WATERPROOF WATCHCASE

Description

Technical field of the invention

[0001] The present invention relates to a waterproof watch case, particularly for a diving watch. Technological background

[0002] To ensure the underwater use of a mechanical or electronic watch, the watch case, which houses a timekeeping movement or module, must be completely watertight. This is achieved by having a case back securely attached to one side of the case middle and a crystal attached to the opposite side. Sealing gaskets are used to assemble the case back, case middle, and crystal. A control or adjustment mechanism for the watch's functions is also mounted securely through the case middle when the watch is not in use.

[0003] Watch cases are generally not designed or assembled to withstand high water pressures, such as those encountered during diving, because the pressure inside the case is close to atmospheric pressure. Simple gaskets used on traditional watches are insufficient to guarantee a watertight seal for the case during dives to great depths underwater.

[0004] Patent application CH 690 870 A5 describes a waterproof watch case. The watch case consists of a crystal fixed on its upper side to a case-bezel and a case back fixed to the case by screwing it into an internal threaded hole in the case. The crystal is secured to the case by a toroidal, annular sealing gasket bearing against an edge of the case. A toroidal sealing gasket is also provided between an outer edge of the case back and a lower surface of the case. Since the threaded hole can be damaged under high water pressure, a resistant metal cup is also provided, bearing against an inner surface of the case back and against an inner edge of the case.However, even with such a watch case arrangement, it does not guarantee good water resistance of the case during a dive to very great depths underwater, especially below 4000 m depth (abyssal zone), which is a disadvantage.

[0005] Swiss patent CH 372 606 describes a waterproof watch case with a central section or case body surrounding a case back and closed by a crystal. A threaded ring rests against an inclined outer surface of the case back to retain it and is screwed into a mounting part connected to the case body. This arrangement does not guarantee a watertight seal for the case during dives to very great depths underwater, particularly below 4000 meters (the abyssal zone), which is a drawback.

[0006] Swiss patent CH 378 792 describes a watertight watch case. The crystal is a disc of transparent mineral material (glass, crystal). A setting of soft or malleable metal (gold, platinum, silver, copper, tin) is pressed onto the periphery of the crystal against an upper rim. This crystal and setting assembly is pressed into a cylindrical bore of a support, such as a case. The diameter of the cylindrical bore is slightly smaller than the outer diameter of the soft metal setting to ensure a good seal when the assembly is pressed into the cylindrical bore. The crystal includes a conical bearing surface on one inner side to make direct contact with a complementary conical bearing surface of the case.One drawback of this type of contact between the crystal and the case is that it's difficult to ensure good direct contact between the two conical surfaces, as there's a risk of misalignment, which could impact the mechanical strength of the assembly. Furthermore, even if a soft metal gasket can provide a good seal, its main disadvantage is that it must be replaced every time the watch case is opened, and as a general rule, it's preferable to use a material resistant to the external environment. Summary of the invention

[0007] The main purpose of the invention is therefore to overcome the disadvantages of the prior art described above by proposing a water-resistant watch case adapted to withstand high water pressures for deep-sea diving.

[0008] For this purpose, the present invention relates to a water-resistant watch case, which includes the features of independent claims 1 to 3.

[0009] Particular embodiments of a water-resistant watch case are defined in dependent claims 4 to 17.

[0010] An advantage of the present invention lies in the fact that direct contact is achieved between the crystal and the case along an annular contact line, preferably centered below a crystal retaining gasket in the upper part of the case, as viewed from the center of the watch case towards the crystal. The retaining gasket is located between an upper annular inner wall of the case and an upper annular outer wall of the crystal.

[0011] Advantageously, the crystal includes an annular peripheral surface inclined at an angle less than 90° to an axis perpendicular to a plane of the watch case. The annular peripheral surface includes a portion of a convex contact surface having a first radius for contacting an annular inner surface of the case with an inclination substantially equal to that of the annular peripheral surface. The contact between the two surfaces defines an annular contact line.

[0012] Preferably, the inner annular surface is inclined at an angle similar to that of the peripheral annular surface, but with a consistent slope and no variation in surface profile towards the center of the watch case. This ensures that the direct contact between the two inclined surfaces is well-centered.

[0013] When pressure is increased on the watch, the crystal is subjected to a force directed inwards. Given the pressure against the case, the consequences are a deflection of the center and a slight rotation of the outer (cylindrical and conical) walls of the crystal.

[0014] Due to the previously described curved geometry, the ice-frame contact zone shifts downwards from the generally conical surfaces at the curved contact area as pressure increases. This pressure also causes an increase in stress in the contact zone, which, through elastic deformation of the materials, increases the ice-frame bearing area and thus reduces local stresses in the frame and the ice. This significantly reduces the risk of compression fracture of the ice.

[0015] According to the prior art, direct contact is intended between two precisely machined surfaces of equivalent shape, for example, a conical annular peripheral surface in contact with a complementary conical annular inner surface. With such conical surfaces, the direct contact can occur at the lower or upper part of each surface, which can damage the glass or the case.

[0016] From a water-resistance standpoint, there are two main factors: first, the way the crystal is attached to the case via the gasket, and second, the effectiveness of the crystal itself should it break. If the crystal breaks, the system is no longer water-resistant, or at least the watch becomes unusable. If the crystal is attached to the case via a polymer gasket, the geometry of the crystal-case contact point directly impacts the crystal's resistance to pressure.

[0017] Advantageously, the convex contact surface can be located on the inner annular surface of the case, while the peripheral annular surface of the crystal has a regular slope towards the center of the watch case. The contact between the two surfaces is also well-centered. Furthermore, in yet another variant, each surface includes its own convex contact surface to establish direct contact with the other surface along a similarly well-centered contact line.

[0018] Advantageously, the watch case can take the form of a cylinder, an elliptical cylinder, a parallelepiped, or in the form of a prism or other shapes adaptable to a watch worn on a person's wrist.

[0019] In the case of a parallelepiped, at least four vertical flat walls are provided and arranged one after the other in the form of a ring. This means that the annular peripheral surface of the crystal, as well as the annular inner surface of the case, each comprises a set of walls inclined towards the center of the watch case and linked together to form a ring. Furthermore, curved sections are formed on the walls of one of the surfaces, while the other surface is composed of flat plates inclined towards the center of the watch case at a consistent slope, thus without variation in the profile of the inclined surface. Rounded edges may be incorporated at each wall connection of each inclined surface.

[0020] Furthermore, all the plates of the two surfaces of substantially complementary shape may include convex portions to come into contact with each other along an annular contact line in the centered position of the surfaces. Brief description of the figures

[0021] The purposes, advantages, and characteristics of a waterproof watch case will be best illustrated in the following non-exhaustive description, with reference to the drawings on which: THE figures 1a to 1c represent in a simplified manner a cross-section of a first embodiment of a water-resistant watch case according to the invention, and a partial detail section of the placement and attachment of the crystal to the case according to the invention, and a partial detail section before attachment of the crystal to the case according to the invention1, the figures 2a to 2crepresent, in a simplified manner, a cross-section of a second embodiment of a water-resistant watch case according to the invention, which is a variant of the first embodiment, and a partial detail cross-section of the placement and attachment of the crystal to the case according to the invention, and a partial detail cross-section before attachment of the crystal to the case according to the invention, the figures 3a to 3c represent, in a simplified manner, a cross-section of a third embodiment of a water-resistant watch case according to the invention, which is a combination of the first and second embodiments, and a partial detail cross-section of the placement and attachment of the crystal to the case according to the invention, and a partial detail cross-section before attachment of the crystal to the case according to the invention, the figures 4a to 4ddepict, from a top view, four case shapes for a watch to receive a circular, square, or rectangular crystal around its periphery, according to the invention; figures 5a and 5b show the state of stress at the mechanical contact of a portion of a convex contact surface, in particular of the annular peripheral surface of the glass in contact with the annular inner surface of the case, on the one hand at 1 bar of pressure of the glass against the case and on the other hand at 750 bars of pressure of the glass against the case according to the invention, and the Figures 6a and 6b show the state of stress at the mechanical contact of the conical annular peripheral surface of the glass in contact with the complementary conical annular inner surface of the case on the one hand at 1 bar of pressure of the glass against the case and on the other hand at 750 bars of pressure of the glass against the case according to the prior art. Detailed description of the invention

[0022] In the following description, all the components of a waterproof watch case, particularly a dive watch, which are well known to those skilled in this technical field, are described in simplified form. The location of the watch case components is given in the direction of the center of the watch case to the crystal.

[0023] THE figures 1a to 1crepresent a first embodiment of a watch case 1, which can be used for a diving watch. The watch case 1 essentially comprises a crystal 3, which may be made of sapphire or mineral glass, fixed to an upper side of a case middle 2 by means of a fixing gasket 5, and optionally a case back 4 mounted on a lower side of the case middle 2. A movement or watch module 10 may be disposed in the watch case 1 in a position indicated by the reference numeral 10. At least one control organ 9, such as a crown stem, may be mounted watertight in a resting position on or through the case middle 2 for setting the time, date, or other functions of the diving watch.

[0024] For attaching the crystal 3 to the upper side of the case 2, the annular fixing gasket 5 is positioned between an inner annular wall 22 of the case 2 and an outer annular wall 23 of the crystal 3. A case back 4 may be provided and sealed tightly to a lower portion of the case 2 by means of a toroidal-shaped annular sealing gasket 6, preferably placed in a groove 16 in the lower portion of the case 2 to hold it in position. An annular bearing surface 24 of the case back 4 comes into contact with an inner annular surface 32 of the case 2, the shape of which is complementary to the bearing surface 24, when the case back 4 is mounted on the case 2. The bearing surfaces 24 and the inner surface 32 are inclined at a predetermined angle with respect to an axis perpendicular to a plane of the watch case 1.

[0025] In the case of a case 2 of general cylindrical shape, the surfaces 24, 32 can be conical in shape and inclined from the outside to the inside of the watch case 1 at a determined angle with respect to a central axis of the watch case 1. This means that the apex of each cone shape is in the direction of the inside of the watch case 1. For a case 2 and a case back 4 made of a material, such as titanium or a specific type of steel, the angle can be on the order of 43° ± 5° with respect to the central axis.

[0026] Generally, the preferred material for case 2 should be a material with high mechanical strength or a high yield strength, i.e., greater than 500 MPa. Furthermore, since there is direct contact with the glass 3, friction between the two surfaces should be minimized as much as possible. Case 2 can be made, for example, of high-nitrogen stainless steel or grade 5 titanium (Ti6Al4V). For comparison, standard stainless steel has a yield strength between 200 and 250 MPa and a Young's modulus between 180 and 210 GPa, while high-nitrogen stainless steel has a yield strength between 500 and 700 MPa and a Young's modulus between 180 and 210 GPa. Grade 5 titanium has a yield strength between 800 and 900 MPa and a Young's modulus between 105 and 115 GPa.

[0027] For any watch case shape, the crystal 3 includes an annular peripheral surface 13 below the upper annular outer wall 23, configured to come into direct contact with an annular inner surface 12 below the upper annular inner wall 22 of the case 2. The annular peripheral surface 13 of the crystal 3 is inclined at a defined angle less than 90° with respect to an axis perpendicular to a plane of the watch case 1. Preferably, the annular inner surface 12 is inclined generally from the outside to the inside of the watch case 1 at the same angle as the annular peripheral surface 13 with respect to a central axis. However, the annular inner surface 12 of the case 2 is inclined with a regular slope towards the center of the watch case.

[0028] If the case 2 is generally cylindrical, the inner annular surface 12 may be conical and inclined at a defined angle from the outside to the inside of the watch case 1 with a regular slope and no variation in the surface profile. This means that the apex of the cone shape points towards the inside of the watch case 1. The defined angle of inclination of the surface 12 may be approximately 43° ± 5° with respect to the central axis. The peripheral annular surface 13, which may have a shape substantially complementary to the inner annular surface 12, may include a convex contact portion with a first radius R1 defined for contact along a circular annular line of contact against the inner annular surface 12 of the case 2, which is substantially conical and inclined towards the center of the watch case.This circular contact line is preferably located at mid-height of the peripheral annular surface 13, i.e., in a centered position. The first radius R1 can be chosen to be approximately 10.7 mm ± 5 mm. This results in a convex portion approximately 0.03 mm thick on the surface 13, which is sufficient to establish well-centered contact with the other surface 12.

[0029] In this case, convex curvature refers to a convex portion on the annular peripheral surface 13 that is in direct contact with the annular inner surface 12. This convex portion is annular in shape. A concave curvature, on the annular peripheral surface 13, would refer to a concave portion that cannot make contact with the annular inner surface 12 along a circular line of contact. Therefore, a convex curvature is chosen for the annular peripheral surface 13, which is the desired characteristic.

[0030] For illustrative purposes only, it is presented on the figures 4a to 4d Different simplified case shapes 2 seen from the top side of the dial. The external shape of case 2 may differ from the internal shape of case 2.

[0031] To the Figure 4a , the case 2 is generally cylindrical on the outside and inside, the annular inner wall 22 is cylindrical, while the inclined annular inner surface 12 is generally conical.

[0032] To the Figure 4b , the case 2 is generally cylindrical on the outside, and on the inside, at least four vertical flat walls 22 are provided and arranged one after the other in the form of a ring, while the annular inner surface 12 comprises four generally flat plates joined one after the other and inclined towards the center of the watch case.

[0033] To the Figure 4c , the case 2 is generally parallelepiped in shape with four sides on the outside and inside, the inner annular wall 22 is cylindrical in shape, while the inner inclined annular surface 12 is generally conical in shape.

[0034] To the figure 4d , the case 2 is generally parallelepiped in shape with four sides on the outside and inside, at least four vertical flat walls 22 are provided and arranged one after the other in the form of a ring, while the annular inner surface 12 comprises four generally flat plates joined one after the other and inclined towards the center of the watch case.

[0035] It should be noted that a different shape than the cylindrical form of the watch case 1 can still be considered, for example, a general cylindrical elliptical or parallelepiped shape, or a prism with more than four vertical walls. The case middle 2 can also be of a different shape, as specified above for the watch case 1, since the case middle 2 forms the major part of the watch case 1. In this case, the annular inner surface 12 can be composed of at least three or four generally flat walls joined to each other in an annular shape. Each flat wall is inclined from the outside to the inside of the watch case at a defined angle less than 90° towards the center of the watch case 1, with a slope that can be regular without variation in the surface profile.For the annular peripheral surface 13, several convex contact portions are made on all at least three or four walls connected to each other for contact on an annular line of contact against the annular inner surface 12. It may be provided further rounding at each connection of walls of each inclined surface by maintaining the convex portion even in the roundings, not shown in figures.

[0036] For comparison, and due to manufacturing tolerances in the case of a cylindrical watch case as shown in the figures 1a to 1c , 2a to 2c And 3a to 3cA cone-on-cone contact is rarely perfect. The point of contact between the two conical surfaces tends to be located towards the lower or upper part of each surface. FEM simulations show that having a portion of the contact surface curved with a radius R1 of surface 13 for ice 3 or R1' of surface 12 for carcass 2 is beneficial in all cases, and especially compared to a perfect cone-on-cone contact as shown in the attached tables.

[0037] It is further provided that an upper portion of the peripheral annular surface 13 of the ice 3 includes a convex curvature of a second radius R2 in contact with the upper outer annular wall 23 of the ice 3, and preferably following the convex curvature of first radius R1. The second radius R2 is smaller than the first radius R1 of convex curvature of the domed portions for the contact of surfaces 12 and 13. Preferably, the second radius R2 is more than 10 times smaller than the first radius R1, for example 0.75 mm ± 0.2 mm. The curvature of radius R2 of the upper portion of the annular peripheral surface 13 of the glass 3 makes it easier to mount the glass 3 on the frame 2 by means of the fixing joint 5. This fixing joint 5 can be made of polyurethane or even cross-linked polyurethane and be annular in shape for example with a thickness of about 0.65 mm ± 0.2 mm and a height of about 2.5 mm ± 0.5 mm.

[0038] It should also be noted that the annular peripheral surface 13 of the ice 3 may include, on its lower part, a convex curve of a third radius R3 to avoid having an excessively sharp edge and thus prevent any contact with a flat surface on the lower part of the annular inner surface 12 of the frame 2. This flat surface may be approximately 3 mm from the ice 3. The third radius R3 is less than, or preferably equal to, the second radius R2. The curvature with a third radius R3, which preferably follows the convex curve of the first radius R1, further prevents the risk of chipping the ice 3.

[0039] For the production of the sapphire crystal 3, a process known as Czochralski or EFG (Edge Defined Film Fed Growth) can be used. The domed portion(s) can be obtained by machining or a finishing process. The machining process for the case 2 is stamping, and the interior is turned, as is the case for the domed portion. The coefficient of friction is determined primarily by the domed portion(s) produced, in combination with the surface roughness of the case 2 and the crystal 3. The coefficient of friction can be reduced depending on the surface finish, i.e., the roughness of the two contacting parts.

[0040] The first three tables below concern, on the one hand, the tensile stress at the center, and on the other hand, the stress on the glass side, and the stress on the frame side with a variation of inclination of +0.5° and -0.5° depending on the coefficient of friction between the glass and the frame:

[0041] The stress calculations are determined above using the tables, depending on whether the glass 3 has a conical support against the frame 2, which also has a conical support, or whether the curvature has a first radius R1 on the glass 3 side or a complementary first radius R1' on the frame 2 side, and this is based on the coefficient of friction as indicated above. In each case, the stress is minimized, ideally remaining below 380 MPa for the tensile strength of the glass 3 and below 560 MPa for a high-yield-strength steel type used for the frame 2.

[0042] The tables above also take into account a -0.5° difference in angle between ice 3 and frame 2 (with support on the outside of the cone at the top) or a +0.5° difference (support on the inside of the cone at the bottom). In this case, we see that, in terms of ice tension, the conical support is good in the ideal case but poses a problem when the support is offset to the outside, whereas in terms of frame stress, it poses a problem in all cases.

[0043] The frame-side shelving 2 works best, but the glass-side shelving 3 is simpler and also allows for absorbing the effect of tolerances.

[0044] In the three tables shown below, the offset error is increased. Thus, the error on the angle of ice 3 has risen to -3°, which shows that in all cases it is the conical support that most degrades the conditions.

[0045] In addition, a comparison is presented below for the use of an amorphous metal gasket or ring (BMG) between surfaces 12 and 13, or for the present invention without the amorphous metal gasket or ring. A type of material is also specified for the case 2, while for the crystal 3, it is sapphire or mineral glass. Firstly, the six tables presented below concern tests of crystal mounting on the case according to the materials used, as indicated below, and with or without an intermediate gasket. In this first test, the first three tables compare the results with and without a BMG ring for a conical support, and the second three tables compare the results with a slightly radiating crystal.

[0046] It is observed that for traction at the center of the lens 3, what matters is how well the lens 3 is supported. At a low coefficient of friction, direct support is better because there are fewer interfaces that can slide against each other, and at a high coefficient of friction, what matters is that the lens 3 rests on a material with a high modulus of elasticity (steel or ceramic rather than gold or BMG). It is likely that even for a radiused lens 3, the coefficient of friction is low enough that the direct-support version is better from this point of view. At the case 2, the BMG joint, on the other hand, allows for limiting stresses at a high coefficient of friction for cone-on-cone support, but it is a priori even more advantageous to have a radius on the lens to achieve this result with direct contact with the surface 12 of the case, which is what the present invention seeks.

[0047] It should also be noted that the previous tables could have included a pressure limit, specifically to indicate a maximum permissible and achievable pressure. One must stop when one of the three limits (maximum ice traction 380 MPa, maximum ice compression 2000 MPa, or maximum frame compression from 500 MPa to 1200 MPa) is reached. However, it remains clear that the most unfavorable case is direct cone-on-cone contact. Furthermore, there is always an advantage to the versions without a seal or BMG ring.

[0048] THE figures 2a to 2c represent a second embodiment of a water-resistant watch case. As this second embodiment closely resembles the first embodiment, only the differences observed compared to the first embodiment will be explained.

[0049] The essential difference of the second embodiment is that the portion of the convex contact surface is no longer located on the annular peripheral surface 13 of the crystal 3, but on the annular inner surface 12 of the case 2. On the other hand, the annular peripheral surface 13 of the crystal is this time inclined at a regular slope without variation in the surface from the outside to the inside of the watch case 1. The complementary first radius curvature R1' can be of the same value as that of the first radius curvature R1, but in an opposite configuration.

[0050] The second radius R2 and third radius R3 curves remain made on the annular peripheral surface 13 of the ice 3 in the same places as for the first form of execution.

[0051] The curvature of the convex portion of radius R1 or R1' is positioned on one of the surfaces 12 and 13, oriented from bottom to top, i.e., in axial section with an arc of a circle placed from bottom to top. The curvatures of radii R2 and R3 are also oriented from bottom to top.

[0052] THE figures 3a to 3c represent a third embodiment of a water-resistant watch case. Since this third embodiment closely resembles the first and second embodiments, only the differences observed compared to the first and second embodiments will be explained. Primarily, the third embodiment incorporates the domed portions described above in the first and second embodiments.

[0053] The annular peripheral surface 13 of the ice 3 comprises a convex contact surface portion of first radius R1, and the annular inner surface 12 also comprises a convex contact surface portion of complementary first radius R1'. The two curvatures are surfaces 12 and 13, which each form annular convex portions to come into contact with each other along an annular contact line and in a centered position on each surface 12 and 13. The two radii R1 and R1' are preferably similar but may also be slightly different from each other.

[0054] The annular peripheral surface 13 of the ice 3 still includes the curves of radius R2 and R3. As mentioned above, the second radius R2 and third radius R3 curves remain on the annular peripheral surface 13 of the ice 3 in the same locations as for the first and second versions. The same values ​​of radius R2 and R3 are also retained.

[0055] In this embodiment, the annular fixing gasket 5 can be made of polyurethane or even cross-linked polyurethane. For a frame 2 with a generally cylindrical shape, the fixing gasket 5 is cylindrical. Once the lens 3 is mounted on the frame 2, the fixing gasket 5 is attached to an annular inner wall 22 of the frame 2 and an annular outer wall 23 of the lens 3 above the annular peripheral surface 13.

[0056] By way of example, the height of the fixing joint 5 can be approximately 2.5 mm. The thickness of the joint can be approximately 0.65 mm.

[0057] It should also be noted that with the attachment of crystal 3 to case 2 in the embodiments described above, and with the contact between a surface with a convex radius of curvature and a conical surface between crystal 3 and case 2, good water resistance and even distribution of stress between crystal 3 and case 2 are guaranteed. This is necessary because the watch is a diving watch that must withstand significant stresses due to the pressure difference between the watch's interior and the water pressure at great depths underwater. Since the contact surface between case 2 and crystal 3 is quite large with this conical shape, there is better stress transmission over a larger area, which is important for reducing stress concentrations in the crystal and thus preventing its breakage during a deep dive. This also ensures the water resistance of the watch case.With this design, the water pressure on the watch case tends to close any gaps between the contact surfaces. Furthermore, it prevents extrusion between the crystal and the inside of the case.

[0058] THE Figures 5A and 5B show the mechanical contact between the ice and the case via the portion of the convex contact surface made on the ice in this embodiment firstly at a pressure of 1 bar ( figure 5A ) and secondly at a pressure of 750 bars ( Figure 5B ). The convex contact surface portion is located on the annular peripheral surface of the glass to come into contact with the annular inner surface of the frame.

[0059] It is still shown on these Figures 5A and 5BThe gray area represents the contact pressure along the interface between the lens and the frame. The thickness of this gray area corresponds to the intensity of the contact pressure as a function of position. In this configuration, with the contact of the convex portion of the annular peripheral surface of the lens on the conical surface of the frame, the pressure is clearly centered on the contact zone. Furthermore, with the larger, high-pressure contact area between the lens and the frame, there is a better distribution of contact forces and less risk of breakage of the lens or the frame, which is advantageous.

[0060] THE Figures 6A and 6B demonstrate, according to prior art, the mechanical contact between two conical surfaces of the glass and the case, firstly at a pressure of 1 bar ( Figure 6A ) and secondly at a pressure of 750 bars ( Figure 6B ).

[0061] It is still shown on these Figures 6A and 6BThe gray area represents the contact pressure along the interface between the lens and the frame. The thickness of this gray area corresponds to the intensity of the contact pressure as a function of position. In this embodiment, with the conical support, not only is the contact made more on the outside, but the maximum pressure is also completely offset towards the outside of the initial contact zone, which is a disadvantage.

[0062] Based on the description above, several variations in the design of the watch case can be conceived by a person skilled in the art without departing from the scope of the invention as defined by the claims. The watch case, by virtue of its shape, can have a general form other than a cylinder.

Claims

1. Water-resistant watch case (1), particularly for a diving watch, the case (1) comprising at least one crystal (3) mounted on a portion of a middle (2), a fastening gasket (5) of the crystal (3) being disposed between an annular inner wall (22) of the middle (2) and an annular outer wall (23) of the crystal (3), - the case being arranged so that, between the annular outer wall (23) and the centre of the watch case (1), the crystal (3) comprises an annular peripheral surface (13) inclined at a defined angle smaller than 90° in relation to an axis perpendicular to a plane of the watch case (1) and coming into direct contact against an annular inner surface (12) of the middle (2), the annular inner surface (12) being inclined at an angle similar to the angle of inclination of the annular peripheral surface (13) and disposed below the annular inner wall (22) of the middle (2), - characterised in that the annular peripheral surface (13) comprises a domed contact surface portion with a convex curvature having a first radius (R1) defining an annular contact line against the annular inner surface (12) of the middle (2).

2. Water-resistant watch case (1), particularly for a diving watch, the case (1) comprising at least one crystal (3) mounted on a portion of a middle (2), a fastening gasket (5) of the crystal (3) being disposed between an annular inner wall (22) of the middle (2) and an annular outer wall (23) of the crystal (3), - the case being arranged so that, between the annular inner wall (22) and the centre of the watch case (1), the middle (2) comprises an annular inner surface (12) inclined at a defined angle smaller than 90° in relation to an axis perpendicular to a plane of the watch case (1) and coming into direct contact against an annular peripheral surface (13) of the crystal (3), the annular peripheral surface (13) being inclined at an angle similar to the inclination of the annular inner surface (12) and disposed below the annular outer wall (23) of the crystal (3), - characterised in that the annular inner surface (12) comprises a domed contact surface portion with a convex curvature having a first complementary radius (R1') defining an annular contact line against the annular peripheral surface (13) of the crystal (3).

3. Water-resistant watch case (1), particularly for a diving watch, the case (1) comprising at least one crystal (3) mounted on a portion of a middle (2), a fastening gasket (5) of the crystal (3) being disposed between an annular inner wall (22) of the middle (2) and an annular outer wall (23) of the crystal (3), the case being arranged so that, between the annular outer wall (22) and the centre of the watch case (1), the middle (2) comprises an annular inner surface (12) inclined at an angle similar to the angle of inclination of the annular peripheral surface (13), and coming into direct contact against the annular peripheral surface (13) of the crystal (3),characterised in that the annular peripheral surface (13) comprises a domed contact surface portion with a convex curvature having a first radius (R1), whereas the annular inner surface (12) comprises a domed contact surface portion with a convex curvature of a first complementary radius (R1') defining an annular contact line against the annular peripheral surface (13) of the crystal (3).

4. Watch case (1) according to claim 1, characterised in that the annular inner surface (12) of the middle (2) is inclined with a regular slope without variation of the profile of the surface in the direction of the centre of the watch case.

5. Watch case (1) according to claim 2, characterised in that the annular peripheral surface (13) of the crystal (3) is inclined with a regular slope without variation of the profile of the surface in the direction of the centre of the watch case.

6. Watch case (1) according to one of claims 1 to 3, characterised in that the fastening gasket (5) is made of polyurethane or of cross-linked polyurethane.

7. Watch case (1) according to one of claims 1 to 3, characterised in that the middle (2) is made of material with elastic limit higher than 500 MPa, and in that the crystal (3) is made of sapphire.

8. Watch case (1) according to claim 7, characterised in that the middle (2) is made of stainless steel with high nitrogen content or of grade 5 titanium (Ti6Al4V).

9. Watch case (1) according to one of claims 1 to 3, characterised in that the first radius (R1) and / or the first complementary radius (R1') are chosen in the order of 10.7 mm ± 5 mm.

10. Watch case (1) according to one of claims 1 to 3, characterised in that a top portion of the annular peripheral surface (13) of the crystal (3) comprises a curvature of a second radius (R2) in connection with the upper annular outer wall (23) of the crystal (3), for which the second radius (R2) is smaller than the first radius (R1) of curvature of the domed portions, to facilitate the mounting of the crystal (3) on the middle (2) by means of the fastening gasket (5).

11. Watch case (1) according to claim 10, characterised in that a bottom portion of the annular peripheral surface (13) of the crystal (3) comprises a curvature of a third radius (R3) to avoid having too sharp an edge, and in that the third radius (R3) is smaller than or equal to the second radius (R2).

12. Watch case (1) according to one of claims 10 and 11, characterised in that the second radius (R2) and / or the third radius (R3) are of value more than 10 times smaller than the first radius (R1).

13. Watch case (1) according to claim 12, characterised in that the second radius (R2) and / or the third radius (R3) are chosen in the order of 0.75 mm ± 0.2 mm.

14. Watch case (1) according to one of the preceding claims, characterised in that the watch case (1) is of generally cylinder shape, in that the annular inner wall (22) of the middle (2) and the annular outer wall (23) of the crystal (3) are of cylindrical shape, and in that the annular peripheral surface (13) and the annular inner surface (12) are of generally conical shape with domed contract surface portions on one of the surfaces or the two surfaces to have a direct contact on an annular contact line.

15. Watch case (1) according to one of claims 1 to 13, characterised in that the middle (2) of the watch case (1) is of generally external cylindrical shape, and in that the annular inner wall (22) consists of four vertical flat walls (22) provided and disposed one after the other in the shape of a ring, whereas the annular inner surface (12) comprises four generally flat plates joined one after another and inclined in the direction of the centre of the watch case.

16. Watch case (1) according to one of claims 1 to 13, characterised in that the middle (2) of the watch case (1) is of generally external parallelepiped shape with four sides, and in that in the inside, the annular inner wall (22) is of generally cylindrical shape, whereas the inclined annular inner surface (12) is of generally conical shape.

17. Watch case (1) according to one of claims 1 to 13, characterised in that the middle (2) of the watch case (1) is of generally parallelepiped shape with four sides on the outside, and in that the annular inner wall (22) consists of four vertical flat walls provided and disposed one after the other in the shape of a ring, whereas the annular inner surface (12) comprises four generally flat plates joined one after another and inclined in the direction of the centre of the watch case.