Cage made of composite materials for bearings.

Abstract

The bearing cage (2) is designed to ensure the circumferential spacing of at least one row of rolling elements and comprises a plurality of recesses (3) to accommodate the rolling elements of said row. The cage is made of fiber-reinforced synthetic material having a glass transition temperature equal to or greater than 120°C. Reference: Figure 2

Description

Title of the invention: Composite material cage for bearings. Technical field of the invention

[0001] The present invention relates to cages for rolling element bearings, as well as bearings provided with these cages and these rolling elements. The invention also relates to methods for obtaining these cages. State of the prior art Rolling element bearings are components intended for the rotational guidance of various mechanical parts. These bearings generally comprise an inner ring and an outer ring, the rolling elements being arranged between the rings. The rolling elements, which can be balls, cylindrical rollers, tapered rollers, needles, are held by a cage.

[0003] Conventionally, cages are made in one piece by molding a synthetic material. To give a cage sufficient mechanical strength, the synthetic material generally comprises a matrix in which fibers are embedded. The matrix may, for example, be a phenolic resin and the fibers cotton fibers.

[0004] Such a cage made of synthetic material is light, inexpensive to manufacture, and provides good support for the rolling elements. Consequently, bearings equipped with these cages are generally satisfactory. This means in particular that, for everyday use, the bearings have a sufficient service life and retain most of their mechanical properties, such as guidance precision.

[0005] It has however been observed that the performance of a bearing equipped with such a synthetic cage is impaired under certain conditions of use.

[0006] First of all, if a bearing is subjected to very high rotation speeds, as is the case for example for certain machine tool spindles, the cage can sometimes deteriorate to the point of rupture. Indeed, high rotation speeds cause temperature increases. Excessive temperatures lead to a reduction in the mechanical strength of the cage, in particular its rigidity. This phenomenon occurs around the glass transition temperature of the matrix, which is notably 80°C for phenolic resin, where the fundamental mechanical properties are reduced. This glass transition temperature value is a glass transition threshold. In addition, high rotation speeds generate high stresses, in particular by centrifugal force, which increases the risk of degradation or rupture of the cage.

[0007] Another condition that can lead to cage damage is an excessive humidity level, i.e., a level beyond the nominal or average humidity level. generally observed. This level may be due to rainy weather, a specific operating environment, a more or less aqueous lubricant, or other. In fact, the cage matrix is ​​capable of retaining a certain amount of water. This is a retention phenomenon that is all the more pronounced as the humidity level is high. But the more water the cage retains, the more it deforms. Sometimes the deformation is excessive and the manufacturing tolerances are no longer respected. This results in more rapid deterioration of the cage.

[0008] Conversely, deterioration of the cage can also occur at an insufficient humidity level, i.e. below the nominal rate or average rate generally observed. This level may be due to very dry weather, a specific operating environment, insufficient lubrication, or other. If it does not retain enough water, i.e. in practice if its humidity level has dropped too much, it is again in conditions of deformation which can cause it to go outside the manufacturing tolerances. Here again, more rapid deterioration of the cage is observed.

[0009] The cages used conventionally are too sensitive to the ambient humidity level, and deteriorate too quickly if the operating temperatures of the bearing are high. Summary of the invention,

[0010] A general object of the invention is to improve the service life of synthetic material cages for rolling element bearings. In particular, this involves preserving the mechanical properties of the cages for the majority of the conditions of use of a bearing.

[0011] More precisely, the invention aims to reduce, or even eliminate, the influence of the humidity level in which a bearing operates.

[0012] The invention also aims to enable a bearing to operate under high temperature conditions.

[0013] To this end, the invention proposes a rolling bearing cage intended to ensure the circumferential spacing of at least one row of rolling elements, the cage comprising a plurality of cells for accommodating the rolling elements of said row and being made of fiber-reinforced synthetic material. According to the invention, the synthetic material has a glass transition temperature equal to or greater than 120°C.

[0014] It is recalled that below its glass transition temperature, the synthetic material retains its mechanical properties such as hardness or rigidity. However, beyond the transition temperature, the synthetic material becomes much more flexible, even viscoelastic. Consequently, with the invention, the bearing can be subjected to high rotation speeds, because the resulting heating temperature, according to what the applicant has determined, which is of the order of 80°C to 120°C, does not exceed the transition temperature. The cage retains its mechanical properties and shape are much more stable. The cage dimensions remain within manufacturing tolerances.

[0015] In one embodiment of the invention, the synthetic material is an epoxy resin whose glass transition temperature is between 130°C and 200°C. This high glass transition point is particularly interesting, because not only does it allow use in a wide range of temperatures in the usual sense of the term, but it also constitutes an additional level of safety in the event of occasional heating which could occur due to an anomaly or other.

[0016] Advantageously, the fibers are continuous, that is to say placed layer by layer, as opposed to cut or chopped fibers. This allows for a uniform distribution of the latter. Another advantageous aspect of the invention is to place the fibers in a circumferential direction. This results in greater homogeneity of structure of the cage and greater rigidity.

[0017] In a particular embodiment, the fibers comprise carbon fibers. Alternatively or in combination, the fibers may comprise glass fibers, allowing a reduction in the cost of the cage, and / or Kevlar® fibers, and / or flax fibers, and / or Vectran® fibers, in order to improve the vibration properties of the cage.

[0018] The invention also relates to a rolling bearing comprising a cage as defined above. The invention also relates to a method for manufacturing cages for rolling bearings made of fiber-reinforced synthetic material and comprising a plurality of cells, the method comprising:

[0019] - a step of producing a cylindrical tube preform by winding it onto a mandrel of continuous pre-impregnated fibers of synthetic material whose glass transition temperature is equal to or greater than 120°C,

[0020] - a step of molding and polymerizing the tube, and

[0021] - a step of cutting the tube obtained to obtain rings with the dimensions of the cages.

[0022] At the end of this last step, the external and internal diameters of the cage are at the required dimensions. It is then not necessary to carry out any machining step on these diameters. It is possible to provide a final step of polishing the internal and external surfaces of the cage, in order to remove loose particles and to optimize the roughness. Then the cage is washed to ensure delivery without fiber or resin particles.

[0023] The production of the preform can for example use conventional winding and coiling techniques. The molding can be done in a mold in two or more parts, which once joined delimit a cylindrical volume for receiving the preform on the form. The tube can be cut by a saw at automated, by a conventional or numerically controlled lathe, by high-pressure water jet, or any other suitable means.

[0024] According to one embodiment, the method further comprises a step of forming cells on the cut rings to obtain the cages.

[0025] Alternatively, it might be possible to form the cells after the molding and polymerization step, but before the tube cutting step.

[0026] This step of forming the cells can for example be carried out by machining.

[0027] According to another embodiment, the method comprises a training step cells during the molding and polymerization stage of the tube.

[0028] To do this, it is possible in the step of producing the preform to use a mandrel equipped with circumferential rows of projections extending radially outwards, each row comprising a plurality of projections spaced apart from each other in the circumferential direction, the rows being spaced axially from each other.

[0029] The cells are thus obtained directly by preforming then molding. However, for certain applications requiring very high precision, a step of finishing the cells by removing material or by over-injection of material may be provided.

[0030] According to a particular embodiment, at least a portion of the fibers, or all of the fibers, form a non-zero angle relative to the axis of the cylindrical shape. The fibers are for example put in place by winding, which provides regularity in their distribution, and consequently dimensional homogeneity in series of cages.

[0031] According to a particular embodiment, the fibers can be made of carbon and the synthetic material is an epoxy resin which has a glass transition temperature between 130°C and 200°C. The high level of the glass transition point provides mechanical stability of the cages for all uses, conventional or extreme. The carbon fibers make the cage very mechanically strong, and also very light.

[0032] In addition, a layer of thermosetting synthetic material can be placed on the periphery of the tube.

[0033] This may be, for example, polyurethane, or any equivalent material. This type of material gives the cage damping properties. As a result, vibrations and operating noise are reduced. Brief description of the figures

[0034] Other aims, characteristics and advantages of the invention will appear on reading the detailed description of non-limiting embodiments, with reference to the figures annexed, for which:

[0035] [Fig-1] is a side view of a tube obtained by winding fibers on a mandrel for the manufacture of cages according to a first embodiment of the invention,

[0036] [Fig.2] is a perspective view of a cage for a rolling element rolling bearing obtained according to the embodiment of [Fig.l], and

[0037] [Fig.3] is a perspective view which corresponds to another mode of implementation of the method of producing the invention. Detailed description of the invention

[0038] In [Fig.l] a hollow tube 1 is shown schematically, with longitudinal axis Ll.

[0039] This hollow tube 1 is obtained from a cylindrical preform of the tube 1 which is itself produced by winding on a mandrel continuous fibers pre-impregnated with a synthetic material whose glass transition temperature is equal to or greater than 120°C.

[0040] For example, the fibers are arranged in layers by techniques such as winding, winding a fiber fabric, or any equivalent. The orientation of the fibers in each layer and the number of superimposed layers are determined based on the desired structural and vibrational characteristics of the cage to be manufactured.

[0041] The fibers are preferably carbon fibers. Alternatively or in combination, the fibers may include glass, Kevlar®, flax, Vectran®, or other fibers. The fibers can thus be used alone or in combination. It all depends on the desired mechanical properties, and also on economic constraints.

[0042] The synthetic material is preferably an epoxy resin whose glass transition temperature is between 130°C and 200°C.

[0043] Then, after this first step of producing the preform, a step of molding and polymerization of the tube 1 is carried out under particular temperature and pressure conditions adapted to the composite material used. This gives the tube 1 all its properties, in particular shape stability and mechanical resistance.

[0044] For more details on the steps of producing the preform and of molding and polymerization, reference may be made to patent application FR 3 053 624 incorporated by reference.

[0045] From a tube 1 obtained, a cutting step is provided to obtain rings with the dimensions of the cages to be formed.

[0046] Then, a step of forming cells on the cut rings is provided, by example by drilling, to obtain cages 2, with longitudinal axis L2, one of which is visible in [Fig.2]. In the illustrated embodiment, the cage 2 comprises circular-shaped cells 3 which are adapted to accommodate balls. Alternatively, the cells may have different shapes to accommodate rolling elements other than balls, for example rollers.

[0047] Alternatively, the cells may be formed on the tube 1 after the molding and polymerization step and before the ring cutting step.

[0048] Thanks to the material(s) that compose it, the cage 2 has properties that allow it to be used in difficult conditions, such as high temperatures, high humidity levels, or particularly low humidity levels. In fact, the cage 2 remains dimensionally stable, it resists heat and significant variations in the humidity level.

[0049] As indicated previously, a very interesting example of material for the fibers of cage 2 is carbon, which in particular provides rigidity and lightness, combined with an epoxy resin having a glass transition temperature between 140°C and 160°C.

[0050] An alternative embodiment is illustrated in [Fig. 3]. The mandrel here comprises a cylinder 12, with axis L4, and a sleeve 11 mounted on the cylinder and provided with projections 13 extending radially outwards. In the illustrated embodiment, each projection 13 is a circular stud with radial axis L5, provided to obtain a cage equipped with circular cells.

[0051] The projections 13 are arranged in circumferential rows, each row comprising a plurality of projections spaced apart from each other in the circumferential direction. The rows are axially spaced apart from each other.

[0052] In this variant, the fibers are wound onto the mandrel equipped with the projections 13 to obtain the preform of the tube 14. The cells are thus formed during the following molding and polymerization step.

[0053] Next, the method then comprises a step of separating the cylinder 12 and the sleeve 11 covered by the polymerized tube 14, and a step of cutting the tube 14 into rings each constituting a cage.

[0054] After cutting the cage, the cage can be introduced into an injection mold to over-inject the skeleton. This allows the exact shape of the cage, cells, internal and external diameter to be obtained in order to reduce the costs incurred by machining the skeleton material.

[0055] To facilitate the step of separating the cylinder 12 and the sleeve 11, the latter is preferably elastically deformable.

Claims

Claims

1. Cage (2) for a rolling bearing intended to ensure the circumferential spacing of at least one row of rolling elements, the cage (2) comprising a plurality of cells (3) for accommodating the rolling elements of said row and being made of fiber-reinforced synthetic material, characterized in that the synthetic material has a glass transition temperature equal to or greater than 120°C.

2. Cage (2) according to claim 1, in which the synthetic material is an epoxy resin whose glass transition temperature is between 130°C and 200°C.

3. A cage (2) according to claim 1 or 2, wherein the fibers are continuous.

4. Cage (2) according to one of claims 1 to 3, in which the fibers comprise carbon fibers.

5. Cage (2) according to one of claims 1 to 4, in which the fibers comprise Kevlar® fibers, and / or flax fibers, and / or Vectran® fibers.

6. Rolling bearing comprising a cage (2) according to one of claims 1 to 4.

7. Method for manufacturing cages for rolling bearings made of fiber-reinforced synthetic material and comprising a plurality of cells, the method comprising: - a step of producing a cylindrical tube preform by winding on a mandrel continuous fibers pre-impregnated with the synthetic material whose glass transition temperature is equal to or greater than 120°C, - a step of molding and polymerizing the tube, and - a step of cutting the tube obtained to obtain rings with the dimensions of the cages.

8. The method of claim 7, further comprising a step of forming cells on the cut rings to obtain the cages.

9. The method of claim 7, wherein the cells are formed during the step of molding and polymerizing the tube.

10. A method according to claim 9, wherein, in the step of making the preform, the mandrel is provided with circumferential rows of projections extending radially outwardly, each row comprising a plurality of projections spaced apart from each other in the circumferential direction and the rows being axially spaced apart from each other.