JPS6246835B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an exterior part for a wristwatch made of cemented carbide and a method for manufacturing the same. Decorative cemented carbide containing more than 85% TaC is
Due to its characteristics as a high hardness material, it is not only resistant to scratches, but also has a beautiful polished surface, making it useful as an exterior material for wristwatches. However, using cemented carbide and directly subjecting it to fine processing such as threading or grooving to form a watch exterior is difficult in terms of processing cost and processing accuracy. For this reason, conventionally, as shown in Fig. 1, an inner shell 1 made of an easily machined material is joined to an outer shell 2 made of a cemented carbide using an adhesive, but the durability of the adhesive varies over time. It is difficult to say that it is a satisfactory product because of deterioration and design limitations. In general, joining members by brazing is advantageous because it has high joint strength and durability, and there are few restrictions on design. However, various difficulties arise when brazing cemented carbide and other metals. Above all, in TaC-based decorative carbide, the content of Ni and Co, which are binders, is limited in order to make the most of the color tone of the polished surface. As a result, high strength cannot be obtained compared to cemented carbide materials with a large amount of binder. For this reason, when high-temperature brazing is performed with alloys such as SUS304 and SUS316F, which have a large difference in coefficient of thermal expansion from cemented carbide, it is not possible to withstand the stress caused by the difference in the amount of shrinkage between the two during cooling. , a crack A shown in FIG. 2 occurs in the TaC cemented carbide matrix. In addition, TaC-based decorative carbide has few bander phases that can be expected to bond with brazing materials, and the binder contains many Cr, Al, etc. added for the purpose of improving corrosion resistance, which causes oxides to form on the binder surface. Since there is a high possibility that they are covered, the wetting between the brazing material and the TaC-based carbide surface is very poor. For this reason, when brazing TaC-based cemented carbide and materials with different coefficients of thermal expansion, it has been difficult to avoid the peeling phenomenon occurring at the boundary between the brazing material and the cemented carbide. Thermal expansion coefficient of TaC-based decorative cemented carbide (7×
10 ^-6 /℃) or smaller than this include W, Zr, Ti, Kovar, SUS430, etc., which satisfy all three elements of brazing properties, machinability, and corrosion resistance. It is not possible. The present invention provides a highly reliable watch exterior made of TaC decorative cemented carbide, which satisfies machinability and corrosion resistance, but is made of stainless steel, which has a large coefficient of thermal expansion that is significantly different from that of cemented carbide. This provides a method for brazing the original. The present invention will be explained below with reference to Examples. FIG. 3 is a cross-sectional view of a wristwatch exterior using TaC-based carbide according to the present invention, in which a threaded bushing 4 made of stainless steel SUS316F is brazed to the exterior body 3 of the TaC, and a waterproof O.
It has a waterproof structure in which the bottom cover 6 is screwed in with the screw 7 through the ring 5. Table 1 shows the alloy composition of the cemented carbide having TaC of 85 wt% or more explained in this example.

[Table] Next, the manufacturing method of the present invention will be described. <Formation of a Ni layer on the shell> The exterior shell made of TaC cemented carbide is machined with a blank hole for brazing a screw bushing by electrical discharge machining, and the damaged layer of the electrical discharge machining on the inner wall of the hole is removed by honing and polishing. After removing, 5 times in Ni plating bath.
Provide a Ni plating layer of μ or more. Through the above processing, the surface of the TaC carbide to be brazed is covered with a metal phase that has excellent wetting properties with the brazing material, and high adhesive strength can be expected, as well as the melting point of the brazing material used at the brazing temperature. Can be set directly above the
It is very advantageous. <Formation of Ni layer on threaded bushings> Screw bushings made of SUS316F material that are brazed to TcC carbide have a Ni layer of 15μ or more on the outer peripheral surface.
After providing the Ni plating layer, annealing is performed for 15 minutes at 900°C in a vacuum furnace. Table 2 shows the thickness of the Ni plating layer formed on a threaded bush made of SUS316F and the frequency of cracks that occur in the cemented carbide during the polishing process after brazing. In this way, the formation of a Ni plating layer on SUS316F material is an essential condition in order to suppress the occurrence of cracks during brazing and enable sound brazing.

[Table] <Brazing method> The exterior body made of TaC carbide and the threaded bushing made of SUS316F are pre-plated with Ni and then assembled, and brazed in a vacuum atmosphere of 10 ^-4 torr or more in a vacuum furnace. Let's do it. The brazing material used is the third one.
Shown in the table.

[Table] Melting points that satisfy the corrosion resistance required for watch exteriors
When brazing materials with different coefficients of thermal expansion, as in this example, a gold brazing material with a composition of 780°C was selected and heat treated using the brazing program shown in Figure 4. The cooling rate below the melting point of the material is particularly important, and when the cooling rate was higher than 300°C/hour, a high rate of cracks occurred around the brazed part of the outer shell made of carbide. The holding time at the brazing temperature during the brazing program is set to promote the diffusion of the Ni plating layer formed on the carbide surface into the carbide base material, thereby improving the adhesion strength between the brazing material and the carbide surface. This is particularly important in the brazing of TaC-based decorative cemented carbide, which is of great necessity. This diffusion treatment can also be achieved by holding TaC cemented carbide plated with a Ni layer at high temperature in vacuum before brazing.
For those that do not undergo any of the treatments, separation frequently occurs between the cemented carbide and the brazing material after cooling, resulting in a decrease in brazing strength. The method of the present invention is extremely effective not only for joining threaded bushes but also for joining stainless steel decorative stones, pipes, etc. As mentioned above, the success of the strong brazing joining of stainless steel parts to the TaC-based super-layer material according to the present invention is due to the fact that in the case of watch exteriors using TaC-based carbide,
It is possible to join parts such as screws, which were considered impossible in manufacturing, and makes it possible to create a highly reliable waterproof structure for wristwatches, and its effects are significant.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view showing the exterior structure for a watch using conventional TaC carbide, and Figure 2 is a cross-sectional view showing the exterior structure for a watch using conventional TaC carbide.
A microscopic photograph showing cracks that occur when TaC carbide and stainless steel are brazed together; Figure 3 is a cross-sectional view of a watch exterior structure using TaC carbide according to the present invention; It is a brazing heat treatment program graph used in the invention. 3...Body, 4...Button, 5...Waterproof O-ring,
6...Urabuta.

Claims (1)

[Claims] 1. A stainless steel threaded bushing having a larger coefficient of thermal expansion than the cemented carbide is attached to a wristwatch exterior body made of a decorative cemented carbide containing 85 wt% or more of TaC.
An exterior part for a wristwatch that has a waterproof structure by being treated with a Ni layer and brazing, and screwing the back cover to the wristwatch exterior body through a waterproof O-ring and the screw bushing. 2. When joining a watch exterior part made of a decorative cemented carbide containing 85 wt% or more of TaC and a part made of a stainless steel alloy having a coefficient of thermal expansion larger than that of the cemented carbide, the wristwatch exterior part and the stainless steel A method for producing exterior parts for wristwatches, which comprises coating the surface to be joined with alloy parts with a Ni layer and then joining them by high temperature brazing.