pressure versus vacuum

[RAdams]

Like alot of guys, i just got into casting, and when i did, i went and bought a pressure pot, and some mica, and some silmar and been going at it since.


I have read alot about air pressure levels, and vacuum levels and such. my question is this:


According to whoever wrote the book on doing this stuff, what is the purpose of pressure? and the purpose of a vacuum?

Anyway, just kinda curious.

 

[Robert Taylor]

being new at this myself my understanding is pressure is used in casting the resins (it squishes the air bubbles into teeny tiny air bubbles) and vacuum is used in stabilizing soft/punky woods (it helps to get the hardeners deeper into the wood).

 

[its_virgil]

Vacuum helps get the air out of solution. With the lower pressure the air expands and escapes from the solution. Vibration also works. You can make or purchase a special vibration table, or use the table of a scroll saw or similar tool with some vibration. Many of us are using an ultrasonic cleaner to help get the air out of solution. I do and really like the results and it's much easier than using a vacuum. My cleaner has a heater and I use the heater to heat the resin which also helps get out the air.

I thought at one time that pressure squeezed bubbles into tiny bubbles but have since learned that is not the case. It sounds good but is not supported by the various gas laws I should have learned in chemistry had I been listening. What the pressure actually does is keep air in the solution from escaping. When air is in the solution is is not visible. It is much like the pressure in a soda bottle. With the cap in place and the soda pressurized the air is not visible because it is in the solution. Once the cap is removed and the pressure released then the air starts escaping and hence the fizz of carbonation. Once the air has escaped the drink goes flat...I really hate flat drinks...but we love flat casting resin.:biggrin::biggrin::biggrin:

I do hope this makes sense. Casting is fun...enjoy it.
Do a good turn daily!
Don

 

[RAdams]

Actually, both of those theories make sense, to me anyway. If you have ever been scuba diving, then you should understand gas under pressure gets smaller.


And if you have ever opened a soda, you could understand the gas in liquid form idea. Either way, thanks for the info.

 

[PTownSubbie]

Understanding these concepts is all good but what is the process you all use to make the blanks?

Vacuum then pressure or pressure then vacuum?

Thanks for the insight. I am just starting and haven't purchased a pressure chamber as of yet but may in the near future......

 

[its_virgil]

I only make snake skin blanks and label blanks. I no longer use vacuum. When I did use vacuum I pulled the vacuum on the raw resin for about 15 minutes. Then I added the catalyst, poured and pressurized. But now, I place the polyresin in a jar in a water bath in an ultrasonic cleaner for about 30 minutes with the heat function on. Then I add the catalyst and I pour the polyresin into the molds I pressurize to 30 psi. You can read an article on how I cast snake skin blanks at htp://www.RedRiverPens.com/articles Just ignore the part about the vacuum. I should revise the article to add the ultrasonic cleaner and omit the vacuum.
Do a good turn daily!'
Don

Understanding these concepts is all good but what is the process you all use to make the blanks?

Vacuum then pressure or pressure then vacuum?

Thanks for the insight. I am just starting and haven't purchased a pressure chamber as of yet but may in the near future......