waterproof 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 from a ceramic material. [Background technology]

[0002] Wristwatch cases are often made from ceramic materials, which have the advantage of being scratch-resistant due to their high hardness. For example, the prior art discloses waterproof watch cases made from ceramic materials, specifically sintered zirconium oxide, which typically has a hardness of around 1200 HV10.

[0003] For watch cases that must remain water-resistant to depths of hundreds of meters, or even up to 600 meters, water-resistance problems have been identified with ceramics with hardnesses exceeding 1600 HV10, such as silicon nitride. After analysis, this loss of water-resistance was attributed to the difficulty of achieving clean machining results for such hardness on the bearing surfaces of the joints that seal the case back and the middle section of the case. These surfaces are typically machined on CNC machines using diamond grinding wheels. These wheels machine the surface by rotating around themselves at high speeds. This rotational motion leaves machining scratches across the machined surface. As shown schematically in Figure 1, these scratches 5 are open to the outside of surfaces 2a and 3a and can create air ingress points that compromise the water-resistance of the case during use. Summary of the Invention

[0004] The aim of the present invention is to overcome this drawback by modifying the shape of the scratches so that they no longer open outside the surface. The invention consists in giving the surface that forms the sealing zone between the middle part and the case back, after machining, a satin finish, resulting in a set of concentric scratches. These grooves are contained within the periphery of the surface and prevent air from entering. When the joint deforms, it conforms to the shape of the grooves. The presence of the grooves on the same axis as the joint creates an air barrier and thus ensures a watertight seal. On the other hand, if the grooves run across the joint, the joint cannot deform enough to fill the grooves completely. This creates micro-channels of air and causes leakage deep within the joint.

[0005] More specifically, the present invention relates to a waterproof watch case, the waterproof watch case comprising a middle part, a back cover, and a sealing joint disposed between the middle part and the back cover, the middle part and the back cover being made of a ceramic material having a hardness of 1600 HV10 or more, the middle part comprising a lower side and the back cover comprising an upper side, the lower side and the upper side facing each other and acting as bearing surfaces for the sealing joint, the waterproof watch case being characterized in that the lower side and the upper side are formed by a set of concentric scratches. According to the present invention, the lower side and the upper side comprise only concentric scratches or are composed of concentric scratches.

[0006] Optimum effect is achieved if the lower and upper surfaces have a given roughness, namely the arithmetic mean of the roughness, referred to as roughness Ra, of the lower and upper surfaces in a direction perpendicular to the tangent at the point of the concentric scratches, of 0.1 to 0.8 μm, said roughness Ra being measured in said direction over the entire width of the lower and upper surfaces in accordance with standard ISO 4287, ASME B46.1-2019.

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

[0008] The invention further relates to a method of finishing said waterproof watch case, which method comprises the step of satin finishing the lower and upper surfaces to obtain a set of concentric scratches. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows a schematic representation of the sealing zone of a watch case according to the prior art, with scratches that open to the outside of the zone after machining. [Figure 2] 4 shows the same sealing zone after a satin finish according to the present invention. [Figure 3a-3b] 3a and 3b are optical microscope observations of the schematic diagrams shown in FIGS. 1 and 2, respectively. [Figure 4a-4b] Figures 4a and 4b show the directions in which the roughness measurements are taken. [Figure 5] FIG. 2 is a partial cross-sectional view of a watch case according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention relates to a waterproof watch case made from a ceramic material having a hardness of 1600 HV10 or greater, or even 1800 HV10 or greater. HV10 hardness is understood to mean the Vickers hardness measured in accordance with standard ISO 6507-1:2018. Preferably, the ceramic material is silicon nitride (Si3N4). According to the invention, the watch case can remain waterproof down to a depth of 600 meters, regardless of whether the system for assembling the back cover to the middle part is screw-type or otherwise.

[0011] The watch case 1 shown in the partial cross section of Figure 5 comprises, as is known, an intermediate part 2 and a back cover 3, with a sealing joint 4 arranged between the intermediate part 2 and the back cover 3 and intended to be compressed between a bearing surface 2a (also referred to as the lower surface) of the intermediate part 2 and a bearing surface 3a (also referred to as the upper surface) of the back cover 3. In the example shown, the watch case is circular and the joint is an O-ring. According to the 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 portion 2 includes a lower surface 2a, and the case back 3 includes an upper surface 3a, these two surfaces 2a, 3a facing each other and acting as bearing surfaces for the interface 4 as described above. Preferably, these bearing surfaces are flat. According to the invention, the lower surface 2a and the upper surface 3a have scratches 5 that do not open to the outer edges of said surfaces. This prevents air or liquid from entering the case. In particular, the scratches 5 visible in FIG. 2 form a set of concentric scratches around the central axis of the watch case. These scratches resemble in shape the surfaces and interface. That is, if the interface is circular, the scratches will also be circular and concentric; if the surfaces are substantially rectangular, the scratches will also be substantially rectangular and concentric, etc.

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

[0014] Advantageously, in the other direction perpendicular to the above direction, as shown in FIG. 4b, measured along the width L of the face from the outer periphery of the face and on the way to the outer periphery of the face, 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 invention, the scratches are produced by satin finishing. Preferably, the satin finishing is achieved using a diamond strip or a grinding wheel. Another technique consists in applying the satin finishing using a laser. The satin finishing is achieved after machining the lower and upper surfaces of the middle part and the back cover, respectively. The scratches are of variable width, typically less than 1 micron wide.

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

[0017] Despite the system used to assemble the middle section and the case back, optimal water resistance up to a depth of 600 metres is guaranteed thanks to the concentric grooves in the sealing zone between the middle section and the case back.

Claims

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

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 direction of the concentric scratches (5), said roughness Ra being measured in said direction over the entire width (L) of the lower and upper sides (2a) and (3a) in accordance with standards ISO 4287, ASME B46.1-2019.

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

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 the upper side (3a) and passing through the entire lower side (2a) and the upper side (3a), the roughness Ra is 0.1 to 0.7 μm and the roughness Rt is 1 to 4 μm.

5. 2. The waterproof watch case (1) according to claim 1, characterized in that the hardness is 1800 HV10 or higher.

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

7. 2. The waterproof watch case (1) according to claim 1, characterized in that the lower surface (2a) and the upper surface (3a) are flat surfaces including the concentric scratches (5).

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

9. 2. 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 surface (2a) and the upper surface (3a) to obtain the set of concentric scratches (5).

10. 10. The method of claim 9, wherein the satin finishing step is performed using a diamond strip or a grinding wheel.

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