In article . com,
wrote:
Dear Sirs
Hi I am looking for some info on glass molds for blowing.
I work for a large Lamp Co in Miami Fl one of our dept is a glass
blowing and slumping.Myself I only know a little about glass as my
background is mold making ceramic, silicone and the like. Even thou I
helped set up the glass dept and build the glass tanks and use to
charge the glass at night before leaving that is about as far as my
knowledge goes.
In which case, you should probably tone back part of your .sig
for a while -- the part which reads:
================================================== ====================
Master Mold Maker
================================================== ====================
:-)
Actually -- what little I know about glass blowing was done
without molds, and was in chem lab class -- just a bit of starting
glasswork.
1.Ceramic molds like used in slumping the mold will be in 3 to 4 parts.
Because of undercuts.
2.Refractory like ZerCar can it be molded and will it last for say 50
blows.
3.Plaster EPK vermiculite mold.
4.Polyurethane mixed with metal powder
Do you *know* that this is used? It strikes me that the
temperatures would be way too high for something like this to be any
more than a single-shot mold.
5.Epoxy mixed with metal powder
Similar feelings about these -- except that they might handle
two or three -- depending on how well cooled the mold is.
6.Graphite molds is there a way for me to make mold using it. I Would
like able to pour it.
*Pour* it? Graphite is a crystalline form of carbon. According
to my old copy of the _Handbook of Chemistry and Physics_, carbon's
melting point is 1350 C, and it *sublimes* (that is goes straight from
solid to vapor form) above 1300 C, so if you were to melt it to pour
(neglecting whether it would form the right crystal form on cooling,
instead of diamond or some amorphous form), you would need to do so in
an inert atmosphere, at some significant pressure. The specific gravity
(and thus relative density) is:
amorphous 1.88
graphite 2.25
diamond 3.51
so my guess would be that it would be some variant of amorphous without
a very carefully controlled pattern of temperature and pressure.
Just to put it into perspective, that melting point, which was
given in degrees C (1350) translates to 2462 F -- well above what I can
reach (1850 F) in my metal hardening oven.
In contrast, glass has a temperature of fusion (close enough to
a melting point for our purposes) of 1100 C (2012 F). And, of course,
different glasses will have differing melting points -- but this is
probably close enough to make my point, and it was what I could easily
look up.
Obviously, if glass melted above the melting point of carbon
(graphite) it would be of little use to you as a mold.
7.Do you have any ideas that may be of help.
For the shaping of the graphite molds, you will want to start
with sold blocks of graphite, and machine away parts to make your mold.
You may be able to do it with a lathe, but a milling machine would be
a better choice -- and a CNC milling machine would probably be the best
choice to get precise shapes. This will require someone to learn how to
run and to program one.
You *could* use a burr in a die grinder to cut the shapes by
hand, but this would make it more difficult to make the halves (or more
parts) of the mold meet properly. This might be reasonable for an
experiment, but not for production.
And since carbon dust from the machining can be rather abrasive,
depending on how pure the graphite is, you may want to get a CNC milling
machine which is nearly worn out anyway (which will reduce the
acquisition cost, if not that of maintenance).
And they could be used to machine the metal molds as well (and
they would probably live longer doing that.)
I don't know what metals are a proper choice for glass molds,
but it would have to be something which could run at a temperature near
that of the molten glass, so you don't get a sudden cooling and
fracture your workpiece.
Good Luck
DoN.
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