HK1079297B - Enamelled watch face with feet and its fabrication method - Google Patents

Description

The present invention concerns an enamelled dial with feet, in particular an enamelled dial for watchmaking, and a process for making such a dial and fixing the feet with precision without requiring any retouching for subsequent placement in housing provided in the platform.

In the case of antique watchmaking, watches or clocks, the enamelling of the visible face of the dial was useful, especially to mask a substrate usually made of copper, or copper alloy for aesthetic purposes. In addition, in small-sized pieces, such as wristwatches, it is necessary that the back of the dial be fitted with feet to ensure the correct positioning of the said dial. It is also necessary that the said back of the dial be backed with a back enamel, even a coarse one, to compensate for the stresses resulting from the enamelling of the visible face. Thus, to obtain a quality enamelled dial, used in high-end watches, the traditional manufacturing process involves a very large number of push-ups requiring a very large share of the manufacturer's know-how to do this, despite the fact that we will not yet understand the percentage of rejection.

In the first step, a gauge slightly larger than the dial shape is cut from a thin copper plate, or copper alloys (0.1 mm for a wristwatch, up to 0.4 mm for a pendulum), holes are drilled for copper dial feet, and then the feet are riveted/welded.

In the second stage, after a stamping process, an enamel composition is applied to both sides of the plate by known processes, such as dipping, screen printing or sieving. In the latter case, the lower face is previously coated with glue. The dial thus prepared is then passed through the oven at a temperature of 750°C to 850°C depending on the composition of the enamel.

For the visible face of the dial, this second step is repeated several times, i.e. 2 to 5 times, until the enamel layer has a thickness of about 0.7 mm, the thickness necessary to mask as best as possible the unsightly appearance of the copper substrate and to give the dial the desired mechanical properties.

The third step is to uncouple the dial hands, apply a thin film of varnish or enamel with a furnace pass, and then press at a specified temperature to give the dial the optimum flatness.

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In a final step, a hole is drilled in the centre and, if necessary, a window is cut, and then the edges of the dial are ground, since the enamel layers have a slope on the circumference. Dials with feet with a substrate that is not necessarily metal are also known.

The present invention therefore aims to overcome the disadvantages of this earlier technique by providing a manufacturing process for an enamelled dial with feet which involves fewer steps and does not require the repositioning of the feet at the end of manufacture, nor a grinding for the edging of the dial.

The invention relates to an enamelled dial with positioning feet in the plate of a watch movement, the latter being formed from a ceramic substrate with one or two layers of enamel on its outer surface and a film on the inner surface of the dial, which allows a thicker metallic layer to be deposited to fix the head of the feet with high precision by bonding. This deposition can be made, for example by galvanic growth. The feet were not subjected to thermal stresses or manipulation due to enamelling when they were placed at the very last stage of manufacture, which prevents their subsequent repositioning on the movement during assembly.

Since the ceramic substrate has a light tint, the small number of enamel layers is sufficient to have, with a thickness between 0.1 mm and 0.4 mm, a very satisfactory surface condition and, conversely, allows a thicker substrate. The thickness of the ceramic substrate is preferably between 0.4 mm, which is a value that already allows satisfactory mechanical properties, and 0.9 mm. The finished dial is therefore substantially the same thickness as the previous art dials, but with an inversion of the substrate/enamel layer thickness ratios.

To ensure even more precise foot positioning, it is also possible to provide a head housing in the ceramic substrate, designed during pressing or later machined.

Other features and advantages of the present invention are described in the following description given for illustrative and non-limiting purposes, by reference to the attached drawings in which: Figures 1A, 1B and 1C show the steps of manufacture in a first embodiment, cut near the edge of an enamelled dial with legs according to the invention; and Figure 2 shows a part of a dial according to the invention obtained in a second embodiment, cut near the edge.

It should first be noted that, for the sake of clarity, not all thicknesses have been shown at the same scale.

Figure 1A shows the first step in the process of coating a ceramic substrate 1 with a thickness of between 0,4 mm and 0,9 mm, preferably 0,7 mm, with one or two layers of enamel with a total thickness of between 0,1 mm and 0,4 mm, i.e. with a substrate at least twice as thick as the enamel layer.

Substrate 1 is obtained by pressing or by the well-known CIM (Ceramic Injection Molting) process from a ceramic powder such as aluminium oxide or zirconium. The mastery of this process is currently sufficient to produce parts with a very tight tolerance without any further editing, especially since the very small number of enamel layers does not produce an edge effect. Given this lack of edge effect, although not represented in Figure 1A, it is also possible to start from a substrate 1 with cross-sections of needle shafts and possibly weakened, or to form the guides before enamelling.

The second step, shown in Figure 1B, is to treat the lower face of the dial to enable the dial foot to be fixed by bonding, brazing, first by evaporation on the ceramic surface, depositing a film of adhesion 5 and then by galvanic growth or other equivalent techniques, depositing a thicker layer 7 to enable the foot to be fixed.

The hook layer 5, which is only a few tens of nanometres thick, is made of titanium, nickel, chromium, tungsten or vanadium, for example. Given the low thickness of the ceramic substrate 1 and enamel layer 3, hook layer 5 can also act as a reflector and make the dial even brighter.

The third step, shown in Figure 1C, consists in attaching the head 11 of foot 9 to the thick layer 7, by bonding, welding or brazing, in the precise position it must occupy for mounting the dial on the board, i.e. without having to apply mechanical stresses to it to reposition it.

Now referring to Figure 2, a dial of the invention has been represented by a second embodiment. It differs from the first embodiment just described in that the positioning of the foot 9 is obtained even more precisely by means of a cylindrical housing 13 provided for during the manufacture of the ceramic substrate 1 or by subsequent machining.

Claims (9)

1. Enamelled dial with location feet (9) including a substrate (1) made of ceramic, the internal surface of said substrate (1) having a hanging film (5) on which a thicker layer (7) is deposited, characterized in that the external surface of said substrate is coated with one or two enamel layers (3), and in that the head (11) of the feet (9) is fastened by bonding to said metallic layer.
2. Enamelled dial according to claim 1, characterized in that the internal surface of the substrate (1) further includes a cylindrical housing (13) permitting a precise location of the feet (9).
3. Enamelled dial according to claim 1, characterized in that the ceramic substrate (1) is at least twice thicker than the enamel layer (3).
4. Enamelled dial according to claim 1, characterized in that the ceramic substrate (1) further includes before enamelling some axis cuttings for needle and if necessary some apertures.
5. Enamelled dial according to claim 1, characterized in that the hanging film (5) is chosen among titanium, vanadium, tungsten and chromium.
6. Enamelled dial according to claim 1, characterized in that the thick layer (7) is chosen among nickel, copper or copper alloy, chromium and gold or gold alloy.
7. Manufacturing method of an enamelled dial with feet, characterized in that it includes the following steps:

   - forming a substrate (1a) made of ceramic with accurate dimensions of the final dial;

   - coating on the external face of the substrate (1) one to two enamel layers;

   - coating on the internal face of the dial a hanging film (5);

   - carrying out a thick metallic deposition (7) on the hanging layer (7), and

   - fastening the feet (9) to the suitable places by bonding.
8. Method of an enamelled dial according to claim 7, characterized in that the internal surface of the substrate (1) further includes a cylindrical housing (13) permitting a precise location of the feet (9).
9. Method of an enamelled dial according to claim 7, characterized in that the substrate further includes some axis cuttings for needle and if necessary some apertures.