I have no practical experience regarding this, but can discuss based
As far as I know there are 3 principles of casting that are
Centrifugal casting where liquid metal is "thrown" SIDEWAYS into
the flask by centrifugal generated gravity. Might be assisted by
vacuum "under and outside" the flask.
Pouring liquid metal DOWN into the flask, assisted by vacuum under
and outside the flask.
Sucking molted metal UP into the flask by vacuum over and outside
To protect against oxidation some prosesses might take place in a
vacuum orprotected by inert gas.
Here is my understanding of the relevant physical laws:
Air pressure and gravity. These two are not the same things...
Internal pressure in the liquid. The "height" of it generates
internal pressure. Like when diving 10 meters down into the sea you
experience the pressure of 2 atmosferes.
Accelleration/decelleration. The "speed" of a liquid might
generateinternal pressure inside the liquid if it is suddenly
"stopped" inside a confined area.
The various casting techniques make use of these principles to
"stuff" the liquid metal into the mold before it freezes.
Like when pouring liquid into a container:
Gravity pulls the liquid down into it.
The height and weight of the liquid (being affected by gravity)
generates liquid pressure on the walls inside the container.
Pressure is higher "deeper" into the liquid.
If the container is purous and there is vacuum under and on the
sides of it, the weight of 1 atmosphere of air can be added to the
So... what makes the liquid move down into the flask, out into the
sprue and up inside the molds?
Basically - the difference between the internal pressure in the
liquid and the pressure in the mold.
Having no experience in casting, I will not speculate in what
casting tecnique is best. To me it looks like investment cost, size
of series and what technique is well known to the caster is most
For you specific problem, I can only summarize based on theoretical
knowledge and lurking in this forum. A "clean" mold (well burnt out
wax) seems important. Also protecting the liquid metal from
oxydation by using inert gas or a propane torch while pouring might
My 2 cents :)))