PR - Pressure, Vacuum, or Nuthin

[thetalbott4]

I'm in the process of setting up for skin casting would like some feedback from the experienced folks. I've read here that pressurizing the casting is better than vacuum for bubble reduction. I can see both sides of the coin on this, but am wondering if anyone has actually tried both methods and compared those results to a casting with no pressure or vac? If I can get some solid feedback, I'll know which way to gear up.

 

[PenWorks]

I cast with neither, but was pretty impressed with the results Don & Serge had with the pressure pots.

 

[thetalbott4]

Anthony - Same here, thats what got me to wondering what may be the best method. Vacuum seems logical, but the blanks from the pressure casting look great too. Makes me wonder if there is ANY difference between methods.

 

[PenWorks]

Scott, if it aint broke, why fix it ? I think they experienced more casting problems or air bubbles because of their very humid climate. (just a guess)

 

[thetalbott4]

My concern is with bubbles in the snake casting and if there IS a method that produces a reduction, then I would like to go that way. Anything to help make the blanks better.

 

[Mudder]

I am far from an expert on this subject so I can only talk about the theory of each.

At work I use a lot of epoxy adhesives and we use a “degassing chamber†to remove air bubbles from the adhesive. The theory is that when you remove atmosphere the bubble expands and rises to the surface and pops. What I am struggling with is the vacuum method also tries to remove any air that might still be trapped in your tube so you either have to seal the ends of your tubes really well or find a way to fill them completely so there is no air present.

The pressure method works on the theory that the pressure will compress the air bubble (air is very compressible) to a point where it is too small to be seen by eye.

I cannot say which method is better because I have not tried both of them. I have found that most of my problems with snakeskin casting are removing the air bubbles that are close to the skin. I was thinking that I would try a thin layer of CA on the skins or maybe painting some of the resin onto the skins before I set them in the mold and pour the resin. Now that the Christmas rush is over I will have more time to experiment. I’ll keep you posted on my progress, or lack thereof.

 

[Deere41h]

Which ever way you use, vacuum or pressure, you will need to find a way to seal the tubes. Otherwise you will either suck or push the PR into them and cause yet a worse problem.

Good luck!

 

[thetalbott4]

I never considered the vacuum pulling air out of the tubes and possibly causing more bubbles and resin getting in the tubes. Duh. Painting the skins with resin prior to the pour is the plan. lots of people said it helps. Looks like I will start with the pressure method first. I'll let you know what happens as it happens. Thanks guys.

Guess I'm off to the kitchen to see what pots and pans I can use as pressure vessels. I'm sure the wife wont mind...[] Disclaimer - Just kidding.

 

[TomServo]

in commercial plastics casting, often times they will first apply vacuum, then pressure- pulling out the air, then pressurizing any voids or bubbles that are left. Check into paint spray equipment for a pressure vessel.. I recently saw one that had a lid opening big enough to fit a gallon paint can into easily. I think it was 3 gallons overall capacity. 60 or 75PSI or something. I'm sure it would hold hard vacuum as well.