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Safety of malleable iron

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Safety of malleable iron

Unread postAuthor: tyrant_bb » Sat Jun 21, 2008 11:58 am

Well before I ask that, I want to know if "black iron" is safe to use in a hybrid. Not sure what kind of iron, it just says black iron nipple.

Then the union and some of the fittings I found are made of malleable iron. Please tell me they can take way more than 150 PSI? Or am I just going to have to buy the insanely expensive 3000 PSI fittings from Mcmaster?

Next, if iron or steel pipe did happen to fail (Mainly the malleable iron fittings I'm worried about), is it going to explode like PVC or rip like ABS?

Finally, if I didn't want to buy the 3000 PSI fittings, would I be better of using SCH80 PVC fittings because those are rated higher than even 150... and about how much pressure does a 4X mix of propane/air make?
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Unread postAuthor: Maniac » Sat Jun 21, 2008 12:36 pm

Do not ever resort to PVC in a hybrid the malleable iron fittings will be fine for a 4X mix. no worries man.
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Unread postAuthor: tyrant_bb » Sat Jun 21, 2008 12:40 pm

You know this from experience? I'll be remote firing this, but still... if iron fails like PVC, I'd rather use PVC because plastic flying into my body might not kill me.
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Re: Safety of malleable iron

Unread postAuthor: starman » Sat Jun 21, 2008 1:31 pm

tyrant_bb wrote:Finally, if I didn't want to buy the 3000 PSI fittings, would I be better of using SCH80 PVC fittings because those are rated higher than even 150... and about how much pressure does a 4X mix of propane/air make?


Depends on a few things, but mainly the mass of the projectile and the burst disk failure point. A golfball (1.6 oz) gun with a small to medium disk (say 80 psi) will produce chamber and barrel pressures in the 250 psi range. Use a 200 psi disk and shoot a 1 to 3 lb slug and you are looking at 400 - 500 psi in your chamber and barrel... :shock: Check out D_Hall's HGDT design tool to play around with the numbers.

You can use sched 80 PVC on some very low X hybrid projects, 3x or smaller and using light projectiles. After that you've got to go to steel.
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Last edited by starman on Sat Jun 21, 2008 2:01 pm, edited 1 time in total.
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Unread postAuthor: FordGtMan » Sat Jun 21, 2008 1:52 pm

DYI used malleable iron fittings on a 20x hybrid without failure, but this doesnt mean that it wouldn't fail for you. I think Fnord used them and blew up at a 8x mix? But i am not sure about that. Sch 40 fittings should hold a 4x mix very easily, as many people on this forum have used them. Just dont use pvc because chances are that sch 80 pvc will blow up way before steel and steel will be cheaper too.
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Unread postAuthor: SpudFarm » Sat Jun 21, 2008 2:04 pm

_Fnord did not manage to blow his test chamber at 11x.

and i have used my hybrid at 6x with a strong arse disk and i did fine.

http://www.spudfiles.com/forums/handheld-hybrid-2-0-t13257.html

that is my hybrid.
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Unread postAuthor: DYI » Sat Jun 21, 2008 2:30 pm

_Fnord never managed to blow up anything in this tests.

I believe I've taken them the highest of anyone yet, a 20x oxy/propane mix with a 128 layer alu. foil disk in a 2" union. The testing I've done indicates a burst pressure of over 1300 psi for that disk. When you think of that, it's no surprise that the chamber, with a calculated burst pressure of over 2200 psi, didn't fail. Apparently, the low quality malleable iron fittings are at least almost as strong as the steel pipe.

As for failure characteristics: steel pipe can shrapnel, but it's very unlikely unless there's a detonation inside the chamber. Other than that, it'll just rip and crack, although it probably would be more dangerous than a copper pipe failure.
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Unread postAuthor: tyrant_bb » Sat Jun 21, 2008 7:21 pm

DYI, your malleable iron fittings have a burst pressure of 2200 PSI?
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Unread postAuthor: SpudFarm » Sat Jun 21, 2008 7:36 pm

i say this once again.

a soda bottle can hold 150psi. then you think of the wall thickness and the soft plastic used in them. do you trust the fittings for 14.6 as high burst pressure as the bottle? (they also has less surface area aswell as the double wall thickness when something is threaded into or outside them)
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Unread postAuthor: pizlo » Sat Jun 21, 2008 7:37 pm

Well you have to realize that Pressure ratings and burst pressures are very different. Burst pressure is pressures, that in testing, were able to break the material. Pressure ratings are what the company decides to tell people will be safe. The reason a pressure rating is safe to trust is that if you get injured using it below the rating the company might have a law suite.
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Unread postAuthor: SpudFarm » Sat Jun 21, 2008 7:41 pm

pizlo: i may blow a pipe up and tell them it was under the rating and make myself a paper cut to get some cash :P
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Unread postAuthor: FordGtMan » Sat Jun 21, 2008 7:44 pm

Sorry, i didn't mean "blow up", as the cannon would be a bomb. i meant a fittings failed. But didn't one of the reducers crack at the 11x?
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Unread postAuthor: pizlo » Sat Jun 21, 2008 7:45 pm

Good luck mate, maybe it will pay for the medical bills of removing Iron or PVC from your body :P Maybe worth it if you use the money to build a sick gun. Hell, once you've done that raid their warehouses and steal all your supplies!
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Unread postAuthor: SpudFarm » Sat Jun 21, 2008 7:49 pm

FordGtMan wrote:Sorry, i didn't mean "blow up", as the cannon would be a bomb. i meant a fittings failed. But didn't one of the reducers crack at the 11x?


it was because the piston slammed into it. it was 6x.
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Unread postAuthor: DYI » Sat Jun 21, 2008 8:37 pm

DYI, your malleable iron fittings have a burst pressure of 2200 PSI?


No idea, I don't have any information on the material they're made of, or even how thick they are. All I know is that I've taken them over 1300 psi, and they're still intact.

This may be against the rules, and if it is, it'll be gone soon, but here goes: I set off 5g of *magic dust* in a small improvised launcher. The barrel was copper tube, and the chamber was a 1/2" steel coupling attached to a sparkplug, and a 1/2" x 6" steel pipe nipple. The copper shredded, the sparkplug got gutted, but the steel components held together. The steel components were the part holding the charge. It would have taken at least 3000psi to burst that copper tube, which says a lot about how strong those ugly malleable iron fittings are.
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