Poured Concrete Hybrid Chambers

[DYI]

On Saturday, the ABS breach on my SCTBDC ripped along the threads. No violent explosions or anything, but I figured I should cast reinforced concrete around the new one to prevent a similar incident. The idea of casting concrete around chamber pipes appeared in my mind while I was making the form yesterday for the concrete (which I poured today).

But this is getting rather off topic. I was hoping someone like Killjoy, with experience in BP cannons would respond to my original questions, but it seems like no one has answered any of them fully yet.

[Hotwired]

Well scott could probably help you on reinforcing issues.

I had wondered about the plastic parts on the SCTBDC in respect to pressure buildup if a jam or at least a particularly massive projectile was in the barrel.

Considering that steel pipe can be easily found with working pressures of several hundred bar I'd have been fine with planning a hybrid with just one layer of steel. Two and a concrete filling isn't going to be shifted by much short of solid chemical mixtures.

A maintenance cap would still be tricky if continuing with the reinforcement all round.

I've been searching but not finding a concrete reinforced BP cannon but I'm suspecting it might come under the same heading as "ghetto" here.

[Fnord]

I'd rather cast aluminum around a thin steel pipe myself. It's surprisingly easy if you can get a hold of an old cracked engine block and a heavy duty steel bucket.

And a furnace fan

[Rokmonkey]

Give it a shot, but concrete really isn't great at with standing tensile strain. I'd be wary about it standing up to a 10x mixture. Collectively as a hall (all engineers, gone through the classes that would pertain to this) it would easily hold up to a combustion spike of 70 psi, but if you could tell us what a hybrid might spike too, we can give you a definitive answer, and a good mixture or way to do it.

[DYI]

Two and a concrete filling isn't going to be shifted by much short of solid chemical mixtures.

My point exactly Which means that I can make a 50x or so hybrid without having to buy expensive fittings from McMaster, other than a union.

@Rokmonkey: I don't have time to draw anything up right now, but the plan is basically some 2" SCH 40 steel pipe and fittings inside a 6" SCH 40 steel pipe with a plate welded on the back of the large pipe, and the space filled with concrete in whichever way scott suggests.

I would like to use aluminum, but my parents would likely have a problem with that quantity of molten metal, and I don't want to have to wait until I find an old engine block lying around.

As for maintenance, that's what thermal lances are for

[Rokmonkey]

What pressure?

[Jared Haehnel]

The new plan is to cast a 2" steel pipe inside a 4" steel pipe for a high mix hybrid chamber.

From my understanding, the concrete, reinforced with rebar and mesh, and with added glass fibers for greater tensile strength, should prevent the inner pipe from expanding, and dissipate the energy, as well as saving me in the event of a failure. Sound good?

As far as I can tell, the general opinion is that the original idea (casting a 4" pipe inside an 8" pipe with reinforced concrete) won't work. Is that correct?

OK I'm going to give this a shot....your right seems as though people are saying it won't work but I think it will.
Black powder generates PSI in the thousands. If people use concrete to reinforce black powder barrels. (Not something I am familiar with) Then it certainly would withstand the pressures generated by a hybrid at 10x. If you did it..you'd want to make sure that you pour evenly and slowly to minimize the amount of air bubbles in your aggregate. With such a small pour this should easily be controlled. Chick wire wrapped around the inner and outer pipe will help to reinforce the concrete.

Hope that helps in some way....

[scottcrete]

strenght comes from more cement than sand and having good aggragate..
wire and rebar are just to keep its shape in case of busting... like to keep a wall from falling over if it cracks.

meaning...

5 cement to 1 ratio on sand = very strong
1 sand to 5 cement = not so strong.. very brittle

wire included in pour = if it exploded if woulod retain its shape
wire not included in pour = if it explodes shit mite fly anywhere.

need to know how much concrete to use?
use this calculator.


http://www.concrete.com/calculatorsmaterials.htm

[Rokmonkey]

Second Scottcrete... But I say give it a shot, concrete could surprise us, I'd like to find out.

[Jared Haehnel]

wire and rebar are just to keep its shape in case of busting... like to keep a wall from falling over if it cracks.

It also gives concrete better tensile strength. Concrete is strong under compression so strong in fact they were talking of making concrete submarines for the military. I don't know if they ever did (if they did I'm sure we don't know about it) But I've read articles of people making sail boat hulls from the stuff as well.

Steel reinforces the concrete weakness. Correct me if I'm wrong but concrete has a fairly low tensile strength and steel has a very high tensile strength. That is why they reinforce bridges and most concrete structures with re-bar. Scott was right in a way it does help to hold things together but it does a bit more then that.

On a separate note... I think it was Poland Spud that brought up a similar idea only using lead...

[Rokmonkey]

Your right Steel has High tensile strength, but Scottcrete is right, It keeps the concrete shape when it cracks, No matter what the concrete still has a low tensile strength, the re-bar helps to keep it together. If it falls apart without re-bar, the concrete goes everywhere and falls off, if the re-bar is there, the concrete will stay in place even when it's broken.

[Gippeto]

" Steel reinforces the concrete weakness. Correct me if I'm wrong but concrete has a fairly low tensile strength and steel has a very high tensile strength. That is why they reinforce bridges and most concrete structures with re-bar. Scott was right in a way it does help to hold things together but it does a bit more then that."

You are correct.

When pouring a concrete foundation, the rebar goes toward the INSIDE of the wall. This allows it to carry the tension loads placed on the wall by the back fill.

I would think that the rebar for your chamber should similarly be placed closer to the outside(3/4-7/8 of thickness). Overlap the joints (standard with rebar is 40*D ie 1/2" rebar would have an overlap of 20")

Mesh would probably be more suitable for your application. Perhaps a "wrap" of 2-3 times around? Tie it together with wire. Or a cylinder made from expanded metal sheet and welded together?

You will need a runny concrete mix (5-6 slump at least) and vibrating the form will be neccesary. (whack it with a board or hammer as you fill)

[biged]

A juice-bottle black powder 60mm mortar. I fabricated it from scratch.
The barrel is from stock used for a hydraulic cylinder for a D-10 loader piston.
If you go to a welding shop or steel shed they will have heavy walled DOM (Drawn Over Mandrel) tubing you can use. Also look for de-milled barrels from artillery pieces.

Being cheap to save a few bucks when experimenting with black powder is a recipe for disaster.

Proceed with caution with your concrete barrel.
Rebar in concrete increases the static load. You are exposing the concrete to sudden pressure spikes. Which over time can result in an immediate and catastrophic failure of areas it is in contact with.

///ed///

[spudman029]

In my opinion, the idea of reinforcing concrete as a cheap, quick alternative to more expensive materials is something that cannot easily be done.

Ex. Benjamin Franklin's concrete houses.

It is also something that, in a post, sounds good (also on paper), but in reality is not very pheasable.

Ex. Marxism.

Lastly, to me it sounds like a bad idea.

Ex. DR's helmet mounted combustion.

-Aaron.

[Jared Haehnel]

You are exposing the concrete to sudden pressure spikes

The concrete will be pour around a steel chamber so it won't be directly exposed to the pressure spike...I don't think it will be a problem...