Part for clock movement

Abstract

The invention relates to a pivot axis for a watch movement comprising at least one pivot (3) made of a first non-magnetic metallic material (4) at at least one end to limit its sensitivity to magnetic fields. At least the external surface of said pivot (3) is coated with a layer (5) of a second material selected from the group including Ni and NiP, and preferably chemical NiP. The invention relates to the field of watch movements.

Description

Field of invention

[0001] The invention relates to a part for a watch movement and in particular to a non-magnetic pivot axis for a mechanical watch movement and more particularly to a non-magnetic balance shaft, anchor stem and escapement pinion. Background of the invention

[0002] The manufacture of a watch pivot shaft consists, starting from a hardenable steel bar, of carrying out bar turning operations to define different active surfaces (bearing, shoulder, pivots, etc.) and then subjecting the bar turned shaft to heat treatment operations including at least one quenching to improve the hardness of the shaft and one or more tempering operations to improve its toughness. The heat treatment operations are followed by a rolling operation of the pivots of the shafts, an operation consisting of polishing the pivots to bring them to the required dimensions. During the rolling operation, the hardness and roughness of the pivots are further improved.

[0003] Pivot shafts, such as balance shafts, typically used in mechanical watch movements are made from free-cutting steel grades, which are typically martensitic carbon steels containing lead and manganese sulfides to improve their machinability. A steel of this type, designated 20AP, is typically used for these applications.

[0004] This type of material has the advantage of being easy to machine, in particular of being suitable for turning and, after quenching and tempering treatments, has high mechanical properties that are very useful for the production of watch pivot axes. These steels, in particular, have a high hardness after heat treatment, allowing very good shock resistance to be obtained. Typically, the hardness of the pivots of an axis made of 20 AP steel can reach a hardness exceeding 700 HV after heat treatment and rolling.

[0005] Although providing satisfactory mechanical properties for the watchmaking applications described above, this type of material has the disadvantage of being magnetic and of being able to disturb the running of a watch after being subjected to a magnetic field, particularly when this material is used for the production of a balance staff cooperating with a balance spring made of ferromagnetic material. This phenomenon is well known to those skilled in the art. It should also be noted that these martensitic steels are also sensitive to corrosion.

[0006] Tests to try to overcome these drawbacks have been carried out with austenitic stainless steels which have the particularity of being non-magnetic, that is to say of the paramagnetic or diamagnetic or antiferromagnetic type. However, these austenitic steels have a crystallographic structure which does not allow them to be hardened and to achieve hardnesses and therefore shock resistances compatible with the requirements for the production of watch pivot axes. The axes obtained then show marks or severe damage in the event of shocks which will then have a negative influence on the chronometry of the movement. One way to increase the hardness of these steels is work hardening, however this hardening operation does not allow hardnesses greater than 500 HV to be obtained. Consequently, in the context of parts requiring pivots with high shock resistance, the use of this type of steel remains limited.

[0007] Another approach to address these drawbacks is described in application EP 2 757 423. According to this approach, the pivot pins are made of austenitic cobalt or nickel alloy and have an external surface hardened to a certain depth. However, such alloys can be difficult to machine for the manufacture of pivot pins. In addition, they are relatively expensive due to the high price of nickel and cobalt.

[0008] Documents US 3863616 and FR 2015873 describe a balance shaft made of non-magnetic material but which cannot be covered with a layer of nickel applied by galvanization in order to obtain a non-magnetic component because such a layer of nickel is magnetic.

[0009] Document EP 1237058 describes a watch movement comprising a generator with magnetized masses, surrounded by non-magnetic blank parts covered with a non-magnetic coating, such as a nickel and phosphorus alloy, used here for its non-magnetic properties.

[0010] Document EP 1927681 describes in its prior art the use of a chemical nickel deposit with alumina spheres on watch components to improve lubrication.

[0011] Document US 3620005 describes a ratchet wheel comprising a shaft and a drive member which can be made of bronze or beryllium copper.

[0012] Document EP 3417347 B1 falling within Article 54(3) EPC describes watch part arbors made of a non-magnetic material, other than beryllium copper, covered with a layer of nickel. Summary of the invention

[0013] The aim of the present invention is to overcome the drawbacks mentioned above by proposing a pivot axis which makes it possible both to limit sensitivity to magnetic fields and to obtain mechanical properties which make it possible to meet the requirements of shock resistance in the watchmaking field.

[0014] The invention also aims to provide a non-magnetic pivot axis which can be manufactured simply and economically.

[0015] To this end, the invention relates to a pivot axis for a watch movement comprising at least one pivot made of a first non-magnetic metallic material at at least one of its ends in order to limit its sensitivity to magnetic fields, according to the characteristics of claim 1.

[0016] According to the invention, at least the external surface of said pivot is covered with a layer of a second material chosen from the group consisting of Ni, NiP and preferably chemical NiP.

[0017] Consequently, the pivot axis according to the invention makes it possible to combine the advantages of low sensitivity to magnetic fields, and at least in the main stress zones, excellent shock resistance. As a result, the pivot axis according to the invention does not exhibit, in the event of an impact, any marks or severe damage likely to impair the chronometry of the movement.

[0018] In accordance with other advantageous characteristics of the invention: the layer of the second material has a thickness of between 0.5 µm and 10 µm, preferably between 1 µm and 5 µm, and more preferably between 1 µm and 2 µm; the layer of the second material has a hardness preferably greater than 400 HV, more preferably greater than 500 HV; the layer of the second material is preferably a layer of chemical NiP, i.e. obtained by chemical deposition.

[0019] Furthermore, the invention relates to a watch movement comprising a pivot axis as defined above, and in particular a balance shaft, an anchor stem and / or an escape pinion comprising an axis as defined above.

[0020] Finally, the invention relates to a method of manufacturing a pivot axis as defined in claim 10 and comprising the following steps: a) forming a pivot axis comprising at least one pivot made of a first non-magnetic metallic material at at least one of its ends to limit its sensitivity to magnetic fields; b) depositing a layer of a second material at least on the external surface of said pivot, said second material being chosen from the group consisting of Ni, NiP and preferably chemical NiP.

[0021] In accordance with other advantageous characteristics of the invention: the layer of the second material is deposited according to step b) to have a thickness of between 0.5 µm and 10 µm, preferably between 1 µm and 5 µm, and more preferably between 1 µm and 2 µm; the second material is NiP and step b) consists of a deposition of NiP according to a process of chemical nickel deposition from hypophosphite. Summary description of the drawings

[0022] Other features and advantages will become clear from the description given below, for information purposes only and in no way limiting, with reference to the attached drawings, in which: there figure 1 is a representation of a pivot axis according to the invention; the figure 2 is a partial section of a balance shaft pivot according to the invention, the figure 3 is a photograph of a bare HIS steel pivot pin that has undergone a shock program, and the figure 4is a photograph of a pivot axis made of HIS steel covered with a layer of NiP according to the invention having undergone the same shock program as the pivot axis of the figure 3 . Detailed Description of Preferred Embodiments

[0023] In this description, the term “non-magnetic” material means a paramagnetic or diamagnetic or antiferromagnetic material, the magnetic permeability of which is less than or equal to 1.01.

[0024] An alloy of an element is an alloy containing at least 50% by weight of said element.

[0025] The invention relates to a part for a watch movement and in particular to a non-magnetic pivot axis for a mechanical watch movement.

[0026] The invention will be described below in the context of an application to a non-magnetic balance staff 1. Obviously, other types of watch pivot staffs are conceivable, such as for example watch mobile staffs, typically escapement pinions, or even anchor stems. Parts of this type have body diameters preferably less than 2 mm, and pivots with a diameter preferably less than 0.2 mm, with a precision of a few microns.

[0027] Referring to the figure 1we can see a balance shaft 1 according to the invention which comprises a plurality of sections 2 of different diameters, preferably formed by turning or any other machining technique by chip removal, and conventionally defining bearing surfaces 2a and shoulders 2b arranged between two end portions defining two pivots 3. These pivots are intended to each pivot in a bearing, typically in an orifice of a stone or ruby.

[0028] With the magnetism induced by objects encountered on a daily basis, it is important to limit the sensitivity of balance staff 1, otherwise it will influence the running of the timepiece in which it is incorporated.

[0029] Thus, the pivot 3 is made of a first non-magnetic metallic material 4 in order to advantageously limit its sensitivity to magnetic fields.

[0030] The first non-magnetic metallic material 4 is chosen from the group comprising an austenitic type steel, preferably stainless steel, an austenitic type cobalt alloy, an austenitic type nickel alloy, a non-magnetic titanium alloy, a non-magnetic aluminium alloy, a brass (Cu-Zn) or a special brass (Cu-Zn with Al and / or Si and / or Mn), a bronze (Cu-Sn), an aluminium bronze, a copper-aluminium (optionally comprising Ni and / or Fe), a copper-nickel, a nickel silver (Cu-Ni-Zn), a copper-nickel-tin, a copper-nickel-silicon, a copper-nickel-phosphorus, a copper-titanium, the proportions of the different elements of the alloys being chosen to give them non-magnetic properties as well as good machinability.

[0031] For example, austenitic steel is an HIS (High Interstitial Steels) austenitic stainless steel, such as Cr-Mn-N P2000 steel from Energietechnik Essen GmbH.

[0032] The austenitic type cobalt alloy may comprise at least 39% cobalt, typically an alloy known as "Phynox" or the DIN designation K13C20N16Fe15D7 typically having 39% Co, 19% Cr, 15% Ni and 6% Mo, 1.5% Mn, 18% Fe and the balance of additives.

[0033] The austenitic type nickel alloy may comprise at least 33% nickel, typically an alloy known as MP35N ®<, typically having 35% Ni, 20% Cr, 10% Mo, 33% Co and the balance of additives.

[0034] The titanium alloy preferably comprises at least 85% titanium.

[0035] Brasses may include the alloys CuZn39Pb3, CuZn37Pb2, or CuZn37.

[0036] Special brasses may include the alloys CuZn37Mn3Al2PbSi, CuZn23Al3Co or CuZn23Al6Mn4Fe3Pb.

[0037] Nickel silver can include the alloys CuNi25Zn11Pb1Mn, CuNi7Zn39Pb3Mn2 or CuNi18Zn19Pb1.

[0038] Bronzes may include CuSn9 or CuSn6 alloys.

[0039] Aluminum bronzes can include CuAl9 or CuAl9Fe5Ni5 alloys.

[0040] Copper-nickel alloys may include the CuNi30 alloy.

[0041] Copper-nickel-tin alloys can include CuNi15Sn8, CuNi9Sn6 or CuNi7.5Sn5 alloys (marketed for example under the name Declafor).

[0042] Copper-titanium alloys may include the CuTi3Fe alloy.

[0043] Copper-nickel-silicon alloys may include the CuNi3Si alloy.

[0044] Copper-nickel-phosphorus alloys may include the CuNi1P alloy.

[0045] Composition values ​​are given as a percentage by weight. Elements without a composition value are either the remainder (majority) or elements for which the percentage in the composition is less than 1% by weight.

[0046] The non-magnetic copper alloy can also be an alloy with a mass composition of between 14.5% and 15.5% Ni, between 7.5% and 8.5% Sn, a maximum of 0.02% Pb and the remainder Cu. Such an alloy is marketed under the brand name Toughmet ®< by the company Materion.

[0047] Obviously, other non-magnetic alloys are possible provided that the proportion of their constituents gives them non-magnetic properties as well as good machinability.

[0048] The first non-magnetic metallic material generally has a hardness of less than 600 HV.

[0049] According to the invention, at least the external surface of said pivot 3 is covered with a layer 5 of a second material chosen from the group consisting of Ni, NiP and preferably chemical NiP, in order to advantageously offer mechanical properties at the level of said external surface making it possible to obtain the desired shock resistance.

[0050] In the second material, the phosphorus content may preferably be between 0% (in which case we have pure Ni) and 15%. Preferably, the phosphorus content in the second NiP material may be a medium content of between 6% and 9%, or a high content of between 9% and 12%. It is obvious, however, that the second NiP material may include a low content of phosphorus.

[0051] Further, when the second material is medium or high phosphorus NiP, the layer of the second NiP material can be hardened by heat treatment.

[0052] The layer of the second material has a hardness preferably greater than 400 HV, more preferably greater than 500 HV.

[0053] In a particularly advantageous manner, the layer of the second material made of unhardened Ni or NiP has a hardness preferably greater than 500 HV, but less than 600 HV, i.e. preferably between 500 HV and 550 HV. Surprisingly and unexpectedly, the pivot axis according to the invention has excellent shock resistance although the layer of the second material may have a hardness (HV) lower than that of the first material.

[0054] When hardened by heat treatment, the layer of the second NiP material can have a hardness between 900 HV and 1000 HV.

[0055] Advantageously, the layer of the second material may have a thickness of between 0.5 µm and 10 µm, preferably between 1 µm and 5 µm, and more preferably between 1 µm and 2 µm.

[0056] Preferably, the layer of the second material is a layer of NiP, and more particularly a layer of chemical NiP, i.e. deposited chemically.

[0057] Particularly preferred are combinations associating: a copper-nickel-tin alloy, and more particularly Declafor or Toughmet ®<, as the first non-magnetic metallic material and a layer of chemical NiP as layer 5 of the second material a stainless steel, and more particularly, a HIS stainless steel, as the first non-magnetic metallic material and a layer of chemical NiP as layer 5 of the second material.

[0058] Consequently, at least the external surface of the pivot is hardened, that is to say that the rest of the shaft can remain little or not modified without significant modification of the mechanical properties of the balance staff 1. This selective hardening of the pivots 3 of the balance staff 1 makes it possible to combine advantages such as low sensitivity to magnetic fields and mechanical properties making it possible to obtain very good shock resistance in the main stress zones.

[0059] In order to improve the strength of the layer of the second material, the pivot axis may comprise at least one adhesion sub-layer deposited between the first material and the layer of the second material. For example, in the case in particular of a pivot axis made of HIS stainless steel type material, a gold sub-layer and / or a galvanic nickel sub-layer may be provided under the layer of the second material.

[0060] The invention also relates to the method of manufacturing a balance shaft as explained above. The method advantageously comprises, according to the invention, the following steps: a) forming, preferably by turning or any other machining technique by chip removal, a balance shaft 1 comprising at least one pivot 3 made of a first non-magnetic metallic material at each of its ends, to limit its sensitivity to magnetic fields and; b) depositing a layer 5 of a second material at least on the external surface of said pivot 3, said second material being chosen from the group consisting of Ni, NiP and preferably chemical NiP in order to improve the mechanical properties of the pivots to obtain appropriate shock resistance at least at the level of the main stress zones.

[0061] Preferably, the layer 5 of the second material is deposited according to step b) to have a thickness of between 0.5 µm and 10 µm, preferably between 1 µm and 5 µm, and more preferably between 1 µm and 2 µm.

[0062] Advantageously, step b) of depositing layer 5 of the second material can be carried out according to a method chosen from the group comprising PVD, CVD, ALD, galvanic and chemical deposits, and preferably chemical.

[0063] According to a particularly preferred embodiment, the second material is NiP and the step of depositing the NiP layer 5 is carried out according to a method of depositing chemical nickel from hypophosphite.

[0064] The various parameters for electroless nickel deposition from hypophosphite to be taken into account, such as the phosphorus content in the deposit, the pH, the temperature, or the composition of the nickel plating bath are known to those skilled in the art. Reference may be made, for example, to the publication by Y. Ben Amor et al., Dépôt chimique de nickel, synthèse bibliographique, Matériaux & Techniques 102, 101 (2014). However, it should be noted that commercial baths with medium (6-9%) and high (9-12%) phosphorus levels are preferably used. However, it is clear that baths with low phosphorus or pure nickel levels can also be used.

[0065] When the second material is NiP, preferably with a medium or high phosphorus content, the method according to the invention may further comprise, after the deposition step b), a step c) of heat treatment of the layer 5 of the second material. Such heat treatment makes it possible to obtain a layer 5 of the second material having a hardness preferably between 900 HV and 1000 HV.

[0066] The electroless nickel deposition process is particularly advantageous in that it allows for a conformal deposit to be obtained without any tip effect. It is thus possible to predict the dimension of the machined pivot axis to obtain the desired geometry after covering with the layer of the second material.

[0067] The electroless nickel deposition process also has the advantage of being able to be applied in bulk.

[0068] In order to improve the resistance of the layer of the second material, the method according to the invention may further comprise, before the deposition step b), a step d) of applying at least one adhesion sub-layer to the first material. For example, in the case in particular of a pivot axis made of HIS stainless steel type material, it is possible to apply a gold sub-layer and / or a galvanic nickel sub-layer before the chemical deposition of nickel.

[0069] The pivot axis according to the invention may comprise pivots treated according to the invention by applying step b) to the pivots only or be made entirely of a first non-magnetic metallic material, its external surface being able to be entirely covered with a layer of the second material by applying step b) to all the surfaces of the pivot axis.

[0070] In a known manner, the pivots 3 may be rolled or polished before or after the deposition step b), in order to achieve the desired final dimensions and surface condition for the pivots 3.

[0071] The pivot axis according to the invention combines the advantages of low sensitivity to magnetic fields, and at least in the main stress zones, excellent shock resistance. As a result, the pivot axis according to the invention does not show, in the event of an impact, any marks or severe damage likely to impair the chronometry of the movement.

[0072] The following examples illustrate the present invention without, however, limiting its scope.

[0073] HIS steel pivot pins are made in a known manner. The bare pins have a hardness of 600HV.

[0074] A batch of these pivot pins is treated according to the method of the invention, the pivot pins being covered with a layer of NiP with a thickness equal to 1.5 µm obtained from a commercial chemical nickel plating bath from hypophosphite.

[0075] These pivot axes according to the invention have a hardness of 500 HV.

[0076] All pivot pins are subjected to the same standard shock program for watchmaking. Bare pins, without NiP coating, are marked as shown in the figure 3 . The axes covered with a layer of NiP according to the invention are intact, as shown in the figure 4 The pivot axes according to the invention combine the advantages of low sensitivity to magnetic fields and excellent shock resistance.

Claims

1. Pivot arbor (1) for a timepiece movement comprising at least one pivot (3) made of a first non-magnetic metal material (4) at at least one of the ends thereof in order to limit the sensitivity thereof to magnetic fields, said first non-magnetic metal material (4) being selected from the group consisting of austenitic steel, an austenitic cobalt alloy, an austenitic nickel alloy, a titanium alloy, an aluminium alloy, a copper and zinc-based brass, a nickel silver, a bronze, an aluminium bronze, a copper-aluminium, a copper-nickel, a copper-nickel-tin, a copper-nickel-silicon, a copper-nickel-phosphorus, a copper-titanium, characterized in that at least the outer surface of said pivot (3) is coated with a layer (5) of a second material selected from the group consisting of Ni and NiP, and preferably chemical NiP.

2. Pivot arbor (1) according to claim 1, characterized in that said pivot arbor (1) is made of a first non-magnetic metal material in order to limit the sensitivity thereof to magnetic fields, and in that the outer surface thereof is coated with a layer of a second material selected from the group comprising Ni and NiP, and preferably chemical NiP.

3. Pivot arbor (1) according to any of the preceding claims, characterized in that the first non-magnetic metal material (4) has a hardness of less than 600 HV.

4. Pivot arbor (1) according to any of the preceding claims, characterized in that the layer (5) of second material has a thickness comprised between 0.5 µm and 10 µm, preferably between 1 µm and 5 µm, and more preferentially between 1 µm and 2 µm,5. Pivot arbor (1) according to any of the preceding claims, characterized in that said layer (5) of second material has a hardness of more than 400 HV, preferably more than 500 HV.

6. Pivot arbor (1) according to any of claims 1 to 5, characterized in that the first non-magnetic metal material (4) is a copper-nickel-tin alloy and in that said layer (5) of second material is a chemical NiP layer.

7. Pivot arbor (1) according to any of claims 1 to 5, characterized in that the first non-magnetic metal material (4) is a stainless steel and in that said layer (5) of second material is a chemical NiP layer.

8. Movement for a timepiece characterized in that the movement comprises a pivot arbor (1) according to any of the preceding claims.

9. Movement for a timepiece characterized in that the movement comprises a balance staff, a pallet staff and / or an escape pinion comprising a pivot arbor (1) according to any of claims 1 to 7.

10. Method for fabricating a pivot arbor (1) for a timepiece movement comprising the following steps: a) forming a pivot arbor (1) comprising at least one pivot (3) made of a first non-magnetic metal material (4) at one of the ends thereof in order to limit the sensitivity thereof to magnetic fields; said first non-magnetic metal material (4) being selected from the group consisting of austenitic steel, an austenitic cobalt alloy, an austenitic nickel alloy, a titanium alloy, an aluminium alloy, a copper and zinc-based brass, a nickel silver, a bronze, an aluminium bronze, a copper-aluminium, a copper-nickel, a copper-nickel-tin, a copper-nickel-silicon, a copper-nickel-phosphorus, a copper-titanium, b) depositing a layer (5) of a second material on at least the outer surface of said pivot (3), said second material being selected from the group constituting of Ni and NiP.

11. Method according to claim 10, characterized in that the layer (5) of second material is deposited to exhibit a thickness comprised between 0.5 µm and 10 µm, preferably between 1 µm and 5 µm, and more preferentially between 1 µm and 2 µm.

12. Method according to any of claims 10 and 11, characterized in that step b) of depositing the layer (5) of second material is achieved by a method selected from the group comprising PVD, CVD, ALD, electroplating and chemical deposition.

13. Method according to claim 12, characterized in that the second material is NiP and in that the step of depositing the NiP layer (5) is produced by a process of chemical nickel deposition from hypophosphite.

14. Method according to any of claims 10 to 13, characterized in that the second material is NiP and in that said method further comprises, after step b), a heat treatment step c) on the layer (5) of second material.

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