Pressure Pot Or Not?

[dhallnc]

Just being curious and having no experience with PR casting, I read about casting with pressure, vacuum and neither. What's the difference?

I ask because I have an interest in trying to cast a handle for something.

Thanks.

 

[its_virgil]

When I first started casting I used vacuum and pressure but now use neither. I almost exclussively do clear casting of snake skin blanks. I now only use an ultrasonic cleaner. What is the difference? Here is my take on what they do (for polyester resin):

(1) Vacuum will allow the air and moisture in the resin to escape. Too much vacuum on polyester resin will cause the styrene solvent to escape. This will happen at 28 inches of mercury so stay at 24-25 inches for safety. The air escaping will cause the amount of resin to expand so a containter larger than the amount of resin will be needed. I think it will expand about 5 times it initial volume. Once vacumum is released the PR will settle down to its original volume. Catalyst is then added for casting.
(2) Pressure will keep the air still in the solution to remail and not allow it to escape. Pressure of 20-30 psi for polytester resin is ample.

As mentioned I now use neither. I made 10 sets of snake skin blanks yesterday and they all came out perfect. Casting without pressure or vacuum is so much more fun.

You can cast larger blanks in layers. Make a mold for the handle blank and pour maybe 1/4 or 1/3 of the mold. Once the PR is hard the next layer can be poured and then the next. The interface between the layers will not be visible.

Good luck...I look forward to seeing your handle. There are several good articles in the library.
Do a good turn daily!
Don

Just being curious and having no experience with PR casting, I read about casting with pressure, vacuum and neither. What's the difference?

I ask because I have an interest in trying to cast a handle for something.

Thanks.

 

[dhallnc]

Thank you Don.

 

[sbell111]

Regarding vacuum and pressure, I use vacuum when stabilizing materials and pressure when casting.

I never use vacuum with PR. I only use it with stabilizing resins such as Mesquiteman's cactus juice. Basically, the vacuum is used to remove as much air from punky woods as possible while the wood is in a container of teh stabilizing resin. Once enough air is evacuated, you then cut the vacuum and the resin is pulled into the wood. PR is too think for this to work properly and sets up too fast for it to be practical (while the stabilizing resins don't set up until the wood is placed in an oven, later in the process).

I use pressure with PR while casting to collapse any bubbles that don't float out. This guarantees a bubble-free blank that has good cohesion with whatever was cast.

 

[its_virgil]

guaranteed? every time? If so, you get better results than I did when I used pressure to cast. I actually have much better results now that I have put the pressure pot in the cabinet.:biggrin::biggrin:
Happy casting. 12 sets of snake skin blanks this weekend and all were perfect. It is so much more fun without dealing with the pressure pot.
Do a good turn daily!
Don

I use pressure with PR while casting to collapse any bubbles that don't float out. This guarantees a bubble-free blank that has good cohesion with whatever was cast.

 

[workinforwood]

So Don...what would you do, and this is just a made up scenario, but lets say you have a mesh screen to cast around a tube. Whether the tube is laying or standing, there's going to be a lot of places for air to get trapped. How would you tackle this? Serious question too, I'm curious your thoughts on that. I'm thinking vaccuum, but i did not know about this 5x bigger container issue you mentioned either, that sounds like a problem.

 

[PenMan1]

Darrel:
As far as layer casting without pressure or vacuumn, I do it all the time with great success. In fact, I keep a "spit bucket" that I use to contain extra catalysed resin. After each pour, I put the extra resin in the spit bucket on top of the hardened resin from the last pour. When it is full, I turn wine glasses and bottle stoppers from this resin.

They always sell quickly because they are layered, unusual and each one is completely different. They always turn easily.

 

[sbell111]

I use pressure with PR while casting to collapse any bubbles that don't float out. This guarantees a bubble-free blank that has good cohesion with whatever was cast.

guaranteed? every time? If so, you get better results than I did when I used pressure to cast. I actually have much better results now that I have put the pressure pot in the cabinet.:biggrin::biggrin:

Zapping bubbles with pressure is simple physics. A bubble simply cannot remain under pressure. It isn't possible. Therefore, yes. Using pressure can 'guarantee' a bubble-free blank every time. Is it possible for a caster to still screw up the process? Of course it is. However, the establishment of good procedures and sticking to same will 'guarantee' bubble free blanks.

 

[its_virgil]

I must fall into the "caster screw up" category.:biggrin::biggrin: Although I taught math I never considered physics simple...not even the simple kind.:biggrin:
Do a good turn daily!
Don

I use pressure with PR while casting to collapse any bubbles that don't float out. This guarantees a bubble-free blank that has good cohesion with whatever was cast.

guaranteed? every time? If so, you get better results than I did when I used pressure to cast. I actually have much better results now that I have put the pressure pot in the cabinet.:biggrin::biggrin:

Zapping bubbles with pressure is simple physics. A bubble simply cannot remain under pressure. It isn't possible. Therefore, yes. Using pressure can 'guarantee' a bubble-free blank every time. Is it possible for a caster to still screw up the process? Of course it is. However, the establishment of good procedures and sticking to same will 'guarantee' bubble free blanks.

 

[its_virgil]

I would heat the resin to thin it out. I now do this with the ultrasonic cleaner and the heater that it has. The thinned resin will allow bubbles to rise more quickly. One draw back is the warmer the resin the quicker it starts to gel. So you will have to experiment with just how warm to make the resin.

Next, I would use a mold the would allow the tube to be rotated once the resin is poured. Rotating gently will bring an bubbles on the bottom of the tube to the top and allow you to move it out of the way. I find that the molds I got from PTownsubbie are excellent for being able to rotate the rubber stoppers and thus rotating the tube. I also make standoffs from old credit cards and drill a hole in the center. I use a small nail through the hole into the stopper and leave the standoff away from the stopper enough to allow me to move the tube with a dental pick.

Be aware that I have not cast the material you question. But, we have seen others cast it and it comes out very nice. Several have made the blanks with the mesh that protects tubing. Carbon fiber has an "air holding" surface as does the snake skins with the scales. Most any rough surface around the tube will a bit problem matic for holding air.

I do not like vertical casting for one reason....the surface area for air to escape is not very much. There is much more surface area exposed when casting flat.

I hope I have answered your questions. I hope this wasn't a test. If it was, I hope I passed.:biggrin:

Do a good turn daily!
Don

So Don...what would you do, and this is just a made up scenario, but lets say you have a mesh screen to cast around a tube. Whether the tube is laying or standing, there's going to be a lot of places for air to get trapped. How would you tackle this? Serious question too, I'm curious your thoughts on that. I'm thinking vaccuum, but i did not know about this 5x bigger container issue you mentioned either, that sounds like a problem.

 

[DozerMite]

To do mesh type materials, I soak the tube with the material attached in un-catalyzed resin while prepping everything else. Pull the tube out and run a acid brush back and forth over the surface with more un-catalyzed resin. Then mold it and pour as usual. Don't get any bubbles... so far.

Never have used a PP.

 

[its_virgil]

I've done that with snake skin hoping the resin would soak into the skin and displace air but I've stopped doing that. I can see how it would work with mesh materials. Thanks for adding to the thread.
Do a good turn daily!
Don

To do mesh type materials, I soak the tube with the material attached in un-catalyzed resin while prepping everything else. Pull the tube out and run a acid brush back and forth over the surface with more un-catalyzed resin. Then mold it and pour as usual. Don't get any bubbles... so far.

Never have used a PP.

 

[workinforwood]

Not a test just a question. I'm going to have stuff I need to use PR on. It is worse than mesh, fine details and pockets .074 deep. That's around 5/64. Just thinking best way for best success because the prep work alone before casting is 24 hrs per single tube. Hopefully I can eventually get to 15 hrs but still a lot of time involved if casting fails.

 

[sbell111]

I use pressure with PR while casting to collapse any bubbles that don't float out. This guarantees a bubble-free blank that has good cohesion with whatever was cast.

guaranteed? every time? If so, you get better results than I did when I used pressure to cast. I actually have much better results now that I have put the pressure pot in the cabinet.:biggrin::biggrin:

Zapping bubbles with pressure is simple physics. A bubble simply cannot remain under pressure. It isn't possible. Therefore, yes. Using pressure can 'guarantee' a bubble-free blank every time. Is it possible for a caster to still screw up the process? Of course it is. However, the establishment of good procedures and sticking to same will 'guarantee' bubble free blanks.

I must fall into the "caster screw up" category.:biggrin::biggrin: Although I taught math I never considered physics simple...not even the simple kind.:biggrin:
Do a good turn daily!
Don

You need not have to have taught Boyle's Law to know that as pressure increases, the volume of a gas decreases.

 

[its_virgil]

I know the gas laws and understand them. Air bubbles are driven back into solution from what I understand and the air that is in solution will stay when pressure is used. I studied the gas laws in chemistry, not physics...never had a physics class. :biggrin: But, I suppose the gas laws are taught in physics also. I probably learned more about them helping students understand the mathematics involved with the gas laws for the 35 yrs I taught along with my research when I frist started casting.
Do a good turn daily!
Don

I use pressure with PR while casting to collapse any bubbles that don't float out. This guarantees a bubble-free blank that has good cohesion with whatever was cast.

guaranteed? every time? If so, you get better results than I did when I used pressure to cast. I actually have much better results now that I have put the pressure pot in the cabinet.:biggrin::biggrin:

Zapping bubbles with pressure is simple physics. A bubble simply cannot remain under pressure. It isn't possible. Therefore, yes. Using pressure can 'guarantee' a bubble-free blank every time. Is it possible for a caster to still screw up the process? Of course it is. However, the establishment of good procedures and sticking to same will 'guarantee' bubble free blanks.

I must fall into the "caster screw up" category.:biggrin::biggrin: Although I taught math I never considered physics simple...not even the simple kind.:biggrin:
Do a good turn daily!
Don

You need not have to have taught Boyle's Law to know that as pressure increases, the volume of a gas decreases.