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 wheel for a watch oscillator, a method of manufacturing a batch of such balance wheels, as well as such a balance wheel as such. State of the art

[0002] Documents EP 2 502 877 A1 and EP 3 769 161 A1 disclose examples of prior art relevant to the present invention.

[0003] The traditional method of setting a metal balance wheel to inertia, in order to help achieve a desired beat frequency for the oscillator in which said balance wheel is integrated, involves the following steps: 1. Machining of metal balance wheels, such as nickel silver, CuBe, Declafor, or similar; 2. Measurement of the weight or inertia of the balance wheel, with or without an axle, using Omegametric or similar classification, to divide the balance wheels into inertia classes and thus allow matching by class with balance springs classified by stiffness. Typically, each class corresponds to 150 seconds of operation per day for the assembled oscillator; 3. Material removal from the balance wheel for balance wheels that require it for inertia adjustment, in order to manufacture balance wheels with sub-class accuracy, i.e., having a variation corresponding to less than 150 seconds of operation per day, such as 50 seconds per day; 4. Application of a protective layer, typically gold plating, another electroplating, a synthetic carbon deposit, or similar; 5.Reclassification with a work dispersion as in point 3, since the application of the protective layer increases the thickness of the balance wheels sufficiently to downgrade them.

[0004] This reclassification is time-consuming, and its elimination is desirable while maintaining classification accuracy and without harming the pendulum's resistance to tarnishing.

[0005] 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

[0006] 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 of said metal balance, such as in 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 measurement of the weight and / or inertia of said balance wheel, for example by means of an Omegametric or similar device; then optionally, classification by material removal of said balance wheel, for example by diamond grinding, thickening or adding holes on the outside or underside of the balance wheel; then application of a passivation layer, such as an oxide, nitride or carbide layer, having a thickness of less than 5nm, preferably less than 3nm, even more preferably less than 2nm, on at least part of the surface of said balance wheel, preferably on the whole surface of the rim of said balance wheel, even more preferably on the whole surface of the metal of said balance wheel.

[0007] A passivation layer, which can be formed by oxidation, nitriding, or carburizing of the balance wheel's metal surface, protects it from tarnishing but does not add enough mass to degrade it, unlike conventional metallization, anodizing, or similar processes. Furthermore, the thickness of the passivation layer is very consistent from one balance wheel to another. Therefore, reclassification of the balance wheels is unnecessary, as the increase in inertia is sufficiently negligible and constant to be disregarded.

[0008] Advantageously, this passivation layer is applied by a dry process, such as by reacting the surface of the balance wheel metal with a gaseous chemical species like oxygen, nitrogen, or a hydrocarbon, if necessary, in a reactor. Such a dry process is not to be confused with anodizing, which is an electrochemical process carried out in a bath of aqueous solution and used to create oxide layers with a thickness ranging from several micrometers to several tens of micrometers.

[0009] 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 following steps: machining of 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 measurement of the weight and / or inertia of said balance wheels, for example by means of an Omegametric or similar device; then classification of said balance wheels according to weight and / or inertia, typically according to classes corresponding to 150 seconds of operation per day; then classification by material removal from at least some of said balance wheels, typically from all of said balance wheels, this material removal being typically, for example, by diamond grinding, thickening or adding holes on the outside or underside of the balance wheel; then application of 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 balance wheels, preferably on the entire surface of the metal of said balance wheels.

[0010] As mentioned above, a passivation layer, which can be formed by oxidation, nitriding, or carburizing of the balance wheel's metal surface, protects it from tarnishing but does not add enough mass to degrade it, unlike conventional metallization, anodizing, or similar processes. Furthermore, the thickness of the passivation layer is very consistent from one balance wheel to another. Therefore, reclassification of the balance wheels is unnecessary, as the increase in inertia is sufficiently negligible and constant to be disregarded.

[0011] Advantageously, said passivation layer is applied by dry means, such as by reacting the surface of the metal of the balance wheel with a gaseous chemical species such as oxygen, nitrogen or a hydrocarbon, as appropriate, in a reactor.

[0012] The invention also relates to a balance wheel for a watch oscillator, typically a balance-spring oscillator. This balance wheel comprises a metal body with a passivation layer, typically an oxide, nitride, or carbide layer, covering at least a portion of the surface of said balance wheel, this passivation layer having a thickness of less than 5 nm.

[0013] 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

[0014] Further details of the invention will become clearer upon reading the following description, made with reference to the attached drawing in which: Fig. 1 is a schematic cross-sectional view of a balance wheel according to the invention. Embodiments of the invention

[0015] There figure 1 The figure illustrates 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 conventionally comprises a rim 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 be part of a watch oscillator in combination with a return spring of any known shape, typically a balance spring.

[0016] The balance wheel 1 is fixed for rotation to an axle 8 of any known shape, fitted with pivots 11 at its two ends. A balance plate (not shown) carrying a pin 15 for cooperation with an escapement lever (not shown) is also provided, fixed for rotation to the axle 9, this plate being a separate element or integrated into either the hub 5 or the axle 9.

[0017] The body of said balance wheel 1, or, in the case of a multi-part construction, at least the rim 3 of said balance wheel, is made of metal, typically of 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). For the present invention, the Declafor alloy is preferred.

[0018] On the surface of at least the serge 3 of said balance 1, preferably on the surface of the entire 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.

[0019] Traditionally, the balance wheel material is protected against tarnishing by gilding or another 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.

[0020] However, the thickness of such a layer is on the order of a few microns, which increases the inertia of balance wheel 1 and is therefore detrimental to grading according to the Omegametric or similar method, as will be discussed in more detail below. Furthermore, the variation in the thickness of the metallic layer can be significant among balance wheels 1 within a production batch.

[0021] 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 high temperature and low pressure (relative to ambient pressure) to provide a layer with a thickness of up to a few nanometers, in a highly controllable manner.

[0022] In a production batch, such a passivation layer 17 has a negligible thickness and is significantly more consistent from one balance wheel 1 to another compared to gilding, other electrolytic coatings, or anodic coatings. Furthermore, the increase in inertia is negligible given that the chemical species added to the surface is relatively light and the quantity added is extremely small. Therefore, a classification of the balance wheels and / or a classification by material removal with subclass precision performed before the passivation step remains valid after passivation, and no reclassification is necessary.

[0023] The use of such a passivation layer 17 thus makes it possible to manufacture balance wheels 1 which are free of metallic layer deposited on the surface, while avoiding tarnishing and without risking downgrading caused by such a metal deposit.

[0024] In order to manufacture such a balance wheel 1, at least the serge 3 is first machined from metal, such as Nickel Silver, CuBe, Declafor or similar, as mentioned above.

[0025] Subsequently, the weight or inertia of the balance wheel 1, with or without axis, is measured by Omegametric or similar classification, in order to assign a class to the balance wheel 1. Typically, a classification of balance wheels 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 the balance wheel 1 is integrated.

[0026] Then, material is removed from the balance wheel 1, if necessary, to bring it into inertia with subclass accuracy, i.e., to a point where it falls within an inertia band with a width corresponding to less than 150 seconds per day, typically 50 seconds per day. This material removal can be achieved by machining, laser cutting, or similar processes. 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] Regarding the manufacture of a batch of such balance wheels 1, a plurality of balance wheels 1 are machined from metal, the weight and / or inertia is measured on all of the balance wheels 1, and they are conventionally classified. Material removal for inertia adjustment with subclass precision is performed on at least some of said balance wheels 1, if not all of said balance wheels 1, in order to obtain even narrower classes, typically of 50 seconds per day each.

[0029] Then, each pendulum 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 as required by the manufacturer.

[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 attached claims.

Claims

1. Method for manufacturing a balance wheel (1)for a horological oscillator, comprising the steps of: - machining said balance wheel (1) from metal; - measuring the weight and / or inertia of said balance wheel (1); - optionally, rectification of classification 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), the method being characterized in that said passivation layer (17) has a thickness of less than 5 nm, preferably less than 3 nm, and more preferably less than 2 nm.

2. Manufacturing process according to the previous claim, in which said passivation layer (17) is applied by dry processing.

3. Manufacturing process according to the previous claim, in which said passivation layer (17) is applied by oxidation, nitriding, or carburization.

4. Method for manufacturing a batch of balance wheels (1) for horological oscillators, comprising the steps of: - machining a plurality of balance wheels (1) from metal; - measuring the weight and / or inertia of said balance wheels (1); - classifying said balance wheels (1) according to weight and / or inertia; - rectification of classification by removing material from at least some of said balance wheels (1); - applying a passivation layer (17) to at least part of the surface of said balance wheels, the method being characterized in that said passivation layer (17) has a thickness of less than 5 nm.

5. Manufacturing process according to the previous claim, in which said passivation layer (17) is applied by dry processing.

6. Manufacturing process according to the previous claim, in which said passivation layer (17) is applied by oxidation, nitriding, or carburization.

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

8. Balance wheel (1) according to the previous claim, wherein said passivation layer (17) is an oxide, nitride or carbide layer.

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

11. Timepiece comprising an oscillator according to claim 10.

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