How long do you pressurize PR?

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Gilrock

Gilrock

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Well I asked in another thread but no one responded....so I'll try again.

Does anyone use pressure to remove air bubble in clear PR castings? If so how long do you leave it under pressure? I'm using Silmar 41. I'm just curious of ballpark answers...is it just 10-20 minutes to remove the bubbles or the 2 days it takes to cure? If it's early then doesn't the PR want to move into places you don't want it like inside the tube?

I'm trying to decide if I want to buy a pressure pot or a jewelry cleaner.

Thanks,
Gil
 
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Gil I casted many cast but I don't use a pressure pot. So far I have done snake skin,abalone,cholla,pinecones, my treat is room temp. on PR stir but gently in one direction,keeps bubbles to min. when pouring pour ONLY in one corner of the mold keep bubbles down to a min. and if you get some bubbles just gently poke them I use a dental pick. Good Luck pouring!!! G with you AZ temp you got this lick !LOL.
Here in Illinois were at 9 degrees right now so I have to wait a while before i can pour in my garage. Louie56
 

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Pressure won't remove the bubbles, it compresses them so small that you can't see them. So if you remove the pressure the bubble will expand again, sometimes in unexpected ways. It may go from a round bubble to an elongated smear, very ugly.
I leave mine under pressure overnight just to be sure, then I release the pressure slowly.
Trying more without pressure just to simplify things.
 
Gil: These are only suggestions. Ultrasonic jewelry cleaner heats and vibrates. You can viberate sitting on a scroll saw bed, you can heat in a toaster oven. (All this after stirring in color and before adding MEKP) You can get it hotter, thus thinner, in the toaster oven. Be careful about going past 150deg. The toaster oven also can be used for post curing. I usually stick my casts, still in the silicone molds, in the T/O at about 125 for a few minutes or until the stickiness on the outside is gone. The toaster oven, to me, has proven to be more versatile.
Reference time in pot~~ Variables AMOUNT OF MEKP, I try NOT to use more than 3 drops per ounce. Much more than that and it means haul a$$ to get it poured, especially if you are mixing two or three colors, before it begins to gel.
SHOP TEMPERATURE, the warmer the ambient air, the quicker setup. Besides trying to have my shop 70 deg. or above, I direct the hot air from a portable electric heater directly on the pot from about 2 or 3 feet. I never check until 3 or 4 hours have passed. I prefer to cast before going to bed and let it set over night. I don't have a lot of time in casting, myself, and I'm always afraid that if I release the pressure too soon, I use 50# (yeh, I know, I already hear the screams from others) I use 50#pressure, that the bubbles could expand enough to become visible or require repair. I DO NOT use 50 # in my (borrowed) Harbor Freight pot. I would not recommend going over forty with it. But in my CA Technologies pot, I don't worry about 50#, at all. It is an extremely solid pot. I hope this helps. Just some food for thought.
 
My main worry is any bubbles on the underside of the tube where you can't see when you do the pour. I know I've read some try to reach under there with a dental pick or something but that doesn't seem reliable if you can't see what you're poking at.
 
Gil with your AZ. temp should have no problem pouring in the corner of mold. May I ask what you are trying to cast?
 
Gil,

I just want to point out that the tutorial posted specifies use of styrene cups. He warns that the PR will eat it in time, but I strongly recomend against using these. Poly Propolene cups are also inexpensive and will not disolve. Look for recycle code 5 on the bottom of the cup. Reportedly thre is another type of plastic cup that works too, but I dont recall it's recydle code. I tryed teh standard styrene cups when I started - made a mess and there is still a few drops of blue resin embedded in my picnick table.

I have not found code 5 cups at any big chain stores. I get mine at a local dollar store.
 
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louie56 said:
Gil with your AZ. temp should have no problem pouring in the corner of mold. May I ask what you are trying to cast?
Click to expand...

This is what I'm casting. This was my first try...my wife will be painting more tubes now with various themes...so it's all clear casting... I might have some fun on the side though...I ordered 7-8 colors or mica.

 
Gil

I just breezed though the post. But I will give you a few tips. As others said pressure dose not remove air it compresses it and keeps it from leaching out of spots you don't want.

Now what I do is preheat the mold with embedded object such as in my case watch parts. Preheat to about 125 deg. I also preheat my resin by putting my mixing cup in hot water it thins the resin and lets the air bubbles rise more quickly. I use only 3-4 drops MEKP per once of resin depending on volume. Then pore and get into the pressure pot lately I have not gone over 25 PSI. I leave in the pot for at least 12 hrs. If you put more MEKP to speed up the cure your cast will be more brittle and harder to turn patience. When you take it out of the pot the top will probably be a little sticky this is normal. Your in AZ so put your molds outside in the sun for several hours it will post cure them and they will be nice and set. You can post cure in an oven but then again not too much heat don't go over 125 for an hour or 2 or it will make your blanks hard and brittle.

Hope I gave some good tips you can use. I use Silmar 41 myself for years and it's an ongoing learning process. There is so much that effects it especially temperature.

Good Luck
Bruce
 
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