Balance wheel for a clockwork

Abstract

An assembly comprising a balance having a hub connected by at least one leg to a ring, at least the ring being formed from a first material whose relative magnetic permeability is less than 1.01 and which is electrically insulating, and a shaft adapted to receive the balance, the shaft being formed from a second material whose relative magnetic permeability is less than 1.01, whose density is higher than 6.5 and which is electrically conductive.

Description

Technical field of the invention

[0001] The invention relates to a balance wheel for a watch and a stem / balance wheel assembly. Technical background

[0002] The regulating organ of a watch generally includes a flywheel, called the balance wheel. This part is crucial for the timekeeping accuracy of the timepiece. The combination of a balance wheel and a hairspring forms an oscillator that allows the movement to be regulated at a specific frequency.

[0003] Currently, the balance ring and balance arms of a watch movement are made of a copper-based alloy, particularly beryllium copper, brass, nickel silver, or Declafor. Beryllium copper, which is predominantly used, offers a favorable combination of properties, including non-magnetism, good chemical stability, and adequate mechanical properties. The density of these alloys is generally higher than 8.

[0004] The problem of magnetic fields is well known to watchmakers and is becoming increasingly common. Magnetic fields are increasingly present in everyday life and disrupt the functioning of mechanical watches, leading to significant deviations in their rate.

[0005] To solve this problem, the previous approaches are all based on non-magnetic materials for the balance spring (Si or base alloys Nb), the pivot points (balance staff, anchor shaft, escape wheel pinion), the wheel plates and the anchor plates.

[0006] The materials used for the balance ring are generally non-magnetic: brass, nickel silver, beryllium copper, but they have good electrical conductivity.

[0007] Despite the combination of all these non-magnetic materials, a watch movement exhibits significant deviation under a magnetic field.

[0008] It is generally believed that this deviation is due to the presence of ferromagnetic elements in components of the movement that are not part of the escapement and oscillator, such as the hairspring stud or the winding stem.

[0009] Even if these parts are replaced with parts made of materials without ferromagnetic elements, this rate deviation can still be observed.

[0010] The inventors discovered that this deviation can be attributed to the influence of eddy currents. These arise when a conductive material is moved in a magnetic field gradient or when a balance wheel rotates parallel to the balance ring in a constant field, which also influences the rate of the balance wheel.

[0011] Some manufacturers are also known to produce balance wheels in which at least the balance ring is made of ceramic or diamond. However, such materials, although non-magnetic, are very difficult to machine for balance wheel production and result in very high production costs.

[0012] An object of the present invention is therefore to create a balance free from these known limitations by using a special alloy that is non-magnetic and insensitive to eddy currents. Another object of the present invention is to propose a balance with a ring whose density is high enough to allow the balance to be integrated into the space available for a given movement. Indeed, if the density is too low, as is usually the case with ceramic, the balance becomes too large for a given inertia and can no longer be accommodated in the movement.

[0013] A further object of the invention is to provide an assembly whose shaft is made of a material that both limits sensitivity to magnetic fields and has mechanical properties that meet the requirements of wear and shock resistance and those in the watchmaking sector. Summary of the invention

[0014] The object of the present invention is to remedy the aforementioned disadvantages in whole or in part by proposing an assembly comprising a balance staff and a balance wheel in which at least the ring is made of a non-magnetic material.

[0015] To this end, the present invention relates to an assembly comprising a balance wheel with a hub connected by at least one leg to a ring, at least the ring being made of a first material whose relative magnetic permeability is less than 1.01 and which is electrically insulating, and comprising a shaft arranged to receive the balance wheel, the shaft being made of a second material whose relative magnetic permeability is less than 1.01, whose density is higher than 6.5 and which is electrically conductive.

[0016] According to further advantageous embodiments of the invention: - the first material preferably has an electrical conductivity of less than or equal to 2.5 MS / m and more preferably less than or equal to 1.5 MS / m; - the first material has a density higher than 2; - the first material has a density higher than 4; - the first material has a density higher than 5; - the first material has a density higher than 6.5; - the second material has an electrical conductivity greater than or equal to 5 MS / m; - the second material has an electrical conductivity greater than or equal to 10 MS / m; - the second material is tungsten; - the second material is tungsten doped with lanthanum oxide; - the first material is selected from: metals or metal alloys, ceramics, ceramic-metal composites, non-magnetic hard metals; - the first material is an alloy containing chromium, iron, nickel and / or cobalt as main components; - the first material has a face-centered cubic crystal lattice structure; - the first material is an austenitic alloy; - the austenitic alloy preferably has a chromium content of more than 10%, preferably more than 15%; - the austenitic alloy is selected from: steel 316L, steel 904L, Phynox or MP35N.

[0017] The invention further relates to a clockwork with a balance wheel according to the invention.

[0018] The invention further relates to a watch with a watch movement equipped with a balance wheel according to the invention. Detailed description of the invention

[0019] The invention relates to an assembly comprising a balance wheel and a balance staff. The balance staff carries a balance wheel comprising a ring, at least one leg formed integrally with the ring, and a hub. The legs extend from the hub, which is located in the center of the balance wheel, with the staff being driven against a shoulder. Typically, the staff also carries a hairspring roller intended for securing a hairspring (not shown).

[0020] According to the invention, at least the balance ring is made of a first non-magnetic and electrically insulating material, and the balance staff is made of a second non-magnetic, electrically conductive material with a density higher than 6.5.

[0021] A non-magnetic material in the sense of the present invention is understood to mean a material whose relative magnetic permeability is less than 1.01.

[0022] An electrically insulating material is a material that is weakly or very weakly electrically conductive or whose electrical conductivity is less than or equal to 2.5 MS / m,

[0023] Electrically conductive material is a material whose electrical conductivity is higher than 5 MS / m.

[0024] According to the invention, the first material from which the balance wheel is made has an electrical conductivity of less than or equal to 2.5 MS / m, and preferably the electrical conductivity is less than or equal to 1.5 MS / m. Such electrical conductivity makes it possible to limit the influence of eddy currents and thus rate deviations when the watch is located in a magnetic field.

[0025] According to the invention, the first material forming the balance has a density higher than 2.

[0026] According to the invention, the first material has a density higher than 4.

[0027] According to the invention, the first material has a density higher than 5.

[0028] According to the invention, the first material has a density higher than 6.5.

[0029] The first material forming the balance wheel is selected from metals, metal alloys, ceramics such as ytterbium oxide, europium(III) oxide, dysprosium oxide, cerium(IV) oxide or neodymium oxide, zirconium dioxide, ceramic-metal composites or non-magnetic hard metals such as tungsten carbide with a nickel binder or even titanium grade 5.

[0030] According to a preferred embodiment of the invention, the first material forming the balance wheel is made of an alloy containing iron, chromium, nickel and / or cobalt as main components and having a face-centered cubic crystal lattice structure.

[0031] Even more preferably, the balance wheel is made of an austenitic alloy selected from steel 316L, steel 904L, Phynox, or MP35N. Of course, other austenitic alloys with similar properties can also be used without particular difficulty for the skilled person.

[0032] Such an austenitic alloy preferably has a chromium (Cr) content of more than 10%, preferably more than 15%.

[0033] The alloy used to make the balance wheel, for example, is a 316L steel, which is made of a maximum of 0.02% carbon (C), a maximum of 1% silicon (Si), a maximum of 2% manganese (Mn), a maximum of 0.04% phosphorus (P), a maximum of 0.03% sulfur (S), between 16% and 18% chromium (Cr), between 2 and 2.5% molybdenum (Mo) and between 10.5% and 13% nickel (Ni).

[0034] According to the invention, the second material from which the balance staff is made has an electrical conductivity equal to or higher than 5 MS / m.

[0035] According to a further embodiment of the invention, the second material from which the balance staff is made has an electrical conductivity equal to or higher than 10 MS / m.

[0036] It should be noted that the effect of eddy currents on the balance staff is negligible compared to that on the balance ring.

[0037] According to one embodiment of the invention, the second material from which the balance staff is formed is tungsten. Tungsten is a paramagnetic material with a density of 19.25 and an electrical conductivity of 17.9 MS / m.

[0038] According to a further embodiment of the invention, the shaft is made of tungsten doped with lanthanum oxide.

[0039] Tungsten combines low magnetic permeability, high hardness, and excellent wear resistance. Furthermore, tungsten with the addition of lanthanum oxide retains most of the above-mentioned properties and is easier to machine.

[0040] For example, an assembly according to the invention may comprise a shaft made of tungsten and a balance wheel made of titanium (grade 5) or a shaft made of tungsten and a balance wheel made of zirconium dioxide or a shaft made of tungsten doped with lanthanum oxide and a balance wheel made of zirconium dioxide or titanium (grade 5).

[0041] Depending on the needs of the specialist, the balance wheel is coated with a layer, especially a decorative layer, by galvanization, PVD or CVD coating.

[0042] The shaft may be coated with a layer, in particular of chemical NiP or NiB, to improve its properties, in particular its hardness, its wear resistance and its resistance to friction.

[0043] The invention also relates to a clockwork movement and a timepiece equipped with a balance wheel according to the invention.

Claims

[1] An assembly comprising a balance wheel having a hub connected by at least one leg to a ring, at least the ring being made of a first material whose relative magnetic permeability is less than 1.01 and which is electrically insulating, and a shaft adapted to receive the balance wheel, the shaft being made of a second material whose relative magnetic permeability is less than 1.01, whose density is higher than 6.5 and which is electrically conductive. [2] Assembly according to claim 1, characterized by that the first material has an electrical conductivity which is preferably less than or equal to 2.5 MS / m and more preferably less than 1.5 MS / m. [3] Assembly according to claim 1 or 2, characterized by that the first material has a density higher than 2. [4] Assembly according to claim 1 or 2, characterized bythat the first material has a density higher than 4. [5] Assembly according to claim 1 or 2, characterized by that the first material has a density higher than 5. [6] Arrangement according to claim 1 or 2, characterized by that the first material has a density higher than 6.

5. [7] Assembly according to one of claims 1 to 6, characterized by that the second material has an electrical conductivity greater than or equal to 5 S / m. [8] Assembly according to one of claims 1 to 6, characterized by that the second material has an electrical conductivity of greater than or equal to 10 MS / m. [9] Assembly according to one of claims 1 to 8, characterized by that the second material is tungsten. [10] Assembly according to one of claims 1 to 8, characterized by that the second material is tungsten doped with lanthanum oxide. [11] Assembly according to one of claims 1 to 10, characterized bythat the first material is selected from metals, metal alloys, ceramics, ceramic-metal composites or non-magnetic hard metals. [12] Assembly according to one of claims 1 to 11, characterized by that the first material is made of an alloy containing iron, chromium, nickel and / or cobalt as main components. [13] Assembly according to one of claims 1 to 12, characterized by that the first material has a face-centered cubic crystal lattice structure. [14] Assembly according to one of claims 1 to 13, characterized by that the first material is an austenitic alloy. [15] Assembly according to claim 14, characterized by that the austenitic alloy has a chromium content of more than 10% and preferably more than 15%. [16] Assembly according to claim 14 or 15, characterized by that the austenitic alloy is selected from: steel 316L, steel 904L, Phynox or MP35N. [17] A clockwork movement comprising an assembly according to any one of claims 1 to 16.