My Vacuum/Pressure Set-up

[dai sensei]

Well I finally got my vacuum set-up done for my pressure pot. I am using a venturi vacuum pump (top left of photos) off the compressor, but arranged my gauges and valves so I can do vacuum and pressure (I need this mainly for banksia). I used a heap of in-line ball valves with simple tee's because the three way ball valves cost a lot more (almost 3 times more).

Photo 1 - Vacuum drawn using air. My venturi pump works under 5.5bar (80psi) air pressure and should draw 29". After 1 min I have 22" Hg (75kPa) vacuum, 4 min 25" Hg(85kPa) and still rising but sloooowly (it is a big old cast aluminium pot).

Photo 2 - Vacuum with air turned off (and pot held vacuum without loss).

Photo 3 - Vacuum released and pressure applied to pot at 3bar (40psi). The pot can take 5.5bar (80psi) max, but I worry about my resin saver moulds leaking at that pressure.

Photo 4 - Pressure holding with air disconnected (and again pot held pressure).

My pot is pretty old, at least 40 years. It started as a glue pot in a workshop, then a paint pot for my father, now a casting pot / paint pot for me. It is a cast aluminium pot and approximately 25mm (1") thick minimum. Hopefully fatigue failure is still a long way off.

Cheers

[dj_pnevans]

What can one say Neil, have you had a go yet. Did you read the post on the IAP site about the pressure pot lid popping off?
David

[dai sensei]

..have you had a go yet...

Only the empty pot. I'm testing some banksia this weekend. Bit worried about the low vacuum, but filling the void with blanks may help reducing the volume. The cooler weather may also allow me to vacuum for longer.


Did you read the post on the IAP site about the pressure pot lid popping off?

Yes, but that is one of the newer pots. Mine is an old one with recessed anchor points in the lid for the solid brass clamps. My only concern is fatigue.

[dj_pnevans]

Good luck with it I hope it last. I just got a new one and have to set it up yet.
David

[MBUMIK]

well neil you should be pumping out the goodies now:U:doh:

sorry couldn't resist

thats amazing if that little black thing in the top left corner is the vacuum pump, was it expensive???

good luck with the casting this weekend

MIK

[dai sensei]

thats amazing if that little black thing in the top left corner is the vacuum pump, was it expensive???

Yes. A few suppliers in Aus varying from $100 (this one) to $300. All these types of mini vacuum pumps provide similar vacuum, but rate of vacuum and working pressure varies, also noise. This one is surprisingly quiet and has a muffla on the outlet.

[dai sensei]

By turning off the valves I can just vacuum the line only, and could only vacuum to just over 25" (about 90kPa) :(. Did a cast today and it seemed to pull the air from the banksia, but I still had problems with some voids when casting horizontally, as the bubbles were being drawn up through the timber not down and out.

I then tried the banksia in my coffee bean set-up (ie vertical casting with electrical conduits), which seemed to allow the bubbles to be extracted via the sides, but the vacuum also pulled the air/resin through the gaffa tape I use to seal my electrical conduits :doh:.

Looks like I need to stick to vertical casting for the banksia, but need to work out a better way of sealing my split conduits. I'm also going to try sealing the rest of the banksia with poly under vacuum, to avoid using so much thin CA.

[MBUMIK]

sounds like your getting somewhere

thanks for keeping us updated on the way things are working out

are you only putting the tape on the bottom of the conduits??

MIK

[dj_pnevans]

Neil try and use the plastic bags that come with your pen kits on the end of the conduite and then tape around the bag.
David

[dai sensei]

I used to use heaps of gaffa tape, around the bottom and up the sides. This took a lot of tape, so I trialled smaller quantities. With pressure I found I could use just a single length down the slit and over the bottom, then a lap around the bottom. With vacuum, any small air pocket pulls the tape away making it leak, so I must go back to using heaps or find another way.

A plastic bag with a quick wrap of gaffa may do the trick. Thanks David I'll give it a go, after all, I have a few kit packets around I could use:rolleyes:.

I'll still percist with trials of the horizontal casting, as it is easier and faster using my moulds. Might just need to leave more room for the resin around the sides, but it does use more resin.

I've also been trialling vacuum to stabilize the bansia after casting using poly, good floor board oil based stuff. This is to save then CA I usually use that is messy. I've trialled solid, with a 7mm hole in middle, and a Sierra hole in middle. Just place them in a jar with plenty of poly in the pot and vacuum for a few hours, after which they sink to the bottom.

I'll post how I go.

[MBUMIK]

do you have slits up the side of your conduit??

i am using conduit but have no slits up the sides, i find that a sharp tap on the bench releases the resin from the conduit without any probs

MIK

[dai sensei]

Yeh I have slits. Under the pressure casting, mine didn't want to come out of the conduits, even with big hits.

I have some casting silicon and now considering making my own mould with vertical tubes, just for my banksias, but could use them for the coffee beans too.

[NewLondon88]

I have some casting silicon and now considering making my own mould with vertical tubes, just for my banksias, but could use them for the coffee beans too.

Cool! If you've got the silicone, you're most of the way there.

( unsolicited advice coming up..)
For making vertical molds, you might want to find some silicone oil, too. It's not 100%
necessary, but with a tall mold, it will help the air bubbles clear and give you a
smoother mold. But it will certainly work without it.

I've made some of the vertical molds and what I find easiest is to make your originals
out of something dense ( I use lignum vitae) so it won't float out of position. I make a
4 walled box out of plywood (sanded and waxed) and then use a good tape for the
bottom. Make sure the bottom won't rock or wobble. If you've sanded well, you can
apply some shellac to the bottom edges so the tape will stick better. In effect, the
tape across the bottom of the box is acting like the bottom of the mold, which will
become the top when you de-mold.

Position your originals, standing up, on the tape at the bottom and pour.
If you're making 3/4" blanks, they might wobble some .. you might put a little tape
across the top of the blanks to hold their position relative to the walls and to each other.. but if you do that, you'll need to make your mold in two pours. (second pour
after the first one hardens and you can remove the tape)

You can also speed up curing by sitting the mold in the oven with just the light bulb on.
That generates enough heat to speed the cure nicely.. and there shouldn't be any
fumes to worry about. Just remember to check that your oven shelf is level. You can
get some funky molds if that isn't checked. DAMHIKT

There.. that's about all I know about molds.. not that you asked :p

[dai sensei]

Thanks for the advice.

I had plans for using hardwood dowels for the vertical mould former screwed to a plywood box of suitable shape. With the other moulds I've made I found olive oil to be the best release, but was going to try margarine this time.

No trouble wit temp, it is around 36 degrees C today.

[NewLondon88]

I had plans for using hardwood dowels for the vertical mould former screwed to a plywood box of suitable shape.

That will certainly work.. just take a little longer to get things apart. Getting the
dowels out is the fun part. A quick shot of compressed air will make them shoot
across the room. You have to aim really well to hit someone coming in the door.
Practice makes perfect.. :p



With the other moulds I've made I found olive oil to be the best release, but was going to try margarine this time.

I haven't tried the olive oil yet. But I've used car wax and furniture paste wax .. they
all work. My favorite is 90% mineral spirits and 10% petroleum jelly (warmed) I put
them in a little spray bottle and shake it up. That way I can spray on the release.
But they all work.



No trouble wit temp, it is around 36 degrees C today.

LOL I forget where I'm posting. I just went outside and scraped ice off of my windshield..

[Dorno]

Well thanks to everyone for all the info reguarding the presure pot. To the best of my knowlage I have it all ready to go (preasure not Vacumn) and all seems ok.
Next I am after a tutourial regarding the rest of the process.

What presure to I need to keep the pot at
How long do i keep it at that presure

and anything else that needs to be done.

If there has been a tutourial posted somewhere just point me in the general direction because I have been unable to find anything.

Thanks again Ian

[dai sensei]

Most things can be cast at low pressures 20-40psi, but worthless wood (including banksia and pine cones etc) as high as your pot can take.