Vulcanising Castable Wax Resin

Hi there!

I own and have been using a Form 2 printer with Castable Wax for just a few months now.

The results I get casting the Castable Wax are inconsistent (i use a vacuum casting machine, plasticas investment, I cast in sterling silver) . The same model, different flasks, same kiln, same casting process, one has perfect surface, the other one has a very porous, kill-me-now/we-cannot-use-this surface. This happened so much that it got me to the point where I would much rather prefer making moulds directly after the prints and cast directly in wax than casting the castable wax resin and not knowing what will turn out.

I remember the formlabs webinar mentioned you could do vulcanised molds directly after you print in castable wax resin. I tried with my usual rubber (165C ) after curing the prints under a UV lamp for about 20 minutes with no success (the print cracks and the mold, well, it has cracks as well :slight_smile: . Is it really possible to make molds after these prints? If so, what am I doing wrong?

Thank you all!

I don’t think they mean vulcanized molds.
I think they mean RTV silicone molds.

I assume you mean vulcanized neoprene molds for centrifugal casting?

If you printed in their High Temp resin, you might be able to use it as a pattern in a vulcanizing press, but any of their regular resins will break down at those temps and pressures.

I suspect even the High Temp resin will get soft and rubbery at those temps and pressures…so your cavity might end up deformed- but its worth a try.

High Temp Resin should be stiff enough for curing a rubber mold negative at 165C, but I still would tend to lean towards making RTV silicone molds that cure at room temperature, just for convenience. Castable Wax is not going to work with a 165C curing process, but just about any Formlabs resin should be usable with RTV silicone.

Georgiana, if you care to provide any more details about your casting models and process, someone else might be able to help figure out what’s causing your surface quality yield problems and how to fix them.

One idea that occurs to me might be able to explain your inconsistent results is how you place your flasks in your kiln for burnout. Even if your kiln has very uniform temperature, if one area of the kiln gets more convection or airflow during the burnout, that could affect the Castatble Wax process.

Castable Wax resin needs to oxidize out of the mold, like if you were investing plant matter, as opposed to melting and running out of the mold like a typical casting wax. Not getting enough air flow can be one factor that leads to a poor internal mold surface, leading to a poor cast.

1 Like

I mean vulcanized rubber molds, for wax injection (I then use the waxes for vacuum casting).

I was hoping I could make some use of the resin I currently own.

Thank you for your answer!

Do you have any idea if it could work with VLT Rubber? (vulcanising temperature 71°C - 82°C ). I have never worked with RTV, this is why I would prefer the first type.

My kiln is quite small, only 4 flasks can be put on each level (2 rows of 2 flasks). Both the flasks containing prints were by the door. The other 2, containing just waxes, turned out just fine.

I really need to finish some pieces really soon and I am trying to find the safest solution for now.


I make silicone rubber molds all the time from Form 2 prints.
I just use RTV silicone rather than gum stock or neoprene.

you can make RTV silicone molds without 100 plus PSI or high temps of a vulcanizing press.

the only trick for jewelry wax casting is that, if you use Tin Cured ( condensation cure ) silicones, they will outgas ethanol vapor at molten wax temperatures- creating tiny bubble in the wax… but all you have to do is bake the cured silicone mold in an oven at a temperate 15 to 20 degrees F higher than you expect to inject wax. for about an hour- and all the ethanol that WILL come out at wax temps will be purged.

RTV rubber is vastly easier than any vulcanized rubber you could use.

It vulcanizes at room temperature. ( hence R-T-V )

You simply mix in the catalyst- vacuum degas the bucket with the mixed rubber in it- and then pour it over your pattern.

You can pour it solid and then simply cut the mold open with an xacto-
Or- since you have a printer- you can also print the pattern as a split master, with the vents and gates modeled in place, and then pour the rubber over each half and put the two rubber halves together to make your wax casting mold.

1 Like

Use RTV, don’t waste your money and time on VLT. The VLT sticks to your model even when you use the sprays or oils. It is also a bit tricky to force VLT to go all the cavities and undercuts, it might not vulcanize on lower side of the temp.

I have got some good results vulcanizing Castable Wax in silicone mold rubber - 172 C, it depends on the geometry of the model, rings might get strecthed out, but simple pendants can be vulcanized really well. The Castable Wax model will be halved by the temperature and might break also. The Castable Wax does not stick to mold making it really easy to cut,

I have used High Temp also, but it sticks with Castaldo Silicone mold rubbers, using sprays and oils did not help me,

1 Like

172 is too high a temp for condensation cure silicones- they swell at those temps- so if you need to get it that hot, you have to use Platinum silicones-

I was thinking using the printed patterns, to make a mold to inject wax in. Using just regular grey resin.
no need for printing in castable resin and no need to burn out with that specific schedule.

If you want to use silicones to make an actual centrifugal mold, you’ll need a platinum cured RTV with a durometer of 45 or higher to prevent distortion of the cavity under spin.
But my understanding was the OP was making investment molds on prints made of Wax Casting resin that she was burning out.

I would use the pattern I print from the form 2 or 3 to make an RTV silicone mold for injecting Wax to make the burning patterns- especially if I wanted to make more than one of a given design.
In particular, I would print the pattern with my sprues and vents in place so that the mold would produce waxes fully ready for investment.

But I agree about avoiding Vinyl— not least of all because it can not safely be used in the home studio- molten vinyl is seriously toxic.

1 Like

Thank you all for your answers!

I will try the RTV, see what happens :smiley:

I wish you all a great week!

This topic was automatically closed 7 days after the last reply. New replies are no longer allowed.