From: nothingness (SHITE) Sep-1 8:25 pm
To: sgian1 (8 of 28)
IMHO, though the ARC titanium one looks absolutely bling, it gets hot under the sun, not to mention damn exp. Personally I like mine better... :P
http://www.bmw-sg.com/photopost/data/500/medium/P1010043s.jpg
From: ViperDrv (RICHARDYE) 8:19 am
To: nothingness (SHITE) (13 of 23)
Propeties of titanium include excellent heat dissipation :p
if it's true titanium.. it dissipates heat so fast that you can't feel it getting hot.. that's one of the reasons why titanium is very hard to weld too
From: Grey Lancher (Cubpolice) 9:46 am
To: ViperDrv (RICHARDYE) (14 of 23)
If titanium is a good conductor, doesn't it conduct heat faster to yr hands too?
From: ViperDrv (RICHARDYE) 4:47 pm
To: Grey Lancher (Cubpolice) (20 of 23)
hahaha ... nope .. it cools so fast that if you heat one end and your hand on the other end .. before the heat gets to you already cool to the touch liao .. of course if you dumb enough to heat the same place where your hands are .. then no bet lor :P ..
Actually .. it conducts heat away from your hands faster .. so you feel titanium always very cool (looks cool too :P)
From: Grey Lancher (Cubpolice) 5:03 pm
To: ViperDrv (RICHARDYE) (22 of 23)
Actually, and don't hold me to this, since I not a Physics degree holder.. a good conductor merely conducts heat quickly in either direction.
When it is colder than your hands for instance, it should conduct heat AWAY from them, making it colder to the touch.
When it is hotter, on the other hand, it should then heat TO your hands quicker, which is what IceZone and I found.
Think cooking pots, which by definition requires good conduction properties. If you heat it up, well, let's just say I wouldn't recommend you try touching it. But in an air-conditioned room, the same pots will feel really cold.
In the gear knob instance, if left to bake in the hot sun, the ARC knob does get very very hot (being the good conductor that it is) but by the same token, once you switch on the air-conditioning, it cools down fast too. What IceZone and I found is that for that brief period while the heat is being conducted away, the knob still feels freaking hot.
Conversely, a bad conductor of heat like, say leather would not feel hot nor cold in the same conditions.
From: ViperDrv (RICHARDYE) 6:32 pm
To: Grey Lancher (Cubpolice) unread (23 of 23)
understand what you're saying .. ok .. let me reSAY what I said :)
DISSIPATE HEAT faster .. how ?? :P
you're referring to this:
"Thermal Conductivity. The ability of a metal to conduct or transfer heat is called its thermal conductivity. Thus, a material, to be a good insulator, would have a low thermal conductivity, whereas a radiator would have a high rate of conductivity to dissipate the heat. The physicist would define this phenomenon as the time rate of transfer by conduction, through unit thickness, across unit area for unit temperature gradient."
Titanium is a poor conductor of heat .. what you feel is just the heat .. hehehehehe :P it doesn't reach your hand any faster ..
From: Grey Lancher (Cubpolice) Sep-2 11:59 pm
To: ViperDrv (RICHARDYE) (28 of 31)
Guess you might need to rephrase that..
"it cools so fast that if you heat one end and your hand on the other end .. before the heat gets to you already cool to the touch liao"
Trust me, where got so fast one.
From: ViperDrv (RICHARDYE) 8:21 am
To: Grey Lancher (Cubpolice) unread (30 of 31)
trust me.. it is that fast!..though it was accident of course.. not stupid u know :p
then again.. yours is ball mine is thin.. aiyah dun believe me nxt time i bring blow torch show u lor!!
I don't think anyone is disputing the fact that any substance which has little mass is able to lose heat quickly, since the specific heat capacity is lower.
Given two knobs made of the same material, one that has a mass of 100g and the other, 200g, both of them at 60 degC, the heavier knob will have twice the heat energy stored in it.
Given two exhaust systems, one made of stainless steel, the other made of titanium. Let's say the steel system weighs 12kg, while the titanium one is 5kg. Both are at 700 degC. Which is hotter?
If you answered the steel system.... then the answer is wrong, because they are at the SAME TEMPERATURE. The steel system has more HEAT ENERGY stored in it due to the greater mass.
4 comments:
What a knob!! :P
Sometimes I think ppl need to take a licence test before signing up for a forum!
"No soup for you" - Soup Nazi, Seinfeld
Actually, titanium is difficult to weld not because it conducts heat very well. If that is the case, then aluminum is more difficult to weld.
"Titanium is a reactive metal that is sensitive to embrittlement by oxygen, nitrogen and hydrogen, at temperatures above 500° F (260° C). Consequently, the metal must be protected from atmospheric contamination. This can be provided by shielding the metal with high purity inert gas in air or in a chamber, and by a vacuum of at least 10 torr. That's why titanium and titanium alloys can be welded by the gas-tungsten-arc, gas-metal-arc, plasma-arc and electron beam welding processes. During arc welding, the titanium should be shielded from the atmosphere until it has cooled bellow 800° F (430°C).
Porosity in titanium welds has been a persistent problem. The most porosity is caused by gas bubbles formed during solidification of the weld. The welding procedures and techniques, as well as filler wire, can affect the porosity. If the content of gases (as impurities) in solution in the metal stays within established limits for filler wire, it is not likely a cause for porosity in the weldment.
Cleanliness of the joint area as well as filler metal is a major factor in producing porosity-free welds. The number of foreign materials, specifically on the surface of the weld wire, that can cause porosity is endless. For example, grinded particles embedded in the metal, fingerprints, dirty rags, lint-bearing gloves, burrs, surface oxides, rust (iron oxide) will cause not only porosity, but weld embrittlement."
Titanium is difficult to weld because it requires the presence of shielding gases such as argon to protect the welding area from contamination from air. Dissolved oxygen and hydrogen may cause severe embrittlement in titanium materials. A minimum of fillers should also be used, hence a very high standard of miting is required. Titanium tends to gall, so cutting it is a nightmare. The areas to be joined also have to be surgically clean.
Titanium also requires special post-welding care. Stress relieving is necessary to avoid cracks and stress corrosion while in service. Chlorinated Fluoro Carbon (CFC) solvents are forbidden for cleaning titanium and titanium alloys as they produce embrittlement. Acetone or Methyl Ethyl Ketone (MEK) are used instead.
*kowtows to materials science guru*
We are not worthy! We are not worthy!
Seriously, that was a really comprehensive post, so deep that it has to be true. (even if smoke out oso dunno, but worth it!)
zeenie,
Hahaha! I read up a lot on titanium and welding quality before settling on a Merlin hardtail. heh! Despite the attractiveness of made-in-China titanium bicycle frames (i.e. Airborne), I still don't trust their quality control and would rather pay the premium for Merlin.
I don't get the titanium shift knob thing though. It seems to remind me of the silliness of aluminum oil caps. I remember those silly people who replaced their lighter plastic stock oil caps with heavier $60 TRD aluminum caps, and then finding out that the metal oil caps are too hot to touch and open by hand when the engine is warm. Doh!
Personally, I prefer the feel of a leather-covered shift knob.
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