O2 + Al + Ignition = 3500+ degrees F

[gunsonwheels]

As we all buy-in to wrapping/bagging charges with aluminum foil, does any one have a concern that the heat of oxidation of aluminum is somewhere above 4000 F and steel melts at 2500 F?
 
 The Thermite reaction produces an extremely hot reaction (up to 2500 °C or 4500 °F), which creates molten iron and aluminum oxide. The molten iron produced from Thermite is white hot and the aluminum oxide is a white smoke.   When I started BP ordnance, I was fresh from dabbling in pyrotechnics and aluminum powders are widely used in that industry.  Because I was aware of the heat of oxidation issue I was afraid to follow NSSA guidlines of bagging with foil and instead used plastic flat tubing to make custom-sized bags with heat sealed ends.   So does the aluminum melt from the BP heat or does it oxidize as it competes with the sulpher and carbon to combine with the oxygen being released from the KNO3??  Are we heat-eroding our combustion chambers?

[keith44]

I won't use aluminum, for other but related reasons.  Working at perhaps the worlds largest aluminum producer (no smaller than number 3) I have been in too many safety reviews of explosions related to aluminum fines.  These are produced everytime aluminum is abraded in anyway.  They ignite as easily (after slight oxidation) as pyrodex, and as noted burn hot enough to melt steel, actually if there is any magnesium in the aluminum alloy (more common than you may think) once lit, it can burn hot enough to cause the carbon in steel alloys to burn, and in sufficient quantities actually cause the steel to burn and leave only the iron component of the alloy that was steel.

[shooter2]

Without pretending to be a ballistics expert I would expect that Centrefire Smokeless rifle rounds would generate considerably more heat and friction than even a large Black powder load, what with being forced through a relatively small hole etc.  That being said, it would be the amount of time the interior metal was exposed to the heat of firing that would the largest contributor rather than the heat itself. An experiment I read by the US Army at one stage concluded barrel erosion increased with the frequency of firing rather than the ignition temp. of the round, which is why machine gun barrels (chamber throats to be technical) wear faster than bolt action rifles.  Sustained firing events are more damaging than steady fire.  As BP cannons have very slow firing rates, I do not see this as being a big issue.

To conclude, its the time in contact not the initial temperature that is the greatest contributor IMHO.

shooter2

[subdjoe]

I examine the foil remnants we pull from most of the charges I roll, as well searching down range for some of the bits and pieces.  This is out of a 3" rifle and using 5, 6, 8, or 16 oz. charges.  I've seen no indication of melting or significant oxidation. 

I did see some evidence of melting, and possibly burning, on some cement filled aluminum cans.

[Double D]

I think if you look for a problem hard enough you will finally imagine it.

 

[Cat Whisperer]

Having seen much aluminum foil come out of the tube and seen some effects of errosion on aluminum cans which I've fired, IF I ever erode a bore to the point where it's unusable, I will have a huge smile on my face for having fired that many rounds!   

Might happen, might be measureable. 

It IS good to know how much the effect is AND what the pitfalls are.  Good discussion.

[gunsonwheels]

I posed the question to Matt Switlik as I figured no-one had more experience with the foil bags than him.  He said as far as he knew no-one had done any definitive tests of melting vs. oxidizing but that from obsevations there are generally tiny balls of melted aluminum from the foil residue that come out from the swabbing and also can be seen just in front of the piece's battery after firing a considerable number of rounds.
 
I still bag with sonic heat sealed flat plastic tubing.  I used to mix aluminum with KClO3 and a few other chemicals and observed how effectively it melts steel... also working on the railroad I observed the crews joining ribbon rail (1/4 mile long sections of heavy mainline rail) with a housing that clamped over the joint, the steel and thermite put in the top and ignited... the steel is melted by the thermite and welds the two rail ends together in less then a minute.  One crew about burned down a forest in our neighborhood when they left a "hot spot" they created from grinding the joint smooth after the welding.
 
It's kind of like a good comprehensive and definitive pressure testing... it hasn't ever been done but things appear to be okay and safe so... we press on.     

[Double D]

You don't think Switliks pressure test were definitive or comprehensive?

If you want really comprehensive and definitive tests get GOEX to spring loose with some of their testing data-they won't. It was hard enough for me to get them to spring loose with specific gravity of there powders.    DoD also has some recent blackpowder testing data as well, that they won't spring loose.

Melting temperature of aluminum foil is a long ways from oxidation temperature.

When did potassium chlorate become a product of the combustion black powder?  Might be concerned with this using Pyrodex.

Where is the evidence of the termite effect is taking place in cannons.  Surely as long as the aluminum foil cartridge practice has been in effect and the thousands upon thousands shoots fired  some evidence would show up suggesting sometime might be going on.

I also have seen the little melted balls of aluminum.  Looking at the remnants of the foil cartridge I can see melting right around the vent and at the front of the cartridge.

I don't doubt for a second that the thermite effect is real.  I just doubt that all the elements necessary for the thermite effect to occur are present in the firing of an aluminum foil wrapped blackpowder cartridge in a steel cannon barrel.

If there was a real danger here this effect would have raised it's ugly head years ago.....



 

[GGaskill]

Thermite is a redox reaction where the iron in iron oxide is chemically freed while the aluminum reacts with the oxygen that was bound to the iron.  The result is free molten iron and aluminum oxide and large quantities of heat. 

In a cannon, the powder combustion is supposedly oxygen poor, meaning there is no excess oxygen available for reaction with other materials so I doubt the aluminum could chemically react. 

In my limited experience, I have only once not found any of the aluminum foil powder bag left in the chamber area after firing and I don't know if that was because it exited the bore or totally melted.

[gunsonwheels]

DD:

If there was a real danger here this effect would have raised it's ugly head years ago.....

I do agree with DD... history and evidence is on the side of melting.  But for me it's just having burned aluminum in the presence of an oxidizer and melted steel by doing so, it continues to make me uncomfortable to introduce aluminum into the flame + oxidizer mix and especially doing that inside tubes which have cost me more than I could really afford whether it was time, $ or both.
 
And from my perspective, "NO" on Switlik's pressure testing.  Knowing/determining a maximum pressure is quite different if it is important to know the rise and fall profile in relation to the position of the projo in the barrel.  If someone is using a mini-ball type projo and needs the pressure to come up quickly enough to swell the skirt near the bottom of the bore so the projo will get a good spin before exiting the bore, with the existing data plus and a projo with good upset,  one still cannot tell but what that swell/upset occurred just before exiting the barrel and thus good spin and stability never occurred.  At that point the pressure data is lacking and one must depend on down-range performance to formulate their conclusions.  The 1800's Ordnance manual would appear to confirm maximums are reached while the projo is at the bottom when the powder's space is limited to its volume (momentarily) before the projo starts to move.  But the presssure profile in relation to the projo position is data which, as far as I have been able to determine, does not exist.
 
In our sport we have many variances if interest and opinion and I believe that is a great value to a board like this one.  I will always be the kind that looks forward to more data than we currently have... After all the availability of the data has changed conclusions in our past from the world being flat and from the earth being the center of the universe!     

[Cat Whisperer]

BUT since the flash and bang occur in such a SHORT period of time, there is little dwell time of the higher temps to affect the foil - ok, maybe a little.  But the majority of the foil gets blown out the muzzle.

[Double D]

Didn't  Dr. F.W. Mann do some work on obturation of projectiles.

 I believe his work shows that obturation takes place when the powder ignites but before the bullet moves. Body at rest tends to remain at rest unless acted upon by some outside force.  The force is transmitted through the material and deformation takes place until the total force over comes the mass and projectile moves.   Once the projectile moves there isn't sufficient force  to continue deformation.

Been a few years since I read Mann, that I don't recall all the specific...is 30 or so years a few years.

Have you read Mann?

[Victor3]

 I doubt you're going to get any substantial reaction similar to thermite, which requires the aluminum and iron oxide be in powdered form and mixed. It also requires a sustained high heat level; I've watched RR crews welding track with it and they sometimes have a hard time getting it going with an oxy-acetylene torch. Here's a pic I took of a thermite weld a couple years back...
 

 
 I think one might should be more concerned that they're creating a capacitor by using a plastic bag and aluminum foil in a BP charge. Even that idea has pretty much been tossed though...
 
 

[Cat Whisperer]

Didn't  Dr. F.W. Mann do some work on obturation of projectiles.

 I believe his work shows that obturation takes place when the powder ignites but before the bullet moves. Body at rest tends to remain at rest unless acted upon by some outside force.  The force is transmitted through the material and deformation takes place until the total force over comes the mass and projectile moves.   Once the projectile moves there isn't sufficient force  to continue deformation.

Been a few years since I read Mann, that I don't recall all the specific...is 30 or so years a few years.

Have you read Mann?

He did.  (I keep my copy by my easy chair.) 


But I think the major difference here is that the burn time is right-much short in a cannon compared to welding which has adequate TIME for heat to transfer.   Hence, the majority of the very thin aluminum observed unscathed.

Is the minor amount of aluminum that is melted an issue?

[gunsonwheels]

CW and DD:
 
Very excitedly curious about what Mann said about obturation/upset.  Will go searching for his data and conclusions.  Maybe CW would post a summary paragraph...??
 
And thanks muchly for the info.  It's info I do not have.

[Double D]

Here is a link to 68 copies of Mann's book.   http://www.abebooks.com/servlet/SearchResults?an=mann&sts=t&tn=the+bullets+flight&x=60&y=14

The best copy to get is the Wolfe Publication edition.   It was published from Harry Popes original copy and includes his Marginal notes.

[gunsonwheels]

Is thisthe treatise you are referring to??:
 
http://castpics.net/subsite2/ClassicWorks/The_bullet_s_flight_from_powder_to_targe.pdf
 
I assume it is as on page 81 he discusses the subject and his test results.
 
GOW

[Cat Whisperer]

Yup.  That's it.

You will find his research is just that, research.

One experiment after another, well documented.

Published in the early 1920's. 

Some of it is slow reading, but what he did was often the first documentation of what was really going on.

[Double D]

Is thisthe treatise you are referring to??:
 
http://castpics.net/subsite2/ClassicWorks/The_bullet_s_flight_from_powder_to_targe.pdf
 
I assume it is as on page 81 he discusses the subject and his test results.
 
GOW

That's the one! I had two copies on my library, but gave one to my son...looking at those book  prices I gave him the most valuable one.


That's where the pictures start, but the discussion start earlier on in the book.  I found with Mann's writing you have to start at the first and read through or you will miss some the points he is working.   

[gunsonwheels]

DD:
 

I found with Mann's writing you have to start at the first and read through or you will miss some the points he is working.

 
 
I thought I noticed this just from the quick perusal getting to p. 81.  Thanks for the "heads-up" though.  We'll go through it slowly and carefully.  I love treatises which are long on data and short on conclusions and thus allow the data to make the conclusions obvious to the reader.
 
Thanks again CW and DD!
 
GOW

[Double D]

DD:

If there was a real danger here this effect would have raised it's ugly head years ago.....

And from my perspective, "NO" on Switlik's pressure testing.  Knowing/determining a maximum pressure is quite different if it is important to know the rise and fall profile in relation to the position of the projo in the barrel.  If someone is using a mini-ball type projo and needs the pressure to come up quickly enough to swell the skirt near the bottom of the bore so the projo will get a good spin before exiting the bore, with the existing data plus and a projo with good upset,  one still cannot tell but what that swell/upset occurred just before exiting the barrel and thus good spin and stability never occurred.  At that point the pressure data is lacking and one must depend on down-range performance to formulate their conclusions.  The 1800's Ordnance manual would appear to confirm maximums are reached while the projo is at the bottom when the powder's space is limited to its volume (momentarily) before the projo starts to move.  But the presssure profile in relation to the projo position is data which, as far as I have been able to determine, does not exist.

I was just reading Greener's Modern Breechloaders 1871 and he touches some what on this subject. He advocates that larger grain powder, slower burning powder  continues to burn as it goes down the barrel.  He states that finer grain powder burns to fast in the bore and  projectile will be slowed by friction when the faster burning is consumed and the projectile has not left the bore.

For extensive testing of the position of projectiles when maximum pressures are achieved, I suggest you read the works of  Sherman Bell of Double Gun journal,  He has a number of works on this subject.

[Double D]

GoW-George,

While meditating this morning this thought came to me on this subject...

Goerge I know we banged on you pretty hard on this subject, but I don't consider your concern nonsenses, it is something to think about.  But consider this, the  Fire Safety code of the state  Massachusetts requires that cannon cartridges be wrapped in foil. 

Further I also believe that we have had posted here the safety regulations of the  National Parks Services for firing of  cannons in the National Parks and they also require charges wrapped in foil.

Do you think these two reputable bodies would require foil wrap if a thermite like reaction was possible?  Your thoughts?


 

[Rickk]

It gets easier if one separates "hot" from "heat". 

Something can get real hot (degrees F), but if there isn't enough of it, there just isn't much heat (BTU's).

It takes a certain amount of BTU's to heat a certain amount of steel up to a certain temperature.

There just isn't enough BTU's in a couple wraps of aluminum foil to accomplish all that much.

Also, when the charge ignites, the aluminum foil gets pressed tightly against the steel barrel. The burning black powder is trying to put heat into the aluminum foil, and the barrel is trying to take it out.

The end result is the bags get wormed out fairly intact ..... no evidence of ignition.

Rick

[GGaskill]

I would consider neither government agency as a source of original (or tested) procedure.  I am sure they just copied the most restrictive prior art for the regulations.

Personally, I do not think that aluminum foil will be burned in a reaction such as we are discussing.  The powder reaction does not have an excess of oxygen that would be available for reacting.

[Artilleryman]

I agree with Rickk.  Not enough aluminum to cause a problem.  We usually remove 25% or more of the aluminum cartridge after firing, and I believe the rest is blown out the barrel at projectile speed.  Not much time to do anything harmful.

[GGaskill]

If you are of a mind to experiment, you could add a little KNO₃ to the powder and see what happens.

[Zulu]

If you are of a mind to experiment, you could add a little KNO₃ to the powder and see what happens.

KNO3??

[GGaskill]

In English, potassium nitrate.

[mcwoodduck]

I understand that AL, Iron dioxide (rust), and magnesium are what makes a thermite reaction.  As far as I can understand you need something easy to light that is hot as 4000 degrees to ignite Al and even if you can ignite the Al with black or pyrodex powders there is not a lot of it to create the heat needed to melt the steel.  The heat needs to be sustaned long enough to tranverse the steel and melt, a small amount of 5000 degree heat, double the melting point will not melt a bar of steel as the bar will absorb the heat and untill it is at 2500 degrees will not melt
My guess is that the small amount of AL used to wrap the charge is going to leave with the charge and not live in the barrel to create thermite with rust in the chamber.

[Double D]

You guys have all missed my point.

My point is that that fire codes are excessively restrictive to the point of near paranoia. 

No Fire Agency is going suggest a regulation that that even remotely has a chance of a thermite like  reaction.