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Placavar magnets in buttons

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Greg Ratcliff

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Placavar magnets in buttons

Post25 Jan 2008, 22:20

Did you guys know that the placavar magnets in the Pulsar watches are made out of platinum?? We found out after sending a few samples to Garfield Refining when we were scrapping GF Pulsar watches and bracelets. I'm not talking about the magnets that were glued to the spring, but the small cylinder type magnets that fit in the solid buttons.
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rewolf

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: Placavar magnets in buttons

Post25 Jan 2008, 22:40

AFAIK, platinum (Pt) is paramagnetic, thus cannot be permanantly magnetized.
At least pure Pt, maybe it was some alloy? But I've never heard of Pt used in magnets.

What does "placavar" mean?
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bruce wegmann

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: Placavar magnets in buttons

Post25 Jan 2008, 23:27

This has actually been known for many years...I have heard the story of the thousand or so Dress cases [ones with green crystals!] that had their buttons punched out to recover the platinum in the magnets [at the time, about fifty cents' worth each]. I've never heard the actual name of the alloy before now, though. BTW, The SETTING magnets are a sintered AlNiCo V alloy, so no need to start melting those... Why they chose that type of magnet has never been made clear; perhaps, once magnetized, it has a high resistance to being altered by high external magnetic fields. Another minor Time Computer mystery...
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rewolf

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: Placavar magnets in buttons

Post27 Jan 2008, 20:37

I couldn't let this rest, did some research.
The material was quite probably a Platinum-Cobalt (PtCo) alloy. It was one of the best magnetic materials at that time, but too expensive, thus soon replaced by other materials like Samarium-Cobalt.

This is interesting:
http://www.electronenergy.com/about_us/company_info.htm
Biography of Electron Energy Corporation founder Marlin S. Walmer:
"...An alumnus of Lehigh University (BS 1952) and Franklin & Marshall College (MS 1958), he began his career as a metallurgical engineer at the Hamilton Watch Company. At Hamilton, he worked with platinum cobalt magnets used in wristwatches. It was this work that laid a foundation for the next 30 years of his pursuit to develop, commercialize, and improve rare earth magnets...."

Very good article about permanent magnets:
http://www.grouparnold.com/mtc/pm_manual_chap_1.htm
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Greg Ratcliff

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: Placavar magnets in buttons

Post28 Jan 2008, 21:32

I just got off the phone with my Dad. He said the name is PLACOVAR and one of the engineers at Pulsar told him the magnets were made out of platinum. When we sent the magnets to Garfield Refining, they in turn sent them to Europe in 1981 to seperate the platinum out. Garfield didn't deal in platinum back then. I don't know what platinum was selling for back then, but we got about $3 for each magnet.
REWOLF : Seeing how Pulsar was a division of Hamilton Watch before they splintered off. I'm sure the guy you were talking about(metallurgical engineer at Hamilton) would have wanted to install the platinum-cobalt magnets in the Pulsar watches.
Bruce: I guess you talked to my Dad about popping the buttons out of the Green Pulsar's. My younger brother and his friend did that one summer for my Dad.
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: Placavar magnets in buttons

Post29 Jan 2008, 09:23

Actually, both Rewolf and Greg’s dad are correct!

The first button assembly was invented by John Bergey. The early Pulsar watches unutilized a Platinum-Cobalt (PtCo) magnet. PLACOVAR was a company trade name for the magnets used in the button assembly. Placovar was a product that came from the Military Division of HMW, which is where Mr. Walmer worked. These small powerful cylindrical magnets produced an average of 1.300 gauss and were pressed into the button vertically, or perpendicular to the reed switch. Although the drawing below shows the magnet in the center, it was offset to the right (looking from inside the assembly) to better align with the reed switch. Both button assemblies used a Million Cycle Havar spring.


Image

Again, Rewolf is correct in that Samarium-Cobalt magnets were used in the latter buttons. PtCo was used until Arthur O’Connor invented an improved button assembly for Time Computer. Using an epoxy to fasten the magnet to the spring clip in the horizontal position, there was no longer a need to press the magnet into the button. This was a much more economical assembly and these magnets were very reliable.

Image

A hammer and a carpenter’s nail-set was used to punch out button after button. Hundreds of cases fell victim and it wasn’t limited to any particular model. I will say that many P4 models are what I have witnessed missing buttons but I have seen others too. As for the 3416 Green Dress, they, for the most part had the Samarium-Cobalt assembly but I have seen a few with the infamous marks from the nail-set punch. This particular one only has one button missing, probably once it was discovered it wasn't the Plantinum button assembly, they left the other button in place?

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rewolf

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: Placavar magnets in buttons

Post29 Jan 2008, 11:17

Wow, this is becoming a really interesting thread :-D (though the picture of that tortured Pulsar hurts almost physically...)
Placovar is something to google for (0 hits wit Placavar).

See here:
Cobalt-platinum, as an intermetallic rather than an alloy, has a coercive force above 4,300 Oe (341,850 A/m) and a residual induction of 6,450 G (0.645 T). It contains 76.8% by weight of platinum and is expensive, but is used for tiny magnets for electric wristwatches and instruments. Placovar, of Hamilton Watch Co., is a similar alloy that retains 90% of its magnetization flux up to 650°F (343°C). It is used for miniature relays and focusing magnets.

A distinctive property of Placovar seems to be its high temperature resistance. Maybe they used Placovar to avoid demagnetization when the buttons are soldered in?

Another source:
...Among its products is Placovar, Hamilton's trade name for platinum-cobalt magnets. Originally developed for the electric watch, Placovar magnets...
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: Placavar magnets in buttons

Post29 Jan 2008, 16:18

Okay Rewolf, seeing you have a handle on this subject, I have a queston for you. Why did you reverse the symbol for the composition? Funny as the patent describes it as Cobalt-Platinum (CoPt), not PtCo? Is there any difference or just the way it is presented? I was going to mention it this way in my post but didn't know the proper symbol to use.
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rewolf

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: Placavar magnets in buttons

Post30 Jan 2008, 20:22

No specific reason for using PtCo instead CoPt. The first sources I found write "platinum cobalt".
Pt is also the main ingredient (76.8% by weight).
Don't know whether PtCo or CoPt makes a difference, are any chemists here?
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azimuth_pl

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: Placavar magnets in buttons

Post03 Feb 2008, 13:20

my Mom is a chemist :)
when specifying the ingredients of an alloy usually you place them in order of percentage thus the CoPt will most likely have more Co.
Sometimes this will not always be true for some formulas.
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