Thursday, October 23, 2014

Molding and Casting Part 1

Recently I have started learning to mold and cast and so I have invested in a Vacuum Chamber.  After watching many you-tube videos [and with some experimentation], I have learned how to degas resin and pour bubble free castings.  

This blog is about the degassing process.  HERE is a video of the process. 

Air bubbles are trapped in the liquid from mixing.
As the Vacuum increases [pressure decreases], the bubbles begin to expand.

 The bubbles will expand many times their original size.
 Once a full vacuum is achieved [-30" or -76cm], the mix will expand up to 10 times the original volume. 
 After a few minutes, the air is evacuated and the mix will collapse back into itself. 
 Once the air is removed from the mix, the rate at which the bubbles rise and pop slows. 
  As the chamber is re-pressurized, any bubbles still in the mix are crushed by the increase of pressure.
 The mix is now bubble free and can be poured into molds.

  I use both polyester resin [it sets like a really a hard plastic] and elastomer [it is flexible like rubber] and both give superior results when degassed.  The polyester is set off by a catalyst and the elastomer is a two part equal mix compound.  Both need to be mixed properly to unsure proper curing or parts of the cast may remain tacky.  You mix air into the liquids as you stir them together resulting in bubbles through the mix.  If you pour with these bubbles still in the mix, your castings will not be great.  Degassing in a Vacuum Chamber removes the trapped air.    

The next blog will be about making a mold. 


Back To The Top