Watertight watch case

Abstract

The water-resistant watch case (1) of a diving watch comprises at least one case back (4) mounted on the lower side of a case middle (2), and a crystal (3) mounted on the upper side of the case middle. The crystal (3) includes an annular peripheral surface (13) for being fixed by means of an amorphous metal gasket (5, 5') to an annular inner surface (12) complementary in shape to the upper side of the case middle. The annular peripheral surface of the crystal is inclined inward toward the watch case at a defined angle less than 90° with respect to a central axis perpendicular to a plane of the watch case in order to distribute stresses between the crystal and the case middle due to water pressure during a dive. Both the annular peripheral surface and the annular inner surface are conical in shape.

Description

TECHNICAL FIELD

[0001] The present invention relates to a waterproof watch case, in particular for a diving watch. TECHNOLOGICAL BACKGROUND

[0002] To provide for the use of a mechanical or electronic watch underwater, the watch case, which includes a watch movement or a time-based watch module, must be closed in a well-sealed manner. To achieve this, the watch case includes a back fixed in a sealed manner to a first side of a caseband and a crystal fixed to a second, opposite side of the caseband. Sealing gaskets are provided at the assembly of the back, the caseband and the watch crystal. A control or adjustment member for functions of the watch is also mounted in a sealed manner through the caseband of the case in the rest position.

[0003] Watch cases are generally not configured or assembled to withstand high water pressures, for example during diving, since the pressure inside the watch case is close to atmospheric pressure. Simple conventional watch gaskets are not sufficient to ensure a good watertightness of the case when diving to very great depths underwater.

[0004] We can cite patent application CH 690 870 A5 which describes a waterproof watch case. The watch case consists of a crystal fixed on an upper side to a caseband-bezel and a back fixed to the caseband by screwing it to an internal thread of the caseband. The crystal is fixed to the caseband by an annular sealing gasket of toroidal shape and resting on an edge of the caseband. A sealing gasket is also provided between an outer edge of the backband and a lower surface of the caseband. Since the threading can be damaged under high water pressure, a resistant metal cup is also provided resting against an internal surface of the backband and against an internal edge of the caseband. However, even with such a watch case arrangement, this does not guarantee good watertightness of the case when diving to very great depths underwater, which is a disadvantage.

[0005] Patent CH 372 606 describes a waterproof watch case, which has a central part or caseband surrounding a back and closed by a crystal. A threaded ring rests against an inclined outer surface of the backband to retain it, and is screwed to a fixing part connected to the caseband. With such an arrangement presented, this does not guarantee good watertightness of the case when diving to very great depths underwater, which is a disadvantage.

[0006] Patent CH 378 792 describes a waterproof watch case. The crystal is a disc of transparent mineral material (glass, crystal). A lining of soft or malleable metal, such as gold, platinum, silver, copper, tin, is driven into the periphery of the crystal against an upper rim. This crystal and lining assembly is driven into a cylindrical bore of a support, such as a caseband, but this does not guarantee very good watertightness of the watch case during a deep dive.

[0007] Patent JP S53 124473 A describes a watch case with a crystal having an outer surface in a cylindrical shape on the top and a conical shape on the bottom to be fixed by means of a gasket in an opening in the cylindrical caseband. Since the surface of the caseband does not have a complementary shape to that of the crystal, fixing the crystal in the caseband by means of the gasket cannot ensure very good watertightness during deep diving. SUMMARY OF THE INVENTION

[0008] The main aim of the invention is therefore to overcome the drawbacks of the state of the art described above by proposing a waterproof watch case suitable for withstanding high water pressure for diving to great depths underwater.

[0009] To this end, the present invention relates to a waterproof watch case, which comprises the features of independent claim 1.

[0010] Particular embodiments of a waterproof watch case are defined in dependent claims 2 to 13.

[0011] An advantage of the waterproof watch case is that the crystal is attached to the caseband by means of a one-piece metal gasket and with inclined contact surfaces of the caseband and the crystal. The metal fixing gasket has a shape complementary to the fixing surfaces before the operation of attaching the crystal to the caseband. In the case of a generally cylindrical caseband, conical bearing surfaces are provided on the crystal and the caseband, or even on the caseback mounted on an opposite side of the caseband. In this way, pressure forces on the crystal and the caseback are transmitted to the caseband via conical bearing surfaces and via the one-piece metal gasket.

[0012] Advantageously, in the case of a single-piece gasket made of amorphous metal, the glass can be fixed to the caseband by means of the fixing gasket, in particular by hot forming. This avoids stress concentrations, ensures good holding of the glass and ensures very good sealing of the watch case.

[0013] Advantageously, during the operation of fixing the crystal to the caseband, the heated amorphous metal gasket is in a softened state to properly apply to the contact surface of the crystal and the contact surface of the caseband, filling any gap in the surface condition of each contact surface. In addition, during the cooling of the crystal fixed to the caseband, the amorphous metal gasket serves as a stress interface between the caseband and the crystal, as the coefficient of thermal expansion of the caseband, for example made of titanium, is greater than that of the crystal, for example made of sapphire. BRIEF DESCRIPTION OF THE FIGURES

[0014] The aims, advantages and characteristics of a waterproof watch case will appear better in the following description in a non-limiting manner with reference to the drawings in which: THE figures 1a et 1b represent in a simplified manner a cross-section of an embodiment of a watch with a waterproof case according to the invention, and a partial section of detail of the attachment of the glass to the caseband according to the invention, the figures 2a à 2c represent a fixing joint in a partially three-dimensional sectional view and different stages of fixing the glass to the caseband by means of the fixing joint of the watch case according to the invention, the figure 3 represents a partial sectional detail of a variant of the attachment of the glass to the caseband according to the invention, the figure 4 schematically represents a top view of an embodiment of a watch case according to the invention, and the figures 5a et 5b represent a crystal with a metallic coating capable of being engraved by a laser to produce an inscription on the surface for fixing the crystal to the caseband, and a portion of the metallic coating on the crystal with the inscription according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] In the following description, all components of a waterproof watch case, in particular of a diving watch, which are well known to a person skilled in the art in this technical field, are described only in a simplified manner.

[0016] THE figures 1a et 1b represent an embodiment of a watch case 1, which can be used for a diving watch. The watch case 1 essentially comprises a crystal 3, which can be made of sapphire or mineral glass, fixed on an upper side of a caseband 2, and possibly a back 4 mounted on a lower side of the caseband 2. A bezel 7 can also be mounted on the upper side of the caseband 2. A watch movement or module 10 is arranged in the watch case 1 in a casing ring 8, and at least one control member not shown can be mounted in a sealed manner in the rest position on or through the caseband 2 for setting the time, date or other functions of the diving watch.

[0017] In the case where a back cover 4 of the watch case 1 is provided, the solid back cover 4 may comprise an annular edge 14 with internal threading to be screwed onto a thread 26 on the lower side of the caseband 2. An annular bearing surface 24 of the back cover 4 comes into contact with an annular inner surface 32 of the caseband 2 of a shape complementary to the bearing surface 24 when the back cover 4 is mounted on the caseband 2. The bearing surfaces 24 and inner 32 are inclined at a determined angle relative to an axis perpendicular to a plane of the watch case 1. In the case of a caseband of generally cylindrical shape, the surfaces 24, 32 are conical in shape and inclined towards the inside of the watch case 1 at a determined angle relative to a central axis of the watch case 1. This means that the apex of each cone shape is towards the inside of the watch box 1.The lower side of the caseband 2 further comprises an annular groove 16 housing a toric-shaped sealing gasket 6 in contact with the bearing surface 24 when the back cover 4 is mounted on the caseband 2. For a caseband 2 and a back cover 4 made of a material such as titanium, the angle may be of the order of 60° ± 5° relative to the central axis. This allows for good distribution of the stresses between the back cover 4 and the caseband 2 due to the water pressure when diving to great depths underwater.

[0018] The crystal 3 comprises an annular peripheral surface 13 to be fixed by means of a one-piece metal fixing gasket 5, 5' on an annular inner surface 12 on the upper side of the caseband 2. The annular inner surface 12 is preferably of a shape complementary to the annular peripheral surface 13. The gasket 5, 5', as an interface between the caseband 2 and the crystal 3, can also be produced before the fixing operation with a shape complementary to the contact surfaces of the crystal 3 on the caseband 2. The annular peripheral surface 13 of the crystal 3 is inclined at a defined angle smaller than 90° relative to an axis perpendicular to a plane of the watch case 1. Preferably, the annular inner surface 12 is inclined generally towards the inside of the watch case 1 at the same angle as the annular peripheral surface 13 relative to a central axis.

[0019] If the caseband 2 is generally cylindrical in shape, the peripheral inner surface 13 and the annular inner surface 12 are conical in shape and inclined at a defined angle towards the inside of the watch case. This means that the apex of each cone shape is towards the inside of the watch case 1. The defined angle of inclination of the surfaces 12 and 13 may be of the order of 43° ± 5° relative to the central axis. This allows for a good distribution of the stresses between the crystal 3 and the caseband 2 due to the water pressure during diving to great depths underwater. The difference in water pressure compared to the pressure inside the watch case 1 tends to close any gap remaining between the contacting surfaces 12, 13 and the fixing gasket 5, 5' thanks to the inclination of the contact surfaces towards the inside of the watch case 1. This guarantees good sealing and resistance to high pressures.

[0020] In this embodiment, the one-piece metal attachment gasket 5, 5' is made of amorphous metal or metallic glass or amorphous metal alloy. It may comprise a first part 5 and a second part 5'. The attachment gasket 5, 5' is annular in shape for hermetically sealing the crystal 3 on the caseband 2. For a caseband 2 of generally cylindrical shape, the first part 5 of the gasket is conical in shape, while the second part 5' is cylindrical. Once the crystal 3 is attached to the caseband 2, the first part 5 is attached to the inclined surfaces of the caseband 2 and the crystal 3, while the second part 5' is attached to an annular inner wall 22 of the caseband 2 and an annular outer wall 23 of the crystal 3 above the annular peripheral surface 13 of the crystal 3.The second part 5' can stop halfway up the glass 3 just below the bezel 7, while the first part 5 of the joint can extend below the level of the connection between the bottom of the glass 3 and the caseband 2.

[0021] By way of non-limiting example, the length of the first part 5 in cross-section may be of the order of 5 mm, while the height of the second part of the seal 5, 5' may be of the order of 2.5 mm. The thickness of the seal may be of the order of 0.65 mm.

[0022] Normally, the one-piece metal gasket 5, 5' for fixing in an annular shape is made of an amorphous metal alloy so as to fix the crystal 3 to the caseband 2, for example by hot deformation. When fixing the crystal 3 to the caseband 2, the aim is to completely fill the space between the crystal 3 and the caseband 2. Thus, by this hot deformation of the gasket with pressure of the crystal 3 on the caseband 2, the surface condition of the contact surface of the crystal 3 and the contact surface of the caseband 2 is replicated by the gasket softened by the heat. It can therefore be envisaged to have a certain roughness at the level of the annular peripheral surface 13 of the crystal 3 sufficient to have a better adhesion of the gasket 5, 5' to the crystal 3 and to the caseband 2. In this way, the gasket made of amorphous metal softened by the heat completely matches the surface condition of the crystal 3 and the caseband 2, which guarantees a good hermetic closure.

[0023] Furthermore, the metal also compensates for any possible angle defect between the conical surface of crystal 3 and the conical surface of caseband 2, and thus ensures perfect support between crystal 3 and caseband 2, which greatly reduces stress concentrations during pressurization. This is very important because crystal 3 is generally made of a fragile material, such as sapphire or mineral glass. Thus, very localized contact of crystal 3 on caseband 2 risks causing breakage during pressurization underwater.

[0024] As explained below, the gasket 5, 5' made of amorphous metal serves as an interface between the caseband 2 and the crystal 3. During the hot-fixing operation of the crystal 3 on the caseband 2 by means of the gasket 5, 5' softened by the heat, this gasket also serves as an accumulation of stresses during the cooling operation. This is important because the thermal expansion coefficient of the titanium caseband 2 is greater than the contact surface of the sapphire crystal 3.

[0025] Several types of amorphous metal alloys can be used to fully produce the one-piece metal joint 5, 5'. In the most common cases, the amorphous metal alloy can be mainly composed of zirconium, which allows the joint to be formed at a temperature above 350°C, i.e. above the glass transition temperature of the alloy. The zirconium-based amorphous metal alloy can be composed of Zr(52.5%), Cu(17.6%), Ni(14.9%), Al(10%) and Ti(5%). The zirconium-based amorphous metal alloy can also comprise Zr(58.5%), Cu(15.6%), Ni(12.8%), Al(10.3%) and Nb(2.8%). The zirconium-based amorphous metal alloy can also include Zr(44%), Ti(11%), Cu(9.8%), Ni(10.2%) and Be(25%), or finally Zr(58%), Cu(22%), Fe(8%) and Al(12%).Preferably, to facilitate the production of such a joint, the amorphous metal alloy may be mainly composed of platinum (Pt), which makes it possible to form the joint at a temperature above 230°C. The platinum-based amorphous metal alloy may comprise Pt (57.5%), Cu (14.7%), Ni (5.3%) and P (22.5%). It may also be provided to produce the single-piece metal joint 5, 5' from an amorphous metal alloy mainly based on palladium (Pd, which makes it possible to form the joint at a temperature above 300°C.

[0026] Other amorphous metal alloys may also be mentioned. A titanium-based amorphous metal alloy may comprise Ti(41.5%), Zr(10%), Cu(35%), Pd(11%) and Sn(2.5%). A palladium-based amorphous metal alloy may comprise Pd(43%), Cu(27%), Ni(10%) and P(20%), or Pd(77%), Cu(6%) and Si(16.5%), or finally Pd(79%), Cu(6%), Si(10%) and P(5%). A nickel-based amorphous metal alloy may comprise Ni(53%), Nb(20%), Ti(10%), Zr(8%), Co(6%) and Cu(3%), or Ni(67%), Cr(6%), Fe(4%), Si(7%), C(0.25%) and B(15.75%), or finally Ni(60%), Pd(20%), P(17%) and B(3%). An iron-based amorphous metal alloy may include Fe(45%), Cr(20%), Mo(14%), C(15%) and B(6%), or Fe(56%), Co(7%), Ni(7%), Zr(8%), Nb(2%) and B(20%). A gold-based amorphous metal alloy may include Au(49%), Ag(5%), Pd(2.3%), Cu(26.9%) and Si(16.3%).

[0027] The production of such a 5, 5' joint in amorphous metal can be done by different shaping processes, namely: directly from the molten metal such as, for example, pressure injection, gravity casting, centrifugal casting, antigravity casting, suction casting, additive manufacturing of powder from amorphous preforms by hot deformation above the glass transition temperature such as, for example, electromagnetic forming, capacitive discharge forming, gas pressure forming, mechanical forming. The objective of this step is to obtain a preform with the correct dimensions and with a sufficient proportion of amorphous phase to allow its deformation during the assembly step described below.

[0028] The annular fixing joint with the first part 5 of conical shape and the second part 5' of cylindrical shape is shown in a three-dimensional partial sectional view at figure 2a . This two-part joint form 5, 5' is used for fixing the crystal 3 to the caseband 2 as shown in figures 2b And 2c .

[0029] To the figure 2b , the gasket 5, 5' is first placed on the upper side of the caseband 2. The first part 5 of the gasket is in contact with the annular inner surface 12, while the second part 5' is close to the annular inner wall 22 of the caseband 2. Then the crystal 3 is mounted on the gasket 5, 5'. The annular peripheral surface 13 of the crystal 3 is in contact with the first part 5 of the gasket, while the annular outer wall 23 of the crystal 3 above the annular peripheral surface 13 is close to the second part 5' of the gasket. In this way, the gasket 5, 5' is arranged between the caseband 2 and the crystal 3.

[0030] To fix the crystal 3 to the caseband 2 by means of a gasket 5, 5' made entirely of an amorphous metal alloy, an anti-overflow tool MC is placed on the upper side of the caseband 2 and in contact with the annular outer wall 23 of the crystal 3. This anti-overflow tool MC serves to prevent the amorphous metal alloy of the gasket from coming out of the upper side of the caseband 2. Another anti-overflow tool, not shown, may also be provided below the inner side of the watch case to prevent the amorphous metal alloy of the gasket from coming out of the lower side. A high tool MH presses the crystal 3 towards the caseband 2, while a low tool MB holds the lower side of the caseband 2 in support.

[0031] With an alloy of amorphous metals based on zirconium in the gasket, a pressure of the order of 10,000 to 80,000 N is exerted on the crystal 3 on the caseband 2 at a temperature of the order of 480 °C for a period of 30 - 250 seconds. Thus, the pressure exerted by the sapphire 3 on the part 5 of the gasket causes the material contained in the part 5 of the gasket to flow towards the part 5' and downwards. The consequences are a downward displacement of the crystal 3 and a thinning of the part 5 of the gasket until the gasket completely fills the space between the caseband 2, the anti-overflow tool MC, the internal anti-overflow tool and the crystal 3. The amorphous metal gasket will, during its flow, mold all the details of the surfaces 12, 13, 22 and 23.During the cooling of the assembly at the end of the gasket deformation step, the dimensions of case 2, gasket 5, 5' and crystal 3 will decrease proportionally to their respective coefficients of expansion α. ​​However, crystal 3 (e.g. sapphire with α = 5 to 8 ppm) has a coefficient of expansion lower than those of case 2 (e.g.: α = 8.5 to 11 ppm for titanium, 12 to 18 ppm for stainless steel; 12 to 16 for gold) and gasket 5, 5' made of amorphous metal (α = 9 to 18 ppm). This generates a compressive force of case 2 and gasket 5, 5' made of amorphous metal on crystal 3 at the level of the second part 5' of the gasket which is cylindrical. This compression ensures both very good strength and very good sealing of the assembly at room temperature.

[0032] Furthermore, the particular mechanical properties of amorphous metals, in particular their very high elastic limit σ e (e.g.: 1700 MPa for a Zr base; 1550 MPa for a Pd base; 1350 MPa for a Pt base) coupled with a very high elastic deformation ε e (1.5 to 2% for all amorphous metals), make it possible to avoid plasticization of the seal 5, 5' in its contact zone with the glass 3 when stressed at very high pressures. Case 2, whose mechanical properties (e.g. for grade 5 titanium: σ e 850 MPa; ε e 0.5 to 0.8%) are inferior to the amorphous metals chosen for the joint, does not plasticize either because the amorphous metal joint 5, 5' makes it possible to homogenize the stresses, which then decrease at the joint - case interface.

[0033] For an alloy of amorphous metals mainly composed of palladium, the fixing of the crystal 3 to the caseband 2 via the joint 5, 5' is done at a temperature of the order of 380°C by applying a pressure of approximately 10,000 - 80,000 N for 30 - 250 seconds.

[0034] For an alloy of amorphous metals mainly composed of platinum, the fixing of the crystal 3 to the caseband 2 via the joint 5, 5' is done at a temperature of the order of 280°C by applying a pressure of approximately 10,000 - 80,000 N for 30 - 250 seconds.

[0035] As described previously, stresses are generated in crystal 3 during cooling due to the differences in expansion coefficients between caseband 2 and crystal 3. These forces depend on the geometry of the assembly, the materials chosen (caseband, amorphous metal, crystal) and the temperature used during assembly. Although these stresses are useful for ensuring the strength and tightness of the assembly, they can cause the crystal to break if they are too high or too local. This is why it is important to choose a suitable amorphous metal to avoid this problem. Indeed, the use of, for example, a Pt-based amorphous metal makes it possible to reduce these forces because the temperature of the assembly process will be low (approx. 280°C) and therefore the differential shrinkage of caseband 2 compared to crystal 3 will be low.

[0036] Another way to reduce the stresses in crystal 3 after the assembly process, as described above, is to partially or completely crystallize the gasket 5, 5' in amorphous metal. Indeed, the crystallization generates a reduction in the volume of the amorphous metal and therefore of the gasket 5, 5', which slightly separates the caseband-gasket and gasket-crystal contact surfaces. During cooling, the differential shrinkage of caseband 2 must first compensate for the void left by the crystallization of the amorphous metal before starting to tighten on crystal 3. In the end, the residual stresses in the sapphire are lower compared to a 100% amorphous gasket.

[0037] The crystallization of the 5, 5' joint can be achieved by maintaining the assembly at a prolonged temperature after the forming phase. For example, in the case of a zirconium-based alloy, maintaining the temperature for 5 minutes at 480°C can generate crystallization of the joint. It is also possible to increase the temperature from 20°C to 100°C after the creep phase in order to accelerate crystallization or to modify its nature (different crystalline phases). It is also possible to reduce the temperature after the creep phase in order to obtain slower and finer crystallization.

[0038] There figure 2c shows the result of fixing the crystal 3 to the caseband 2 after removing the tools used for this. A bezel 7 covers the upper side of the caseband 2. The first part 5 of the joint fixedly connects the annular peripheral surface 13 of the crystal 3 to the annular inner surface 12 of the caseband 2. The second part 5' of the joint fixedly connects the annular inner wall 22 of the caseband 2 and the annular outer wall 23 of the crystal 3. Normally the first part 5 of the joint extends below the level of the connection between the bottom of the crystal 3 and the caseband 2, which therefore does not include the inner beak shown in figures 2b And 2c .

[0039] There figure 3 represents a partial sectional detail of a variant of the attachment of the crystal 3 to the caseband 2. The crystal 3 comprises an annular peripheral surface 13 to be attached by means of a single-piece metal joint 5, 5' for attachment to an annular inner surface 12 on the upper side of the caseband 2. If the caseband 2 is of generally cylindrical shape, the peripheral inner surface 13 of the crystal 3 is of conical shape, whereas the annular inner surface 12 of the caseband 2 is in the plane of the watch case 1 in the form of a portion of a disc. The first part 5 of the joint is between the peripheral inner surface 13 and the annular inner surface 12, whereas the second part 5' of the joint is between the annular inner wall 22 of the caseband 2 and the annular outer wall 23 of the crystal 3.

[0040] There figure 4 schematically shows a top view of an embodiment of a watch case 1. The watch case 1 comprises the caseband 2, the crystal 3, a bezel 7 and a control member 9 in the form of a stem-crown passing through the caseband 2. The stem-crown comprises a conical surface not shown in contact with a conical inner surface of the caseband 2 in the rest position to ensure watertightness and resistance to water pressure when diving. An inscription 103 of a word or a number or drawings is made at the connection of the annular peripheral surface 13 of the crystal 3 on the first part of the fixing joint.

[0041] As shown in the figures 5a et 5bto produce the inscription 103, it may also be provided to have a contact surface of the glass 3 structured and / or with a decorative layer deposited on its surface. This structuring and / or deposit 63 may be arranged on the annular peripheral surface 13 of the glass 3. It may also be provided to write one or more words, or numbers or designs by engraving the deposit 63 using a laser beam L coming from a laser device 50. The deposit 63 may be of a different color from the first part of the fixing joint. Therefore, after engraving the inscription 103 on the deposit 63, the annular peripheral surface 13 of the glass 3 may be placed or fixed on the first part of the fixing joint, which is of a different color than the deposit 63.

[0042] It may also be provided to create a pattern on the contact surface of the crystal 3 by selectively structuring its surface. It is possible to structure the surface for example by a laser, by a chemical process or even by a mechanical process (for example grinding, milling). Thus, once the crystal 3 is fixed to the caseband 2, it is possible to read the inscription made through the crystal 3, which may also be the indication of the watch brand.

[0043] It should also be noted that with the attachment of the crystal 3 to the caseband 2 of the embodiment variants described above and with the contact of conical surfaces between the crystal 3 and the caseband 2, good watertightness and good stress distribution between the crystal 3 and the caseband 2 are guaranteed. This is necessary given that the watch is a diving watch which must withstand high stresses due to the pressure difference between the inside of the watch and the water pressure at great depths underwater. Since the contact surface between the caseband 2, the gasket 5, 5' and the crystal 3 is quite large with this conical shape, there is a better transmission of stresses over a larger surface, which is important for reducing stress concentrations in the crystal and thus preventing it from breaking during a deep dive underwater. This also ensures the watertightness of the watch case.With this arrangement, the water pressure on the watch case tends to close any gaps between the mating surfaces. In addition, this prevents the mounting gasket from extrusion.

[0044] From the description which has just been given, several variant embodiments of the watch case can be designed by those skilled in the art without departing from the scope of the invention defined by the claims. The watch case, by its middle, can have a general shape different from a cylinder.

Claims

1. A water-resistant watch case (1), in particular for a diving watch, the case (1) comprising at least one crystal (3) mounted on an upper side of a middle part (2), wherein the crystal (3) comprises an annular peripheral surface (13) to be fastened by means of a metal gasket (5, 5') of the watch case (1), that is annular in shape, on an inner annular surface (12) on the upper side of the middle part (2), and wherein the annular peripheral surface (13) of the crystal (3) is inclined towards the inside of the watch case (1) at a determined angle less than 90° relative to a central axis perpendicular to a plane of the watch case in order to distribute stresses between the crystal (3) and the middle part (2) due to the water pressure during a dive, and wherein the inner annular surface (12) on the upper side of the middle part (2) is of a shape complementary to the annular peripheral surface (13) of the crystal (3), and wherein the metal gasket is made in one piece and is composed of a first portion (5) arranged between the annular peripheral surface (13) of the crystal (3) and the inner annular surface (12) of the middle part (2), and of a second portion (5') in contact between an inner annular wall (22) of the middle part (2) above the inner annular surface (12) and an outer annular wall (23) of the crystal (3) above the annular peripheral surface (13), and wherein the annular peripheral surface (13) of the crystal (3) and the inner annular surface (12) of the middle part (2) are two conical surfaces of the watch case (1), and the inner annular wall (22) of the middle part (2) and the outer annular wall (23) of the crystal (3) are cylindrical surfaces.

2. The watch case (1) according to claim 1, characterised in that the one-piece metal gasket (5, 5') is made of metal alloy that is at least partially amorphous in a phase during which the crystal (3) is fastened to the middle part (2).

3. The watch case (1) according to claim 1, characterised in that the one-piece metal gasket (5, 5') is made of a metal alloy that is at least partially amorphous.

4. The watch case (1) according to claim 2, characterised in that the crystal (3) is fastened to the middle part (2) by the one-piece metal gasket (5, 5') made of metal alloy that is at least partially amorphous after hot working.

5. The watch case (1) according to claim 1, characterised in that the annular walls (22, 23) are parallel to the central axis.

6. The watch case (1) according to claim 3, characterised in that the amorphous metal alloy of the gasket (5, 5') is based mainly on zirconium.

7. The watch case (1) according to claim 3, characterised in that the amorphous metal alloy of the gasket (5, 5') is based mainly on platinum.

8. The watch case (1) according to claim 3, characterised in that the amorphous metal alloy of the gasket (5, 5') is based mainly on palladium.

9. The watch case (1) according to claim 1, characterised in that the defined angle of inclination of the annular peripheral surface (13) of the crystal (3) is of the order of 43° ± 5° relative to the central axis.

10. The watch case (1) according to claim 1, characterised in that the defined angle of inclination of the annular peripheral surface (13) of the crystal (3) and the inner annular surface (12) of the middle part (2) is of the order of 43° ± 5° relative to the central axis.

11. The watch case (1) according to claim 1, characterised in that the annular peripheral surface (13) of the crystal (3) comprises a deposit (63) for etching an inscription (103) by laser beam.

12. The watch case (1) according to claim 11, characterised in that the colour of the deposit (63) is different from the colour of a first portion (5) of the fastening gasket so as to view the inscription through the crystal (3) from outside the watch case.

13. The watch case (1) according to claim 1, characterised in that the annular peripheral surface (13) of the crystal (3) comprises a structuring intended to create a decoration (103).

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