I have been paying very much attention to my barrel on my 338 thunder as far as how fast it cools off but I got absolute concrete facts about it recently with the help of a thermal imaging camera owned by my good friend, Idaho Preacher.
Pictures will be posted here soon of the heat getting sucked right out of the barrel! For more details, check out my thunder thread here. In one word: AMAZING!
A month or so ago, I took a little time and checked the thermal conductivity of barrel stainless steel versus carbon fibers. Conductivity is a measure of the speed at which heat will flow from one spot to another or from one area to another. It appears that there are so many differrent formulations of fibers that you can make it do whichever you want it to insulate or dissapate. Some types of fibers are a 100 times more conductive than barrel stainless steel and some are only two times more. Then there is the gel that is used to bind the fibers together and make it stick to the barrel (if any). I do not know what it is but it would have a major bearing on heat transfer. Even a thin film can be a major barrier or help to heat transfer. An example of this is in building tank armor. A thin layer of air will shut down a lot of heat transfer and will absorb a lot of shock transmission so air sandwiched between steel layers is better protection than solid steel for a shaped charge explosive head. So any thin film between the steel and the fibers is vitally important to know about.
My original impression on carbon fiber was the same as Kirby's that it was used as insulation and what I now believe is you really must look carefully at the metal of each application and the type of carbon fiber that is used in order to determine what the final outcome will be. Heat may be retained or transfered. A lot of science involved in order to get the right combination.
Just one note on the thermal imaging. The external surface of the barrel is obviuosly not what is at issue. It is just what can be measured. The critical area is the first few 0.01 inches of of steel inside the barrel. There will be a temperature gradient from the throat area inside the barrel to the outside. The current theory on fire cracking inside a gun barrel or even other steel seems to be linked to the inside (not outside) surface layer temperature versus the temperature just a few hundreds of an inch deeper in the steel and the coeffeicient of expansion of the steel. The difference in temperature in those few hundreds of an inch of steel casues differences in expansion and therefore stress cracks appear. The heat also causes some hardening of the steel which then not only increases the stress fractures but also creates a spalling effect. In other application besides barrels, the term heat cycles is used. In other words, a boiler is fired up and run at temperature (or a car engine) for a while and then shut down and is considered one cycle. With a bolt action rifle, it is unclear what a cycle is. I have seen demonstrations where M-60 (308) machine guns were fired until the rounds were cooking off from the chamber temperature and then continued until the barrel was actually red with heat. This one time destroys a barrel in one "cycle". The question of what actaully causes heat checking is still being debated and thusly the cure for it is still at question. And finally, I would simply say that my looking into it on the internet does not constitute any real research of a scientific nature. If you want to find bad science the internet is definitely the place to go. Lastly, this post is not to contradict anybody or anything it was just that I tried to spend some time understanding what was actaully going on and thought that I would post my understanding of carbon fiber barrels and throat life. Mostly I concluded that there is a big debate over what causes heat checking - except that it is heat.
If carbon wrapped barrel help throat life then it is going to be a big boon to people who shoot lots of rounds.
It fits here a little better than over there.
It is my understanding that the whole purpose of machining a barrel as thin as you could possibly get and wrapped it with carbon fiber was to reduced barrel weight without sacrificing rigidity. As an added bonus, the carbon fiber can act as an insulator. As far as heat dissipation is concerned though, I don't see any contributing characteristic a carbon fiber have to make me believed that it will help to facilitate barrel cooling. The rapid cooling I believed can be attributed to the barrel being thin and therefore has less mass. On the opposite extreme, it is my belief that you could easily cooked these barrel if you aren't carefull. Don't get me wrong though, I like to own one of these barrel. As a matter of fact now that I got an okay from the wifey, I'll be ordering one of Dave's 338 SnipeTac rifle with one of these pole. Just my 1 cent. [img]/ubbthreads/images/graemlins/confused.gif[/img]
To achieve the maximum possible accuracy, all variables must be remove or at least minimize.
As I said before, one needs to be careful with internet "science" but here is some that illustrates what I was trying to say. There are different types of "carbon" fibers. A barrel wrapper has to choose the right one or else he will be making an oven to cook the barrel.
[ QUOTE ]
Currently, high thermal conductivity fibers are being evaluated as a reinforcement for metal matrix composites. The objective is to produce a less dense material with an even higher conductivity than that of the metal matrix. A carbon fiber/copper composite with a 39 percent volume fraction of fibers has a density of 6.24 g/cc, as compared to 8.96 g/cc for pure copper. However, the density of carbon/carbon composites, approximately 1.5 -1.9 g/cc, is considerably lower. Thus, from the viewpoint of weight reduction, the use of carbon/carbon would still appear to be preferable.
Surprisingly, studies have shown that the thermal conductivity of a composite often depends more on the matrix than on the fibers. One possible reason is that often some of the fibers are broken and are thus discontinuous down the length of the composite, reducing thermal transport. Therefore, when a high thermal conductivity matrix such as graphitic carbon is used, not only do the fibers contribute to high thermal conductivity, but the matrix does as well. Since the thermal conductivity of graphite is higher than that of any metal, carbon/carbon would appear ideal for high thermal conductivity composites. Furthermore, at temperatures exceeding 1100°F, carbon/carbon composites exhibit higher strengths and moduli than metal matrix composites (see Figure 1). Thus, this combination of higher strength, lower density, and higher thermal conductivity makes carbon/carbon preferable to metal matrix composites in numerous applications.
I'm looking forward to those images. ID Preacher's camera is a real boon to the project.
I also appreicate the 'round table' discussion that is going on here.
My feable attempts at documenting barrel temp across the length of the barrel have been more than a little confusing. For an all metal barrel heat seems to flow out from the bore and along the barrel from hotter to colder areas.
I'll have my test barrel back maybe today and will continue the attempts to measure temperature and heat flow patterns.
My Nukalure training left me with two heat xfer eqn's:
Q = MCdeltaT Q=Heat transfer. M = mass flow rate and delta C = constant for the type of material T = temperature difference.
This eq'n doesn't apply to our subject.
Q = uAdeltaT, the other eq'n, seems to be more appropriate for the subject.
Q = heat transfer
u = a constant for the type of material
delta T = temperature difference
However this eq'n is usually applied where there is a constant temperature along the pipe, so to speak.
It seems to be generally understood that the hottest barrel temperature would be at the throat and the lowest somewhere towards the muzzle.
My attempts at altering this heat pattern is to concentrate the higher temperature more towards the case head than the throat.
However, if the carbon fiber not only enhances heat flow away from the bore but also along the barrel at a rapid rate it wouldn't be long until every high intensity cartridge would have a properly carbon wrapped barrel. And all of this because gg is pushing the envelope a bit. Good goin!
So much for that. I'm off to Rexburg to see if that idiot has the RUM barrel fitted yet. The first estimated delivery date back in January [img]/ubbthreads/images/graemlins/frown.gif[/img]
I may be the slowest guy on the mountain . . . . but . . . . I'm on the mountain!
maybe you and Buffalo Bob should just go to Rock Creek Barrels web site and hit the links to ABS inc.
It explains how and why Carbonmans fiber works as a heat dissapater.
The independent testing was done by the University of Nebraska School of Enginering.
Mike Degerness (Carbonman) receive a patent on this technology because it works!! It will cool a barrel 3.72 times faster than a steel bbl.
I was there when GG and Idaho P were doing the test and it is very obviouse how good the carbon wrap works at cooling the barrel.
It seems like it would be more productive to read about Mikes technical data and patent data(he includes the patent number so you can check it out)instead of typing speculation as to why something couldn't-shouldn't-wouldn't work even though you have no personal experiance with an A.B.S.Inc. barreled gun.----RHB