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Help with wax injection problem


#1

Hello all,

I need some advice on how to cure a problem I am experiencing with my
injected wax models. I am ending up with what appears to be an
"Orange Peel" effect on my models which I suspect is due to excessive
talc as a release agent. However if I use no talc the models tend to
have a wavy look to the wax which is probably due to the wax dragging
against the rubber. I have tried using a silicon mold release spray
instead of the talc but have not been able to generate models without
the wavy effect. My set up is as follows:

  1. Using a low temp injection wax (155 degrees F)

  2. Using low pressure to fill the mold (all detail is filled with
    very little wax fanning out into the vents which leads me to believe
    that the injection pressure is correct).

  3. Using an RTV silicon mold rubber

  4. I dust the mold with the powdered talc (dusting into the vents)
    and then blow out as much as I can. After this I usually make two to
    three models before dusting again.

The first model usually has a lot of the orange peel effect. The next
model has less, and a third usually starts to drag in the mold.

I would appreciate it greatly if someone could give me some
ideas to try out to eliminate this problem. The orange peel is
somewhat difficult to remove from the wax and very difficult to
remove from the finished castings.

Thanks in advance,
Cheers,
Ralph


#2

Ralph, Do you have enough air vents?


#3

Hi Ralph,

I need some advice on how to cure a problem I am experiencing with
my injected wax models. I am ending up with what appears to be an
"Orange Peel" effect on my models 

as with everything ‘it depends’

Is your model particularly thin?

Is your sprue large enough?

Since the talc is only to let the air out, brush it out of the model
cavity with a small soft paintbrush.

I have a pattern with long thin wires that didn’t fill well.
Remembering another jeweller leaving his patterns on to of the wax
injector to warm them up, I made a shallow flat wooden box with a
thin aluminium top, then mounted a 15 watt soldering iron inside.
This gave me a surface at about 35 deg C. leave your moulds on it all
the time and the wax will flow much better. If it is too hot layers
of card will insulate.

Conversely thick patterns need the mould to be allowed to cool
between waxes.

The ripples are from the wax momentarily freezing and then more
molten wax flowing over the cold ridge, a warmer mould will stop
this.

Have you tried a different wax? Or a new batch, I sometimes wondered
if it gets old and the properties change for the worse.

I have tried to be scientific about problems I have had, once you
start splitting the wax flow you can trap air bubbles, keep it
simple, I have one pattern that nearly always gets a bubble, no
matter what air vents i have cut, still don’t understand why.

The MJSA do an interesting book, ‘The AJM Guide to Lost Wax Casting’,
http://www.ganoksin.com/gnkurl/ep820v and there are Santa Fe
Symposium reports about various aspects, but I suspect that it is a
cold mould problem.

best wishes,
Tim Blades


#4

Wax too cold / pressure too low mould held too tight just to start
powder mould inject throw 1st wax ease up on the talc


#5
I am ending up with what appears to be an "Orange Peel" effect on
my models which I suspect is due to excessive talc as a release
agent. 

You really shouldn’t need much (or any) talc or silicone release
spray with good RTV silicone molds (the non-silicone types of RTV may
vary. Not sure). At most, you might need to dust a new mold so
there’s a trace of the talc in the vent cuts. Then you throw out the
first couple waxes to get rid of the talc that’s actually in the mold
cavity, so the waxes again come out clean and shiny. The talc in the
vents is all you need to insure enough air can get out of the mold
cavity for a good fill. Many molds don’t need even this if they’re
well cut. If you’re getting wavy surfaces, that probably is either
too low a wax temp or too low an injection pressure. Or both. Don’t
make big changes. Try raising the temp 5 degrees at a time and see if
that helps (And remember that you might have your wax temp set right
at the manufacturer’s recommended setting, but if your wax
thermometer is off, then that’s a problem that can happen…). Try
raising the PSI a couple points at a time. In my molds, I’m usually
injecting at around 8 psi, but pressures vary depending on the type
of wax, the type of injector, the nature of the mold, and more I have
a few molds that need as much as 14 psi or more. It may also be that
you’re not using a wax well suited to your models. If you’re getting
flashing of the wax into the vents, but not getting a good fill,
you’re probably not clamping the mold closed well enough. And
finally, even if you’re using the right kind of wax, some waxes have,
if not a shelf life, a pot life, where eventually they get a bit
stiffer and less fluid. If the wax is really old in your pots,
replace it with new, and see if that helps.

Hoping there’s something in there you can use.

Peter Rowe


#6

First, you might try teflon spray rather than silicon or talc. Also
cornstarch in place of the talc might be given try. I would bump the
heat 10-25 degrees, get a bit more liquid wax, won’t cool so fast as
to give the injection lines, inject at a higher pressure (bump a few
psi at a time), preheat your molds a bit so you don’t get the freeze
lines so easily. Anyone of these might solve the problem. Are you
using a new wax? I know every time we change to a different wax, it
is a rather steep learning curve learning how to get good
injections. If the same wax, did you recently add new wax to the
injector pot? Is the “new wax” REALLY the same formula as the older
wax (mfgrs change things and don’t let the users know about the
changes).

Hope some of these work for you. I really like suing teflon for wax
releases as it is so VERY CLEAN, no powder marks in the wax, no
build up, etc.

John
john dach


#7

I’m not answering your question exactly but I use Castaldo LiquiFast
ICE RTVmolding material and don’t need a release agent at all. It’s
fairly expensive but it works great. Mark


#8

I’d suggest the wax is not hot enough for the speed of injection -
you are getting a skin cooling on the mould that then becomes
detached.

the reason it gets less with time is the mould is heating up = less
surface quench.

Try heating the mould up a bit before you start.

The above is just a guess, so an experiment is needed…