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High pressure wax injection

Hi All,

Does anyone out there have any on injecting wax patterns
into hard rubber molds at 50+ psi?

I’m using 50 psi as a guess starting point because I believe that
would be somewhat the force needed to collapse any trapped air and
force liquid wax into the sharp mold corners to achieve a crisp

I’ve been told a long time ago it was possible by making some kind
of modifications to maybe a standard air pressure jewelry wax
injector or creating one from some type of heated pressure boosted
vessel — bulk grease gun, industrial hot adhesive applicator etc.

I’m very familar with making standard jewelry injection molds and
low pressure patterns with air over wax injectors… about 35 years
the last time I counted. And I’ve constructed hydaulic paste wax
injectors that injected into rigid molds, but those were very
specialized and mechanically elaborate machines.

Any help, info, guidance, drawing, or just a thumbs down would be
most appreciated.


This is what comercial /industrial casters do, your rubber is
generally quite hard about 60-70 Shore hardness. It has to be made
inside a hard mould frame and used in it to support the rubber. The
wax is squeezed in as a warm paste, this cuts down shrinkage
considerably. I know someone who has made a system like this, it only
did small quantities though, I think he used an arbor press and some
kind of thing like a heated grease gun. it has to be able to
withstand (from memory) about 30 PSI, I could ask if you like. The
industrial casters seemed to keep their methods pretty close to their
chests, I have seen some info on the web.

regards Tim.

Dear Frank,

This is Michael Knight at CASTALDO. We make a rubber that you can
use to inject at up to 50 or 70 psi. But please read further before
even considering this approach.

You CANNOT compress the air trapped inside a mold, not at 50 psi
anyway. At 10,000 psi, maybe. You are trying to solve this problem
with a sledge hammer.

So what you need to do is RELEASE the trapped air. That is, give the
trapped air a way to get out ahead of the wax.

The modifications you need to make in the molds are called air
release vents. They are cuts in the rubber from the extreme points of
the pattern area to the outside of the mold. That is, to the open
air. If your wax is entering the mold at the bottom of the shank,
then the extreme furthest point might be at the tips of the prongs.

You’ll know because these areas are the ones that are not filling.

And you’ll need to keep the vents open with a very thin dusting of
talc. Apply sparingly from time to time and try your best to keep
the talc out of the pattern area. If it gets into the wax pattern it
will cause porosity in the final casting. Not to mention degrading
the surface finish.

You can increase the pressure or choose a wax that is more fluid,
but those are just further refinements on the sledge hammer idea.

About the high pressure rubber: It’s called CASTALDO Titanium Label.
You can read more about it on our web site at:

But remember that hot wax forced out of the back of a improperly or
insufficiently clamped rubber mold at 50 psi might do nasty things
to your skin. Set up some sort of plexi shield to work behind. And
use gloves and common sense, too.

I’d be happy to send you – or anyone else out there who is
interested --a small free sample to try out.

Please let me have you delivery address – no P. O. Boxes – and
your telephone number – UPS insists on it.

Michael Knight

This is Michael Knight at CASTALDO. We make a rubber that you can
use to inject at up to 50 or 70 psi. But please read further before
even considering this approach. 

I don’t know anything about this. I want to thank Michael and
Castaldo for having such a great product line, and great customer
service, too… Cool place, Orchid!!


This is Michael Knight at CASTALDO. We make a rubber that you can
use to inject at up to 50 or 70 psi. But please read further
before even considering this approach. 

You were definitely on my “to call list”, in fact I called last week
and you were out but I didn’t have time to follow up.

I’m very aware of the need to vent molds to release trapped air.
I’ve made conventional rubber, vulcanized silicone, and RTV molds for
35+ years. About 20 years ago I began producing belt buckles,
keytags, medallions, and varuious decorative hardware via vulcanized
molds and soon found out it was very difficult for a production wax
person to achieve consistent results. Getting lettering and small
detail to fill crisply required a mold that, on close inspection,
seemed like sliced up shredded wheat with a little mold material
holding it togethter. After investigating metal molds and all the
effort that had to go into them, I began to create an epoxy mold
system for water cooled platten hydaulic paste injectors that I built
myself. I used this system/technique for about 20 years with GREAT
results…super crisp waxes, quickly made, with little cavitation.

Along the way (15 years ago), I had the opportunity to see other
waxes that were made via black organic white metal rubber molds, but
got no details about how they were produced other than with a
conventional liquid jewelry wax — Kerr’s Aqua at the time and that
they were made with a Romanoff injector that had been modified to
some unknown extent. They were as crisp as waxes I was making at
500-700 psi. I put some time into trying to work out the method, but
my other way was working fairly well so “paying the rent” won out
over R&D. Two of the downsides to my method were the time and skill
it took to make an epoxy mold and the fact it could have zero
undercuts (in fact it actually had to have negative draft to release
the master and subsequent injections). I no longer have the need for
the paste injectors and they were “put up for adoption”.

Now I’d like to revisit the whole thing and see what can be done.

I know the risk of shooting higher pressure waxes due to the day I
cranked up the standard wax pot to 30+, put a test mold to the
nozzle, and bent over forward to see if it was leaking around the
sprue former hole. About that time something shifted slightly and a
stream of 160 deg wax made a beelline for my eye. I blinked just as
the paiful material hit my eye and wax welded my eye lashes together.
It was a “first” for the ER when I arrived to have my eye lashes
surgically cut apart and eye lids treated. I believe that is one of
the reasons God inspired safety glasses!

I’ll certainly call next week to give you my address for the rubber

I’m using your Super Tear silicone daily now and really like it’s
ease of use, no waste and the great molds it makes.