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Vacuum Chamber & Pump Questions

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Vacuum Chamber & Pump Questions

Postby thomen » Wed Feb 16, 2011 8:53 am

Hi All,
I'm from sydney Australia and trying to hunt down a suitable vacuum chamber and pump.

I was looking at this 8cfm pump from ebay and wondering if it'd do the trick?
with regards to a pump what should i be looking for?
http://cgi.ebay.com.au/NEW-HUGE-8-CFM-REFRIGERATION-VACUM-VACUUM-PUMP-FREE-OIL-/190496308055?pt=AU_Pumps&hash=item2c5a76fb57#ht_8073wt_1139


and also does anyone know where i could find a decent vacuum chamber..something like this is what im after but google hasn't been overly helpful!
Image


aka!
WHAT DO I NEED TO GET A DECENT VACUUM SETUP FOR CASTING!
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Re: Vacuum Chamber & Pump Questions

Postby mangozac » Wed Feb 16, 2011 10:12 am

Welcome to RA Thomen!

Well the size of pump you need depends mainly on the size of your chamber. I use my 10L pressure pot as a vacuum chamber too. The pump you linked to is a massive 8 cubic feet per minute, which equals 226L/min. It would therefore evacuate a 10L pressure pot in 2.65 seconds (in practice it wouldn't be quite that fast, but in any case that is far too much)!

To suit the 10L pressure pot I personally would go for the 2 CFM pump sold by the same seller. Much cheaper and will evacuate the 10L pot in around 10 seconds.

Buying a proper vacuum chamber is expensive. One option is to just get a pressure pot like we all use and buy a thick (like 20mm) piece of clear plexiglass. Route a circle channel into it so it will mount to the top of the pressure pot (instead of the normal lid), line the channel with some silicone and you're good to go. But if you don't need to see the material being vacuumed then you can just use the normal pressure pot lid - you don't even have to do up the clamps. See here.
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Re: Vacuum Chamber & Pump Questions

Postby Dragonforge » Wed Feb 16, 2011 10:14 am

According to the specs, that pump will only draw 25 Microns, 0.001 Inch/Hg, 0.0005 PSI

You need a pump that draws 29 Microns, 0.001 Inch/Hg to properly degas RTV.
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Re: Vacuum Chamber & Pump Questions

Postby thomen » Wed Feb 16, 2011 10:47 am

thanks so much for the welcome and the info..
yeah i've been struggling to find a cheap vacuum pump that'll do 29 microns..

wow i didn't know you could use the pressure pot as the vacuum chamber as well.. that's handy killing 2 birds with one stone!


so if you can't see what you're degassing how do you know when it's ready!
pardon my ignorance im just new to all of this!

so how does the process work.. hook up the pump and set a timer based on the amount of silicone you're using?

re the pressure pot modification does anyone on here sell the plexiglass? (i don't have access to a router)


how about something like this: http://cgi.ebay.com.au/4-2CFM-REFRIGERATION-AIR-CONDITIONING-VACUUM-PUMP-GST-/280553094805?pt=AU_B_I_Electrical_Test_Equipment&hash=item4152447e95#ht_1764wt_1139 says 75 microns.. could that be true?

OR this guy http://cgi.ebay.com.au/VACUUM-PUMP-MOTOR-ICME-240VOLTS-/330527666846?pt=LH_DefaultDomain_15&hash=item4cf4fbf29e#ht_700wt_1139 has no specs but was thinking of calling the guy

any preferred pressure pots or would something from supercheap just work!
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Re: Vacuum Chamber & Pump Questions

Postby mangozac » Wed Feb 16, 2011 11:14 am

Yep pressure pot as a vacuum chamber is the way to go. It's kind of trail and error working out how long to vac for, but yeah effectively you just use a timer. I always used 5 mins to degas Ultrasil silicone. For degassing resin I do about 20 seconds once vacuum is reached.

Nobody on here sells plexiglass, and to be honest it's not as easy to do as I made out unless you have the right tools. Thick stuff can be quite expensive too.

The 4.2CFM pump would be suitable - it will evacuate a 10L pot in a few seconds - but is still a little overkill for casting.

Pressure pot can e had from Super Cheap (periodically on sale) or eBay (that's where mine came from).

What are you planning to cast?
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Re: Vacuum Chamber & Pump Questions

Postby thomen » Wed Feb 16, 2011 11:22 am

My wife's in to resin jewellery and we wanted to make and cast bubble free!

I am looking at moulding and casting some vintage car rubber mud flaps so casting in craftsil and then moulding in craftmould 75a

But you could use the pressure pot without using the plexiglass? you could just close the lid?

if i didnt want to do the plexi setup what would i use to plug the hole in the top where the paint came out?

im assuming something like this would be alright?

http://cgi.ebay.com.au/10-Lt-PRESSURE-POT-SPRAY-GUN-TANK-HOUSE-PAINT-AIR-TOOLS-/400195259697?pt=AU_Air_Tools&hash=item5d2d7f0d31

sorry for so many questions! Im just keen and would like to work out how you'd hook it all up..

the setup in that post looks interesting.. so black is to your vac pump.. yellow is to your compressor.. is the gauge at the top of the yellow hose a vac or a pressure gauge?

where would i find fittings? bunnings? plumbers store?
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Re: Vacuum Chamber & Pump Questions

Postby blind pig » Wed Feb 16, 2011 11:30 am

thomen wrote:But you could use the pressure pot without using the plexiglass? you could just close the lid?


Yup. it works fine. The plexiglass just allows you to have a stickbeak of whats' going on inside the pot when degassing.



That is perfect and what most of us use. You can pick them up at Supercheap Auto, they are about $190 normally there, but go on sale for $90 occasionally. A lot of the hoses, fittings and the gague can be used. You will need to go to a tool store that sells compressors and get a higher pressure rated safety valve (60-80 PSI and $20) as the one on that pot is only good for 40 PSI.

thomen wrote:where would i find fittings? bunnings? plumbers store?


Try Glenfords or Tradetools Direct (wher i got my fittings and guages) or look in the Yellow Pages for refridgeration supplies.
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Re: Vacuum Chamber & Pump Questions

Postby mangozac » Wed Feb 16, 2011 11:35 am

thomen wrote:if i didnt want to do the plexi setup what would i use to plug the hole in the top where the paint came out?

Stick a gauge into it.

thomen wrote:where would i find fittings? bunnings? plumbers store?

The fittings are air fittings, not plumbing fittings, (and a mix of metric and imperial) so you won't be able to get most of them from a plumbing shop or Bunnings.
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Re: Vacuum Chamber & Pump Questions

Postby thomen » Wed Feb 16, 2011 11:43 am

awesome!
thanks so much for the info!

looks like i need 1x vac gauge, 1x uprated release valve, 1x 2 way line splitter with lever valve.

rig up some kind of baffle!
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Re: Vacuum Chamber & Pump Questions

Postby thomen » Wed Feb 16, 2011 2:22 pm

http://cgi.ebay.com.au/VACUUM-PUMP-MOTOR-ICME-240VOLTS-/330527666846?pt=LH_DefaultDomain_15&hash=item4cf4fbf29e#ht_700wt_1139

this guy said the pump runs at 25 meters cubed an hour.. what would that be in microns? would it be sufficient?
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Re: Vacuum Chamber & Pump Questions

Postby mangozac » Wed Feb 16, 2011 2:49 pm

OK so 25m^3 = 25,000 L per hour
= 416L/min
= 14.69 cubic feet per minute

There is one word to describe that: hardcore.

Actually I wonder if the figure he's quoted you is incorrect. Either way it will certainly be more than powerful enough for anything you want to do. If it's too powerful there are solutions to decrease it's suction slightly.

You seem a little confused about vac pump specs. There are two main things to be concerned about: speed and vacuum.
The CFM or L/min figures indicate the speed, or how fast it will evacuate the chamber.
The "micron" figure you refer to is a measure of just how close to a full vacuum it is able to reach. All of these kind of pumps will get close enough for what we want to do.

For what it is that pump is a pretty good deal. But it really is overkill. I'd personally prefer to buy one of the other ones linked to (the 2 or 4.6 CFM) since they are a more appropriate speed and brand new...
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Re: Vacuum Chamber & Pump Questions

Postby thomen » Wed Feb 16, 2011 3:04 pm

thanks for clarifying and explaining what the units of measurement are.
That actually makes alot of sense!
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Re: Vacuum Chamber & Pump Questions

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