Vacuum/pressure chamber advice

ZOMBIEREPELLENT

Sr Member

• Jul 11, 2012

• #1

Hey guys, check out my recent score!

I was helping my landlord clean out his garage, so I could cast my proton pack shells without worrying about the weather, and he threw this on the trailer to be taken to the dump! I wasted no time in claiming it, I've started cleaning it up with some high grit sand paper and some steel wool, its inner diameter is about 13" and about 13" deep. He used to use it for canning, and before that he used it to sterilize tattoo needles and whatnot. It's missing the gauge but I figured those are easy enough to replace.

My question is, what parts will I need to make this into a good vacuum/pressure casting chamber? How many CFM will I need to be able to pump to make it efficient? At some point and time I was thinking of making an acrylic top for it so I could see silicones when I degass them but that's not my top priority right now. It's my understanding that the set up is identical but using a vac in the place of a compressor. Or am I wrong?

Thanks for your guys input!

 

Tommyfilth

Well-Known Member

• Jul 11, 2012

• #2

If you're going for vacuum you will need to replace the pressure relief with an air hose fitting. The CFM question depends on what you're doing for degassing silicone you have some time so a lower CFM will work, but for resin you may want a external tank, the only problem with these pots is you can't see what's going on inside.

 

ZOMBIEREPELLENT

Sr Member

• Jul 11, 2012

• #3

I usually use mold max 20-30.

I was under the understanding that you want to vacuum degass the silicone, but when you cast in resin you want to pressure cast. Not being able to see in is why I have hopes of replacing the lid some day with an acrylic one for degassing and just use this lid for pressure casting.

 

Tommyfilth

Well-Known Member

• Jul 11, 2012

• #4

you can vacuum resin before you pour like with silicone, but It is generally easier to pressure cast it. I would suggest keeping the pressure relief on the existing lid for pressure casting and making a thick lexan lid for vacuum.

 

zorg

Master Member

RPF PREMIUM MEMBER

• Jul 12, 2012

• #5

i use a similar old pressure pot, binks bellows i think.

all you need is a 20mm acrylic clear lid (its cheaper and up to the task)and a sheet of 2mm silicone (ebay).

cut a circle out of the silicone and use it as a gasket between the pressure pot and lid

i have a big new vacuum pump that does a full pull in no time.

it works without any hitch what so ever.

ill get a pic later

-z

 

ZOMBIEREPELLENT

Sr Member

• Jul 12, 2012

• #6

The ones I've been seeing are 3cfm is that enough?

 

Zombie Killer

Master Member

RPF PREMIUM MEMBER

• Jul 12, 2012

• #7

Keep an eye on Craigslist for vac pumps. I see them all the time on there at good prices. Missed a nice 7cfm yellow jacket for $200 a few weeks back. I ended up with a 5cfm JB for $200 brand new still sealed.

I have to have the most ghetto vac chamber ever. Stainless cooking pot and a duck tape gasket. It works though, i only get around 27hg but that is enough to degass.

 

Mostly Fantasy

Well-Known Member

RPF PREMIUM MEMBER

• Jul 12, 2012

• #8

I cut an acrylic top, poured in silicone for a seal, and put the hardware store pipes on the outside of the pot, after drilling through with the proper sized bit. I hooked up a Robinair vac pump with flexible reinforced tubing. I usually pull about 27-28 in. Hg.

 

ZOMBIEREPELLENT

Sr Member

• Jul 12, 2012

• #9

Thanks for the advice guys, It really helps a lot. My plan with the clear top was to cut a channel and pour in some silicone.

What's the difference between the stages of a pump? I've seen some that are single and two stage, but still the same amount of cfm. I'm assuming its the same concept as a single and dual cam engine.

 

G

Greg in MO

New Member

• Jul 12, 2012

• #10

I don't think that CFM is very important in these cases...

The pressure/vacuum pots (chambers) in these pictures are not that big. If they are only 1 cubic feet capacity, then a big 4 CFM set-up would fill/empty it in 15 seconds. While a tiny 1 CFM set-up would take 1 minute. For most resins that difference of 45 seconds probably does not matter.

Compressed air CFM only makes a big difference for things like a paint sprayer or a pnuematic die grinder. Vacuum system CFM only makes a big difference for things like a vacuum former where you need to pull the soft plastic sheet down tight quickly.

Just be sure your vacuum pump can pull the 27 inches that the previous posters mentioned. And I think a pressure pot only runs about 20 psi (Can anybody verify that for us?) These are fairly small low-power units.

 

zorg

Master Member

RPF PREMIUM MEMBER

• Jul 13, 2012

• #11

ZOMBIEREPELLENT said:

My plan with the clear top was to cut a channel and pour in some silicone.

Click to expand...

you don't need to, trust me. a sheet of silicone with a hole is all you need.

-z