Do you think this would work?

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Wood Butcher

Wood Butcher

Local Chapter Leader
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Jun 8, 2005
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Westfield, IN, USA.
I have been messing around with casting and mostly goofed up all I have done but that's to be discussed in a future posting. I have a compressor and know that pressure casting opens doors to new things but can't justify investing well over a$100 in a HF paint tank and all that goes with it.....what if you took a 6" dia schedule 40 PVC pipe a foot long and capped one end. The other end would have a screw off end cap cemented to it and an auto tire valve installed in it. Put a "floor" in it so a mould would sit flat and then close it up and pump it up. Now wait, don't use the compressor, use a bicycle pump. I checked and a 6" PVC pipe will handle around 150 psi, depending on the temperature and the length of the pipe so at 35 or 40 psi it should be safe. If more caution makes you feel more comfortable, wrap the PVC with an old innertube or something to disallow a blow out. If you installed a check valve or a ball valve there should be no loss of pressure and a gauge threaded into it would verify the pressure (my pump has a pretty acurate gauge on it. So, I'm guessing the bottom line cost may total $25 if you already have a bike pump. What say you experienced folks?
WB
 
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I thought down these same lines, and I think the pressure rating is for liquid, and not air. Therefore this idea is a hazard.

I am working on another idea using black pipe, but the closer I get to having it worked out, I am 3/4 of the way to the cost of a pressure pot. I think waiting for the thing to go on sale for $80ish, and then using a 20% coupon for it.

My .02
 
Yikes, That idea scares me. I picked up my Pressure Pot on Ebay for $75 shipped. It is an older Made in USA pot so I feel a lttle better. Like many have noted before, the lid is as heavy as the entire HF Pot
 
I use a 8 in pipe welder flat on one end and a flat top that bolts on with a rubber gasket.I have ran it up to about 90 psi which is way more than needed. I would bet you could find a fabrication shop to build you one pretty cheap out of scrap or for a nice pen.
 
Bill:
This is a very good way to blow your head clean off your shoulders! I know this from my days of making "tater cannons". PVC (or even ABS, for that matter) can't handle the pressure necessary for pressure casting.

Additionally, PVC loses its strength with each use and each exposure to UV (important if you cast outdoors).

If you want to make a pressure vessel on the "cheap", find a piece of well pump or oil pump casing. Take it to your local welder and have the welder attach a 1/4 piece of plate steel to the bottom and top. Then saw the casing, put a gasket at the joint and fabricate thumbscrew "lid locks". These pots can usually handle as much as 100 PSI with no difficulties.

You may want to PM Truckfixer as he has a nifty design that he was kind enough to share.
 
Additionally, these days, both pawn shops and Craigs list are loaded with Binks paint pots. I found a very good quality pot on CL for $40.
 
The pressure rating is not for liquid only. We have to test our pipes to withstand a minimal pressure of 80 psi. So the pressure would not be hazardous. It is a matter now of whether you can get the pipe to seal. The six inch pipe is rather small on the inside diameter, I would think it would be better to use a bigger pipe size. You have got me to thinking about it now
 
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So what is the bare minimum pressure needed to cast or to stabilize? I searched cyberspace for a whole evening on the pressure limits of the PVC and specifically air pressure. The larger the pipe the lower the POW point. One report said that they reached 180 psi (air) with schedule 80. What if you encased one size in the other such as a 6" inside an 8", if that's even possible. I'm just cogitating here. I enjoy working through a project almost as much as doing it and this came to mind as I pumped up a bicycle tire. I thought, hmmm, 40 psi in that puny tire? Maybe it could be used for casting. So that's when I went to the net to see what I could see. I assure you the "bomb" would be in another room or a wood box or somewhere that would contain the pieces and protect me until I could be sure.
WB
 
I know it's stated to be unsafe to explosive to use PVC for air pressure, even against OSHA regs. With that said, last shop I worked in had our shop air piped with 1.5" pvc to 150 psi. We never had a problem even when the lines froze from the water in the lines. Now I'm not saying it's safe but I might have to try it myself just for experimentational purposes.
 
Just get a tank. There's enough debate on safety with tanks made for this sort of thing.

I love my HF tank. But if you watch CL, or even post a want ad on CL, you might get lucky.
 
Found a good pressure tank.


http://www.ebay.com/itm/DIVE-DECOMP...ultDomain_0&hash=item25697dafd1#ht_1261wt_887



How many blanks do you think will fit? And how long to reach operating pressure......


I've seen several shops with the air lines run in PVC. With pressure topping out at 100psi (most seem to think 50 is enough), I bet it could be done without too much worry. I wouldn't even bother with a double walled design, but wrap it in some duct tape (heck mythbusters made a cannon out of that stuff), or maybe fiberglass insulation to prevent a blowout from being dangerous.
 
if it does blow into many peaces , like flying scrapinal - i dont think plastic will show up on x rays ? i dont think i would use it , just me
 
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I guess that I've just been lucky. I make spud guns out of sch 40 and have never had one blow. These are not the guns using hair spray and combustion - just air pressure. I've also used a 4" pipe for casting pen blanks. I've done dozens and although I started out using a HF paint pot and 65 psi, I found that I didn't need any more than 30 psi to squeeze the bubbles into invisible size. After hearing about too many of those pots exploding, I went with sch 40 pipe. I pressurize to 30 psi and silmar comes out bubble free.
 
gwilki said:
I found that I didn't need any more than 30 psi to squeeze the bubbles into invisible size. After hearing about too many of those pots exploding, I went with sch 40 pipe. I pressurize to 30 psi and silmar comes out bubble free.
Click to expand...
This is really the important part. The thing to remember is there is a dimished return for additional pressure. It only tales about 15 psi to reduce the size of a bubble in half. Then another 15 psi to get it to 25% of the original size. So you only reduce it by 25% more when you double the pressure from 15 to 30 psi. And if you double it to 60 psi, you only reduce the volume about another 18%.
 
gwilki said:
I guess that I've just been lucky. I make spud guns out of sch 40 and have never had one blow. These are not the guns using hair spray and combustion - just air pressure. I've also used a 4" pipe for casting pen blanks. I've done dozens and although I started out using a HF paint pot and 65 psi, I found that I didn't need any more than 30 psi to squeeze the bubbles into invisible size. After hearing about too many of those pots exploding, I went with sch 40 pipe. I pressurize to 30 psi and silmar comes out bubble free.
Click to expand...

I tried to make a 4" PVC chamber, but I couldn't never get the threaded cap to seal. have you ever had any issue with this?
 
Unless you have extensive training in pressure techniques using a homemade tank to pressurize is the same as asking for an obituary. You are creating a potential bomb.
 
If a pressure filled with liquid fails it goes "....spurt....". If a pressure vessel filled with gas (e.g. air) fails, it goes "......BANG...." and shoots shrapnel all over the place.

DON'T DO IT!

Tom
 
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