Water-tight watch case

The water-tight watch case is disclosed wherein the case provides a water-tight enclosure for an electronic watch module and wherein the case includes a removable cover portion for providing physical access to the interior of the case for replacement of batteries and the like. The removable cover portion includes a truncated conically tapered sealing ring surface having an angle of taper less than 8.degree. and preferably in the range of 7.degree. to 3.degree. for providing an interference-contact axial press fit with a mating truncated conically tapered surface of the case. A water-tight seal is formed between the cover and the case essentially solely due to the axially pressed interference-contact fit between the pair of mated tapered sealing ring surfaces.

BACKGROUND OF THE INVENTION 
The present invention relates in general to water-tight watch cases and 
more particularly to an improved back cover seal for such watch cases. 
DESCRIPTION OF THE PRIOR ART 
Heretofore, fluid tight wristwatch cases have included a removable back 
cover for gaining access to the interior of the watch case. Such back 
covers have typically been secured to the main body of the watch case 
structure, in a fluid or water tight manner, by either a threaded coupling 
including an O-ring seal or by means of a snap-on coupling which also 
included a resilient compressible O-ring or elastomeric gasket to provide 
a water-tight seal therebetween. 
The problem with the back cover seal which employs a compressible resilient 
gasket or O-ring, is that the O-ring is relatively fragile and can 
withstand only a relatively few number of opening and closing cycles 
before the O-ring is damaged so as to allow leakage of liquid 
therethrough. In addition, machining of the retaining grooves for the 
O-ring and machining of the threaded coupling grooves for a threaded case 
is relatively expensive. 
Therefore, it is desirable to provide an improved back cover mechanism for 
a wristwatch case which is inexpensive of manufacture, permits a good 
water-tight seal to be formed, allows opening and closing of the watch 
cover without incurring damage to the water-tight integrity of the seal, 
and which provides a closure mechanism utilizing a minimum of the 
thickness of the watch casing so that the closure mechanism may be 
employed in thin wristwatch configurations. 
SUMMARY OF THE PRESENT INVENTION 
The principal object of the present invention is the provision of an 
improved water-tight wristwatch case having an improved removable cover 
portion for providing access to the interior of the watch case. 
In one feature of the present invention, a removable cover portion of the 
watch case is sealed in a water-tight manner to the main body of the watch 
case via the intermediary of a mated annular truncated conically tapered 
sealing ring surface portion which provides a water-tight seal due to an 
interference-contact fit between the mated sealing portions. 
In another feature of the present invention, a removable cover portion of 
the watch case is sealed to the remainder of the watch case body via the 
intermediary of a truncated conically tapered sealing ring portion having 
an angle of taper falling within the range of 7.degree. to 3.degree. . 
In another feature of the present invention, a removable cover portion of 
the watch case is sealed to the remainder of the watch case body by means 
of mated truncated conically tapered sealing ring portions providing an 
interference-contact fit and seal therebetween such seal being essentially 
free of resilient compressible packing structure. 
Other features and advantages of the present invention will become apparent 
upon a perusal of the following specification taken in connection with the 
accompanying drawings wherein:

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings there is shown an electronic wristwatch 11 
incorporating features of the present invention. More particularly, the 
wristwatch includes a watch casing 12, as of stainless steel having a 
window portion 13 as of glass, sealed, as by a compression seal or glue at 
14, for closing the upper face of the casing 12. The window permits 
viewing of the watch display, not shown, carried on the upper face of a 
circular disc-shaped electronic watch module 15 contained within a 
circular cavity 16 of the watch casing 12. The back face of the watch 
casing 12 is closed off by means of a cover cap 17, as of stainless steel. 
The watch module 15 includes electronic circuitry forming the timepiece of 
the watch assembly 11. Certain functions of the electronic watch, such as 
setting of the time, display of the time, display of the month and day, 
and the like are generated by actuating one or more switch assemblies 18 
carried with recesses generally at the outer periphery of the watch module 
15 at circumferentially spaced positions. The switch assemblies 18 are 
actuated by means of actuator pin assemblies 19 passing through radially 
directed bores 21 in the side wall of the watch casing 12. 
Referring now to FIG. 3, the back cover cap 17 and its seal are shown in 
greater detail. More particularly, the back face portion of the watch case 
12 includes an outside truncated conically tapered surface 31 for mating 
with a similarly tapered inside truncated conical surface 32 on the 
outside lip portion 33 of the cover cap 17. The angle of taper .theta., 
i.e., the angle .theta. that the conically-shaped surfaces 31 and 32 make 
with the axis of revolution of the respective surfaces is chosen at an 
angle less than 8.degree. so that a water-tight interference-contact seal 
is obtained between the two mated press-fitted conical surfaces 31 and 32. 
The angle of taper .theta. is preferably as large an angle as possible, 
compatible with obtaining a water-tight interference seal between the 
mating surfaces 31 and 32, due to the loss of precision in the axial 
spacing of the parts 17 and 12 when the angle of taper is in the low end 
of the range, i.e., less than 3.degree.. A particularly suitable taper 
angle .theta. is 5.degree. .+-. 1.degree.. 
The cover cap 17 is merely axially press-fitted over the open end of the 
watch case 12 to provide the watertight interference fit between the 
surfaces 31 and 32. The cover is removed by merely prying the cover 17 off 
of the case 12 by means of an implement placed between the inner edge 
portion 34 of the lip 33 and the watch case 12. In a typical example, the 
cover cap 17 has an outside diameter of 1.210 inches and an outside depth 
of the lip portion 33 of 0.090 inch. 
Referring now to FIG. 4, there is shown an alternative embodiment of the 
cover cap 17 of FIG. 3. More particularly, the alternative cover cap 36 
has an outside truncated conically tapered sealing surface 37 mating with 
a similarly tapered inside truncated conical surface 38 on the watch case 
12. The cover cap 36 includes an outer lip portion 39 so that a prying 
tool may fit between the lip portion 39 and the case 12 for prying the 
cover 36 from the watch case. As in the previous example of FIG. 3, the 
angle of taper .theta. is less than 8.degree. and in a preferred 
embodiment is approximately 5.degree. .+-. 1.degree.. 
The advantage to the cover caps 17 and 36 of the present invention is that 
the cover cap makes a water-tight seal to the case solely due to an 
interference-contact fit between the truncated conically tapered sealing 
surfaces. The cap may be removed as many times as desired to replace 
batteries or the like within the case 12 without destroying the integrity 
of the seal formed between the mating surfaces. The seal is also made 
without the aid of a resilient compressible packing ring material or the 
like which can deteriorate with time and with usage to cause malfunctions 
of the water-tight seal. 
Although the preferred embodiment of the present invention employs a pair 
of mated truncated conical sealing surfaces, it is not a requirement that 
both the inside and outside sealing surfaces be conical. More 
particularly, it is only necessary that the inside facing sealing surface 
be of truncated conical shape. The sealing surface facing outwardly for 
mating with the inside surface may have circular contours other than 
conical, such as rounded, pointed, etc. However, when both sealing 
surfaces are conical, the depth of the mating surfaces helps to axially 
align the cover 17 to the case 12, i.e., prevents canting of the cover 
relative to the case 12. The sealing surface finish is preferably better 
than 16 microinches RMS.