Threaded watch components

Abstract

The present invention relates to a watch component, which comprises a first axis and a first threaded portion for cooperating with a second threaded portion provided on a second watch component. The first threaded portion is configured such that a contact area between the first threaded portion and the second threaded portion extends to a range of less than 50% of a thread height of the second threaded portion, or is configured such that a contact area between the first threaded portion and the second threaded portion extends to a range of less than 0.3 times a pitch of the threaded portion.

Description

Technical Field

[0001] The present invention relates to a threaded component for a timepiece, a timepiece case comprising the threaded component, and a timepiece comprising the threaded component and / or the timepiece case. Background Art

[0002] The watch closure is subject to numerous restrictions, in particular with regard to sealing, robustness, appearance and must be carried out in a manner that prevents any irreparable accidental disassembly reflected in after-sales service for replacement of seals, cleaning, lubrication or repairs.

[0003] For parts with fragile mechanical properties (e.g. made of ceramic (zirconia, alumina, composite materials, etc.), glass, sapphire, etc.) that need to provide sealing and / or enable assembly and disassembly, such as bottom covers or bracelet links, traditional assembly methods are not applicable.

[0004] In fact, brittle materials such as ceramics, glass, sapphire, etc. have very good compressive strength but poor tensile strength. This is why thread systems of brittle materials are not suitable for components that are subject to higher tensile loads. For example, if the tightening torque is too high, tensile and / or shear stresses will be generated in the threads, causing them to crack or even break.

[0005] Their use is therefore essentially limited to fields with limited mechanical stresses that exploit other properties of ceramics (chemical resistance, resistance to extreme temperatures, non-magnetic properties, biocompatibility, etc.).

[0006] The case of a known watch comprises one or more closing elements made of natural or synthetic hard mineral materials (e.g. sapphire, ceramics, natural or reconstructed gemstones, etc.). These materials are not ductile and have only a limited ability to absorb shocks by deformation. This means that they have a lower tensile stress resistance than metal parts with the same geometry. In general, this lower tensile stress resistance does not match the stresses to which the parts are subjected (assembly, high pressure, etc.).

[0007] The metal back cover is conventionally assembled to the metal intermediate part by means of a screw connection, as described in particular in documents CH 1359773 and CH 486059. The threads are standard and the internal and external threads conform to the same standards with the maximum possible thread contact area.

[0008] To ensure a secure fit and to minimize the risk of seizure, the metal bottom cover assembled with the metal middle piece is usually lubricated and tightened to a torque of 1 to 6 N.m (inclusive). This type of bottom cover may also be required to withstand high pressures, particularly during diving.

[0009] To ensure that the same assembly / disassembly tools can be used as for metal bottom covers, the threads of the fragile material bottom cover must be able to resist the same tightening torque, ie 1 to 6 N.m. It should also withstand high pressures depending on the degree of tightness envisaged (e.g. 50m, 100m, 1220m or 3900m sealing).

[0010] If ceramic threads were manufactured according to the same conventional standards, the tensile stresses generated by tightening and / or high pressure would exceed the strength of the ceramic, resulting in irreversible deformation, cracking or even breakage, particularly at the level of the thread.

[0011] Also known is a self-locking thread assembly system, as described in document WO2013 / 072389, whose nominal diameter is less than 1.5 mm and whose threaded elements are characterized by a second thread with an asymmetrical pitch in longitudinal section. This assembly corresponds in particular to the Swiss Watch Industry Standard (NIHS) and to the internal standards of watchmakers. The continuous contact between the assembly elements allows the tensile forces to be distributed over the entire length of the threads of the threaded parts in contact and thus reduces fatigue in the nut-screw system.

[0012] In order to ensure that the two (internal and external) parts of a threaded assembly fit correctly and withstand specific loads, the threads must meet specific standards. Threads are defined by their profile, including the diameter of the parts (outer diameter, inner diameter, etc.), the thread angle, the pitch and, where appropriate, the helix angle.

[0013] Various standards define the shape of the thread, in particular the angle of the thread profile, the pitch and the diameter of the thread, such as NIHS 60-30, ISO (e.g., EN 10226-1 or ISO 261), UN (e.g., ASME B1.1), Whitworth, British Standard (BSPT), American National Standard, Pipe Thread Standard, NPT, NPTF, DIN 405, MJ, UNJ, etc.

[0014] The complete specification gives the values ​​corresponding to the form and tolerances of the thread.

[0015] For example, the cross-section of threads with NIHS, ISO and UN thread profiles resembles an equilateral triangle, i.e., the thread flanks form an angle of 60 degrees (the angle between the flanks). In a Whitworth thread, the thread flanks form an angle of 55 degrees.

[0016] Ceramic components are often assembled to metal components by methods other than making threads in the ceramic, or by integrating metal threaded bushings into the ceramic component to make screw tightening reliable.

[0017] Document EP0520224 describes a watch case comprising a metal middle piece and a ceramic bottom cover. The ceramic bottom cover is fixed to the middle piece by screws which pass through the bottom cover and are screwed into threads formed in the middle piece.

[0018] Document EP1916576 describes a watch case comprising a metal middle part and a ceramic bottom cover. The ceramic bottom cover is held on the middle part by a metal threaded clamping ring.

[0019] Document EP3276432 describes an assembly suitable for fixing a bottom cover made of ceramic or sapphire to a ceramic or metal middle piece, in particular a gold middle piece. It discloses that the extremely low ductility of ceramic materials does not allow conventional fixing methods, in particular direct threaded connections, according to those skilled in the art. In order to solve this problem, the document proposes a bayonet-type connection of a specific geometry that compresses the ring. The choice of the material of the ring determines the maximum tightening torque. For example, an amorphous alloy ring allows a tightening torque of about 3.2 Nm, which is similar to the tightening torque commonly used for threading the bottom cover to the middle piece for a seal of the same size.

[0020] Apple Inc. provides a watch with a housing (eg, made of aluminum) and a cover (carrying the biosensor) made of ceramic, sapphire or tempered glass (ion-x glass). The cover is "sandwiched" and held by a PTFE seal.

[0021] Furthermore, assembly systems using threads (or threaded connections), also known as "thread systems", are generally used to secure at least two components to each other. Such thread systems are suitable for providing a permanent assembly throughout their working life. Their advantages derive in particular from their simplicity (the assembly element forms part of the component to be assembled), their ability to be disassembled and the applications obtained.

[0022] In general, a thread system comprises a first threaded element, for example in the form of a screw, and a second threaded element, for example in the form of a nut, and mounting it comprises combining the screw with the nut by applying a tightening torque during a threading operation. Tightening the nut on the screw causes the parts to be assembled to be compressed. The screw is thus prestressed. The axial force to which it is subjected is called tension. During the threading, a tightening torque is applied to the screw to cause it to spiral in the nut and to force the screw to lengthen and thus stretch it when the parts come into contact. In this threading method, the tension generated by tightening the nut on the screw is therefore associated with the torque applied to the nut. The relationship between tension and torque is associated with a variety of parameters.

[0023] The elements of the threaded system are therefore subjected to different types of mechanical stresses, such as tension, compression, shear and the like. Summary of the invention

[0024] The object of the present invention is to provide a threaded timepiece component that improves upon known prior art components and solves the above-mentioned drawbacks. In particular, the present invention proposes a reliable threaded timepiece component made of a brittle material.

[0025] The invention enables a simple replacement of a metal component by a ceramic component without changing the design of the second component to be matched with the ceramic component. It also enables the retention of the same assembly / disassembly tools as those developed for assembling metal components.

[0026] In a first aspect, the present invention provides a timepiece component comprising a first axis and a first threaded portion, the first threaded portion having a pitch and being used to cooperate with a second threaded portion provided on a second timepiece component, the first threaded portion being constructed so that a contact area between the first threaded portion and the second threaded portion extends over a range less than 50% of a thread height of the second threaded portion, or being constructed so that a contact area between the first threaded portion and the second threaded portion extends over a range less than 0.3 times the pitch, and the extension of the contact area is measured radially relative to the first axis from the thread bottom of the first thread.

[0027] In one embodiment of the first aspect, the first thread portion has a first thread angle, wherein the second thread portion has a second thread angle, and wherein a value of the first thread angle is 2 to 4 degrees greater than a value of the second thread angle.

[0028] In another embodiment of the first aspect, the thread height of the first thread portion is less than 0.3 thread pitches.

[0029] In another embodiment of the first aspect, a thread root radius of the first thread portion is greater than 0.2 times the thread pitch of the first thread portion or greater than 0.4 times the thread pitch of the first thread portion.

[0030] In yet another embodiment of the first aspect, the first threaded portion is connected to the bearing surface via a connecting fillet, and a radius of the connecting fillet is greater than 0.4 times the pitch of the first threaded portion or greater than 0.8 times the pitch of the first threaded portion.

[0031] In another embodiment of the first aspect, the second threaded portion is a conventional thread.

[0032] In another embodiment of the first aspect, the second threaded portion is a thread that complies with ISO standards, NIHS standards, UN standards, BSPT standards, NPT standards, NPTF standards, DIN standards, MJ standards, UNJ standards, or is based on a Whitworth profile.

[0033] In yet another embodiment of the first aspect, the timepiece component is made of a brittle material, or the timepiece component is mainly made of metal or a metal alloy and the first threaded portion has a surface consisting of a coating of a brittle material.

[0034] In another embodiment of the first aspect, the timepiece component is made of ceramic or sapphire or zirconium oxide or glass. .

[0035] In yet another embodiment of the first aspect, the timepiece component is mainly made of metal or metal alloy and the first threaded portion has a surface consisting of a ceramic coating.

[0036] In another embodiment of the first aspect, the watch component is a bottom cover and the second watch component is a middle piece or an inner middle piece; or the watch component is a middle piece or an inner middle piece and the second watch component is a bottom cover; or the watch component is a middle piece and the second watch component is an inner middle piece; or the watch component is an inner middle piece and the second watch component is a middle piece; or the watch component is a crown and the second watch component is a crown tube; or the watch component is a crown tube and the second watch component is a crown; or the watch component is a crown and the second watch component is a crown cover; or the watch component is a valve tube and the second watch component is a valve; or the watch component is a corrector tube and the second watch component is a corrector; or the watch component is a cover and the second watch component is a crown or a crown tube or a center minute wheel; or the watch component is a screw and the second watch component is a bracelet link.

[0037] In a second aspect, the present invention provides a housing for a timepiece, comprising the timepiece component according to the first aspect and the second timepiece component.

[0038] In one embodiment of the second aspect, a case for a timepiece includes a middle piece and a bottom cover, wherein the bottom cover is the timepiece component described in the first aspect, and the middle piece is the second timepiece component.

[0039] In one embodiment of the second aspect, the intermediate piece is a metal intermediate piece.

[0040] In another embodiment of the second aspect, a case for a timepiece comprises a bottom cover and a middle piece, wherein the middle piece is the timepiece component described in the first aspect, and the bottom cover is the second timepiece component.

[0041] In one embodiment of the second aspect, the bottom cover is a metal bottom cover.

[0042] In a third aspect, the present invention provides a timepiece, comprising the timepiece component according to the first aspect and / or the case for a timepiece according to the second aspect.

[0043] In one embodiment of the third aspect, the timepiece is a watch.

[0044] In another embodiment of the third aspect, the timepiece is a watch. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings show, by way of example, one embodiment of a timepiece.

[0046] Figure 1 A first embodiment of the timepiece is shown.

[0047] Figure 2 shows the maximum stress in the bottom cover (S 1max ) is evolved according to the tooth bottom radius (R) of the threaded portion of the bottom cap for different angles of the threaded portion of the bottom cap.

[0048] Figure 3 shows the maximum stress in the bottom cover (S 1max ) Evolution according to the root radius (R) of the threaded portion of the bottom cap for different components with various characteristics in terms of the bottom cap thread angle and the intermediate piece thread. DETAILED DESCRIPTION

[0049] Reference below Figure 1 One embodiment of a timepiece 200 is described.

[0050] The timepiece 200 is, for example, a watch, in particular a wristwatch.

[0051] The timepiece 200 comprises a timepiece case 100. The timepiece case 100 is used to receive the movement, thereby protecting it from the external environment. The case is preferably sealed.

[0052] A watch movement can be an electronic movement or a mechanical movement, especially an automatic movement.

[0053] The watch case comprises a first member 10 or first component and a second member 20 or second component for being screwed together. In other words, each of the two members comprises a thread and one of the two members is screwed into the other by the cooperation of the two threads. The two threads therefore have the same pitch and generally have the same dimensional characteristics so that they can cooperate with each other.

[0054] The first timepiece component 10 has a first axis A10 and comprises a first threaded portion 11 having a pitch p and intended to cooperate with a second threaded portion 21 provided on the second timepiece component 20. First threaded portion:

[0055] - is adapted or configured such that the contact area C between the first thread portion and the second thread portion extends over less than 50% of the thread height h of the second thread portion, or less than 30% of the thread height h of the second thread portion, or less than 15% of the thread height h of the second thread portion; or

[0056] - adapted or configured such that the contact area C between the first thread portion and the second thread portion extends over a range of less than 0.3 times the thread pitch p, or less than 0.2 times the thread pitch p, or less than 0.1 times the thread pitch p.

[0057] The extension e of the contact area C is measured radially from the thread root 15 of the first thread relative to the first axis A10 .

[0058] These geometrical features are preferably applied to all or nearly all or most of the threaded portions that make contact. In other words, these features are not only applicable at the level of the threaded connection interface portion between the first component and the second component.

[0059] Each threaded portion includes one or more threads and has an overall spiral shape around the axis A10. Each thread is a spiral portion whose length measured along the axis is equal to the pitch. The root 15 of the threaded portion is the junction between two flanks 16 of adjacent threads. The thread flank 16, i.e., the side of the thread corresponds to the portion located between the crest 14 and the root 15 of the thread. The crest 14 of the thread is the portion where two flanks 16 of the same thread join.

[0060] The first thread portion 11 preferably has a first thread angle 12, the second thread portion 21 preferably has a second thread angle 22, and the value of the first thread angle 12 is 2 to 4 degrees, which is greater than the value of the second thread angle 22. The thread angle is defined as the angle formed by two flanks of the thread at the same level of the axial section of the thread portion.

[0061] By adjusting the size of the threaded portion of the first component and / or the second component, it is possible to provide for the assembly of a first component of fragile material with a second component having a standard threaded portion.

[0062] While the threads of the prior art are designed to maximize the bearing surface of the two threaded parts so as to better distribute the forces at the level of the interface during assembly and thus make the thread flanks of the two components as parallel as possible, in this embodiment, as described above, one threaded part has an appropriate thread angle so that the flanks of the first threaded part of the first component are carried on or in contact with the flanks of the second threaded part of the second component at the level of a contact area extending as close as possible to the thread root of the first threaded part. The contact area preferably extends at most over a distance (measured radially relative to the axis A10) of less than h / 2 or less than h / 4 or less than h / 8, where h corresponds to the thread height of the first threaded part or the thread height of the second threaded part.

[0063] The difference in thread angle between the first thread portion and the second thread portion must not significantly affect the characteristics of the assembly, such as strength, sealing, snap fit, etc.

[0064] The modification of the thread angle of the first threaded portion may be determined based on the nominal size of the second threaded portion so that the contact area between the two threaded portions is shifted in an appropriate manner (relative to an extended contact configuration when the two thread angles are equal).

[0065] For example, as shown by the inventors' calculations, for a threaded portion conforming to the ISO standard, increasing the thread angle of the first threaded portion by 2° to 4° relative to the angle specified in the standard can reduce the tensile stress by about 20%. The thread angle of the first threaded portion is therefore between 62° and 64°. With this dimensioning, the contact between the thread flank of the first component and the thread flank of the second component is located at the lower part of the flank of the first threaded portion, close to the thread root of the first component.

[0066] Alternatively or additionally, the threads of the first threaded portion may be truncated to reduce the contact area by a thread height of the first threaded portion that is less than 0.3 pitch. This configuration can prevent the "point-like" loading of the threads of the first threaded portion from generating increased stress through leverage. In this embodiment, the thread angles of the first threaded portion and the second threaded portion may be:

[0067] - are equal; or

[0068] - Not equal as above.

[0069] The thread of the first thread portion may be truncated such that a crest of an axial cross section of the thread of the first thread portion has a straight line or a convex shape.

[0070] The thread bottom radius r of the first thread portion is preferably greater than 0.2 times the thread pitch of the first thread portion or greater than 0.4 times the thread pitch of the first thread portion.

[0071] Optimizing the radius r of the thread root 15 can also help reduce the tensile stress in the first component. Figure 2 and 3 as shown in the diagram.

[0072] For zirconia bottom caps assembled with stainless steel intermediates with standard threads (ISO standard), Figure 2 The impact of the thread bottom radius under stress experienced by the threaded portion of the bottom cap for different thread angles of the bottom cap is shown.

[0073] Figure 3 The use of threads with thread angles other than 60° is shown. The choice of thread standard has little influence on the performance requirements. Larger angles of 2° to 4° than conventional are used mainly on the threaded portion of the bottom cap to reduce stresses, while the evolution to thread angles of 55° or 65° has little influence.

[0074] When the first component is a screw-type component, the first threaded portion is preferably connected to the bearing surface 5 by a connecting fillet 13, the radius of which is greater than 0.4 times the pitch p of the first threaded portion or greater than 0.8 times the pitch p of the first threaded portion. The bearing surface extends radially outward from the first threaded portion and is used to abut against a second surface 25 provided on the second watch component. For example, a sealing portion can be provided between the two surfaces to provide a seal between the two components.

[0075] For example, the connecting fillet 13 forms a part of a groove or cavity having two groove walls and a groove bottom and realizing the connection between the bearing surface 5 and the first threaded part 11. On the thread side, the first groove wall part can have a straight and / or curved axial cross section. The curvature can be defined by the groove radius 18a. On the bearing surface 5 side, the groove wall part can have a straight and / or curved axial cross section. The curvature can be defined by the groove radius 18b.

[0076] The groove bottom may have a "point-shaped" axial cross section, that is, its axial cross section may be the intersection of the axial cross sections of two groove wall portions. Alternatively, the groove bottom may be further extended, such as Figure 1 As shown, two curved portions 18a and 18b are connected by a straight section portion.

[0077] The first member is also subjected to tensile stress in the vicinity of the groove.

[0078] For a watch case type component, typically a bottom cover-middle piece assembly, the metal first member has a thread side groove radius 18a and a bearing surface side radius 18b between 0.06 mm and 0.15 mm (inclusive). Their nominal value is 0.05 mm.

[0079] The thread side groove radius 18a and the load bearing surface side radius 18b may be the same or different.

[0080] If the thread side groove radius 18a increases from 0.1 mm to 0.2 mm, the value of the mechanical stress decreases by about 20%. If the thread side groove radius 18a increases from 0.1 mm to 0.4 mm, the value of the mechanical stress decreases by about 40%.

[0081] The connection angle between the groove and the load-bearing surface can be right angle, acute angle or obtuse angle, with or without pitting of the material.

[0082] The connection between the groove and the load-bearing surface may be planar or concave without affecting the tensile strength of the groove.

[0083] The second threaded portion 21 is preferably standard. In particular, the second threaded portion may be a threaded portion that complies with ISO standard, NIHS standard, UN standard, BSPT standard, NPT standard, NPTF standard, DIN standard, MJ standard, UNJ standard, or based on Whitworth profile.

[0084] In the description and in Figure 1 In the example shown in , the first threaded portion is an external or outer threaded portion, ie formed on a protruding surface, for example on the surface of a shaft.

[0085] In the description and in Figure 1 In the example represented in , the second threaded portion is an internal or intrinsic threaded portion, ie formed on a recessed surface, for example on the surface of a hole.

[0086] In the description and in Figure 1 In the example shown in , the first component is a bottom cover of fragile material, in particular made of ceramic or sapphire or zirconium oxide or glass, whose first threaded portion is subjected to tensile loads. The bottom cover is assembled to a second component consisting of an intermediate piece. The intermediate piece is made of a more ductile material, in particular made of metal or a metal alloy.

[0087] The following constructions can be thought of, for example:

[0088] - first horological component 10 is a bottom cover and second horological component 20 is a middle piece or inner middle piece; or

[0089] - first horological component 10 is a middle piece or inner middle piece and second horological component 20 is a bottom cover; or

[0090] - the first timepiece component 10 is a middle piece and the second timepiece component 20 is an inner middle piece; or

[0091] - the first horological component 10 is an inner middle piece and the second horological component 20 is a middle piece; or

[0092] - the first timepiece component 10 is a crown and the second timepiece component 20 is a crown tube; or

[0093] - the first timepiece component 10 is a crown tube and the second timepiece component 20 is a crown; or

[0094] - first timepiece component 10 is a crown and second timepiece component 20 is a crown cap; or

[0095] - the first clockwork element 10 is a valve tube and the second clockwork element 20 is a valve; or

[0096] - the first timepiece component 10 is a corrector tube and the second timepiece component 20 is a corrector; or

[0097] - the first timepiece component 10 is a cover and the second timepiece component 20 is a crown or a crown tube or a central hour wheel; or

[0098] The first horological component 10 is a screw and the second horological component 20 is a bracelet link.

[0099] The invention can be converted into any other type of screw fastening of a first member of brittle material (in particular made of ceramic or sapphire or zirconia or glass) in cooperation with a second member of a more ductile material (in particular metal or metal alloy) to form an assembly. The invention can also be converted into any other type of screw fastening of a first member of brittle material (in particular made of ceramic or sapphire or zirconia or glass) in cooperation with a second member of brittle material (in particular made of ceramic or sapphire or zirconia or glass) to form an assembly. For example, the first member and the second member are screwed one into the other so that they are subjected to mechanical stress, the members constituting the screw being subjected to tensile mechanical stress, for example.

[0100] During the placement or installation of the threaded assembly, i.e. during the screwing of one of the first and second components into the other by rotation of one component around the axis A10, it is of primary importance to apply a tightening torque which generates an appropriate mechanical stress, in particular an appropriate tensile force, which must be able to take into account the elements of the first and second components which are in contact with each other and compensate for any additional forces arising from impacts, vibrations, pressure, from expansion or contraction, from thermal or humidity changes, etc.

[0101] In the case of sealing or secure assembly, the tightening torque applied must be particularly mastered. If it is too low, the system has the risk of leaking or loosening; if it is too high, there is the risk of components, especially one of the threads, being damaged or even broken.

[0102] Conventional material curves are able to determine, for a given material and predetermined dimensions in a standard reference system, the limit values ​​applicable before a nut-screw pair is damaged. Curves do not exist for material pairs involving metal alloys and brittle materials such as ceramics, sapphire, zirconia or glass.

[0103] When the components of a threaded assembly are tightened, only some of the threading / tightening energy actually contributes to the tightening (deformation of one or both components along the axis of the screw connection), the rest of the energy is dissipated, in particular, by friction on the threads. Friction is necessary to prevent loosening over time. However, these mechanisms are prone to causing the assembly to seize when the friction is too high.

[0104] The sticking threshold of a pair of materials is defined by the value of the contact pressure that causes the material to transfer from one surface to another. There is a sticking threshold for each pair of materials. In addition to the surface state, the threshold is based on the chemical and / or metallurgical properties of each of the two materials in contact.

[0105] In the case of a threaded assembly, seizure may occur in two steps, namely slight seizure followed by total seizure where appropriate.

[0106] Micro-seizure occurs when the tension does not increase in a linear manner but increases as the tightening torque increases. This is, for example, the case where micro-welds are formed and subsequently broken by the tightening torque that follows their formation and the torque that was applied when they were formed (this is the "stick-slip" phenomenon). Relative rotation between the elements can be maintained but tightening is disturbed. This phenomenon can be localized.

[0107] Minor galling usually increases as the tightening torque increases until total galling occurs. When total galling exists, all rotation is prevented.

[0108] Disassembly of prestressed threaded assemblies is provided without seizure between components after tightening. This means that to ensure that the threaded assembly can be disassembled, specific precautions are required, in particular to prevent any micro-seizure during initial tightening, to prevent any corrosion in use and to maintain the correct coefficient of friction during the life of the assembly.

[0109] It is therefore necessary to find solutions to limit the friction in order to obtain a torque / tension relationship that is as constant as possible in the assembly. It is known, by measurement or from curves, how to determine the tightening torque that creates a risk of seizure: in fact, knowing that the coefficient of this friction must be constant, a significant increase of this coefficient, according to a certain torque value, indicates a seizure phenomenon. Therefore, in order to increase the seizure threshold, it is necessary to act on the friction at the contact surfaces of the assembly.

[0110] Stainless steel, aluminum and titanium threads are particularly susceptible to galling.

[0111] To reduce or even avoid these phenomena, stainless steel components are often treated, such as with lubricants or "anti-seize" coatings. These treatments are susceptible to degradation over time.

[0112] For stainless steel bottom covers assembled to stainless steel housings without lubrication, seizure issues have been observed when the tightening torque is less than 3 N.m.

[0113] It has been observed that ceramic components according to the invention, such as zirconium oxide components, have a lower likelihood of seizure than the metal components they replace. For the zirconium oxide components, at a tightening torque of 5 N.m, no seizure or deformation was observed even without processing the metal parts.

[0114] The above solution thus makes it possible to prevent the elements of the thread system from getting stuck, in particular during tightening, thereby ensuring that the assembly can be disassembled.

[0115] The system also withstands higher tightening torques without seizing. For example, even without treating the metal parts, a torque of 10 N.m has been applied to a zirconium oxide bottom cover according to the invention assembled on a stainless steel middle piece without causing seizing or deformation of the components.

[0116] Alternatively, instead of a threaded portion of brittle material, the threaded portion may be a ceramic-coated metal threaded portion, i.e., a threaded portion whose threaded surface is composed of a ceramic coating. The ceramic coating may be obtained by ceramic thermal spraying, surface treatment, heat treatment or any other suitable technique. In this case, the present invention can minimize the risk of cracking or breaking of the ceramic layer and the risk of component jamming. The base material is, for example, stainless steel, titanium, etc. The ceramic layer is, for example, an oxide ceramic layer (zirconium oxide, aluminum oxide, aluminum titanate, etc.) or a non-oxidizing ceramic layer such as a nitride or carbide (aluminum nitride, silicon nitride, silicon carbide, tungsten carbide, etc.).

[0117] Thanks to the invention, it is possible to manufacture bottom caps of fragile materials or metal alloys having identical or substantially identical geometries and being interchangeable so as to cooperate with identical intermediate pieces, in particular identical metallic intermediate pieces. Moreover, these bottom caps can be mounted without requiring changes in the manufacturing or after-sales service tools used to assemble / remove them, regardless of the material from which they are manufactured.

[0118] By means of the invention, it is possible to manufacture a sealed watch case comprising a fragile material, in particular ceramic, sapphire, zirconium oxide or glass, to replace the metal bottom cover without modifying the metal middle piece.

[0119] By means of the invention, it is possible to modify the threaded portion of a base cap of fragile material so as to maintain its integrity during the screw connection, under tightening action and in the same conditions of use as a metal base cap. Furthermore, the problems of seizure encountered with metal base caps are avoided, even at higher tightening torques than those normally used with metal alloy base caps.

[0120] Thus, by means of the invention, the dimensions of the thread of a fragile material component can be specifically determined so that it resists the same range of stresses as the metal part that it replaces, so that it adapts to a standard thread, for example one that complies with the Swiss Watch Industry Standard (NIHS). This dimensioning takes into account the magnitude of the stress field and the likelihood of fracturing the fragile material component.

[0121] Since the invention makes it possible to provide a ceramic bottom cover, it in fact facilitates a solution for dimensioning a thread on a fragile material, in particular a ceramic material, which thread can match a standard thread and enable the assembly of fragile material parts by screw connection. An example of this benefit is provided by a ceramic bottom cover mounted on a metal intermediate with a thread of increased strength, in particular with regard to the stresses generated during assembly and / or by the environment, such as compression of the assembly when diving.

[0122] This design advantageously enables the metal bottom cover to be simply replaced with a ceramic bottom cover without changing the design of the metal parts for receiving the bottom cover and / or the tools for assembling / removing the bottom cover, while ensuring an acceptable seal, a secure assembly and minimizing the risk of sticking.

[0123] On the contrary, according to the prior art, the external and internal threads are machined according to the same category and with the same tolerances, so as to be able to match each other and maximize the contact area between the external and internal threads. If the external and internal threads are machined according to the same category, the flanks of the internal thread and the flanks of the external thread are in contact over the largest possible area, taking into account the tolerances, the flanks being as "flat" as possible. The purpose of these dimensions according to the prior art is to control assembly, in particular the phenomena of tearing out and seizure of the threads, and to optimize the strength of the assembly.

[0124] According to another aspect of the invention, an assembly, in particular a watch case, comprises:

[0125] a first component 10 made of a brittle material, in particular ceramic or sapphire or zirconia or glass, or having a threaded surface comprising a coating of a brittle material, in particular ceramic or sapphire or zirconia or glass; and

[0126] A second component 20 which consists of, in particular predominantly consists of, metal or a metal alloy.

[0127] The first component and the second component are advantageously connected via a threaded connection or are screwed to one another.

[0128] According to this further aspect of the invention, a timepiece comprises such an assembly.

[0129] This further aspect of the invention may comprise any combination of the features described in this document in the absence of logical or technical incompatibility.

Claims

1. A timepiece component (10), comprising a first axis (A10) and a first threaded portion (11), the first threaded portion having a pitch (p) and being used to cooperate with a second threaded portion (21) provided on a second timepiece component (20), the first threaded portion being configured so that a contact area (C) between the first threaded portion and the second threaded portion extends to a range of less than 50% of a thread height (h) of the second threaded portion, or being configured so that a contact area (C) between the first threaded portion and the second threaded portion extends to a range of less than 0.3 times the pitch (p), and an extension (e) of the contact area is measured radially relative to the first axis (A10) from a thread root (15) of the first thread.

2. The timepiece component according to claim 1, in, The first thread portion (11) has a first thread angle (12), wherein the second thread portion (21) has a second thread angle (22), and wherein the value of the first thread angle (12) is 2 to 4 degrees greater than the value of the second thread angle (22).

3. The timepiece component according to claim 1 or 2, in, The thread height of the first thread portion is less than 0.3 thread pitches.

4. The timepiece component according to claim 1 or 2, in, The radius of the thread root (15) of the first thread portion is greater than 0.2 times the thread pitch of the first thread portion or greater than 0.4 times the thread pitch of the first thread portion.

5. The timepiece component according to claim 1 or 2, in, The first threaded portion is connected to the bearing surface (5) via a connecting fillet (13), the radius (18b) of the connecting fillet being greater than 0.4 times the pitch of the first threaded portion or greater than 0.8 times the pitch of the first threaded portion.

6. The timepiece component according to claim 1 or 2, in, The second threaded portion is a conventional thread.

7. The timepiece component according to claim 6, in, The second threaded portion is a thread that complies with ISO standards, NIHS standards, UN standards, BSPT standards, NPT standards, NPTF standards, DIN standards, MJ standards, UNJ standards, or is based on a Whitworth tooth profile.

8. The timepiece component according to claim 1 or 2, in, The timepiece component (10) is made of a fragile material, or wherein: The timepiece component (10) is mainly made of metal or metal alloy and the first threaded portion has a surface consisting of a coating of brittle material.

9. The timepiece component according to claim 8, in, The watch component (10) is made of ceramic, sapphire, zirconium oxide or glass.

10. The timepiece component according to claim 8, in, The timepiece component (10) is mainly made of metal or metal alloy and the first threaded portion has a surface composed of a ceramic coating.

11. A timepiece component (10) according to claim 1 or 2, in: The timepiece component (10) is a bottom cover and the second timepiece component (20) is a middle piece or an inner middle piece; or The timepiece component (10) is a middle piece or an inner middle piece and the second timepiece component (20) is a bottom cover; or The timepiece component (10) is a middle piece and the second timepiece component (20) is an inner middle piece; or The timepiece component (10) is an inner middle piece and the second timepiece component (20) is a middle piece; or The timepiece component (10) is a crown and the second timepiece component (20) is a crown tube; or The timepiece component (10) is a crown tube and the second timepiece component (20) is a crown; or The timepiece component (10) is a crown and the second timepiece component (20) is a crown cap; or The clock component (10) is a valve tube and the second clock component (20) is a valve; or The timepiece component (10) is a corrector tube and the second timepiece component (20) is a corrector; or The timepiece component (10) is a cover and the second timepiece component (20) is a crown or a crown tube or a center wheel; or The timepiece component (10) is a screw and the second timepiece component (20) is a bracelet link.

12. A case (100) for a timepiece (200), comprising the timepiece component (10) according to any one of claims 1 to 11 and the second timepiece component (20).

13. A case (100) for a timepiece (200), comprising a middle piece and a bottom cover, wherein the bottom cover is the timepiece component (10) according to any one of claims 1 to 11, and the middle piece is the second timepiece component (20).

14. The housing (100) for a timepiece (200) according to claim 13, in, The intermediate piece is a metal intermediate piece.

15. A case (100) for a timepiece (200), comprising a bottom cover and a middle piece, wherein the middle piece is the timepiece component (10) according to any one of claims 1 to 11, and the bottom cover is the second timepiece component (20).

16. The housing (100) for a timepiece (200) according to claim 15, in, The bottom cover is a metal bottom cover.

17. A timepiece (200) comprising a timepiece component according to any one of claims 1 to 11 and / or a case (100) for a timepiece (200) according to any one of claims 12 to 16.

18. The timepiece (200) according to claim 17, in, The timepiece is a watch.

19. The timepiece (200) according to claim 17, in, The timepiece is a wristwatch.

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