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Re: [Norton AntiSpam] Re: [PSUBS-MAILIST] Composite Huls - self annealing?



Actually, the vacuum is provided via bag placed around the part, then placed in the autoclave where its heated and pressurized to further compress it.  
 
Sometimes they just vac. and bake.
 
My idea is more like using pressure and heat alone to kill the voids as the matrix sets.  It would only work using the autoclave as the form itself.  The only issue I'm leary about is re-expanding air (during cooling) that wasnt forced out. 
 
Most likely, this idea wont work for that very reason... there's no negative pressure for the trapped air to escape to.   It would probably be less hassle simply to ship the whole assembly to a giant autoclave, but you'd be limited in size.
 
Anyways, I'm still gonna maintain some correspondence with some composite dudes on this once I get a flowchart together.  If they kill the idea then so will I.
 
Aside from that, there's a "green light" for taking your typical psub and simply wrapping pre-preg CF around it, building a vac bag for it, and tralering it to the autoclave.  It'd be a decent chunk of change but it will also get you past 1000ft easily.
----- Original Message -----
Sent: Saturday, November 12, 2005 4:55 PM
Subject: Re: [Norton AntiSpam] Re: [PSUBS-MAILIST] Composite Huls - self annealing?

shawn
autoclaves work on vacume so they suck out any air traped in the matrix. so you whould end up building a sub hull to build a sub hull
 
rick m
----- Original Message -----
From: Shawn H.
Sent: Tuesday, November 08, 2005 9:16 AM
Subject: [Norton AntiSpam] Re: [PSUBS-MAILIST] Composite Huls - self annealing?

I just came up with another interesting idea.  We all know the basis behind the autoclave right?  An autoclave is basically a huge PRESSURE VESSEL with a heating element inside.  So, why re-invent the wheel?  Simply reverse the thinking:
Prefab D.O.T. pressure vessels usually have the stringers on the outside, this is good.  They also come with endcaps.  Simply have one made that can handle internal pressures with temps 250F+. (most chemical storage tanks meet this I presume).
Next, we install a compressor at one endcap.  Then, a power supply with a heating element on the other, that runs the length of the cylinder.  Or better yet, if you can, install them both on the same side.
The CF is then laid on the INSIDE of the tube, closed up,  and pressure cooked. The autoclave itself is the outside shell of the sub.   
Once you've laid as much CF as you want, you remove the compressor and the heating element and voila - strongest personal sub. in the world.  You could also have the heat source on the OUTSIDE, but this doesnt guarantee uniform temp. dispersal.
 
This technique makes simple sense to me, because the high internal pressures are pushing the CF to the shell while curing, as well as eliminating the voids WITHIN the CF and between it and the shell. 
 
 
Only other thing I could think of is maybe using the shell to lay some kind of thermoplastic, probably on the outside.  The shell could be heated to accomodate it and then cooled to solidify it.   Thermoplastics are actually going to put autoclaves out of business eventually, so they say.  
 
Shawn
----- Original Message -----
From: Shawn H.
Sent: Monday, November 07, 2005 8:44 PM
Subject: Re: [PSUBS-MAILIST] Composite Hull Calculations

Yah, the more I dig into composite sub construction the more I realize how cutting edge it is.  Hell, the Navy is BARELY scratching the surface with this stuff.  There ARE autoclaves big enough to anneal a pretty large submarine (I think the biggest U.S. autoclave is like 30ft x 75feet).  The biggest expense here seems to me in transporting the vessel and fabricating a jig. Having something sit inside a pressure-cooker cant be all that expensive can it? Also, everything would have to be pre-designed before you lay the CF, that is, anything that's going to lie outside the normal geometry of the pressure hull.  Very complex, just in the design phase... but once designed, it's conceivable the construction wouldnt be too difficult - MUCH easier then working 1/2" steel.  In reality, it IS wrapping a pressure vessel in CF; namely a 1/4" D.O.T. vaccuum tank; another option is chemical storage tanks.  Without the wrapping or going to 1/2" steel it's just not worth it designing anything that big and expensive, as you cant go very deep, even with stringers every foot.
 
So like said before, getting the voids out of the CF is the "sticky" part... hehe  Laying up the CF is tough too and you'd probably need laser guidance and multiple bakings. 
 
This pressure hull would be fitted inside an ambient outer hull/frame able to hold its weight + lead ballast.  This makes it super strong and sturdy, as well you're not attaching anything directly to the pressure hull later on in life.  Areas of acrylic could be used to transfer EM through the hull, as well as a solid slab of steel in one section of the pressure hull void of CF.  Otherwise your standard electrical through-hulls would be pre-installed. 
 
BTW, if you're wondering why I'm referring to 1/2" steel, it's because the boat I'm drawing up is 9 feet x 45+ (havent decided length yet).  
 
All this is fascinating to me...  'course, anything can be done if u throw enough money at it.  :)
----- Original Message -----
Sent: Monday, November 07, 2005 6:12 PM
Subject: Re: [PSUBS-MAILIST] Composite Hull Calculations

It looks like a lot of the research and analysis software out there is aimed at wrapping a metal pressure vessel with carbon fiber, or other filament materials.  I think the fibers are mostly in tension in this application and it just seems to me a little easier problem than wrapping a steel shell for compression.  It might be a unique use or situation: even a scuba tank will always have a greater internal pressure than ambient so I'm having trouble thinking of an application other than a 1atm diving vessels where you'd see a higher external pressure applied to a shell.  ??  And the added buoyancy would be a negative...


I found some mention of this software, but couldn't actually find much description or anywhere to download or purchase it. It sounds fairly good but is for filament winding and for pressure vessels.  And I'd say too that any through-hulls will greatly increase the engineering over a simple pressure bottle with one fitting/valve.

NASA code CF-72124 computer program for the analysis
of filament wound reinforced metal shell pressure vessels



On 11/7/05, Shawn H. <gambit7@bellsouth.net > wrote:
Yah, I was thinking about the autoclave process.  What about a huge vacuum bag??  Would that be sufficient?  (I have a feeling you're gonna say no)   Ideally, a 1/2" steel tank would be great...  but really hard to find pre-fab from what I can see (in the size I'm looking for).   Doing the hull in sections small enough to bake and/or place under vacuum is another idea, but then you have to worry about joining.  Argh!  Now I see how this can get obsessive.