NL2019761B1

NL2019761B1 - Annular bearing assembly

Info

Publication number: NL2019761B1
Application number: NL2019761A
Authority: NL
Inventors: Roodenburg Joop; Jacobus Weterings Hendrikus
Original assignee: Itrec Bv
Priority date: 2017-10-18
Filing date: 2017-10-18
Publication date: 2019-04-25

Abstract

An annular bearing assembly comprising a lower ring and an upper ring, which upper ring comprises a first upper ring part and a second upper ring part. The upper ring is adapted to be moveable relative to the lower ring. The bearing assembly according to the invention comprises, when seen in a cross-section of the annulus, exactly one roller and three slide pads. The roller is arranged to carry the vertical forces. The rollers are arranged in a circumferential series in a circumferential series of cages. There is further a first slide pad which is absorbs vertical upward forces. The bearing assembly further comprises a second and a third slide pad, which are each subjected to horizontal forces.

Description

ANNULAR BEARING ASSEMBLY

The invention relates to an annular bearing assembly, which can for example be integrated in an annular slew bearing assembly in a hoisting crane, for example in a mast crane. Hoisting cranes of the latter type have already been commercially available from the applicant for decade.

Various bearings assemblies for such hoisting cranes are known, for example from WO2017045734 and EP2092204. However, the known bearings have disadvantages such as suboptimal distribution of forces, wear and fatigue, being complex to manufacture, and being cumbersome in maintenance.

It is an object of the invention provide an improved or at least alternative annular bearing assembly.

This object is achieved with an annular bearing assembly according to claim 1.

Thus, the object is achieved with an annular bearing assembly comprising a lower ring and an upper ring, which upper ring comprises a first upper ring part and a second upper ring part. The upper ring is adapted to be moveable relative to the lower ring.

Preferably the lower ring is to be mounted stationary and in a horizontal plane, e.g. onto a column of a hoisting crane, and the upper ring is mounted to rotate about a rotation axis which extends vertically through a bearing centre of the bearing assembly. However, it is also possible for the upper ring to be stationary and the lower ring to rotate.

It is further envisaged for the bearing assembly to be used with the rotation axis of the bearing in vertical position. That is, said rotation axis is substantially vertical, and the annulus formed by the rings of the bearing assembly is in a substantially horizontal plane.

The lower ring comprises a protruding mating part, which is adapted to be arranged in a hollow mating part of the upper ring.

The bearing assembly preferably has, when seen in a transverse cross-section of the annulus, exactly one cage with one or two rollers therein, and three slide pads. The roller is arranged to carry the vertical downward forces, which is envisaged to be the vast majority of the overall forces exerted on the bearing assembly, since the bearing assembly is intended to be used with the rotation axis in vertical position and subjected to heavy vertical load.

The rollers are arranged in a circumferential series in a circumferential series of cages.

There is further a first slide pad which is absorbs vertical upward forces, but these forces are considerably less than the roller than those carried by the roller.

The bearing assembly further comprises a second and a third slide pad, which are each subjected to horizontal forces.

The inventors have found that particular arrangement of the lower ring and upper ring, in combination with the one cage and three slide pads in transverse cross-sectional view, results in an improved distribution of the forces among the components of the bearing assembly.

In the context of this invention, terms as “inner” and “inwards” are meant to mean closer to the bearing centre in the horizontal plane, while terms as “outer” and “outwards” are meant to mean further away from the bearing centre in the horizontal plane. Terms as “top”, “above” and “higher” on the one hand, and “bottom”, “under” and “lower” are meant to be interpreted in the conventional meaning, i.e. seen in vertical direction.

The invention further pertains to a method for assembling a bearing assembly according to the invention. Said method comprises the steps of: • attaching a guide block on the bottom surface of the outer leg of the hollow mating part of the first upper ring part, • arranging the first upper ring part on the lower ring, such that the protruding mating part of the lower ring is arranged in the hollow mating part of the first upper ring part, and the first upper ring part is supported by the rollers, • detaching the guide block from the first upper ring part, • attaching the second upper ring part on the bottom surface of the outer leg of the hollow mating part of the first upper ring part.

According to the invention, a guide block is provided during assembly. The guide block enables to avoid metal to metal contact during the arranging of the first upper ring part on the lower ring, thereby avoiding damage.

In a possible embodiment of the bearing assembly according to the invention, the second upper ring part consists of two half-annular parts, such that the two half-annular parts combined form the annular shape.

This embodiment advantageously simplifies the assembling of the bearing assembly, and can thus also be applied in the method according to the invention. Conventionally, the second upper ring part is manufactured as a single annular part. It must therefore be brought into an assembling position before the first upper ring part is arranged on the lower ring. Furthermore, it cannot be removed, e.g. for maintenance, without first dissembling the first upper ring part and the lower ring. With the second upper ring part according to this embodiment which consist of two half-annular parts, these parts can be brought from the side inwards under the first upper ring part when the first upper ring part is already arranged on the lower ring. Each of the parts can then be attached to each other and/or the first upper ring part. Similarly, the second upper ring part can also be removed to the side outwards, which simplifies maintenance..

Further advantageous embodiments are described in the dependent claims and in the following description with reference to the drawings. In the various drawings, like reference numbers are used to indicate like features.

In the figures:

Fig. 1 diagrammatically depicts a vessel comprising a hoisting crane;

Fig. 2 shows a hoisting crane at the rear side of a vessel, partially in the form of a cutaway view;

Fig. 3 shows an annular bearing assembly according to the invention in top view

Fig. 4 shows an a cross section of annular bearing assembly according to the invention arranged in a hoisting crane

Fig. 5a shows a groove of a lower ring of a bearing assembly according to the invention, with therein arranged a cage comprising a roller

Fig. 5b shows a top view of a plurality of cages comprising a plurality of rollers of a bearing assembly according to the invention

Fig. 6 illustrates a method to assemble a bearing assembly according to the invention

Fig. 1 is a side view of a vessel 1 comprising a hoisting crane 20 comprising a bearing structure 25 according to the invention. The vessel 1 has a hull 2 with a working deck 3 and, at the front of the hull 2, a superstructure 4 for crew accommodation, etc. The vessel 1 has a hoisting crane 20, disposed at the rear side of the vessel 1, which hoisting crane 20 has a vertical structure fixed to the hull 2. The hoisting crane 20 will be described in more detail below.

The hoisting crane 20, which is illustrated in detail in fig. 2, has a substantially hollow vertical column 21 with a foot 22, which in this case is fixed to the hull 2 of the vessel 1. Alternatively, the foot 22 of the crane 20 can be fixed to any other support, e.g. a quay on the mainland. Furthermore, the column 21 has a top 23. Between the foot 22 and the top 23, the column 21 has a body 21a. Furthermore the hoisting crane 20 comprises a jib 24.

An annular bearing structure 25 extends around the vertical column 21 and guides and carries a jib connection member 28, so that the jib connection member 28, and therefore the jib 24, can rotate about the column 21. The annular bearing structure will be discussed in more detail below. In this case, the jib 24 is connected pivotably to the jib connection member 28 via a substantially horizontal pivot axis 45, so that the jib 24 can also be pivoted up and down. There is at least one drive motor 27 for displacing the jib connection member 28 along the annular bearing structure 25.

To pivot the jib 24 up and down, there is a topping winch 30 provided with a topping cable 31 which engages on the jib 24.

Furthermore, the hoisting crane 20 comprises a hoisting winch 35 for raising and lowering a load, with an associated hoisting cable 36 and a hoisting hook 37. At the top 23 of the column 21 there is a top cable guide 40 provided with a cable pulley assembly 41 for the topping cable 31 and with a second cable pulley assembly 42 for the hoisting cable 36.

One or more third cable pulley assemblies 43 for the hoisting cable 36 and a fourth cable pulley assembly 44 for the topping cable 31 are arranged on the jib 24. The number of cable parts for each cable can be selected as appropriate by the person skilled in the art.

The winches 30 and 35 are in this case disposed in the foot 22 of the vertical column 21, so that the topping cable 31 and the hoisting cable 36 extend from the associated winch 30, 35 upward, through the hollow vertical column 21 to the top cable guide 40 and then towards the cable guides 43, 44 on the jib 24.

The top cable guide 40 has a rotary bearing structure, for example with one or more running tracks around the top of the column 21 and running wheels, engaging on the running tracks, of a structural part on which the cable pulley assemblies are mounted. As a result, the top cable guide can follow rotary movements of the jib about the vertical column 21 and adopt substantially the same angular position as the jib 24.

The top cable guide 40 may have an associated drive motor assembly which ensures that the top cable guide 40 follows the rotary movements of the jib 24 about the column 21, but an embodiment without drive motor assembly is preferred.

The winches 31 and 35 are in this embodiment arranged on a movable winch support 38, which is mounted movably with respect to the vertical column 21. The winch support 38 here is located in the vertical crane structure, preferably in the region of the foot 22 under the circular cross section part of the column 21, and is mechanically decoupled from the top cable guide 40. The support 38 could e. g. also be arranged in the hull of the vessel below the column, e. g. the foot could have an extension which extends into the hull.

Fig. 3 shows a top view of a part of an annular bearing assembly according to the invention. The bearing assembly has a bearing centre (not shown) which is the centre point of the concentric circles visible in fig. 3. The bearing assembly comprises an lower ring 101 and an upper ring (not shown).. The lower ring 101 is located on the inside of the circle formed by the annular bearing assembly, and is in the shown application connected to the column 21. The upper ring is connected the jib connection member 28, and further provided with a plurality of teeth 121. The teeth 121 are adapted to be engaged by a rotatable driving gear 201, of which in fig. 3 two are shown. The driving gear 201 are driven by a motor (not shown). By rotating the driving gear 201, rotating of the upper ring relative to the lower ring 101 and thus of the jib connection member 28 relative to the column 21 can be achieved. There is further provided a bearing assembly support structure 130, which supports the bearing assembly. The bearing support structure 130 is widened on the location of the driving gear 201, such that the driving gear 201 can also be supported by the bearing support structure 130. In alternative embodiments, the driving gear 201 can also be arranged on the inside of the annular bearing assembly.

Fig. 4 shows a cross-section of the annular bearing assembly in an assembled state. The annular bearing assembly comprises the lower ring 101, which is the assembled state is attached to the column 21. The annular bearing assembly further comprises the upper ring which comprises of a first upper ring part 102. As can be seen, the lower ring 101 has a protruding mating part 101a, which fits into a hollow mating part 102a of the upper ring part 102. The protruding mating part 101a comprises an inner surface 101c, an outer surface 101d and a top surface 101b. Furthermore, in the shown example the hollow mating part 102a has a U-shaped form, which U in assembled state is in fact an upside-down or inverted U. The hollow mating part 102a has an inner leg 102c, an outer leg 102d and a horizontal leg 102b.. The upper ring further comprises a second upper ring part 103, which is attached to a bottom surface the outer leg 102d the first upper ring part 102. The second upper ring part 103 extends partially below the protruding mating part 101a of the lower ring 101, such that an upper surface 103e of the second upper ring part 103 faces a lower surface 101e of the protruding mating part 101a of the lower ring 101.

In the context of this invention, terms as “inner” and “inwards” are meant to mean closer to the bearing centre in the horizontal plane, while terms as “outer" and “outwards” are meant to mean further away from the bearing centre in the horizontal plane. Terms as “top”, “above” and “higher” on the one hand, and “bottom”, “under” and “lower” are meant to be interpreted in the conventional meaning, i.e. seen in vertical direction. In fig. 4, inwards is to the left, and higher is to the top.

The annular bearing assembly according to the invention, when seen in a cross-section as in fig. 4, is provided with exactly four components 110, 111, 112, 113 that guide the movement of the first upper ring part 102 and the second upper ring part 103, relative to the lower ring 101. Those four components consist of one roller 110, and three slide pads 111, 112, 113, 114.

As can be seen, the protruding mating part 101a of the lower ring 101 comprises a groove 211 at the top surface 101b. This is shown in more detail in fig. 5a. In the groove 211, there is a cage 210 provided. The cage 210 is arranged to receive the roller 110, which in turn supports the upper ring and associated structures. The roller 110 absorbs the vertical downward forces.

Fig. 5b illustrates a top view of the cages 210. As can be seen, the cages 210 are arranged in circumferentially in series. The bearing assembly comprises plurality of cages 210, which each in turn comprise a plurality of rollers 110, in this case six rollers 110 in each cage. The rollers 210 are also arranged circumferentially in series. The rollers 110 are thus arranged in series when seen in a direction following the annular form of the bearing assembly. In other words, the centre of each roller 110 is located substantially on the same distance of the bearing centre. As is further visible in fig. 5a, it is possible to arrange a some subsequent cages 210 directly in contact with each other, while maintain a gap between other subsequent cages 210.

For example, the distance of the centre of the rollers to the bearing centre may be 3687 mm, and the bearing assembly may be provided with 78 cages 210, resulting in 468 rollers 110. This results in a distribution of the vertical forces over said rollers 110, and thus over the bearing assembly.

Preferably, each cage 210 comprises at least four, five, six or seven rollers 110. Preferably, the bearing assembly comprises at least fifty cages 210.

Referring back to fig. 5a, wherein it is shown that optionally a raceway 202 of horizontal leg 102b of the hollow mating part of the first upper ring part 102 which is located above the rollers 110 is manufactured in another metal than the rest of the first upper ring part 102. The raceway 202 is made from a metal that is suitable for contact with the rollers 110 and movement relative to the rollers 110. For example, the raceway 202 can be made from hardened steel or the material commercially available under the trademark HARDNOX.

Further optionally, a part 201 of horizontal leg 102b of the hollow mating part of the first upper ring part 102 which is located above the rollers 110 is manufactured in a material, e.g. plastic, that is more elastically deformable than the rest of the first upper ring part 102. This gives a small degree of elastic support to the upper ring 102 and the associated components. Optionally, the material of said part 201 is the same material as used for the slide pats 111, 112, 113. Optionally, said material is the material commercially available under the trademark ORKOT.

The part 203 below the groove 211 is preferably made in a strong material, e.g. a strong metal, to minimize elastic deformation thereof due to the vertical forces, since such deformation would lead to suboptimal interaction of the lower ring and the upper ring, i.e. more friction. The part 203 is optionally made from hardened steel or HARDNOX.

Referring now back to fig. 4, the first slide pad 113 of said three slide pads is arranged on, i.e. comprised by, the upper surface 103e of the second upper ring part 103. It is thus arranged to enable sliding of the upper surface 103e of the second upper ring part 103 relative to the lower surface 101e of the protruding mating part 101a of the lower ring 101. The first slide pad 113 is, when the annular bearing assembly is assembled, located below the roller 110, and radially outwards from the roller 110. That is, at least the centre of the first slide pad 113 is arranged radially outwards from a centre of the roller 110. The first slide pad 113 is exposed to vertical upward forces; however, these are considerably lower than the vertical forces to which the roller 110 is exposed. The first slide pad 113 thus prevents the upper ring from getting disconnected from the lower ring 101 when upwards forces are present, e.g. because of tilting of the jib connection member.

The second slide pad 111 of said three slide pads is arranged on, i.e. comprised by, the inner leg 102c of the first upper ring part 102. It is thus arranged to enable sliding between the inner leg 102c of the first upper ring part 102 and the inner surface 101c of the protruding mating part 101a of the lower ring 101. As can be seen in fig. 4, the second slide pad 111 is arranged below the roller 110, and radially inwards from the roller 110. Furthermore, the second slide pad 111 is arranged above the first slide pad 113, and radially inwards from the first slide pad 113. The second slide pad 111 is exposed to horizontal forces.

The third slide pad 112 of said three slide pads is arranged on, i.e. comprised by, the outer leg 102d of the first upper ring part 102. It is thus arranged to enable sliding between the outer leg 102d of the first upper ring part 102 and the outer surface 101d of the protruding mating part 101a of the lower ring 101. As can be seen in fig. 4, the third slide pad 112 is arranged below the roller 110, and radially outwards from the roller 110. It is thus also arranged radially outwards from the second slide pad 111. Furthermore, the third slide pad 112 is arranged above the first slide pad 113, and radially outwards from the first slide pad 113.

The roller 110 and the first slide pad 113 are arranged such that the absorb the vertical forces. However, the roller 110 carries the vast majority of those vertical forces, since the upper ring is supported on the rollers 110, which as such carry the weight of the jib as well. In normal operations, the vertical upward forces should be limited or non-existing. The second slide pad 111 and the third slide pad 112 are engaged by radial forces. Preferably, as is in the shown example, the roller 110 is located substantially in the centre of protruding mating part 101a when seen in the radial or horizontal direction.

The arrangement of the annular bearing assembly according to the invention has proven to result in an improved distribution of the forces over the component of the bearing assembly, including the roller 110 and the slide pads 111, 112, 113. This results in more stability, as well as leas wear and fatigue of the components.

It should further be noted that is advantageous to arrange the sliding pads 111, 112, 113 in or on the upper ring, such that no recesses must be made in the lower ring 101 for such arrangements. As such, the lower ring 101 is maintained as strong and robust as possible, which is advantageous considering the large vertical forces that must be carried by the lower ring 101.

As is clearly visible in fig. 4, in a cross section as shown in fig. 4 the bearing assembly comprises exactly one roller 110, one slide pad 113 exposed to vertical forces, and two slide pads 111, 112 exposed to horizontal forces. As is already explained with reference to figures 5a-5b, the bearing assembly in practice comprises a plurality of rollers 110. Similarly, it is possible that each for one or more of the slide pads 111, 112, 113 in practice multiple slide pads are provided. That is, over the circle that each of these slide pads 111, 112, 113 forms in the annular bearing assembly, it is possible that said slide pad is formed by multiple slide pads, each covering a part of the circle. This may be easier in construction and maintenance. Furthermore, it is possible that on small parts of said circle no sliding pad is provided, because of practical considerations.

The bearing assembly according to the invention can be used for applications such a hoisting crane, and is thus relatively large. The diameter of the bearing assembly may for example be at least 5m.

Furthermore shown in fig. 4, is a temperature sensor 104. The temperature sensor 104 is adapted to measure the temperature of at least a part of the bearing assembly. When the temperature becomes too high, the slide pads 111, 112, 113 may be damaged. Therefore, the temperature sensor 104 is connected to a system that is adapted to stop the use of the bearing assembly when the temperature rises too high, or it is at least connected to a system which is adapted to indicate such a situation to an operator.

Furthermore shown in fig. 4 are seals 301 and 302. These seals 301, 302 are arranged to prevent liquid, e.g. lubricant such as oil-based lubricants, from leaking.

Fig. 6 illustrates a method according to the invention that can be applied to assemble a bearing assembly according to the invention. To assemble the bearing assembly according to the invention, the upper ring should be arranged on the lower ring 101 such that the hollow mating part 102a of the first upper ring part 102 receives the protruding mating part 101a of the lower ring 101. However, since the second upper ring part 103 in assembled position extends below the lower ring 101, it is not possible to arrange the upper ring while the first upper ring part 102 and the second upper ring part 102 attached to each other. Furthermore, it should be avoided as much as possible that metal of the lower ring 101 and metal of the upper ring are in contact with each other during such arrangement, since this would result in scraping and damaging of the components.

Considering the above, it is envisaged by the inventors to attach a guide block 301 on the bottom surface of the outer leg 102d of the first upper ring part 102. The guide block 301 guides the arrangement of the first upper ring part 102 onto the lower ring 101.

After the arrangement of the first upper ring part 102 on the lower ring 101, the guide block 301 is detached from the first upper ring part 102, and the second upper ring part 103 is attached thereon.

In a possible embodiment, the second upper ring part 103 is arranged below the lower surface 101e of the protruding mating part 101a of the lower ring 101 prior to the arrangement of the first upper ring part 102 on the lower ring 101. After said arrangement, the second upper ring part 103 is arranged against the first upper ring part 102 and attached thereto.

In a possible embodiment, the second upper ring part 103 consists of two half-annular parts, which together form the annular form of the second upper ring part 103. That is, the two parts each form a part of said annulus. It is then possible to first arrange the first upper ring part 102 on the lower ring 101, and thereafter slide each of the two half-annular parts from the side under the first upper ring part 102, and then attach them thereto.

Claims

A ring-shaped bearing assembly with a bearing center, the bearing assembly comprising: a lower ring, the lower ring comprising a protruding fitting portion, comprising: o an inner surface, an outer surface and an upper surface, wherein a groove is present in the upper surface in which a series of cages is arranged in circumferential direction, wherein each cage comprises at least one series of rollers spaced apart in circumferential direction, e.g. only one series or precisely two parallel series of rollers, e.g. substantially cylindrical rollers, • an upper ring, wherein upper ring comprises: o a first upper ring part comprising an inverted U-shaped hollow fitting portion with an inner leg, an outer leg and a horizontal leg, the hollow fitting portion being adapted to receive the protruding fitting portion of the lower ring such that the horizontal leg of the hollow ring fitting part is in contact with the rollers and the upper ring is supported vertically by the rollers, wherein the rollers absorb vertical forces; o a second upper ring part which is arranged against a bottom surface of one of the outer leg and the inner leg of the hollow fitting part of the first upper ring part, the second upper ring part protruding horizontally below the projecting fitting part of the lower ring such that an upper surface of the second upper ring part is partially directed towards a lower surface of the protruding fitting portion of the lower ring, the bearing assembly further having, when viewed in a cross-section, exactly three sliding blocks, comprising: o first sliding block of the three sliding blocks, o arranged to allow sliding between the upper surface of the second upper ring part and the lower surface of the protruding fitting portion of the lower ring facing the upper surface of the second upper ring part, o wherein the first sliding block absorbs vertical upward forces, o wherein the first sliding block is arranged lower than the roller or rollers in the cross section the, and a center of, the first sliding block is arranged at a horizontal distance, e.g., outwards, from a center of the roll or rollers; o a second sliding block of the three sliding blocks, which is arranged to allow sliding between the inner surface of the protruding fitting portion of the lower ring and the inner leg of the hollow fitting portion of the first upper ring portion, o wherein the second sliding block absorbs horizontal forces, o the second sliding block being arranged lower than the roll or rollers in cross-section and arranged at a horizontal distance, e.g. inward of the roll or rollers, and above the first sliding block o a third sliding block of the three sliding blocks, o that is arranged to allow sliding between the outer surface of the protruding fitting portion of the lower ring and the outer leg of the hollow fitting portion of the first upper ring portion, o wherein the third sliding block absorbs horizontal forces, o wherein the third sliding block is mounted lower than the roller or rollers is arranged in cross-section and at a horizontal distance, e.g. outwards, from the roll or roll and above the first sliding block.

2. Bearing assembly according to claim 1, wherein the second upper ring part comprises the first sliding block and / or the first upper ring part comprises the second sliding block in the inner leg of the hollow fitting part and / or the first upper ring part comprises the third sliding block in the outer leg of the hollow fitting part.

3. Bearing assembly as claimed in claim 1 or claim 2, wherein the second upper ring part consists of two half ring parts, such that the two half ring parts together form the ring shape.

Bearing assembly according to one of the preceding claims, wherein the horizontal leg of the hollow fitting portion of the first upper ring part is provided with an embedded running track that is above the rollers and is made of metal suitable for contact with the rollers, e.g. Hardox.

Bearing assembly according to one of the preceding claims, wherein a part of the horizontal leg of the hollow fitting part of the first upper ring part which is situated above the rollers, and when applicable above the running track according to claim 4, is manufactured in a material, e.g. plastic, which is more elastically deformable than the rest of the first upper ring part and / or the career.

Bearing assembly according to one of the preceding claims, further comprising a temperature sensor for measuring the temperature of at least a part of the annular bearing assembly, e.g. mounted in a hole in the lower ring.

Bearing assembly according to any of the preceding claims, wherein each cage comprises six elongated cylindrical rollers, and wherein the bearing assembly comprises at least fifty cages in series in circumferential direction.

8. Bearing assembly according to one of the preceding claims, wherein the inner diameter of the bearing is at least 5 meters.

A crane, comprising: o a column, e.g. a substantially hollow vertical column comprising a foot and a top, and a body between the foot and the top, o a crane arm, o a crane arm connecting element placed on the column and to which the crane arm is hingedly connected, the bearing assembly according to any of the preceding claims, wherein the lower ring is connected to the column and the upper ring is connected to the crane arm connecting element.

A method for mounting a bearing assembly according to any one of the preceding claims, wherein the method comprises the steps of: o attaching a guide block to the bottom surface of the outer leg of the hollow fitting portion of the first upper ring part, o applying the first upper ring part on the lower ring, such that the projecting fitting part of the lower ring is arranged in the hollow fitting part of the first upper ring part and the first upper ring part is supported by the rollers, o releasing the guide block from the first upper ring part, o attaching the second upper ring part on the bottom surface of the outer leg of the hollow fitting part of the first upper ring part.

The method of claim 10, further comprising the steps of: o applying the first top ring portion to the bottom ring: placing the second top ring portion below the bottom surface of the protruding fitting portion of the bottom ring; and o after applying the first upper ring part to the lower ring and detaching the guide block from the first upper ring part, but before attaching the second upper ring part to the first upper ring part: applying the second upper ring part to the bottom surface of the outer leg of the hollow fitting portion of the first upper ring portion.

A method according to claim 10, wherein the second upper ring part consists of two half-ring parts, each of these parts forming a part of the ring shape of the second upper ring part, such that the two half-ring parts combined form the ring shape, the method further comprises the steps of: o after applying the first upper ring part to the lower ring and releasing the guide block from the first upper ring part, but before attaching the second upper ring part to the first upper ring part: applying each of the two half-ring parts of the side under the first upper ring part.