Patent Publication Number: US-7901129-B2

Title: Sealed wrist watch case

Description:
The present invention relates to a sealed wrist watch case comprising a protective casing surrounded by a middle and a bezel. 
     A sealed watch case intended for depths greater than 300 meters and consisting of a middle-cum-bezel and a bottom made of a material less strong than steel, which has an interior dome made of a high mechanical strength material which fits the inner face of the bottom and at least partially fits the inner wall of the middle-cum-bezel and bears via its edge against the side of a shoulder of the middle-cum-bezel opposite the side on which the glass bears, has already been proposed by CH 690 870. 
     This solution has two weak points which limit the depth that can be tolerated by the sealed case: firstly, the presence of a shoulder on the middle made of a material of lower mechanical strength and arranged between the glass and the interior dome, which would be crushed under a pressure exceeding the elastic limit of the material of the middle-cum-bezel; the second weak point is due to the fact that the portion of the dome bearing against the shoulder of the middle-cum-bezel projects from the wall of the dome, creating poor conditions for transferring the compressive force exerted on the dome. 
     The document mentions that the case having a dome made of titanium 3 mm thick can reach a depth of a thousand meters. The presence of the shoulder on the middle held between the glass and the interior dome would, however, not make it possible to descend much deeper without risking permanent crushing of this shoulder. 
     A sealed watch case of which the body is at least partly made of plastic and part of which surrounds the rim of the glass is described in CH 343 949. A middle-cum-bezel surrounds the plastic case body and has a frustoconical interior shoulder acting on the part of the plastic case body surrounding the rim of the glass in such a way that when the bottom is screwed on it exerts axial traction on the middle-cum-bezel, by virtue of which traction the part of the case body is elastically deformed due to the axial pressure exerted thereon. 
     That document still includes a case body made at least partly of compressible material. It does not therefore include a casing having a pressure resistant structure since it is designed specifically to deform under a force of axial traction exerted on the case body, unlike a normal watch case. 
     The ability to deform required in CH 343 949 as a result of an axial force being exerted on the plastic case body is therefore intended for a purpose opposite to that of the present invention. 
     The object of the present invention is to overcome the limitations of the prior art solutions while limiting the increase in the thickness of a sealed wrist watch case which is able to tolerate a predetermined pressure. 
     The problem which occurs when making a sealed wrist watch case which is resistant down to very great depths, typically of between 3000 and 5000 meters, is in particular its thickness. Sealed wrist watch cases are known which are resistant to pressures of around 10 to 15 MPa, corresponding respectively to depths of 1000 and 1500 meters. These cases are already around 14.5 mm thick which is already relatively thick for a wrist watch. In order to be resistant to pressures 3 to 4 times greater, the thickness of such a case would have to be increased by more than 5 mm, which presents problems for a wrist watch. Above a certain thickness, every extra millimeter is a millimeter too much. 
     For this reason, the subject of the present invention is a sealed wrist watch case comprising a protective casing surrounded by a middle and a bezel, according to claim  1 . 
     The main advantage of this sealed watch case is that it can tolerate pressures of several tens of MPa with substantially less of an increase in thickness compared to conventional watch cases, this allowing a watch case to be produced which can tolerate depths of several thousand meters, typically between 3000 and 5000 meters, and the thickness of which allows it to be worn as a wrist watch. Since the bezel and the middle do not protect the movement of the watch which is entirely protected by the protective casing, they can be made of the same material as is traditionally used for watch cases, ranging from plastic to platinum via stainless steel and the various alloys of gold. 
     Another advantage of the invention is that the sealing and the pressure resistance are obtained from completely different components which have no influence whatsoever on each other. By contrast, the sealing members are involved in the assembly of at least some components of the protective casing. 
    
    
     
       The attached drawings illustrate schematically and by way of example an embodiment and two variants of a sealed wrist watch case according to the present invention. 
       In the figures: 
         FIG. 1  shows a vertical cross section through a watch case according to the prior art; 
         FIG. 2  shows a vertical cross section through the embodiment of the sealed wrist watch case according to the invention; 
         FIG. 3  shows a vertical cross section through a first variant of  FIG. 2 ; and 
         FIG. 4  shows a vertical cross section through a second variant of  FIG. 2 . 
     
    
    
       FIG. 1  shows a watch case according to the prior art. This watch case has been chosen because it is a commercially available sealed wrist watch case, tested to 1550 meters, which makes it a wrist watch that is resistant to great depths. 
     When consideration was given to making a watch case resistant to pressures of around 50 MPa, it was found that the conventional sealed watch case, such as that illustrated in  FIG. 1 , would lead to a case thickness close to 20 mm and this would be barely acceptable for a wrist watch. 
     The wrist watch case of the present invention and illustrated in  FIG. 2  includes an entirely closed protective casing which comprises in this embodiment a bottom  1  made of a material having a Young&#39;s modulus sufficient to limit deformation. It will be seen in the following that this Young&#39;s modulus must be &gt;100 000 MPa. The flexural strength of this material must in particular be substantially greater than that of the two traditional materials, stainless steel and gold. In the example illustrated, this material could be a ceramic such as zirconia. The material could also be titanium which in particular has a high flexural strength and a Young&#39;s modulus &gt;100 000 MPa. 
     This bottom  1  has an arcuate profile which improves its flexural strength. At its edge there is a planar surface  1   a  on which a side wall  2  rests which is made of a material the compressive strength of which is substantially greater than that of stainless steel or gold. Given that this side wall  2  must be perforated to allow the passage of the winding stem, a metal-ceramic alloy is preferred. An alloy such as a nickel-free steel of the Biodur 108 type can be used, the properties of which are shown in table II. 
     This side wall  2  is defined by two planar surfaces, one in contact with the surface  1   a  of the bottom  1  and the other in contact with a planar surface  3   a  of the periphery of the glass  3 , which is made of sapphire having an appropriate Young&#39;s modulus and flexural strength as shown in table I. 
     The protective casing formed here by the bottom  1 , the side wall  2  and the glass  3  includes a pressure resistant structure SR having parallel lateral faces perpendicular to the bearing surfaces between this side wall  2  and the bottom  1 , on the one hand, and between this side wall  2  and the glass  3 , on the other, and which extends without a gap as far as the bottom  1  of the casing and overlaps at least part of the side wall  2  and the bottom  1  of the casing. This pressure resistant structure SR is defined in  FIGS. 2 to 4  by two dot-dash lines. As will be seen in table III, the compressive strength of this side wall  2  can be modified by adjusting the radial thickness of the resistant structure SR. 
     The side wall  2  has an outer side wall  2   a  situated in the extension of the lateral surface of the glass  3 , the cross sections defined by these lateral surfaces being constant. These two lateral surfaces are surrounded by an annular seal  4 . The base  4   a  of this seal  4  is compressed in the radial direction by an inner lateral surface part  5   a  of a middle  5  surrounding the side wall  2  of the protective casing. An inner shoulder provided between the inner lateral surface part  5   a  of the middle  5  and the rest of this lateral surface surrounding the side wall  2  abuts against an outer shoulder of this side wall  2 . 
     The part of the middle  5  situated at the bottom  1  of the protective casing has a thread for receiving a threaded clamp ring  6  between the middle  5  and the bottom  1 . A seal  7  is arranged between an outer shoulder of the bottom  1  and the base of the middle  5 . 
     The part of the annular seal  4  which surrounds the lateral face of the glass  3  is compressed in the radial direction by a clamp ring  8 , preferably made of titanium. Thus, the annular seal  4  serves both as a seal between the glass  3  and the side wall  2  and for fixing these two pieces together. A bezel  9  is also fixed around the clamp ring  8  by a connecting ring  10  straddling an annular depression  8   a  in the clamp ring  8  and an annular groove  9   a  in the inner lateral face of the bezel  9 . 
     This sealed mounting of the glass  3  by way of a ring compressed in the radial direction has the advantage of completely separating the compressive strength from the sealing function. Moreover, while a slight elastic compression of the side wall  2  occurs at very great depths, the annular seal  4  allows the glass to slide and to remain permanently in contact with the adjacent end of the side wall  2  of the protective casing. 
     The variant of  FIG. 3  differs essentially from the embodiment of  FIG. 2  in that the side wall  2 ′ is reduced mainly to the resistant structure SR, a flange  11  being attached to the inside of the side wall  2 ′ instead of being integrated in the side wall  2  as in the example of  FIG. 2 . 
     The second variant of  FIG. 4  differs from  FIGS. 2 and 3  mainly in that the side wall and the bottom form a single piece in the form of a cap  12  with a flange  11  attached in the same way as in  FIG. 3 . This flange  11  can serve to hold the movement M of the watch which can only be put in the case from above by bearing on a shoulder  12   a  of the inner lateral face of the side wall of the cap  12 . The rest of the case is similar to the cases from  FIGS. 2 and 3 . 
     Combining the two pieces  1  and  2  into a single piece  12  currently causes a problem for manufacturing when this piece  12  is made of ceramic, given the perforation required for the passage of the winding stem. 
     It would not be possible to make the whole piece  12  from the alloy Biodur 108 used for the side wall alone in  FIGS. 2 and 3  given that this material does not have sufficient flexural strength. By contrast, there is nothing to prevent this piece  12  being made from titanium because, as  FIGS. 5 and 6  show, this material fulfills equally well the conditions of compressive strength required of the side wall and the conditions of flexural strength required of the glass or the bottom, as well as the relative conditions of Young&#39;s modulus, fixed so as to limit the deformation of the materials of the protective casing, which, if this deformation were excessive, would require increasing the thickness of the case, which is obviously not acceptable. 
     The following two tables summarize the conditions that the materials used for various components of the protective casing must satisfy in order to provide a watch case resistant to pressures of up to 50 MPa. 
     
       
         
           
               
               
             
               
                   
                 TABLE I 
               
             
            
               
                   
                   
               
               
                   
                 Glass and bottom 
               
            
           
           
               
               
               
            
               
                   
                   
                 Unsuitable 
               
               
                   
                 Suitable 
                 materials 
               
            
           
           
               
               
               
               
            
               
                   
                 materials 
                 Stainless 
                 Yellow 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Titanium 
                 Zirconia 
                 Sapphire 
                 steel AISI 
                 gold 3N 
               
               
                   
                 TA6V grade 5 
                 (ZrO 2 ) 
                 (Al 2 O 3 ) 
                 904L 
                 (Au 750) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Young&#39;s 
                 114 000 
                 220 000 
                 355 000 
                 193 500 
                 85 500 
               
               
                 modulus 
               
               
                 (MPa) 
               
               
                 Flexural 
                    900 
                   1400 
                    570 
                    250 
                   350 
               
               
                 strength 
               
               
                 (MPa) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE II 
               
             
            
               
                   
                   
               
               
                   
                 Side wall 
               
            
           
           
               
               
               
            
               
                   
                   
                 Unsuitable 
               
               
                   
                 Suitable 
                 materials 
               
            
           
           
               
               
               
               
            
               
                   
                 materials 
                   
                 Yellow 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Titanium 
                   
                   
                 Sap- 
                 Stainless 
                 gold 
               
               
                   
                 TA6V 
                 Biodur 
                 Zirconia 
                 phire 
                 steel 
                 3N (Au 
               
               
                   
                 grade 5 
                 108 
                 (ZrO 2 ) 
                 (Al 2 O 3 ) 
                 AISI 904L 
                 750) 
               
               
                   
               
               
                 Young&#39;s 
                 114 000 
                 195 000 
                 220 000 
                 355 000 
                 193 500 
                 85 500 
               
               
                 modulus 
               
               
                 (MPa) 
               
               
                 Compres- 
                   1100 
                    770 
                   3000 
                   2950 
                    250 
                   350 
               
               
                 sive 
               
               
                 strength 
               
               
                 (MPa) 
               
               
                   
               
            
           
         
       
     
     It can be seen from these tables and from simulations carried out on the basis of the values in these tables, that the lower limit that can be fixed for the Young&#39;s modulus is 100 000 MPa, while the flexural strength and compressive strength can each be fixed at 500 MPa. 
     The following table III is a comparative table relating to the dimensions of the wrist watch case, on the one hand according to the present invention and on the other according to the prior art case illustrated in  FIG. 1 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE III 
               
             
            
               
                   
                   
               
               
                   
                 Case according to the 
                 Case according to the 
               
               
                   
                 invention 
                 prior art 
               
            
           
           
               
               
               
               
               
            
               
                   
                 15.5 MPa 
                 49 MPa 
                 15.5 MPa 
                   
               
               
                   
                 pressure 
                 pressure 
                 pressure 
                 49 MPa pressure 
               
               
                   
                 equiv. to 
                 equiv. to 
                 equiv. to 
                 equiv. to 
               
               
                   
                 1550 m 
                 4900 m 
                 1550 m 
                 4900 m 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Glass 
                 2.8 mm 
                  5.5 mm 
                   3 mm 
                 5.7 mm 
               
               
                 thickness 
               
               
                 Bottom 
                 1.8 mm 
                 3.28 mm 
                 2.55 mm 
                   5 mm 
               
               
                 thickness 
               
               
                 Side wall 
                 5.76 mm × 0.80 mm 
                 5.76 mm × 1.48 mm 
                 — 
                 — 
               
               
                 cross section 
               
               
                 (int. diam. 
               
               
                 28.54 mm) 
               
               
                 Total 
                 13.5 mm  
                 17.68 mm  
                 14.52 mm  
                 19.7 mm  
               
               
                 thickness of 
               
               
                 case 
               
               
                   
               
            
           
         
       
     
     It can be seen that at the same pressure of 49 MPa, the reduction in the thickness is 2.02 mm, or 10.25%. This comparison is of interest given that it was carried out on two sealed wrist watch cases for two identical watch movements M, which means that the 2.02 mm reduction in the thickness of the case is solely a result of the case concept according to the present invention. 
     This shows that, no matter what depth the sealed wrist watch case is intended to be resistant to, the structure of the case according to the invention allows the thickness to be reduced. Of course, the greater the depth the greater the reduction, but table III shows that this reduction is already virtually 1 mm at a pressure of 15.5 MPa.