How does air not get trapped when when you pack a model in rubber and vulcanize it?

I have bee curious about this, can some one please explain how air does not get trapped in between the rubber in this process. There is certainly some air pockets when you pack the mold, and then the clamping certainly seems like it would seal that air in between the layers. So with out any vacum how does all the air get out? Not having tried this I am amazed that it all would just squeeze out every tiny last bubbel? How does it work?


It has never been a problem that I have noticed

When I crank the plates down I can hear popping sounds coming from the layers of rubber in the mold. I presume that is the sound of air pockets micro exploding.
Have fun and make lots of jewelry.
Jo Haemer

Jo Haemer
You are correct! The two hot plates are squeezed tight after the rubber is
getting hot. The ‘captured air’ does also get squeezed out the many layers
of the vulcanized rubber, this is quite normal! Remember to squeeze the two
plates that are holding the rubber, as tight as you can!!!

*Gerry Lewy *
*Toronto. (905) 886-5961 *

Thanks for those replies,

I know the process works well,

I am just looking for a explanation, perhaps more scientific as to what forces the air out, It must be the pressure that causes the air to move in a horizontal direction an go out between the layers of the rubber and then past the rubber and mold frame. But I would think that an air bubble could still get trapped in place under pressure, of course this bubble would shrink in size under pressure but I dont think a vulcanizer is designed ti do that.

If any one knows whats the physics going here, I would love to know.


In 48 years of jewelry making I have never encountered an air bubble in a
vulcanized rubber mold.
When I place my mold in the vulcanizer I crank the handle down hard. Then
after about ten minuted I crank again.
that’s when I hear the pops of the air being squeezed out.
It’s not like investment plaster that gets air incorporated in it during
stirring. I’m just collapsing the voids where the rubber doesn’t quite fill
around the model during the packing process.
-Jo Haemer

Under pressure, there is nothing
to prevent air from escaping. Sometimes
there is air around the model that when
pressure from the vulcanizer is released
will cause the rubber to puff up, after it cools
it is not visible.
If you do not tighten the vulcanizer after 10
minutes, it results in a spongy texture.
So, air trapped and heated results in air
pockets, under pressure, the air is squeezed
out… or has no room to expand…
How does investment “boil” while under
a vacuum?

Thanks richard, Investment boils because the atmospheric pressure is removed from the vacum chamber and the air in that camber now expands and if in a liquid as a bubble that air gets bigger and rises to the top.

Bruce, vacuum investing, the air is removed
reducing atmospheric pressure, which
allows water to boil at room temperature.
YouTube has a video demonstrating and
explaining how it happens.
"Boiling cold water in a vacuum"
Purpose of vacuum investing is to
remove all air, so your castings do not have
air bubbles attached, which become
tiny spheres of metal attached to the
wax model.