Air bubbles

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jack barnes

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I poured some PR today, left it under pressure for 3 hours. at 50 psi. Put in toaster oven at 175 degrees for 2 hours. It cured nice. I turned a blank and it has lot of air bubbles. What went wrong?

Jack
 
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It got air in it!


Seriously, what was the ambient temp? Humidity? How long did it sit, before it got to the pressure pot? How many "drops" of MEK per ounce of resin?
 
jack barnes said:
I poured some PR today, left it under pressure for 3 hours. at 50 psi. Put in toaster oven at 175 degrees for 2 hours. It cured nice. I turned a blank and it has lot of air bubbles. What went wrong?

Jack
Click to expand...

sounds like moisture reacting with the resin, if you didn't over-stir and aerate
 
That's something I'm having to battle again since I've been using pipe for the mold. Luckily it seems to mostly stay on the outside against the pipe.

One thing I do is put the cup with mixed resin in the ultrasonic jewelry cleaner for a couple of minutes before pouring. Last night I forgot about it and left it in too long. Gelled before I poured. Sigh.
 
I've found that when you put the PR under pressure, that pressure must be maintained until the material has cured. Also that the increased pressure appears to increase the time to cure. A full day under pressure seems to take care of this problem---otherwise, when the pressure is released, air bubbles are almost immediatley present
 
The temp was about 80 degrees and humidity wasn't bad used 10 drops mekp per ounce. Mixed and in pot in about 15 min. I don't know how moisture could be the problem. 3 hours at 50 psi might be the problem as I normally let set 24 hours, but it was setup and solid when I took it out. Once it sets up how can air bubbles escape? making the time under pressure unimportant?

jack
 
At that temp and with 10 drops per ounce, I would GUESS that it set up before it hit the pressure pot.

Just my opinion and I don't do casting --- but I watch a fair amount of it.
 
ed4copies said:
At that temp and with 10 drops per ounce, I would GUESS that it set up before it hit the pressure pot.

Just my opinion and I don't do casting --- but I watch a fair amount of it.
Click to expand...

Yeah..the bubbles never had a chance to get out, gelled before they could get out. Try reducing your MEKP. like in the 3-4 drops range.
 
Fortunately for me I've not experienced any or what you've experienced. I usw heated resin in the ultrasonic cleaner for 20 minutes, add the MEKP at 3 drops per ounce, pour into the molds and pressurize at 30 psi and remove them from the tank in 4 hours. I'm sure I could remove them sooner......I've taken them out in two hours when in a real rush. Also, I must add that I only cast snake skins and adding pigments, colors, and dyes... both powders and liquids can have an effect on curing times and I suppose air bubbles.
Do a good turn daily!
Don

Adding colors
jppensplus said:
I've found that when you put the PR under pressure, that pressure must be maintained until the material has cured. Also that the increased pressure appears to increase the time to cure. A full day under pressure seems to take care of this problem---otherwise, when the pressure is released, air bubbles are almost immediatley present
Click to expand...
 
I only have this problem when I label cast I have tried vacuum and vibration. But I still get air bubbles, now I am getting more into it I measure the resin and the hardener put it in my light box (the temp is around 30deg's C). DurocShark you say you use pipe what type of pipe is it.
David
 
jack barnes said:
The temp was about 80 degrees and humidity wasn't bad used 10 drops mekp per ounce.
Mixed and in pot in about 15 min. I don't know how moisture could be the problem. 3 hours at 50 psi might be the problem as I normally let set 24 hours, but it was setup and solid when I took it out. Once it sets up how can air bubbles escape? making the time under pressure unimportant?
jack
Click to expand...

It sounds like a lot of MEKP.. about 3 times what I would have expected.
You're right that the time under pressure is unimportant once it is hard.
You just need it under pressure until it is solid. Once it gels, the air won't
clear. But you mention 15 minutes before getting it under pressure..
That seems long.. especially with that amount of catalyst. It could be
generating bubbles inside for a while before you get it into the pot.

As for moisture .. that's still what it sounds like to me.
I don't think the humidity has been under 90% in the last several weeks.

I would try a small batch with 3 drops per ounce.. try warming the resin
in some warm water before adding the MEKP.. then get it under pressure
as soon as you mix. See if that helps at all. I don't know how to avoid
the moisture except to wait till autumn.. :tongue:
 
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