Vacuum or Preasure

[dgelnett]

This might of been covered before but I did not see it. Which is better to do with a casting, vacuum or preasure? I think I have seen both mentioned but not sure or does it matter?

I have a old preasure cooker that I hook my vacuum pump up to for stabilizing wood for turning. I think I would like it better if I could take the lid off and replace it with a clear top so I can see in. I guess all that you could see is bubbles in the liquid otherwise not much to see with the absent of air but still would like to look in. Do you think I could buy half inch thick clear pastic sheet to stick on top? Or would it break?

Thanks

 

[NewLondon88]

half inch might not be heavy enough, but that would depend on the size
of the pot, I think. (I wouldn't try it with a pressure cooker.. it might not
hold up to vacuum)
But the idea of using a clear top is fine. For the small piece you're looking
to use, might as well go with something thicker. Overkill won't hurt in
this case. If it were me, I'd probably go 1" just to be safe.

 

[snyiper]

I would do as suggested and use a clear plexi lid for Vacuum only. Try 1/2 if that dosent work double it up!

 

[lorbay]

Check out Curtis's (MesquiteMan ) web site for the video on his cactus juice same idea what your looking for. Or this thread.
http://www.penturners.org/forum/showthread.php?t=76510

Lin.

 

[dgelnett]

Thanks the other question is vacuum or pressure? Is one better to use when getting the bubbles out of castings?

 

[jason_r]

The answer to that is "it depends".

Early on in the process, vacuum will expand the bubbles so they rise and exit the mix faster.

Later in the process (as the resin is thickening), pressure will compress the bubbles to where they are (hopefully) invisible.

Complicating the matter is that alumilite will generate its own bubbles as it cures. PR has styrene in it that will boil off under low enough pressure.

So, if I had to pick one for casting resin, I'd go with pressure.

Stabilizing blanks or preparing rubber for casting a mold? I'd go vacuum.

 

[ldb2000]

Pressure casting does not compress the bubbles , what it does is that it keeps the gasses in solution . Think of a bottle of soda , when the cap is on and the soda is under pressure the carbon dioxide gas is kept in solution , when you unscrew the cap the soda is no longer under pressure and the gas comes out of solution and creates bubbles .
The best way to avoid bubbles in your castings is to never put them in there to begin with . Pour your resin and mix your pigments , if your using them , then let it sit for awhile , it won't start to harden until you add the catalyst , this allows the bubbles to rise to the top and pop , warming the resin helps by thinning the resin allowing the bubbles to rise more quickly . When you mix in the catalyst don't introduce any new bubbles , mix slowly with your mixing stick kept on the bottom of your mixing cup . When you pour your resin , pour it in a small stream on one side of your mold and don't create any bubbles . I have done many gallons of castings , including clear casts , without using pressure and without any bubbles .