Painted barrels and heat

[Hoplophile]

Does a painted on coating like Duracoat make any noticable difference in the ability of a barrel to dissipate heat?

I've been wondering about this for a while but don't have the time to do anything about testing it for myself. Since the barrel is completely coated the heat has to be transferred from the metal to the paint to the air instead of just metal to air so there is potential for it to act as an insulator. Does anybody have any hard data on this?

[Sweep]

i imagine anything you put on a barrel short of carbon fiber will become a heat sink ...thou ive never seen any diffrence or taken a thermal gauge to diffrent barrels im sure some one has and will pipe up :cool:

[twl]

The answer is yes, unless the paint is specially formulated for heat dissipation, and that kind of paint would more appropriately be called a "thermal dispersant coating" or "high thermal conductivity coating", paint will interfere somewhat with the cooling of the barrel.
To qualify the statement, it won't be a huge difference, or you may not even notice any difference in your type of usage.

The paint does two things. It covers the barrel, and fills in the little pores in the metal. Since most paints don't have thermal conductivity equal to steel, this will interfere with the transfer rate of the heat to the air, and will also reduce the surface area(by filling in the pores) that the heat will radiate from.

Neither of these things is good.

However, it may not cause any issue for you and your barrel, if you don't use the gun in a way that will stress it to the point where the paint makes any difference. The barrel will still absorb the heat, and it will (more slowly) dissipate it thru the paint, and if you don't take the barrel to the limit, then you probably won't notice any/much difference.

On the "good side", paint can improve the weather resistance of the barrel, can provide some camo use, and alot of people seem to like having paint on there. So you have to weigh the good and bad points, and do what works best for your use.

Regarding the comment above about the carbon fiber, most forms of carbon fiber used on barrels do form an insulator on the outside that would interfere with the cooling. However, there is one carbon fiber barrel maker(ABS) which uses a specific process that provides a super-fast thermal conductivity, and ABS is the only one which can make this claim(patented). ABS does not recommend painting the carbon fiber surfaces, because they have a very high thermal conductivity, and paint would definitely impede the performance of those barrels.

[KevinB]

I have KG on a Douglas Barrel --
http://img.photobucket.com/albums/v193/EvilKev/Courses/ContractorDriving427.jpg

http://img.photobucket.com/albums/v193/EvilKev/Courses/PictureorVideo009.jpg

http://img.photobucket.com/albums/v193/EvilKev/Courses/Barrel1.jpg

I'm not a science type and so I would defer to TWL - I have not noticed any problems with it - only issues with the damage to it due to harsh use.

[Sweep]

The answer is yes, unless the paint is specially formulated for heat dissipation, and that kind of paint would more appropriately be called a "thermal dispersant coating" or "high thermal conductivity coating", paint will interfere somewhat with the cooling of the barrel.
To qualify the statement, it won't be a huge difference, or you may not even notice any difference in your type of usage.

The paint does two things. It covers the barrel, and fills in the little pores in the metal. Since most paints don't have thermal conductivity equal to steel, this will interfere with the transfer rate of the heat to the air, and will also reduce the surface area(by filling in the pores) that the heat will radiate from.

Neither of these things is good.

However, it may not cause any issue for you and your barrel, if you don't use the gun in a way that will stress it to the point where the paint makes any difference. The barrel will still absorb the heat, and it will (more slowly) dissipate it thru the paint, and if you don't take the barrel to the limit, then you probably won't notice any/much difference.

On the "good side", paint can improve the weather resistance of the barrel, can provide some camo use, and alot of people seem to like having paint on there. So you have to weigh the good and bad points, and do what works best for your use.

Regarding the comment above about the carbon fiber, most forms of carbon fiber used on barrels do form an insulator on the outside that would interfere with the cooling. However, there is one carbon fiber barrel maker(ABS) which uses a specific process that provides a super-fast thermal conductivity, and ABS is the only one which can make this claim(patented). ABS does not recommend painting the carbon fiber surfaces, because they have a very high thermal conductivity, and paint would definitely impede the performance of those barrels.
that is the exact barrel i was thinking of and i would never paint a six hundred+ dollar barrel but id sure love to have one:D

[Hoplophile]

The paint does two things. It covers the barrel, and fills in the little pores in the metal. Since most paints don't have thermal conductivity equal to steel, this will interfere with the transfer rate of the heat to the air, and will also reduce the surface area(by filling in the pores) that the heat will radiate from.
I guessed as much. What I'm wondering is whether or not anybody has ever quanitifed this in any way. If I had the time I'd get a couple of identical barrels, paint one and go to the range with a case of ammo and a couple of thermistors. The thermistor would need to be in direct contact with the metal of the painted barrel, of course.

[twl]

Well, here are some thermal conductivity ratings that I found in some web searches. Bear in mind that thermal conductivity can vary somewhat, depending on the exact sample tested, but these figures will show what the relative differences are between the materials.
Ratings are shown in units w/mK(watts/meter Kelvin) which is the standard thermal conductivity rating method.
The higher the number, the better the thermal conductivity is.
The highest thermal conductivity known is pure crystal diamond, which can be anywhere from 1100w/mK - 2000w/mK.


Acrylic(commonly used as the base in paints) = 0.2 w/mK
Vinyl Esters( also used in paints) = 0.25 w/mK

Steel = 54W/mK

Aluminum = 270 w/mK

Copper = 390 w/mK

Silver = 407 w/mK (most thermally conductive metal)


The material used in the ABS carbon fiber barrels to conduct the heat for cooling purposes is between 700w/mK - 800w/mK.
This is the second most thermally conductive material in the world, and ranks behind pure diamond as the only thing higher.

Regarding the paint being poor thermal conductive material, there is a saving grace that there is only a thin coat of it on there, so the heat can get thru it better than if it were thick.
You can see that steel conducts heat around 270 times better than the acrylic does. So the acrylic would tend to slow things down a bit.
Anytime you put something like that onto a thermally conductive surface, it is sure to cut down effectiveness, and since steel is not exactly that great at thermal conductivity anyway, making it worse with anything isn't really a great idea unless you really have to do it.
But, steel is an excellent barrel making material for all the other needs that a barrel has, so the thermal conductivity rating is acceptable because of that. There have been a variety of things done to cool barrels for machine guns, etc., and some have been better than others, and all had some issues of their own. The usual method now is to just change barrels when they overheat.
An ABS barrel can typically triple the number of rounds fired before cook-off, and drastically increase the number of rounds fired before eventual thermal failure. Also, it will weigh only about 1/2 the weight of the old type all-steel barrel. And it is capable of match-grade accuracy, and has 65% less throat erosion for longer barrel life.

[olds442tyguy]

The same people that make Cerakote also offer a thermal dissipation coating for industrial applications. We've used it one a multitude of automotive products with alot of success. While I'm not capable of doing heat temperature readings under most circumstances, a simple hand hold over makes it obvious that there is same very significant heat sheding that was not evident before the coating.

I know Cerakote has recently went public with their gun coatings, but I'm still unsure about their policy for commercial applications of their industrial products. I've been wanting to try it out on a barrel, but I have yet to get up the courage.

[Ned Christiansen]

I t pleases me greatly to find somebody else interested enough to wonder!

I figured the same thing-- any coating of paint would act as an insulation layer. On the other hand, black radiates heat more than other colors.... I took six 4" lengths of 1" cold rolled steel and did made the following:
Solid, polished
Solid, blasted
Fluted, polished
Fluted, blasted
Fluted, blasted, painted black
Solid, blasted, painted black

I capped each on the ends with some fiberglass insulation board to take that out of the equation. Heat-soaked all in the oven for 3+ hours at 350, took them out and monitored the heat loss over the next hour with an infra red pyrometer.

This was not super-scientific and the IR pyro was not the ideal way to read the temps, I think. The actual data is not lost but location unknown-- long story short, polished lost big time, blasted and painted black won, no noticeable dif between fluted or solid. YM, and actuality in lab conditions, MV.

Figured polished would not be good-- the fine surface reflects heat back into the mass. Machinery's Handbook gives heat radiation of various materials and copper, although it's a great conductor of heat, holds it a long time, and especially if it's polished.

I think just going from polished to blasted helps. Fluting can't hurt but there are other issues and I doubt anyone has missed the big important shot because their barrel was too hot from not being fluted. I'd say a thin coating of black does at least as much good as harm. Schlep it on too thick and it's sure to hold more heat in though, I'd think. An actual black finish like bluing or chrome sulphide on SS has got to be better yet.

Anybody here work for HP White Laboratories?

:cool:

[Pat_Rogers]

Excellent Ned!
Thanks for taking the time to do all that!

[Hoplophile]

Yes, thanks much for the info. I guess the next question is how much of an impact color will have on this. As you say, black is the most emmissive color so I wonder how well coyote brown or tan would compare.

Too many irons in the fire right now but maybe later this fall I can try a similar test.

[stephen]

...no noticeable dif between fluted or solid.


I find this part extremely interesting. Thanks for sharing.

Stephen

[Hoplophile]

I find this part extremely interesting. Thanks for sharing.

Stephen
I've been told several times that bead blasting actually adds more surface area than fluting. Don't know if it's true or not, but I have to admit that it's kept me from dropping money on a fluted barrel.

[Cold]

Wow

great info Ned!!