GB2086095A

GB2086095A - Bezel and crystal assembly

Info

Publication number: GB2086095A
Application number: GB8129701A
Authority: GB
Original assignee: Timex Corp
Current assignee: Timex Group USA Inc
Priority date: 1980-10-08
Filing date: 1981-10-01
Publication date: 1982-05-06
Also published as: JPS5791232A; FR2491644B3; FR2491644A1

Abstract

A transparent crystal 4 of thermoplastic material is received in the central opening in a watchcase or bezel 2 and includes a rear wall 4c supported on an annular shoulder 2d of the case, and a side wall 4d adjacent the case wall 2a which defines the case opening and which also defines an annular groove 2c extending into the case. The crystal 4 also includes a front wall 4a having a narrow band of material around its periphery which is thermoplastically worked by means of a heated tool 6 and deformed toward the supported rear wall 4c to form in situ a narrow annular trough 4e in the front wall and a flange 4f on the side wall extending into the groove 2c in the case to stake the crystal 4 and case 2 together and reduce infiltration of foreign matter into the case. A dust and water-resistant case/crystal assembly can be made by interposing a sealing gasket (not shown) between the case and crystal such that the gasket is compressed during thermoplastic writing and maintained in the compressed condition by staking of the flange of the crystal into the case groove. During heating and deformation of the narrow band of material on the front wall of the crystal, the case wall 2a in effect functions as a mould surface for the thermoplastic working step, and the shoulder 2d provides support against unwanted deformation of the crystal. <IMAGE>

Description

SPECIFICATION Bezel and crystal assembly The present invention relates to a bezel and crystal assembly, for example as part of a watchcase, and to a method for making the assembly.

Various arrangements have been utilized by prior art workers to assemble a watch crystal to a watchcase or bezel in a fashion which is resistant over long times to infiltration by dust and/or moisture.

In US-PS 2,308,189 a plastics crystal is united to a circular projection on a cylindrical movement ring (or inner case) under heat and pressure. The movement ring is heated and placed in a mould with a core extending through the movement ring. A transparent plastics sheet is then heated to a sufficiently high temperature to effect softening and then is positioned over the mould, heated movement ring and core. A piston is thereafter brought to bear on the softened sheet and the piston pressure works the sheet into a desired crystal shape against the core and at the same time moulds portions of the sheet around the circular projection of the movement ring to tightly unite the components. Pressure is maintained until the movement ring and crystal sheet cool down.The piston apparently also functions as a punch for removal of excess sheet not needed for the watch crystal, or the excess sheet is removed in a separate trimming operation. The core is necessary in the process since the crystal sheet is softened overall and would deform to an unacceptable shape without proper support and shaping on the core. In one embodiment of the patent, the movement ring/crystal assembly is placed in an outer watchcase which bears externally upon the crystal. In another embodiment, the crystal is united under heat and pressure directly to an outer case.

In US-PS 2,607,082 a thermoplastic watch crystal having an outer groove is pressed into a metallic bezel having an inwardly projecting flange such that the flange is received in the crystal groove. The crystal/bezel subassembly is then placed on a support within the coils of an induction heater. When the coils are energized, the metallic bezel is heated sufficiently by induction to soften the plastics of the crystal in the vicinity of the bezel flange and cause plastic flow around the flange, thereby creating a tight seal.

US-PS 2,357,904 heats the peripheral rim of a thermoplastic crystal to a plastic state and concurrently flexes or bows the crystal by contact with suitable flexing members. While the crystal is flexed with its rim in a plastic state, a bezel with an inner annular groove is placed around the rim of the crystal. As soon as the bezel is properly positioned, the flexing members contacting the crystal are released and the springiness of the crystal resulting from its being flexed causes the crystal to expand in diameter and thereby force the crystal rim in the plastic state into the groove in the bezel to provide a fluid-tight and dust-tight union therebetween.

US-PS 530,817 discloses a technique for inlaying a celluloid sheet in a metal frame by placing the celluloid sheet in the metal frame and pressing the celluloid sheet from both sides with heated plates to compress the sheet and cause lateral expansion of the sheet edges into a groove in the metal frame.

US-PS 2,720,748 provides a watertight watchcase/crystal assembly by swaging or pressing a thin metallic frame and then injection moulding transparent plastics material around the frame to form a transparent crystal integrally with a case.

Other prior art workers have used a watchcase and crystal held together by compressive force exerted by a movement ring or the like and have employed a sealing gasket between the components to provide watertightness.

DE-OFS 28 1 7 770 discloses a number of different watchcase/crystal/sea li ng gasket assemblies in which a plastics crystal is premoulded to include a projecting flange to fit in a groove in the sealing gasket and the sealing gasket in turn includes a pre-moulded projecting flange to fit in a groove in the watchcase.

Briefly, the present invention concerns a bezel and crystal assembly in which the crystal is made of thermoplastic material and is received in a central opening in the bezel. The bezel opening is defined by a first wall which also defines an annular groove around the opening extending into the case. A second wall intersects the first wall to provide an annular shoulder extending into the bezel opening. The watch crystal includes a rear wall supported on the annular shoulder, a side wall adjacent the first wall of the bezel and a front wall.The front wall includes a narrow annular band of material around its periphery thermoplastically worked toward the rear wall of the crystal, forming in situ a narrow annular trough in the front wall and a flange on the side wall extending outwardly into the groove in the bezel to stake the crystal and bezel together and to reduce infiltration of foreign matter at the joint.

The invention also concerns a method for making a bezel and crystal assembly, comprising the steps of: a) providing a bezel having a first wall defining a central opening and an annular groove extending outwardly into the bezel and having a second wall intersecting the first wall to form an annular shoulder extending inwardly into the opening, b) making a transparent crystal of thermoplastic material to include a rear wall, a side wall and a front wall, c) placing the crystal in the central opening of the bezel with the rear wall supported by the annular shoulder of the bezel and the side wall adjacent the first wall of the bezel the front wall of the crystal facing away from the annular shoulder, and d) heating and pressing a narrow annular band of material around the periphery of the front wall of the crystal toward the rear wall while the rear wall is supported against deformation on the annular shoulder to effect thermoplastic working of said band of material and formation of a narrow annular trough in the front wall and a flange on the side wall with the flange extending into the annular groove in the first wall of the bezel to stake the bezel and crystal together.

Typically, the front wall of the crystal includes a peripheral lip of selected narrow width which is worked by a heated shell punch having a plan outline like that of the lip. It is important to note that only a narrow annular band of the crystal front wall is heated and worked by the tool.

Working occurs in situ in the bezel and is possible because the annular shoulder of the bezel supports the rear wall of the crystal against deformation and the first wall of the bezel functions as a mould surface. The annular trough formed in the front wall of the crystal is formed narrow enough that it does not materially detract from the crystal appearance.

A sealing gasket may be disposed between the bezel and crystal to provide a dust and waterresistant assembly. In one preferred embodiment, the sealing gasket is disposed between the rear wall of the crystal and the annular shoulder of the bezel and is compressed when the front wall of the crystal is thermoplastically worked. In another preferred embodiment, the first wall of the bezel defines an additional groove which is adapted to receive the sealing gasket with a portion of the gasket projecting out of the groove. The side wall of the crystal includes a portion overlying and contacting the projecting portion of the gasket so that when the front wall is thermoplastically worked, the sealing gasket is compressed for effective sealing. In both embodiments, the sealing gasket is maintained in the compressed condition by staking of the flange of the crystal in the groove of the bezel.

Some preferred embodiments of the invention will now be described by way of example, reference being made to the accompanying drawings in which: Figure 1 a is a partial cross-section of a watchcase and crystal assembly before thermoplastic working of the crystal, Figure 1 b is a partial cross-section of the same assembly with the heated shell punch being lowered onto the crystal, Figure 1 c is a partial cross-section of the assembly after thermoplastic working of the crystal, Figure 2a is a partial cross-section of another embodiment of case/crystal/gasket assembly before thermoplastic working of the crystal, Figure 2b is a partial cross-section of the assembly of Figure 2a after thermoplastic working of the crystal, Figure 3a is a partial cross-section of a further embodiment of case/crystal/gasket assembly before thermoplastic working of the crystal, and Figure 3b is a partial cross-section of the assembly of Figure 3a after thermoplastic working of the crystal.

Figure 1 a shows a watch bezel or case 2 and a watch crystal 4 loosely assembled prior to thermoplastic working of the crystal. The case includes a first wall 2a which defines a central opening 2b in which the crystal is received and an annular groove 2c extending around the opening outwardly into the watchcase. A second wall 2d intersects the first wall 2a and forms an annular shoulder extending inwardly into central opening 2b. The case typically is metallic although high temperature plastics or other material which will not be deformed by the heat necessary for thermoplastic working of the crystal can be employed.

The crystal is made of transparent thermoplastic material, such as acrylic, and is preferably made to include a front wall 4a having a peripheral lip 4b generally co-planar with the adjacent front lip 2e of the case for purposes to be described hereafter, a rear wall 4c supported on the second wall 2d (annular shoulder) of the case and a side wall 4d adjacent the first wall 2a and groove 2c of the case. Side wall 4d of the crystal is spaced slightly from first wall 2a to allow easy placement of the crystal in the case opening. Of course, the overall plan outline of the crystal is matched to that of the case opening 2b and may be circular, oval, rectangular or other shapes. The crystal may be moulded with the features described or it may be provided in simple sheet form.

Figure 1 b shows a heated steel shell punch 6 about to be brought to bear against the crystal 4.

The shell punch includes a depending annular rib 6a having a plan outline like that of peripheral lip 4b of the front wall 4a of the crystal. The width of the rib 6a is sufficiently small that only a narrow annular band of material corresponding to lip 4b on the front wall 4a of the crystal wall be heated and worked. For example, a rib width of 0.25mm has been employed. The punch including rib 6b is heated by electric heating element 7, e.g., 125 watt/240 volt, to a sufficiently high temperature to place the narrow band of material in the plastic condition when the rib 6a is pressed on lip 4b of the front wall 4a, thereby forming an annular trough 4e (Figure 1 c) and displacing the material outwardly into contact with the first wall 2a of the case and, importantly, into groove 2c in the form of a flange 4f to stake the crystal and case together, e.g., as shown in Figure 1 c. Annular lip 4b on the front crystal wall should be substantially co-planar with lip 2e on the case so that first wall 2a of the case can act more or less as a mould surface during thermoplastic working of the narrow band of crystal material adjacent thereto.

During pressing of the rib 6a onto lip 4b of front crystal wall, the second wall 2d (annular shoulder) of the case supports the rear wall 4c of the crystal against unwanted deformation. The watchcase/crystal assembly thus produced provides a dust-resistant joint between these components.

Figures 2a and 2b show a preferred embodiment for providing an assembly which is dust and water-resistant, wherein like features are represented by like numerals primed. For example, case 2' includes first wall 2a' providing the central opening 2b' and annular groove 2c' and second wall 2d' providing the annular shoulder extending inwardly into the central opening. The crystal 4' includes front wall 4a' with lip 4b', rear wall 4c' and side wall 4d'. However, in addition to these components, an annular sealing gasket 8' is provided between the rear wall of the crystal and the annular shoulder of the case. The gasket 8' may be a bead of resilient material such as silicone rubber applied to the rear wall of the crystal or, alternatively, to annular shoulder, e.g., by a conventional screen printing process.Of course, the gasket can also be preformed of rubber or other resilient material and simply placed between the components.

It should be apparent that when the rib of the punch (not shown) is brought to bear downwardly against lip 4b' of the front wall of the crystal, as described hereinabove, the gasket 8' will be compressed between the rear wall of the crystal and annular shoulder of the case to provide a very effective seal, Figure 2b, which imparts water resistance as well as dust resistance to the assembly. The sealing gasket will be maintained in the compressed state by the flange 4f' being staked into groove 2c' of the case.

Figures 3a and 3b illustrate another preferred assembly having dust and water-resistence, wherein like features are represented by like numerals double primed. It is apparent that the first wall 2a" of the case is modified in this embodiment to define the first groove 2c" provided in the above described embodiments and in addition a second groove 2f" below the first groove to receive a portion of sealing gasket 8" while a portion projects out of the groove. It-is also apparent that side wall 4d" of the crystal is modified to include a shoulder 4g" overlying and contacting the projecting portion of the sealing gasket. When the rib of the heated shell punch is pressed onto lip 4b" of the front crystal wall, the sealing gasket is compressed radially and axially, Figure 3b, to form a tight seal resistant to penetration by water as well as dust and is maintained in this condition by staking of the flange 4f" into groove 2c".

As used herein, a "bezel" is intended to include any frame or housing for holding a crystal, including but not limited to a watch bezel and watch case.

Claims

1. A bezel and crystal assembly, comprising a bezel having a first wall defining a central opening and an annular groove extending outwardly into the bezel and having a second wall intersecting the first wall to form an annular shoulder extending inwardly into the opening; and a transparent crystal of thermoplastic material received in the opening, said crystal having a rear wall supported on the annular shoulder, a side wall adjacent the first wall of the bezel and a front wall having a narrow annular band of material around its periphery thermoplastically worked toward the rear wall, forming in situ an annular trough in said front wall and a flange on the side wall, the flange extending outwardly into the groove in said bezel to stake the crystal and bezel together and reduce infiltration of foreign matter between said bezel and crystal.

2. A bezel and crystal assembly, comprising a bezel having a first wall defining a central opening and an annular groove extending outwardly into the bezel and having a second wall intersecting the first wall to form an annular shoulder extending inwardly into the opening, a transparent crystal of thermoplastic material received in the opening, said crystal having a rear wall supported on the annular shoulder, a side wall adjacent the first wall of the bezel and a front wall having a narrow annular band of material around its periphery thermoplastically worked toward the rear wall, forming in situ an annular trough in said front wall and a flange on the side wall, the flange extending outwardly into the groove in said bezel to stake the crystal and bezel together; and a sealing gasket disposed between the bezel and crystal, said sealing gasket being in a compressed condition by action of the crystal thereagainst and held in the compressed condition by said flange being staked into the groove in said bezel.

3. A bezel and crystal assembly according to Claim 2, wherein said sealing gasket is disposed on the annular shoulder of the bezel, and is compressed between said annular shoulder of the bezel and rear wall of the crystal.

4. A bezel and crystal assembly, comprising a bezel having a first wall defining a central opening and a first annular groove and a second annular groove extending outwardly into the bezel, the second groove being below the first groove, and having a second wall intersecting the first wall to form an annular shoulder extending inwardly into the opening; a sealing gasket disposed in the second groove of the bezel with a portion of said gasket projecting out of said second groove into the bezel opening; and a transparent crystal of thermoplastic material received in the bezel opening, said crystal having a rear wall supported on the annular shoulder, a side wall adjacent the first wall of the bezel with a portion of the side wall overlying and contacting the projecting portion of the sealing gasket and a front wall having a narrow band of material around its periphery thermoplastically worked toward the rear wall, forming in situ an annular trough in said front wall and a flange on said side wall, the flange extending outwardly into the first groove in said bezel to stake the crystal and bezel together, said sealing gasket being compressed partially into the second groove and maintained in the compressed condition by the flange staked in the groove to provide a water resistant seal.

5. A method for making a bezel and crystal assembly, comprising the steps of a) providing a bezel having a first wall defining a central opening and an annular groove extending outwardly into the bezel and having a second wall intersecting the first wall to form an annular shoulder extending inwardly into the opening, b) making a transparent crystal of thermoplastic material to include a rear wall, a side wall and a front wall, c) placing the crystal in the central opening of the bezel with the rear wall supported by the annular shoulder of the bezel and the side wall adjacent the first wall of the bezel, the front wall of the crystal facing away from the annular shoulder, and d) heating and pressing a narrow annular band of material around the periphery of the front wall of the crystal toward the rear wall while the rear wall is supported against deformation on the annular shoulder to effect thermoplastic working of said band of material and formation of a narrow annular trough in the front wall and a flange on the side wall with the flange extending into the annular groove in the first wall of the bezel to stake the bezel and crystal together.

6. A method according to Claim 5 including the additional step of placing a sealing gasket between the bezel and crystal prior to step (d) so that the gasket is compressed during step (d) and maintained in the compressed condition by staking of the flange into the groove in the bezel.

7. A method according to Claim 6 wherein the sealing gasket is applied to the rear wall of the crystal before it is placed in the bezel opening.

8. A method according to Claim 5 wherein the front wall of the crystal includes a peripheral lip of selected width to define the narrow band of material to be thermoplastically worked.

9. A method according to Claim 8 wherein heating and pressing of the narrow band of material on the front wall of the crystal is effected by a heated shell punch having a projecting annular rib of a width adapted to engage the peripheral lip on the front wall.

10. A bezel and crystal assembly substantially as hereinbefore described with reference to the accompanying drawings.

11. A method for making a bezel and crystal assembly according to Claim 5 and substantially as hereinbefore described.