Over the past week I have been shell investing some different parts for casting in aluminum using the SuspendaSlurry system and fused silica sand. I am very please with the result so far. All my parts are now ready to be burned out and cast. Hopefully this week. The SuspendaSlurry is much easier to work with than my 2 previous brands of slurry. I just stir the container before each dip for the day. It seems to dry very quickly in 70F workshop. I used fine 50-100 fused silica for the facing sand and 30-50 for the subsequent coats. I will try burnout on the wax patterns first and then see about the Polycast burnout. Jgaertner
Just an FYI. I was doing some of these and dealt with cracking when I fired them. Found a guy on YT wrapping them with light fencing wire after 4-5 dips. Says it has worked well for him. Just in case you run into that.
Thanks BattyZ, I sure hope I do not suffer that issue. I saw the same video. I went with 8 coats of slurry/Fused Silica. I am going to try the burn out on my wax pattern first. I have an electric burn out oven so I feel I can have good control of the temperature. Will report back to the forum what happens? Jgaertner
Get a roll of .032 airplane safety wire and wrap between layers 4-5. The stuff is very sensitive to long thin edges and can blow out from the weight of your metal. What is under that slurry? Wax or foam? You'd be surprised the kind of crazy crap you can cover in slurry and burn out. Wood, pinecones, foam, rope, pretty much anything that will burn out. I do suggest after burning crap out, let the shells cool nice and slow and water test them. They should also ring when ya tap it with a finger. If ya get more of a thud, find the crack. I patch with a mix of slurry and silica. Often times, I'll even add another layer or two. Be careful, if you get any slurry inside your shell, you will see it in metal, so watch vent holes if you use them. Maybe david will be so kind and show you his ceramic shell lost foam buttplug.... I'm sure it's still sitting on his desk at home.
I did my burn out yesterday for 8 wax patterns and one PolyCast. They all burned out great but I suffered a oven element burn out during the second batch. I will need to replace the element and try sintering the invested patterns again to try and remove the remaining soot. I am happy with all the parts burn outs. No cracks or issues. I did slowly cool them in sand and I did water test some of the ones that were cool at the end of the day. No leaks.
Good job John. Couple of questions for ya... 1. What wax are you using? 2. How many layers did you do? 3. Did you burnout low and slow or hot and fast? Just tossing shelled waxes into a kiln and melt it out seldom works. I'm guessing you've seen the what some of have had to do to prevent shell cracks? It's the Achilles heal with this process...
I have been lucky. Only the Shellspan invest I used in the past cracked badly. I use Freeman Flakes "Tuf Guy Green" jewelry wax. I used two slurry layers and then 2 layers of fine silica sand and finally 4 layers of course silica sand from Barron's distributor in VA. One last cover coat of slurry. Allowed all parts to try at room temperature for 1 week in my shop. I placed room temperature invested parts in a 750 F oven until the smoke stops for the most part in my un-vented burn out oven. Smoke leaks from under the lid. Then I ramp the temp to 1250 F at 150 F increments. Hold that for 30 minutes. Allowed the oven to cool for a while, then removed the burned out patterns and then bury them partially, in metal cans with PetroBond sand that has no oil mixed into it. I allowed them to cool to the touch. Picture shows cooled patterns. I plan on re-heating all the parts before casting. The one with all the soot on it need a longer firing, I think. Not sure why it did not clean up as well. The other parts are very clean inside and out.
If you are still looking at black shells, it's because the wax is still there somewhere. That black is just soot from the burning wax. Do not ever pour metal into a black shell. Very bad things could happen when molten metal hits that wax! Heat that shell again until snow white. When pouring bronze, I preheat shells to around 1700 and I think guys have best results around 900 for aluminum. So whatcha making?
Thanks, I plan on re-firing all my shells as soon as I get the new element in. Will take all the shells up to 1250 F and hold for 30 minutes, like I have done before. I will know then whether all the soot has burned off. Jgaertner
I've opened my kiln wide open when I thought everything was gone! Boy did I get a surprise! BIG WOOF! The good news, eyebrows do eventually grow back! Now I just play, sneak a peak.
