Vacuum pump

[RJSakowski]

If the epoxy isn't thinned, probably OK. However, one thing I learned when trying to de-air epoxy with a vacuum pump is that it can froth over in a heartbeat if the pressure gets too low. I'm not sure what caused it -- dissolved water (or air??), some organic component with a a relatively high vapor pressure/whatever -- but it definitely caused problems for me in that regard. It was bad enough that I worried about the stuff getting into the vacuum pump (it didn't).

The company that I worked for 35 years ago made epoxy composites. The epoxy was mixed in a vacuum chamber to prevent air inclusions. I did some experiments with evacuating the chamber with the epoxy components and. as you say, when the vacuum dropped down to below 20 microns, the Jeffamine hardener would froth. The amount of frothing could be controlled with the amount of vacuum pulled but it wouldn't subside over time. My conclusion was that ir wasn't a case of moisture ir included air but rather the Jeffamine itself was boiling or decomposing. This was in contradiction to the published vapor pressure specs.

We used Varian rotary vane pumps capable of pulling better than a 10 micron vacuum. To measure vacuum, we used thermocouple gauges that were calibrated with a Mc Leod gauge to meet ISO9000 requirements.. The chambers we used were made from 1/2" aluminum plate with a 1" thick Plexiglas door and were about 24" cubes.

 

[Mill Lee farm]

So… sort of a hijack here, but there seems to be some pretty knowledgeable folks in this thread!

Can anyone tell me an intended use for this little guy? It was an orphan no one wanted at an auction. I couldn’t pass it up….

HVAC maybe? .9 cfm sounds slow compared to what you have been talking about.

 

[Ice Czar]

a medium vacuum mechanical pump similar to mine (though eventually I could get down to 1x10-4 torr near a high vacuum/ Welch 1400 DouSeal)

typically:
vacuum furnace evacuation, backing turbomolecular pumps, backing diffusion pumps, rotary evaporation, refrigeration system evacuation, epoxy degassing, vacuum sterilization, backing mass spectrometers, freeze drying, vacuum centrifugal applications, vacuum distillation

https://solarmfg.com/wp-content/uploads/2016/02/Understanding-Vacuum-9.pdf

Vacuum - Pressure Units Converter

Converting between vacuum units like % vacuum - mm Mercury - psi - torr - micron - kPa.

www.engineeringtoolbox.com

https://sites.chemengr.ucsb.edu/~ceweb/courses/che142242/pdfs/lecture_14_chex42.pdf

mine has hitherto been used for degassing molding materials, but I've vacuum furnace ideas now after getting a IGBT driven induction heater\forge\furnace

 

[Mill Lee farm]

interesting!
Question: the term 'backing' for pumps and the spectrometer. Does backing mean they are used in a support role to other pumps? Or does backing just mean they are THE pump to create the system vacuum?

I see in your links that there are apparetly multiple style of vacuum pumps used in a system (ex: vacuum furnace)

 

[homebrewed]

interesting!
Question: the term 'backing' for pumps and the spectrometer. Does backing mean they are used in a support role to other pumps? Or does backing just mean they are THE pump to create the system vacuum?

I see in your links that there are apparetly multiple style of vacuum pumps used in a system (ex: vacuum furnace)

Pumps used to get down to very high vacuum can't work against full atmospheric pressure. The "backing pump" or "roughing pump" is used for two purposes -- to get the system vacuum down to the point where the high-vacuum pump can start to do its job; and also to pull the gasses coming out of the high-vacuum pump's exhaust port. The typical usage is to connect the backing pump up to the high-vac pump's exhaust. It's turned on and the system pressure is monitored until it's low enough, then the high-vac pump is turned on. More sophisticated systems leave the high-vac pump running all the time and use high vacuum valves to direct gas flow as needed.

Diffusion pumps should NEVER be turned on when at atmospheric pressure. They use special silicone oil as the pumping medium, heated above its boiling point to create gas jets that capture the gas molecules and moves them to the exhaust port. With a boiling point around 300C, the silicone oil will oxidize if it comes into contact with air, messing up your pump something awful. As a grad student AKA lab slave I got the unwelcome job of cleaning a diffusion pump where that had happened. What a mess!

 

[Mill Lee farm]

Thanks! That makes it a little more comprehensible

 

[Ice Czar]

I defer to homebrewed who obviously has experience with employment as a backing pump. My experience is as mentioned before largely degassing moulding materials and casting resins in old pressurized paint pots or pressure cookers. I'd add rudimentary foreline traps (a smaller pressure sealed container inbetween where the flow goes through a filter media) to hopefully "strain out" contaminates extending the vacuum pump's oil life.

 

[homebrewed]

I defer to homebrewed who obviously has experience with employment as a backing pump. My experience is as mentioned before largely degassing moulding materials and casting resins in old pressurized paint pots or pressure cookers. I'd add rudimentary foreline traps (a smaller pressure sealed container inbetween where the flow goes through a filter media) to hopefully "strain out" contaminates extending the vacuum pump's oil life.

Excellent suggestion regarding a foreline trap. In some cases just a small reservoir to intercept liquids on their way to the pump will do.