METHOD FOR ASSEMBLING A GLASS WITH A WRISTWATCH CASE

Description

Technical field of the invention

[0001] The invention relates to a method of assembling a glass with a watch case, more particularly a glass provided above an analog time display.

[0002] In the context of the invention, it is provided to fix the glass to the case by gluing to form a watch. In the advantageous case where the case comprises a part forming a bezel, the assembly is preferably carried out without an elastomer seal between the side wall of the glass and the inner wall of the bezel located opposite this side wall. Technological background

[0003] The fixing of a watch glass, in particular made of crystal, by gluing has been proposed for various watches, in particular for designs without an upper rim of the case radially surrounding the glass, that is to say without a conventional bezel. Such an embodiment is proposed for example in patent document CH 622 151 which describes a watch case formed from a caseband having a horizontal upper face on which a sapphire glass is glued by the peripheral zone of its inner face, which is located opposite the horizontal upper face of the caseband. To hide the glue from the view of a user observing the finished watch, the glass may have in said peripheral zone of the glass a thin, opaque metallic coating with high adhesion for the glue selected for assembly.This coating may be provided so that it extends inwards a little beyond said peripheral zone, so as to also mask the edge of the dial in an axial view through the glass.

[0004] This document teaches a technique for improving the aesthetic appearance of the assembled 'case and glass' assembly, namely machining, in particular grinding, the lateral surface of the glass and the top of the outer surface of the caseband. This results in a continuous surface between the lateral surface of the glass and the caseband, and in addition such machining makes it possible to remove any glue residue that may have flowed outside the horizontal upper face, which is very likely. It should be noted that removing excess glue from the outside of the case can also be done by other means, in particular by using a chemical product. However, a major problem arises from the fact that the glue can flow inside the case, into the space provided between the dial and the glass for an analog time display, in particular along the inner vertical surface of the caseband delimiting this space.For this reason, vision into this space has been reduced by the metallic masking coating that extends over the area at the edge of the dial.

[0005] Document JP S56-27686 U describes various variant embodiments of an upper part of a watch case arranged to receive a glass and its attachment to the case by gluing. The upper part defines an annular surface which is glued to a lower surface of the glass. The glue easily overflows from the inner side of the annular surface, along a lateral surface defining an enclosed space under the glass and visible through the glass, so that any overflow of the glue from the central side of the watch, as shown in the first figure, is clearly visible.

[0006] Document FR 2524992 describes, with reference to its figures 1 to 3, a watch with a glass glued to a flange, which is fixed to a caseband by claws. In the variant shown in the figure 3, a projecting part of the case, forming an upper edge of the caseband, covers the lateral surface of the glass. A slot between the outer vertical surface of the flange and the projecting part allows excess glue to flow into this slot. This solves the problem of excess glue on the outer side of the flange provided that the top of the slot can be uniformly covered by the glue, but another problem arises from the fact that the flange is then glued to the case, which complicates the disassembly of the `flange and glass' assembly in the event that, for example, the glass needs to be replaced, in particular after a possible crack in this glass. Concerning the problem of excess glue being able to flow along the inner lateral surface of the flange, which is visible through the glass, it remains unresolved in document FR 2524992. Summary of the invention

[0007] The main objective of the present invention is to solve the problem mentioned above in connection with the bonding of a glass to an annular shoulder, in particular a horizontal annular surface, of a watch case, by preventing glue from flowing into the enclosed space intended for the display, in particular analog, of the watch. A secondary objective is to achieve the main objective while ensuring that the annular surface of the watch case, intended to be bonded with a peripheral lower surface of the inner face of the glass, can receive sufficient glue to ensure that this annular surface is entirely covered with glue, preferably uniformly.

[0008] To this end, the invention relates to a method for assembling a glass to a case to form a watch, the case having an annular surface which is intended to be bonded to a lower peripheral surface of an inner face of the glass. The watch comprises a flange having an upper surface and dimensioned to be able to be force-fitted, along an insertion axis, along an axial surface, also called vertical, inside an upper part of the case, the axial surface, or even vertical inside, limiting the annular surface of the central side of the case.

[0009] The assembly process includes the following steps: partial insertion of the flange inside an opening defined by said axial surface, or even interior vertical surface; depositing glue on the annular surface of the box and / or on said lower peripheral surface; and then the following steps: bringing the glass against the upper surface of the flange in a final horizontal position of the glass in which its peripheral lower surface is axially superimposed on the annular surface, the upper surface of the flange then being in contact with a contact surface of the inner face of the glass adjacent to the peripheral lower surface, this contact surface and the upper surface of the flange being configured so that there is at least one continuous annular contact zone between these two surfaces;exerting axial pressure on an outer face of the glass with an intensity allowing the insertion of the flange to continue progressively in said opening until the upper surface of the flange has reached a final axial position, which is provided above said annular surface, and the lower peripheral surface of the glass is covered by the glue so as to form a continuous ring of glue between said annular surface of the case and the lower peripheral surface of the glass; hardening of the glue to form a watertight seal.

[0010] According to an advantageous variant, at the end of the step of exerting axial pressure on the outer face of the glass, the upper surface of the flange is located axially above the annular surface of the case, at an axial distance greater than 20 µm and less than 100 µm. For this purpose, in a particular variant, the case comprises a shoulder forming an axial stop for the flange. Preferably, the stop defines an annular stop surface which is continuous and parallel to a lower surface of the flange, which bears against the entire continuous annular stop surface at the end of the step of exerting axial pressure on the outer face of the glass.

[0011] In another advantageous variant, said inner vertical surface is parallel to at least one continuous annular zone of an outer lateral surface of the flange, which is configured such that this continuous annular zone is continuously in contact with the inner vertical surface once this continuous annular zone is inserted along this inner vertical surface.

[0012] According to a main embodiment, the upper part of the box comprises a projecting part forming a rim defining a side wall which rises axially from the outer periphery of said annular surface, this side wall radially surrounding the glass at the end of the step of exerting axial pressure on the outer face of the glass. In an advantageous variant, a part of the glue rises in a slot left between a side face of the glass and the side wall of the rim, the tight seal formed entirely covering said annular surface and at least partially filling the slot. Brief description of the figures

[0013] The invention will be described below in more detail with the aid of the appended drawings, given as non-limiting examples, in which: there Figure 1shows a watch case and a flange in a first intermediate state which occurs during the assembly process according to the invention; the Figure 2 shows the case, the flange and a glass in a second intermediate state occurring during the assembly process according to the invention; and the Figure 3 shows the case, the flange and the glass in a final state resulting from the assembly process according to the invention. Detailed description of the invention

[0014] With reference to the attached figures, a main embodiment of the method of assembling a glass to a case according to the invention, to form a watch, will be described below.

[0015] The case 4, intended for the watch 2, is formed in a single piece defining a back 6 and a caseband-bezel. Other variants with a separate back and / or a bezel separate from the caseband are also envisaged. It will be noted that, in the description of the invention, the terminology used distinguishes, for the sake of clarity, the case 4 from the flange 18 and the glass 26 which thus form three separate elements which are initially separate. The case comprises an upper part 5 which has a first shoulder defining an annular surface 13, which is horizontal in the variant described. By 'horizontal surface' is meant a surface perpendicular to a central axis of the case 4. This annular surface is intended to be bonded with a lower peripheral surface 25 of an inner face 27 of the glass 26, the lower peripheral surface defining a surface parallel to this annular surface.In other variants, the lower peripheral surface of the glass is generally parallel to the annular surface, this annular surface or the lower peripheral surface being parallel except for example in a median annular zone where an annular groove is provided, located substantially in the middle of the width of the annular surface, to form a recess for receiving an adhesive 20a provided for assembling the glass to the box and thus forming a median zone of the watertight seal 20b, obtained following this assembly, with a greater thickness of adhesive.

[0016] Next, the upper part 5 of the case 4 defines an inner vertical surface 14 which limits the annular surface 13 on the inner side of the case, this inner vertical surface descending from the inner periphery of the annular surface. The upper part 5 comprises a projecting part forming a rim 12, which defines a side wall 28 which rises vertically from the outer periphery of the annular surface 13, this vertical side wall being intended to radially surround, in a conventional manner, the glass 26 once the latter is placed in the upper opening of the bezel of the case 4 to close this case. It will be noted that the adjective 'vertical' and the adverb 'vertically' respectively mean 'axial' and 'axially', that is to say along a central axis of the watch case.The watch 2 further comprises a flange 18 which is distinct from the upper part 5 of the case and which is sized to be able to be inserted by force, along an insertion axis coinciding with the central axis of the case, into an opening of the upper part 5, along the interior vertical surface 14 which defines this opening. This interior vertical surface limits the annular surface of the central side of the case. The flange 18 has an upper surface 19 provided opposite a contact surface 29 of the interior face 27 of the glass once the glass is mounted in the case, this contact surface 29 being adjacent to the peripheral lower surface 25.Generally, the upper surface 19 and the contact surface 29 are configured so that there is at least one continuous annular contact zone between these two surfaces when the glass 26 is applied against the flange 18 once this glass has been introduced into the housing formed by the upper opening of the bezel of the case 4. Preferably, the upper surface 19 and the contact surface 29 of the glass are parallel.

[0017] The case also comprises a second shoulder forming a stop 15 for the flange 18. It will be noted that the stop, provided to define a final axial positioning of the flange 18 or a lower limit for this flange, can also be formed by a casing circle provided for the movement 8, by the movement itself or by the dial 10 arranged above the movement. However, given the manufacturing tolerances of each part and also the assembly tolerances of the various elements provided in the case, it is preferable that the stop provided for the flange 18 be formed by the case itself. More generally, it is advantageous for the annular surface 13 and the stop 15 to be defined by the same part, which makes it possible to precisely manage the axial distance between the annular surface 13 and the stop 15. This advantage will emerge more precisely from the following description of the assembly method according to the invention.The stop 15 defines an annular stop surface which is parallel to a lower surface 32 of the flange, which is located opposite this annular stop surface once the flange is inserted along the inner vertical surface 14 of the case 4. Preferably, the inner vertical surface 14 of the case 4 is parallel to at least one continuous annular zone of the outer lateral surface 30 of the flange, which is configured such that this continuous annular zone is continuously in contact with the inner vertical surface 14 once this continuous annular zone is inserted along the inner vertical surface. In an advantageous variant, the continuous annular zone is formed by a lower part of the outer lateral surface 30 of the flange.In a particular variant, the interior vertical surface 14 of the box 4 is parallel to the external lateral surface of the flange, at least to the part of this external lateral surface which is provided opposite the interior vertical surface once the flange is in its final position in the box 4.

[0018] To form the watch 2, it is planned to introduce into the case 4 firstly a movement 8 with a dial 10, this movement being provided with a minute hand 22 and an hour hand 23 forming an analogue display of the time 24.

[0019] The process of assembling the glass 26 to the box 4 comprises the following two steps: partial insertion of the flange 18 inside the opening defined by the interior vertical surface 14 over an axial distance which is less than the height of the flange, the upper surface 19 of the flange being positioned, following this partial insertion, above the annular surface 13 and above a final axial position provided for this upper surface; depositing an adhesive 20a on the annular surface 13 of the box and / or on the lower peripheral surface 25 of the glass; and then the following three steps: bringing the glass 26 against the upper surface 19 of the flange 18 and positioning this glass substantially in a final horizontal position, in which the annular surface 13 of the case is axially superimposed on the lower peripheral surface 25 of the glass, and so that the upper surface of the flange is in contact with a contact surface 29 of the inner face 27 of the glass, the contact surface and the upper surface of the flange being configured so that there is at least one continuous annular contact zone between these two surfaces;exerting axial pressure on the outer face of the glass with an intensity allowing the insertion of the flange 18 to continue progressively in the corresponding opening, defined by the inner vertical surface 14, until the lower peripheral surface 25 of the glass is covered by the glue 20a so as to form a continuous ring of glue between the annular surface 13 of the case and the lower peripheral surface 25 of the glass, and the upper surface 19 of the flange has reached said final axial position, which is provided above said annular surface 13; and curing of the glue to form a watertight seal 20b. ;

[0020] Thanks to the characteristics of the method of assembling the glass to the case according to the invention, no glue flows along the internal lateral face 34 of the flange 18. It will be noted that the introduction of the movement 8 with the dial 10 from the top can, in a variant, be provided between the deposition of the glue and the partial insertion of the flange mentioned above. In a variant where the case comprises a back which is provided to be removable relative to the caseband, the introduction of the movement and the dial with the analog display can take place from the bottom, that is to say through an opening intended to be closed by the back, following the assembly method.

[0021] In an advantageous variant, the flange 18 is brought into abutment against the stop 15 at the end of the step of exerting axial pressure on the outer face of the glass. The lower surface 32 of the flange then bears against an entire annular stop surface, which is defined by the stop. In another variant, a stop for the flange can be formed by the dial 10. However, as already indicated, this latter variant presents a problem of tolerances, so that it is more difficult to be able to properly manage the final level of the upper surface 19 of the flange at the end of the step of exerting axial pressure.

[0022] In another advantageous variant, it is provided that, at the end of the step of exerting axial pressure on the outer face of the glass, the upper surface 19 of the flange 18 is located axially above the annular surface 13 of the case, at an axial distance greater than 20 microns (20 µm) and less than or equal to 100 microns (100 µm). In particular, given the manufacturing tolerances, an axial distance between 60 and 70 microns (60 - 70 µm) will be taken, for example, as a set value. This ensures that the watertight seal 20b, formed by the glue 20a and obtained after the step of hardening this glue, has a certain non-zero thickness.

[0023] In a first variant of another embodiment of the assembly method, a certain thickness of the adhesive joint 20b can be obtained by structuring the annular surface 13 or the corresponding peripheral lower surface 25. In particular, the annular surface has a structuring defining hollow zones and / or paths for the adhesive 20a. In a second variant, provision is made to introduce spacers, in particular small-sized balls (for example having a diameter between 50 and 150 micrometers), into the adhesive. The spacers are incorporated into the adhesive 20a to ensure a minimum thickness for the leaktight joint 20b over the entire annular surface 13. This other embodiment of the invention not only makes it possible to guarantee a certain non-zero thickness for the adhesive forming the leaktight joint, but also for this thickness to be substantially constant. Thus, the thickness of the adhesive before hardening can be well managed.It will be noted that in this other mode, the presence of a stop 15 to determine a final axial positioning of the flange is not essential to prevent the flange from finally arriving at the same level as the annular surface 13, because it is the aforementioned structuring or the spacers, in particular glass beads or synthetic beads, which guarantee that the axial pressure exerted on the glass 26 does not bring these two surfaces to the same level, that is to say to the same axial position.

[0024] The exertion of axial pressure on the outer face of the glass 26 is preferably maintained at least during a first part of the step of hardening the glue 20a.

[0025] In the variant shown in the figures, as already indicated, the upper part 5 of the box 4 comprises a projecting part forming a rim 12 which defines a side wall 28 rising axially from the outer periphery of the annular surface 13, this side wall radially surrounding the glass 26 at the end of the step of exerting axial pressure on the outer face of the glass. Preferably, the quantity of glue 20a supplied during the step of depositing a glue is provided so that, during the step of exerting axial pressure on the outer face of the glass, a part of the glue rises in a slot left between a side face of the glass and the side wall 28 of the rim 12. Thus, the watertight seal 20b formed entirely covers the annular surface 13 and at least partially fills the slot.This slot therefore has the function of a reservoir for receiving excess glue, in addition to also participating in the fixing of the glass 26 to the box 4 by gluing and ensuring sufficient sealing of the glue joint 20b obtained.

Claims

1. Method for assembling a glass (26) to a case (4) to form a watch (2), the case having an annular surface (13) which is intended to be bonded to a peripheral lower surface (25) of an inner face (27) of the glass; characterised in that the watch comprises a flange (18) having an upper surface (19) and sized to be able to be forcibly inserted, along an insertion axis, along an inner vertical surface (14) of an upper part (5) of the case, the inner vertical surface (14) bounding the annular surface (13) on the central side of the case; this assembly method comprising the following steps of: - partially inserting the flange into an opening defined by said inner vertical surface (14); - depositing an adhesive (20a) on the annular surface (13) of the case and / or on said peripheral lower surface (25); followed by the following steps of: - bringing the glass against the upper surface (19) of the flange (18) in a final horizontal position of the glass in which the peripheral lower surface (25) thereof is axially superimposed on the annular surface (13), the upper surface (19) of the flange thus being in contact with a contact surface (29) of the inner face (27) of the glass adjacent to the peripheral lower surface (25), this contact surface (29) and the upper surface (19) of the flange being configured such that there is at least one continuous annular contact zone between these two surfaces; - exerting an axial pressure on an outer face of the glass with an intensity that allows the insertion of the flange into said opening to gradually continue until the upper surface (19) of the flange has reached a final axial position, which position is provided above said annular surface (13), and until the peripheral lower surface (25) of the glass is covered by the adhesive so as to form a continuous ring of adhesive between said annular surface (13) of the case and the peripheral lower surface (25) of the glass; - hardening the adhesive to form a tight joint (20b).

2. Assembly method according to claim 1, characterised in that the case (4) comprises a shoulder forming a banking (15) for the flange (18).

3. Assembly method according to claim 2, characterised in that the banking (15) defines an annular stop surface which is continuous and parallel to a lower surface (32) of the flange, which bears against the entire continuous annular stop surface at the end of the step of exerting an axial pressure on the outer face of the glass.

4. Assembly method according to any one of the preceding claims, characterised in that said inner vertical surface (14) is parallel to at least one continuous annular zone of an outer side surface (30) of the flange, which is configured such that this continuous annular zone is continuously in contact with the inner vertical surface (14) once this continuous annular zone has been inserted along this inner vertical surface.

5. Assembly method according to any one of the preceding claims, characterised in that the axial pressure on the outer face of the glass (26) is maintained at least during a first part of the step of hardening the adhesive.

6. Assembly method according to any one of the preceding claims, characterised in that, at the end of the step of exerting an axial pressure on the outer face of the glass (26), said upper surface (19) is located above said annular surface (13), at an axial distance of greater than 20 micrometres and less than 100 micrometres.

7. Assembly method according to any one of the preceding claims, characterised in that the annular surface (13) of the case or the peripheral lower surface (25) of the glass (26) has a pattern defining concave zones and / or paths for the adhesive.

8. Assembly method according to any one of claims 1 to 6, characterised in that spacers are incorporated into the adhesive (20a) so as to guarantee a minimum thickness of the tight joint (20b) over the entire annular surface (13).

9. Assembly method according to any one of the preceding claims, characterised in that the upper part (5) of the case comprises a projecting part forming a rim (12) defining a side wall (28) which rises axially from the outer periphery of said annular surface, this side wall radially surrounding the glass at the end of the step of exerting an axial pressure on the outer face of the glass.

10. Assembly method according to claim 9, characterised in that the amount of adhesive provided in the step of depositing an adhesive is designed such that, in the step of exerting an axial pressure on the outer face of the glass, some of the adhesive rises into a groove left between a side face of the glass and the side wall of the rim, said formed tight joint (20b) completely covering said annular surface and at least partially filling the groove.