CH714549A2 - A method of lubricating a watch exhaust. - Google Patents

Abstract

The invention relates to 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 mobile to block or free its rotation alternately, said mobile and said stop member respectively having first and second contact members for cooperating with each other, at least the first or second contact members being made of silicon. According to the invention, the process is characterized in that it comprises a step of applying a grease comprising particles of PTFE type dispersed in a base oil of PFPE type, and said step of application being carried out without a step of épilamage.

Description

Description

Technical Field [0001] The present invention relates to the field of watchmaking, particularly mechanical watchmaking. It relates to a method of lubricating an exhaust.

[0002] In the field of mechanical watches, the escapement makes it possible to regulate the supply of energy supplied by the barrel and to maintain the oscillations of the regulating member.

The most common mechanisms are said to be Swiss anchors and interact with a pivotally mounted anchor, in particular with an escape wheel which the anchor alternately blocks by an input pallet and by an output pallet, that it contains.

Traditionally, the pallets are made of ruby, while the escape wheel is made of steel. Optimizing the tribological conditions between the pallets of the anchor and the escapement wheel leads to lubricating the contact areas with each other so as to reduce energy losses by friction and increase the efficiency of energy transmission.

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

The lubricants meeting these specifications are generally fairly fluid. To be effective, it is imperative to keep the lubricant used in the contact area sufficient without hampering the movement of the moving components. It must also remain in place during the operation of the escapement and in the event of impact so as not to weaken the contact and contaminate the components inside the movement. This is achieved by the application of an epilame which contributes to the general and global complexity of the lubrication of an exhaust. Indeed, the epilame forms a film on the surface of the lipophobic type pallets. The exhaust should be operated dry so that the contact of the toothing of the escapement wheel is free of epilame, so as to form a trench, in which the oil will then be applied and contained , due to the lipophobic properties of the epilam.

In order to constitute a lubricant reservoir enabling the contact to be supplied and the contact surfaces to be reduced, the teeth constituting the escapement 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, antimagnetic properties and improved performance of the exhaust by its low density. Quite quickly, the use of SiO2 obtained by thermal oxidation or diamond obtained by CVD deposition became necessary to improve the mechanical strength and the tribological properties. Watchmakers have long argued that the silicon components thus coated would overcome the lubrication difficulties previously known. However, in practice, it is generally observed that, in order to obtain the expected performance levels, the use of lubrication with traditional lubricants used for steel / ruby escapements is also necessary with a silicon escapement.

This is all the more restrictive since the parts produced in Silicon are more fragile than the Steel parts, and that the current industrial epilamage processes are not applicable to the silicon parts. Indeed, the use of a bulk epilamation treatment would inevitably damage the silicon parts, given the brittleness of the silicon. Piece-by-piece epilameting would be tedious, expensive and ineffective.

Similarly the production of a bevel like steel parts to form a reservoir, complicates and increases the costs of manufacturing parts in Silicon.

State of the art Document EP 2 120 105 discloses a lubrication solution for a micromechanical part, in particular a silicon escapement wheel, the lubricant possibly being a grease. A hydrophilic coating acting as an epilam is interposed between the part 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 the silicon parts, which remains a drawback 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 [0014] More specifically, the invention relates to a lubrication process as proposed in the claims.

CH 714 549 A2

Brief description of the drawings [0015] Other details of the invention will appear more clearly on reading the description which follows, made with reference to FIG. 1 appended representing comparative performance tests for three movements of the same caliber, with different lubrication configurations, after 24 hours of running-in.

Embodiment of the invention As explained in detail in the introduction to the present application, the question of the lubrication of the exhaust mechanisms is a subject of permanent research for watchmakers, with the aim of improving:

- the exhaust efficiency,

- 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 step.

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

More particularly, the object of the invention is a method of lubricating a watch escapement mechanism comprising a mobile intended to receive a driving force and a stop member intended to cooperate with the mobile to block or alternately allow free rotation. The mobile and the stop member respectively have first and second contact members intended to cooperate with each other. At least the first or the second contact members are made from silicon.

Advantageously, the escapement 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 input pallet and an output pallet, intended to cooperate with the toothing of the escapement wheel. The paddles on the one hand, and the teeth of the escapement wheel on the other hand, define contact members, since they are intended to interact with each other, during the successive stages of the escapement. 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 in one piece, that is to say a one-piece piece, based on silicon, possibly covered by a surface layer, for example of oxide, natural or produced by an oxidation step. The anchor and / or the wheel can be multi-stage, produced in a monolithic manner by assembling several elements. A person skilled in the art can also envisage other coatings or surface treatments on the contact members.

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

According to the invention, the lubrication of the exhaust is characterized in that it comprises a step of applying a grease comprising particles of the PTFE type (polytetrafluoroethylene) dispersed in a base oil of the PFPE type ( Perfluoropolyether), and said application step being carried out without performing epilamage.

[0023] FIG. 1 shows the amplitude measurements of the pendulum. These measurements were taken on three watch movements of the same caliber, with standard geometry of the anchor and the escapement wheel. The graph represents the average values of the amplitude readings in 6 positions, at Oh of operation (barrel loaded to the maximum except sliding sling) after a break-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 dismantled and degreased, then lubricated with the following lubricant.

The reference measurement is a standard exhaust, with a steel escape wheel (with bevelled teeth) and ruby anchor paddles, epilamated and lubricated according to the methods of the prior art. The following 7 measurements relate to silicon escapements, with geometries identical to the standard reference exhaust, but without a bevel on the teeth of the escapement wheel. The 1st measurement corresponds to dry running, without lubrication. Measurement A corresponds to lubrication according to the state of the art, that is to say with epilamage and lubrication as in the reference exhaust.

Measure B relates to the fat used according to the method of the invention. Measures C to F relate to different types of lubricants tested, with or without epilam, depending on the consistency and flow of the grease.

It can be seen that the grease B makes it possible to obtain higher yields than the other solutions, with a significant improvement 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 an epilame, and with a simplified geometry of the escapement wheel teeth (without bevel), which represents an industrial advantage.

In terms of composition, different fats from the above family have been tested, with comparable results. Thus, the base oil (PFPE) can have a viscosity measured at 40 ° C, between 15 and 330 cSt, preferably between 18 and 310cSt. The PTFE particles dispersed in the base oil are substantially submicron and the density can be adjusted by a person skilled in the art, so as to obtain a grease which, in the end, has a grade between 3 and 1, preferably a grade 2. In practice, the PTFE load is adjusted in relation to the specific surface of the

CH 714 549 A2 particles depending on the grade targeted. Typically, the particles have a size between 20 nm and 1.2 μm. Advantageously, the size is between 50 nm and 1 μm.

This grade corresponds to a fairly viscous grease, qualified according to the NLGI (National Lubricating Grease Institute) table below.

NLGI consistency numbers

ASTM worked (SO strokes)

NLGI number penetration at 25 ⁼ C tenths of a millimeter Appearance Consistency food analog ooo 445-475 'luid cooking oil 00 400-430 semi-'luid sauce sauce 0 3OO-3 & O very self brown riustard 1 310-340 ground tonato paste 7 265-295 normal grease peanut butter 220-250 ΊΓΓΊ vegetable shortening 4 175-205 very ίγπ Tozen vogurt 130-160 hard snooth paté 6 65-115 verv hard cheddar cheese

This type of grease can be deposited using an oil pick, usually used, or using other equipment or dispensers allowing at least partial automation of the dispensing of the lubricant on the functional surfaces contact bodies.

Obtaining this level of performance for a grease of this viscosity is particularly surprising. Indeed, having regard to the relative displacement speeds of the contact members, the use of a grease is not a priori indicated, since its response to a shear stress, as undergone during a contact with the exhaust is not fast enough.

However, it has been found that the mechanical resistance of this type of grease drops suddenly when it is subjected to a shear stress, in other words, it quickly fluidizes during friction experienced during operation. On the other hand, the flow threshold also quickly returning to its normal level after the end of the application of mechanical stress, the grease advantageously remains in place on the contact members, despite the absence of epilame. Thus, a method of lubricating an exhaust is proposed, making it possible to lubricate an exhaust, the main parts of which, namely the escapement wheel and the anchor, can be made of silicon or based on silicon, while improving the efficiency compared to a standard exhaust or a conventionally lubricated silicon exhaust. In addition, the family of greases identified makes it possible to dispense with epilam and therefore makes it possible to simplify the process and increase industrial performance.

Claims (8)

claims 1. Method of lubricating a timepiece escapement mechanism comprising a mobile intended to receive a motive force and a stop member intended to cooperate with the mobile to block or allow its rotation to alternate, said mobile and said member stop having respectively first and second contact members intended to cooperate with each other, at least the first or the second contact members being made from silicon, the method is characterized in that it comprises a step applying a grease comprising particles of the PTFE type dispersed in a base oil of the PFPE type, and the said application step being carried out without the epilamation step. 2. Lubrication method according to claim 1, characterized in that said grease has a grade between 3 and 1, preferably a grade 2 according to the NLGI scale (National Lubricating Grease Institute). 3. Lubrication method according to one of claims 1 and 2, characterized in that said base oil has a viscosity measured at 40 ° C between 15 and 330 cSt, preferably between 18 and 310 cSt. 4. Lubrication method according to one of the preceding claims, characterized in that the PTFE particles have a size between 20 nm and 1.2 μm. preferably between 50nm and 1 μm. CH 714 549 A2 5. Lubrication method according to one of the preceding claims, characterized in that the grease is applied using an oil pick or an automatic dispenser. 6. Lubrication method according to one of the preceding claims, characterized in that the mobile is an escapement wheel intended to be mounted mobile in rotation and the stop member is an anchor also intended to pivot on its axis. 7. Lubrication method according to claim 6, characterized in that the anchor is provided with an inlet pallet and an outlet pallet, intended to cooperate with a toothing which comprises the escapement wheel. 8. Lubrication method according to claim 7, characterized in that one and / or the other of the anchor and the escapement wheel are made in one piece based on silicon. CH 714 549 A2 Comparison »» of average amplifiers ó pos. to Oh for caliber X