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assorted hybrid questions

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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assorted hybrid questions

Unread postAuthor: ramses » Thu May 29, 2008 8:07 pm

Hi, I have a few questions about hybrid construction.

1) I was looking at using a 3" diameter steel chamber of undetermined length. McMaster doesn't have high pressure 3" to whatever reducing couplings. The highest I can find is 150psi malleable steel. I think my gun may push 650psi, according HGDT (simulator). Is this type of fitting sufficient for non-remote ignition? if not is a 150psi cast iron hex bushing sufficient? All threaded, BTW, I don't have a welder yet.

2) For projectiles, I was thinking about 1" steel ball bearings. For barrels, I was thinking about 60"-72" long and 1" diameter. seamless steel this long is painfully expensive. does the welded pipe have burrs, or roughness that would mess with the projectile? this would obviously cause pressure rise and might blow it.

3) I really don't want to tap holes in my chamber, and Tees are around $40 for black malleable iron, 150 psi. any alternatives?

4) is galvanized pipe really necessary? black iron/steel is a lot cheaper

5) the length of barrel i was going to try to use is a little long to transport/store (at least for me). are there any air tight, seamless-ish ways to join pipes end to end and be able to un-join them fairly easily.

thanks for answering all of my stupid noobish questions

ramses
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Unread postAuthor: LikimysCrotchus5 » Thu May 29, 2008 8:16 pm

ramses wrote:1) I was looking at using a 3" diameter steel chamber of undetermined length. McMaster doesn't have high pressure 3" to whatever reducing couplings. The highest I can find is 150psi malleable steel. I think my gun may push 650psi, according HGDT (simulator). Is this type of fitting sufficient for non-remote ignition? if not is a 150psi cast iron hex bushing sufficient? All threaded, BTW, I don't have a welder yet.


Yes they do, you just gotta make the right search.

ramses wrote:2) For projectiles, I was thinking about 1" steel ball bearings. For barrels, I was thinking about 60"-72" long and 1" diameter. seamless steel this long is painfully expensive. does the welded pipe have burrs, or roughness that would mess with the projectile? this would obviously cause pressure rise and might blow it.

Im not sure about that but ten feet of 1 inch pipe isnt too expensive at homedepot

ramses wrote:3) I really don't want to tap holes in my chamber, and Tees are around $40 for black malleable iron, 150 psi. any alternatives?


40 for what size, bt if you refine your search better, then i think that you can find a better price on mcmaster that is 3000 psi pressure rated.

ramses wrote:4) is galvanized pipe really necessary? black iron/steel is a lot cheaper


Its not, but if your gonna measure the volume, use canola oil, it wont make the black/iron steel rust.

ramses wrote:5) the length of barrel i was going to try to use is a little long to transport/store (at least for me). are there any air tight, seamless-ish ways to join pipes end to end and be able to un-join them fairly easily.


Well, try local places, like homedepot has pretty good price. You can use copper as well for a barrel.
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Unread postAuthor: DYI » Thu May 29, 2008 8:18 pm

1) McMaster-Carr has forged steel bushings rated for up to 3000 psi in those sizes (3" to 2"), so I don't see what the problem is. Or are you too cheap for forged steel parts? If so, it would probably be okay at 650, but I wouldn't want to be very close to it.

2) Don't use welded pipe. Why don't you just use 1" copper tube? It can probably take more pressure than 1" welded steel, and is completely seamless (as well as reasonably cheap).

3) Instead of using threaded pipe and fittings for the chamber, make it out of unthreaded pipe with plates welded on both ends (or a bushing welded on the front, and a plate on the back). With a 1" or thicker steel plate on the back, there shouldn't be any problems with tapping holes for ignition and fueling.

4) Galvanised pipe isn't necessary. It's just convenient, because it won't corrode terribly like black pipe often does when exposed to water. The threads will still rust anyway.

5) There are loads of ways. A union is the simplest one I can think of. It won't be seamless, but the projectile won't care, and it won't deviate off course enough to cause any problems in the 2" or so where the tube widens at the fitting. But I though the barrel was only going to be 6' max?
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Unread postAuthor: bigbob12345 » Thu May 29, 2008 8:18 pm

1. Just dont take the malleble iron fitting over 5x and youll be fine
2. Just use copper, although I would reccomend a larger barrel for a hybrid with a 3in chamber such as a 1.5in sdr21 barrel reniforced with 2in sch80pvc
3. Well when you reduce the pipe down to the size of your union you can just buy a tee in the lower size saving you a ton of money.
4.Galvanised is not nessesarry altough it is reccomended ad it does n0t corrode ass fast.
5. How bought some threaded fittings.
And sorry if I mispelled a couple things in this post

Edit: Crap, I got beaten
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Unread postAuthor: LikimysCrotchus5 » Thu May 29, 2008 8:22 pm

DYI, i have a semi-related question (well not really)

When measuring volume with canola oil, would 100mL be the same as 100mL of water? Just wanna make sure

I just know that 1mL of water equals 1 gram of water which is useful.
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Unread postAuthor: DYI » Thu May 29, 2008 8:26 pm

Litres are a measure of volume. One litre of anything is the same volume (1000cc, to be precise). A litre of canola oil won't weight 1kg, but it will still occupy 1000cc of space.
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Unread postAuthor: LikimysCrotchus5 » Thu May 29, 2008 8:31 pm

DYI wrote: A litre of canola oil won't weight 1kg, but it will still occupy 1000cc of space.


I know it only applies to water. I was just making a statement, but thanks, just wanted to be reassured.
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Unread postAuthor: D_Hall » Thu May 29, 2008 8:41 pm

May I recommend that you skip the canola oil and instead use alcohol?

Still won't rust and it's a LOT easier to clean up.
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Unread postAuthor: rp181 » Thu May 29, 2008 9:21 pm

Arn't you on 4HV?
Wouldn't a PVC barrel work? killjoy used PVC on FEAR.
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Unread postAuthor: psycix » Fri May 30, 2008 5:30 am

Or just use galvanised steel and water. Wouldnt oil stick to your wall, greasing up your whole chamber AND losing a few cc of oil in the water(oil!)-metering process to that?

With barrels under 6' long, whats your transporting problem?
I take stuff that long with me on the bicycle :D
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Unread postAuthor: DYI » Fri May 30, 2008 4:45 pm

Wouldn't a PVC barrel work?


Go and read my post in the ITWOST thread on page 35, and ask yourself the above question.
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Unread postAuthor: ramses » Fri May 30, 2008 5:17 pm

rp181 wrote:Arn't you on 4HV?
Wouldn't a PVC barrel work? killjoy used PVC on FEAR.


yep, 3kj induction launcher in the works 8)

the one thing i was worried about with a PVC barrel was the mechanical stress on the fitting connecting it to the chamber. 10' of pipe acting as a lever on a little plastic fitting might not work too well. IIRC, Killjoy used chairs to support his barrel. i wanted this to be portable, and carrying a few chairs limits portability.

Should i put the tee in the back or the front of the chamber? Is it better to have propane/air enter the barrel or the combustion byproducts?

with the galvanized thing, i would like to point out that hydrocarbons release water when they burn. Odds are this will condense on the cool metal chamber and rust it just as well. Could I just use heat proof paint all over black steel/iron? This would save some money. I plan on measuring the pressure rise for fueling, so i don't need to know any volumes, so no filling with fluid.

DYI wrote:1) McMaster-Carr has forged steel bushings rated for up to 3000 psi in those sizes (3" to 2"), so I don't see what the problem is. Or are you too cheap for forged steel parts? If so, it would probably be okay at 650, but I wouldn't want to be very close to it.

...

3) Instead of using threaded pipe and fittings for the chamber, make it out of unthreaded pipe with plates welded on both ends (or a bushing welded on the front, and a plate on the back). With a 1" or thicker steel plate on the back, there shouldn't be any problems with tapping holes for ignition and fueling.


1)all i can find in forged steel is 3"-2 1/2"

they have couplings 3"-2" for $65. I'm not cheap, but thats too much for me.

3) unfortunately, i lack a welder.
[/quote]

one thing I noticed is that sometimes forged steel is cheaper than cast/malleable iron. Why?

Thanks again,

ramses
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Unread postAuthor: DYI » Fri May 30, 2008 7:18 pm

with the galvanized thing, i would like to point out that hydrocarbons release water when they burn. Odds are this will condense on the cool metal chamber and rust it just as well. Could I just use heat proof paint all over black steel/iron? This would save some money. I plan on measuring the pressure rise for fueling, so i don't need to know any volumes, so no filling with fluid.


In theory, that's exactly right. In pracitce, you'll end up with a decent layer of some unidentified, hard powder on the inside of the chamber wall composed of products of secondary reactions in the chamber that will do a decent job of protecting it from corrosion. You could clean this stuff out, but it's actually beneficial, so why bother?

unfortunately, i lack a welder.


Welded steel is the way to go in this case.
Why would you need a welder? There are plenty of welding shops out there that would be willing to do it for a very minimal fee, especially if you tell them what you're building.
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Unread postAuthor: ramses » Sat May 31, 2008 10:41 am

unfortunately, i lack a welder.


Welded steel is the way to go in this case.
Why would you need a welder? There are plenty of welding shops out there that would be willing to do it for a very minimal fee, especially if you tell them what you're building.


fair enough, but sometimes welded fittings are more expensive then threaded ones. and the ability to take it apart will definitely help with troubleshooting any problems that probably will arise. i don't know that there are any welding shops in my area, either.[/quote]
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Unread postAuthor: King_TaTer » Sat May 31, 2008 12:53 pm

ramses I may have a possible solution to your "welding problem"

I was wondering if you were still in high school, and if so is there a metal fabrications class at your school? This would be a practically free way to have your metal welded. I am currently in a class like that at my school and they have many welding machines such as a 2 Mig welders, one stick welder and one TIG welder. Just a thought, figured I'd point that out as a possible option even though you may have thought of this already. Good luck.
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