I recently took the plunge and bought casting equipment incl. mold
making equipment to try to mass produces some of my filigree. I cast
filigree about 12 years or so ago, with reasonable results. I’m
using bellicone red mold compound and Rio’s precision pink, but I’m
not happy with the results so far. Earlier, I used dark blue
plast-o-wax which tolerated being pulled out of the mold better. The
results I"m getting so far are inconsistant. either it’s not filling
the whole pattern, or I’m getting too much flashing, or it is
breaking on removal from the molds. I’m about to call Rio and order
some plast o wax, but I’m not totally sure that is where my problem
lies. My injector is a hand pump model which is wide open and the
nozzle is on the top of the pot and must manually be pushed down to
draw wax up from the bottom of the pot.
At one time, I had a teenager injecting my waxes. I built and
installed a nozzle on a manual injector and powered it with a CO2
tank with a good regulator - low budget research. It worked well,
especially for the non-jeweler. Later, I went back to hand operated
because I had more control over injection pressures. Some of my work
is heavy and I think I get a better surface when I hold pressure for
a few seconds after injection. So, I am thinking injection works
according to the casting paradigm of sprues being shrinkage
reservoirs as well as delivery channels. I like a mold in which I can
tell when it is filled because the hand pump stops moving. This way,
I can establish the maximum pressure I should use to fill without
without getting flashing.
I usually use Castaldo Gold rubber because it is reliable, and soft
and tear resistant working with undercuts. I have more control over
the cuttting than I do with the RTV I also use. When my molds do not
fill, I increase wax temperature and make more air release cuts (the
vertical ones) until I get good results. Sometimes, I get a more even
pressure on the mold using two pieces of masonite, rather than a
commercial mold clamp. Occasionally, I use multiple sprues in a
rubber mold to distribute the wax before it cools. Were I a
manufacturer of delicate pieces and up for the investment, I would
explore the capabilities of vacuum asisted injector.
I made a masonite top for my injector. Very funky but it conserves
heat in the pot and I think it stabililzes the wax temperature. That
allows me to consistently find the temperature I need to make the wax
flow best, without overheating it. I know less about waxes; every
supplier has a list of candidates to try. I use Serra Red and add
something for flexibility, as needed.
I hope it helps to run through the variables. Moreover, I have
written a lot, partly because I have a question of my own: Does
anyone have suggestions as to how I can achieve a slick surface on an
injected pattern using vulcanized rubber. My casting often has a
slight surface porosity that I do not get when casting the original
carving.
It’s very hard to say anything without actually seeing the mold(s)
in question. Are these the same molds that worked in the past? If
they are new molds they may need more vents cut or if they are molds
of castings then the shirkage might be too much. If they are the same
are they hard? I’d be very hesitant to play too much with the heat,
burnt wax is no good for anything and then you have to clean out the
whole pot. (I have about 5 years experience doing wax injection BTW.)
Take the time to get to know your wax injector so that is not a
random factor.
Just in case lets go over the basics.
Always let the injector heat up thoroughly before starting, let the
temperature stabalize.
Always powder the mold, esspecially the vents and release cuts.
(Always get rid of excess powder.)
Always apply even presure to the mold plates (however you choose to,
hands or clamps. There are some exceptions I make for poorly made
molds but those are rare exceptions)
Always hold the mold that little bit longer then you think you need
to. (I recommend books on CD for this job)
Always be sure what you are doing has been consistant for at least
three waxes before trying to diagnose a problem.
Always make sure the wax is solid all the way through before
releasing it from the mold.
How many molds are you trying?
And yes I find the blue plast-o-wax to be a really good work horse
all around injection wax, has good flow into to tight spaces and not
bad for chunkier patterns either.
Jon–I had similar trouble with what appeared to be porosity in
castings. I found the problem was little bumps that grew in my Gold
Label rubber and transferred into the injected waxes. Inspect the
surface of the pattern in your rubber molds.
I use Quick cure silicone rubber from Zero-D now. It gives me very
slick waxes.
I think you might benefit from a free sample of our Golden River wax
additive. A handful or two added to your wax pot when you are having
trouble makes your favorite injection wax flow like water and all
but eliminates no-fills and excessive flashing. Later, when your
problem is solved, you can return the pot to its original state by
adding more of your regular wax.
It’s in the Rio catalog, but I’d be happy to send you (and also
anyone else out there who is interested) a free sample. But please,
give me your shipping address-- no P.O. boxes, please.
I want to thank you and your company for being a pioneer in the
jewelry casting art. Your company has created many products over the
years that have broadened the ability of jewelers to create items
that may not have been possible in the past.
I also want to thank you for the sample you sent me several weeks
ago of Rapido rubber to try out. Rapido is an easy to use product
that works very much like molding clay or putty that is worked around
the model. The waxes that are shot from the mold have a very smooth
surface.
I also tryed the LiquaCast 2 part room temprature curing rubber on a
Starfish and was very pleased with the outcome. I can see that I
will be using this rubber on many items that i would never have given
thought to in the past.
Please keep up the great work.
Disclaimer: I am not associated with Castaldo except as a very
satisfyed customer.
I’m not sure what you are describing when you wrote about your
castings having a “slight surface porosity.” Is there a surface
defect in the rubber mold, or only in the wax injection or only in
the casting? Obviously, there are different questions to ask in each
case.