CH715376B1 - Clock movement comprising a non-magnetic mechanical bearing, and watch comprising such a bearing. - Google Patents

Abstract

The invention relates to a clock movement comprising a non-magnetic mechanical bearing comprising, coaxial around a common axis of rotation (D), an internal cage (2) and an external cage (3) respectively comprising an internal track (20) and an outer track (30) between which a plurality of mobiles (4) slide or roll during relative movement between the inner cage (2) and the outer cage (3). At least one of the inner cage (2) and outer cage (3) is a dynamic cage made of weakly paramagnetic material, of relative magnetic permeability µ r between 1.00002 and 1.0009, limits included. The invention also relates to a watch comprising such a movement.

Description

Field of the invention

The invention relates to a clockwork movement comprising a non-magnetic mechanical bearing comprising, coaxial around a common axis of rotation, an internal cage and an external cage respectively forming an internal track and an external track between which a plurality of mobiles slide or roll during a relative movement between said inner cage and said outer cage, at least one of said inner cage and outer cage being a dynamic cage.

The invention also relates to a watch comprising such a movement.

The invention relates to the field of clockwork mechanisms and more particularly to rotation guides.

Background of the invention

[0004] In order to limit friction as much as possible when pivoting an oscillating weight of a watch, a ball bearing is generally used as the suspension. Bearing components are usually metallic, especially steel, and must be lubricated in order to function properly.

[0005] In addition, in some clock movements it is necessary to provide protection against magnetic fields, and such mentioned standard bearings made of steel or the like can be problematic due to components made of magnetic materials.

[0006] In order to solve the problem of sensitivity to magnetic fields, certain ball bearings use stainless steel and/or ceramic components. This tends to increase manufacturing costs because these materials are not easy to machine.

Summary of the invention

The object of the invention is to provide a mechanical bearing, in particular a ball bearing, whose sensitivity to magnetic fields is less than that of a traditional bearing, but whose manufacturing cost is similar.

The invention consists in choosing non-magnetic materials, easier to machine than stainless steel, and capable of withstanding the mechanical stresses imposed by the functions of the ball bearing.

[0009] To this end, the invention relates to a timepiece movement comprising a non-magnetic mechanical bearing according to claim 1.

The invention also relates to a watch comprising such a movement.

Brief description of the drawings

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, with reference to the accompanying drawings, where: FIG. 1 represents, schematically, and in section passing through its axis of rotation, a non-magnetic ball bearing, with ceramic balls, and the other components in stainless steel; FIG. 2 represents, similarly to FIG. 1, an economical non-magnetic mechanical bearing according to the invention, in an economical embodiment, which in this example is a ball bearing with ceramic balls, an outer ring of copper-beryllium alloy , and the other components made of stainless material, in particular stainless steel; FIG. 3 is a block diagram which represents a watch comprising a movement with at least one bearing according to the invention.

Detailed Description of Preferred Embodiments

The invention relates to a non-magnetic mechanical bearing 1 intended to be mounted in a clock movement.

[0013] By “amagnetic” is meant here that this bearing, as a whole, is hardly mobile under the action of a magnetic field, in attraction or in repulsion. This concept does not imply that all the constituents of such a bearing are each non-magnetic, insofar as certain constituents can form a shielding cage to protect others from the effects of a magnetic field. Of course, the overall non-magnetic behavior of the bearing is even more insensitive to a magnetic field if almost all, or all of its constituents, are each non-magnetic.

The mechanical bearing 1 comprises, conventionally, coaxial around a common axis of rotation D, an internal cage 2 and an external cage 3.

The inner cage 2 and the outer cage 3 respectively comprise an inner track 20 and an outer track 30, between which a plurality of mobiles 4 slide or roll during a relative movement between the inner cage 2 and the outer cage 3 antagonists who guide them. The invention is illustrated in Figure 2 in the simplified case of a single inner cage 2 and a single outer cage 3, the person skilled in the art can extrapolate it to a bearing comprising several stages, each of which comprises a track movement of mobiles 4 between an internal cage 2 and an external cage 3.

[0016] Advantageously the mobiles 4, in particular balls, are made of non-magnetic material, in particular ceramic, Si3N4, nickel-titanium, zirconia, or other suitable materials known to those skilled in the art, in particular superelastic materials.

[0017] At such a stage comprising a circulation track, at least the inner cage 2 or the outer cage 3 is a dynamic cage, that is to say it is mobile during the normal operation of the bearing. relative to a static component of a clock movement, such as a plate, bridge, or the like. In a particular variant not shown, the inner cage 2 is a dynamic cage and the outer cage 3 is a dynamic cage. In another variant illustrated by FIG. 2, the inner cage 2 is a static cage, and the outer cage 3 is a dynamic cage. In yet another variant, not shown, the inner cage is a dynamic cage, and the outer cage 3 is a static cage.

[0018] Various tests have shown that the static components of a bearing, in particular of a ball bearing, that is to say the components which constitute one of the cages of the bearing, in particular the internal cage in the example not limitation of the figures, contribute only very little to the magnetic sensitivity of the whole. Therefore, it turns out that the magnetic sensitivity of the bearing assembly is mainly conditioned by the material of the dynamic components, in this case of the mobiles 4, in particular of the balls, and of the other cage, in particular of the outer cage in the example of the figures, where the outer cage consists of a single outer ring. Of course, the outer cage can also be composed of several juxtaposed outer rings. In the non-limiting example illustrated, the outer cage 3 carries a toothing 31.

According to the invention, at least one said dynamic cage is made of weakly paramagnetic material, of relative magnetic permeability μr comprised between 1.00002 and 1.0009, limits included. More particularly, each dynamic cage is made of weakly paramagnetic material, of relative magnetic permeability μr comprised between 1.00002 and 1.0009, limits included.

More particularly, at least one outer cage 3 is made of weakly paramagnetic material, of relative magnetic permeability µrcomprise between 1.00002 and 1.0009, limits included; even if this outer cage is a static cage, it then constitutes effective magnetic shielding for the inner cage which is then a dynamic cage: this dynamic inner cage can be made with such a weakly paramagnetic material, which gives the best results, and can also, in a slightly less efficient variant, be made of traditional material such as bearing steel. More particularly still, each outer cage 3 is made of weakly paramagnetic material, of relative magnetic permeability μr comprised between 1.00002 and 1.0009, limits included.

[0021] Figure 2 illustrates an embodiment according to the invention, where only the material of the outer ring is modified compared to a standard all-steel bearing, with in particular an embodiment of this outer ring in a copper alloy, in particular a cupro -beryllium. The bearing retains its original magnetic properties and lubrication, while having a lower production cost, since the machining of the teeth is faster in a copper alloy than in stainless steel.

[0022] More particularly, in order to improve operation and durability, the outer ring is coated. More particularly still, this outer ring is coated with a layer of nickel offering a higher surface hardness than that of a bare copper alloy, in particular a bare cupro-beryllium.

As the toothing of the outer ring must be adapted to each gauge, only the material of the outer ring is modified in this bearing according to the invention, compared to a standard all-steel bearing. The other components, which may remain the same for the different calibers produced, remain manufactured in the original material so as not to complicate the logistics, particularly in terms of supplies, different set-ups, stock management, management of these other components remaining unchanged.

[0024] Naturally, depending on the applications, and in particular depending on the magnetic phenomena used or combated in the watch movement in which such a bearing is incorporated, it is possible to modify the material of all or part of the components of the ball bearing. .

Advantageously, the weakly paramagnetic material of at least one dynamic cage and/or of at least one outer cage is a copper alloy.

The materials that can be used are preferably chosen from copper alloys, with a possible surface coating such as nickel plating. The example cited above uses an outer ring in CuBe2Pb, with a layer of chemical nickel of 1.5µm.

[0027] More particularly, this alloy of the CuBe2Pb type comprises, by mass, and terminals included, from 1.80% to 2.00% beryllium, from 0.20% to 0.60% lead, with a total of cobalt and nickel greater than or equal to 0.2% with a total of cobalt and nickel and iron less than or equal to 0.60%, with traces less than 0.5%, the remainder being copper, with a total of copper and beryllium and cobalt and nickel and iron and lead greater than or equal to 99.5%, and has a modulus of elasticity between 125 kN/mm<2> and 131 kN/mm<2>, terminals included, and a relative magnetic permeability µr close to 1.0006.

[0028] Such an outer ring thus coated offers good resistance, in cooperation with Si3N4 or similar balls. The other components of the bearing, which do not include teeth and whose machining is therefore simpler, can be made of stainless steel, among those commonly used in watchmaking.

[0029] An aluminum alloy is theoretically advantageous, because of the very low relative magnetic permeability μr of pure aluminum, equal to 1.000022. Certain aluminum alloys with mechanical properties similar to those of mild steels may then be suitable: aluminum alloys comprising copper (2XXX series), aluminum alloys comprising magnesium and silicon (6XXX series), aluminum alloys comprising zinc (7XXX series), all capable of hardening by heat treatment, or even aluminum alloys comprising silicon (4XXX series), or aluminum alloys comprising magnesium (5XXX series). More particularly, this aluminum alloy is heat-treated and has a tensile strength greater than or equal to 240 MPa.

[0030] Other possibilities exist, with the selection of materials chosen from the group comprising an austenitic type steel, preferably stainless steel, an austenitic type cobalt alloy, an austenitic type nickel alloy, a titanium alloy non-magnetic, a non-magnetic aluminum alloy, a brass (Cu-Zn) or a special brass (Cu-Zn with Al and/or Si and/or Mn), a bronze (Cu-Sn), an aluminum bronze , a copper-aluminum (optionally comprising Ni 30 and/or Fe), a copper-nickel, a nickel silver (Cu-Ni-Zn), a copper-beryllium - 6 - (Cu-Be), a copper-nickel-tin , a copper-nickel-silicon, a copper-nickel-phosphorus, a copper-titanium, the proportions of the various elements of the alloys being chosen to give them non-magnetic properties as well as good machinability. A synthetic material (for example made of PTFE, POM) or a ceramic (for example based on Al2O3, or ZrO2) can also be chosen as an alternative to a non-magnetic metallic material.

[0031] Thus, more particularly, it is advantageous to use, at least for the outer ring, a material chosen from: - copper-beryllium alloy; – austenitic steel, and, without limitation: o Fe Cr15 a 20Ni8a19Cu4à6C0.1, o Fe Cr16à18Ni10à15Cu1C lower than 0 1, o Fe Cr24a26Ni19à22Mn lower than 2Cu4 to 6C0.1, – austenitic type cobalt alloy, o iron-cobalt alloy; – non-magnetic aluminum alloy; – brass; – brass with aluminum and/or/silicon and/or manganese; – bronze with aluminium; – cupro-aluminum; – copper-aluminum with nickel and/or iron; – cupronickel; – nickel silver; – cupro-nickel with tin; – cupro-nickel with silicon; – cupro-nickel with phosphorus; – copper-titanium – niobium-titanium; – aluminum; – platinum; – barium; – gadolinium; – strontium; – tungsten; – magnesium.

[0032] Naturally, it should be verified that the choice of materials confers both the behavior required in a magnetic environment, and a saving in production, with in particular a reduction in production costs.

As regards the material of the static cage, in particular but not limited to the inner ring, or inner rings if several inner rings are juxtaposed to form the inner cage of the bearing, for example with a retaining ring 21 attached on a main ring 22, several choices are possible: a material different from that of the dynamic cage, and in particular a traditional material such as bearing steel; the same material as the dynamic cage; a material chosen from the same group as the material of the dynamic cage.

[0034] Figure 2 illustrates the non-limiting case of a static internal cage, and a dynamic external cage, but one can also have: a dynamic inner cage, and a static outer cage a dynamic inner cage, and a dynamic outer cage.

The important thing is that the dynamic cage is non-magnetic.

[0036] It is also advantageous for the outer cage to be non-magnetic. If the two cages, external and internal, are dynamic, it may be sufficient for only one of the two to be non-magnetic, and in this case, rather the external cage which then plays the role of shielding for the internal cage.

According to the invention, at least one dynamic cage is non-magnetic.

Preferably, the material is chosen for at least one non-magnetic cage, and more particularly for each non-magnetic cage, of the slightly paramagnetic type, with a relative magnetic permeability μr comprised between 1.00002 and 1.0009, limits included.

In the variant where the constituent material of a non-magnetic dynamic cage is covered with a coating giving it improved mechanical and tribological properties, the coating material is chosen, or the coating materials in the case of superimposed layers, so as to form a magnetic shield.

[0040] Although it is also possible to inexpensively improve an existing bearing by such a shielding coating of at least one of its cages, it remains preferable to combine the manufacture of a non-magnetic dynamic cage and of such a coating.

[0041] Depending on the material selected, it is possible to add at least one other coating, among galvanic nickel plating, PVD or DLC layer, nitriding, chromium layer, or the like, compatible with this material.

[0042] Such bearings are designed for watchmaking applications, and therefore have very small dimensions: primary diameter DP, on which the centers of inertia of the mobiles move, between 1.9 mm and 7.5 mm, limits included; diameter DM of the balls when the mobiles are balls, between 0.3 mm and 0.6 mm, terminals included; thickness El of the internal cage according to the direction of the axis of rotation between 0.5 mm and 1.2 mm, terminals included, and less than or equal to 1.0 mm when the mobiles are balls with a diameter between 0.3 mm and 0.5 mm, terminals included; thickness EE of the outer cage in the direction of the axis of rotation between 0.5 mm and 1.2 mm, terminals included, and less than or equal to 1.0 mm when the mobiles are balls with a diameter between 0.3 mm and 0.4 mm, terminals understood.

More particularly, the smallest bearings have balls with a diameter of 0.3 mm, for a primary diameter of 1.9 mm, their thicknesses are between 0.5 and 1 mm.

[0044] And the largest bearings have balls with a diameter of up to 0.6 mm, for a primary diameter of 7.5 mm, their thicknesses go up to 1.2 mm.

The bearing illustrated in Figure 3 is a ball bearing according to the invention, with a primary diameter of 5.7 mm, a ball diameter of 0.5 mm, a thickness of the internal cage of 1.0 mm, and a thickness of the outer cage of 1.2 mm.

The invention relates to a clock movement 100 comprising at least one mechanical bearing 1 as described above.

The invention also relates to a watch 200 comprising such a movement 100.

In short, the invention offers various advantages: the reduction of manufacturing costs thanks to the selection of a material that is easier to machine than a stainless steel or a ceramic; the retention of the original magnetic properties of the ball bearing; the preservation of the mechanical properties of the ball bearing thanks to the addition of a surface coating; the preservation of the original lubrication of the ball bearing.

Claims (11)

1. Clock movement comprising a non-magnetic mechanical bearing (1) comprising, coaxial around a common axis of rotation (D), an internal cage (2) and an external cage (3) respectively comprising an internal track (20) and an outer track (30) between which a plurality of mobiles (4) slide or roll during relative movement between the inner cage (2) and the outer cage (3), at least one of said inner cage (2) and outer cage (3) being a dynamic cage, characterized in that said dynamic cage is made of weakly paramagnetic material, of relative magnetic permeability µr comprised between 1.00002 and 1.0009, limits included. 2. Clock movement according to claim 1, characterized in that the mechanical bearing comprises several dynamic cages which are each made of weakly paramagnetic material, of relative magnetic permeability µrcomprise between 1.00002 and 1.0009, limits included. 3. Clock movement according to claim 1, characterized in that the outer cage (3) is made of weakly paramagnetic material, of relative magnetic permeability µrcomprise between 1.00002 and 1.0009, limits included. 4. Clock movement according to claim 3, characterized in that the mechanical bearing comprises several outer cages which are each made of weakly paramagnetic material, of relative magnetic permeability µrcomprise between 1.00002 and 1.0009, terminals included. 5. Clock movement according to one of claims 1 to 4, characterized in that said weakly paramagnetic material is a copper alloy. 6. Clock movement according to claim 5, characterized in that said weakly paramagnetic material is a copper alloy comprising copper and beryllium. 7. Clock movement according to claim 6, characterized in that said copper alloy is of the CuBe2Pb type and comprises, by weight, and limits included, from 1.80% to 2.00% beryllium, from 0.20% to 0.60% lead, with a total of cobalt and nickel greater than or equal to 0.2% with a total of cobalt and nickel and iron less than or equal to 0.60%, with traces less than 0.5%, the remainder being copper, with a total of copper and beryllium and cobalt and nickel and iron and lead greater than or equal to 99.5%. 8. Clock movement according to one of claims 1 to 4, characterized in that said weakly paramagnetic material is an aluminum alloy comprising copper, or magnesium and silicon, or zinc, or silicon, or magnesium, heat-treated and having a tensile strength greater than or equal to 240 MPa. 9. Clock movement according to one of claims 1 to 8, characterized in that the mechanical bearing (1) is a ball bearing, of which said mobiles (4) are non-magnetic balls. 10. Clock movement according to one of claims 1 to 9, characterized in that said mobiles (4) are made of Si3N4. 11. Watch comprising a clock movement according to one of claims 1 to 10.