Low-noise composite material bearing cage and associated bearing unit and process

Abstract

Low noise composite material bearing cage and associated bearing unit and method Bearing cage (3) comprising an annular body (7) having a plurality of pockets or housings (8) for receiving bearing bodies of a bearing;the annular body (7) being made of a fiber-reinforced synthetic plastic material comprising a plurality of superimposed layers (15) of high tensile strength reinforcing fibers (13) embedded in a synthetic plastic material having a glass transition temperature of at least 90 °C, the annular body having been subjected to a tumbling process so as to substantially eliminate any burrs from its respective inner and outer lateral surfaces, the peripheral edges of the pockets or housings and the opposite axial front edges of the cage body, so that the bearing cage is not subject to substantially any rattling during use. [Figures 2 and 3];

Description

Title of the invention: Low-noise composite material bearing cage and associated bearing unit and method Technical field of the invention

[0001] The present invention relates to a low noise bearing cage obtained from a fiber-reinforced composite synthetic plastic material and an associated bearing unit and a manufacturing method. Prior art

[0002] It is well known that a rolling bearing unit comprises a rolling bearing having an outer ring, an inner ring and a plurality of rolling bodies (for example balls) interposed between the inner and outer rings to make them relatively rotatable with low friction, and a rolling bearing cage to retain the rolling bodies in position, the cage being arranged in the radial space delimited between the inner ring and the outer ring.

[0003] A bearing housing retainer cage comprises an annular body delimited between inner and outer cylindrical lateral surfaces and a plurality of pockets or housings, each configured to house and freely retain a respective bearing body of the roller bearing. The cage body is generally made of a synthetic plastic material, for example, a phenolic resin or a polyamide or other suitable synthetic materials, and supports the pockets or housings, which are located radially through it, for example, consisting of radial through holes.

[0004] Generally, a preform consisting of a hollow tube is obtained by molding the synthetic material, then the hollow tube is radially cut into a plurality of slices, each of which constitutes a cage body. Before or after the cutting operation, pockets or recesses are drilled through the cage body.

[0005] To improve performance, it is also known to obtain the cage body from a fiber-reinforced synthetic material, for example, phenolic resins reinforced with cotton fibers embedded in the synthetic material matrix. More recently, fiber-reinforced polymer cages have been proposed, which consist of an epoxy resin reinforced with high-tensile-strength fibers, such as carbon fibers, glass fibers, and the like.

[0006] In this case, the hollow tube constituting the preform can be produced by a process known as "continuous filament winding" (CFW), by winding clamped on a metal mandrel of one or more filaments of composite material consisting of continuous fibers impregnated with a synthetic plastic resin.

[0007] Here and hereafter, "plastic resin" means a synthetic material that is either thermosetting or thermoplastic, for example the impregnation of the fibers can be carried out either by a liquid thermosetting resin or by a solid thermoplastic powder.

[0008] After a predefined number of superimposed radial layers of pre-impregnated fibers have been obtained, the preform is hardened in a way known to cause the consolidation of the synthetic material impregnating the fibers into a solid matrix, in which the wound fibers remain embedded to constitute a reinforcing material.

[0009] Hardening can occur as disclosed for example in FR3053624A1.

[0010] Polymer-based cages such as those described above tend Rattling noises can occur during operation, particularly when used in rolling bearings for machine tool applications, and especially under specific operating conditions. For example, at certain RPMs (revolutions per minute), the rattling can be considerable. Rattling is a noise that degrades the perceived quality of the rolling bearing for the user of a vehicle in which such cages are used, and in any case, it generates an extremely unpleasant rattling noise.

[0011] Recent tests have demonstrated that cages made of fiber-reinforced synthetic material consisting of epoxy resins reinforced with carbon fibers, although superior in every respect to conventional cotton-fiber-reinforced phenolic cages, are also affected by the rattling problem. These types of polymer cages, in addition to generating unwanted noise, can also exhibit delaminated layers and loose particles inside the bearing housing, which can impair the performance and service life of the cage itself and the bearing housing in general. Summary of the invention

[0012] The objective of the present invention is to overcome the drawbacks of the prior art by providing a composite material bearing cage with an improved service life and preserving the mechanical properties of the cage under all operating conditions. A further objective of the invention is to provide a composite material bearing cage exhibiting non-existent or considerably reduced rattling behavior under all operating conditions, and no or extremely limited presence of delaminated layers and loose particles even at high speeds. high rotation and high loads, as well as a manufacturing process for such a bearing cage.

[0013] An objective of the invention is also to provide a high-precision rolling bearing unit equipped with a CFW composite material cage suitable for use in applications with particularly high stresses, such as those requiring high rotational speeds and / or subjected to high loads and high temperatures.

[0014] According to the invention, a bearing cage made of composite material having improved mechanical behavior and an associated bearing unit are provided, as defined in the attached claims. Brief description of the figures

[0015] Other features and advantages of the present invention will become clear from the following description of non-limiting examples thereof, made with reference to the figures in the accompanying drawings, in which:

[0016] - Figure [1] schematically represents a rolling bearing unit equipped with a bearing body retaining cage made according to the invention;

[0017] - [Fig.2] schematically represents, at an enlarged scale, a restraint cage of a bearing body for a rolling bearing provided according to the present invention; and

[0018] - Figure 3 schematically represents a preform tube mounted on a mandrel, tube from which the retaining cage of [Fig.2] can be obtained. Detailed description of the invention

[0019] With reference to Figures 1 to 3, reference number 1 indicates a rolling bearing unit ([Fig.1]) comprising a rolling bearing 2 of any known type and a rolling bearing cage 3, made of a composite material.

[0020] The bearing assembly comprises an inner ring 4, an outer ring 5 and a plurality of elements or bearing bodies 6, in the non-limiting embodiment shown, consisting of balls.

[0021] The bearing bodies 6 are arranged, in the example shown, in a ring of balls around an axis of symmetry A of the bearing housing, which is also the axis of symmetry of the cage 3. In different embodiments, not shown for reasons of simplicity, the bearing housing 2 can comprise two rings of bearing bodies arranged side by side and the bearing bodies can be, indifferently, balls, cylindrical or conical rollers, small cylinders, depending on the operating requirements.

[0022] In any case, the bearing cage 3 ([Fig.2]) comprises an annular body 7 and a plurality of pockets or housings 8, each configured to freely accommodate, during use, a respective bearing body 6 of the bearing housing 2 for maintain the bearing bodies 6 correctly spaced from each other by a predefined pitch; each pocket or housing is delimited by a peripheral edge 9.

[0023] The annular body 7 has an axis of symmetry A and a predefined axial width or length. The pockets or recesses 8 are located radially throughout the annular body 7, through respective inner and outer cylindrical lateral surfaces 10 and 11 ([Fig. 2]) of the annular body 7, substantially perpendicular to them, and, in the example shown, consist of simple radial cylindrical holes. The lateral surfaces 10 and 11 radially delimit the annular body 7 from each other.

[0024] The annular body 7 is made of a fiber-reinforced synthetic plastic material comprising a plurality of superimposed layers 15 of high tensile strength fibers 13, for example carbon fibers, impregnated with a synthetic resin, for example an epoxy resin, and is preferably obtained by a process known in the art as CFW (continuous filament winding), by first obtaining a preform forming tube 12 ([Fig.3]), represented schematically in a non-limiting manner, solely for the purposes of illustration and for a better understanding of the invention.

[0025] With reference to [Fig.3], in a CFW production process, a plurality of reinforcing fibers 13 are impregnated in a known manner with a resin / synthetic plastic material consisting for example of an epoxy resin, and then wound around a mandrel 14 at a predefined inclination with respect to the axis of symmetry A of the final cage 3, until the preform forming tube 12 is obtained. Alternatively, pre-preg (pre-impregnated) fibers or sheets of carefully ordered fibers may be used.

[0026] Next, a plurality of annular bodies 7 are obtained from a single preform tube 12, after hardening the latter in any known and appropriate way (for example according to FR3053624A1), in order to polymerize the epoxy resin impregnating the fibers 13 to form a solid matrix 16, by radially cutting the latter into slices each consisting of an axial section 18 of the preform tube 12, cut in a radial direction, for example along the dashed lines ([Fig.3]), such that each axial section 18 of the preform tube 12 has the same axial width / length as a cage 3 to be obtained.

[0027] Before or after the cutting step, but generally after the hardening step, a plurality of radial holes configured to form the pockets or recesses 8 are drilled through each axial section 18 of the preform tube 12. Alternatively, the pockets or recesses 8 can be obtained, in a known manner, for example during winding by correctly arranging the axial position of the fibers 11b and by equipping the mandrel 14 with a plurality of pins making radially projecting (not shown) configured to form, each, a hole corresponding to a pocket or a housing 8.

[0028] The continuous filament winding technique allows for continuity of the fibers throughout the circumference of the cage and helps to improve the rigidity, strength and dimensional stability of the cage.

[0029] The annular body 7 of a cage 3 according to the invention, therefore, comprises a plurality of superimposed layers 15 of reinforcing fibers 13 embedded in a synthetic resin, preferably an epoxy resin, and arranged with respect to the axis of symmetry A according to a predefined pattern.

[0030] After the cutting step, each section 18 forming a respective cage body 7 remains axially delimited by two opposite axial front edges 20 (figures 2 and 3).

[0031] In certain embodiments, the preforming tube 12 can be obtained either from a polymerized fiber-reinforced thermosetting resin or from a polymerized thermoplastic resin. In the latter case, the hardening step of the preforming tube 15 would no longer be necessary, since the thermoplastic powder for impregnating / coating the fibers must be melted (and therefore also polymerized) directly on the mandrel 14, for example by means of a laser beam or by means of a hot air stream.

[0032] According to a first and principal feature of the invention, in association with obtaining the cage body 7 by means of radially superimposed layers 15 of high-strength reinforcing fibers 13 embedded in / impregnated with a synthetic resin having a glass transition temperature greater than or equal to 90 °C, preferably 120 °C, and consisting preferably of an epoxy resin, the inner and outer cylindrical lateral surfaces 10, 11 of the annular cage body 7, the peripheral edge 9 of each pocket or housing 8 and the opposite axial front edges 20 of the annular body 7 have a deburring finish, namely, they do not have substantially any burrs, since, according to the principal aspect of the invention, the whole cage 3 according to the invention, after obtaining the annular cage body 7 completed by the required number of pockets or housings 8, has been subjected to a tumbling process / operation.

[0033] Tumbling is a well-known technique and consists of subjecting the parts to be tumbled (in this case, an appropriate number of cages 3 already completed in all their constituent parts) to vibrations when they are in the presence of an abrasive medium, for example, gravel, pebbles, or ceramic particles, which process is also known in technical terms as "tribofinishing". The abrasive medium is specially designed to cause friction with the parts to barrel (a number of completed cage bodies 7, in this case), so as to present the effect of polishing the barreled parts in a regulated manner.

[0034] There are established parameters, well known to those skilled in the art and therefore not disclosed here for reasons of simplicity, governing the mixture of medium and elements to be barreled, and the period of time during which the elements to be barreled remain in the barrel, depending on the material, dimensions and shape of the elements, as well as the type of machine (barrel) used.

[0035] The barreling is carried out in a vibrating barrel, which consists of a large toroidal drum with parts that rotate in a circular direction while the drum is shaken at high speed. This causes the barreling medium and the workpieces to rub against each other, wearing down the workpieces and removing any burrs that may be present.

[0036] Once a necessary time has elapsed, the barrels are emptied into a belt conveyor and the barreled parts / product are sent through a cleaner and a dryer.

[0037] The barreling process is usually carried out after each production process which causes burrs, or after heat treatment in the case of metal parts, where black scale remains on the parts and must be removed.

[0038] In general, the amount of material that can be removed in a barreling process can, in some cases, be as little as 0.0005 inches, for example, using suitable vibratory media and an extended finishing time. Generally, this is an economical way to obtain a smooth product within given tolerances and dimensions compared to other machine removal methods, such as milling or grinding. The removal is uniform, but it may not be precise on all parts of the treated surfaces, making the use of such a surface finishing process easily recognizable simply by examining the finished product.

[0039] However, contrary to what is known in the art, in the case of the present invention, the barreling is not carried out only as a surface finishing process, but for another specific and novel purpose.

[0040] Research carried out so far by the present Applicant has indeed demonstrated that when the specific composite material disclosed above, i.e. high tensile strength fibers impregnated with / embedded in a synthetic plastic resin having a glass transition temperature of at least 90 °C, preferably 120 °C, are used to obtain a bearing cage, the tendency of the cage to be subject to rattling during use is surprisingly suppressed or almost suppressed.

[0041] Consequently, the barreling is used, according to the present invention, to solve the rattling problem, the surface finishing effect of cage 3 being to be considered only as a secondary effect.

[0042] This surprising result, however, is present only when a specific composite material for cage 3 is selected, namely a synthetic plastic resin reinforced by high tensile strength and rigid fibers having a glass transition temperature greater than or equal to 90 °C, preferably 120 °C, and consisting preferably but not exclusively of an epoxy resin.

[0043] According to another feature of the invention, the reinforcing fibers 11 are selected from the group consisting of: carbon fibers, glass fibers, Kevlar® fibers, ceramic and metallic fibers and fibers of biological origin and any synthetic fiber similar to these in terms of tensile strength and stiffness.

[0044] In some embodiments, the reinforcing fibers may consist of mineral fibers such as basalt and quartz fibers and also of ceramic fibers, such as A12O3 or SiC fibers, and even of metallic fibers such as steel or aluminum fibers.

[0045] In some embodiments, the reinforcing fibers may consist of other organic fibers such as cotton, cellulose, flax, jute, hemp and sisal fibers.

[0046] According to a preferred embodiment, the reinforcing fibers 13 are continuous fibers embedded in / impregnated with the aforementioned synthetic resin and wound around the axis of symmetry A at predefined winding angles.

[0047] According to one aspect of the invention, the bearing unit 1 of [Fig. 1] therefore comprises a bearing, for example bearing 2 or any other type of bearing having a plurality of bearing bodies 6 arranged in a defined radial space between the inner ring 4 and the outer ring 5 to make them relatively rotatable with low friction, and a bearing cage 3 as described above for retaining the bearing bodies 6 in a spaced manner. The bearing 2 is preferably of the high-precision bearing type, characterized by high-speed and / or high-load operation.

[0048] Based on what has been disclosed above, it is further clear that the present invention relates to a method for producing a bearing cage made of composite material 3 comprising an annular body 7 and a plurality of pockets or housings 8, each configured to house, in use, a respective bearing body 6 of a bearing 2, the annular body 7 having an axis of symmetry A and a predefined axial width and the pockets or housings 8 being located radially throughout the annular body 7, through cylindrical lateral surfaces internal and external 10, 11 respectively of the annular body 7 radially delimiting it, the pockets or housings being delimited by respective peripheral edges 9 thereof; the process comprising the steps of:

[0049] a) production of a preform forming tube 12 made of fiber-reinforced synthetic plastic material, in which the fibers are made of a high tensile strength and rigid material impregnated with a synthetic resin having a glass transition temperature greater than or equal to 90 °C, preferably 120 °C;

[0050] b) hardening of the tube forming preform 12 to polymerize the synthetic plastic material in order to form a consolidated synthetic plastic matrix 15 in which the reinforcing fibers 13 are embedded according to a predefined pattern;

[0051] c) radial cutting, in the preform tube 12, of a plurality of axial sections 18 thereof, each having an axial width identical to that of the bearing cage 3 to be obtained, each axial section 18 of the preform tube 15 having a plurality of pockets or housings 8 situated through it and configured to house, when in use, the bearing bodies 6 of a bearing 2, the pockets or housings 8 being obtained in step a) or being drilled in the preform tube 12 after step b);

[0052] d) after step c) submitting the (of each) whole cages 3, obtained by cutting the preform tube 12 into a plurality of axial sections 18 and by producing through these the pockets or housings 8, to a barreling step or process, until substantial removal of any burr from the radially internal and external lateral cylindrical surfaces 10, 11, as well as from the peripheral edges 9 of the pockets or housings 8 and from the respective opposite axial front edges 20 of each cage body 7.

[0053] According to a preferred embodiment of the process of the invention, the synthetic plastic material is an epoxy resin.

[0054] According to a preferred embodiment of the process according to the invention, the fibers 13 are selected from the group consisting of: carbon fibers, glass fibers, Kevlar® fibers, mineral fibers such as basalt and quartz fibers, ceramic fibers, for example A12O3 or SiC fibers, metallic fibers, for example steel or aluminum fibers, organic fibers including cotton, cellulose, flax, jute, hemp and sisal fibers, any synthetic, organic or inorganic fiber similar to these in terms of tensile strength and stiffness.

[0055] According to a preferred embodiment of the process of the invention, the preforming tube 12 is obtained by means of a continuous filament winding technique, by winding it onto a mandrel 14 having a coincident axis of symmetry with the axis of symmetry A of the bearing cage 3 to be obtained, of at least one continuous fiber 13 made up, as already disclosed, of a high tensile strength and rigid material impregnated with a synthetic resin having, after hardening, a glass transition temperature greater than or equal to 90 °C, preferably 120 °C, to form a plurality of radially superimposed layers 15 of impregnated reinforcing fibers 13.

[0056] The barreling step is carried out in a vibrating barrel machine, loaded with an (appropriate) number of identical complete cage bodies 7 mixed with abrasive particles having a dimension at least one order of magnitude smaller than an outside diameter of the cage body 7, namely of the outside lateral surface 11. The abrasive medium may preferably consist of small pebbles and / or ceramic particles.

[0057] The present invention is now further disclosed according to the following operating example. Example 1

[0058] Sixty cages 3 as disclosed with reference to Figures 2 and 3 are produced using the same material, namely carbon fibers impregnated with an epoxy resin and as disclosed here above.

[0059] In a barrel-making machine from the producer Levi Tunisi, model LT VBT 600L, having a usable capacity of 560 L and a total power of 5.5 kW, twenty of the cages 3 produced are randomly mixed with an abrasive medium consisting of a 1 / 8" ceramic barrel-making product marketed by the company GANGOU.

[0060] Operating according to the machine instructions for barreling polymer products, the twenty cages are barreled. At the end of the barreling cycle, the twenty cages appear to be perfectly smooth on all their surfaces and all their exposed edges and without loose fibers.

[0061] Two different speed tests are carried out on the sixty cages, comparing the behavior of the barrel-shaped cages with that of the non-barrel-shaped cages.

[0062] The results are presented in Table 1 below, where the cages made of composite material consisting of epoxy resin and carbon fibers are indicated by EPYCA and where the test parameters are also presented. “Y” means the presence of a rattle or clicks, “N” means no noise.

[0063] [Tables 1]

[0064] As can be seen, in only one test did the barrel-shaped cages produce a (limited) rattling noise, which was no longer present in a second test carried out with the same test parameters. The barrel-shaped epoxy / carbon fiber cages exhibited virtually no rattling.

[0065] It has therefore been demonstrated that implementing a barreling on epoxy / carbon fiber cages has a positive impact on the cage's rattling performance.

[0066] It has been observed that the tumbling (and subsequent washing operation) after machining (for example for the separation by cutting of the sections 18 of the tube forming preform 12 and for the production of the holes forming the pockets or housings 8) has eliminated or at least mitigated the possible delamination of the carbon fiber layers in the cage and reduces the generation of free particles in the interior of the rolling bearing equipped with such cages.

[0067] Consequently, the trussing stabilizes the cage surface and prevents grease contamination by loose fibrous particles during operation. The performance of trussed epoxy / carbon fiber cages was among the best observed among fiber-reinforced polymer cages.

[0068] The advantages of the combination: tonneau cover as opposed to epoxy / carbon fiber cages were as follows: • stabilization of the cage surface • Removal of burrs / fibers resulting from subsequent machining • Removal of surface imperfections • Reduction of delamination of carbon fiber layers on the outer and inner diameters and in the cage pockets • reduction in particle generation during operation • preventing grease contamination • elimination of unwanted noise.

[0069] All the objectives of the invention are therefore achieved.

Claims

Demands

1. Low-noise composite material bearing cage (3), comprising an annular body (7) and a plurality of pockets or housings (8), each configured to freely house, during use, a respective bearing body (6) of a bearing (2), the annular body (7) having an axis of symmetry (A) and a predefined axial width and the pockets or housings (8) being located radially throughout the annular body, through respective inner and outer cylindrical lateral surfaces (10, 11) of the annular body radially delimiting it, the annular body (7) being made of a continuous fiber-reinforced synthetic plastic material comprising a plurality of superimposed layers (15) of reinforcing fibers (13) embedded in the synthetic plastic material and arranged according to a predefined pattern;characterized in that a) the reinforcing fibers (13) of each layer are embedded in a synthetic plastic resin; b) said inner and outer cylindrical lateral surfaces (10, 11) of the annular body, a peripheral edge of each said pocket or housing (8) and the opposite axial front edges of the annular body (7) have a deburring finish, namely, they do not have substantially any burrs, the whole cage having been subjected to a barreling operation.

2. Bearing cage made of composite material according to claim 1, characterized in that the synthetic plastic resin has a glass transition temperature greater than or equal to 90 °C, preferably 120 °C, and preferably consists of an epoxy resin.

3. A bearing cage made of composite material according to claim 1 or 2, characterized in that the reinforcing fibers (11) are selected from the group consisting of: carbon fibers, glass fibers, Kevlar® fibers, mineral fibers, such as basalt and quartz fibers, ceramic fibers, for example Al2O3 or SiC fibers, metallic fibers, for example steel or aluminum fibers, organic fibers including cotton, cellulose, flax, jute, hemp and sisal fibers, any synthetic fiber, organic or inorganic similar to these in terms of tensile strength and / or stiffness.

4. Bearing cage made of composite material according to any one of the preceding claims, characterized in that said reinforcing fibers (13) are continuous fibers embedded in / impregnated with said synthetic resin and wound around said axis of symmetry (A) at predefined winding angles.

5. A bearing unit (1) comprising a bearing (2) comprising an outer ring (5), an inner ring (4) and a plurality of bearing bodies (6) arranged in a defined radial space between the inner ring and the outer ring to make them relatively rotatable with low friction, and a bearing cage (3) according to any one of the preceding claims for retaining the bearing bodies in a spaced manner by means thereof.

6. A method for producing a bearing cage made of composite material (3) comprising an annular body (7) and a plurality of pockets or housings (8), each configured to house, in use, a respective bearing body (6) of a bearing (2), the annular body (7) having an axis of symmetry (A) and a predefined axial width and the pockets or housings (8) being located radially throughout the annular body, through respective internal and external cylindrical lateral surfaces (10, 11) of the annular body radially delimiting it, said pockets or housings being delimited by respective peripheral edges (20) thereof;the process comprising the steps of: a) production of a preform forming tube (12) made of fiber-reinforced synthetic plastic material, in which the fibers (13) are made of a high tensile strength and rigid material impregnated with a synthetic resin having a glass transition temperature, after hardening, greater than or equal to 90 °C, preferably 120 °C; b) hardening of the tube forming preform (12) to polymerize the synthetic resin to form a consolidated synthetic plastic matrix (15) in which the reinforcing fibers (13) are embedded according to a predefined pattern; c) radial cutting, in the preform tube (12), of a plurality of axial sections (18) thereof, each having a axial width identical to that of the bearing cage (3) to be obtained, each said axial section (18) of the preform tube (15) having a plurality of pockets or housings (8) situated through it and configured to house, when in use, the bearing bodies of a bearing; the pockets or housings (8) being obtained in step a) or being drilled in the preform tube (12) after step b); characterized in that: d) after step c) the whole cages (3) obtained by cutting the preform tube (12) into a plurality of axial sections (18) and by producing through these said pockets or said housings (8) are subjected to a barreling step, until substantial removal of any burr from said radially internal and external lateral cylindrical surfaces (10, 11), from said peripheral edges (9) of the pockets or housings (8) and from the respective opposite axial front edges (20) of each cage.

7. A method according to claim 6, characterized in that said synthetic plastic resin is an epoxy resin.

8. A method according to claim 6 or 7, characterized in that the fibers (13) are selected from the group consisting of: carbon fibers, glass fibers, Kevlar® fibers, mineral fibers such as basalt and quartz fibers, ceramic fibers, for example A12O3 or SiC fibers, metallic fibers, for example steel or aluminum fibers, organic fibers including cotton, cellulose, flax, jute, hemp and sisal fibers, any synthetic, organic or inorganic fiber similar to these in terms of tensile strength and stiffness.

9. A method according to any one of claims 6 to 8, characterized in that said preform forming tube (12) is obtained by means of a continuous filament winding technique, by winding on a mandrel (14) having an axis of symmetry coinciding with the axis of symmetry (A) of the bearing cage (3) to be obtained, at least one continuous fiber (13) made of a high tensile strength material impregnated with a synthetic resin having, after hardening, a glass transition temperature greater than or equal to 90 °C, preferably 120 °C, to form a plurality of radially superimposed layers (15) of impregnated reinforcing fibers (13).

10. 15 Method according to any one of claims 6 to 9, characterized in that said barreling step is carried out in a vibrating barrel machine loaded with a number of identical complete cage bodies (7) mixed with abrasive particles having a dimension at least one order of magnitude smaller than an outside diameter of the cage body (7).

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