Back to Ganoksin | FAQ | Contact

Burnout kiln ventilation system


#1

Hi all

I just got myself into 3d printing with castable resin and (as many) I am experiencing resin residue which leads to bad casting surface. Nothing major but still I would like to solve this problem.
I have tired increasing temperature but this didnt helped much. So next try would be adding more air.
I have small electric burnout furnace 14x20x16cm. There is one exhaust port on the back. I tried to keep door slightly open but this is still not enough. I know you can drill holes in bottom of kiln but I would like to dont do it if I can.
There is Neycraft Vulcan Venturi furnace which some say works very well for this task. So I would like to modify my kiln to have similar exhaust fan like Neycraft.
Problem is There is no blueprints or pictures of how it is constructed on Neycraft Vulcan. I do not know anyone nearby or any shop who have this furnace so I could look at it in person.
So is there anyone willing to take few pictures of Neycraft Vulcan Venturi exhaust system? I would like to know how it is connected, what is inside fan exhaust duct etc.
Any suggestions and help are welcome :slight_smile:

Cheers,
Marek


#2

Hello Marek,

congratulations, you joined the crowd of those who suffer from the results of so-called castable resin and complain about bad casting surface.

Surface defects may be caused by multiple effects. In order to verify your initial guess of resin residue just take a random, reasonably solid pattern with a clear structure. Put it into a new crucible and burn to the burn-out temperature recommended by the resin manufacturer. You may check every 50°C what happens - this will give you some extra insights. If there’s any visible residue at the recommended burn-out temperature, you might want to change to another resin or/and another 3D printer.

If there are no residues, then your problem originates from other causes along the process. These may be (among others):

  • chemical reaction of the resin with the liquid/fluid of the investment during the setting phase,
  • swelling of the pattern caused by hydrophilic properties of the resin,
  • expansion of the pattern without melting during ramp-up temperature,
  • and many more.

I assume that you are not interested to contribute an academic essay on possible causes and effects. Therefore it is not reasonable to investigate on the causes of chemical reaction, swelling and the like.

A more pragmatic approach would be to use an investment with increased thermal expansion and preferably one with setting expansion as well. By this you can eliminate the effect of intrinsic force generated by pattern expansion. We have developed Invest RP for this purpose and you may contact the smart guys at Stuller for this.

To get back to your inital question to get a better burn-out result, the approach to add air or oxygen, to be precise, will lead to a faster carbonization but the result will be the same as long you have residues.

J. Tyler Teague is savvy with this, and if I’m not mistaken he addressed the procedure of how to increase air ventilation in burn-out kilns either in the MJSA Journal or in this forum. You might contact him for advice if he’s willing to give a helping hand.

All other causes, addressed or not, you don’t want to know and don’t want to solve either but turn to a resin/printer without these troubles.

My 2c.

Sandor


#3

Thanks for quick reply.

Sorry, i have forgot to mention about these few things.

Investment is R&R plasticast, benchset for about 3hr after investing.
Burnout is very similar to that recomended for plasticast but to be safe I use one provided with resin - which have only longer high-end time(4hr instead of 2)
Flask up to 2"x2" but usualy smaller than that.
Prints are cured rock-solid.
I am sure it is not investment brakedown. For me it looks like residue inside mold - incomplete burnout. Its not major but some very small surface depressions in few places on object.
I have also tried what you say with burning investment without investing it. And it burns clean. But This is somehow different than burnout inside invested flask - reason is airflow, which is drasticly reduced when something is covered with investment.

I know that this resin can be cast without surface defects - but persone who does it have diferent casting setup. Big old burnout kiln and induction centrifugal casting machine.


#4

James Binnion has done the research and published a paper on this. You can find it online for free through the Santa Fe Symposium site. It is in the 2016 catalogue of papers. “ A New Method for Preparing 3-D Printed Acrylic Photo Polymers for Investment Casting.”
Have fun and Make lots of jewelry
Jo Haemer
www.timothywgreen.com