Vacuum bell jar

I know there are a few people out there who are experienced with vacuum systems, so I was wondering how to make an inexpensive small vacuum chamber for degassing epoxies. Is this something I would try to buy from scientific supply houses?

I don't think you would need a high vacuum to get the bubbles out of epoxy. This could probably be done with a quart sealer and a diaphragm type vacuum pump, getting about 15" of mercury.

If you need better, a mechanical rotary oil-sealed pump like an Alcatel 2002 might be about right. It will run a few hundred or more used/refurbished probably.

OK, so I am looking at cheap solutions.

I found this for pulling a vacuum on Airconditioners. I have a compressor already, so would this pump work?

http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=3952

I think I would need a space a bit bigger than a quart jar since I want to put a small cup of epoxy in the jar. I don't want to have to clean the epoxy out of a jar.

I seriously doubt it.

I tried the venturi type vacuum system for desoldering many years ago... never had much joy with it.

Keith

I agree, a Venturi would be a no go. I've done alot of degassing of silicone polymers which had a similar viscosity to most epoxies. I would typically run at ~100-200 torr absolute. Any higher vacuum and the silcone would just blow up out of container because a small bubble becomes a really BIG bubble before it pops.

Check out coleparmer.com. They have some pretty affordable vacuum pumps. I also strongly reccomend you get a vacuum dessicator for about $65. It hold a vacuum well and has a shutoff valve too. You can pump down to degass, and then just leave it alone while the bubbles rise and pop. With this setup, You might even be able to get away with a strong vacuum cleaner or shop vac depending on the epoxy's viscosity.

Speaking of silicone polymers, you might want to also check out Dow's Sylgard series. They are designed for electronic encapsulation and are capable of being reworked if nescesary. Lots of different formulas for different properties, dielectric strength, K value, mechanical, etc... I have also found a direct to consumer source for the products, but unfortunately I cant remeber where off the top of my head.

-Chris

How about FoodSaver jars? There's a handheld pump too.

--Bob

You need more vacuum for good evacuations on an air conditioner system than a venturi will pull. But you shouldn't need that for degassing epoxy. Bell jars are a bit pricey and you probably don't need it for the vacuum level you need to degas.

At work, we used a heavy-duty pressure cooker and an old refrigerator compressor. I seem to recall we needed to only pull about 15 or 20 inches but let it sit for quite a while - something like half and hour or an hour for all the air bubbles to come out. Then we pressurized the pressure cooker after the degas process, and opened up a dispensing valve to pour it into the controllers we were potting.

Make sure the pressure cooker won't collapse - it needs to be very heavy duty to not do that, because you are reversing the pressure differential from what it is designed to do.