I am having a problem getting perfect wax models out of a vulcanized
rubber mold. I am injecting the wax and i get tiny pockets and
bubbles. I am using a silicon mold release, but it is so important i
get high detail and nice dense models- all advise is appreciated.
Cindy Leffler
Manney B’s Jewelers
I am having a problem getting perfect wax models out of a vulcanized rubber mold. I am injecting the wax and i get tiny pockets and bubbles. I am using a silicon mold release, but it is so important i get high detail and nice dense models- all advise is appreciated.
You could be having any of several types of problem. One, if the
details are 'blind, without release cuts in the mold, air simply might
not be able to get out of the mold, giving you a little cavity in the
wax. Too much silicone spray can actually seal the release cuts, so
try using a little less. Often, I find the best waxes are those I
pull about two or three models after I last sprayed the mold, and I
use only a very little bit of spray. Also, i use a combination of
releases when injecting. I first dust the mold with talc (actually,
it’s baby powder, which is probably cornstarch. But that’s ok. It’s
a powder, which is what’s important). In dusting, I make sure all
the release cuts are spread open so a bit of powder gets into them.
then I use compressed air to blow off as much of the powder as I can,
especially in the vent/release cuts. enough will be left so that the
cuts can still allow air to escape. I toss the first model injected
after powdering the mold, since it’s surface usually is a bit
rougher. Then I spray just a little bit of silicone on the mold,
and use injections pulled with the spray. As I said, often the best
models are ones pulled a couple cycles after spraying. don’t spray
again until models start to have trouble with sticking.
If the wax is sticking significantly, it’s probably too hot. That
too, can give you depressions in the wax, as the hot wax shrinks.
And you might need just a little bit more pressure, though few molds
will need more than 8 to 10 pounds, and most should inject fine at
6-8 pounds air pressure.
If these steps don’t give you complete fill of details, then you
might need to add some additional release cuts to the mold to let air
out of the mold better. Study the mold carefully to decide where to
do that before you cut, since too many release cuts just give you
additional mold marks. But mold marks are not always a problem, if
they don’t involve misalignment of the two sides of the mold, and the
marks occur somewhere where they’re easily cleaned back off the
casting in normal clean up work. If the mold rubber is getting old
and stiff, additional cuts might be a bad idea…
If you are seeing bubbles actually trapped within the wax, meaning
they are not caused by trapped air in the mold, or incomplete fill of
the mold, then it’s time to clean out the wax pot and change the wax.
it does age over time. Air lines can introduce water or other
contaminants, for example, and these can cause problems. At the very
least open the pot and make sure there’s enough wax in it. If the
wax level is pretty close to the nozzle outlet, you might just be
getting bubbles from air coming right from the injector. And if
you’re cleaning out the wax pot, take the time too, to disassemble
the injector nozzle and clean it out. Over time and use, the nozzles
can get caked up with residue, reducing the amount of wax that flows
through, effectively reducing the injection pressure. Cleaning out
that gunk can make the injector work a lot better, and with fresh
wax, you’ll find injecting easier too. Among other things, most
modern injection waxes include release agents and plasticizers, both
of which can age some, so old wax in the pot that’s gone through many
many heating and cooling cycles may just be getting too aged to work
well. Kinda like me, at the end of a long friday… (grin)
Peter
Cindy, Your problem with getting air bubbles on the wax may be any of
the following:
The air pressure may be too high. Adjust the air pressure by
lowering it.
The wax may be too hot or too cold. Adjust the temperature and
try to gently stir the wax to eliminate trapped air. Always make
sure you are using the manufacturer’s recommended temperature
setting.
You may be holding the rubber mold at an improper angle against
the nozzle. Always make sure that the level of the mold is at the
same angle as the nozzle.
There may not be enough wax in the pot. Never allow the level
of wax to drop below half full.
I know some of these sound simple, but it helps to have several
ideas to check out. All of these solutions were taken from our
website. You can get more technical solutions at
http://www.westernwax.com/technical.html. Also, please feel free to
e-mail me off list.
Kind Regards,
Ben Adams
Western Wax
www.westernwax.com