ABS cannon explosion

[Fnord]

"Combustion, by definition, produces CO2 and H2O."

MAPP doesn't produce H2O does it?

I thought one of the gasses commonly used doesnt produce water. If I made a chamber that I couldnt dry out, I would either paint the inside or galvanize it first.

[SpudBlaster15]

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[BC Pneumatics]

"A hybrid the size of mine weighs no more than 10 pounds, and cost less than $50 to build."

Do you think that everyone will settle for a cannon so small as to weight 10lbs? Of course, cost is will increase with the larger cannons people want as well.


"The water produced by combustion transitions to gas form due to the heat of combustion, and is evacuated from the chamber by the flowing air used to vent."

You cannot expect people to believe that all the water is expelled during this process, that just isn't reasonable.


"Plus, the steel is galvanized, which is done specifically to prevent rusting."

Galvanization acts more as a deterrent to rust. Threads in particular have a tendency to start rusting, at which point the damage can easily proceed underneath the zinc layer.
I don't know if the propane's heat has an effect on the zinc (Which has a relatively low melting temperature) over time, and I doubt it does, but it is also something to consider.


Don't think I am saying steel is a bad construction material, I an just pointing out why it is far from ideal.

[SpudBlaster15]

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[Fnord]

I don't know if the propane's heat has an effect on the zinc (Which has a relatively low melting temperature) over time, and I doubt it does, but it is also something to consider.

Zinc will burn off when steel reaches about 1500 F(it has a cool green flame too).

I dont think you'll be able to expel all the water by combustion, but if you kept the chamber hot and allowed it ventilation, it would evaporate before the metal can oxidize.

[BC Pneumatics]

Spudblaster, Untwist your panties, you seem defensive.


"Since when does the discussion of steel as MY preferred construction material have anything to do with other people's desires? "

I thought we were trying to discuss better solutions to this problem, for everyone, not just yourself.


"Of course it isn't, as water is present in atmospheric air. However, the quantity left over under normal circumstances is not sufficient to rust the steel to any degree of concern. The thread sealer/lubricant I apply to all threaded connections will prevent any rust from forming, so this is not an issue."

I very much feel that there is not enough data to support these statements. It will be interesting to see how steel is effected over very extended periods of time.


"I don't believe ~20 - 50ms of heat exposure will have any effect on the zinc coating. "

As I already said, neither do I, but I simply do not know.


"And I never once said or implied that it is the "ideal" building material, just that I prefer it over PVC and ABS."

That is fine. Just don't get so hyped up when I point out some of the down sides to your preferred material.

[BC Pneumatics]

Zinc will burn off when steel reaches about 1500 F(it has a cool green flame too).

Even though that is well under the maximum burning temperature of propane, I am not sure if it will happen, in the same way the PVC will melt at temperatures much lower than those propane is capable of. Hopefully someone that knows more about these things will chime in.

Also, we seem to be acting as if gaseous H2O doesn't oxidize steel. By all logic I can think of, it should do so at a rather accelerated rate.

[Bubba05]

Ok boys settle down!! Steel is a good construction material! I have a few mates with metal cannons. But they built them like this out of sheerfear that they would explode if they used PVC! One such cannon my mate has a spark plug as the ignition and he hooks it up to the dizzy on hi car so it fires with his timing! But hey thats a hard coe cannon and can send a golf ball flying over a km!
BC Pneumatics another mate of mine i an Aluminium fabricator and is starting to experament with it in a cannon he s building copied off a PVC design. Onceagain he fears an explosion so he's going for a harder material. I'll let you guys know how he gets on!

Bubba

[Killjoy]

Again, practically useless.

The pressure comes almost totally from the hot gases, so when that heat is lost, which will happen very fast, then the gauge will zero again, with no recorded result.

well actually it does work (for hybrids at least). i know this cause i have a set up on fear like that and every shot it records about the estimated pressure for that mix. Doesn't last long though, theres about a 15 second window before the pressure drops and the results are screwed up, but thats enough time to check.

[SpudBlaster15]

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[joannaardway]

Actually, once the surface of steel has rusted, then the lower layers are effectively protected.
It might rust a bit to begin with, but after that you'll be fine.

Consider steam locomotives - they are/were continually filled with pressurised boiling water, and they don't explode because the rust has weakened them. Ok, they do need the boilers replacing every 10 years or so, but that's not that often - and it's more to do with health and safety than any risk (not that you'd want a 100+ psi tank full of boiling water rupturing)

Under the conditions of a hybrid, which isn't treated to regular and extreme exposure to huge masses of heated water, then as long as you don't try to remove the rust, the cannon will remain reliable and safe for more than the rest of your life time.

So, steel hybrids are definately safe - there is no large loss of strength should it start rusting.

[jimmy101]

Actually, once the surface of steel has rusted, then the lower layers are effectively protected.
It might rust a bit to begin with, but after that you'll be fine.

Consider steam locomotives - they are/were continually filled with pressurised boiling water, and they don't explode because the rust has weakened them. Ok, they do need the boilers replacing every 10 years or so, but that's not that often - and it's more to do with health and safety than any risk (not that you'd want a 100+ psi tank full of boiling water rupturing)

Under the conditions of a hybrid, which isn't treated to regular and extreme exposure to huge masses of heated water, then as long as you don't try to remove the rust, the cannon will remain reliable and safe for more than the rest of your life time.

So, steel hybrids are definately safe - there is no large loss of strength should it start rusting.

Uh, joannaardway, I think you have your metals mixed up. Copper and aluminum oxides will both protect the un-oxidized metal below the oxide layer. Iron (and steel) oxide do not, they flake off, though a good stainless steel oxidizes and flakes very slowly.

That is why copper and aluminum will both out last iron in an air/water environment even though both copper and aluminum are more easily oxidized than iron (or steel).

If you take a hunks of iron, copper and aluminum and lay them outside in the grass then after a few months (or years) the iron will completely disintegrate into a pile of dust. The copper and aluminum will both still be there, they'll just have a thin layer of oxide on their surfaces.

Back to the running "discussion"... Small amounts of water+oxygen(air), for short lengths of time, will not have an appreciable affect on a steel (or iron) pipe. Chances are that a lot more oxidation will take place in storage then in actual use. If you dry the gun after use, perhaps give it a light coat of oil (particularly threaded parts), and store it in a dry place then rust just is not going to be a safety problem. Heck, real guns have steel barrels (for a long time they had iron barrels), real guns generate water when they are fired. Real guns will rust if not properly cleaned before storage. If properly cleaned even an iron gun will last practically forever. I can't see any reason why a steel (or iron) spud gun would be any different.

[noname]

I leave my hybrid (steel) outside, because of it's length, and it has rained a couple of times. I usually just dry it or whatever, and there have been no signs of rust, even on the threads. You can worry about it or you can get stainless steel, but I will keep on using mine at 350+ psi.

[BC Pneumatics]

I appreciate the input Jimmy!
Iron rust does flake pretty prolifically compared to other metals.

I'm not worried about any steel cannon exploding or anything, since the rust damage would be very obvious far in advance of this happening, but rust is still something to think about with steel cannons. (For cosmetics if nothing else.)

In response to "steel hybrids are definately safe - there is no large loss of strength should it start rusting."
No worries Joanna, it seems pretty obvious that steel is at least better than the plastics used now.

[Killjoy]

Killjoy, what kind of readings are you getting on each shot with say, a 3x or a 4x mix?

Off the top of my head i can't recal (its been a long couple of weeks), but i know the readings were close to that of the estimated pressure for those mixes. i think the 4x mix read over 350 psi but i'm not sure. Let me see if i can dig up the video and review it.
And by the way, the pipe i used for my combustion chamber had been sitting outside for 25 plus years in the snow and rain, and it only had minimal surface rusting on the inside (the outside was painted).