[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

Hehe... glad someone likes the idea, may have actually stumbled onto something here.  I have a dialog started with a CF-expert and I'm waiting a response from him now on specific material definitions.  I'll also do a neat diagram to better explain what I'm thinking.  The design is everything here, I dont have the money to build much of anything to begin with.  The idea in itself is to accomodate LARGE pressure vessels, as most autoclaves cant handle anything really big, hence you usually have to build it in sections (which lowers strength and is a pain).
 
If you're building something SMALL, like a psub; then you simply get a large cardboard cylinder and coat the outside with CF... send that to the local autoclave and your'e set.  Or like you said, use a propane tank strengthened externally.  They're usually small enough to get into the cooker.
 
CF blows away steel in this application... in every way.  There's a chance here for a nearly "unlimited" depth rating; assuming you have enough money for the CF... obviously, the smaller the cheaper.
 
I calculated a NON-pre-pregnated CF hull (wet application) for a sub 8x45 feet and it came out to over $100,000 in CF at nominal thickness.  Once I get the numbers from the expert it'll be easier to narrow down a figure.  Granted, pre-pregnated CF is much more expensive - heck, I cant even find a price for the stuff.  But, in the long run, it's cheaper then fabricating a 1+" 537 steel hull.
 
In answer to your question, the cylinder is only capped at one end, the other end will have the viewport obviously.  Once all the CF is laid you seal it up and then pressurize and heat it.  You could also simply add the endcaps later, but like I said... one-piece is the goal.  Pre-preg CF has a working time of like 30 days, so that's not an issue.
 
 
more later...
 
Shawn
----- Original Message -----
From: Akins
Sent: Wednesday, November 09, 2005 1:52 AM
Subject: Re: [PSUBS-MAILIST] Composite Huls - self annealing?

Hi Shawn.
 
What a marvelous idea you have. Use the existing autoclave and make it the hulls outer layer while cooking under pressure laid down cf to reinforce and increase the autoclave's
 
thickness from the inside. Sounds great except for one thing. As mentioned with propane tanks here in the past and recently as well, these pressure vessels are made to hold pressure
 
from the inside not the outside. Remember it is hard to blow up the beer can but easy to crush it. However, it would be interesting to compute what the autoclave's external crush pressure would be
 
and then compute what that increased crush depth would be if reinforced with cf like you suggest. The addition of the cf on the inside of the hull might overcome any shortcomings of the original autoclave's
 
unreinforced hull and make it so it would withstand greater pressures afterall. Very interesting! If I was you and going to do this, before I spent any money I would find out everything about the tensile strength
 
and makeup of the autoclave's metalic hull, its thickness and how much pressure it could hold from the inside without blowing up. Then I would have someone compute those figures into what its external pressure holding
 
force would be. Then compute the tensile strength of the autoclave's hull reinforced with cf. You never know, you just may have something here. But I would do it all on paper and computing first before spending
 
a dime. Just one question though. How do you propose worker access to lay down the cf from inside the autoclave and then pressurize it?
 
Bill
 
 
----- Original Message -----
From: Shawn H.
Sent: Tuesday, November 08, 2005 12:16 PM
Subject: 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