High Percision Vacuum Gauge

[coolbreeze]

Has anyone ever had a problem with vaporization of a curing agent with an epoxy mix? After mixing our chemicals together, we vacuum to remove entrained air. We are having problems with gas(air?) bubbles that remain trapped in the cured structure. The vapor pressures of the curing agent are fractions of a Torr up to 175 Deg F. Our gauges don't have that type of precision, so I am left wondering if this is a real problem. Any thoughts on high precision vacuum gauges? Has anyone seen this problem?

Thanks for any help.

 

[Compositepro]

I use a mercury manometer for absolute pressure measurements but they are getting hard to find and many companies will not allow their use. I've looked for alternatives and they are there but they are all much more expensive so I haven't had to switch yet. But that is not really your your problem.

The vapor pressure of the resin is not causing bubbles - air is. If you get to very high vacuum you can expand and pop the bubbles but this can take a long time. Bubbles that don't pop will shrink when you release vacuum but will remain as a foam on the surface. Volatiles, like water, acetone or other solvents, will boil under vacuum and expand air bubbles causing them to pop and then the solvent vapor will sweep the air out to the pump. Resin that is boiling will have new bubbles constantly being created and breaking. When you release vacuum, boiling will quickly stop and all bubbles will completely disappear. This is because the bubbbles contain only solvent vapor and no non-condensible air. Volatiles that are below their boiling point will be liquid.

So the trick to degassing resin is to add a few drops of solvent to the surface before pulling vacuum. BYK sell degassing aids. One is simple heptane.

You mention gas trapped in your cured structure so you may be referring to voids which can have many causes. The most common, though, is still trapped air.

 

[IRstuff]

There are vacuum gauges that measure 10^-10 Torr, so I'm unclear as to what you're looking for:

http://en.wikipedia.org/wiki/Vacuum_gauge#Electronic_pressure_sensors

TTFN

FAQ731-376

 

[jedward]

Is it possible to add the curing agent and perform the mixing in a vacuum (low pressure)environment to minimize or eliminate the air from being entrained in the epoxy?

There are suppliers of such commerial equipment, just search.

There can be concerns for catalysts generating some outgassing products but you do no seem to be concerned about them. this is important for minimizing contamination on spacecraft.