Vacuum Degassing.

suwalski · Post by **suwalski** » Sat Feb 27, 2010 7:22 pm

Hi guys,

I've been getting to clear casting, and I'm getting lots of little air bubbles.

This video:

http://www.freemansupply.com/video/prep ... cdegas.htm

Shows exactly the kind of bubbles I'm talking about in their clear urethane, and that vacuum degassing gets rid of them nicely.

In this walkthrough:

http://www.b9robotresource.com/molding1.htm

The writer shows how he uses pressurized food preservers from WalMart to make a decent vacuum chamber. I'd like to try that approach.

My question is: 29 in-Hg seems to be the magic number for degassing silicone rubbers, but what's good for resin?

Thanks.

Joseph Osborn · Post by **Joseph Osborn** » Sat Feb 27, 2010 9:17 pm

I use Smooth-On Crystal Clear, and the instruction on that stuff is to vac it in the pouring container, then pressure cast it after the mold has been filled. It starts bubbling really well at about 25", but I've always let my vacuum pump pull all it can, up to >29.5". I've never stopped it at anything lower to see if it works.

Are you pressurizing your clear castings and still getting bubbles? If you aren't, then you may find that you can get rid of the bubbles just as easily by skipping the vacuum step and simply pressurizing the filled mold.

suwalski · Post by **suwalski** » Sat Feb 27, 2010 11:18 pm

Wicked response.

Actually, I want to vacuum degass, and then not presure cast.

My understanding is that once the bubbles are gone, the pressure casting is quite optional.

Also, I live in an apartment, so extended periods of noise are generally frowned upon.

So, I guess I'll need to get a pump that will suck 29-30 in-Hg.

Joseph Osborn · Post by **Joseph Osborn** » Sat Feb 27, 2010 11:48 pm

FWIW, whenever I pour clear resin that I've vacuumed, the little bit that's left in the cup is perfectly clear after it hardens. So depending on the configuration of your molds, you may have no problems with bubbles if you degas but do not pressurize. Also, a typical vacuum pump isn't exactly silent so your neighbors may still frown

Stu Pidasso · Post by **Stu Pidasso** » Sun Feb 28, 2010 7:22 am

This is what I've been using for about 2 1/2 years now. Relatively quiet (compared to my compressor for the pressure pot, like 3 times as quiet) and pulls 29.5" Hg in about 30 seconds in a 2.5 gallon pot. Hope this helps!

suwalski · Post by **suwalski** » Mon Mar 01, 2010 11:54 am

Excellent, thanks for the suggestions. That pump is decently priced and looks very good for what you get. I'll look for something just like that.