BALANCE FOR A HOROLOGICAL MOVEMENT

Abstract

The present invention relates to a balance (1) including a hub (2) connected to a fellos (3) by at least one arm (4), characterised in that the felloe is made of a material whose relative magnetic permeability is less than 1.01, whose density is greater than 6.5, and which is electrically insulating.

Claims

1. An assembly comprising a balance including a hub (2) connected to a felloe (3) by at least one arm (4), at least the felloe being made of a material whose relative magnetic permeability is less than 1.01, whose density is greater than 6.5, and which is electrically insulating, and a staff arranged to receive said balance, the staff also being made of a material whose relative magnetic permeability is less than 1.01, whose density is greater than 6.5, and which is electrically insulating.

2. The assembly according to claim 1, characterised in that the material has an electrical conductivity of preferably less than or equal to 2.5 MS/m, and more preferably less than 1.5 MS/m.

3. The assembly according to claim 1, characterised in that the material is chosen from metals, metal alloys, ceramics, ceramic-metal composites or non-magnetic hard metals.

4. The assembly according to claim 1, characterised in that the material is made from an alloy which contains iron, chromium, nickel and/or cobalt as its main constituents.

5. The assembly according to claim 1, characterised in that the material has a face-centred cubic crystal structure.

6. The assembly according to claim 1, characterised in that the material is an austenitic alloy.

7. The assembly according to claim 6, characterised in that the austenitic alloy has a chromium content greater than 10%, and preferably greater than 15%.

8. The assembly according to claim 6, characterised in that the austenitic alloy is chosen from: 316L steel, 904L steel, Phynox or MP35N.

9. A movement comprising the assembly according to claim 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0026] The invention relates to a balance which includes a staff made of non-magnetic material. The staff supports a balance comprising a felloe and at least one arm made in one piece with the felloe. The arms extend from the hub at the centre of the balance, into which the staff is pressed against a shoulder. Conventionally, the staff also supports a collet for attaching a balance spring (not shown).

[0027] According to the invention, the felloe is made of a non-magnetic, electrically insulating material with a density greater than 6.5.

[0028] For the purposes of this invention, a non-magnetic material is understood to mean a material with a relative magnetic permeability of less than 1.01.

[0029] An electrically insulating material is understood to mean a material with low or very low electrical conductivity.

[0030] According to the invention, the material from which the felloe 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 drifts in rate when the watch is in a magnetic field.

[0031] The balance is made from a material selected from metals, metal alloys, ceramics such as ytterbium oxide, Europium (III) oxide, dysprosium oxide, cerium (IV) oxide or neodymium oxide, ceramic-metal composites or non-magnetic hard metals such as tungsten carbide with a nickel binder.

[0032] In a preferred embodiment of the invention, the balance is made from an alloy containing iron, chromium, nickel and/or cobalt as its main constituents, and has a face-centred cubic crystal structure.

[0033] Even more preferably, the balance is made from an austenitic alloy selected from 316L steel, 904L steel, Phynox or MP35N. Obviously, other austenitic alloys with similar properties can be used without any particular difficulty for a person skilled in the art.

[0034] Such an austenitic alloy preferably has a chromium (Cr) content greater than 10%, preferably greater than 15%.

[0035] For example, the alloy used to make the balance is a 316L steel consisting 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% sulphur (S), between 16% and 18% chromium (Cr), between 2 and 2.5% molybdenum (Mo), and between 10.5% and 13% nickel (Ni).

[0036] According to the needs of a person skilled in the art, the balance is coated with a layer, in particular a decorative layer, by electroplating, PVD or CVD.

[0037] The invention further relates to a staff and balance assembly in which the staff receiving the balance is made from a material of the same type as the material from which the balance is made, namely a material whose relative magnetic permeability is less than 1.01, whose density is greater than 6.5, and which is electrically insulating. For example, a 316L steel balance could be mounted on a 904L steel staff.

[0038] The staff can be coated with a layer, in particular chemical NiP or NiB, to improve its properties, in particular its hardness and resistance to wear and friction.

[0039] The invention further relates to a horological movement and a timepiece equipped with a balance in accordance with the invention.