EP3511780A1 - Method for lubricating an escapement - Google Patents

Abstract

The invention relates to a method of lubricating a timepiece escapement mechanism comprising a mobile intended to receive a driving force and a stop member intended to cooperate with the mobile to block or allow its rotation to rotate alternately, said mobile and said stop member having respectively first and second contact members intended to cooperate with each other. According to the invention, the method is characterized in that it comprises a step of applying a grease comprising particles of the PTFE type dispersed in a base oil, the charge of PTFE being adjusted relative to the specific surface of the particles so as to obtain a grease having a grade between 3 and 1, preferably a grade 3 or 2 depending on the NLGI (National Lubricating Grease Institute) scale.

Description

Technical area

The present invention relates to the field of watchmaking, particularly mechanical watchmaking. It relates to a method of lubricating an exhaust.

In the field of mechanical watches, the exhaust makes it possible to regulate the supply of energy supplied by the barrel and to maintain the oscillations of the regulating organ.

The most common mechanisms are said to Swiss anchor and interact a pivoting anchor, including an escape wheel that the anchor blocks alternately by an entry pallet and an output pallet, it includes.

Traditionally, pallets are made of ruby, while the escape wheel is made of steel. The optimization of the tribological conditions between the pallets of the anchor and the escape wheel leads to lubricate the contact areas between them so as to reduce the energy losses by friction and increase the energy transmission efficiency.

This lubrication is delicate and complex, and is the subject of much research, know-how and innovation. Indeed, the relative speeds of movement between the vanes and the teeth of the escape wheel are high, of the order of 70 mm / s during the pulse phase and the lubricant used must therefore have a viscosity adapted to be effective. at these speeds.

Lubricants that meet these specifications are usually quite fluid. To be effective, it is imperative to maintain the lubricant used in the contact area enough without hindering the movement of moving components. It must also remain in place during the operation of the exhaust and in case of shocks so as not to deplete the contact and contaminate the components inside the movement. This is achieved by applying an epilame that participates in the complexity general and overall lubrication of an exhaust. Indeed, the epilame forms a film on the surface of the lipophobic type pallets. The exhaust must be operated dry so that the contact of the toothing of the escape wheel is free of epilame, so as to form a trench, into which the oil will then be applied and contained. due to the lipophilic properties of epilame.

In order to constitute a lubricant reservoir for supplying the contact and reducing the contact surfaces, the teeth constituting the escape wheel can be bevelled.

More recently, watchmakers have explored the use of silicon to make the anchor and the escape wheel, because this material offers, in addition to freedom in the realization of complex geometry, reduced friction coefficients, especially for silicon interactions. -Silicon. Quite quickly, the use of SiO ₂ obtained by thermal oxidation or diamond obtained by CVD deposition has imposed itself to improve the mechanical strength and the tribological properties. Watchmakers have long argued that the silicon components thus coated would make it possible to overcome the difficulties of lubrication known until then. However, in practice, it is generally found that, to achieve the expected levels of performance and reliability, the use of lubrication with conventional lubricants used for steel / ruby exhausts is also necessary with a silicon exhaust.

This is all the more constraining as the parts produced in Silicon are more fragile than the steel parts, and the current industrial epilamization processes are not applicable to silicon parts. Indeed, the use of bulk epilamization treatment inevitably damage the silicon parts given the fragility of silicon. Room-to-room epilamization would be tedious, expensive and inefficient.

Similarly, the realization of a bevel like steel parts to form a reservoir, complicates and increases the manufacturing costs of silicon parts.

Watchmakers also explored the use of lithography techniques known as LIGA to make the anchor and escape wheel. These techniques make it possible to reproduce given forms with great precision. The parts are made of nickel or nickel alloy, in particular NiP, by growth in structures defined by lithography.

In spite of the complex shapes that the LIGA makes it possible to obtain favoring a geometrical optimization and more important theoretical performances, it is nevertheless still necessary to lubricate the surfaces of the contact bodies of the exhaust, with a step of epilamage and the application an oil of the prior art to achieve the expected performance and ensure reliability of the exhaust.

State of the art

The document EP2120105 discloses a lubrication solution of a micromechanical part, in particular a silicon escape wheel, the lubricant being a grease. A hydrophilic epilame coating is interposed between the workpiece and the lubricant to retain the lubricant in the friction zone.

This teaching therefore induces the difficulty of epilating the parts of the exhaust, including for silicon parts, which remains a disadvantage in terms of industrialization.

The present invention aims to provide a method of lubricating an exhaust, at least partially overcoming the aforementioned drawbacks.

Disclosure of the invention

More specifically, the invention relates to a lubrication process as proposed in the claims.

Brief description of the drawings

• la figure 1 représente des essais comparatifs de performance pour trois mouvements d'un premier calibre, avec différentes configurations de lubrifications, après 24h de rodage,
• les figures 2a et 2b montrent respectivement, en termes d'amplitude et de rendement, des mesures effectuées pour 10 mouvements d'un second calibre et trois lubrifiants,
• les figures 3a, 3b et 3c montrent des comparaisons d'amplitude, tandis que les figures 4a, 4b et 4c montrent des comparaisons de rendement, pour 3 lubrifiants, par rapport à un lubrifiant A de référence ; les mesures sont effectuées sur des jeux de mouvements d'un troisième calibre,
• la figure 5 montre une comparaison des rendements de l'échappement pour des lubrifiants selon l'invention, obtenus avec différentes huiles de base.

Other details of the invention will emerge more clearly on reading the description which follows, made with reference to the appended drawing, in which:

• the figure 1 represents comparative performance tests for three movements of a first caliber, with different lubrication configurations, after 24 hours of break-in,
• the Figures 2a and 2b show respectively, in terms of amplitude and efficiency, measurements made for 10 movements of a second gauge and three lubricants,
• the Figures 3a, 3b and 3c show amplitude comparisons, while Figures 4a, 4b and 4c show performance comparisons, for 3 lubricants, with respect to a reference lubricant A; the measurements are made on movements of a third caliber,
• the figure 5 shows a comparison of the exhaust yields for lubricants according to the invention, obtained with different base oils.

Embodiment of the invention

• le rendement des échappements,
• la stabilité dans le temps des lubrifiants, tant en termes de performance qu'en terme de composition (stabilité chimique),
• leur mise en oeuvre pour faciliter l'industrialisation de l'étape de lubrification.

As explained in detail in the introduction of the present application, the issue of lubrication of exhaust mechanisms is a constant research topic for watchmakers, with the aim of improving:

• exhaust performance,
• the stability over time of the lubricants, both in terms of performance and in terms of composition (chemical stability),
• their implementation to facilitate the industrialization of the lubrication stage.

The Applicant has identified after many researches, particularly interesting effects in the use of specific lubricants, to lubricate an exhaust.

More particularly, the subject of the invention is a method of lubricating a watch exhaust mechanism comprising a mobile intended to receive a driving force and a stop member intended to cooperate with the engine. mobile to block or leave free rotation alternately. The mobile and the stop member respectively have first and second contact members for cooperating with each other. At least the first or second contact members are made of silicon, or based on nickel or a nickel alloy (especially NiP) by LIGA type technology.

Advantageously, the escape mechanism is a so-called Swiss anchor mechanism. The mobile is an escape wheel intended to be pivotally mounted and the stop member is an anchor also intended to pivot on its axis. The anchor is provided with an entry pallet and an output pallet, intended to cooperate with the toothing of the escape wheel. Pallets on the one hand, and the teeth of the escape wheel on the other hand, define contact members, since they are intended to interact with each other during the successive stages of the escape. This type of mechanism is well known and does not need to be described in detail.

Preferably, the anchor on the one hand, and the escape wheel on the other hand are made of a silicon-based part, optionally covered by a surface layer, for example oxide, natural or made by a step oxidation. The skilled person may also consider other coatings or surface treatments on the contact members.

We can also consider other configurations in which only one of the anchor or the escape wheel is silicon-based, or only the contact members are based on silicon.

Alternatively, the anchor on the one hand, and the escape wheel on the other hand are made of a piece based on nickel or a nickel alloy, obtained by LIGA type technology. The nickel or nickel alloy used may also contain additives of the doping or solid lubricant type (hBN, talc, etc.). The skilled person may also consider other coatings or surface treatments on the contact members.

It is also possible to envisage other configurations in which only one of the anchor or escape wheel is nickel-based or a nickel alloy, or only the contact members are based on nickel or a nickel alloy.

According to the invention, the lubrication of the exhaust is characterized in that the process is characterized in that it comprises a step of applying a grease comprising PTFE-type particles (polytetrafluoroethylene) dispersed in a base oil, the PTFE feed being adjusted with respect to the specific surface of the particles so as to obtain a grease having a grade of between 3 and 1, preferably a grade 2 according to the NLGI scale (National Lubricating Grease Institute), given below .

Preferably, the base oil is PFPE (Perfluoropolyether) type. More preferably, the application step is carried out without an epilamation step.

The figure 1 shows amplitude measurements of the pendulum. These measurements were made on three watch movements of the same type, with a standard geometry of the anchor and the escape wheel. The graph represents the average values of the amplitude readings in 6 positions, at 0h of walking (maximum loaded barrel without sliding flange) after a running-in of 24 hours, measured for each movement. A line represents, for each lubricant, the average of the measurements of the three movements. Between each lubricant, the movements are disassembled and degreased, then lubricated with the next lubricant.

The reference measurement is a standard exhaust, with a steel escapement wheel (with beveled teeth) and ruby anchor pallets, epilamed and lubricated according to the methods of the state of the art. The following 7 measurements concern silicon escapements, with geometries identical to the standard reference exhaust but without bevel on the teeth of the escape wheel. 1 measures ^era corresponds to a dry run without lubrication. Measurement A corresponds to lubrication according to the state of the art, that is to say with epilamization and lubrication as in the reference exhaust.

Measurement B relates to the grease used according to the method of the invention. The measurements C to F concern different types of lubricants tested, with or without epilame, depending on the consistency and the flow of the grease.

It is found that the grease B makes it possible to obtain higher yields than the other solutions, with a significant improvement in the amplitude of the balance of 24 ° compared to the reference, and at least 22 ° compared to the alternatives tested. In addition, this level of performance is obtained without the application of epilame and with a geometry of the teeth of the simplified escape wheel (without bevel), which represents an industrial advantage.

On the figure 2 , the performance of other lubricants were studied on an escapement with an anchor and a NiP anchor wheel whose teeth are not beveled. 10 movements of a second caliber (different from that used on the figure 1 ) were used for the measurements. The graph represents the average values of amplitude readings ( Fig. 2a ) in 6 positions, at 0h of walking (barrel loaded to the maximum off slippery flange) after a running-in of 24 hours, and the yields ( Fig. 2b ) measured for each movement, in low horizontal position. A line represents, for each lubricant, the average of the measurements of the different movements. Between each lubricant, the movements are disassembled and degreased, then lubricated with the next lubricant. Lubricant A is a reference lubricant of the state of the art, B is the lubricant according to the invention and C is another lubricant tested.

There is an amplitude gain of 25 ° and a gain of 9 points of yield in the horizontal position, for the grease according to the invention compared to the reference.

On the figure 3 other lubricants have been studied on an escapement with an anchor and a NiP anchor wheel whose teeth are not beveled, on series of movements of a same caliber of a second type. The graph represents the average values of the amplitude readings in 6 positions, at 0h of walking (barrel loaded to the maximum off slippery flange) after a running-in of 24 hours. A line represents, for each lubricant, the average of the measurements of the different movements. For each comparison, the measurements are carried out on different batches, that is why the results are presented 2 to 2 and not all on the same graph. The lubricant A is a reference lubricant of the state of the art known for its performance, B is the lubricant according to the invention and G and H are other lubricants tested.

An amplitude gain of 16 ° was found for the grease according to the invention relative to the reference, which is a significant improvement over the amplitudes obtained with G and H.

On the figure 4 , are represented the yields corresponding to the amplitudes measured at the figure 3 .

A gain of 6 points is found, or 14% for the fat according to the invention compared to the reference, which is a significant improvement over the yields obtained with G and H.

The improvements obtained are considerable (between 6 and 9 points of performance) compared to the generally low optimizations, which are of the order of those obtained with the other lubricants tested (between 0 frequently and 3 points for a single lubricant).

In terms of composition, different fats from the above family have been tested, with comparable results. Thus, the base oil (PFPE) may have a viscosity measured at 40 ° C between 5 and 330 cSt, preferably between 10 and 310 cSt. The PTFE particles dispersed in the base oil are micron to submicron and the density can be adjusted by those skilled in the art, so as to obtain a fat which ultimately has a grade of between 3 and 1, preferably In practice, the PTFE load is adjusted to the specific surface area of the particles according to the target grade. Typically, the particles have a size between 50 nm and 10 microns. Preferably, the particle size is between 1 .mu.m and 7 .mu.m. These particles form agglomerates whose size is less than 150 microns. As the lubricant interacts with the contact surfaces of the exhaust, the aggregates are broken and the particles are redistributed to other aggregates.

This grade corresponds to a quite consistent fat, qualified according to the table NLGI (National Lubricating Grease Institute) below. NLGI consistency index ASTM worked (60 cycles): penetration at 25 ° C in tenths of a millimeter Appearance of lubricating grease Consistency of the analogue food product 000 445-475 Very fluid Ketchup 00 400-430 Fluid Applesauce 0 355-385 Semi-fluid Mustard 1 310-340 Very soft Double concentrated tomatoes 2 265-295 Soft Peanut butter 3 220-250 Semi-hard Margarine 4 175-205 Tough Frozen yogurt 5 130-160 Very hard Fudge 6 85-115 Extremely hard Cheddar cheese

This type of grease can be deposited using a spade-oil, usually used, or with other equipment or automatic or semi-automatic dispensers, allowing at least partial automation of the dispensing of lubricant on the functional surfaces of the contact members.

Obtaining this level of performance for a fat of this consistency is particularly surprising. Indeed, with regard to the relative speed of movement of the contact members, the use of a grease is a priori not indicated, because its response to a shear stress, as experienced during a contact with the exhaust, is not fast enough. However, it has been found that the mechanical strength of this type of fat falls abruptly when subjected to shear stress, in other words, it becomes rapidly fluid during friction during operation. On the other hand, the flow threshold also returning quickly to its normal level after the end of the application of a mechanical stress, the fat remains advantageously in place on the contact members, despite the absence of epilame.

• stabilité chimique : afin de ne pas se dégrader dans le temps ;
• maintien dans les zones de contact : afin de ne pas être dispersé en cas de choc ou lors du fonctionnement du mécanisme et venir souiller le mouvement ;
• maintien de la performance mécanique : la répétition des sollicitations ne doit pas avoir d'incidence (aussi faible que possible) sur le comportement du lubrifiant.

In the context of a traditional escapement, in particular with Swiss anchor, with interactions between ruby pallets and a steel escapement wheel, the grease according to the invention has significant advantages. In terms of performance, these are improved by a few points compared to a reference exhaust. However, it can be noted that traditional escapements have been optimized in a very important way as the historical evolutions. In addition, the lubricant according to the invention makes it possible to simplify the geometries and therefore the industrial process. In addition, the durability of the lubricant according to the invention is improved according to the following criteria:

• chemical stability: so as not to degrade over time;
• maintenance in the contact areas: in order not to be dispersed in the event of shock or during the operation of the mechanism and to contaminate the movement;
• maintenance of the mechanical performance: the repetition of the stresses must not have an impact (as low as possible) on the behavior of the lubricant.

Thus, even for an escapement with ruby / steel interactions, the lubricant according to the invention has advantageous effects.

Other base oils can be envisaged. For better compatibility with PTFE particles, a synthetic base oil, and without metallic soap, will be preferred in the grease composition. Indeed, a grease comprising a metal soap can generally not contain more than 10% by weight of PTFE. However, preferably, the advantageous performance of the grease is obtained with contents (mass percentage) of PTFE between 10 and 55%.

As shown on the figure 5 , good performance improvement results were obtained with an ester base oil, with 4-point efficiency improvements over traditional lubrication as a reference. More particularly, di-ester or polyol-ester esters are indicated.

Good results were also obtained with a PAO (Polyalphaolefin) type base oil, with 6-point efficiency improvements over traditional lubrication. On this batch of movements, a base oil of type PFPE makes it possible to obtain an improvement of 8 points compared to the reference.

Various base oils can be blended, especially ester base oils and PAO base oils.

It is these associations between PTFE particles and a base oil, with a viscosity measured at 40 ° C between 5 and 330 cSt, preferably between 10 and 310 cSt, to incorporate these PTFE particles to achieve a grade. NLGI between 1 and 3, which give surprising and advantageous performance, within the framework of a watch exhaust. Thus is proposed a method of lubricating an exhaust, for lubricating an exhaust whose main parts, namely the escape wheel and the anchor can be made of silicon or silicon-based, while improving the efficiency by compared to a standard exhaust or Silicon exhaust or made by conventionally lubricated LIGA. In addition, the identified grease family makes it possible to do without epilame and thus simplifies the process and increases the industrial performance.

Claims (18)

A method of lubricating a clockwork escapement mechanism comprising a mobile intended to receive a driving force and a stop member intended to cooperate with the mobile to block or free its rotation alternately, said mobile and said body of stop respectively having first and second contact members for cooperating with each other,
the method is characterized in that it comprises a step of applying a grease to at least one of the first and second contact members, said grease comprising PTFE-type particles (polytetrafluoroethylene) dispersed in a base oil, the PTFE load being adjusted relative to the specific surface of the particles so as to obtain a grease having a grade of between 3 and 1, preferably a grade 3 or 2 according to the scale NLGI (National Lubricating Grease Institute). Lubrication process according to claim 1, characterized in that said base oil is a synthetic oil and in that said grease contains no metallic soap. Lubrication process according to one of claims 1 and 2, characterized in that said grease comprises between 10 and 55% (mass percentage) of PTFE. Lubrication process according to one of claims 1 to 3, characterized in that said base oil is PFPE type (Perfluoropolyether). Lubrication process according to one of claims 1 to 3, characterized in that said base oil is of ester type. Lubrication process according to one of claims 1 to 3, characterized in that said base oil is of PAO (Polyalphaolefine) type. Lubrication process according to one of claims 1 to 3, characterized in that said base oil is a mixture comprising ester base oils and PAO base oils. Lubrication method according to one of the preceding claims, characterized in that said base oil has a viscosity measured at 40 ° C between 5 and 330 cSt, preferably between 10 and 310 cSt. Lubrication process according to one of the preceding claims, characterized in that the PTFE particles have a size between 50 nm and 10 μm, preferably between 1 μm and 7 μm, forming agglomerates whose size is less than 150. .mu.m. Method according to one of the preceding claims, characterized in that said applying step is carried out without an epilamation step. Lubrication process according to one of the preceding claims, characterized in that the mobile is an escape wheel intended to be rotatably mounted and the stop member is an anchor also intended to pivot on its axis. Lubrication process according to claim 11, characterized in that the anchor is provided with an inlet pallet and an outlet pallet for cooperating with a toothing that includes the escape wheel. Lubrication method according to one of the preceding claims, characterized in that at least the first or second contact members are made from nickel or a nickel alloy. Lubrication method according to claim 11 or claim 12, and according to claim 13, characterized in that one and / or the other of the anchor and the escape wheel are made in one piece from nickel or a nickel alloy. A lubricating method as claimed in claim 12, characterized in that the contact members of the stopper member are made of ruby and that the contact of the movable members are made of steel. Lubrication process according to one of claims 1 to 12, characterized in that at least the first or second contact members being made of silicon. Lubrication method according to claim 11 or claim 12, and according to claim 16, characterized in that one and / or the other of the anchor and the escape wheel are made of a piece based on of silicon. Lubrication method according to one of the preceding claims, characterized in that the grease is applied by means of a spade oil or a semi-automatic or automatic dispenser.

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