EP0286948B1 - Workpiece for a watch band - Google Patents

Description

• The present invention relates to a watch band link employed for forming a watch band for a wrist watch.
Description of the Prior Art
• A band for a wrist watch, which is easily scratched, is preferably formed by a hard alloy. In particular, cemented carbide is employed as a material for the band of a high-grade wrist watch.
• However, it is difficult to work an extremely hard material such as cemented carbide into a desired configuration which is applicable to a watch band. Such a watch band must be provided with holes for receiving pins or screws, which are adapted to couple parts of the watch band with each other. In the case of a workpiece for a watch band made of cemented carbide, such holes are formed by electric discharge machining, which requires a long time.
• On the other hand, parts of cemented carbide for a watch band may be formed to be previously provided with such holes. However, sufficient dimensional accuracy cannot be attained if the parts are previously formed to have holes of desired diameters.
• The EP-A-0 169 292 discloses wearparts or cutting tools. The part comprises a composite structure body having a core consisting of high speed steel or tool steel and a cover consisting of a material being difficult to ground.
• The US-A-3 837 163 discloses a mar-proof watch-band of materials having a hardness greater than Hv 1,000. The watch-band consists of materials like hard nitrides, oxides and carbides in combination with metallic binders.
• The object of the present invention is to provide a watch-band link of excellent machinability for a watch band, which can be manufactured at a low cost, by employing unscratchable cemented carbide.
• The workpiece for a watch band link according to the present invention comprises a worked part to be machined and a base part joined through a diffusion junction with the worked part, which is prepared by a material which is superior in machinability to the base part. Thus, the worked part of the watch band link according to the invention can be easily machined in high accuracy, to require no electric discharge machining for a long time as in the conventional case. Further, a diffused junction is employed in order to join the worked part to the base part. Therfore, the worked part can be joined to the base part simultaneously with sintering of the base part. Thus, steps for manufacturing the watch band link are not complicated. The watch band link according to the invention is given in claim 1.
• The worked part of the watch band link of the invention consists of a material which is superior in machinability to that for the base part. When the base is prepared by cemented carbide, the worked part is preferably prepared by a metal selected from groups IVa, Va and VIa of the periodic table or an alloy of two or more such metals. Particularly when the cemented carbide is WC-Co cemented carbide, the material for the worked part is preferably prepared by Mo, W or Ta, most preferably by Mo in view of junction strength. When the cemented carbide is TaC-Ni cemented carbide, the worked part is preferably prepared by Mo or a W-Ni alloy, most preferably by the W-Ni alloy in view of junction strength.
• A diffused junction is preferably performed by sintering or HIP (hot isostatic pressing). Sintering and HIP may be combined with each other. In case of such combination, HIP may be performed after sintering, or sintering and HIP may be simultaneously performed.
• For example, a sintered worked part may be brought into close contact with an unsintered base part, which in turn is sintered in this state, to thereafter perform HIP forming. Alternatively, an unsintered worked part may be brought into close contact with an unsintered base part so that both the base part and the worked part are sintered in this state, to thereafter perform HIP forming. Further, a sintered worked part may be brought into close contact with a sintered base part to be re-sintered, to thereafter to perform HIP forming.
• It may be considered that carbide of the material for the worked part is formed in the junction interface in diffused junction, to improve junction strength.
• A material of excellent machinability is joined by diffused junction to the worked part of the workpiece for watch band link according to the invention, which can be easily machined to obtain watch band links of high dimensional accuracy. Further, the worked part can be worked by general machining with no electric discharge machining, which has been generally required in the prior art, whereby the working time can be extremely reduced.
• Due to employment of diffused junction, the worked part can be joined to the base part in sintering or HIP forming of the base part. Thus, the manufacturing steps are not complicated.
• These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, in which
• Fig. 1 is a front sectional view of a workpiece for forming a watch band link according to an embodiment of the present invention;
• Fig. 2 is a side elevational view of the workpiece of Fig. 1;
• Fig. 3 is a front sectional view showing a state in which the workpiece of Figs. 1 and 2 is worked to be provided with holes; and
• Fig. 4 is a side elevational view showing the state in which the workpiece of Figs. 1 and 2 are worked to be provided with holes.
• Figs. 1 and 2 are a front sectional view and a side elevational view showing a workpiece for a watch band link according to an embodiment of the present invention. Referring to Figs. 1 and 2, a workpiece 1 for a watch band link comprises a base part 2 of cemented carbide and worked parts 3 embedded in holes formed in the base part 2. This workpiece 1 is obtained by embedding sintered worked parts 3 in the holes of the base part 2 being in an unsintered state, sintering the base part 2 and thereafter performing HIP forming.
• Various samples of such workpieces 1 were manufactured by combining materials for the base parts 2 and the worked parts 3 as listed in Table 1. As shown in Figs. 3 and 4, each workpiece 1 thus obtained was formed with holes 5 in the worked parts 3 through machining, and workability thereof was evaluated as an index. Evaluation was made on the working step and working ability thereof. As to the working step, the average value in working ability of hole working by drilling was expressed as an index.
• For the purpose of comparison, workability indices were also evaluated as to the case of working holes in base parts 2 being joined with no worked parts 3, i.e., being provided with no holes themselves. The results are also listed in Table 1. In each case, such evaluation was made on the working step and working ability thereof, similarly to the above. As to the working step, the average value in working ability of hole working by electric discharge machining was expressed as an index.
• In table 1, a best possible workability index is "100", lower numbers indicating a poorer machinability. Table 1

  	Base Part	Worked Part	Workability Index
  Example A	WC-Co Cemented Carbide	Mo	100
  Example B	-do.-	W	100
  Example C	-do.-	Ta	90
  Reference Example D	-do.-	None	37.5
  Example E	TaC-Ni Cemented Carbide	Mo	100
  Example F	-do.-	W-Ni Alloy	100
  Reference Example G	-do.-	None	35

• Although the workpiece 1 is formed with through holes to be filled with the worked parts 3 in the aforementioned embodiment, non-through type holes may be formed from both of longitudinal end portions of the workpiece 1 toward its center to be filled with the worked parts 3, which are then provided with holes respectively to receive pins in both of longitudinal end portions. Further, the holes to be filled with the worked parts 3 are not restricted to be circular in section as shown in the drawings, but the same may be provided in an arbitrary sectional configuration such as a square one.

Claims (9)

1. A watch band link comprising a base part prepared by a cemented carbide having blind holes or throughholes provided with bushings for receiving connecting pins inter-connecting the watch band links with each other, characterized in that the bushing are formed by worked parts (3) prepared by a metal selected from the groups IVa, Va and VIa of the periodic table or an alloy or two or more such metals and being joined with the base part (2) by diffused junction, wherein the bushing is formed by working the worked part (3) which is superior in machinability to the said base part (2).
2. A link in accordance with claim 1, wherein said cemented carbide is WC-Co cemented carbide.
3. A link in accordance with claim 1, wherein said cemented carbide is TaC-Ni cemented carbide.
4. A link in accordance with claim 2, wherein said worked part (3) is prepared by Mo, W or Ta.
5. A link in accordance with claim 3, wherein said worked part (3) is prepared by Mo or a W-Ni alloy.
6. A link in accordance with claim 1, wherein said diffused junction is sintering diffused junction.
7. A link in accordance with claim 1, wherein said diffused junction is HIP a diffused junction.
8. A link in accordance with claim 1, wherein said diffused junction is achieved by sequentially performing sintering and HIP.
9. A link in accordance with claim 1, wherein said diffused junction is achieved by simultaneously performing sintering and HIP.

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