Degassing – What Is It and Why Do I Need It?

“Degassing” is the term used to remove bubbles from a solution (as in a mixture, not what you need to solve a problem). It’s necessary when using a two-part compound that has to be mixed because not only are the two parts mixed together, so are air bubbles  Those air bubbles can and will show up in the least appreciated places.

The way to get those bubbles out of solution is to expose the mixture to a vacuum, which by definition is a pressure less than atmospheric (getting a hard vacuum is possible, just expensive, and I’m a hobbyist, not a manufacturer). The bubbles, having been formed at normal atmospheric pressure (15 lbs/, if memory serves), are pulled out of the mixture by the drop in air pressure (partial vacuum) and then pop. To do that, one needs something to create the vacuum (a pump) and some place to contain and maintain the vacuum (a vacuum chamber).

Okay, so that’s what a degassing set up is. So…why would I need one?

Sometimes I have to make a part that doesn’t come with the kit or isn’t commercially available. If I need multiple copies of this part then I need some way to reproduce them, because my skills aren’t up to making two, five, a dozen that are identical. Making a mold and casting the part I make solves that situation. And since both the mold making rubber and resin* I’m using are two-part compounds, being able to get rid of bubbles is necessary.

What the degassing rig is for is to pull air bubbles out of both the mold making rubber and the resin* I pour into the mold.

I went online, googled “vacuum pumps,” and ended up being very glad I’m bald, because my hair would have fallen out at some of the prices I encountered (scientific applications need a harder vacuum than my wallet can provide). While searching (and listening to the delicate patter of hair falling out; I won’t have to trim my nose for a month) I found this little gem:

PVC vacuum pump 

(Go to “How to Make a Vacuum Pump,” it’s a little over 9 minutes long. If you’ve gone to that site and find the video of use, I’ve found a very useful online utility that will allow you to save YouTube videos to your computer: Clip Converter )

If you decide to build this pump, be aware that there are a few things that can turn and bite you during its construction that aren’t covered in the video. I’ve tried to cover them in the section on vacuum pumps but if you run into problems building one, feel free to contact me. I might be able to help.

*Some resins don’t respond well to degassing; certainly the one I’m using presently doesn’t. When exposed to vacuum the resin froths up. VERY messy. When poured into a mold and degassed, the frothing resumes and actually makes more bubbles not less. I’ve no idea why this is (I’m not a chemist). If the resin you’re using reacts the same way, try pressure casting.

Go here to find out more about pressure casting: Pressure Casting

One response

  1. […] Degassing – What it is and why do I need it […]


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