Potting electronic plastic boxes question

I make a few electrical/electronics items where I pot the circuit board into a plastic box. My question is air bubbles left in the potting material. I made my own mixing stick. It is a 1/4" rod that has a small propeller on the end. I spin the mixer stick with a hand drill at low speed to mix the potting material. My problem is small bubbles. I do not get a lot of them but some. Bubbles larger than 1.5 mm or so I can push to the sides of the plastic box and get out or pop. Bubbles less than 1 - 1.5 mm I can't seem to do anything with. I have this idea if I could devise a way to put a tube at the bottoms of my plastic containers I use for mixing I could mix up a batch and let it sit. After a while before it starts to set drain it from the bottom leaving the air bubbles on the top. I doubt I ever do that. Just wondering if there are any tricks I have utilize. I've tried a heat gun thinking the potting material will get more viscous and want to let the bubbles pop. That does not work.

Thanks
Rodney

 

Why do you have a problems with the bubbles? Is this something you are reselling in which the bubbles look bad? They certainly will not harm any of the circuits you are potting.

 

You need a vacuum pump and chamber.

After you mix the compound you place it in a chamber and pull a vacuum. After a minute or two it will have outgassed a lot of dissolved gases and you can cast bubble free.

Word to the wise, put the compound in a MUCH deeper cup than you would think is necessary.

Think 32 oz soda cup for 4 oz of mix.

 

Erich nailed it.

You need a degassing chamber. You put the epoxy in there and create a vacuum. It will bubble up (like boiling) and then collapse like a bursting bubble. Then you know the air is out of it. Then you can pour your epoxy without worrying about any bubbles.

Here's a cheap vacuum chamber that can be used for epoxy

http://www.alumilite.com/Category.cfm?Category=Equipment


Here's a walkthrough of using the chamber to cast a part using epoxy, with pictures

http://www.alumilite.com/HowTos/TailLightMoldingEquipment.cfm

 

In my case it is cosmetics. I would probably not invest in a chamber and vacuum pump just for my stuff. But at least I know how now.

Thanks
Rodney

 

Stupid question but: How much Vacuum are we actually talking here?

Could you rig something up with an old pressure cooker and a bicycle pump?

 

A friend of mine has made very good experience with a do-it-yourself vacuum....pump, sort of. It doesn't sound as if it would work, but it seems to work amazingly well. I just asked him, he sent me a link to the following pictures:

First is the "pump" itself. it's a combination of copper tubes, all dimensions are in mm. It is open at the upper end, the lower end, and the right end. You attach a water hose to the upper end, and when the water flows from the upper to the lower end, the pressure at the right 5mm opening falls dramatically.
As seen in the second picture, you attach said 5mm opening with a hose to your vacuum chamber, in this case (obviously only meant for small parts) a marmelade glass, with an opening in the cap (which has to be sealed against the surrounding air, obviously).
According to the DIY website where that "plan" is taken from (http://www.jogis-roehrenbude.de/Formteile.htm, pics are from there), the vacuum is so strong that you can easily implode the marmelade glass if you don't take care. They also say that you can buy that kind of "pump" at laboratory equipment shops and show a picture of it: Water inlet at the left, water outlet at the right, and the opening where the vacuum hose is attached.
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login

 

That Venturi guy was on to something me tinks

 

Obviously, yes But even after fluid dynamics lectures and loads of formulas to calculate all that stuff, I STILL find it amazing that you can shatter glasses only with the, eh, power of tap water!

 

Hook this Vacuum Chamber up to your vacuum pump to effectively and safely remove air from your moldmaking rubber and casting resin prior to casting.



I call it potting material. Is the correct trade name casting resin?

Rodney