Bearing cage made of composite material and associated bearing unit

Abstract

Composite material bearing cage and associated bearing unit Bearing cage (3) comprising an annular body (7) and a plurality of pockets or housings (8) configured to receive bearing bodies (6) of a bearing (2), the annular body (7) having an axis of symmetry (A) and being delimited between internal and external cylindrical lateral surfaces (9, 10) thereof; the annular body (7) being made of a fiber-reinforced synthetic plastic material formed by superimposed layers (18) of reinforcing fibers (11) embedded in a synthetic plastic material (13);at least one of the radially inner and outer layers (18) of fibers (11) being configured such that all their fibers (11) form with the axis of symmetry an angle (β1) substantially identical to the angle (β) formed with the axis of symmetry (A) by a geometric tangent (T) to the two peripheral edges (19) of two adjacent pockets or housings (8). [Figures 2 and 4];

Description

Title of the invention: Composite material bearing cage and associated bearing unit. Technical field of the invention

[0001] The present invention relates to a bearing cage made of a fiber-reinforced composite synthetic plastic material, and to an associated bearing unit comprising such a cage. 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 may be made of a synthetic plastic material, for example a phenolic resin or any other higher-performance synthetic material, for example epoxy resins, and supports the pockets or housings, which are located radially through it, for example consisting of radial through holes.

[0004] To improve performance, the synthetic plastic material can be reinforced with fibers having high tensile strength and rigidity, for example carbon fibers, glass fibers, or any other fibers of similar strength and rigidity. This is generally achieved by stacking several layers of fiber-reinforced polymer tape in different orientations to achieve the desired performance level.

[0005] A preferred method for obtaining fiber-reinforced polymer cages comprises the step of producing a preform consisting of a hollow tube and the step of cutting the tube forming the preform in the radial direction to obtain a plurality of slices consisting of axial sections of the tube forming the preform, each of them being cut to a length identical to the axial width of a cage to be obtained. The pockets or recesses are drilled either before or after the cutting operation, for example directly through the tube forming preform or through the cut slices, so that each axial section cut from the tube forming the preform comes to constitute a desired cage body.

[0006] The tube forming preform can be produced by stacking several layers of fiber-reinforced polymer tape, as mentioned above, or, preferably, by a process known as "continuous filament winding" (CFW), by tightly winding one or more filaments of composite material consisting of continuous fibers impregnated with a synthetic plastic resin, for example a continuous carbon fiber impregnated with an epoxy resin, onto a metal mandrel.

[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 predetermined number of superimposed radial layers of prepreg fibers have been obtained, the preform is cured in a manner known to cause the synthetic material impregnating the fibers to consolidate into a solid matrix, in which the wound fibers remain embedded to constitute the reinforcing material. The curing can occur as disclosed, for example, in FR3053624A1.

[0009] A fiber-reinforced bearing cage of the aforementioned type is disclosed in a pending patent application of the same Applicant, where the high-strength, rigid reinforcing fibers are impregnated with a synthetic resin material having a glass transition temperature after curing of 120 °C or more.

[0010] Especially when such a composite cage body is obtained through CFW processes, it is possible to configure the preform forming tube with a sequence of carbon fiber layers oriented at different angles to each other, both to prevent the composite preform forming tube from exhibiting strongly anisotropic behavior and to improve its mechanical properties and, consequently, the mechanical properties of the final cage body.

[0011] However, cages produced in the manner disclosed above may have the disadvantage that at least the outermost and innermost fiber-reinforced polymer layers, consisting indifferently of either fiber-reinforced strip layers or layers obtained by CFW techniques, are subject to delamination either during the operation of the cage or even already during the machining of either the tube forming preform or its cut axial sections, for example when drilling the holes configured to make the pockets or housings required to accommodate the bearing bodies of a roller bearing during use.

[0012] Delamination can occur, in particular, when the reinforcing fibers in such innermost and outermost layers are oriented at 90° with respect to the axis of symmetry of either the tube forming preform or the cage body.

[0013] The delamination problem, even if limited to specific layers of the composite cage body, can impair the performance of the cage during operation and, above all, can lead to scrap during the production cycle, which increases production costs, since the delamination is located just at the circumferential portions of the cage body separating adjacent pockets or housings from each other. Summary of the invention

[0014] 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 primary objective of the invention is to produce a composite material bearing cage in which the radially inner and outer layers of the composite material do not delaminate during machining or subsequent operation, even at high rotational speeds and under high loads.

[0015] An objective of the invention is also to provide a high-precision rolling bearing unit equipped with a cage made of composite material suitable for use in applications with particularly high stresses, such as those requiring high rotational speeds and / or subjected to high loads.

[0016] According to the invention, a bearing cage made of composite material and an associated bearing unit are provided, as defined in the attached claims. Brief description of the figures

[0017] 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:

[0018] - Figure [1] schematically represents a rolling bearing unit equipped with a bearing body retaining cage made according to the invention;

[0019] - [Fig.2] schematically represents, at an enlarged scale, a bearing cage bearing for retaining the bearing bodies of a bearing housing provided according to the present invention;

[0020] - Figure 3 schematically represents a preform tube, parts of which have been removed to improve understanding, mounted on a mandrel, tube from which the retaining cage of [Fig.2] can be obtained; and

[0021] - [Fig. 4] represents a simple schematic top view and to scale enlarged by two circumferential portions of the cage of [Fig.2], arranged side by side to improve understanding, schematically representing the essence of the invention. Detailed description of the invention

[0022] With reference to Figures 1 to 4, 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.

[0023] The bearing 2 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.

[0024] 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.

[0025] 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 house, during use, a respective bearing body 6 of the bearing 2 to properly maintain the bearing bodies 6 spaced from each other by a predefined pitch.

[0026] 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 9 and 10 ([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 8 and 10 radially delimit the annular body 7 from each other.

[0027] The annular body 7 is made of a fiber-reinforced synthetic plastic material and is preferably obtained by a process known in the art as CFW (continuous filament winding). First, a preform-forming tube 15 ([Fig. 3]) is obtained by winding, in a known manner, around an axis of symmetry A and on a metal mandrel 14, one or more reinforcing fibers 11 impregnated with a suitable synthetic resin material 13, for example, carbon fibers impregnated with an epoxy resin, and then cured, for example according to FR3053624A1, to consolidate the synthetic resin material 13 impregnating the fibers 11 into a matrix of solid synthetic plastic material 12 in which the fibers 11 are embedded in an arrangement according to a predetermined pattern. Then, selected axial sections 16 of the preform-forming tube 15 are cut radially from it, before or after piercing the pockets or recesses 8 through it.

[0028] Consequently, each section 16 comes to constitute, after the cutting step, an annular body 7.

[0029] In substance, the cage body 7 of the synthetic fiber-reinforced bearing cage 3 of the invention is obtained as the axial portion of the preform forming tube 15.

[0030] Each annular body 7, therefore, comprises a plurality of superimposed layers 18 of reinforcing fibers 11 embedded in a synthetic plastic material 13 and arranged with respect to the axis of symmetry A according to predefined patterns.

[0031] Alternatively, the preform forming tube 15 can be obtained using other manufacturing processes, for example using superimposed pre-preg strips or films of fiber-reinforced polymers, in each of which the reinforcing fibers have a selected orientation, resulting in the obtaining of a preform forming tube 15 and, consequently, of a plurality of cage bodies 7 detached from the preform forming tube 15 as axial sections or portions 16 thereof by cutting, formed by superimposed layers of fiber-reinforced polymer strip 18.

[0032] In certain embodiments, the preforming tube 15 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.

[0033] According to a first feature of the invention, and regardless of the method of obtaining the tube forming preform 15 and the layers 18, at least one radially inner layer 18 and / or at least one radially outer layer 18 of the superimposed layers of reinforcing fibers 11 are configured ([Fig.4]) such that all their fibers 11 are oriented so as to form with the axis of symmetry A a first angle [31 substantially identical to, or less than, a second angle [3 formed with the axis of symmetry A by a geometric tangent T to the two peripheral edges 19 of any two adjacent pockets or housings 8.

[0034] The expression "substantially identical" means that the first angle, due to the operating tolerance, may be identical to or less than the second angle to within ± 3°.

[0035] The value of the second angle [3] is unique and can be easily established at the design stage of the cage 3, when the internal and external diameters of the cage body 7 and the dimensions of the pockets or housings 8 are determined. Therefore, the orientation of the fibers 11 at an angle

[31] substantially identical to, or less than, the angle [3] established at the design stage can be easily obtained by winding, at the production stage, the fiber(s) 11 around the mandrel 14 at such an angle

[31] or by means of layers of fiber-reinforced polymer tape 18, for example, made of a pre-preg material, in which the fibers 11 have been arranged so as to form the angle

[31] with the axis of symmetry A when the preform forming tube 15 is formed.

[0036] In bearing cages 3 designed for high-precision bearings, the first angle

[31] can generally be equal to or less than about 34.2°, where "about" means an operating tolerance of ±3°, but, more generally, this angle value of 34.2° is valid only for a specific cage size, the angle value depending on the pocket size and the number of pockets per cage and the cage diameter, and can be easily determined by a person skilled in the art.

[0037] According to a preferred embodiment, both the at least one radially inner layer 18b and the at least one radially outer layer 18c are such that their reinforcing fibers 11 are oriented along the first angle [31.

[0038] In addition, the at least one radially inner layer 18 and the at least one radially outer layer 18 whose fibers 11 are oriented along the angle [31 are the layers 18b and 18c ([Fig.3]) closest to the inner and outer lateral surfaces 9 and 10 of the annular cage body 7, for example are the radially innermost and outermost layers 18b, 18c of the "group" of superimposed layers 18 forming the cage body 7.

[0039] Such radially innermost and outermost layers 18b, 18c of the superimposed layers 18 forming the cage body 7 delimit and consequently define the lateral surfaces 9 and 10, respectively, of the cage body 7.

[0040] According to a preferred embodiment, in at least the radially inner layer 18b and the radially outer layer 18c of the plurality of superimposed layers 18, the reinforcing fiber or fibers 11 thereof is / are arranged in a crisscross configuration, where the fiber(s) 11 is / are parallel to each other and arranged at an angle equal to or less than one of the two tangents geometric T at the two peripheral edges 19 of any two adjacent pockets or housings 8.

[0041] It is evident, in fact, that there always exists, geometrically, a pair of tangents T (only one shown in [Fig. 4] for simplicity) at the two edges 19 of any pair of adjacent pockets or housings 8 relating to a bearing cage 3, so the fiber(s) 11 can be arranged to form angles with the axis of symmetry substantially equal to or less than the angle formed with the axis of symmetry A by one or both tangents of such a pair of tangents T, in the latter case using an interlaced configuration. Consequently, the angle

[31] can adopt either a positive or negative value, adopting for 0° the orientation of the axis of symmetry A.

[0042] In a preferred embodiment, the synthetic resin material 13 forming the solid matrix 12 after hardening has a glass transition temperature greater than or equal to 120 °C.

[0043] In a preferred embodiment, the synthetic plastic material 13 consists of an epoxy resin.

[0044] In a preferred embodiment, the reinforcing fibers 11 are chosen from the group consisting of: carbon fibers, glass fibers, Kevlar® fibers, any synthetic fiber similar to these in terms of tensile strength and stiffness.

[0045] 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.

[0046] In some embodiments, the reinforcing fibers may consist of other organic fibers such as cotton, cellulose, flax, jute, hemp and sisal fibers.

[0047] In a preferred embodiment, the reinforcing fibers 11 are continuous fibers embedded in the synthetic resin 13 and wound around the axis of symmetry A at predefined winding angles; such angles that the fibers 11 of each layer 18 form with the axis of symmetry A correspond to the winding angles with respect to it.

[0048] According to one aspect of the invention, the bearing unit 1 of [Fig. 1] comprises a bearing, for example the bearing 2 or any other bearing design 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 such a way spaced. The bearing 2 is preferably of the high-precision bearing type, characterized by high-speed and / or high-load operation.

[0049] In fact, a bearing cage 3 made according to what has been described above, taking care to provide the fibers 11 of at least the innermost and outermost layers 18b and 18c oriented at the angle [31 substantially identical to the angle [3 that the tangent T to the edges 19 of two adjacent pockets or housings 8 form with the axis of symmetry A avoids surprisingly completely or practically completely the phenomenon of delamination at the level of the lateral surfaces 9 and 10 or near them, particularly in correspondence with the circumferential portions of the cage body 7 which separate the pockets or housings 8 from each other.

[0050] The experimental tests carried out by the Applicant have in fact demonstrated that the orientation of the fibers 11 of the strip layers 18 on the inner diameter and on the outer diameter of the cage 3 are critical to allow the correct machining of the cage pockets 8.

[0051] A specific fiber orientation of the fibers 11 of the strip layers 18 on the inner and outer diameters of the cage 3, namely at the inner and outer lateral surfaces 9 and 10 of the cage body 7, prevents delamination of the strip layers 18b, c during machining of the cage 3.

[0052] In a specific case tested for a cage designed for high-precision bearings, the fiber angle defined by the invention gives a value of 34.2°. This means that the inner and outer strip layers 18b, 18c of the composite cage 3 as such, or their reinforcing fibers 11 in the case of manufacturing by a CFW technique, must be oriented at a fiber angle between 0° and 34.2°.

[0053] By doing so, it is certain that the inner and outer layers 18b, 18c will remain continuous in the inter-pocket area, that is, in the circumferential portion of the cage body 7 between each pair of adjacent pockets or housings 8. This results in improved structural performance in the inter-pocket area. Thus, during machining or in service, the risk of delamination is considerably reduced, or even completely avoided.

[0054] All the objectives of the invention are therefore achieved.

Claims

Demands

1. A 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 (9, 10) of the annular body radially delimiting it, the annular body (7) being made of a fiber-reinforced synthetic plastic material comprising a plurality of superimposed layers (18) of reinforcing fibers (11) embedded in a synthetic plastic material (13) and arranged with respect to said axis of symmetry (A) according to a predefined pattern;characterized in that at least one radially inner layer and / or at least one radially outer layer of said superimposed layers (18) of fibers (11) are configured such that all their fibers (11) are oriented so as to form with the axis of symmetry a first angle ([> 1 ) substantially identical to, or less than, a second angle (|3) formed with the axis of symmetry (A) by a geometric tangent (T) to the two peripheral edges (19) of any two adjacent pockets or housings (8).

2. Bearing cage made of composite material according to claim 1, characterized in that said first angle ([> 1 ) is substantially the same as, or less than, the second angle (|3) with a tolerance measure of ± 3°.

3. Bearing cage made of composite material according to claim 1 or 2, characterized in that said first angle ([> 1 ) is less than or equal to 34.2°.

4. A bearing cage made of composite material according to any one of the preceding claims, characterized in that both at least one radially inner layer (18b) and / or at least one radially outer layer (18c) are oriented along said first angle; said at least one radially inner layer (18b) and / or at least one radially outer layer (18c) being the layers of said superimposed layers (18) closest to said inner and / or outer lateral surfaces (9, 10) of the body of annular cage (7), preferably said at least one radially inner layer (18b) and / or at least one radially outer layer (18c) delimiting and defining said lateral surfaces (9, 10) of the cage body (7).

5. Bearing cage made of composite material according to any one of the preceding claims, characterized in that in said at least one radially inner layer and / or at least one radially outer layer (18b, 18c) of said plurality of superimposed layers (18) the reinforcing fiber or fibers (11) is / are arranged in an interlaced configuration, where the fiber(s) (11) forms with the axis of symmetry (A) an angle equal to or less than the angle formed with the axis of symmetry (A) by either of the two geometric tangents (T) to the two peripheral edges (19) of any two adjacent pockets or housings (8).

6. Bearing cage made of composite material (3) according to any one of the preceding claims, characterized in that the synthetic plastic material (13) has a glass transition temperature greater than or equal to 120 °C after curing.

7. Bearing cage made of composite material according to any one of the preceding claims, characterized in that the synthetic plastic material (13) consists of a hardened epoxy resin.

8. A bearing cage made of composite material according to any one of the preceding claims, characterized in that the reinforcing fibers (11) are selected from the group consisting of: carbon fibers, glass fibers, Kevlar® fibers, mineral fibers, preferably basalt and quartz fibers, ceramic fibers, preferably A12O3 or SiC fibers, metallic fibers, preferably 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 bearing cage made of composite material according to any one of the preceding claims, characterized in that said reinforcing fibers (11) are continuous fibers embedded in said synthetic resin material (13) and wound around said axis of symmetry (A) according to predefined winding angles; said angles which the fibers (11) of each layer form with the axis of symmetry (A) corresponding to the winding angles with respect to it.

10. 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.

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