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Magnesium stems(15 posts)

Magnesium stemsDathon
Aug 25, 2003 6:15 AM
Other than weight, what is the advantage of using a magnesium stem as opposed to an alloy one? Is there any disadvantage in choosing magnesium?
Read somewhere...Nessism
Aug 25, 2003 6:35 AM
that magnesium damps vibration quite well, hard to justify the price though in my opinion.

On the plus side, magnesium has a very low density which makes for light weight parts. On the negative, magnesium is not very strong, reacts with oxygen in the air if the paint is scratched, is fairly brittle, and is expensive.

You pays your money, and you takes your chances.

Good luck.

Ed
Magnesium frames, too--but there was an issue...retro
Aug 25, 2003 2:09 PM
There was a magnesium frame several years ago, too, called something like the Kirk. Last time this came up, a year or so ago, somebody posted a link. I remember essentially what everybody else does, but it seems to me there was an additional issue that made it a worse material than it looks like at first glance--fatigue life, or catastrophic failure (it goes POOF and falls apart instead of bending and breaking), something like that.
See a magnesium frame here:retro
Aug 25, 2003 2:14 PM
Just found a Kirk link:
http://www.firstflightbikes.com/KirkPrecision.html
I read that...PsyDoc
Aug 25, 2003 6:41 AM
...one manufacturer of magnesium stems (ITM I think) stated that you should not flip their stem to get more rise.
Magnesium stems - great in an emergency...PdxMark
Aug 25, 2003 6:57 AM
http://www.southsummit.com/Magnesium.htm

Magnesium Fire Starter
why mag wheels banned at Indy -- they burn nmDougSloan
Aug 25, 2003 7:45 AM
re: Magnesium stemsrussw19
Aug 25, 2003 2:35 PM
There are a few companies that make great Mag stems, but they are very hard to work with. I have heard that when you weld them, the fumes are toxic, and will kill you, so a lot of companies don't chance it. The best part of Mag stems is that they get stiffer over time. The more the stem flexes, the stiffer it gets.

Some of the big problems are manufacturing and corrosion. They have a tendency to develop what looks like greenish-yellow pimples when you sweat on them.

Also, they are currently hard to find because only 4 plants in the world were making them.. one was the Easton plant here in the states... it wasn't actually Easton's plant, but were subcontractors making Easton's stems. Once it became obvious that we were going to war with Iraq, that plant went back to making weapons for the governmnet.

Russ
I REALLY doubt it.Synchronicity
Aug 25, 2003 3:58 PM
QUOTE:
The best part of Mag stems is that they get stiffer over time. The more the stem flexes, the stiffer it gets.
---

I'e never heard that before. Magnesium is a metal, just like any other. They do not "Get stiffer" over time. Metals have what is called a Modulus of Elasticity, a measure of stiffness. The higher the number the stiffer the material. For magnesium I think it is 45GPa. For aluminium it is 70Gpa and for steel it is around 210Gpa. They don't change with time.

As a bit of a supporter of unconventional things, I have to defend these materials sometimes, for at times, a lot of heresy goes around.
I REALLY doubt it.maximum15
Aug 25, 2003 4:02 PM
Perhaps confusing getting stronger with work hardening and increasing yield strength. Just a thought and no reference material (in paper form) handy to investigate.
Maybe.Synchronicity
Aug 25, 2003 9:16 PM
But work hardening does not occur spontaneously all by itself with a part just sitting there. Nor would a stem in use exert enough force on it to work harden it.

Work hardening is when you force the material into the "plastic elongation" region, and the material's strength increases as the dislocations in the metal's structure entangle.
Also the crystal grains within the metal change shape. nmSynchronicity
Aug 25, 2003 9:17 PM
Also the crystal grains within the metal change shape.russw19
Aug 26, 2003 12:28 AM
Which in theory is what makes them stiffer... keep in mind, I never said it was going to be either drastic or even percievable to you and I. Just repeating what some guy in a lab coat once told me...

But in truth, it is probably about as noticeable as the vibration damping characteristics of a carbon seat post...

Russ
Also the crystal grains within the metal change shape.Synchronicity
Aug 26, 2003 6:11 PM
No, the size/shape of the grains doesn't effect the stiffness. As I said it is a constant for metals. e.g. Quenched steel has the same stiffness as annealed steal, even though you may not think it - only the ductility/toughness/hardness changes.

BTW, russ I'm not trying to disagree with everything you say. The guy in the lab-coat was wrong. Besides, I have a lab-coat too! :-)

No the only real danger you have with using magnesium is corrosion. Provided the manufacturer uses the proper precautions, it will be fine.
Also the crystal grains within the metal change shape.maximum15
Aug 28, 2003 3:41 AM
Yes, you are right. There is no way someone would sell a stem with normal riding stress levels high enough to cause work hardening. The only time that I know of metal getting "harder" or "softer" is with temperature changes. Then, most metals will have a small change in Young's Modulus of Elasticity. But this small change would be not be noticable unless you mounted strain gages, or some other form of strain measuring equipment, on the device.