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Authored by Ikuo Tokunaga

Scans and page layout and post by Takuya (Tachy), translation by Ryan.

""THE SECRET STORY OF SEIKO'S WORLD-LEADING TECHNOLOGY; Study of the Outer Protective Cover Design and Strength"




What's the role of the outer protective cover [on Seiko Prospex Professional Diver's watches], which is characteristic of the watches' appearance?

Last time, we studied about Seiko Professional Diver's watches' "L" gaskets. This time, we focus on the outer protective cover, which is an important feature making these watches strong and shock proof, and that also makes for a good style of design.

Ikuo Tokunaga: "Originally, the idea to put the cover on the professional diver's watches was aiming to heighten anti-shock, to make them scratch resistant, and to increase protection from corresion and safety, all to the ultimate level. To achieve those aims, stainless steel materials were not good enough, so we made a removable protective cover using titanium material. At that time [mid-'70's], no other company had yet focused their attention on titanium."

The 61 caliber automatic movement professional diver released in 1975, and the 75 caliber quartz model that was released three years later used a titanium protective outer cover, coated with high-tech ceramic finish. Since 1986, the 7C quartz caliber model 1000m model has used an all-ceramic outer cover which Seiko Corporation developed with ceramic manufacturer Kyocera.

Titanium is well-known as a material which is gentle on human skin, it is a very anti-allergic metal. But, it also has a certain adhesive characteristic and it is hard to cut and polish. With Seiko's innovative and high quality techniques, it was able to overcome those problems and use titanium for the protective outer cover in the 1970's, and we have to remember that it was used for it's functionality.

Tokunaga: "To achieve [the highest level of] anti-shock titanium was used for the outer cover and for the case itself, but to complete the design one more thing was needed in order to operate the bezel smoothly. So, we integrated slots into the cover [so the bezel could more easily be gripped by the user's fingers and operated]."

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So, Tokunaga was concerned with the actual usage of the watch. Working with Taro Tanaka and Shigeyuki Kurebayashi on the design. The outer cover was completed with a high level of skill, and is fashionable even now.





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The 1st model (61 caliber automatic 600m Professional Diver's watch) which was released in 1975 had four screws which were made out of titanium to attach the protective outer cover to the watch case. Titanium was used for the screws because it was thought this would make the watch more shook proof, and for durability. However, these screws had to be made by hand, so it was extremely expensive. By 1978, when the 2nd model (75 caliber quartz 600m Professional Diver's watch), it was found that machine made stainless steel screws were just as effective as titanium ones and have been used from then on.


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61 caliber automatic 600m Professional Diver's watch, released in 1975.

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75 caliber quartz 600m Professional Diver's watch, released in 1978.

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7C caliber quartz 1000m Professional Diver's watch, released in 1986.


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7549 caliber quartz 300m Professional Diver's watch, released in 1978. It had a standard two-piece case (main case and protective cover made of stainless steel), and an extra screw on retention ring to secure the crystal and prevent helium gas penetration. It was the first model released with a "wave-type" rubber strap.

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1982's Hybrid Diver 150m "Sports Diver." It was the first diver's watch in the world which featured a digital alarm chronograph display. This watch was used by a team comprised of members from Japan, China, and Nepal when they climbed Mt. Everest in 1988.



[img]http://www.tokunaga.ne.jp/images/SCF/20030121/wb3p1.jpg
Patents received in 1981 for innovative bezel/cover structure.



Patents received in 1977 for bezel/cover design.


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Patents received in 1984 for protective polyurethane rubber system used to make the watches shock proof.



Click on link below for Kyocera's website in English.
[url=http://www.kyocera.de/english/default.htm]http://www.kyocera.de/english/default.htm[/url]



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Information from: "Watch BEAT; HYPER WATCH & SHOP MAGAZINE, Vol. 3" (Narumido Publishers, Tokyo, March 2003) page 102 - 105. ISBNT1108658030567.
 

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Re: THE SECRET STORY: Outer Protective Cover Design and Strength

Interesting. I was under the impression those screws had to be Ti also. After all, two different metals can interact and fuse together, specially in a saline environment.
 

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Re: THE SECRET STORY: Outer Protective Cover Design and Strength

LUW said:
Interesting. I was under the impression those screws had to be Ti also. After all, two different metals can interact and fuse together, specially in a saline environment.
I don't think "fusing" is technically what happens, but there is a problem... Let me google:

http://www.stainless-steel-world.net/titanium/ShowPage.aspx?pageID=173
[list type=decimal]
'Galvanic' corrosion may occur when dissimilar metals are coupled together and requires:

  • one metal to be substantially less corrosion resistant than the other
    a good electrical contact between the metals
    an electrolytic path (water, sea water, acid, alkali or salt solution) between the metals
If one or other of these requirements is absent galvanic corrosion will not occur.
The galvanic corrosion rate of the less resistant (less noble) metal in the couple will vary according to the active or exposed surface areas of the two coupled metals, the anode (corroding)/ cathode ratio. The greatest corrosion on the less noble anodic metal occurs when the cathode is large in relation to the anode. Little or no damage may be caused when the anode is large in relation to the cathode.
Titanium is highly corrosion resistant, and will usually cause more rapid damage to a less resistant active material to which it is coupled. Titanium will usually be the more noble metal and the cathode in the galvanic cell.
Titanium should not be coupled directly to less noble metals, such as magnesium, zinc, and aluminium. These are likely to experience accelerated corrosion and, in the process, titanium may pick up hydrogen which is generated as the cathodic product of the corrosion reaction.
Titanium may be coupled to copper based alloys and carbon steel. Effective protection against galvanic attack must be provided for these less noble metals.
Titanium may safely be coupled directly in neutral, slightly reducing and oxidising environments to corrosion resistant metals and alloys of similar potential in the galvanic series, such as super duplex stainless steels, 6Mo austenitic steel, 22% chromium duplex steel, 625, C-276 and the like. Care must be taken to check compatibility for the intended working environment. For example 22% chromium duplex steel may be coupled to titanium in mildly sour oil and gas brines, but not in sea water, unless cathodic protection is provided to overcome the susceptibility of the steel to crevice corrosion.[/l][/l]
So - coupling titanium and stainless steel depends on the corrosion resistance of the steel used. If it as resistant as the ti - and some steels are very resistant - then no problem. (I don't think Seiko would have used "cathodic protection" as this means have a coating that does corrode - not what you want on a screw, where it could jam the threads.)
[/list]
 

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Re: THE SECRET STORY: Outer Protective Cover Design and Strength

Thanx for the explanation, scuttle!

Definitively "fusing" is an exaggerated term, but I'm glad to see that my general thought process was right. But that article cites carbon steel and even some alloys of SS, but not the ubiquitous 316L that we usually see in watches, and I agree they would not use some sort of coating for the threads. So did Seiko use some special steel for the screws?
 

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Re: THE SECRET STORY: Outer Protective Cover Design and Strength

everyone should own a Tuna but they are too expensive IMO
 
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