Vacuum / pressure pot advice.

[voice in the crowd]

All,

Just wondering when propmakers on the forum use a vacuum / pressure pot to remove bubbles from resin if you pump out your pot do you have a vacuum / pressure gauge on it. If you do have a gauge what level of vacuum do you require medium or high. If you have a setpoint in a vacuum scale like Torr or Pascals that would be great.

Any information would be much appreciated.

Cheers Chris.

 

[exoray]

Yes I have a vac/pressure gauge on my pot, as for vac as much as you can get. Pressure 60psi, double regulated once on the air compressor and a second regulator on the pot itself, I don't need the lid blowing off ...

 

[voice in the crowd]

<div class='quotetop'>(exoray @ Sep 24 2006, 02:47 AM) [snapback]1325279[/snapback]</div>

Yes I have a vac/pressure gauge on my pot, as for vac as much as you can get. Pressure 60psi, double regulated once on the air compressor and a second regulator on the pot itself, I don't need the lid blowing off ...
[/b]

Thanks exoray,

Forgive my ignorance I understand the vacuum theory behind vacuuming down a pot to remove bubbles but what process would you be doing by pressurising the pot to a positive pressure of 60psi.

The reason I am enquiring is I may be making a vacuum chamber / pressure chamber and would like to know all its uses and obviously be looking to make it safely as well.

Cheers Chris.

 

[BlindSquirrel]

Dumb question from someone who's never used one of these...

I thought a pressure pot pulled the air OUT of your resin...or does it build up pressure to SQUEEZE out the air bubbles.

I didn't find the answer on Wikipedia so I'm asking here.

 

[exoray]

You vacuum the resin/silicone to make the bubbles expand and the resin/silicone also become less dense under vac, so the bubbles rise to the top and pop easier... ie de-gassing or boiling

Second once you have done that you apply pressure and it will squeeze the remaining little bubbles to literally microscopic sizes, once the resin/silicone set the bubble can't expand and you won't see them ever again...

This is the reason clear resins generally have a longer working time, I generally vacuum de-gas the resin for about 5-10 minutes (my tank is solid without a clear window so I can't tell when it's done boiling) then switch over to pressure for 12-24 hours... I also wrap my pressure tank in a heating pad to get a head start on the post cure

 

[replicaprops]

I think this question comes up every 3 months.

You don't need to Vac if the mold or resin will be cast under pressure. Totally pointless to take the extra step
You do both under pressure.
Vac is only required if your mold can not fit in the pressure pot.

 

[exoray]

<div class='quotetop'>(replicaprops @ Sep 23 2006, 11:00 PM) [snapback]1325322[/snapback]</div>

I think this question comes up every 3 months.

You don't need to Vac if the mold or resin will be cast under pressure. Totally pointless to take the extra step
You do both under pressure.
Vac is only required if your mold can not fit in the pressure pot.
[/b]

I beg to differ, I have tried just pressure casting clear resins and still had plenty of visible bubbles... Now maybe if you take extra care in mixing the clear and doing a fine stream pour to pop bubbles prior to pressure casting it might work out OK... A lot will also depend on the viscosity of your resin, Alumilite clear is pretty damn thick compared to Smooth On and thus traps lots of bubbles...

One thing I didn't mention is that if you pressure cast make sure you mold is designed to be overfilled a bit... And on the flip side when you are under vacuum make sure your mold or container can take the extra volume...

 

[LeMarchand]

I think what Rob means is, that you don't necessaraly have to degas silicon rubber when making a mold. You put the curing mold in a pressurepot (if your master can stand the pressure ofcoarse) till it is cured. You can then make pressurecast casts too without deformations.

Rob was ridiculed when he first mentioned this technigue (even after posting pics of clear dragonskin molds done this way), but i have tried it myself at 4 BARs and, at least for smaller molds, works.

Marc

 

[blufive]

I think it's important to remember that everyone has different techniques when they make molds or cast parts.

I vacuum the rubber and use pressure when I cast resin.

I have tried vacuuming my resin but that didn't work well in my situation.

I was able to cast this communicator by only using pressure.

 

[replicaprops]

Ya thats a good point, if you are using really thick resin, you can get bubbles, however I never used the resin you are refering to. But I know I have had that problem when I left rubber out to long and the rubber started to cure before I applied pressure.

I always max out the pressure at 80 psi which is the max for the pot I use.
I also must mention, that the viscosity of smooth-on is much thinner than most clear resins, and I must mention that I leave the casting in the pot 12 hours. The demold time is only 90 min. So if you remove pressure before the resin is cured, all the air you squeezed into suspension will expand if the resin is still soft.
Leaving the cast under pressure for extra time is probably a good idea.

 

[blufive]

Again, it depends on what you're using.



For the Cage Communicator, I used Smooth On Crystal Clear 220. I don't remember the working time but you can demold it in four hours. I found that four hours was perfect in my situation. I kept it at 60 PSI for four hours for every pour (there were three pours per communicator).

The moral of the story is - EXPERIMENT.

Every situation and every product will act a little different. Do what works for you.

Some people vacuum resin - some don't.

Some use pressure on the rubber - some use vacuum.

 

[voice in the crowd]

Thanks guys

Great advice :thumbsup

Cheers Chris