Method for lubrication of a non-magnetic balance shaft of a timepiece

Abstract

The invention relates to a method of lubricating the balance shaft of a watch part using a lubricant whose composition includes a multi-alkylated cyclopentane (MAC), as well as the use of such a lubricant for such a purpose.

Description

Technical field

[0001] The present invention relates to the field of watchmaking and concerns, more particularly, a method of lubricating a non-magnetic balance shaft of a timepiece. State of the art

[0002] The lubrication of watch parts is based on knowledge acquired over many years through experimentation and also empiricism. The tribology of a system depends on many parameters, the surface conditions of the interacting parts, the contact speeds and pressure, the lubricant (chemical nature, viscosity, etc.). The complexity of these interactions means that once a tribological system has been optimized to give satisfaction, it is difficult to develop it at an industrial level. Indeed, experience shows that a modification of a parameter can completely unbalance the system and the search for a new system with the same performance is particularly difficult.

[0003] In practice, if we take the example of the lubrication of the balance shaft, the system that traditionally works includes a shaft made of 20AP carbon steel, the pivots of which have been rolled and then polished to give them a specific shape, hardness and surface finish. These pivots cooperate with ruby / corundum stones, and the whole thing is generally lubricated with an oil supplied by the manufacturer Moebius, under the reference Synt-A-Lube 9010. At present, all these parameters allow for a high-performance tribosystem, and an oil with satisfactory chemical stability so that the performance is long-lasting.

[0004] With the significant increase in the presence of magnetic fields in the modern environment, due to waves of all kinds, watch movements made with traditional iron-based materials, which are highly sensitive to magnetic fields, can become deregulated after exposure to these magnetic fields. One way to overcome this defect is to use non-magnetic materials on certain specific parts of the watch movement, particularly on elements of the regulating organ or on moving elements.

[0005] Thus, watchmaking players are currently working on new materials to produce watch components, particularly balance shafts, and there are an ever-increasing number of patent applications on these subjects. However, with these materials, conventional lubricants are not always satisfactory, either in terms of friction or in terms of pivot aging. Counterintuitively, these two parameters do not go hand in hand, and it is possible to have a lubricant that reduces the friction of a tribological system, while allowing premature wear of the shaft or bearing to be observed.

[0006] Furthermore, for logistical reasons, we also understand that on the platforms of watch brands providing maintenance services for watch parts in circulation, we will soon have to be able to deal with watch parts with conventional steel components and watch parts with components made of non-magnetic materials. Given the complexity of the parameters involved mentioned above, it follows that it seems inevitable to have to manage different lubricants, to be implemented according to the tribosystem. On an international scale, monitoring the supply of several references is in itself a challenge. Identifying a lubricant that could operate with equivalent performance in different tribosystems would present a decisive advantage.

[0007] Furthermore, document CN111019744 describes a lubricant comprising multi-alkylated cyclopentanes (MAC) for the lubrication of micro-electromechanical systems of space machines, in particular due to its low volatility which therefore makes it particularly suitable for use in space or in a low-pressure environment. However, there is no indication in this document that such a lubricant is suitable for the lubrication of a balance shaft, or even for use in mechanical watchmaking considered more generally. Especially since, as explained above, modifying one of the parameters of a tribological system is not at all obvious if one wants to obtain similar performances, or even improve them.

[0008] The present invention aims to solve the above-mentioned problems. Disclosure of the invention

[0009] More specifically, a first aspect of the invention relates to a method of lubricating a non-magnetic balance shaft of a timepiece as claimed in the claims, as well as a use of a specific lubricant for such a purpose. Brief description of the drawings

[0010] Other details of the invention will appear more clearly on reading the following description, made with reference to the appended drawing in which: there figure 1 represents comparative results of tribometer tests of different lubricants in different tribosystems, the figure 2 represents results of oxidation tests of different lubricants. Method of carrying out the invention

[0011] Faced with the need to find lubricants which make it possible to solve the problems set out in the introduction to the present application, the applicant has identified lubricants of a new type for watchmaking, presenting particularly interesting results.

[0012] Thus, as we will detail later, a lubricant whose composition is based on at least one multi-alkylated cyclopentane (MAC), is particularly interesting in a watchmaking context, to lubricate a non-magnetic balance shaft.

[0013] It has been represented on the figure 1comparative results presenting tribometer tests, establishing tribological conditions similar to those of a balance shaft rubbing in its bearing. These tests are carried out with a Tribolab tribometer marketed by Brücker, with a lubricated metal-ruby contact, of the sphere / plane type. The relative movement between the metal and the ruby is of the alternating linear type, to be comparable to the real friction of a balance shaft in its bearing. The volume of metal affected by the friction is then measured over a certain period.

[0014] These results indicate on the abscissa the volume worn on the measuring pin and the coefficient of friction measured between the pin and the base surface. The area located on the left of the figure, and indicated by an area delimited by a dashed line, corresponding to non-quantifiable wear or acceptable wear, indicates material / lubricant pairs which meet the specifications.

[0015] The figure therefore shows the points obtained for the following lubricants: INV, which is a MAC type oil according to the invention, Synt-A-Lube 9010, which is the reference oil, marketed by Moebius, respectively tested on specimens made of conventional steel, type 20AP, Chrome and Manganese base steel, Chrome and Nickel base steel.

[0016] It is found that INV oil gives exceptional results for lubricating a contact between a Cr, Mn base steel and a ruby, and also gives satisfactory results with other specimens made of 20AP type steel or Cr, Ni base steel. 9010 oil, for lubricating a 20AP steel on ruby, determines the current reference. However, it is also noted that it does not meet expectations for a Cr, Mn or Cr, Ni base steel, and that it can therefore only be suitable for a limited number of tribosystems.

[0017] Oxidation stability tests were also carried out using equipment known as RapidOxy, which involves applying a defined oxygen pressure at a certain temperature. A pressure drop corresponding to the absorption of oxygen by the lubricant is measured, which makes it possible to detect the lubricant's sensitivity to oxidation.

[0018] There figure 2 shows us the results of these tests for INV oil, compared to the Synt-A-Lub 9010 reference, for a pressure of 700kPa, at 100°C, with a target pressure difference of a drop of 10%. We can see that the pressure drop is much slower for INV oil than for Synt-A-Lub 9010 oil, with a factor of 2 between the two. This means that INV oil is much more resistant to oxidation and therefore also ages better.

[0019] Thus, the MAC-based lubricant tested, with a Cr, Mn-based steel shaft, presents much better performances than the current reference (Moebius 9010 + 20AP shaft). With shafts of other types, the results are substantially at the level of the reference and therefore allow results to be obtained in accordance with the specifications.

[0020] Furthermore, this family of lubricant still has optimization ranges depending on the desired uses. We know that it is preferable to adapt the viscosity of a lubricant according to the contact speeds and pressures experienced, depending on the intended application.

[0021] Particularly advantageously, it is possible to formulate MAC type oils, i.e. comprising at least one multi-alkylated cyclopentane, of different viscosities (in the present application, unless otherwise stated, all viscosities are given for a temperature of 40°C), between 40 mPa.s and 2200 mPa.s, with or without additives, chosen from the following additives: anti-wear, anti-oxidation, friction modifier, an Extreme Pressure additive and a viscosity index modifier.

[0022] MAC type oils can also be used as base oils to form greases, with a thickening agent chosen, for example, from organic or inorganic thickening particles, waxes or metallic soaps. More particularly, PTFE particles dispersed in the base oil can be used as thickener. For example, it is possible to work with greases having a grade between 3 and 00, preferably a grade between 2 and 1 according to the NLGI (National Lubricating Grease Institute) scale.

[0023] With these different possibilities, in addition to the non-magnetic balance shaft covered by the invention, it is also possible to lubricate all the components of the watch which are in motion or which are subject to friction. Examples include the wheels, and in particular the working surfaces of certain gears, for example of a winding mechanism; the jeweled or simple bearings and the shafts of mobiles housed therein; the escapement organs comprising the teeth of the escape wheel and the pallets; the mainspring and the barrel, the oscillating weight bearing. This list of examples is not part of the invention and is not exhaustive.

[0024] This allows us to optimize the viscosity ranges according to the type of contacts to be lubricated. For example, for the balance shaft, we can choose a viscosity range between 40mPa.s and 250mPa.s, preferably between 50mPa.s and 120mPa.s.

[0025] For fast gear pivots (escapement, balance wheel, second wheel, etc.), a viscosity range between 40mPa.s and 250mPa.s can be chosen, preferably between 50mPa.s and 120mPa.s.

[0026] For winding mechanisms, bearings with and / or without oiler (metal / ruby and / or metal / metal), we can cite in particular the automatic system (eccentric, pivot), the pivots of slow gears (barrel, medium wheels, timer, etc.), we can choose a viscosity range between 200mPa.s and 2200mPa.s, preferably between 350mPa.s and 2100mPa.s, and even more preferably between 380mPa.s and 2080mPa.s

[0027] For mass bearings, in Steel or Ceramic, a viscosity range between 40mPa.s and 120mPa.s can be chosen, preferably between 45 and 60mPa.s.

[0028] In terms of materials with which MAC-based lubricants can perform well, we can cite, in particular, non-magnetic balance shafts made from the following alloys: Mn base and Mn-Cr alloy (Biodur), Cr base and Cr-Ni alloy (Inox), Co base (Nivaflex, Phynox,...), Pd base (Isoplus); Non-magnetic bulk metallic glasses (i.e., massive amorphous metals, also known as "bulk metallic glasses"); Ceramics; Non-magnetic Inconel alloys; Non-magnetic ISO P, ISO S and ISO H alloys; Austenitic stainless steel alloys.

[0029] With regard to Inconel alloys, these comprise at least 50% Nickel, between 13 and 30% Chromium and elements selected from Fe, Mo, Nb, Ta, Co, Mn, Cu, AI, Ti, Si, C, S, P and B. More particularly, suitable alloys may be an Inconel 718. This alloy comprises between 50 and 55% Nickel, between 17 and 21% Chromium, between 2.8 and 3.3% Molybdenum, between 4.75 and 5.50% Niobium, between 0 and 1.0% Cobalt, between 0 and 0.35% Manganese, between 0 and 0.30% Copper, between 0.20 and 0.80% Aluminum, between 0.65 and 1.15% Titanium, between 0 and 0.35% Silicon, between 0 and 0.08% Carbon, between 0 and 0.015% Sulfur, between 0 and 0.015% Phosphorus, and between 0 and 0.006% Boron, and the balance Iron.

[0030] As for the other alloys mentioned above, the following materials can be used: ISO P: High-alloy steels (> 5% alloying elements), annealed, quenched and tempered; ISO S: Heat-resistant superalloys excluding titanium (Iron base, nickel base, cobalt base), annealed, aged, cast; ISO H: Quenched, quenched and tempered steels, shell iron (cast or cast and aged); Austenitic stainless steels: 1.4472 and Biodur ®< 108.

[0031] The various materials above can further be treated on their surface, either by structuring or by chemical modification (diffusion of atoms in the original matrix, for example by ion implantation as described in application CH0883 / 20 in the name of the applicant). The application of a coating to further improve the tribology is not excluded, for example a layer of CuSnZn alloy, as described in application CH0284 / 20 in the name of the applicant).

[0032] Fluorescent tracers can also be incorporated to provide better possibilities for monitoring the lubrication process.

[0033] This description has been given as a non-limiting illustration of the invention. Those skilled in the art may add additions within its scope, without, however, departing from the scope of the invention defined by the claims.

Claims

1. Method of lubricating a balance shaft of a timepiece using a lubricant whose composition is based on multi-alkylated cyclopentane (MAC), said balance shaft being made of nonmagnetic material.

2. Method according to claim 1, characterized in that the lubricant is an oil.

3. Method according to claim 2, characterized in that said oil has a viscosity of between 40 mPa.s and 2200 mPa.s at 40°C.

4. Method according to claim 3, characterized in that said oil has a viscosity of between 40 and 250 mPa.s, preferably between 50 and 120 mPa.s at 40°C.

5. Method according to one of claims 2 to 4, characterized in that the oil comprises at least one of the following additives: anti-wear, anti-oxidation, friction modifier, an extreme pressure additive and a viscosity index modifier.

6. Method according to claim 1, characterized in that the lubricant is a grease, comprising a base oil whose composition comprises at least one multi-alkylated cyclopentane and a thickening agent.

7. Method according to claim 6, characterized in that the thickening agent is chosen from inorganic or organic particles, waxes or metal soaps.

8. Method according to claim 7, characterized in that the thickening agent is PTFE particles.

9. Method according to one of claims 7 and 9, characterized in that the grease has a grade of between 3 and 00, according to the NLGI (National Lubricating Grease Institute) scale.

10. Method according to one of the preceding claims, characterized in that said balance shaft is made of solid metallic glass, ceramic, an Inconel alloy, an ISO P alloy, an ISO S alloy, an ISO H alloy or an austenitic stainless steel alloy.

11. Method according to claim 10, characterized in that the lubricant is an oil with a viscosity of between 40mPa.s and 250mPa.s, preferably between 50mPa.s and 120mPa.s, at 40°C.

12. Use of a lubricant whose composition is based on multi-alkylated cyclopentane (MAC) for lubricating a balance shaft of a timepiece, said balance shaft being made of nonmagnetic material.

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