A fixture for functional testing of a bearing cage and a method for functional testing of a bearing cage

Abstract

The present disclosure relates to a fixture (1) for functional testing of a roller bearing cage (10) for a roller bearing, the roller bearing cage (10) comprising a first annular portion (12) and a second annular portion (13), a plurality of pillars (14) interconnecting the first annular portion (12) and the second annular portion (13), adjacent pairs of the plurality of pillars (14) each defining a pocket (15) for holding a roller (11), the roller bearing cage (10) having a rotation axis (R), wherein the fixture (1) is configured to be attached to the roller bearing cage, the fixture (1) having a circumferential extension (CE) about a fixture (1) centre axis (R1) which is aligned with the rotation axis (R) of the roller bearing cage when the fixture (1) is attached to the roller bearing cage (10), wherein the circumferential extension (CE) of the fixture (1) is less than 360 degrees, and the fixture (1) is configured to hold at least one roller (11) at a predefined radial position relative to the roller bearing cage, when being attached to the roller bearing cage and when the roller bearing cage (10) is rotated in relation to the fixture (1). The present disclosure also relates to a system and a method for functional testing of a roller bearing cage (10).

Description

[0001] A FIXTURE FOR FUNCTIONAL TESTING OF A BEARING CAGE AND A METHOD FOR

[0002] FUNCTIONAL TESTING OF A BEARING CAGE

[0003] TECHNICAL FIELD

[0004] The disclosure generally relates to testing of bearing cages. In particular aspects, the disclosure relates to a fixture for functional testing of a roller bearing cage, a system for functional testing of a roller bearing cage and a method for functional testing of a roller bearing cage.

[0005] BACKGROUND OF THE INVENTION

[0006] Functional testing of bearing cages for roller bearings is mandatory during the design and manufacturing process of bearing cages. A bearing cage is a structure which holds rollers in place by building pockets for each respective roller. The pockets of the bearing cage have contact surfaces intended to be in contact with the rollers. It is of high importance for the functionality and the durability of a bearing that rollers have contact with the cage only at the intended contact surfaces and not at other positions. Bearing cages thus have to be tested during the design and manufacturing process, to make sure that the contact surfaces between the rollers and the bearing cage are correct. This can be done by assembling a bearing with at least an inner ring, an outer ring, the bearing cage and the rollers. The testing of the contact surfaces is usually done with a dye inside the bearing, which makes contact patterns visible after the bearing has been rotated a few times.

[0007] Assembling the whole bearing may, however, be time-consuming and costly. Further, if the tests are performed elsewhere, e.g. at a supplier’s location, the whole bearing has to be shipped for the test, which may lead to extensive shipping costs and CO2 emissions.

[0008] Consequently, there is a need for an improved testing procedure, that allows for inexpensive and environmentally friendly testing of bearing cages. Further, there is a need for a fixture and a system allowing for inexpensive and environmentally friendly testing of bearing cages. SUMMARY OF THE INVENTION

[0009] According to a first aspect of the disclosure, there is provided a fixture for functional testing of a roller bearing cage for a roller bearing, the roller bearing cage comprising a first annular portion and a second annular portion, a plurality of pillars interconnecting the first annular portion and the second annular portion, adjacent pairs of the plurality of pillars each defining a pocket for holding a roller, the roller bearing cage having a rotation axis, wherein the fixture is configured to be attached to the roller bearing cage, the fixture having a circumferential extension about a fixture centre axis which is aligned with the rotation axis of the roller bearing cage when the fixture is attached to the roller bearing cage, wherein the circumferential extension of the fixture is less than 360 degrees, and the fixture is configured to hold at least one roller at a predefined radial position relative to the roller bearing cage, when being attached to the roller bearing cage and when the roller bearing cage is rotated in relation to the fixture.

[0010] The first aspect of the disclosure may seek to provide a fixture for functional testing which decreases cost and time needed for the testing procedure of bearing cages. The fixture according to the first aspect makes an assembly of the bearing cage with an outer and an inner ring for functional testing unnecessary. Instead, the fixture may be attached to the bearing cage to be tested and at least one roller may be inserted in a respective pocket of the bearing cage. The fixture aims on holding the at least one roller in a predetermined radial position which corresponds to a radial position of the rollers in an assembled bearing, while allowing for a rotation of the bearing cage in relation to the fixture. In other words, the fixture aims for mimicking an outer ring of a roller bearing. Thereby, a bearing cage may be functionally tested without the need for an outer and / or an inner bearing ring. Thus, a functional test of the bearing cage with fewer components is achieved, which leads to decreased cost and time for the functional testing. In case the testing is performed by a supplier or the like, costs and CO2 emissions associated with shipping of the needed components may be decreased significantly.

[0011] Optionally, the fixture comprises: at least one first radial retainment portion being configured to engage with the first annular portion of the roller bearing cage when the fixture is attached to the roller bearing cage, and at least one second radial retainment portion configured to engage with the second annular portion of the roller bearing cage when the fixture is attached to the roller bearing cage, the first and the second radial retainment portion being configured such that the first and the second radial retainment portion retain the fixture in a predefined radial position radially outside the roller bearing cage relative to the rotation axis of the roller bearing cage when being attached to the roller bearing cage while allowing for rotation of the roller bearing cage about the rotation axis of the roller bearing cage relative to the fixture. Thereby, it is made sure that the fixture maintains its radial position in relation to the bearing cage when attached. Thus, a reliable testing of the bearing cage is achieved.

[0012] Optionally, the fixture comprises: an inner surface facing the centre axis for holding the at least one roller at the predefined radial position relative to the roller bearing cage, when said at least one roller is placed in respective pockets of the roller bearing cage.

[0013] Optionally, the inner surface is a section of an annular surface corresponding to a raceway surface of an outer ring of the roller bearing. Thereby, a mimicking of an outer ring of the roller bearing to be tested may be achieved and the test results may be comparable to the ones performed with an assembled bearing.

[0014] Optionally, the inner surface is a section of a curved surface, such as a spherical surface with a centre coinciding with the centre axis or as a toroidal surface with a centre not coinciding with the centre axis. Thereby, the inner surface may be adapted to a spherical roller bearing shape or a toroidal roller bearing shape.

[0015] Optionally, the inner surface is a cylindrical surface around the centre axis. Thereby, the inner surface may be adapted to a cylindrical roller bearing shape.

[0016] Optionally, the inner surface is a conical surface with a centre coinciding with the centre axis. Thereby, the inner surface may be adapted to a conical roller bearing shape.

[0017] Optionally, the fixture comprises a first axial abutment surface configured to axially abut the first annular portion and a second axial abutment surface configured to axially abut the second annular portion of the roller bearing cage when the fixture is attached to the roller bearing cage. Thereby, the fixture may be axially fixed in relation to the roller bearing cage.

[0018] Optionally, the first axial abutment surface is a plane surface configured to abut a plane abutment surface of the first annular portion. Thereby, an improved axial fixation of the fixture in relation to the roller bearing cage may be achieved, while at the same time allowing for a rotating motion of the roller bearing cage in relation to the fixture.

[0019] Optionally, the second axial abutment surface is a plane surface configured to abut a plane abutment surface of the second annular portion. Thereby, an improved axial fixation of the fixture in relation to the roller bearing cage may be achieved, while at the same time allowing for a rotating motion of the roller bearing cage in relation to the fixture.

[0020] Optionally, the fixture comprises at least two parts which are fastened together for attachment to the roller bearing cage. Thereby, an attachment of the fixture to the roller bearing cage may be facilitated.

[0021] Optionally, the circumferential extension around the centre axis of the fixture is less than 180 degrees, preferentially less than 120 degrees, more preferentially equal to or less than 90 degrees.

[0022] Optionally, the circumferential extension around the centre axis of the fixture is more than 10 degrees, preferentially more than 25 degrees, more preferentially more than 40 degrees.

[0023] Optionally, the circumferential extension around the centre axis of the fixture is such that the fixture can hold at least one roller.

[0024] Optionally, the at least one first radial retainment portion comprises two or more projections configured to radially abut the first annular portion of the roller bearing cage, when the fixture is attached to the roller bearing cage. The fixture is herein hanging on the roller bearing cage by the one or more projections abutting the first annular portion. Thus, the fixture has a fixed radial position when hanging on the roller bearing cage. Optionally, the at least one second radial retainment portion comprises two or more projections configured to radially abut the second annular portion of the roller bearing cage, when the fixture is attached to the roller bearing cage. Thus, the fixture has a fixed radial position when hanging on the roller bearing cage.

[0025] According to a second aspect, there is provided a system for functional testing of a roller bearing cage, the system comprising a hanging arrangement for hanging the roller bearing cage in a vertical direction, the hanging arrangement allowing for rotation of the roller bearing cage around a rotation axis of the roller bearing cage, a fixture according to the first aspect, positioned at a lowermost position in the vertical direction. The second aspect of the disclosure may seek to provide a system for improved functional testing of a roller bearing cage. In particular, the second aspect provides cost- and time-efficient testing. By hanging the roller bearing cage in a hanging arrangement and by hanging the fixture on the roller bearing cage, the fixture has a defined radial position in relation to the roller bearing cage. At the same time, the roller bearing cage is rotatable in relation to both the hanging arrangement and the fixture, which allows for the functional testing of the bearing cage without the use of additional bearing components, such as an outer and / or an inner ring of a bearing.

[0026] Optionally, the system comprises at least one roller, wherein each one of the at least one roller is arranged to be placed in a respective pocket of the roller bearing cage. Thereby, the roller bearing cage may be evaluated in terms of contact patterns of the pockets of the roller bearing cage and the rollers.

[0027] According to a third aspect, there is provided a method for functional testing of a roller bearing cage, the method comprising:

[0028] - hanging the roller bearing cage in a way allowing for rotation of the cage;

[0029] - attaching the fixture of any one of the examples disclosed herein to the roller bearing cage at a lowermost position;

[0030] - inserting at least one roller into respective pockets of the roller bearing cage being covered by the fixture;

[0031] - rotating one of the at least one roller while holding the fixture in place;

[0032] - evaluating the functionality of the roller bearing cage.

[0033] The third aspect of the disclosure may seek to provide a method for improved functional testing of a roller bearing cage. In particular, the second aspect provides cost- and time- efficient testing. The underlying idea of the method is to use the fixture of the first aspect to mimic an outer and / or inner ring of a bearing. In other words, the present method enables testing of a roller bearing cage without bearing components, such as an inner and / or an outer bearing ring. The fixture holds the rollers at a predetermined radial distance corresponding to the radial position the rollers would have in an assembled roller bearing with an inner and an outer ring. By rotating the at least one roller, the operation of the bearing may be simulated in a simple way and the bearing cage may be evaluated as in an assembled bearing.

[0034] Optionally, evaluating the functionality of the roller bearing cage comprises evaluating contact patterns between the respective rollers and the respective pockets. Thereby, the function of the roller bearing cage in terms of contact patterns with the rollers is evaluated. Hence, the present method enables evaluation of where the rollers are in contact with the roller bearing pockets. In a nonlimiting example, a dye may be used to color the rollers for visualization of the contact patterns.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] With reference to the appended drawings, below follows a more detailed description of embodiments of the disclosure cited as examples.

[0037] In the drawings:

[0038] Fig. 1 shows a schematic view of a fixture for functional testing attached to a roller bearing cage according to an embodiment of the present disclosure;

[0039] Fig. 2 shows a sectional view in a section plane A-A depicted in Fig. 1 of a fixture for functional testing according to an embodiment of the present disclosure;

[0040] Fig. 3 shows a schematic view of a fixture for functional testing according to an embodiment of the present disclosure;

[0041] Fig. 4 shows a sectional view in a section plane A-A depicted in Fig. 1 of a fixture attached to a roller bearing cage according to an embodiment of the present disclosure; Fig. 5 shows a sectional view in a section plane A-A depicted in Fig. 1 of a fixture for functional testing according to an embodiment of the present disclosure;

[0042] Fig. 6 shows a schematic view of a system for functional testing according to an embodiment of the present disclosure;

[0043] Fig. 7 represents a flow-chart of a method for functional testing according to an embodiment of the present disclosure; The drawings show diagrammatic exemplifying embodiments of the present disclosure and are thus not necessarily drawn to scale. It shall be understood that the embodiments shown and described are exemplifying and that the disclosure is not limited to these embodiments. It shall also be noted that some details in the drawings may be exaggerated in order to better describe and illustrate the disclosure. Like reference characters refer to like elements throughout the description, unless expressed otherwise. Some of the reference characters in some of the drawings may have been omitted for the sake of clarity.

[0044] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0045] An aim of the present disclosure is to alleviate at least one drawback of the prior art, or at least to provide a suitable alternative. In particular, an aim of the present disclosure is to provide a fixture and a method that allow for inexpensive and environmentally friendly testing of roller bearing cages.

[0046] Fig. 1 shows a fixture 1 for functional testing of a roller bearing cage 10 according to an embodiment. In Fig.1 , the fixture 1 is shown attached to a roller bearing cage 10. In the embodiment shown in Fig. 1 five rollers 11 are inserted in the roller bearing cage 10. However, for the purpose of testing the roller bearing cage 10 any numbers of rollers 11 , such as at least one roller 11 , may be suitable. The fixture 1 substantially has a shape of a segment of a ring surrounding the roller bearing cage 10 intended to be functionally tested. Hence, as can be seen in Fig. 1, the fixture has a circumferential extension CE about a fixture 1 centre axis R1 which is aligned with a rotation axis R of the roller bearing cage 10 when the fixture 1 is attached to the roller bearing cage 10. The circumferential extension CE of the fixture 1 is less than 360 degrees, i.e. only a part of the roller bearing cage 10 is covered by the fixture 1. The underlying idea of the fixture 1 is that the fixture 1 is configured to hold at least one roller 11 at a predefined radial position relative to the roller bearing cage 10, when being attached to the roller bearing cage 10. For facilitating the testing procedure, the fixture 1 allows for a rotation of the roller bearing cage 10 in relation to the fixture 1. The circumferential extension CE of the fixture 1 may be chosen to serve the purpose at hand. The larger the circumferential extension CE the more rollers 11 can be inserted and tested simultaneously. However, smaller circumferential extensions CE may be chosen for simper manufacturability and / or assembly. As non- limiting examples, the circumferential extension CE may be less than 180 degrees, preferentially less than 120 degrees, more preferentially equal to or less than 90 degrees. Further, the circumferential extension around the centre axis R1 of the fixture 1 may be more than 10 degrees, preferentially more than 25 degrees, more preferentially more than 40 degrees. In another example, the circumferential extension CE may be chosen such that the fixture 1 can hold at least one roller 11.

[0047] Fig. 2 shows a sectional view along a section plane A-A depicted in Fig. 1. As can be seen, the roller bearing cage 10 is a conventional roller bearing cage 10 with a first annular portion 12 and a second annular portion 13. The first annular portion 12 and the second annular portion 13 are connected by pillars 14 forming pockets 15. Each pocket 15 is configured to receive a roller 11. When attached to the roller bearing cage 10, the fixture 1 holds at least one roller 11 inserted in the respective pockets 15 of the roller bearing cage 10 in a predetermined position which corresponds to a radial position of the roller 11 in an assembled bearing with an inner and outer ring (not shown). Hence, the motion of the at least one roller 11 relative to the roller bearing cage 10 may be mimicked by attaching the fixture 1 to the roller bearing cage 10 and rotating one of the at least one roller 11. The motion of the at least one roller 11 relative to the roller bearing cage 10 is then equivalent to the motion in an assembled bearing. Hence, the bearing cage 10 may be evaluated in terms of its holding properties relating to the at least one roller 11. In particular, the pockets 15 of roller bearing cage 10 may be evaluated in terms of contact patterns with the at least one roller 11. Also, the distance between the rollers 11 and the pockets 15 at particular positions may be evaluated and checked against requirements. The contact patterns may represent positions on the rollers where the rollers are in contact with the pockets 15 during rotation of the rollers 11. For example, a dye may be applied to the at least one roller 11 before rotating the roller for visualizing where the at least one roller 11 is in contact with the respective pocket 15 of the roller bearing cage 10. The distance between the at least one roller 11 and the pocket 15 may be measured while rotating the respective roller 11.

[0048] The fixture 1 for functional testing is now further described referring to figs. 3-5. Fig. 3 shows a three-dimensional view of the fixture 1 in an unattached state, whereas figs. 4 and 5 show sectional views of two example embodiments. The fixture comprises at least one first radial retainment portion 2 and a second radial retainment portion 3. The first radial retainment portion 2 is configured to engage with the first annular portion 12 and the second radial retainment portion 3 is configured to engage with the second annular portion 13 of the roller bearing cage 10, as depicted in Fig. 2. The radial retainment portions 2 and 3 as depicted in Fig. 3 may each comprise at least one first projection 8 and at least one second projection 9, respectively, for hanging the fixture 1 on the roller bearing cage 10. Any other suitable number of projections may however be used. For example, the radial retainment portions could be formed as a single guide portion along the circumferential extension CE of the fixture 1. The radial retainment portions 2 and 3 may delimit the motion of the fixture 1 in a radial direction pointing outwards of the roller bearing cage 10. Hence, the fixture 1 may be held in its intended radial position when gravity acts to push the fixture 1 away from the centre of the bearing cage 10. For the purpose of functional testing it is of importance that the roller bearing cage 10 is rotatable in relation to the fixture 1 while maintaining the fixture’s predetermined radial position in relation to the roller bearing cage 10. For this purpose, the at least one first projection 8 may be configured to radially abut the first annular portion 12 of the roller bearing cage 10 and the at least one second projection 9 may be configured to radially abut the second annular portion 13 of the roller bearing cage 10, when the fixture 1 is attached to the roller bearing cage 10. Thereby, the first projection 8 and the second projection 9 may be slidable along the first and second annular portion, respectively.

[0049] Further, the fixture 1 may comprise an inner surface 4 facing the centre axis R1 for holding the at least one roller 11 at the predefined radial position relative to the roller bearing cage 10, when said at least one roller is placed in respective pockets of the roller bearing cage 10. The inner surface 4 may be a section of an annular surface corresponding to a raceway surface of an outer ring of the roller bearing. In order to mimic the raceway surface of an outer ring, the inner surface 4 may be a section of a curved surface, such as a spherical surface with a centre coinciding with the centre axis R1 or as a toroidal surface with a centre not coinciding with the centre axis R1. In other examples, the inner surface 4 may be a cylindrical surface around the centre axis R1 or a conical surface with a centre coinciding with the centre axis R1. The selection of the shape of the inner surface 4 may depend on the type of the roller bearing to be tested.

[0050] For axial fixation of the fixture 1 to the roller bearing cage 10, the fixture may comprise a first axial abutment surface 6 configured to axially abut the first annular portion 12 and a second axial abutment surface 7 configured to axially abut the second annular portion 13 of the roller bearing cage 10 when the fixture 1 is attached to the roller bearing cage 10, as can be seen in Figs. 4 and 5 together with Fig. 2. The first axial abutment surface 6 may be a plane surface configured to abut a plane abutment surface of the first annular portion 12. Likewise, the second axial abutment surface 7 may be a plane surface configured to abut a plane abutment surface of the second annular portion 13. In the example embodiments shown in Figs. 4 and 5, the first and second abutment surface 6, 7 are parallel and essentially perpendicular to the rotation axis R1. The distance between the first and the second abutment surfaces 6, 7 may essentially correspond to the distance between the corresponding plane abutment surfaces of the roller bearing cage. In order to allow rotation of the roller bearing cage relative to the fixture, the distance between the first and the second abutment surfaces 6, 7 may be slightly larger than the distance between the corresponding plane abutment surfaces, e.g. by applying a positive tolerance on the distance measured between the first and the second abutment surfaces 6, 7.

[0051] In an example embodiment, shown in Fig. 5, the fixture may comprise two parts, 1 a / 1 b, that are configured to be assembled with the roller bearing cage 10. However, even though not shown in Fig. 5, the fixture may also be configured to be assembled of more than two parts. The fixture 1 may be assembled around the roller bearing cage 10 by any conventional fastening means, such as bolts, or adhesive. Alternatively, when the fixture 1 may be manufactured in only one part and fixed to the roller bearing cage 10 by inserting spacing elements between at least one of the abutment surfaces 6, 7 and corresponding abutment surfaces of the roller bearing cage 10.

[0052] Preferably, the fixture 1 is manufactured in a plastic material. However, any other suitable material may be chosen, such as aluminum or steel.

[0053] With reference to Fig. 6, a system 20 for functional testing of a roller bearing cage 10 is described. The system comprises a hanging arrangement 21 for hanging the roller bearing cage 10 in a vertical direction. The hanging arrangement 21 may be any conventional means for hanging the roller bearing cage 10 to a frame 22 of a test rig or the like. The hanging arrangement 21 allows for rotation of the roller bearing cage 10 around a rotation axis R of the roller bearing cage 10. The hanging arrangement may be a rope, a ring or the like. Further, the system 20 comprises a fixture 1 according to the present disclosure mounted in a lowermost position as seen in a gravitational direction. As depicted in Fig. 6, at least one roller 11 is inserted into respective pockets 15 of the roller bearing cage 10 that are covered by the fixture 1. The system 20 allows for functional testing of the roller bearing cage 10 as described above, by allowing a relative rotation of the roller bearing cage 10 around the rotation axis R both in relation to the fixture 1 and in relation to the hanging arrangement 21 . Hereby, the fixture 1 is intended to be held in the lowermost position throughout the testing.

[0054] Fig. 7 shows a method for functional testing of a roller bearing cage 10. The method comprises the following actions:

[0055] Action S1 : hanging the roller bearing cage 10 in a way allowing for rotation of the roller bearing cage 10. As already mentioned in connection with the system 20, the roller bearing cage is hanged vertically, i.e. such that its rotation axis R is approximately perpendicular to a gravitational direction. For example, the roller bearing cage is hanged into a hanging arrangement 21 allowing for rotation of the roller bearing cage around its rotation axis R.

[0056] Action S2: attaching the fixture 1 to the roller bearing cage 10 at a lowermost position. The lowermost position herein refers to a gravitational direction.

[0057] Action S3: inserting at least one roller 11 into respective pockets 15 of the roller bearing cage 10 being covered by the fixture 1.

[0058] Action S4: rotating one of the at least one roller while holding the fixture 1 in place. By rotating at least one roller while holding the fixture 1 in place, also the roller bearing cage 10 will start to rotate about its rotation axis R. Thus, the at least one roller 11 and the roller bearing cage 11 experience a motion which corresponds to the motion in an assembled bearing. However, using the disclosed fixture 1, an assembly with bearing parts, such as an outer and an inner ring is made redundant.

[0059] Action S5: evaluating the functionality of the roller bearing cage 10.

[0060] While or after simulating the motion of the at least one roller and the roller bearing cage by actions S1-S4, functional tests of the roller bearing cage 10 may be performed.

[0061] For example, contact patterns between respective rollers 11 and respective pockets 15 may be evaluated. For this purpose, a dye or paint may be applied to the at least one roller 11. It can then be visualized where the pockets 15 are in contact with the rollers 11. Often these contact patterns are seen as lines on the rollers where the dye has been scraped off. It can then be evaluated if the contact patterns or lines are at the intended positions on the roller. Also, during the testing, distances between the rollers 11 and the pockets 15 can be measured and checked against tolerances.

[0062] When the testing of one or more pockets is finished, the at least one roller 11 may be inserted into different pocket(s) and the testing procedure may be repeated.

[0063] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Claims

CLAIMS1 . A fixture (1) for functional testing of a roller bearing cage (10) for a roller bearing, the roller bearing cage (10) comprising a first annular portion (12) and a second annular portion (13), a plurality of pillars (14) interconnecting the first annular portion (12) and the second annular portion (13), adjacent pairs of the plurality of pillars (14) each defining a pocket (15) for holding a roller (11), the roller bearing cage (10) having a rotation axis (R), wherein the fixture (1) is configured to be attached to the roller bearing cage, the fixture (1) having a circumferential extension (CE) about a fixture (1) centre axis (R1) which is aligned with the rotation axis (R) of the roller bearing cage when the fixture (1) is attached to the roller bearing cage (10), wherein the circumferential extension (CE) of the fixture (1) is less than 360 degrees, and the fixture (1) is configured to hold at least one roller (11) at a predefined radial position relative to the roller bearing cage, when being attached to the roller bearing cage and when the roller bearing cage (10) is rotated in relation to the fixture (1).

2. The fixture (1) according to claim 1 , comprising: at least one first radial retainment portion (2) being configured to engage with the first annular portion (12) of the roller bearing cage (10) when the fixture (1) is attached to the roller bearing cage (10), and at least one second radial retainment portion (3) configured to engage with the second annular portion (13) of the roller bearing cage (10) when the fixture (1) is attached to the roller bearing cage (10), the first and the second radial retainment portion (2, 3) being configured such that the first and the second radial retainment portion (2, 3) retain the fixture (1) in a predefined radial position radially outside the roller bearing cage (10) relative to the rotation axis (R) of the roller bearing cage (10) when being attached to the roller bearing cage (10) while allowing for rotation of the roller bearing cage (10) about the rotation axis (R) of the roller bearing cage (10) relative to the fixture (1).

3. The fixture (1) according to any of claims 1 or 2, comprising: an inner surface (4) facing the centre axis (R1) for holding the at least one roller (11) at the predefined radial position relative to the roller bearing cage (10), whensaid at least one roller is placed in respective pockets of the roller bearing cage (10).

4. The fixture (1) according to claim 3, wherein the inner surface (4) is a section of an annular surface corresponding to a raceway surface of an outer ring of the roller bearing.

5. The fixture (1) according to claim 3, wherein the inner surface (4) is a section of a curved surface, such as a spherical surface with a centre coinciding with the centre axis (R1) or as a toroidal surface with a centre not coinciding with the centre axis (R1)6. The fixture (1) according to claim 3, wherein the inner surface (4) is a cylindrical surface around the centre axis R1.

7. The fixture (1) according to claim 3, wherein the inner surface (4) is a conical surface with a centre coinciding with the centre axis R1.

8. The fixture (1) according to any one of the preceding claims, comprising a first axial abutment surface (6) configured to axially abut the first annular portion (12) and a second axial abutment surface (7) configured to axially abut the second annular portion (13) of the roller bearing cage (10) when the fixture (1) is attached to the roller bearing cage (10).

9. The fixture (1) according to claim 8, wherein the first axial abutment surface (6) is a plane surface configured to abut a plane abutment surface of the first annular portion (12).

10. The fixture (1) according to claim 8 or 9, wherein the second axial abutment surface (7) is a plane surface configured to abut a plane abutment surface of the second annular portion (13).11 . The fixture (1) according to any one of the preceding claims, wherein the fixture (1) comprises at least two parts (1a, 1b) which are fastened together for attachment to the roller bearing cage (10).

12. The fixture (1) according to any one of the preceding claims, wherein the circumferential extension (CE) around the centre axis R1 of the fixture (1) is less than 180 degrees, preferentially less than 120 degrees, more preferentially equal to or less than 90 degrees.

13. The fixture (1) according to any one of the preceding claims, wherein the circumferential extension (CE) around the centre axis R1 of the fixture (1) is morethan 10 degrees, preferentially more than 25 degrees, more preferentially more than 40 degrees.

14. The fixture (1) according to any one of the preceding claims, wherein the cirumferential extension (CE) around the centre axis R1 of the fixture (1) is such that the fixture can hold at least one roller (11).

15. The fixture (1) according to any one claims 2-14, wherein the at least one first radial retainment portion (2) comprises at least one first projection (8) configured to radially abut the first annular portion (12) of the roller bearing cage (10), when the fixture (1) is attached to the roller bearing cage (10).

16. The fixture (1) according to any one of claims 2-15, wherein the at least one second radial retainment portion (3) comprises at least one second projection (9) configured to radially abut the second annular portion (13) of the roller bearing cage (10), when the fixture (1) is attached to the roller bearing cage (10).

17. System for functional testing of a roller bearing cage (10), the system comprising a hanging arrangement for hanging the roller bearing cage (10) in a vertical direction, the hanging arrangement allowing for rotation of the roller bearing cage (10) around a rotation axis R of the roller bearing cage (10), a fixture (1) according to any one of claims 1-16, positioned at a lowermost position in the vertical direction.

18. The system according to claim 17, further comprising at least one roller (11), wherein each one of the at least one roller is arranged to be placed in a respective pocket (15) of the roller bearing cage (10).

19. Method for functional testing of a roller bearing cage (10), the method comprising- hanging (S1) the roller bearing cage (10) in a way allowing for rotation of the roller bearing cage (10);- attaching (S2) the fixture (1) of any one of claims 1-16 to the roller bearing cage (10) at a lowermost position;- inserting (S3) at least one roller (11) into at least one respective pocket (15) of the roller bearing cage (10) being covered by the fixture (1);- rotating (S4) one of the at least one roller (11) while holding the fixture (1) in place;- evaluating (S5) the functionality of the roller bearing cage (10).

20. The method according to claim 19, wherein evaluating the functionality of the roller bearing cage (10) comprises evaluating contact patterns between the at least one respective roller (11) and the at least one respective pocket (15).

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