Boiling out Ceramic Shell

Add one more thing to the to do list!

I came across an interesting article on the web late one night. http://digitalcommons.buffalostate.edu/cgi/viewcontent.cgi?article=1000&context=noreaster After reading it, I dropped this chick an email asking for some advice. I showed her the video of one of the foxes pissing wax before Artospy and I fingered out the slurry had a thickness problem. Some of you will remember seeing the photo of an unfired fox with a crack.

Anyway, here is the email I sent to her and her reply is most fascinating. Time to run an experimental rig. WHO WANTS A BP???? Anyone else interested in seeing this???? Please be sure to chime in with any suggestions. Thanks!

Hello! My name is Jason and I cast bronze art pieces at home. I recently found a small piece you wrote about boiling wax from ceramic shell. http://digitalcommons.buffalostate.edu/cgi/viewcontent.cgi?article=1000&context=noreaster
Do you have any more information on this? I recently have been getting cracked shells and would like to explore other options. Here is an example of shell cracking I had despite taking the usual precautions.


Thank you!

Jason

Her Reply........

Hello,
Sorry for my late response. Unfortunately I do not have any paper published. John Hachmeister at Kansas University and Green Foundry in the northeast also practice the boil-out routinely. After watching the video- the cracking is definitely because of the “slow” temperature rise. The wax is expanding long before burning out. This is avoided by “flashing” molds – preheating a kiln to 1600 + degrees F before introducing the mold.

That being said, I actually prefer burn-outs over boil-outs, due to time required as I note below. We went to boil out due to smoke production complaints on campus. We do exclusively boil out our shells with a nearly 100% success rate (much higher than most burn-outs), however it is a long process waiting for water to boil. Usually it takes 2 hours to get the water ready, then only 45 minutes to boil out as many as a dozen or two small molds. You can keep running a few boil-outs while the water is hot until it is too saturated with wax. I know people who have developed troughs to skim the wax off the top but I never have bothered as I usually only have 2 or 3 rounds of molds at a time.

Key points- cups up always, no need to drill holes, pack molds tight (we use a basket that we lower into the tank and if there are not enough molds to pack it tight I wire molds to the basket as the boiling water can crash small molds around), before pouring take up to around 700 degrees F for at least a few hours to eliminate moisture.

I hope this helps- it is a very clean process, you do reclaim almost 100% of wax (and it is clean!) but it is something that you have to prepare for the time commitment of waiting for water to boil.

Best
Elizabeth

 

This is great info jason, thanks.
I will definitely give it a go in the next month or so (moving house and workshop again). If i can plan to take the extra time to boil this will be great for me to reclaim all the wax and not have to deal with the smoke. I could probably do it indoors too while getting on with other things. I guess it takes a bit more propane but small price to pay.

 

Hmmm.. I must be burning up all my wax during flash fire. I don't think I have much smoke, but I can't really tell dodging flames and trying to keep my recently grown back eyebrows!
Remember when I did the dimensional dewax over at AA? I did it low and slow. The main issue I saw was the shell was going bell jar on me. The shell withstood that slow torture of going in hot water just fine so I'm really thinking if the water is at a roaring boil, the wax should get out really fast and leave the shell intact. She says cup up and tied in place to keep from banging around. That kinda tells me they don't screw around and just dunk that sucker to the bottom! That will be my plan. I'll get to work on it and you can bet I'll film the boiling!

 

Yep, i understood it as bringing the water to the boil and lowering in the shells ASAP.
Im thinking of cobbling a quick rebar basket to lower the wired shells into the water.
I should probably test it on a small mould first before i weld up a tank and basket tho. I am feeling quite positive that Elizabeth says she gets near 100 percent success with no drilled holes. That to me is worth the 2 hour heat up time for the water.

 

TOTALLY worth the 2hr investment to boil some water. Gives me plenty of time to have a few beers watching water boil.

This my friend could be a serious game changer for screwballs like us!

 

Exactly what i was thinking, game changer!

 

Here is the test mule. I whacked off about 6inches of a lantern frame.
Only spent 2mins chasing the wax so don't expect much.
After the layers of shell, I'm going to follow my usual routine of removing the hook
and opening up the cup until I can see the main hollow sprue before dewax.

 

Hmm. 2 hours is a while. I'd like to see how that piece works out. Especially the thin parts.

Also, I imagine cleaning wax off the surface of the water is going to be a pain. Every time I've mixed wax and water I've regretted it. It becomes difficult to separate out properly.

 

2hrs to boil. I bet it takes less than 5mins to remove the wax. I found a big ass pot and we should see something in the next day or two.

 

They sell huge pots at walmart for cheap. They rust pretty easily though. As one local down here told me "all you need is water, fire, and a hog head... or a possum"

 

Found a big tall aluminum pot down in cajun country. Pretty sure its had a possum or two boiled in it. They don't make them like this unless you drop some bucks.

 

Pics!

 

In progress now..

made a home made burner and cobbled up a stand for the shell to be zippy tied to. Water is heating up. Time for another cold one while I wait.

 

Burner is a beast. took 25mins to boil. took about 5mins to boil the shell.

Looks like a winner!

 

Hmmm. Looks like a good boil out. How was it to get the wax off the surface of the water after? I wonder how long you'd need to wait to fire the mold before using? The water in the shell might flash to steam and cause issues if wet.

 

No different than regular dewax. Ya let the water cool and pick it off the top. The only difference, the wax is clean when you boil it out. With flash fire, the wax gets little bits of silica that has to be filtered out via my panty hose method. I checked the shell last night sitting in a hot and dry garage after about 8hrs. She was just about dry as a bone. I gave it one coat of slurry and a sprinkle of coarse silica and called it a day. Now if the winds here will give me a break, I'l heat it up to 1700 and pour some metal.

 

Nice. Go for it! I'll be watching from the side lines haha. I might get the second furnace made this weekend.

 

I wanna see how you guys plan to collect the wax in the bottom of that thing. It would be best to get the furnace up to temp and then put the shell in it without losing all its heat. This is why I am considering a 2nd rig with a lift off top. The burner will lift with the top and stay running while I sneak the shell in from the side, lower the unit and instant full on even heat to the shell. Collection point of water directly under and bob's your uncle. Lots of ways to skin this cat with many pitfalls for each method.

 

YAHTZEEE!!!!!!!! Surface is bang on the money! I've spent hours with this and I know every detail on this piece.
I will be using this boil out method again for sure! I would not take a second dip as it wasn't required. I gave it about
18hrs before putting in the kiln. I didn't pussy foot around either. I set it to high and walked away.
Maybe by doing a small section from one of my lantern frames, this will light a fire under me to get rolling.



And a video of course to go with it. No theatrics, no music, just the pour and breakout. I don't think the shell
breaks off any easier or harder really.