Using a vacuum chamber.

[Uruk-Hai]

Hi Figureteers!

I have some question about using a vacuum chamber when casting resin.

How long does it take for you setup to reach vacuum? And how large are the chamber in volume and what capacity does the pump have?

How long do you usually have to degass the resin when vacuum is reached? Could it be degassed for too long?

Does the degassing slow the hardenng process? If not so what potlife do you have for the resin of your choice?

Does a good vacuum chamber makes it possible to cast very complicated undercuts withou thanels?

Does a vacuum chamber works for plaster as well.

Cheers
Janne Nilsson

Any other comments?

 

[Ferris]

Hi Janne,

I know there's a very instructional movie on YouTube, but i can't find it now. Maybe you can find it.

Some things I do know:
- a good pump reaches low pressure pretty fast, say less than 10 seconds. As the resin becomes more and more viscous soon, which impedes the movement of bubbles, a fast vacuum is important.
- You need a pump optimised for large pressure difference, not one for high volume, like that of a vacuum cleaner. The latter doesn't get the pressure low enough.
- the higher the volume, the bigger and more capable the pump. Keeping things small keeps it simple.
- I don't think you can degass for too long. Point is to force out air bubbles and once they're out, no need to pump longer.
- hardening is not slowed by the low pressure
- indeed, with good degassing, you can cast vey fine things without channels.
- yes, it also works for plaster. Actually with any liquid containing bubbles. Dentists sometimes use a similar thing when casing plaster.

Hope this gives you some pointers.

Adrian

 

[Gra30]

Hi Janne, PM sent
Just a couple of points ref above and from my pretty rapid learning of casting.
You can de gas too long as the resin will set with bubbles.
The curing time is if anything fastened in a vacuum.
Channels are required, or rather sprues as the air needs to escape, the vacuum forces the air out.
Without feeds the air can get trapped in under cuts.

 

[stu]

Hi Janne

You need to match your chamber to your pump and vice versa.

You need something that reaches maximum pressure quickly.

You need to factor in your resins characteristics,,,, these characteristics will answer most of your questions.

If you vac a mould too long you will end up with more bubbles as it sets, kinda like an aero bar of chocolate, you also need to move it out of the chamber before it "gels" or you will ruin the castings also.

Unfortunately its not that simple as mix ,pour , vac , demould until you know what your doing and learn from your mistakes like everything else.

The main skill is not "vacing the mould",,,,,its making the mould !!!!

If your going to do it you need to play and learn.

Big tip,,,,make sure its well ventilated !!!!!

Hope this helps

Stuart

 

[ausf]

In regards to plaster, be careful since it contains a fair amount of moisture which will adversely affect the oil in your vacuum pump. Last time I vacuumed plaster, the oil went white and that will be the last time I vacuum plaster.

 

[Mark Dollery]

Well Guys, I do my own casting of parts for various projects & use a pressure pot in reverse by adding a thick lexan clear sheet & a vac/ pressure gauge. I use my Bambi Air compressor twin air intake ports for the vac lines into the pressure pot & can vac silicone virtually straight away. I will post some pictures of my set up tonight when I get in from work (BTW been using this system for 5 / 6 years with no mishaps yet! )
Mark D

 

[martin tabony]

Depending on the size of castings I use a de-gasser and a pressure pot.

Martin

 

[martin tabony]

I think you might find some of the information on this site of interest http://theclubhouse1.net/phpBB3/index.php

Martin

 

[Uruk-Hai]

Thank you all for your input and sharing of experience.

Hopefully I will have one as a loan over christmas and start experimenting.

Cheers
Janne Nilsosn