METHOD FOR MANUFACTURING A GUIDE DEVICE WITH ROLLING ELEMENTS FOR MEDICAL SYSTEMS - Patent application

Abstract

The present invention relates to a method for manufacturing a bearing (100) for a medical rolling element guide device, comprising components, at least one of the components (20; 6, 2, 4, 5, 5') being made of titanium or a titanium alloy, said method comprising the following steps: - machining said titanium or titanium alloy component; - carrying out a diffusion hardening treatment on the machined component, so that said component is provided with a surface layer (21) having a hardness in the range of 900 Hv to 1100 Hv; The present invention allows medical rolling element guide devices to be manufactured from materials that do not pre-exist the properties required for these applications.

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a rolling element guide device for watchmaking, medical, semiconductor or ion beam mechanisms. The present invention also relates to a rolling element guide device for watchmaking, medical, semiconductor or ion beam mechanisms. The present invention also relates to a watchmaking mechanism, a medical device, a semiconductor area or a device for ion beam applications comprising such a rolling element guide device. [Background technology]

[0002] The term "rolling element guide device" refers to a device comprising (at least) a first element, (at least) a second element, and rolling elements held between the first and second elements, for facilitating relative movement of the first element relative to the second element, or vice versa. A rolling element guide device in this context has rolling elements with a maximum static load factor C0 of 2000 N, a maximum dynamic load factor C of 2000 N, and a maximum diameter of 1.6 mm.

[0003] In this context, the term "rolling element" refers to any object capable of rolling, such as, but not limited to, balls or rollers, e.g., cylindrical or tapered rollers, needles, etc.

[0004] A rolling bearing is an example of a rolling element guide. It generally comprises (at least) one outer ring (first element), (at least) one inner ring (second element, generally with two parts fixed together), and rolling elements held between the outer and inner rings. In some cases, a cage may be used to space the rolling elements between the rings.

[0005] Generally, the cage (also known as the rolling element separator) is an integral unit. The rolling elements located between the inner and outer rings of the bearing are generally held at a fixed distance by the cage, which guides them and facilitates their rotation. The cage may be composed of several independent segments. In addition to separating the rolling elements, the cage may also perform additional functions, such as but not limited to a locking function.

[0006] The number of contact points (eg, if the rolling elements are balls) or the number of contact lines (eg, if the rolling elements are rollers) between the rolling elements and the rings can vary depending on the type of bearing.

[0007] The surfaces on which the rolling elements roll are commonly called the raceways, which support the loads (axial and / or radial) applied to the bearing.

[0008] A linear bearing is another example of a rolling element guide. It typically comprises a sleeve (first element), a shaft (second element) and rolling elements held between the sleeve and the shaft. A linear bearing may include a cage for holding the rolling elements and for recirculating the rolling elements. In this case, the cage does not act as a rolling element separator. There are also configurations in which the rolling elements are inserted into a cage that acts as a rolling element separator. In this case, there is no recirculation of the rolling elements.

[0009] A ball screw is another example of a rolling element guide. It typically comprises a nut (first element), a screw (second element) and rolling elements held between the nut and the screw.

[0010] In general, rotary bearings are used to support and guide elements that are rotated, such as but not limited to gears, screws, axles, etc.; linear bearings are used to guide elements that move in a linear manner, such as but not limited to axles; and ball screws are used to convert rotary motion to linear motion, or vice versa, while minimizing friction (and maximizing efficiency).

[0011] To ensure that a rolling element guideway functions properly and has a long service life, certain properties of its components are particularly desirable, in particular the following: - High precision rolling element geometry (e.g. ISO Grade 3); - good mechanical properties, e.g. hardness and Young's modulus (in particular with regard to the rolling elements and the rolling area on the rolling element track of the first and / or second element); - Matching of the shape of the rolling surfaces, both the first and second elements.

[0012] Titanium or titanium alloys offer a combination of properties that make them attractive for a wide range of mechanical applications, especially: - its relatively low density for dynamic applications; - its chemical stability for applications in contact with the external environment; - Its low magnetic permeability for applications where residual magnetic fields are harmful.

[0013] These properties, plus the chemical biocompatibility of titanium or titanium alloys, make it a suitable material for the medical field.

[0014] In this context, the term "titanium alloy" refers to an alloy (especially a metal) that contains titanium and other chemical elements. Non-limiting examples of titanium alloys include the phase alloys α, α / β, β, ω, etc.

[0015] However, the low Young's modulus and / or limited hardness of titanium or titanium alloys (eg, compared to steel) makes them unsuitable for certain applications.

[0016] In the case of watchmaking or medical bearings, titanium or titanium alloys have been the materials of choice for the reasons mentioned above, in particular their insensitivity to magnetism and biocompatibility, respectively. Their low density is also an advantage that may prove important for certain applications.

[0017] The low Young's modulus of titanium is not an obstacle to its use in rolling element guides for watchmaking or medical applications.

[0018] However, the very limited hardness that titanium can achieve is an inhibiting factor for its use in the field of guide devices for watchmaking or medical rolling elements.

[0019] The latter are required to support large loads whilst maintaining a small footprint. For example, the maximum diameter of the outer elements (outer rings or bushes) of rolling element guides for watches or medical mechanisms is 28 mm. The materials used must therefore have excellent mechanical properties. The stresses at the contact between the balls and the rolling surfaces are extremely high, for example point stresses of the order of 4600 MPa in watchmaking or the medical sector.

[0020] In the watchmaking and medical fields, a high level of surface hardness is required to ensure that the rolling element guide device operates smoothly during use. The higher the hardness, the more the rolling element guide device can withstand the large loads and stresses of daily use and therefore extend its service life.

[0021] A wide variety of processes are available for imparting high surface hardness to titanium.

[0022] PVD (physical vapor deposition) and CVD (chemical vapor deposition) deposition processes are capable of depositing layers ranging from a few nanometers to a few micrometers on the surface of titanium components.

[0023] These treatments, such as TiN / CrN / TiC / TiCN typically used for cutting tool surfaces, have shown satisfactory results for many applications, but for guiding devices with rolling watches and / or medical bodies, the maximum deposition thicknesses of the order of a few micrometers do not allow effective load transfer.

[0024] Furthermore, a sharp boundary between the deposit and the base layer creates a discontinuity that is unfavorable for charge transport between the deposit and the base layer.

[0025] DLC (Diamond-Like Carbon) processes are a subfamily of PVD processes. They allow the deposition of carbon layers, generally with a thickness between 0.5 μm and 3 μm, adopting a partial diamond structure. This layer consists of a fraction of carbon in the diamond form (sp3 hybridized state), a fraction of graphite / graphene (sp2 hybridized state) and may also contain a certain amount of hydrogen. The properties of the layer depend on the ratio of these three components.

[0026] Despite their high surface hardness, DLC-type coatings are not suitable for rolling element guide devices for watchmaking and / or medical applications, because the coating thickness does not allow sufficient load transfer. Combined with the variable (weak) adhesion of the coating to the surface, there are cases of layer destruction and delamination, making this treatment impractical.

[0027] Titanium or titanium alloy surfaces can be anodized to give them color. Anodizing titanium or titanium alloys also changes the friction coefficient and surface topology of the base component. However, the properties of the anodized titanium or titanium alloy layer are not sufficient to withstand the stresses of rolling element guides such as watch bearings.

[0028] Micro-arc oxidation can also be used to create a dense surface layer on alloys that contain naturally dense passive oxide wires. The alloy part is immersed in a basic bath and an alternating current is applied. The resulting electric arc oxidizes the surface to a thickness of about 10 μm to 150 μm. Only the underlayer (about 65%) is dense, the outer surface is porous and must be removed.

[0029] The surface roughness induced by this treatment is detrimental to the properties of the degrees of freedom required for the correct operation of watchmaking or medical rolling element guide devices. Moreover, the dimensions of the components used in watchmaking and / or medical rolling element guides are below the limits of the dimensions that can be achieved using this technique.

[0030] Structural hardening of titanium or titanium alloys is also possible, but the hardness values ​​achieved by this treatment do not meet the requirements of rolling element guide devices for watchmaking or medical applications.

[0031] The galvanic deposition process allows for the deposition of various types of materials. Hardened electroless nickel can reach high hardness levels, but the risk of delamination from processing prevents their use for high-load applications.

[0032] To sum up, it is currently not possible to manufacture rolling element guide devices from materials (such as titanium or titanium alloys) that do not already have the properties required for watchmaking or the medical sector.

[0033] Document FR2136037 relates to a hardening process for metal parts, such as watch cases, boutons de machette, etc., which have a visible surface and therefore must meet aesthetic requirements. The parts are made of titanium and are first shaped and subsequently exposed to a diffusion of oxygen, nitrogen, hydrogen or a mixture of these gases at high temperature (approximately 1100°C or 1400°C to 1500°C) and low pressure, followed by rapid cooling. The treatment is carried out at low pressure and for a limited time.

[0034] Document CH539128 (Patent Document 2) is similar to document FR2136037.

[0035] Document EP1146136 (Patent Document 3) relates to a decorative article, such as an external decorative part of a watch, which comprises a substrate comprising stainless steel, titanium or a titanium alloy. An external force is first applied to generate a deformation layer having a thickness of 2 μm to 100 μm. Then, a hardened layer having a thickness of 5 μm to 50 μm is formed by diffusion of carbon, nitrogen or oxygen atoms at a temperature of 100 to 500 °C. A hard coating film such as TiC or TiN is deposited on the hardened layer.

[0036] Document US2020199725 (Patent Document 4) describes a hardening process for achieving a surface hardness of 900 HV or more, sufficient to provide scratch resistance to components in watches, jewellery, glasses etc. where visual appeal is important. [Prior art documents] [Patent documents]

[0037] [Patent Document 1] FR2136037 [Patent Document 2] CH539128 [Patent Document 3] EP1146136 [Patent Document 4] US2020199725 Summary of the Invention [Problem to be solved by the invention]

[0038] One object of the present invention is to provide a method for manufacturing a medical rolling element guide device that does not have the limitations of known bearings.

[0039] It is a further object of the present invention to provide a method for manufacturing a medical rolling element guide device from a material that does not pre-exist the properties required for a medical rolling element guide.

[0040] It is a further object of the present invention to provide a method for manufacturing a medical rolling element guide device which meets the requirements of watchmaking or medical rolling element guide devices. [Means for solving the problem]

[0041] According to the invention, these objects are achieved in particular by a method for producing a rolling element guide device as claimed in claim 1 and by a rolling element guide device as claimed in claim 10 .

[0042] The present invention relates to a method of manufacturing a rolling element guide device for a medical mechanism, the rolling element guide device comprising a component, the component comprising: - the first element, - a second element, - rolling elements disposed between the first and second elements for facilitating relative displacement of the first element with respect to the second element or vice versa Including, At least one component is made from titanium or a titanium alloy; The method comprises the steps of: - processing, e.g. machining, said titanium or titanium alloy component; - performing a diffusion hardening treatment of the machined component such that said component comprises a surface layer having a hardness in the range of 900Hv to 1100Hv; The method comprising:

[0043] In accordance with the present invention, the titanium or titanium alloy component of the medical rolling element guide device is first machined (in its "soft" state, ie, before hardening) and then diffusion hardened.

[0044] The process therefore involves fabricating, e.g. machining, at least one component of the rolling element guide device from a material that does not have the properties required for a medical rolling element guide device, and then hardening it so that it has these required properties.

[0045] This does not prevent, in a variant, said component being reworked (or re-machined) after the hardening treatment: the hardening treatment may, if necessary, have to be repeated after this subsequent re-machining step.

[0046] The use of titanium or titanium alloys in medical rolling element guide devices is surprising since their hardness is not sufficient for such devices.

[0047] Among all the known methods for hardening titanium or titanium alloys, the Applicant has selected a particular type of hardening treatment which is known in the watchmaking industry, in particular for watch cases, but not for rolling element guide devices.

[0048] This particular type of hardening treatment was known to improve the aesthetic appearance of a watch case. In many cases, aesthetics is not important for rolling element guide devices, which generally remain hidden to the user of the part or device in which they are fitted. The applicant therefore had no incentive to attempt known treatments of this type.

[0049] Moreover, medical rolling element guides have small dimensions compared to the parts that are hardened with this particular type of known hardening process. For example, the maximum diameter of the outer element (outer ring or bush) of a rolling element guide device for a medical mechanism is 28 mm. Small parts react differently to thermal cycling (e.g. by deformation), so again the applicant had no incentive to attempt this known type of process.

[0050] In particular, this solution has the advantage over the prior art of obtaining (at least) one component of the rolling element guide device, at least one of which is made of titanium or a titanium alloy, having a surface layer with a hardness in the range of 900 Hv to 1100 Hv, thereby making it suitable for the medical field.

[0051] Furthermore, the Young's modulus of the treated component material, as well as its geometric dimensions, is barely or not affected by the diffusion hardening treatment, which only alters and improves its surface hardness.

[0052] The aesthetic appearance of the treated components differs slightly from that of the untreated components (slightly darker in color and less shiny). However, for the application of medical rolling element guide devices, this slight change is not critical. It may also be possible to remove a few micrometers of the surface layer after the hardening treatment, for example by pickling, in order to obtain an aesthetic appearance more similar to that of the untreated components.

[0053] It is essential to first process, e.g. machine, the medical rolling element guide component and then harden it, because otherwise there is a high risk of removing a large part of the surface layer (i.e. the hardened or treated layer) during machining, which would make it impossible to obtain a high-quality rolling element guide device suitable for the medical field.

[0054] In one variation, the surface layer is defined between an outer surface and an inner surface, the inner surface being adjacent to a base layer (i.e., a non-treated layer) of the component, and the process comprises the steps of: - carrying out a (purely or mainly) interstitial diffusion hardening treatment such that the hardness of the surface layer decreases from the outer surface towards the inner surface.

[0055] In this variation, the gradual decrease in hardness improves charge transfer between the surface layer and the base layer.

[0056] In another, less preferred variant, the diffusion is (purely or predominantly) displacement type.

[0057] According to the invention, the diffusion hardening process involves immersing the component in a gas.

[0058] According to the invention, this gas comprises at least one atom selected from carbon, nitrogen, argon or oxygen.

[0059] According to the invention, the process includes the step of selecting a temperature at which curing is carried out, for example a temperature significantly higher than ambient temperature, for example in the range of 300°C to 1100°C, preferably 500°C to 800°C.

[0060] In one variation, the process includes controlling the temperature during hardening to allow diffusion while avoiding the growth of undesired phases or compounds such as carbides, nitrides or oxides.

[0061] According to the invention, the process includes the step of selecting a pressure for carrying out the curing, for example a pressure higher than atmospheric pressure, for example a pressure which may reach several times atmospheric pressure.

[0062] According to the present invention, the curing treatment time is in the range of 1 hour to 24 hours.

[0063] In one variant, the step of diffusion hardening of the machined components is the final step in the manufacturing process.

[0064] In one variant, the processed component has at least one dimension and / or mass greater than that of the desired final component, and the process comprises, after the hardening step, the following steps: - cutting the processed component in order to limit the deformations caused by the hardening process.

[0065] In fact, the curing process deforms the processed component, so that in order to obtain a component with a desired shape, dimension and / or mass, it is desirable to process a component with at least one dimension and / or mass larger than that of the desired component, for example at least twice as large, in order to limit its deformation during processing and to cut it after processing.

[0066] In rolling bearings, the clearance depends on the dimensions of the parts. The axial clearance of the bearing is very important as it determines the contact angle between the rolling elements.

[0067] This means that after the hardening treatment, the rolling bearings (e.g. deep groove bearings) have to be adjusted. Adjustment on components treated with the hardening treatment according to the invention is not possible because the layer thicknesses are too small.

[0068] In one embodiment, the guide device is a rolling bearing and the process comprises, after the hardening step, the following steps: - adjusting the axial clearance of the rolling bearing during assembly of the guide device.

[0069] In one embodiment, the guide device comprises a first inner ring (cone) and a second inner ring (core), and the axial clearance is adjusted by pressing the first inner ring (cone) against the second inner ring (core). The invention also relates to a rolling element guide device for a watch or medical mechanism, comprising (at least) one first element and (at least) one second element. The rolling elements are arranged between the first and second elements to facilitate the relative displacement of the first element with respect to the second element or vice versa.

[0070] According to the invention, at least one component is made of titanium and / or a titanium alloy and includes a surface layer of treated titanium and / or treated titanium alloy, said surface layer having a hardness in the range of 900 Hv to 1100 Hv.

[0071] This hardness ensures efficient load transfer and meets the requirements of rolling element guidance devices used in watchmaking and the medical sector.

[0072] In one variant, the surface layer is defined between an outer surface and an inner surface, the inner surface being adjacent to a base layer (i.e., an untreated layer) of the component, and the hardness of the surface layer decreases from the outer surface to the inner surface, in this variant there is a continuum that favors load transfer between the surface layer and the base layer.

[0073] In one variant, the surface layer 21 has a thickness in the range of 5 μm to 50 μm, which also provides a sufficient load-bearing capacity for watchmaking and / or medical applications.

[0074] In one variant, the component comprises a cage arranged to hold the rolling elements.

[0075] In one variant, the rolling element guide device is a rolling bearing.

[0076] In one variant, the rolling element guide device is a linear bearing.

[0077] In one variant, the rolling element guide device is a ball screw.

[0078] The invention also relates to an implantable medical device comprising a rolling element guide device according to the invention. In one variant, the rolling element guide device according to the invention is used to minimize friction losses and / or to extend the service life of a medical implant. [Brief description of the drawings]

[0079] An embodiment of the invention is illustrated in the following description, which is illustrated by the accompanying drawings, in which: FIG. 1 shows a perspective view of an example of a timepiece mechanism equipped with a rotary bearing according to an embodiment of the invention.

[0080] FIG. 2 shows a top view of the clock mechanism shown in FIG.

[0081] FIG. 3 shows a cross-section along plane BB of the clock mechanism shown in FIG.

[0082] FIG. 4 shows a top view of a part of the bearing of the clockwork mechanism shown in FIG.

[0083] FIG. 5 shows a perspective view of the bearing shown in FIG.

[0084] FIG. 6 shows diagrammatically the steps of a manufacturing process according to the invention.

[0085] FIG. 7 shows a cross-sectional view of some of the components of a rolling element guide device according to the invention.

[0086] FIG. 8A shows a perspective view of a component of a rolling element guide device before the diffusion hardening treatment of the process according to the invention.

[0087] FIG. 8B shows a perspective view of a part of a component of a rolling element guide device after the diffusion hardening treatment and after the cutting step of the process according to the invention.

[0088] FIG. 9A shows a cross-sectional view of a rolling element guide device in the form of a rolling bearing to illustrate an example of radial clearance.

[0089] FIG. 9B shows a cross section of the rolling element guide device shown in FIG. 9A to illustrate an example of axial clearance.

[0090] FIG. 10 shows a cross-section of a rolling element guide device in the form of a rotation bearing according to the invention to demonstrate one embodiment of adjusting the axial clearance.

[0091] Example(s) of embodiment of the present invention In the following description, by way of example and for the sake of simplicity, reference is made to a one-way rolling bearing, however the invention is not limited to such a one-way bearing but also covers other rolling element guide devices, such as bidirectional rolling bearings, linear bearings or screw balls.

[0092] In the following exemplary description, for the sake of simplicity, reference is made to a bearing with an outer ring (monoblock), two inner rings fixed between them, a cage, and rolling elements held in the cage and arranged between the outer ring and the two inner rings. However, the invention is not limited to such an embodiment and also includes all rolling element guide devices covered by the claims, such as a bearing with several similar but more than two inner rings; a bearing with (at least) two outer rings, a (monoblock) inner ring, a cage, and rolling elements held in the cage and arranged between the outer ring and the inner ring; a bearing with (at least) two outer rings, (at least) two outer rings, a cage, and rolling elements held in the cage and arranged between the outer ring and the inner ring; or a bearing with a one-piece inner ring, a one-piece outer ring, a cage, and rolling elements held in the cage and arranged between the outer ring and the inner ring, a cage-free bearing, or a linear bearing or ball screw.

[0093] The invention has applications in the field of watchmaking. It also has applications in the medical field, in particular when the rolling element guide device is used in medical devices that can be implanted in living organisms, such as the human body.

[0094] Fig. 1 shows a perspective view of an example of a clock mechanism comprising a bearing 100 (here rotatable) according to an embodiment of the invention. The clock mechanism 101 of Fig. 1 comprises a wheel 200 cooperating (directly or indirectly) with a rotating pan (not shown) and a pinion 400 cooperating (directly or indirectly) with an energy source (not shown) of a clock movement, for example a barrel.

[0095] In the example shown, the wheel 200 and the pinion 400 are coaxial, i.e. they rotate about the same axis of rotation A.

[0096] When wheel 200 rotates about its center in a first direction, bearing 100 transmits this rotation to pinion 400. When wheel 200 rotates in a second direction opposite the first direction, bearing 100 does not transmit this rotation to pinion 400.

[0097] Figure 2 shows a top view of the clock mechanism shown in figure 1. Figure 3 shows a cross-section of the clock mechanism shown in figure 2 along plane BB.

[0098] The bearing 100 shown in Fig. 3 comprises a cage 1, an outer ring 6 and two inner rings 2, 4, which are fixed together, for example in a removable or non-removable manner. It also comprises rolling elements 5, for example balls, held in the cage 1 and arranged between the outer ring 6 and the two inner rings 2, 4.

[0099] As shown in Fig. 4, which shows a top view of a portion of the bearing 100 of the clock mechanism of Fig. 1, the cage 1 comprises three segments 11, which have the same shape and are equally spaced between them. However, the invention is not limited to a cage 1 comprising several segments 11, since the invention is also applicable to a one-piece cage 1. The invention is also not limited to the number of segments 11 shown in Fig. 4, since for a cage 1 including segments 11, a number of segments 11 other than three can be envisaged.

[0100] Each segment 11 in Figure 4 comprises two ramps 10, 10'. However, the invention is not limited to segments 11 each including two ramps 10, 10' since only one ramp 10 or 10' is required per segment / retainer, nor is the invention limited to the presence of ramps on the retainer.

[0101] 4, the angle α of the inclined surfaces 10, 10' of each segment 11 is identical to each other and to the angles of the other segments 11. In one variant, the value of the angle α is between 78° and 88°.

[0102] In another variation, one or more segments 11 each have a sloped surface along a non-linear slope. In one variation, the non-linear slope is diminishing such that as the rolling element moves up the slope, there is always the same angle between the slope and a line passing through the rolling element and the center of the bearing. This type of slope improves blocking, especially in small bearings.

[0103] Each segment 11, together with the inner ring 2, 4 and the outer ring 6, defines a space 15 designed to receive a rolling element 5, for example a ball. In a preferred variant, the ball has three or four contact points with the rings 2, 4, 6.

[0104] In the locking direction of rotation, when the wheel 6 is driven clockwise in Fig. 4, the balls 5, 5' move up the inclined faces 10, 10', respectively, of each segment 11, until they are trapped between the segment 11 and the inner wheel 2 on the one hand and the outer wheel 6 on the other hand. In this case, the bearing 100 is in clutch mode and the rotation of the wheel 200 fixed to the outer wheel 6 is transmitted to the pinion 400 via the inner wheels 2, 4.

[0105] 5, in the direction of rotation opposite to the locking direction, which is counterclockwise in FIG. 4, the balls 5, 5' move down the inclined faces 10, 10' respectively of each segment 11 until they are blocked by the stop faces 12, 12' respectively of each segment 11. In this case, the bearing 100 is in release mode and the rotation of the wheel 200 is not transmitted to the pinion 400.

[0106] Each segment 11 in FIG. 4 has a shape that creates a second space 16, and this shape / space holds the segment 11 in place during EDM cutting. However, this shape is not limiting, and its presence is not required. For example, if the segments were stamped, each segment 11 would lack the shape that creates this second gap 16.

[0107] 6 shows diagrammatically the steps of a manufacturing process according to the invention, which comprises the following steps: - machining at least one component of the rolling element guide device (step 1000), - subjecting the machined component to a diffusion hardening treatment (step 2000) such that the component comprises a surface layer having a hardness in the range of 900Hv to 1100Hv.

[0108] According to the invention, the titanium or titanium alloy component of a watch or medical rolling element guide device is first machined (in its "soft" state, i.e. before hardening) and then diffusion hardened.

[0109] The process therefore involves processing, e.g. machining, at least one component of the rolling element guide device from a material that does not have the properties required for a watch or medical bearing, and then hardening it so that it has these required properties.

[0110] A hardness in the range of 900Hv to 1100Hv makes the rolling element guide device according to the invention suitable for the watchmaking or medical sector. In addition, the Young's modulus of the treated component material as well as the geometric dimensions of the treated parts are hardly or not affected by the diffusion hardening treatment.

[0111] It is essential to first process, e.g. machine, a component of the watch or medical rolling element guide device (step 1000) and then harden it (step 2000), because otherwise it would be impossible to obtain a bearing of suitable quality for the watch or medical sector due to the high risk of removing the surface layer (i.e. the hardened or treated layer) during machining.

[0112] 7 shows a cross-section of a part of a component 20 of a rolling element guide according to the invention. This component 20 may be the outer ring 6, the inner ring 2, 4, the rolling elements 5, 5' or possibly the cage.

[0113] Preferably, the component 20 is an inner ring 2, 4, since this component 20 is subjected to high stresses in watches or medical bearings.

[0114] In one variant, the surface layer 21 is defined between an outer surface 210 and an inner surface 212, the inner surface 212 being adjacent to the base layer 22 (i.e., the untreated layer) of the component. The proportions of the layers 21, 22 shown in Figure 7 do not necessarily correspond to the actual ones.

[0115] In one variant, the process comprises the steps of: performing a (purely or mainly) interstitial diffusion hardening treatment such that the hardness of the surface layer 21 decreases from the outer surface 210 towards the inner surface 212.

[0116] In this variation, the gradual decrease in hardness improves load transfer between the surface layer and the base layer.

[0117] In another, less preferred variant, the diffusion is (purely or predominantly) displacement type.

[0118] In one variant, the surface layer has a thickness e (as seen in FIG. 7) ranging from 5 μm to 50 μm. This thickness e also provides sufficient load-bearing capacity for watchmaking and / or medical applications.

[0119] According to the invention, the diffusion hardening process comprises the step of immersing the part in a gas, for example a gas containing at least one atom selected from carbon, nitrogen, argon or oxygen.

[0120] According to the invention, the process includes the step of selecting a temperature at which curing is carried out, for example a temperature significantly higher than ambient temperature, for example in the range of 500°C to 800°C.

[0121] In one variation, the process includes controlling the temperature during hardening to allow diffusion while avoiding the growth of undesired phases or compounds, such as carbides, nitrides or oxides.

[0122] According to the invention, the process includes the step of selecting a pressure for carrying out the curing, for example a pressure higher than atmospheric pressure (for example, it may reach several times atmospheric pressure).

[0123] According to the present invention, the curing treatment time is in the range of 1 hour to 24 hours.

[0124] The retention time in the processing chamber at the target pressure and temperature determines the thickness of the surface layer 21 for a given material.

[0125] In an unclaimed variant, the bearing components which are diffusion hardened are made of stainless steel.

[0126] FIG. 8A shows a perspective view of a rolling element guide device component 20 before the diffusion hardening treatment of the process according to the invention.

[0127] The hardening treatment according to the invention deforms the processed component 20. In particular, the hardening treatment may change the shape, at least one dimension and / or mass of the processed component. In one embodiment, the hardening treatment changes at least one dimension by up to 1% of its length. Thus, in order to obtain a component with a desired shape, dimension and / or mass, it is desirable to process the component 20 with at least one dimension and / or mass larger than that of the desired final component, for example at least twice as large, in order to limit its deformation during processing and to cut it after processing. For example, when obtaining a flat and thin processed component (i.e. having at least one dimension less than one tenth of its other dimensions), in one embodiment, a thick (i.e. not thin) initial component is treated with a hardening treatment and then cut to obtain the desired thin component, so that the cut surface is flat: since the cut surface has not been processed, there is no change in shape due to processing and it has the desired flatness.

[0128] In one variant, the processed component has at least one dimension and / or mass greater than that of the desired final component, and the process comprises, after the hardening step, the following steps: - cutting the processed component in order to limit the deformations caused by the hardening process.

[0129] FIG. 8A shows a possible cut line D for component 20 after processing.

[0130] FIG. 8B shows a perspective view of a part of a (final) component 20' of a rolling element guide device after the diffusion hardening treatment of the process according to the invention and after cutting along the cutting line D in FIG. 8B.

[0131] Component 20' includes (at least) one non-treated surface (bottom surface 23 in FIG. 8B), but cutting line D is selected such that this non-treated surface is non-functional in the guide device.

[0132] FIG. 9A shows a cross-sectional view of a rolling element guide device 100 in the form of a rotation bearing to illustrate an example of a radial clearance JR after application of a radial force FR.

[0133] FIG. 9B shows a cross-sectional view of the rolling element guide device 100 of FIG. 9A to illustrate an example of an axial clearance JA after application of an axial force FA.

[0134] In rotary bearings, the clearance depends on the dimensions of the parts. The axial clearance JA of the bearing is very important since it defines the contact angle between the rolling elements 5 and the ring(s).

[0135] This means that after the hardening treatment, rolling bearings (e.g. deep groove bearings) have to be adjusted. Adjustment on components treated with the hardening treatment according to the invention is not possible because the layer thickness is too small. Adjustment would remove at least a part (but not all) of the treated layer. In one embodiment, the guide device is a rolling bearing and the process comprises, after the hardening treatment step, the following steps: - Adjusting the axial clearance of the rolling bearing during assembly of the guide device.

[0136] This avoids removing the treated layer when adjusting the axial clearance.

[0137] In one embodiment, the guide device comprises a first inner ring 4 (cone) and a second inner ring 2 (core), and the axial clearance is adjusted by pressing the first inner ring (cone) 4 against the second inner ring (core) 4.

[0138] FIG. 10 shows a cross-sectional view of a rolling element guide 100 in the form of a rotary bearing according to the invention to demonstrate one embodiment of adjusting the axial clearance RJA by pressing a first inner ring (cone) 4 against a second inner ring (core) 4.

[0139] Numbers and symbols used in the diagram 1 Cage 2. The First Inner Circle 4. The second inner circle 5 Rolling elements 6 Outer ring 10,10' slope 11 Cage segment 12,12' Stop surface 15,15' First Space 16 The Second Space 20,20' Components 21 Surface layer 22 Base Layer 23 Untreated surface 100 Bearings 101 Clock mechanism 200 cars 210 External Surface 212 Internal surface 400 Pinion 1000 machining stages 2000 Diffusion Hardening Treatment Steps A Rotation Axis D cutting line e Surface layer thickness FA Axial force FR radial force JA Axial clearance JR radial clearance RJA Axial clearance adjustment

Claims

1. A method of manufacturing a rolling element guide device (100) for a medical mechanism, comprising components, the components comprising: a first element (6), a second element (2, 4), - rolling elements (5, 5') arranged between the first element (6) and the second element (2, 4) for facilitating the relative displacement of the first element (6) with respect to the second element (2, 4); Including, At least one component (20; 6, 2, 4, 5, 5') is made of titanium or a titanium alloy; The method comprises the steps of: - machining said titanium or titanium alloy component, - performing a diffusion hardening treatment on the machined component, Including, said diffusion hardening treatment comprising the step of immersing said titanium or titanium alloy component (20; 6, 2, 4, 5, 5') in a gas; The gas contains at least one atom selected from carbon, nitrogen, argon, or oxygen, The process consists of the following steps: - selecting a temperature in the range of 500°C to 800°C; - selecting a pressure higher than atmospheric pressure and the curing treatment time is in the range of 1 hour to 24 hours, so that the component is provided with a surface layer (21) having a hardness in the range of 900Hv to 1100Hv. The method.

2. 2. The method of claim 1, wherein a surface layer (21) is defined between an outer surface (210) and an inner surface (212), said inner surface being adjacent to a base layer (22) of said component, said method comprising the steps of: performing an interstitial diffusion hardening treatment, whereby the hardness of the surface layer (21) decreases from the outer surface (210) towards the inner surface (212).

3. The method according to claim 1 or 2, wherein the surface layer (21) has a thickness (e) in the range of 5 μm to 50 μm.

4. The processed component has at least one dimension and / or mass greater than in the desired final component, and the process includes, after the hardening step, the following steps: - cutting the processed component in order to limit the deformations caused by the hardening process, The method according to any one of claims 1 to 3, comprising:

5. The guide device is a rotary bearing, and the method comprises the steps of: - adjusting the axial clearance of the guide device during assembly of the guide device, The method according to any one of claims 1 to 4, comprising:

6. 6. The method of claim 5, wherein the rolling bearing includes a first inner ring and a second inner ring, and the axial clearance is adjusted by pressing the first inner ring against the second inner ring.

7. A rolling element guide device (100) for a medical mechanism manufactured using the method according to any one of claims 1 to 6, comprising at least the following components: a first element (6), a second element (2, 4), - rolling elements (5, 5') arranged between the first element (6) and the second element (2, 4) for facilitating the relative displacement of the first element (6) with respect to the second element (2, 4); Including, At least one component (20; 6, 2, 4, 5, 5') is made of titanium and / or a titanium alloy and is provided with a surface layer (21) of treated titanium and / or a treated titanium alloy, said surface layer (21) having a hardness in the range of 900 Hv to 1100 Hv; The rolling element guide device (100).

8. 8. The device of claim 7, wherein a surface layer (21) is defined between an outer surface (210) and an inner surface (212), said inner surface being adjacent to a base layer (22) of said component, and wherein the hardness of the surface layer (21) decreases from the outer surface toward the inner surface.

9. A device according to claim 7 or 8, wherein the surface layer (21) has a thickness (e) in the range of 5 μm to 50 μm.

10. The device according to any one of claims 7 to 9, wherein the component comprises a cage arranged to hold the rolling elements.

11. The device according to any one of claims 7 to 10, which is a rotary bearing, a linear bearing or a ball screw.

12. An implantable medical device comprising a rolling element guide device (100) according to any one of claims 7 to 11.

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