Barrel coatings test

needing said:

Hi comnoz.
Regarding your cooment:
"First, I recondition batches of barrels for CNW and others and I had a dozen of them waiting. The past several years I have been using [aerospace] heat dissipating coating on the barrels. It is difficult to deal with, requiring a special gun and extreme care. It produced a nice finish but like many ceramics it is brittle and sometimes chipped around the bolt holes. It's also pricey. I wanted to switch to a stoving enamel that was little less expensive and hopefully tougher and easier to deal with but I wanted to make sure that I was not going to mess with the piston clearances I had been using. The heat tests have done that..."

Why was the "pricy" "heat dissipating coating" chosen originally without conducting testing as the economics of coating costs remain constant?

Hi all.
What testing has actually been done to validate claims made for other products in this market?

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comnoz said:

...aerospace coatings barrel, the thinnest coating - 308 F.
powder coat barrel, the thickest coating - 281 F.
enameled barrel, 3 medium coats - 272 F.

That is over 30 degrees difference from highest to lowest.....

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hobot said:

Ah shoot the fried oil is thought to be recovered when its mixed with cooler oil in cases and then run through a cooler so the reactions can reverse in the oil tank as montiored by those very satisified with their temp gauges and thermostats in healthy zone, Thanks for the Svante Arrhenius reaction activity source. The black body emission coating tests like Rockefeller's Cough syurp in Commanod barrels so would be educational what sort of testing they base their space age claims on and get and id of why it don't seem to apply to Cdo's. Some of us still remain restless on alloy barrels heat flow comparision. As tough as the spacy coat was maybe good on swing arms.

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comnoz said:

As a followup to the testing. I have re-run most of the tests and come to the conclusion that there is little if any difference in the heat dissipating qualities of the tested barrel coatings ..... On a re-test the temps were within a couple degrees of one another. Jim

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lcrken said:

Wow, think of the options that opens up. Wonder how tangerine metalflake would look? Or what about camo? Endless possibilities for the creative amongst us.

Ken

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comnoz said:

As a followup to the testing. I have re-run most of the tests and come to the conclusion that there is little if any difference in the heat dissipating qualities of the tested barrel coatings or colors.
. Jim

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texasSlick said:

comnoz said:

As a followup to the testing. I have re-run most of the tests and come to the conclusion that there is little if any difference in the heat dissipating qualities of the tested barrel coatings or colors.
. Jim

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Any coating is expected to be only 0.002 inches thick, and regardless of the thermal conductivity of the coating material, such a small thickness affects the heat conductivity to an insignificant degree.

Theoretically, any additional thickness to the barrels and fins, be it a coating or even the base material, will reduce the heat transfer. If the barrels and fins are 0.375 inch thick, adding 0.002 will reduce the heat conductivity to 0.375/0.377 or 0.995 (0.5%) if the coating conductivity equals that of the base metal. Even a markedly different conductivity of the coating will not change that value very much.

Convective heat transfer is not affected by a coating, unless the coating reduces or eliminates surface roughness. I have commented on this effect earlier.

Radiative heat transfer is affected by color. The Stefan-Boltzmann Law of Radiation states a body will radiate or absorb heat depending on whether it is hotter or cooler than its surroundings

J = e x s x T pwr 4

where J is the radiated heat energy, e the emissivity of the surface (this varies with color, but some of the new hi tech coatings have nearly the theoretical maximum e of 1.0), s is Stefan's constant, and T pwr 4 is the fourth power of Temperature (surface temp in absolute degrees ... 460 plus F or 273 plus C)

Air is transparent to radiation, thus the air temp does not make for the surroundings. The surroundings are anything capable of absorbing and re-radiating energy back to the body. In Jim's shop, the surroundings were the walls, ceiling etc at 68 F. A large part of the surroundings were the walls of the box at temp = ?

Jim's thermocouple was not measuring the surface temp of the barrels. The thermocouple temp was about 109 F. The surface temp at the front and sides of the barrels was probably much closer to ambient or 68. Thus the radiation temperature difference between the surface of the barrels and the surroundings was probably small, and radiative heat transfer was insignificant. Radiation becomes significant when the barrel surface temp exceeds 300 F and the surroundings do not re-radiate back, such as a cloudless night sky.

Thus, understanding the three modes of heat transfer, conductive, convective, and radiative, Jim's results and conclusion are quite predictable.

Slick

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hobot said:

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