Finally, 100 psi, SAFELY!

Signed-In Members Don't See This Ad
MesquiteMan

MesquiteMan

Retired Head Moderator
Joined
Oct 18, 2005
Messages
5,678
Location
San Marcos, TX, USA.
Well, I got one of the new pressure pots from the scarp yard all up and working tonight! I am FINALLY able to cast at 100 psi SAFELY!

attachment.php


attachment.php


And before anyone jumps my butt about the pressure I am running this at:eek:, notice the certification stamp. 110 psi Actual Working Pressure (AWP) (I believe that is what AWP stand for in this case. Please correct me if I am wrong!)
attachment.php
 

Attachments

  • pot5.JPG
    pot5.JPG
    48.2 KB · Views: 785
  • pot3.jpg
    pot3.jpg
    36.8 KB · Views: 853
  • pot6.JPG
    pot6.JPG
    43.4 KB · Views: 800
Last edited:
Signed-In Members Don't See This Ad
Curtis, I don't cast anything, but I've followed your posts about pressure and vacuum because I find it interesting and it is definitely something that I'll be trying someday. It seems to me that most cast at significantly lower pressure. What is the advantage to casting at 100 psi?
 
I notice that it says made in 2004. Might want to call the company and ask whether they recommend periodic pressure testing and recertification. Also, you don't know the history of the pot and whether it was lovingly cared for or abused (and put out to pasture for a reason). Metal fatigue and micro cracks may not become evident to the casual user until the pot explodes.

Maybe I'm just overly cautious, but I don't like having to ask myself "am I feeling lucky today?" each time before I use a tool.

Ed
 
The reason to use 100 psi...as Hank says above, because I can!

Actually, it has to do with Boyles Law. Just for grins, lets assume that a piece of "Worthless Wood" has an air pocket in it that is 1 microliter (cubic millimeter) at sea level. The volume of the air pocket is reduced as the air pressure is increased. Here is the size of the pocket at various pressures: (assuming my math is correct!)

0 psig = 1 µL
30 psig = .32886 µL
40 psig = .26874 µL
60 psig = .19679 µL
80 psig = .15523 µL
100 psig = .12816 µL

So, as you can see from above, higher pressure will reduce the volume of the air "pocket" more than lesser pressure. That is why I want to go as high as I can, to get even better reduction of air "pockets" so I can make even better blanks.
 
Good deal, Curtis!

I've never seen it expressed as AWP, but MAWP in the certification criteria is "Maximum Allowable Working Pressure". Like you, I assume that AWP is just a "shorthand" notation of maximum working pressure.

Just looking at those beasts, I can tell that they are rated WAY above anything I have used. I'd be hard pressed to move one of these pots without help. According to the Mfg spec, they look to weight about 45-50 pounds, EMPTY.
 
You take GREAT photos!

I can look at your photo and see that what you are quoting is actually MAWP, which is "maximum allowable working pressure".
 
MesquiteMan said:
The reason to use 100 psi...as Hank says above, because I can!

Actually, it has to do with Boyles Law. Just for grins, lets assume that a piece of "Worthless Wood" has an air pocket in it that is 1 microliter (cubic millimeter) at sea level. The volume of the air pocket is reduced as the air pressure is increased. Here is the size of the pocket at various pressures: (assuming my math is correct!)

0 psig = 1 µL
30 psig = .32886 µL
40 psig = .26874 µL
60 psig = .19679 µL
80 psig = .15523 µL
100 psig = .12816 µL

So, as you can see from above, higher pressure will reduce the volume of the air "pocket" more than lesser pressure. That is why I want to go as high as I can, to get even better reduction of air "pockets" so I can make even better blanks.
Click to expand...
Nice score and while I don't disagree with your results, I think you overestimate the effects of Boyle. The math is a little off as you should calculate with absolute pressure, not psig. Additionally a 7 fold decrease in volume would only be about a 2 fold decrease in the diameter as volume is proportional to the cube of the radius. As for shrinking a void in a solid object such as worthless wood, I don't see how that is possible.

I'm in no way saying higher pressure doesn't make better blanks. As for bubbles in resin, pressure keeps the air and other gases in solution as the resin hardens rather than significantly shrinking them.

And please be careful with the hoses and fittings. Operating at 100 psi requires due diligence.
 
low_48 said:
I'm pretty sure AWP is Allowable Working Pressure. Sure looks like a beauty!
Click to expand...

But that's at 250°F....what would it be if the temp is around 90°F when you're casting? Would it be a higher 'Allowable Working Pressure' if the temp is a lot lower than the listed 250°F?

Just a thought.....


Barney
 
You must log in or register to reply here.
Back
Top Bottom