Tungsten springs

[tjgalyean]

Can tungsten wire be shaped to make springs? If so what would the life span be compared to a music wire spring?
Thanks for any help.

 

[EnglishMuffin]

I'm pretty certain that you can make springs with tungsten filament wire - it bends OK. It would probably need to be annealed and tempered afterwards. But what the fatigue life is, I have no idea.

 

[unclesyd]

It is easily coiled as in filament. We used a lot of very small diameter tungsten wire. In use it was flexing all the time. It had to be annealed prior to use and like cable the sheaves had a minimum diameter limit or the wire would break.

Here is one site that mentions W springs

http://www.hytechspring.com/wire-forms.html

On personal note I've wound several coils to use as a stylus on Thermal Paper Fathometers. The extended wire, .002 about 1" long, under went a lot flexing and I never had any reports of one breaking. It fact they didn't ever were out

 

[tjgalyean]

What I am trying to do is reduce my spring diameter and increase the force produced on an existing product. Currently I have a .055" piece of music wire that is actually acting more like a torsion bar than a spring.
Is it possible that Tungsten wire would give me these results in maybe .035"-.040" diameter?

 

[EnglishMuffin]

Sorry - didn't notice your last post - was rather preoccupied. Nobody else has answered - but my take on it would be that pure Tungsten has about twice the G value of steel, and I believe that this would also apply to Tungsten filament wire. A comparable wire diameter in Tungsten to give the same torsional stiffness as .055" steel wire would therefore be about .046", since torsional stiffness depends on the 4th power of the diameter. The wire of helical springs experiences torsion when the spring operates axially, so the same thing would actually apply in that case also.

 

[tjgalyean]

I finally got my tungsten wire in. I have to bend the wire to the shape that I need, kind of like an L shape with a long lower leg. Any way it bent like a wet noodle, can tungsten be heat treated at all? I know it has the highest melting point of all metals, but I don't know if heating it up will help it at all.

 

[EnglishMuffin]

Well, the heavy gage filament wire that I had experience with once was not exactly like a wet noodle - it was pretty "springy", and you had to overbend it quite a bit to get it where you wanted it, although probably the yield point was considerably lower than that of music wire.
Here is one source you could try - they usually deliver pretty quickly on items that I have ordered in the past:

http://www.smallparts.com/products/descriptions/TW.cfm

According to this site:

http://www.tungsten.com/mtstung.html

the tensile strength varies between 100,000 and 500,000 psi. My guess is that one factor affecting the variance would be the cold work effects of drawing the wire. If you annealed it after drawing - say by heating above the recrystallization temperature - it would presumably become softer. However, unlike the case of iron-carbon alloys, I doubt if heating it up and quenching it would do much good in regard to restoring the hardness - but you would have to talk to a metallurgically knowledgeable person on that.

 

[btrueblood]

From my experience in purchasing tungsten coils, you can't cold bend most tungsten alloys, any permanent deformation or "plastic deformation" you get is due to minute fractures forming in the wire. Tungsten filaments I've ordered were always wound at "red" to "orange" heat, either by resistance heating, or by a reducing flame. This was from work done using approx. .090 diameter tungsten wire, in W/3Re alloy and GE218 alloy.

Secondly, good tungsten wire filaments (GE 218 wire, for instance), have a potassium dopant. After winding, the strength of the wire is greatly increased by recrystallization (heating in vacuum or in hydrogen to 2000 to 2200 deg. F). The potassium migrates to the grain boundaries of the alloy, and provide an anti-slip mechanism. The cold strength as well as high-temp. creep strength of the wire are both improved greatly by the above treatment. It is also used on the W/3Re wire, mainly to "repair", by solid annealing, any micro-cracking generated during winding.

Hope that helps.

Ben T.