WO2000023742A1

WO2000023742A1 - Swivel

Info

Publication number: WO2000023742A1
Application number: PCT/NO1999/000313
Authority: WO
Inventors: Knut Bekkevold; Harald Gjessing
Original assignee: Kongsberg Offshore As; GJESSING, Mathilde, Ann
Priority date: 1998-10-16
Filing date: 1999-10-14
Publication date: 2000-04-27
Also published as: NO984842L; GB2358448B; NO984842D0; GB2358448A; NO309242B1; AU6374199A; GB0111576D0

Abstract

A swivel with a first and a second main part (7 and 20) which are arranged for relative rotation about a longitudinal axis and to be influenced by axial forces, which are exerted against the main parts (7, 20), attempting to pull them away from each other. Between contact faces (32, 37) of the main parts (7, 20) there is mounted a rolling bearing (23). The contact face (37) of the first main part (2, 7) is a surface of a nut (34) which can be moved axially and then secured on this main part (2, 7). Between the nut's contact face (37) and a shoulder (36) of the first main part (7) facing the contact face, there is provided a pressure casing (35), which can be elastically compressed during a movement of the nut (34) towards the shoulder (36). The spring characteristic of the pressure casing (35) corresponds to the spring characteristic of the portion (81) of the first main part (2, 7) which is located between the shoulder (36) and the nut (34).

Description

Swivel

The invention relates to a swivel with a first and a second main part which are arranged for relative rotation about a longitudinal axis and to be influenced by axial forces, which are exerted on the main parts, attempting to pull them away from each other, where the main parts have respective contact faces which face each other, between which there is mounted a rolling bearing, and the axial forces can be transferred from one main part to the other via the contact faces and the bearing.

Reference should be made to the applicant's simultaneously filed application in which further features of the swivel device are described.

In GB application no. 9615534 there is disclosed a swivel with a central stem, which is circular in cross section and at one end of which there is a first attachment lug, which can be connected to an anchor chain or the like. Round the lower portion of the stem there is provided a casing at one end of which is a second attachment lug, and at two places which are located at an axial distance apart, two conical roller bearings are mounted between the stem and the casing. Under the lower bearing a nut is screwed on to the stem for securing the bearing between shoulders of the casing and the stem. The attachment lugs may be connected to respective portions of an anchor chain. When the attachment lugs are loaded with a tractive force which attempts to pull them away from each other in the stem's longitudinal direction, the tractive force is transferred from one attachment lug to the other via the casing, the bearings and the stem.

The tractive force causes the stem to be stretched, with the result that the distance between the stem's contact faces and thereby the bearing clearance increases. Too large a bearing clearance may cause the stem to tilt relative to the casing. If the swivel is mounted between portions of a string which in addition to axial forces can also transfer bending moments to the swivel, i.e. moments about transverse axes of the swivel, and a sealing device is installed which provides a seal between the casing and the stem on each side of the bearing device, this sealing device may be damaged by tilting of this kind.

When no tractive force is exerted between the attachment lugs, there is no load or only a minimal load on the threads of the nut and the stem. When a maximum tractive force is exerted, corresponding major stresses occur in these threads. A repeated stress variation of this type is injurious and can lead to fatigue fractures.

An object of the invention is to provide a swivel where the bearing clearance is maintained even though a maximum operational load is exerted against the swivel, with the result that sealing portions of the swivel are not damaged.

A second object is to provide a swivel where there is less risk of fatigue fracture in components thereof particularly as a result of repeated swelling or fluctuating forces, i.e. forces which repeatedly vary between zero and a maximum value, and which are exerted against the swivel. The characteristics of the invention are set forth in the characterising features indicated in the claims.

The invention will now be described in more detail with reference to the drawing which schematically illustrates embodiments of a swivel according to the invention. Fig. 1 illustrates a longitudinal section through a first embodiment of a swivel according to the invention.

Fig. 2 illustrates a longitudinal section through a second embodiment of a swivel according to the invention.

In the following, the specification "up" should be understood to refer to the direction towards the edge of the drawing facing away from the reader.

Even though fig. 1 and fig. 2 illustrate two different embodiments, they have components which resemble one another and have a similar function. In the following description, therefore, reference should be made to both figs. 1 and 2, where the components of the two embodiments which have a similar function are indicated by the same reference numerals.

As illustrated in fig. 1 , the swivel 1 comprises a first casing 2 with a first, upper casing portion 3, which is provided with an attachment lug 4, and which is provided at its lower portion with internal threads 5.

The first casing 2 has a lower, second casing portion or skirt 6 which is securely connected to the upper casing portion 3. An upper end portion 8 of an elongated stem 7 is provided with external threads corresponding to the internal threads 5 of the first casing portion 3, and which are screwed into it, with the result that the first casing 2 and the stem 7 are securely interconnected. The first casing 2 and the stem 7 and the components securely connected thereto form a first main part.

As is also illustrated in fig. 2, at a central portion 21 of the stem 7 there is provided a second casing 20 which is arranged to rotate about this portion 21. For this purpose there is mounted on the central portion 21 a bearing device 25 comprising a first, upper and a second, lower rolling bearing 22 and 23 respectively, which are arranged to absorb both radial and axial loads, and which in the illustrated embodiment are formed from conical roller bearings. The first bearing has an inner bearing ring 26 and an outer bearing ring 27, and the second bearing 23 has an inner bearing ring 28 and an outer bearing ring 29.

The inner bearing ring 26 of the first bearing 22 abuts against a first downwardly facing contact face 24 of the stem 7, and the outer bearing ring 27 of this bearing abuts against a second upwardly facing contact face 31 of a radially inwardly projecting portion or dividing portion 30 of the second casing 20.

The outer bearing ring 29 of the second bearing 23 abuts against a third, downwardly facing contact face 32 of the dividing portion 30.

At the portion 21 of the stem 7 below the location of the second bearing 23, the stem 7 has external threads 33, on to which is screwed a nut or adjusting element 34. Radially inside the dividing portion 30 and with radial clearance relative thereto there is mounted a body, here in the form of a pressure casing 35, whose upper end abuts against a downwardly facing shoulder or collar 36 of the stem 7, this shoulder 36 being located below the first contact face 24 and below the location of the inner bearing ring 26 of the first bearing 22. The lower end of the pressure casing 35 is arranged to abut against the upper top side of the inner bearing ring 28 of the second bearing 23 when its outer bearing ring 29 abuts against the third, downwardly facing contact face 32 of the dividing portion 30 and the pressure casing 35 abuts against the stem's shoulder 36. When the nut 34 is screwed on, its upper surface or fourth contact face 37 (fig. 2) can be brought into abutment against the underside of the inner bearing ring 28 of the second bearing 23, and by means of an initial tightening of the nut 34, this inner bearing ring 23 can be brought into abutment against the lower end of the pressure casing 35. The outer ring 29 of the second bearing 23 is simultaneously pressed against the third contact face 32 of the dividing portion 30.

As the nut 34 is tightened, the second casing 20 is further pressed upwardly relative to the stem 7 until the upper end of the pressure casing 35 comes into abutment against the shoulder 36 of the stem 7. The nut's minimal distance from the lower contact face 32 of the dividing portion 30 is thereby substantially determined. At the same time the minimal distance between the first contact face 24 and the second contact face 31 of the dividing portion 30 is substantially determined. By this means the minimal, axial dimension of the spaces, which are defined by these parts for the first and the second bearing 22, 23, is determined. By means of a further tightening of the nut 34, during which these components, i.e. the first and the second bearing 22, 23, the pressure casing 35, the nut 34, the second casing 20 and the stem 7, but mainly the pressure casing 35 and a stem portion 81 between the shoulder 36 and the nut 34, are elastically deformed, the first and the second bearing 22 and 23 respectively can thereby be axially prestressed. The axial prestressing is limited only by the stresses permitted in these components. By means of a suitable sizing and material choice for these components, a substantial degree of prestressing can be achieved. As illustrated in fig. 1 , a first disc 40, which has a central hole, is arranged to be threaded from below on to a lower, substantially cylindrical end portion 41 of the stem 7 with a reduced diameter, and to be sealingly securely connected thereto under the nut 34. At its periphery the disc 40 has a gasket 50 which is arranged to abut slidingly and sealingly against the inside of the second casing 20.

Above the first rolling bearing 22, there is mounted on the second casing 20 a sealing device 83 which seals the space below the sealing device, between this casing 20, the stem 7 and the first disc 40. As is also illustrated in fig. 2, this space can be filled with a lubricant via a channel 64, which extends through the wall of the second casing 20, and a lubricant nipple 65, which is connected to this channel 64.

A third casing 44 is securely and sealingly connected to the lower end of the second casing 20, e.g. by means of screws 39, and provided with a second attachment lug 53.

An end cap 58 is sealingly connected to the third casing 44, closing the space which is defined by this casing 44 and the lower disc 43.

The embodiment of the swivel which is illustrated in fig. 2 is arranged to form a portion of a riser or the like and must therefore be arranged to absorb the tractive forces which are exerted on those portions of the riser which are disposed above and below the swivel, in addition to bending moments. Central, mutually aligned and communicating channels 78 and 79 extend through the stem 7 and the third casing 44 respectively. The upper portion of the stem 7 can be provided with a flange 85 which is arranged, e.g. via screws 86 (illustrated only by their centre lines), to be securely and sealingly connected to a flange 87 of an upper riser portion 88.

Similarly, the third casing 44 may have a contact face 89 and be arranged, e.g. via screws 90 (illustrated only by their centre lines) to be securely connected to a flange 91 of a lower riser portion 92, the flange 91 being arranged to abut sealingly against the contact face 89.

Between the third casing 44 and the stem 7 there is provided a sealing device 93 which provides a seal between these components, while at the same time permitting a relative rotation of the components.

Alternatively, the stem 7 may be solid, i.e. containing no channels, and constitute only a component of an anchoring device such as a chain device with a single chain, e.g. for use in ships, which are anchored in such a manner that they can turn with the wind. Instead of the flange 85 and the contact face 89, the stem 7 and the third casing 44 may then have attachment lugs 4, 53 like those illustrated in fig. 1. As illustrated in fig. 2, the second casing 20 may be provided with internal threads 84 and the third casing 44 may have corresponding internal threads and be screwed on to the second casing 20, thereby being securely connected thereto. The bearing device is mounted as follows.

First of all, the first bearing 22 is threaded on to the lower portion of the stem 7 until its inner bearing ring abuts against the first contact face 24. The pressure casing is then threaded on to the stem 7 until it abuts against the shoulder or collar 36. The casing 20 is then threaded on to the stem 7 until the dividing portion's second, upper contact face 31 comes into abutment against the outer path 27 of the first bearing 22. Thereafter the second bearing 23 is pushed into the casing 20 until its outer bearing ring 29 abuts against the third, lower contact face 32 of the dividing portion 30. The bearings now have a bearing clearance corresponding to that which they have in a condition in which they are under no strain.

The nut 34 is then screwed on to the threads 33 of the stem 7 until the nut 34 comes into abutment against the lower surface of the inner bearing ring of the second bearing 23 and the upper surface of this bearing ring comes into abutment against the pressure casing 35. When these components abut against the respective shoulders and contact faces with only a small force, the bearings' bearing clearance is established, the relative axial position of the stem 7 and the nut 35 being determined by the axial length of the inner bearing ring 28 of the second bearing 23, and the length of the pressure casing 35.

It should be understood that the spring characteristic of the pressure casing 35 corresponds to the spring characteristic of the portion 81 of the stem 7 which is located between the nut 34 and the second shoulder 36. Other portions of the stem 7 preferably have greater rigidity then the portion 81. The nut 34 is then tightened. The pressure casing 35 is hereby compressed, but since the portion 81 is stretched to the same extent due to its identical spring characteristic, the nut's position relative to the dividing portion's third, lower contact face 32 and the shoulder 36 and thereby the bearing clearance for both the bearings 22, 23 is maintained. The nut 34 is preferably tightened until the force it exerts against the pressure casing 35 and thereby the force which is transferred via the threads 33 is greater than the force which the swivel is expected to transfer during use. If a force is exerted against the swivel's attachment lugs which attempts to stretch the swivel, this force is transferred from the second casing 20 to the outer ring 29 of the second bearing 23 via the third, lower contact face 32. The inner ring 28 of this bearing 23 transfers the force to the nut 34, but as the load against the nut 34 increases, the stem portion 81 is extended with the result that the force which is exerted by the pressure casing 35 against the nut is reduced to the same extent. The force which is exerted against the nut can thereby be kept constant. The bearing clearance can thereby also be constant, since the negligible extension of other portions of the stem 7 can hereby be disregarded.

By ensuring the maintenance of the bearing clearance, tilting of the stem 7 relative to the casing 20 is avoided. Thus no damage is caused to any sealing devices 83, 93 between the stem 7 and the casing 20.

The prestressing of the bearings 22, 23 in this manner therefore also contributes to a reduction in the risk of cracking of the nut's threads 33 and the corresponding threads in the stem 7.

Claims

PATENT CLAIMS

1. A swivel with a first and a second main part (2,7 and 20,44) which are arranged for relative rotation about a longitudinal axis and to be influenced by axial forces, which are exerted against the main parts (2,7,20,44), attempting to pull them away from each other, where the main parts

(2,7,20,44) have respective contact faces (32,37) which face each other, between which there is mounted a rolling bearing (23), and the axial forces can be transferred from one main part (2,7,20,44) to the other via the contact faces (32,37) and the bearing (23). where the contact face (37) of the first main part (2,7) is a surface of an adjusting element (34) which can be moved axially and then secured on this main part (2,7), characterized in that between the contact face (37) and the first main part (2,7) and against a shoulder (36) of the first main part (2,7) facing this contact face, there is provided a body (35) which may be elastically compressed during a movement of the adjusting element (34) against the shoulder (36), and that the spring characteristic of the body (35) corresponds to the spring characteristic of the portion (81) of the first main part (2,7) which is located between the shoulder (36) and the adjusting element (34).

2. A swivel according to claim 1 , characterized in that the adjusting element (34) is arranged to be moved towards the shoulder (36) until the force which is exerted against the body (35) is at least as great as the force which is exerted against the swivel ( 1 ) during use thereof.

3. A swivel according to claim 1 or 2, characterized in that the adjusting element (34) has threads and is arranged to be screwed on to corresponding threads of the first main part (2,7), thereby influencing the body (35).

4. A swivel according to one of the preceding claims, characterized in that an additional bearing (22) is provided between contact faces (24,31 ) of the main parts (2,7 and 20,44).

5. A swivel according to one of the preceding claims, characterized in that the bearing or bearings are conical roller bearings.