The use of titanium to manufacture watch case parts began in the United States and Germany in the late 1970s. At that time, it was only used in the manufacture of advanced watches. However, due to the excellent performance of titanium and the gradual decline in its price, titanium case watches are increasing day by day and are now quite popular. , "run" in front of the stainless steel.
The requirements for watch case materials can be divided into user requirements and process performance requirements. The requirements of users are: harmless to the human body, strong biocompatibility, long use time, anti-scratch, can maintain a pleasing and sparkling luster for a long time; it can be used to design elegant and beautiful products. Biological test research and actual use have proved that titanium and titanium alloys are highly compatible with biological fluids, while Hg, Ni, Sn, Co, and Cr can cause human skin allergies. Stainless steel contains Ni or Cr. Therefore, stainless steel watches are not suitable for certain people to wear. , while titanium watches are for everyone.
Although the hardness of titanium is not very high, after surface treatment, a thin solid solution diffusion layer of nitrogen and oxygen can be formed on the surface, which has high hardness and scratch resistance and still maintains a mirror-like state without coloring. Favored by consumers.
The requirements of the watchmaking industry are abundant raw materials, easy procurement, reasonable and stable price, excellent processing formability (forging, cutting, bending), and good surface treatment (painting, electroplating, etc.) performance.
The surface treatment process of case materials and parts: wash the surface of the material with an organic solution; put it into a vacuum furnace with a pressure of 10-4Pa, and fix it securely; pass N2 containing H2O into the furnace with a vacuum degree of 10-4Pa; at 730 ℃ Cool down after 3 hours. After this treatment, a nitrogen-oxygen compound layer is formed on the titanium with a thickness of 20 μm to 30 μm and hardness of more than 1000HV. The uppermost 5 μm thick surface layer contains more nitrogen, and from 5 μm to 30 μm The lower layer contains more oxygen.
The scratch test shows that titanium has strong scratch resistance after surface treatment, and no scratches are seen in the micro-scratch test; untreated pure titanium has many filamentous scratches and loses luster, while hardened treatment After the titanium surface still maintains a shiny surface. Today, Japan has developed surface-treated titanium alloys, which not only have high scratch resistance but also have high strength properties and good processing and forming properties. titanium watch.
Some large case parts for titanium watches can be manufactured by the Metal Injection Molding (MIM) process, which began in the mid-1970s and was used in Japan to mass-produce watch parts in the late 1980s (Figure 2). The injection molding process is a combination of injection molding and powder metallurgy technology.
The specific process of injection molding is as follows: mixing metal powder and an organic binder to form raw materials of pellets, putting the obtained raw materials into the injection molding machine, heating and forming, removing the binder in the molded parts, and heating to remove the binder. The workpiece is sintered into powder metallurgy products.
The key to this technology is to choose the appropriate titanium powder. Titanium powder is available in gas atomized and hydrogenated, hydrogenated-dehydrogenated (HDH). Atomized powder is mostly used in the MIM process. The atomization process can produce high-purity titanium powder in a spherical shape. The spherical powder has the smallest volume, which can reduce the amount of binder.
Binder dosage. The organic binder will degrade the performance of the product because it contains interstitial elements (C, O, N) and become the culprit of pollution. On the premise of ensuring product quality, the binder should be used as little as possible.
Demould as soon as possible after forming. During the high-temperature forming process, if the binder stays in the mold for a long time, oxidation will occur, so the mold release should be fast.
Degreasing and sintering. Titanium powder is easily contaminated by interstitial elements at high temperatures, and corresponding preventive measures must be taken. The degreasing process includes extraction method and heating method and also combines them, which can shorten the healing time. It should also be noted that during sintering, due to the use of a vacuum pump with high pumping capacity, contamination caused by fine inclusions in the surrounding air should be guarded against.
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