I’ve spent many hours carving a couple of models, and just heard
that I should NOT steam dewax carving/milling waxes…
Have I just been really lucky and done that with no problem, or is
there a specific reason that carving or milling wax should not be
steamed out? (not sure if this is relevant, but I use PlastiCast
investment in most of my flasks).
Thank y’all in advance if you can shed any light on this for me, I’ve
casting scheduled for Monday morning and now have this concern in my
world.
Have I just been really lucky and done that with no problem, or is
there a specific reason that carving or milling wax should not be
steamed out?
it’s not that you can’t, it’s just that it doesn’t work so well.
Most carving waxes have a melting point too high for steam dewaxing
to melt out the carving wax. It does remove your sprues, so at least
there is that.
But try it. Boil some water on the stove with a chunk of your
carving wax floating in it. (most steam dewaxing equipment doesn’t
get the steam much hotter than boiling water) Does it melt fully? If
so, you can steam dewax. If not, you’re wasting your time. It doesn’t
hurt anything to try, but if it isn’t removing your wax, then there
is little benefit to bothering to do it.
Do note that you might have another option if you wish to steam
dewax higher melting waxes. If you were to try this with a pressure
cooker rather than the usual dewaxers that operate at normal room
pressures, you’d get higher temperature steam. That might be able to
melt the carving wax. You still might have issues with the viscosity
of the wax even if molten. Some carving waxes simply never get runny
enough when melted to really flow all that well. But hey, try it and
see if you like.
If you can get it to actually work, there are some benefits to steam
dewaxing. For one, fewer burnout fumes, and you can use a shorter
burnout and still have fully removed all carbon residues in the
investment. For another, carving waxes in particular sometimes have
higher rates of thermal expansion before they melt. In some cases,
this can cause more stress on the investment, causing cracks or
breakage of details, especially with fast burnouts, or improperly
mixed investment. Steam dewaxing might be more gentle, That’s just a
guess.
Have I just been really lucky and done that with no problem, or is
there a specific reason that carving or milling wax should not be
steamed out?
Carving wax has two properties that make steam dewaxing a potential
problem. First it has a melting point well above the typical
temperature in a steam dexaxer so it will not melt out so why
bother? Second it has a significantly higher coefficient of thermal
expansion than the investment so it will expand more than the
investment does as it is heated. This will often lead to loss of
detail, rough surfaces, and even cracked investment. So why risk it?
I've spent many hours carving a couple of models, and just heard
that I should NOT steam dewax carving/milling waxes...
Tim, If you have steam dewaxed using this wax before go ahead.
BUT… we quit this many years ago. I really found it caused more
problems than it ever helped. Mostly what the steam eliminates is
just the sprue wax… because typically, the sprue wax is a lower
melting point than carving wax of any kind. I just have never found
any advantage to dewaxing. We do flasks from 100 pieces to single
pieces and just do a normal burnout without problems 99% of the
time.
Carving wax has two properties that make steam dewaxing a potential
problem. But hey, try it and see if you like.
Thank you very much Peter and Jim, I appreciate your answers (and
learned from them). I guess the Plasticast investment has given an
edge with thermal expansion, I got to liking it from casting from
polymer models, but I hadn’t thought of the higher melting points of
those waxes (duh), so I’ll see if the carving and milling waxes I use
will melt fully when not invested.
For now, my labor intensive waxes in the casting schedule will get
the usual slow ramp burnout as I truly have not had problems with
that. Past that, it’s try and see and learn, such is life.