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Use of Wax Injector


This is a question for anyone experienced in using a wax injector.
I have recently started a job with a jewellery manufacturing company
in the casting area. Wax injecting is one of the skills I am meant
to be learning but often I do not get the chance to use one of the
wax injecting machines very much or very often for practice and when
I do there is often no one available to help me. Therefore I am
requesting some simple guidelines for injecting. What I really
need to know is a general set of rules for which settings to change
to combat which problems, which ways to move the settings and how
far. The main problems I have come up against so far are air
bubbles and shrinkage.

Thanks all.

The main problems I have come up against so far are air bubbles and

Shrinkage usually means the wax is too hot. Reduce the temp a
little bit at a time, until it has a hard time fully filling the fine
details. You can also try referring to the documentation that may be
available about the wax being used. Most waxes list recommended
injection temps. Now, there will always be a little shrinkage, and
large flat surfaces may tend to get depressions when this is too
much. That part will be helped by using lower wax temps, and if
needed, upping the pressure. The pressure is too high if your
getting significant finning, but up to that point, higher pressures
can help keep a mold filling with lower wax temps.

bubbles? You’re wax level in the pot is too low, so air is getting
trapped along with the wax flowing out the nozzle, or the wax that
was last added to the pot didn’t have enough time to fully melt so
bubbles are still there. Another possibility is contamination in
the air line. If your compressed air has water or oil in it, for
example, it can make a mess of the wax. If this is the case, drain
the wax pot and start over with new wax. It will also help, in
avoiding such problems, not to reuse old wax, including partial or
otherwise reject injections. Put only clean new wax in the pot.
Once it’s been through the process, it collects dirt, etc, and this
just ends up making your job more difficult. Wax is cheap enough.
This is for bubbles inside the wax. If you get air bubbles right on
the surface, breaking the surface, such that details don’t quite
fill, but end with an air pocket, then you have air trapped in the
mold blocking the wax from fully filling the mold. the mold will
need a bit more talcum powder in the release cuts and parting lines
in those areas. It may even need additional release cuts made. The
talcum powder is only partly a release agent to help free the wax
from the mold, and actually, most modern waxes don’t need a specific
release agent, unless they’re running too hot. The talcum means that
the rubber won’t totally close up and seal, leaving enough of a
microscopic space to allow trapped air to get out. I find that if
I actually need a release agent to be able to easily remove the wax
from the mold, I prefer the silicone sprays. So I use both talc and
the sprays, but for different purposes. After powdering a mold, with
all the release cuts spread apart to allow the talc in them all, I
then let the rubber relax, mostly closing the cuts, and blow off all
the talc I can with compressed air. Then if needed, a little spray
can be added.


The main problems I have come up against so far are air bubbles and

One cause of air bubbles can be having the wax too hot. Try turning
the wax down a few degrees and see if that helps. Tyler Teague had a
great article in AJM magazine in Feb. 2003- ‘Identifying and
Preventing Wax Defects’ that is well worth reading. Best Regards, Kate
Wolf, Portland, Maine hosting dynamic workshops by the bay.


One additional possible cause of bubbles in wax injections is
improper sprueing. We have seen this many times and
re-working/re-positioning the sprue or increasing the size of the=
sprue will cure the problem.

Check this after you have gone through the list Peter Rowe= posted.

Ken Kotoski
MPG Repair