How long under pressure?

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Camardelle

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I got my vacuum system and cactus juice in, as well as my pressure pots and alumilite with dyes and stoner. I plan to build my cutting board molds and then head to the races with this whole process.

Using HF pots I was hoping to hang at around 40 psi. At that pressure, how long should I leave the molds in the pot? Is there a general rule regarding length or time under pressure in relation to how much pressure the mold is under?

Any help would appreciated. Thanks in advance.
 
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I have done just a bit, 50-100 blanks in Alumilite. I used a HF pot, tested for leaks for 12 hrs at 45 PSI; held full pressure overnight. I cast for 60 minutes at 40 PSI (Stamps and foil/steampunk blanks). This was for my set-up only.

Warmed my molds (PTownSubbie). Kept the Alumilite inside the house (62-72 degrees). Kept the pressure pot inside the house to keep it at 62-72 degrees. Casted in the garage with equal temperatures and low humidity (Alumilite does not play well with moisture).

I have done just a bit of casting, but no stabilization.

Cheers, have fun!
 
It depends on what type of Alumilite you're using, but the demold times are listed at their website. Clear is fine at 60-90 min tops which is the best for pens. White will easily set before you get the lid on the pot firmly. Or even while you're pouring the colors. Not that either has ever happened to me...
 
I leave my alumilite under pressure for 2 hours and my silmar 41 polyresin over night for at least 20 hours (but I only use 3 drops of hardner per ounce so it doesn't get too hot or brittle).
 
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I leave my Alumilite cast under pressure 3-4 hours just to be sure everything's hardened. Also I'm not in a hurry to try to start turning them. When I was using P.R. Resin I left them in the pot 12 hours using 3 drops of hardener per oz. of resin. Something I also use as a guide is I watch the left over resin in the cup. When it's rock hard I figure the blanks in the pot are close to the same.
 
I think your real question is "Is there a general rule regarding length or time under pressure in relation to how much pressure the mold is under?" The answer is no. Whether you put the blanks under 40# of pressure or 70# of pressure has no impact on the amopunt of time the molds have to stay in the pot. They need to be in the pot long enough to harden so that when you release the pressure they will not allow the micro bubbles that are trapped inside expand. Follow the instructions on your resin container in regards to the time and you shouldn't have any problems.

Edit in: I just noticed how old this post is. Oh well, maybe someone can use the information.
 
mbroberg said:
I think your real question is "Is there a general rule regarding length or time under pressure in relation to how much pressure the mold is under?" The answer is no. Whether you put the blanks under 40# of pressure or 70# of pressure has no impact on the amopunt of time the molds have to stay in the pot. They need to be in the pot long enough to harden so that when you release the pressure they will not allow the micro bubbles that are trapped inside expand. Follow the instructions on your resin container in regards to the time and you shouldn't have any problems.

Edit in: I just noticed how old this post is. Oh well, maybe someone can use the information.
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So if I leave my molds overnight at 60 pounds I should be fine the next morning is this correct
 
If you are using Alumilite, yes. Leave it in for at least as long as your resin's instructions say de-mold time is. I use Alumilite Clear Slow, which has a demold time of 4 hours. I've left molds under 70# of pressure for as little as 4 hours and as long as two days without problems.
 
mbroberg said:
If you are using Alumilite, yes. Leave it in for at least as long as your resin's instructions say de-mold time is. I use Alumilite Clear Slow, which has a demold time of 4 hours. I've left molds under 70# of pressure for as little as 4 hours and as long as two days without problems.
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Hi, I have a pressure pot that will take up to 80# and am only going to 45# for my casting. Is there a reason that you use 70#?
 
Stefan, when I first joined this forum, most of the folks that talked about casting only used about 35 to 40 psi in their tanks and never had a problem with bubbles in their blanks. At least that's how I remembered it.
 
Sdusedau said:
Hi, I have a pressure pot that will take up to 80# and am only going to 45# for my casting. Is there a reason that you use 70#?
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More pressure will not hurt anything. Not enough pressure can cause problems. I use more to avoid those problems. However, never take your pot up to max pressure. My pots are rated for 80# so I never go above 70#
 
I run at 60 psi for pressure. I'm not selling blanks at all so I just leave them in there until I get to them. Sometimes 6 hours, and sometimes a couple of days.
 
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