Method for manufacturing a balance wheel for a clock oscillator

Abstract

Method for manufacturing a balance wheel (1) for a watch oscillator, comprising the steps of: - machining said balance wheel (1) in metal; - measuring the weight and / or inertia of said balance wheel (1); - optionally, classifying by material removal of said balance wheel (1); - applying a passivation layer (17) to at least a part of the surface of said balance wheel (1), said passivation layer (17) having a thickness of less than 5nm, preferably less than 3nm, even more preferably less than 2nm.

Description

Technical field

[0001] The present invention relates to the field of watchmaking. It relates, more particularly, to a method of manufacturing a balance for a watch oscillator, a method of manufacturing a batch of such balances, as well as such a balance as such. State of the art

[0002] The traditional way of putting a metal pendulum into inertia, in order to help achieve a desired beat frequency for the oscillator in which said pendulum is integrated, involves the steps of: 1. Machining of metal balances, such as Maillechort, CuBe, Declafor or similar; 2. Measurement of the weight or inertia of the balance, with or without shaft, by Omegametric classification or similar, in order to divide the balances by inertia classes and thus allow matching by classes with balance springs classified by stiffness. Typically, each class corresponds to 150 seconds of running per day for the assembled oscillator; 3. Removal of material from the balance for balances that require it for inertia setting, in order to be able to manufacture balances with sub-class precision, i.e. having a variation corresponding to less than 150 seconds per day of running, such as for example 50 seconds per day; 4. Application of a protective layer, typically gold plating, another galvanic coating, a synthetic carbon deposit or similar; 5.Reclassification with a dispersion of work as in point 3, since the application of the protective layer increases the thickness of the balances sufficiently to downgrade them.

[0003] This reclassification is time-consuming, and its elimination is desirable while maintaining classification accuracy and without harming the balance wheel's resistance to tarnishing.

[0004] The aim of the invention is therefore to provide a timepiece in which the aforementioned defects are at least partially overcome. Disclosure of the invention

[0005] More specifically, the invention relates to a method for manufacturing a balance wheel for a watch oscillator, typically a balance-spring oscillator. This method comprises the following steps: machining said balance wheel into metal, such as Nickel Silver alloy (an alloy of 50% copper, 30% zinc and 20% nickel, by weight), copper-beryllium alloy, or Declafor alloy (a copper-nickel-tin alloy typically comprising 7.5% nickel and 5% tin, as well as up to 0.3% manganese, by weight); then measuring the weight and / or inertia of said balance, for example using an Omegametric device or similar; then optionally, classifying by removing material from said balance, for example by diamond plating, thicknessing or adding holes on the outside or underside of the balance; then applying a passivation layer, such as a layer of oxide, nitride or carbide, having a thickness of less than 5nm, preferably less than 3nm, more preferably less than 2nm, on at least part of the surface of said balance, preferably on the entire surface of the rim of said balance, more preferably on the entire surface of the metal of said balance.

[0006] A passivation layer, which can be formed by oxidation, nitriding or carburizing the surface of the balance metal, protects it from tarnishing, but does not provide enough mass to downgrade it, unlike conventional metallization, anodization or similar. Furthermore, the thickness of the passivation layer is very constant from one balance to another. Reclassification of the balances is therefore not necessary, the increase in inertia being sufficiently negligible and constant to be ignored.

[0007] Advantageously, said passivation layer is applied by a dry process, such as for example by reacting the surface of the metal of the balance with a gaseous chemical species such as oxygen, nitrogen or a hydrocarbon, where appropriate, in a reactor. Such a dry process is not to be assimilated to anodization, which is an electrochemical process carried out in a bath of an aqueous solution, and which serves to create oxide layers having a thickness of the order of several micrometers to several tens of micrometers.

[0008] The invention also relates to a method for manufacturing a batch of balance wheels for watch oscillators, typically balance-spring oscillators. This method comprises the steps of: machining a plurality of metal balance wheels, such as a Nickel Silver alloy (an alloy of 50% copper, 30% zinc, and 20% nickel, by weight), copper-beryllium alloy, or Declafor alloy (a copper-nickel-tin alloy typically comprising 7.5% nickel and 5% tin, as well as up to 0.3% manganese, by weight); then measuring the weight and / or inertia of said balances, for example using an Omegametric device or similar; then classifying said balances according to weight and / or inertia, typically according to classes corresponding to 150 seconds of operation per day; then classifying by removing material from at least some of said balances, typically from all of said balances, this removal of material typically being for example by diamond plating, thicknessing or adding holes on the outside or underside of the balance; then applying a passivation layer, such as an oxide, nitride or carbide, having a thickness of less than 5nm, on at least part of the surface of said balances, preferably on the entire surface of the metal of said balances.

[0009] As mentioned above, a passivation layer, which can be formed by oxidation, nitriding or carburizing the surface of the balance metal, protects it from tarnishing but does not provide enough mass to downgrade it, unlike conventional metallization, anodization or similar. Furthermore, the thickness of the passivation layer is very constant from one balance to another. Regrading the balances is therefore not necessary, as the increase in inertia is sufficiently negligible and constant to be ignored.

[0010] Advantageously, said passivation layer is applied by a dry method, such as for example by reacting the surface of the metal of the balance with a gaseous chemical species such as oxygen, nitrogen or a hydrocarbon, where appropriate, in a reactor.

[0011] The invention also relates to a balance for a watch oscillator, typically a balance-spring oscillator. This balance comprises a metal body provided with a passivation layer, typically a layer of oxide, nitride or carbide, on at least part of the surface of said balance, this passivation layer having a thickness of less than 5nm.

[0012] This balance wheel can be assembled with a return spring of any known type to form an oscillator, such as a balance-spring oscillator, which can be integrated into a watch movement of a timepiece. Brief description of the drawings

[0013] Other details of the invention will appear more clearly on reading the following description, made with reference to the appended drawing in which: Fig. 1 is a schematic sectional view of a balance according to the invention. Embodiments of the invention

[0014] There figure 1illustrates a balance wheel 1 according to the invention. The shape of the balance wheel 1 is not limited to a particular configuration, and therefore encompasses any known shape, typically of the screwless and / or weightless type. However, the non-limiting shape illustrated comprises, in a conventional manner, a conventional felloe 3 connected to a hub 5 by a plurality of arms 7 of any suitable shape. Typically, the balance wheel 1 is a single-piece, but multi-piece constructions are also possible. The balance wheel 1 is, of course, intended to form part of a watch oscillator in combination with a return spring of any known shape, typically a balance spring.

[0015] The balance wheel 1 is mounted so as to rotate with an axle 8 of any known shape, provided with pivots 11 at its two ends. A balance wheel plate (not shown) carrying a pin 15 for cooperation with an escapement anchor (not shown) is also provided, so as to rotate with the axle 9, this plate being able to be a separate element or integrated with either the hub 5 or the axle 9.

[0016] The body of said balance 1, or, in the case of a multi-piece construction at least the rim 3 of said balance, is made of metal, typically of Maillechort alloy (an alloy of 50% copper, 30% zinc and 20% nickel, by weight), copper-beryllium alloy, or Declafor alloy (a copper-nickel-tin alloy typically comprising 7.5% nickel and 5% tin, as well as up to 0.3% manganese, by weight). For the present invention, the Declafor alloy is preferred.

[0017] On the surface of at least the rim 3 of said balance 1, preferably on the surface of the entirety of said balance 1, a passivation layer 17 is provided having a thickness of less than 5nm, preferably less than 3nm, even more preferably less than 2nm.

[0018] Traditionally, the balance wheel material is protected against tarnishing by gilding or other electrolytic deposition of a suitable metal. This metallic layer can also improve the aesthetic appearance of the balance wheel, particularly in the case of gilding.

[0019] However, the thickness of such a layer is of the order of a few microns, which increases the inertia of the balance 1 and is therefore detrimental to classification according to the Omegametric or similar process, as will be discussed in more detail below. Moreover, the variation in the thickness of the metal layer can be significant among the balances 1 of a production batch.

[0020] A passivation layer 17 is typically created by dry oxidation, carburization, or nitriding of the surface, i.e., by reacting the surface with oxygen, a hydrocarbon, or nitrogen (respectively) in a reactor. The reaction is typically carried out at an elevated temperature and reduced pressure (compared to ambient pressure), in order to provide a layer having a thickness of up to a few nanometers, in a well-controllable manner.

[0021] On a manufacturing batch, such a passivation layer 17 has a thickness which is negligible, and is significantly more constant from one balance 1 to another compared to a gilding, to another electrolytic deposition, or to an anodic deposition, and in addition, the increase in inertia is negligible in view of the fact that the chemical species added to the surface is relatively light, and that the quantity added is extremely small. A classification of the balances and / or a classification by removal of material with sub-class precision carried out before the passivation step thus remains valid after passivation, and no reclassification is therefore necessary.

[0022] The use of such a passivation layer 17 thus makes it possible to manufacture balances 1 which are free of a metal layer deposited on the surface, while avoiding tarnishing and without risking suffering a downgrade caused by such a metal deposit.

[0023] In order to manufacture such a balance 1, at least the rim 3 is first machined from metal, such as Maillechort, CuBe, Declafor or similar, as mentioned above.

[0024] Subsequently, the weight or inertia of balance 1, with or without axis, is measured by Omegametric classification or similar, in order to assign a class to balance 1. Typically, a classification of balances 1 groups them into inertia ranges called "classes" which each correspond to a rate difference of 150 seconds per day of the oscillator in which balance 1 is integrated.

[0025] Then, a removal of material from the balance 1 is carried out, if necessary, in order to put it into inertia with sub-class precision, that is to say so that it fits into an inertia slice having a width corresponding to less than 150 seconds per day, typically 50 seconds per day. This removal of material can be carried out by thicknessing by bar turning, laser machining or similar.

[0026] Finally, a passivation layer 17 is applied to the surface of at least a portion of the balance wheel 1, as described above.

[0027] The balance wheel can subsequently be mounted on its axis 9.

[0028] With respect to the manufacture of a batch of such balances 1, a plurality of balances 1 are machined from metal, the measurement of the weight and / or inertia is made on all of the balances 1, and they are classified in a conventional manner. The removal of material for inertia setting with sub-class precision is carried out on at least some of said balances 1, if not on all of said balances 1, in order to obtain even narrower classes, typically of 50 seconds per day each.

[0029] Then, each balance wheel 1 is subjected to the passivation treatment as described above.

[0030] Other known steps, such as deburring, polishing or similar, can also be carried out according to the manufacturer's requirements.

[0031] Although the invention has been described with reference to particular embodiments, variations are possible without departing from the scope of the invention as defined by the appended claims.

Claims

1. Method for manufacturing a balance wheel (1) for a watch oscillator, comprising the steps of: - machining said balance wheel (1) from metal; - measuring the weight and / or inertia of said balance wheel (1); - optionally, classifying by removing material from said balance wheel (1); - applying a passivation layer (17) to at least part of the surface of said balance wheel (1), said passivation layer (17) having a thickness of less than 5nm, preferably less than 3nm, more preferably less than 2nm.

2. Manufacturing method according to the preceding claim, in which said passivation layer (17) is applied by dry means.

3. Manufacturing method according to the preceding claim, wherein said passivation layer (17) is applied by oxidation, nitriding or carburizing.

4. Method for manufacturing a batch of balances (1) for watch oscillators, comprising the steps of: - machining a plurality of balances (1) made of metal; - measuring the weight and / or inertia of said balances (1); - classifying said balances (1) according to weight and / or inertia; - classifying by removing material from at least some of said balances (1); - applying a passivation layer (17) to at least part of the surface of said balances, said passivation layer (17) having a thickness of less than 5nm.

5. Manufacturing method according to the preceding claim, in which said passivation layer (17) is applied by dry means.

6. Manufacturing method according to the preceding claim, wherein said passivation layer (17) is applied by oxidation, nitriding or carburizing.

7. Balance wheel (1) for a watch oscillator, comprising a metal body provided with a passivation layer (17) on at least part of its surface, said passivation layer (17) having a thickness of less than 5nm.

8. Balance wheel (1) according to the preceding claim, for which said passivation layer (17) is a layer of oxide, nitride or carbide.

9. Oscillator for a watch movement comprising a balance (1) according to one of claims 7 and 8; 10. Clock movement comprising an oscillator according to claim 9.

11. Timepiece comprising an oscillator according to claim 10.

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