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Does anyone have information on the maximum temperature reached in a Golfball Mortar?
 

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Left mine out in the 114 degree desert sun a couple months back.... got it pretty darned warm.
 

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Quick web search app 1400 C or 2552 F for an extremely short amount of time


Abstract
An earlier thermo-analytical study of black powder, using small sample masses and slow heating rates, has been extended to an examination of the behaviour of black powder under the less-controlled conditions of ignition and combustion, by simultaneous measurement of temperature profiles and burning rates.
Burning-rate against composition curves for various charcoal/KNO3, mixtures (sulphurless black powder) and for charcoal/KNO3, mixtures with various proportions of sulphur, were concave-down-type curves. The compositions of mixtures with maximum burning rates did not correspond with the compositions of mixtures with maximum enthalpy-of-reaction. Maximum temperatures of 1400°C were recorded. Burning rates were found to decrease with increasing particle size of the constituents: with increasing compaction of the mixtures, or when inert diluents or subsidiary fuels were added to the mixtures. Burning rates were also affected by moisture contents above 276, and failure of burning occurred at >15% moisture.
 

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The abstract didn't say at what pressure or confinement the testing burned the powder. With the minimal confinement that a golf ball provides, the temperature may not get that high.
 

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Neither mike nor I know how pressure relates to temperature of BP conflagration, but intuitively there seems to be a correlation between increased pressure and higher temperature. Just wondering if one of you engineers or scientist types out there agree with our supposition?

As the firing of a blank charge from a short tube exemplifies lower pressure, we borrowed El Cazador's beautiful Calendar pic for a look at a lower pressure flame color.





As just one example of a higher pressure gas, we chose the firing of our 7" Brooke Rifle firing 518 gr. of BP behind a 9 oz. milled base, solid steel bolt at a measured 1,400 fps. The incandescent flame color here is quite different from the flame color in the howitzer shot. Do you think this is a result of a notable pressure differential??

 

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I would agree but I think the lighting of the photo and, perhaps, even the differing cameras has some affect also.
 

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Really hard to tell from the color in a photo - I know I have posted these before, but look at the color in these blanks



(I do like that you can see both Old Scratch in the first one - looking up and slightly towards the viewer, the end of the plume is the point of his beard, and the face of a cherub about the center of the plume, looking foreward)


 

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Subdjoe , It is late , and I've indulged in a couple of adult bevs . Am I to believe that there is a 'beard' out there somewhere ? you MUST be delutional ! :eek:

Now the cherub I see clearly ;D oh yea ,there he is lookin kind of like he'd rather be someplace else .

But HE IS there smack in the middle and not too happy , A pinheaded ,scortched ,bald ,screaming flaming cherub

you dont see those everyday . :D
 

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The Ideal Gas Law as shown below, describes the relationship of pressure, temperature, and volume.

The state of an amount of gas is determined by its pressure, volume, and temperature. The modern form of the equation is:

pV = nRT

where p is the absolute pressure of the gas; V is the volume of the gas; n is the amount of substance of the gas, usually measured in moles; R is the gas constant (which is 8.314472 JK−1mol−1 in SI units[4]); and T is the absolute temperature.
http://en.wikipedia.org/wiki/Ideal_gas_law
If you solve for T, you have the following:

T = pV/nR

As the temperature goes up, so does the pressure, for a given volume. This describes the ignition stage of the powder. At the beginning of ignition, volume is a constant, and temperature goes from the atmospheric temperature to roughly 1400*C, according to their abstract (it will likely vary depending on a number of factors), which raises the pressure in the chamber. Once the pressure is greater than the frictional (drag) force holding the projectile in the barrel, the volume becomes variable as the projectile is...projected out the barrel.

Notice that volume and pressure have an inverse relationship - if you have a larger volume with the same amount of powder combusting, the pressures will be lower. This explains the differences in the use of various types of cannon. In a mortar, the bore is relatively large and the depth of the bore relatively small compared to a cannon with a smaller bore. Using the same size load, the initial volume will be the same, assuming the projectile is sufficiently seated on the powder, but as the projectile moves (which will occur at different pressures for different size projectiles, as the drag force is a function of mass), the volume increases more quickly in the large bore mortar than in the small bore cannon, relieving some of the pressure in the barrel (though more is being made by the still burning powder). Having a longer bore in a cannon allows the pressure to build up for a longer before the projectile exits the barrel, contributing to higher muzzle velocity. That paired with the size and wieght of the projectile can be used to determine range, and thus you have long range "small" bore guns and sgnificantly larger bore short range guns.

Of course having proper windage for a projectile is important as well, because as the pressure builds to the point that it can move the projectile, the explosion is still taking place, resulting in more material being involved in the reaction that produces the gas that propels the projectile. If the projectile were oversized and became lodged, the pressure would continue to rise until either the powder is fully incinerated, or until the volume of the explosion is increased. If the powder fully incinerates without the volume increasing, you'll have a pressure vessel. This is unlikely, because it would mean that you grossly underloaded the gun, and that the vent was plugged during ignition. A volume increase is the most likely reaction to the increase in pressure. This could happen by the pressure finally exceeding the friction force holding the projectile (hopefully, since this is the intended purpose of the gun), it could escape through the vent, or, if the pressure goes unrelieved to the yield strength of the material, it could have catastrophic failure. In any case where the volume is no longer restricted by the load, the volume becomes the atmosphere, and is therefore, practically infinite, which is why the pressures normalize after firing.

I hope all that makes sense. It's kind of late, and I'm tired.
 

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RocklockI said:
Subdjoe , It is late , and I've indulged in a couple of adult bevs . Am I to believe that there is a 'beard' out there somewhere ? you MUST be delutional ! :eek:
LOL
The right eye of the 'cherub' is the left eye of Old Scratch, and the bright left side of the cheubs head is Scrathches forehead. The bright leading end of that plume is his beard.
 

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Blackpowder, when it burns is to some extent self-limiting on pressure as the higher the pressure the more the gasses emitting from the granule of powder are reduced - slowing the burning. Hence one gets very even burns from shot-to-shot in match rifle shooting with blackpowder.

I would think that the the length of the tube, and perhaps the ratio of volumes of the powder chamber to the tube (expansion ratio) coupled with the mass of the projo and the clearances involved would all affect the time of the burn which would affect the temperatures achived.

Hence, I would ASSUME that mortars would get to much less temperature extremes than longer barreled howizters or even longer barreled cannons. Thus the difference in signatures seen in the above and other pictures.

Isn't that what was just said?
 

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subdjoe said:
RocklockI said:
Subdjoe , It is late , and I've indulged in a couple of adult bevs . Am I to believe that there is a 'beard' out there somewhere ? you MUST be delutional ! :eek:
LOL
The right eye of the 'cherub' is the left eye of Old Scratch, and the bright left side of the cheubs head is Scrathches forehead. The bright leading end of that plume is his beard.
The chrub I see is looking straight toward the cammera with his head tilled slightly his right ,our left . how can he grow a breard right our of the side of his head ?
 

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Cat said:
Blackpowder, when it burns is to some extent self-limiting on pressure as the higher the pressure the more the gasses emitting from the granule of powder are reduced - slowing the burning. Hence one gets very even burns from shot-to-shot in match rifle shooting with blackpowder.

I would think that the the length of the tube, and perhaps the ratio of volumes of the powder chamber to the tube (expansion ratio) coupled with the mass of the projo and the clearances involved would all affect the time of the burn which would affect the temperatures achived.

Hence, I would ASSUME that mortars would get to much less temperature extremes than longer barreled howizters or even longer barreled cannons. Thus the difference in signatures seen in the above and other pictures.

Isn't that what was just said?
I think the color temperature differences in the photos hae more to do with camera differences, exposures, and ambient light/backdrop, than the actual heat of the flame. I'd think the best way to check is to directly measure the color temperature using the same load out of different barrels.
 

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RocklockI said:
The chrub I see is looking straight toward the cammera with his head tilled slightly his right ,our left . how can he grow a breard right our of the side of his head ?
I sort of circled what I see as the cherub, and labled it. I also circled what I see as the beard (well, most of the beard) and the nose of Ol' Scratch. See if it makes sense to you now. Remember, Scratch is looking up and a bit out.

 

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the cherub is in the square looking straight on except his pinhead that goes up and out of the square on top . The circles have no place in my veiw .

Now ,I have a twisted image of the 'beard' really being his brains being blown out of his head by Scratch ! THANK YOU ! ;)

Eh , whats another twisted image in my head ? ;D ;D ;D . In behind the left ear and out the right temple , with flaming brains !!! (Very Professional)

Another good night of sleep now !.....and the cherub is not happy about it ! Also I'm not altogether sure it is a Cherub .....it looks a little like ......never mind .
 
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