Watertight watch case

Abstract

To provide a watertight watch case.SOLUTION: A watertight watch case 1 includes: a middle part 2; a back cover 3; and a sealing joint 4 disposed between the middle part and the back cover. Therein: the middle part and the back cover are made of a ceramic material having a hardness of 1600 HV10 or more; the middle part includes a lower lateral face 2a; the back cover includes an upper lateral face 3a; the lower and upper lateral faces face each other and act as bearing surfaces for the sealing joint; and the watertight wristwatch case is characterized in that the lower and upper lateral faces are formed by a set of concentric scratches. The other aspect of the present invention relates to a method of finishing a waterproof watch case. The method includes a step of performing satin-finishing to obtain a set of concentric scratches.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Watch cases are often made of ceramic materials. Ceramic materials have the advantage of being highly hard and difficult to scratch. For example, the prior art discloses a waterproof watch case made of a ceramic material, specifically, a zirconium oxide sintered body typically having a hardness of around 1200 in terms of HV10.

[0003] In the case of a watch case that must maintain waterproofness up to several hundred meters, or even up to 600 meters, in water, problems with waterproofness have been confirmed in ceramics with a hardness exceeding 1600 in terms of HV10, such as silicon nitride. After analysis, such loss of waterproofness was due to the difficulty of achieving a clean machining result for such hardness on the bearing surfaces of the joints that seal the middle part and the back cover of the case. These surfaces are typically machined on a CNC machine using a diamond grinding wheel. These wheels machine the surface by rotating at high speed around themselves. This rotational movement leaves machining scratches on the entire machined surface. As schematically shown in FIG. 1, these scratches 5 open to the outside of the surfaces 2a, 3a and can form air entry points that impair the waterproofness of the case during use.

Summary of the Invention

[0004] The object of the present invention is, in order to overcome this drawback, to modify the shape of the scratch so that it no longer opens to the outside of the surface. The present invention aims to obtain a set of concentric scratches on the surface forming the sealing zone between the intermediate part and the back cover after machining. These grooves are included within the periphery of the surface to prevent air intrusion. When the joint deforms, the joint conforms to the shape of the groove. The presence of the groove on the same axis as the joint provides an air barrier and thus ensures a waterproof seal. On the other hand, when the groove runs across the joint, the joint cannot deform enough to fill all the grooves. This results in a micro-passage for air and leakage occurs deep within the joint.

[0005] Specifically, the present invention relates to a waterproof watch case, which includes an intermediate part, a back cover, and a sealing joint disposed between the intermediate part and the back cover. The intermediate part and the back cover are made of a ceramic material having a hardness of HV10 of 1600 or more. The intermediate part includes a lower surface, and the back cover includes an upper surface. The lower surface and the upper surface face each other and act as a supporting surface for the sealing joint. The waterproof watch case is characterized in that the lower surface and the upper surface are formed by a set of concentric scratches. According to the present invention, the lower surface and the upper surface include only concentric scratches or are composed of concentric scratches.

[0006] Optimal results are obtained if the lower surface and the upper surface have a given roughness. That is, the arithmetic mean of the roughness, designated as Ra, of the lower surface and the upper surface is 0.1 to 0.8 μm in a direction perpendicular to the tangent at the point of the concentric scratches, and the roughness Ra is measured over the entire width of the lower surface and the upper surface in said direction in accordance with standard ISO 4287, ASME B46.1-2019.

[0007] Furthermore, the maximum roughness, designated as Rt, measured in accordance with standard ISO 4287, ASME B46.1-2019 in the same direction over the entire width of the lower surface and the upper surface is 1 to 5 μm.

[0008] The present invention further relates to a method of finishing the waterproof watch case, the method including the step of satin-finishing the lower and upper surfaces to obtain a set of concentric scratches.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figures 3a - 3b

Figures 4a - 4b

Figure 5

Embodiments for Carrying Out the Invention

[0010] The present invention relates to a waterproof watch case made of a ceramic material having a hardness of HV10 of 1600 or more, or also having a hardness of HV10 of 1800 or more. The HV10 hardness is understood to mean the Vickers hardness measured according to the standard ISO 6507-1:2018. Preferably, the ceramic material is silicon nitride (Si 3 N 4 ). According to the present invention, the watch case can remain waterproof up to a depth of 600 meters, regardless of whether the system for assembling the back cover to the middle part is a screw-in type or other type.

[0011] As is well known, the watch case 1 shown in the partial cross-sectional view of FIG. 5 includes an intermediate part 2 and a back cover 3, and a sealing joint 4 is arranged between the intermediate part 2 and the back cover 3, and is intended to be compressed between the bearing surface 2a (also referred to as the lower surface) of the intermediate part 2 and the bearing surface 3a (also referred to as the upper surface) of the back cover 3. In the illustrated example, the watch case is circular and the joint is an O-ring. According to the present invention, the watch case may be of any shape (square, oval, etc.), and the joint may be of any shape or material.

[0012] The intermediate part 2 includes a lower surface 2a, and the back cover 3 includes an upper surface 3a. These two surfaces 2a, 3a face each other and act as bearing surfaces for the joint 4 as described above. Preferably, these bearing surfaces are flat. According to the present invention, the lower surface 2a and the upper surface 3a have scratches 5 that do not open towards the outer peripheral edges of the two surfaces. Thereby, air or liquid is prevented from entering the case. Specifically, the scratches 5 visible in FIG. 2 form a set of concentric scratches around the central axis of the watch case. The shape of these scratches is similar to that of the two surfaces and the joint. That is, if the joint is circular, the scratches are also circular and concentric. If the two surfaces are substantially rectangular, the scratches are also substantially rectangular and concentric, etc.

[0013] According to the present invention, the surface finish is determined by the shape of the scratches and the roughness of the surface including the scratches. For the purpose of obtaining the optimal effect, the arithmetic mean roughness Ra measured in accordance with the standards ISO 4287, ASME B46.1-2019 is 0.1 to 0.8 μm in the direction perpendicular to the tangent of the points of the concentric scratches over the entire width L of the lower surface and the upper surface, as shown in FIG. 4a. In the same direction, the maximum roughness Rt measured in accordance with the same standard is 1 to 5 μm.

[0014] Advantageously, in another direction perpendicular to the above direction, as shown in FIG. 4b, when measured along the width L of the surface from and towards the outer peripheral edge of the surface, the arithmetic mean roughness Ra is 0.1 to 0.7 μm, and the maximum roughness Rt is 1 to 4 μm.

[0015] According to the present invention, the scratches are produced by satin finishing. Preferably, the satin finishing is performed using a diamond strip or a grinding wheel. Other techniques consist of applying satin finishing using a laser. The satin finishing is performed after machining the lower and upper surfaces of the intermediate part and the back cover, respectively. The scratches have a variable width and are typically less than 1 micron wide.

[0016] Figure 3a shows the surface of one of the two faces after machining without satin finishing according to the present invention, while Figure 3b shows the same surface after the satin finishing step. These results are shown in Figures 1 and 2, respectively.

[0017] Despite the system used to assemble the intermediate part and the back cover, the concentric grooves in the sealing zone between the intermediate part and the back cover ensure optimal waterproofness up to a depth of 600 meters.

Claims

1. A waterproof watch case (1), comprising an intermediate part (2), a back cover (3) and a sealing joint (4) arranged between said intermediate part (2) and said back cover (3), said intermediate part (2) and said back cover (3) being made of a ceramic material having a hardness HV10 of 1600 or more, said intermediate part (2) comprising a lower side (2a) and said back cover (3) comprising an upper side (3a), said lower side and upper side (2a, 3a) facing each other and acting as bearing surfaces for said sealing joint (4), The waterproof watch case (1) is characterized in that the lower and upper sides (2a, 3a) are formed by a set of concentric scratches (5).

2. 2. Waterproof watch case (1) according to claim 1, characterized in that the arithmetic mean of the roughness, referred to as roughness Ra, of the lower and upper sides (2a, 3a) is between 0.1 and 0.8 μm in a direction perpendicular to the tangent of the point of the concentric scratch (5), said roughness Ra being measured in said direction over the entire width (L) of the lower and upper sides (2a) and (3a) according to standards ISO 4287, ASME B46.1-2019.

3. 3. Waterproof watch case (1) according to claim 2, characterized in that the lower side (2a) and the upper side (3a) have a maximum roughness, referred to as roughness Rt, measured in accordance with standards ISO 4287, ASME B46.1-2019 in said direction over the entire width (L) of between 1 and 5 μm.

4. A waterproof watch case (1) as described in claim 2 or 3, characterized in that in a direction perpendicular to the direction, along the width (L) of the lower side (2a) and upper side (3a) and passing through the entire lower side (2a) and upper side (3a), the roughness Ra is 0.1 to 0.7 μm and the roughness Rt is 1 to 4 μm.

5. 2. A waterproof watch case (1) according to claim 1, characterized in that the hardness is equal to or greater than HV10, i.e. 1800.

6. 2. Waterproof watch case (1) according to claim 1, characterized in that the ceramic material is silicon nitride.

7. 2. Waterproof watch case (1) according to claim 1, characterized in that the lower side (2a) and the upper side (3a) are flat.

8. 2. The waterproof watch case (1) according to claim 1, characterized in that it can maintain waterproofness up to a depth of 600 meters.

9. A method for finishing a waterproof watch case (1) according to claim 1, characterized in that it comprises the step of satin finishing the lower side (2a) and the upper side (3a) to obtain the set of concentric scratches (5).

10. 10. The method for finishing the waterproof watch case (1) according to claim 9, characterized in that the satin finishing step is performed using diamond strips or grinding wheels.

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