Watertight watch case

Abstract

One aspect of the invention relates to a waterproof watch case (1) comprising a case middle (2), a back (3) and a seal (4) arranged between the case middle (2) and the back (3), the case middle (2) and the back (3) being made of a ceramic material having a hardness greater than or equal to 1600 HV10, said case middle (2) comprising a lower face (2a) and the back (3) comprising an upper face (3a), said lower and upper faces (2a, 3a) being opposite each other and serving as bearing surfaces for said seal (4), the waterproof watch case (1) being characterized in that said lower and upper faces (2a, 3a) are formed of a set of concentric stripes (5). Another aspect of the invention relates to the method for finishing the waterproof watch case comprising a satin-finishing step to obtain the set of concentric stripes (5).

Description

Technical field of the invention

[0001] The invention relates to a waterproof watch case made of a ceramic material. Technological background

[0002] Watch cases are frequently made from a ceramic material which has the advantage of having a high hardness which guarantees its ability to resist scratching. For example, a waterproof watch case made from a ceramic and in particular from a sintered zirconium oxide which typically has an HV10 hardness of around 1200 is known from the prior art.

[0003] For watch cases that need to remain watertight to depths of several hundred meters, or even up to 600 meters, watertightness problems have been observed for ceramics with hardnesses greater than 1600 HV10, such as silicon nitride. After analysis, this loss of watertightness was attributed to the difficulty of performing clean machining for such hardnesses on the bearing surfaces of the gasket ensuring watertightness between the caseband and the case back. These surfaces are typically machined on numerically controlled machines with diamond grinding wheels. These grind the surface by rotating on themselves at high speed. This rotational movement leaves machining scratches across the entire machined surface. As shown schematically in Figure 1 , these scratches 5 open outside the surface 2a, 3a and can form air entry points in use which compromise the sealing of the box. Summary of the invention

[0004] The present invention aims to overcome this drawback by modifying the shape of the grooves so that they no longer open outside the surface. The invention consists of carrying out, after machining, a satin finish on the surfaces forming the sealing zone between the caseband and the back so as to obtain a set of concentric grooves. These grooves are contained within the perimeter of the surface, which prevents air from entering. The gasket, by deforming, follows the shape of the grooves. Having grooves in the same axis as the gasket makes it possible to act as a barrier to air and thus guarantees sealing. On the contrary, when the grooves are transverse to the gasket, the latter cannot deform sufficiently to fill the entirety of the grooves. This leads to micro-passages for air and makes the assembly non-watertight at great depths.

[0005] More specifically, the present invention relates to a waterproof watch case comprising a case middle, a back and a seal disposed between the case middle and the back, the case middle and the back being made of a ceramic material having a hardness greater than or equal to 1600 HV10, said case middle comprising a lower face and the back comprising an upper face, said lower and upper faces facing each other and serving as bearing surfaces for said seal, the waterproof watch case being characterized in that said lower and upper faces are formed of a set of concentric stripes. According to the invention, said lower and upper faces comprise only, are made up of, concentric stripes.

[0006] An optimal effect is obtained if the lower and upper faces have a given roughness. Thus, the arithmetic mean of the roughness, called roughness Ra, of said lower and upper faces is between 0.1 and 0.8 µm in a direction which is a direction perpendicular to the tangent at a point of the concentric scratches, said roughness Ra being measured according to ISO 4287, ASME B46.1 - 2019 over the entire width of the lower and upper faces in said direction.

[0007] Furthermore, in this same direction over the entire width of the lower and upper faces, the maximum roughness, called roughness Rt, measured according to ISO 4287, ASME B46.1 - 2019 is between 1 and 5 µm.

[0008] The present invention also relates to the method of finishing said waterproof watch case comprising a step of satin-finishing the lower and upper faces to obtain all of the concentric stripes. Brief description of the figures

[0009] There Figure 1 schematically represents a sealing area of ​​the watch case with scratches opening outside the area following machining, according to the prior art. Figure 2 represents this same sealing zone after satin finishing according to the invention. The Figures 3a and 3b are optical microscopy observations of the respective schematic representations of the Figures 1 and 2 . THE Figures 4a and 4b represent the directions in which roughness measurements are made. The Figure 5 is a partial sectional view of the watch case according to the invention. Detailed description of the invention

[0010] The invention relates to a waterproof watch case made of a ceramic material having a hardness greater than or equal to 1600 HV10, or even greater than or equal to 1800 HV10. HV10 hardness is understood to mean a Vickers hardness measured according to the ISO 6507-1:2018 standard. Preferably, the ceramic material is a silicon nitride (Si 3 N 4 ). According to the invention, the watch case is capable of remaining waterproof to a depth of 600 meters regardless of the assembly system of the back and the caseband, by screwing or otherwise.

[0011] Watch case 1 shown partially in section at Figure 5comprises in a known manner a case middle 2 and a back 3 with a seal 4 arranged between the case middle and the back and intended to be compressed between a bearing surface 2a, also called the lower face, of the case middle 2 and a bearing surface 3a, also called the upper face, of the back 3. In the example illustrated, the watch case is circular and the seal is an O-ring seal. According to the invention, the watch case can have any shape (square, oblong, etc.) and the seal can be of any shape and material.

[0012] The case 2 comprises the lower face 2a and the back 3 comprises the upper face 3a, the two faces 2a, 3a being opposite each other and serving as bearing surfaces for the seal 4 as mentioned above. Preferably, these bearing surfaces are flat. According to the invention, the lower face 2a and the upper face 3a have grooves 5 which have the characteristic of not opening onto the outer perimeter of said faces. Thus, air or a liquid cannot infiltrate inside the case. More precisely, the grooves 5 visible at Figure 2 form a set of concentric stripes around the central axis of the watch case. These stripes have a shape similar to that of the faces and the gasket. Thus, if the latter are circular, the stripes will be circular and concentric. If the faces are approximately rectangular, the stripes will be approximately rectangular and concentric, etc.

[0013] According to the invention, the surface condition is conditioned by the shape of the scratches as well as by the roughness of the surface comprising the scratches. For an optimum effect, the arithmetic mean roughness Ra measured according to ISO 4287, ASME B46.1 - 2019 is between 0.1 and 0.8 µm in a direction perpendicular to the tangent at a point of the concentric scratches as shown diagrammatically in Figure 4a over the entire width L of the lower and upper faces. In this same direction, the maximum roughness Rt measured according to the same standard is between 1 and 5 µm.

[0014] Advantageously, in another direction perpendicular to the aforementioned direction, with measurements taken at mid-width L of the face, from and towards the outer perimeter of the face as illustrated in Figure 4b , the arithmetic mean roughness Ra is between 0.1 and 0.7 µm and the maximum roughness Rt is between 1 and 4 µm.

[0015] According to the present invention, the scratches are made by satin finishing. Preferably, the satin finishing is carried out with diamond strips or wheels. Another technology is to carry out the satin finishing by laser. The satin finishing is carried out after machining the lower and upper faces of the caseband and the back respectively. The scratches can be of variable widths with a size width typically less than one micron.

[0016] There Figure 3a presents the surface of one of the two faces after machining, without the satin finishing step according to the invention, whereas the Figure 3b presents this same surface after the satin finishing step. These results are shown diagrammatically respectively at Figures 1 and 2 .

[0017] Regardless of the assembly system between the case and the back, optimal water resistance up to a depth of 600 meters is ensured thanks to the concentric grooves in the waterproofing zone between the case and the back.

Claims

1. Waterproof watch case (1) comprising a case middle (2), a back (3) and a seal (4) arranged between the case middle (2) and the back (3), the case middle (2) and the back (3) being made of a ceramic material having a hardness greater than or equal to 1600 HV10, said case middle (2) comprising a lower face (2a) and the back (3) comprising an upper face (3a), said lower and upper faces (2a, 3a) being opposite each other and serving as bearing surfaces for said seal (4), the waterproof watch case (1) being characterized in that said lower and upper faces (2a, 3a) are formed from a set of concentric stripes (5).

2. Waterproof watch case (1) according to claim 1, characterized in thatthe arithmetic mean of the roughness, called roughness Ra, of said lower and upper faces (2a, 3a), is between 0.1 and 0.8 µm in a direction which is a direction perpendicular to the tangent at a point of the concentric scratches (5), said roughness Ra being measured according to standard ISO 4287, ASME B46.1 - 2019 over the entire width (L) of the lower (2a) and upper (3a) faces in said direction.

3. Waterproof watch case (1) according to claim 2, characterized in that , in said direction over the entire width (L) of the lower (2a) and upper (3a) faces, the maximum roughness, called roughness Rt, measured according to standard ISO 4287, ASME B46.1 - 2019 is between 1 and 5 µm.

4. Waterproof watch case (1) according to claim 2 or 3, characterized in thatin a direction perpendicular to said direction, crossing entirely said lower (2a) and upper (3a) faces at mid-width L, the roughness Ra is between 0.1 and 0.7 µm and the roughness Rt is between 1 and 4 µm.

5. Waterproof watch case (1) according to one of the preceding claims, characterized in that hardness is greater than or equal to 1800 HV10.

6. Waterproof watch case (1) according to one of the preceding claims, characterized in that The ceramic material is silicon nitride.

7. Waterproof watch case (1) according to one of the preceding claims, characterized in that in that the lower (2a) and upper (3a) faces are flat.

8. Waterproof watch case (1) according to one of the preceding claims, characterized in that It is able to remain waterproof up to a depth of 600 meters.

9. Method for finishing the waterproof watch case (1) according to one of the preceding claims,characterized in that it comprises a step of satin finishing the said lower (2a) and upper (3a) faces to obtain all of the concentric stripes (5).

10. Method for finishing the waterproof watch case (1) according to the preceding claim, characterized in that The satin finishing step is carried out with diamond bands or wheels.

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