bottle 12 and the corresponding cap 14 to ensure the sealing of the bottle 12, especially when the bottle contains aerated liquid.

[0036] To provide better sealing performance, seal 1 is made of a material more suitable for this purpose, such as polymers, PVC, polyethylene, polypropylene, elastomer copolymers, ethylene-vinyl acetate copolymers, polyethylene-polypropylene alloys, and other similar materials.

[0037] Structurally, the seal 1 includes a central deformable sealing disc 2 having an adhesive side A designed to adhere to the inner surface 18 of the flat circular portion 15 of the cap 14, and a support side B which rests on the opening 13 of the bottle 12 when the cap is applied to the bottle.

[0038] According to the present invention and also referring to Figure 7 The seal also includes a single circular lip 4 positioned on the support side B of the deformable sealing disc 2, such that it extends toward the open bottom 17 of the cover 14 when the seal 1 is inserted into the cover 14. Figure 2A and Figure 2B ).

[0039] It should be noted that the lip 4 has an inclined outer side 5 (that is, facing the outer perimeter of the seal) so that when the cap 14 is applied to the bottle, it rests on the inner edge 11 of the opening 13 of the bottle 12.

[0040] According to the present invention, the lip 4 has a triangular cross-section ( Figure 7 The inclined side 5 is made at an angle between 10° and 80° (more preferably between 30° and 60°), and preferably, the side 6 opposite to the inclined side 5 is substantially perpendicular to the deformable sealing disc 2.

[0041] This allows the gas present inside the bottle to exert pressure on the edge 11 of the lip 4 facing the opening of the bottle 13, improving the seal of the cap.

[0042] In short, the experimental studies conducted by the applicant demonstrate how this profile enables the bottle to achieve optimal performance while allowing for material optimization.

[0043] To achieve optimal seal performance, the side portion connected to the deformable sealing disc 2 may have an extension H between 0.3 and 2 mm, more preferably 0.7 to 1.5 mm, and even more preferably 0.8 to 1.2 mm.

[0044] Preferably, the lip 4 with a triangular cross-section has a side connected to the deformable sealing disc 2, the extension H of which is between 0.5 and 1.5, more preferably equal to 1.00 mm, and the inclined side 5 is oriented at an angle between 35° and 55°, preferably 45°.

[0045] These dimensions have been shown to give the lid 14 the best sealing properties.

[0046] To further optimize the sealing features, the thickness (M, X) of the peripheral edge 3 on the outer side of the lip 4 is greater than the thickness P of the portion of the deformable sealing disc 2 that is more inner than the lip 4.

[0047] More specifically, the peripheral edge 3 of the deformable sealing disc 2, which is located outside the lip 4 and is intended to rest on the upper edge of the opening 13 of the bottle 12, has a thickness between 0.3 and 2 mm, more preferably between 0.85 mm and 1.05 mm.

[0048] Preferably, the peripheral edge 3 of the deformable sealing disc 2 has a concave shape, such that the minimum thickness M at the lowest point of the concave shape is 0.85 mm, while the maximum thickness X of the peripheral edge 3 reaches 1.05 mm.

[0049] This feature is Figure 7 More clearly, the figure shows magnified details of seal 1.

[0050] An important feature of the seal 1 made according to the present invention is that the diameter D of the deformable sealing disc 2 is smaller than the diameter T of the flat circular portion 15 of the cover 14.

[0051] The reduction in diameter D must ensure that the perimeter of the deformable sealing disc 2 is positioned before the curved section 19, which connects the flat circular portion 15 to the peripheral annular portion 16, for fitting and securing to the opening 13 of the bottle 12. Figure 2A and Figure 2B ).

[0052] It should be noted that this feature is important for achieving the purpose mentioned in the introduction, because it prevents the edge portion of the seal 1 from getting caught in the fold of the perimeter annular portion 16 when the perimeter annular portion 16 is secured to the opening 13 of the bottle 12.

[0053] This prevents the deformable sealing disc 2 from being stretched or even torn, which could happen if the edge of the seal 1 is pulled outward and downward when the cap 14 is rolled over the opening 13 of the bottle.

[0054] As mentioned above, Figure 2A and Figure 2B An assembly is shown, comprising a cap 14 for sealing a container, particularly a bottle, and a corresponding seal 1, the cap 14 consisting of a flat circular portion 15 and a peripheral annular portion 16 fitted and secured to an opening 13 of a bottle 12, the seal 1 being applied inside the cap 14.

[0055] To produce seal 1, a production apparatus including a punch 20 is used, which is designed to perform molding of thermoplastic material according to known methods to obtain seal 1.

[0056] The punch 20 has a cavity on its lower head to form the seal 1 as described above.

[0057] More specifically, the punch 20 includes a central rod 21 for supporting the tool, the lower section 22 of which is separated from the remaining body by a discharge portion, that is, a groove 23 with a diameter larger than that of the remaining body.

[0058] The circular lower surface 24 of the lower section 22 is flat and preferably mirror-polished.

[0059] There is an intermediate ring 25 around the lower section 22, which is positioned such that the flat, circular lower surface 24 of the lower section 22 of the rod 21 remains protruding relative to the corresponding retracted end 26 of the intermediate ring 25.

[0060] To achieve this mutual positioning, the intermediate ring 25 has a stepped inner surface 30, such that the shoulder 34 formed therefrom contacts the corresponding shoulder formed by the lower end section 22, which has a diameter greater than that of the remaining body of the rod 21.

[0061] Furthermore, the inner edge 27 of the retracted end 26 of the intermediate ring 25 is beveled according to the angle of inclination corresponding to the inclined side 5 facing the outside of the seal 1.

[0062] Advantageously, the angle is tilted at 45°, because this tilt value has proven to be the optimal value for obtaining a seal 1 inserted between the opening 13 of the cap 14 and the bottle 12.

[0063] The outer surface 31 of the intermediate ring is also stepped to form corresponding shoulders 35, and the corresponding shoulders of the outer receiving ring 28 fitted on the intermediate ring 25 abut against these shoulders 35.

[0064] It should be noted that by placing the corresponding shoulders 35 side by side, the end 29 of the receiving ring 25 protrudes relative to the flat, circular lower surface 24 of the lower end section 22 of the rod 21, and the degree of protrusion is greater than the thickness P of the deformable sealing disc 2 of the seal 1. Figure 8It even protrudes more than the retracted end 26 of the intermediate ring 25, and the degree of protrusion corresponds to the thickness (M, X) of the peripheral edge 3 of the deformable sealing disc 2 of the seal 1.

[0065] The inner diameter of the receiving ring 28 is larger than the diameter of the end section 22 of the rod 21, to the extent that it defines the total width C of the perimeter edge 3 and the lip 4 (see again). Figure 8 ).

[0066] It should be noted that this spatial configuration of the three elements constituting the punch 20 allows the lip 3 to be formed in the proportions and shapes described above.

[0067] Discharge channels 32 are respectively made at the transition points between one step and another on the inner surfaces 30 and 33 and the outer surface 31 of the intermediate ring 25 and the receiving ring 28.

[0068] In short, once the seal 1 is formed by molding using the punch 20 according to known methods, it is applied by adhering the adhesive side A to the inner surface 18 of the flat circular portion 15 of the cover 14, such that the support side B remains facing the open bottom 17 of the cover.

[0069] The cap 14—the sealing component 1—is then applied to the opening 13 of the bottle 12 filled with the liquid product using an automated handling and application system.

[0070] The crimping of the cap 14 is performed by the plastic deformation process of the peripheral annular portion 16 of the cap 14, which is fitted and held in this manner to the opening 13 of the bottle 12.

[0071] During this operation, the peripheral edge portion of seal 1 is not subjected to stress, so that no other part of the seal is subjected to tension, tearing or overall damage.

[0072] The elasticity of the material used to produce the seal subsequently ensures the seal, even when the peripheral annular portion 16, which is fixed to the opening 13 of the bottle 12, performs a slight return movement due to the elasticity of the metallic material.

[0073] The use of the seal obtained according to the present invention allows for simple and convenient production of the cap, while improving sealing properties and saving a significant amount of material.

[0074] Advantageously, the production apparatus described herein makes it possible to easily obtain seals without causing particular problems due to the (non)complexity of their shape.

[0075] Figure 9A , 9B Figures 10A and 10B show the results of some tests performed using the seal 1 according to the invention.

[0076] Multiple seals are applied to the crown-shaped cap.

[0077] The caps were then used in the tests described below, and the caps thus obtained were subsequently applied to a batch of bottles, which comprised bottles of the same type, and were the subjects of the first and second experimental tests, designed to examine the sealing performance of the seal 1 according to the invention.

[0078] As Figure 9A The first experimental test on the topic of the chart (the so-called "safety seal test") involves blowing pressurized air into a capped bottle and using a puncture nozzle inserted into the cap to check the seal.

[0079] The test is performed as follows: 1. Put the caps on all the bottles; 2. Pasteurize all bottles; 3 - Waiting time (24 hours); 4 - Expose the bottle to 7.0 bar, wait for the predetermined time (1 minute), and then increase the pressure of the bottle to 10 bar.

[0080] Figure 9B The results show that the tested bottles withstood an average pressure of 9.5 bar, with a minimum of 8.5 bar and a maximum of 10 bar (standard deviation 0.56 bar). These numerical results related to the batches tested are summarized in... Figure 9B middle.

[0081] These performance levels are excellent, meaning they are perfectly acceptable, highlighting how all capped bottles withstood a pressure of at least 7 bar, resulting in no defective products.

[0082] on the other hand, Figure 10A The second experimental test, the so-called "impact test," is shown.

[0083] The procedure performed in this second so-called "impact test" is as follows: 1. Put the caps on all the bottles; 2. Pasteurize all bottles; 3 - Waiting time (24 hours); 4 – Tilt each capped bottle at a 45° angle and strike each capped bottle with a single impact using a 35g calibration weight dropped from a height of 0.5m (the impact essentially occurs at...). Figure 2A (Area 19 on) 5 - Waiting time (24 hours); 6 - Follow the above reference Figure 9A and Figure 9B The SST (“Safety Seal Test”) is described.

[0084] Figure 10A The results of the "safety seal test" obtained according to the above procedure are shown.

[0085] Similarly, in this case, such as summarizing the overall results Figure 10B As shown, the maximum pressure the caps withstood averaged 9.6 bar, while the minimum pressure the caps withstood never dropped below 7 bar in any sample (therefore no bottles were rejected).

[0086] In this case, the performance level is also absolutely outstanding.

[0087] The above experimental results demonstrate that seal 1 achieves excellent performance in terms of the pressure the cover can withstand, while also saving significant amounts of material and cost.

[0088] The applicant also observed that there were no signs of bottle breakage or cap dents in the bottle samples subjected to impact testing, unlike what is observed in most prior art seals / closure capsules. This aspect should not be overlooked, as attention should be paid to the seal 1, especially its ability to cushion the impact from collisions with the mass of the "sample" during impact testing, preventing damage to the cap or bottle.

Claims

1. A seal (1) for sealing a container (12), particularly a bottle, with a closure (14) each comprising a flat circular portion (15), extending from the edge of the flat circular portion (15) to a peripheral annular portion (16) intended to fit and secure to an opening (13) of the container (12) and defining an inner surface (18) and an outer surface, the seal (1) intended to be applied to the lid (14) to be positioned between the upper part of the opening (13) of the container (12) and the opposite lid (14), and comprising a central deformable sealing disc (2) having an adhesive side (A) intended to adhere to the inner surface (18) of the flat circular portion (15) of the lid (14), a support side (B) intended to rest on the opening (13) of the bottle (12), and a peripheral edge (3). The seal (1) is characterized in that it further includes a single circular lip (4) positioned on the support side (B) of the deformable sealing disc (2) such that it extends toward the open bottom (17) of the cover (14) when the seal (1) is inserted into the cover (14). Furthermore, the lip (4) has an inclined outer side (5) such that when the lid (14) is applied to it, it rests on the inner edge (11) of the opening (13) of the container (12), and The peripheral edge (3) of the deformable sealing disc (2) outside the lip (4) has a thickness (M, X) greater than the thickness (P) of the portion of the deformable sealing disc (2) further inside the lip (4).

2. The seal (1) according to claim 1, characterized in that, The lip (4) has a triangular cross-section and an extension (H) between 0.3 and 2 mm on the side connected to the deformable sealing disc (2).

3. The seal (1) according to claim 1 or 2, characterized in that, The inclined side (5) is inclined at an angle between 10° and 80°, and the side (6) opposite to the inclined side (5) is substantially perpendicular to the deformable sealing disc (2).

4. The seal (1) according to any one of the preceding claims and claim 2, characterized in that, The lip (4) having a triangular cross-section has a side portion connected to the deformable sealing disc (2), the extension (H) of which is between 0.5 and 1.5 mm, preferably equal to 1.00 mm.

5. The seal (1) according to any one of the preceding claims, characterized in that, The inclined side (5) is inclined at an angle between 35° and 55°, preferably 45°.

6. The seal (1) according to any one of the preceding claims, characterized in that, The perimeter edge (3) is outside the lip (4) and is intended to rest on the upper edge of the opening (13) of the bottle (12) in use.

7. The seal (1) according to any one of the preceding claims, characterized in that, The perimeter edge (3) has a thickness between 0.3 mm and 2 mm.

8. The seal (1) according to any one of the preceding claims, characterized in that, The perimeter edge (3) has a surface (7) on the outside of the lip (4) for resting on the opening (13) of the container (12), the surface (7) having a concave shape such that the minimum thickness (M) at the lowest point of the concave shape is less than 1.5 mm, preferably 0.85 mm, and the maximum thickness (X) of the perimeter edge (3) is less than 2 mm, preferably 1.05 mm.

9. The seal (1) according to any one of the preceding claims, characterized in that, The diameter (D) of the deformable sealing disc (2) is smaller than the diameter (T) of the flat circular portion (15) of the cap (14) so ​​as not to correspond to the curved section (19) that connects the flat circular portion (15) to the peripheral annular portion (16) for fitting and securing to the opening (13) of the bottle (12).

10. The seal (1) according to any one of the preceding claims, characterized in that, Made from one or more of the following materials: polymers, PVC, polyethylene, polypropylene, elastomer copolymers, ethylene-vinyl acetate copolymers, polyethylene-polypropylene alloys, and other similar materials.

11. An assembly comprising a cap (14) for closing a container (12), particularly a bottle, and a seal (1), said cap (14) comprising a flat circular portion (15) extending a peripheral annular portion (16) from the edge of said flat circular portion (15), intended to fit and secure to an opening (13) of the container (12), preferably a bottle (12), and defining an inner surface (18) and an outer surface of said flat circular portion (15), said seal (1) for sealing said cap (14) onto the container (12), characterized in that, The component includes a seal (1) made according to any one of the preceding claims.

12. The component according to the preceding claim, characterized in that, The cover (14) is made of a crown-type (14A) or pull-out (14B) metal cover (14).

13. An apparatus for producing a seal (1) for sealing containers (12), particularly bottles, characterized in that, The device includes a punch (20) for molding thermoplastic material, the punch (20) having a cavity on its underside to form a seal (1) as defined in one or more of claims 1 to 10.

14. The production apparatus according to claim 13, characterized in that, The punch (20) includes a central rod (21) for supporting the tool, the central rod (21) having a lower end section (22) separated from the remaining body by a discharge portion (23) and having a flat circular lower surface (24); an intermediate ring (25) located around the lower end section (22) and the flat circular lower surface (24) of the rod (21) protruding relative to a corresponding retracted end (26) of the intermediate ring (25), the inner edge (27) of the retracted end (26) being beveled according to an angle corresponding to the inclined side (5) facing the outside of the seal (1); and fitted onto the intermediate... An outer receiving ring (28) on the ring (25) having an end (29) protruding relative to the intermediate ring (25) to the thickness (M, X) of the peripheral edge (3) of the deformable sealing disc (2) corresponding to the seal (1) and to the thickness (P) of the deformable sealing disc (2) corresponding to the seal (1) relative to the flat circular lower surface (24) of the rod, the receiving ring (28) having a diameter greater than that of the end section (22) of the rod (21) to define the total width (C) of the peripheral edge (3) and the lip (4).

15. The production apparatus according to claim 13 or 14, characterized in that, The intermediate ring (25) has an inner surface (30) and an outer surface (31) that are stepped and have grooves (32) at the transition points, and wherein the receiving ring (28) has an inner surface (33) that is stepped.

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