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Vacuum casting vs. centrifugal casting


#1
I do believe that the molecular density may be slightly more
compact with Centrifugal, but have no scientific data to back that
statement. 

According to tests published from the Rio Grande seminars, vacuum
casting produces denser casting.

I also use both centrifugal and vacuum, with the preference to
vacuum. I use centrifugal casting for sluggish metals such as some
white golds. I find the quality of vacuum cast pieces to be of better
quality. The metals enters the flask with far less pressure so there
is less stress on the investment, and with less turbulence so there
is far less entrapped gas. The vacuum assist also helps oxygen given
off by the solidifying metals to leave the cavity. I find vacuum
assisted casting to have better surface finish and less porosity. Of
course melting technique along with the alloys used will always
impact the quality of the castings.

Jeffrey Everett


#2
I find vacuum assisted casting to have better surface finish and
less porosity. Of course melting technique along with the alloys
used will always impact the quality of the castings. 

Jeffrey, I have to agree on the melting technique and alloy but by
vacuum assist, do you mean vacuum assist as like in setting a solid
walled flask on a silicon pad and having the vacuum drawing on the
end of the flask? Or are you referring to using perforated flasks, I
never could get decent results with what I was told was vacuum
assist, (using a conventional flask and sitting it on a silicon pad)I
tried straws, wax web, all sorts of (remedies) however, I swear by
perforated flask vacuum casting.

Was there any mention by Rio as to what system was used? I would
imagine it was a Neutec system or some exotic shielded system, I wish
I could afford one. I have been using the Neutec flask bases and
tapered sprue wax though, very good concept I like the idea of being
able to gently remove the base, and the sprue holder is easy to fit
in a swivel vise. Makes sprueing so easy, Also the material has a
very fast dwell time, so you don’t have to hold the piece in place
while the sticky wax sets. Just for an experiment, I cut part of the
bottom off one of the sprues and used sticky wax to attach it on a
conventional sprue base and cast some Brass findings today on my
large centrifugal, very nice castings. The taper helps keep the mass
and weight down, so think I’ll cut the ball shape down on some bases
and use the Neutec sprue wax for everything just glue it down with
sticky wax. I would like to see or find out about some of the
equipment coming out of Germany and Israel; I have heard some
incredible stories of how thin they can cast pieces. I’ve heard down
to 28 to 30 Ga. Over a 1.5 to 2 sq in. area. I’m sure that will be
the next criteria customers will be looking for before heading for a
developing nation!!

Do you recall in which issue of the Symposium the article was
published?. I certainly miss many technical issues being out in the
middle of the swamps of the Natchez Trace. Of course, I suppose I
could just buy the Symposium books each year (DUH) but then I could
be intelligent and that would scare my friends and family. Not to
mention the few customers I have left (the ones not learning
2nd or 3rd languages) !

Do any Orchidians do “flask less or Paper Flask casting”?. I’m
curious if this is a viable alternative for small, as in very small
shops?

Is Orchidians actually a suitable term or would Orchidites be more
acceptable.

Kenneth Ferrell
Enjoying not having any Tornado warnings today.
(but wait till tomorrow)


#3
    I have to agree on the melting technique and alloy but by
vacuum assist, do you mean vacuum assist as like in setting a
solid walled flask on a silicon pad and having the vacuum drawing
on the end of the flask? Or are you referring to using perforated
flasks, I never could get decent results with what I was told was
vacuum assist, (using a conventional flask and sitting it on a
silicon pad) I tried straws, wax web, all sorts of (remedies)
however, I swear by perforated flask vacuum casting. 

I’m just using a silicon pad and only casting one-offs recently. I
no longer cast commercially. However, I always had good luck with
both wax web or bent rods hung over the side of the flask. Now I’m
just casting into small flasks. I’ve always used hydrogen and oxygen
for torch melting. I seem to get better results with it. I’ve used
the Aurum induction machine (going back a few years) and resistance
melting (Thermotrol and hand held melters). I don’t know why you
didn’t get good results, maybe your investment mix? I’m sure someone
more knowledgeable than me can answer.

    Do you recall in which issue of the Symposium the article was
published?. I certainly miss many technical issues being out in
the middle of the swamps of the Natchez Trace. Of course, I suppose
I could just buy the Symposium books each year (DUH) but then I
could be intelligent and that would scare my friends and family.
Not to mention the few customers I have left <grin> (the ones not
learning 2nd or 3rd languages) <not grinning>! 

Sherman and the professor enter the WayBack machine… Enter the
year 1985… give or take a year. I’m at the MJSA New York show
looking at vacuum casting machines and reading literature given to me
by a salesman in which microphotographs (from an electron
microscope?) are featured. The photos show the molecular structure,
in a side by side comparison of centrifugally cast and vacuum cast
cross sections. The vacuum cast example is clearly more dense, the
centrifugally cast example exhibiting voids on a microscopic scale.

I remembered the above while looking for the Symposium book. The
only book easily found was from 1987 and the did not contain the
I had hoped to find, at least at a quick run through. I
may have been wrong about the source. (grimace) I’m going to go out
on a limb here and state that AJM magazine may have also had an
article about differences in density between vacuum and centrifugally
cast pieces.

I’ll keep looking for the other volumes, but can make no promises.
They may have been loaned out permanently, if you know what I mean…

I have been using the Neutec flask bases and tapered sprue wax
though, very good concept I like the idea of being able to gently
remove the base, and the sprue holder is easy to fit in a swivel
vise. Makes spruing so easy, Also the material has a very fast
dwell time, so you don't have to hold the piece in place while the
sticky wax sets. Just for an experiment, I cut part of the bottom
off one of the sprues and used sticky wax to attach it on a
conventional sprue base and cast some Brass findings today on my
large centrifugal, very nice castings. The taper helps keep the
mass and weight down, so think I'll cut the ball shape down on some
bases and use the Neutec sprue wax for everything just glue it down
with sticky wax. I would like to see or find out about some of the
equipment coming out of Germany and Israel; I have heard some
incredible stories of how thin they can cast pieces. I've heard
down to 28 to 30 Ga. Over a 1.5 to 2 sq in. area. I'm sure that
will be the next criteria customers will be looking for before
heading for a developing nation!! 

Maybe you’re referring to the over-pressure casting machines. Nice
machines!

I’m curious how you melted the brass. I use my old Thermotrol for
casting brass and for casting large thin pieces. I don’t like to
torch melt brass.

    Do any Orchidians do "flask less or Paper Flask casting"?. I'm
curious if this is a viable alternative for small, as in very
small shops? 

I used to used a ringless casting system back in the 80’s when I was
doing a lot of photopolymer burnout. The investment had to be mixed
in a vacuum and only had a 4 minute working time. Came out of the
oven hard as ceramic and required a hydrofluoric acid substitute
(anyone crazy enough to use real hydrofluoric acid?) to dissolve the
investment. Pain in the rear!

Is Orchidians actually a suitable term or would Orchidites be more
acceptable.
Kenneth Ferrell Enjoying not having any Tornado warnings today. (but
wait till tomorrow) 

Tornados always freak me out. One day I found myself looking up into
about a 300 foot vortex opening a few hundred feet above me. The
tornado had just torn up the town just west of us and was easing off.
The clouds can do some truly amazing things (read either awesome or
scary) in tornado weather. Darn tornados sound and feel like a
speeding freight train 3 feet away… If I never see another one
that’s okay with me!

I think Orchidians is more appropriate. :slight_smile:

Jeffrey Everett