FUNCTIONAL MECHANICAL PART MADE OF POLYETHYLENE FURANOATE

Description

Technical field of the invention

[0001] The present invention relates to a mechanical part of a watch movement comprising a functional surface intended in use to come into contact by friction with another functional surface. Technological background

[0002] In the 1970s, Tissot introduced the Astrolon, the first plastic watch with internal movement components, notably a Swiss lever escapement made of polymer. The initial specifications for this watch were simple: Reduce the number of movement components, eliminate lubrication, improve the production process.

[0003] The manufacturing process is injection molding, and the polymers, due to their properties, will meet these needs and produce this watch. Document CH 334708 describes the injection molding process and the selected material, which is polyamide 66 (PA66).

[0004] In the 2000s, Swatch introduced the Sistem51, which is based on essentially the same specifications. The injection molding process remains the same, but the polymer selected is polyoxymethylene (POM). Very fine lubrication of the escapement allows the movement to achieve the required performance.

[0005] To date, improvements in tribological performance are still being sought. Furthermore, these polymer materials, such as POM, known for their tribological performance, have the disadvantage of being petroleum-based and difficult to recycle. Summary of the invention

[0006] The present invention aims to find a polymer material exhibiting improved tribological performance compared to POM.

[0007] The present invention also aims to find a bio-based alternative, i.e. of non-petroleum origin, to the materials commonly used for a tribological application.

[0008] To this end, numerous tests have highlighted a polymer which is ethylene polyfuranoate (PEF).

[0009] More specifically, the present invention relates to a mechanical part comprising a functional surface intended to come into contact by friction with another functional surface, said at least functional surface of the mechanical part being made of ethylene polyfuranoate (PEF).

[0010] PEF has mechanical properties similar to POM and is injectable like the latter, but with the added benefits of being bio-based and recyclable. Tribological tests have shown that using PEF polymer for watch parts, among other applications, improves performance in lubricated contact, with a reduction in the average dynamic coefficient of friction compared to POM, without altering contact wear.

[0011] Another aspect of the invention relates to a functional assembly comprising the mechanical part as described above and another mechanical part comprising a functional surface intended to be in contact by friction with the functional surface of said mechanical part, said assembly being characterized in that at least the functional surface of the other part is made of a material chosen from ethylene polyfuranoate, ruby ​​and steel.

[0012] Other features and advantages of the invention will become apparent from the detailed description that follows, with reference to the attached drawings. Brief description of the figures

[0013] There figure 1 represents the curves of the average dynamic friction coefficient as a function of load for the PEF / PEF and POM / POM pairs. figure 2 represents the curves of the average dynamic friction coefficient as a function of load for the PEF / PEF pair, the PEF / ruby pair, and the PEF / steel pair. figure 3 partially represents a functional assembly comprising two parts, namely an escape wheel and an anchor pallet with a wheel made of PEF according to the invention. Detailed description of the invention

[0014] The present invention relates to a mechanical part of a watch movement, subjected on one or more of its so-called functional or contact surfaces to friction with one or more functional surfaces of another part or of the same part. The mechanical part can be used in any system where friction is a concern. According to the invention as defined by the attached claims, it is a mechanical part of a watch movement. Examples of such parts include a pallet, an escape wheel, a pivot of a moving part, a bearing, a mainspring, or gear teeth. This part may be in contact with another part. For example, in the watchmaking field, the functional assembly 1 visible in the figure 3It may comprise a first part 2, which is a pallet 4 of an anchor 5, and a second part 3, which is an escape wheel 6. More specifically, the pallet 4 has a rest plane A and an impulse plane B that cooperate with the rest plane C and impulse plane D of the tooth 7 of the escape wheel 6. These planes A, B, C, and D are highly stressed functional surfaces subject to high levels of friction and / or contact, requiring the use of special materials to reduce friction. Typically, at least the wheel is made of PEF to improve tribological performance. Alternatively, one functional surface of a part may be in contact with another functional surface of the same part. For example, this could be a barrel spring formed of a leaf with one face of the spring intended to be in contact with another face of the spring.

[0015] According to the invention, the mechanical part is at least partially made of ethylene polyfuranoate (PEF). Thus, at least the functional surface(s) are made of PEF. Preferably, the part is made entirely of PEF. Comparative tribological tests with POM were carried out, with the results presented at the figure 1The tests were performed with a lubricated contact using watch oil and a ball-on-plane tribometer in linear alternating mode with a 2 mm diameter ball. The ball and plane were made using PEF (Positive Element Pattern) for one pair and POM (Positive Element Pattern) for the other. The tests were carried out with a maximum sinusoidal velocity of 10 mm / s, an amplitude of 4 mm, and normal forces of 1, 5, 10, 25, 50, and 100 mN over a distance of 15 m. The loads were swept over a wide range to represent the various possible contacts in the movement, and in particular the evolution of the escapement contact during the different release and impulse phases.

[0016] It is observed that the coefficient of friction (CoF) of the PEF / PEF combination is at least equivalent to, if not lower than, that of the POM reference. As soon as the load is sufficient, the oil allows the CoF to be reduced to extremely low values, typically found in hydrodynamic friction. By using PEF, it is possible to lower the CoF even further, achieving values ​​below 0.05. Furthermore, with an improved coefficient of friction, no increase in wear is observed.

[0017] Maintaining the same test conditions, friction with other typical watchmaking antagonists, namely ruby ​​and steel, was evaluated using the ball made of these materials during the tests. The results are presented at the figure 2Compared to the PEF / PEF pair, the CoF is generally even lower because the elastic deformations of the opposing material are limited, thus reducing frictional stresses. The values ​​achieved are well below 0.05 across a fairly wide load range. The hardness of these opposing materials and the use of a high load do not damage the PEF, and no wear is visible.

[0018] In conclusion, the results of tribological tests carried out on parts made of PEF are at least as good as those carried out on parts made of POM.

Claims

1. Mechanical part (2, 3) of a horological movement, which part comprises a functional surface intended to come into frictional contact with another functional surface, characterised in that at least said functional surface of the mechanical part (2, 3) is made of polyethylene furanoate.

2. Mechanical part (2, 3) according to the preceding claim, characterised in that the entire mechanical part (2, 3) is made of polyethylene furanoate.

3. Mechanical part (2, 3) according to one of the preceding claims, characterised in that it is a mechanical part (2, 3) selected from a pallet (4), an escape wheel (6), an arbor of a wheel set, a bearing, a mainspring and toothings of gear wheels.

4. Functional assembly (1) comprising the mechanical part (2, 3) according to one of the preceding claims and another mechanical part comprising the other functional surface intended to be in frictional contact with the functional surface of said mechanical part (2, 3), characterised in that at least the other functional surface of the other mechanical part is made of a material selected from polyethylene furanoate, ruby and steel.

5. Functional assembly (1) according to the preceding claim, characterised in that the frictional contact is lubricated.

6. Functional assembly (1) according to the preceding claim, characterised in that the frictional contact is lubricated using an oil.