Homebrew PCBs

On Thu, 05 May 2005 19:57:19 -0000, Robert Hedan  
<robert.hedan@...> wrote:

> About degassing liquid plastics, unless I read wrong you have 2
> alternatives (I'm not sure if this applies to other liquids):
> 1. place the unpoured mix in a vacuum chamber.
> 2. place the cast along with the poured mix in a high-pressure
> chamber.
> Robert
>


there is a good group on casting (casting@...).
Go there!

You can basically degass both, the moulding material and the stuff you use  
to make the part.
You do not _need_ to degass anything, if you don't run into problems.

Vacuum makes the gas huge, causing it to rise to the surface and be  
removed.
Pressure compresses the bubbles, they are still there, just compressed.

vacuuming removes the gas, it basically can't be bad. (tho make sure you  
don't "cook" the material beyond the point where all gass is gone, at  
enough reduced pressure everything will cook at room temperature). But if  
you don't run into trouble don't bother to do it.

Pressuring is what i have read only useful in very limited applications,  
for example casting clear parts where the gas is shrunk so tiny you can no  
longer see it. (The casting must be put in the chamber, with the mould,  
and stay pressurized until cured).

remember that if you pressurize a mould with bubbles, it will form small  
hollows where the bubbles are close to the surface.

And most importantly: remember vacuum chanber failures are REALLY BAD!!  
And pressure chamber failures are REALLY BAD!!. Even something like a seal  
blowout can seriously damage your hearing. a 1 liter container opening  
rapidly at only 1 or 2 athmospheres is really loud, you would not expect  
it.
And also remember i did only lurk around the casting group for a few days,  
deciding it is to complicated and expensive for me to get involved with at  
this point, so i know nothing about it, at all.

But this is the wrong group for this anyway.

ST