Guide: Wanna hear a joke about a vacuum? Nevermind, it sucks

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Guide: Wanna hear a joke about a vacuum? Nevermind, it sucks

Postby Hiflt4@juno.com » Fri Nov 09, 2012 5:37 am

Sorry for grammar and spelling errors I was not a english major.

Outgassing
The term outgassing has nothing to do with the defects, and those bubbles have nothing to do with gas being formed from the epoxy reaction. The reaction is exothermic and can produce a significant amount of heat and therefore vapour from certain volatile components. Gas masks and ventilation suggested.

Back to the original problem then: Why did the bubbles appear after I left it to cure? Firstly, they may have been a collection of very small bubbles (introduced mechanically while mixing) that moved around, joining up with other small bubbles to eventually form a large bubble that rose to the surface. Or are a result of a entraped bubble of air from the initial pour.

Want to fix this?
This guide has the hopes to match you with a pump that best suits your application. And present the casting style that I employ.

First of all Understanding Vacuum
EQUIVALENCE TABLE FOR PRESSURE / VACUUM MEASUREMENTS
1 bar = 14.5 psi
1 Kg/cm2 = 14.223 psi
1 inch-25.4 mm
1 cubic foot = 28.32 liters
1 cubic meter = 35.31 cubic feet
1 micron = 1 millionth of a meter
1 millimeter = 1000 microns
1 micron = .001mm or 1 x 10 (-3)mm

Image

5.0 mmHg (Torr) = 5,000 microns (2 to 5 mmHg is needed to make low to medium
viscosity resins visibly air-free. This range of vacuum levels is five to ten times
better than 29″ of vacuum.)

Now before you freak out
As a home caster with out a professional pressure chamber or a feed through line system simply this will not happen and thats fine as we do not aim to degass the resin we aim to remove any trapped air in the solution and then apply pressure to reduce air pockets to the non-visable range.

Generally vacuum pumps will be used for two reasons.
Atleast for the purpose of this guide
1. To degass mold compound or resin before pouring.
2 To degass or remove trapped air in the solution after pouring.

1. To degass mold compound or resin before pouring. 29″ Vacuum = 25.4 mmHg
Rember when exposed to vacuum the solution will expand to around 2x its volume make sure your container can contain it
I reccomend exposing your mold compound to a solid vacuum after mixing, and after pouring. Longer set time compounds are best for this especially if you use a larger chamber. But it will remove the air that is mixed into the compound a low vacuum is all that is required to allow for the air to work its way through the material. This can be done with less Vacuum and depends on the viscosity. Do not let it set under Vacuum, after its degassed pull it out and set it out on a flat table, or apply your pressure. Same goes for resin this will help remove air trapped from mixing however for resin casting if you plan to use #2, skip this step it will just waste pot life.

2 To degass or remove trapped air in the solution after pouring.29″ Vacuum = 25.4 mmHg
Rember when exposed to vacuum the solution will expand to around 2x its volume make sure your container can contain it
Vacuum for untill desired pull is aquired, vent and apply pressure.
This is a crude picture and not to scale but it get the point across, a chamber up top to allow for the expansion without overflowing is required for style.
Image

Chooseing a Vacuum pump
Now I am based in the US, so depending on the shipping other vendors may be best but Manufacturer: Mastercool via http://www.toolsdelivered.com are some of the best prices I have found. You want a Two Stage for best vacuum, 110V Two Stage 6 CFM Pump.
Item Id: MAS-90066-2V-110 is currently the best bang for your buck at only 185.77 USD, 145.774 EUR , 116.274 GBP. It is a discontinued product so there are only so many of them and will not be restocked.

However for a normal 2.5 gallon pressure pot a 3cfm will do you fine, even a 1.5 if you use longer set time resin. I use a 15 gallon with the pump above and come to the nessasary vacuum in about 2.5 min.


Thats all I can think of atm
Feel free to add or request info
Hiflt4@juno.com
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Re: Guide: Wanna hear a joke about a vacuum? Nevermind, it s

Postby Deadmeat30 » Fri Nov 09, 2012 8:43 am

An excellent thread! and one that deserves a sticky!
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Re: Guide: Wanna hear a joke about a vacuum? Nevermind, it s

Postby mangozac » Fri Nov 09, 2012 10:08 am

Excellent thread indeed! You've explained things quite succinctly Hiflt4, and even managed to clarify one or two things that I wasn't 100% certain on!

The thread is now stickied!
Oh yeah I can make that....
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Re: Guide: Wanna hear a joke about a vacuum? Nevermind, it s

Postby SSB » Fri Nov 09, 2012 10:19 am

It's like magic.
You talk about it and it appears.

Many thanks to you for synthetizing and adding info to the subject of vaccum... :)
Si Dieu existe, j'espère qu'il a une bonne excuse !
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