Help me make another attempt at shell casting

Damn that was pretty cool. They both look pretty good. I would plan that center sprue to be a good half inch in diameter. I like the looks of the 2nd model on your fancy github thingamajigger.
I have to keep reminding myself you are pouring aluminum. If I had to do that jewelry box again, I would have moved those yellow sprues to the TOP of the pouring cup. I would do the same with yours too. Attach them high. Remember the front of the liquid aluminium. You will fill from the bottom, through the piece and last up to the cup. This keeps the very first part of the metal which is cooling as you pour, heading up and ultimately away from the final part. Savvy?

 

Hah! That is savvy. Spruing now!

 

I connected the secondary sprues higher as you recommended.



Looks like I am immediately hitting one of the issues I had before: the primary layer is developing hairline cracks.



Here's the first dip:



...and the second dip:



I did sift the sand on the area with the crack, but it did not stick. One thing to note is the slurry viscosity is supposed to be 14-16 seconds in #8 zahn cup, but when I measured 16 seconds there was still a quarter of slurry left in the cup and simply got "stuck" in there and stopped flowing entirely. I mixed for 20 minutes and added 1/4 gallon of de-ionized water. That took viscosity down just slightly, but I am afraid to add more water... What if the zahn cup measurement is wrong somehow? If there are particles that are clogging the zahn cup, then maybe I already have the 16 seconds of viscosity and if I keep adding water, all of a sudden it jumps to 4 seconds and there is nothing I could do, since I can't add slurry.

I double checked the sprues, I believe I am using 1/2" and 1/4" bulk extruded sprues from Rio Grande:
https://www.riogrande.com/product/Bulk-Extruded-Red-Sprue-Wax-12-dia/700020

 

If that main sprue is 1/2", it should keep flowing if you don't dink around when you pour. Pour it hot and hard. Now I remember why I don't use a zahn cup. lol Ya buy a precise instrument and then get left wondering if it's right. That crack in the first layer is interesting. It shouldn't effect anything too much, but still I don't like it. Is your wax the same temp as your slurry? I keep my crap in the air conditioning, then setup in the garage, do the dip, sprinkle the silica and then rush the piece back inside the house. I removed the lock off my pail and I keep the damn lid clean and I STILL have to strip to my drawers to grip the bucket with my legs sitting on the floor to get it off. This usually leads me to do dipping in my scibbies. Wife thinks it's hilarious to see my method. ANYWAYS.... lol Have you seen me do the thing with the air hose yet on my first layer? I learned this trick from Brother Bonzai on youtube. I dip, use a chip brush to make sure it coated, and while holding it over the bucket, I hit it with some low pressure compressed air. It makes the first layer of slurry nice and even and blows the excess off. The only time I experienced cracking so far was when my stuff got thick on me. Seems to me your bucket is probably still pretty full right? SO I doubt too much of the water has evaporated away as long as you've been good about keeping it closed up and tight. Last thing I will say and your probably already know this... If the stuff freezes, it's trash. Last question and this might be it... After you dip, how long are you waiting to sprinkle with silica? I don't putz around. Cracking can also be caused by rushing the coats. No forced air on the first or second coats. Third layer and on, fine.

 

Hopefully it

Yeah, better to feed fat sections first, but if he keeps his shell hot and pours quickly, I bet it will work.

 

Ahh.... Yeah you guys and this gofast, lightweight space age metal have that problem. Good reminder.

 

Still shelling, applied the first rough stucco layer today. Got two small fans and they decreased drying time by 400% it seems (corners getting orange after an hour). Just to double check, I am I supposed to go for 3 dips with small grain sand and 3 dips with large grain?

"Shell casting 245 pieces times 6layers of shell is 1500 dips." -Jason

 

According to R&R, it's 2 layers of fine and 3 or 4 layers of coarse. I recently have gone to 3 layers of fine and 3 or 4 layers of coarse. I haven't notice much change, but I seem to be cracking less shells. So I think you are on the right foot with this one. 3 fine and 4 coarse is plenty. Silica is cheap. After I move to the coarse silica, I am re dipping about once every 6hrs if I keep the piece INSIDE the AC with a small fan blowing on it. When it turns orange, I hit it again. I'm glad to see you are not casting all 245 pieces. You'll be on social security by the time you finish!

 

I have R&R instructions for burnout, but what's your timing and temperature control like? What would you do for the two shells I am working on?

 

I've read it. I violate about 6things on that paper. lmao. They want no flame impingement on the shell... And of course they won't tell you about the boiling water trick to remove wax.
I would be tempted to boil those 2 in water. It appears all your plumbing is going in the right direction and should let the wax float up. How have you been doing it so far? Flame thrower like I do sometimes? The best would be a preheated kiln or box that would evenly bathe the piece in nice even heat. The down side to this, if you don't have an opening under the show to get the wax outta there, you get a tower of flames! I did a boil out recently on my cattle brand and thought I had all the wax evacuated.. I inverted the pieces and stuck them in my pottery kiln. Did I mention microcrystalline wax stinks like hell and smokes like crazy in a kiln. I am working on a final solution for this goofiness and maybe someday will put it into practice. Barry at outbackfoundry.com has a good solution. He preheats the kiln, opens the bottom swinging doors and loads the pieces. Wax drips out the floor into a pan of water for collection, after it's done draining, he closes the doors and heads to 1700 degrees. He cracks very few shells.

To answer your question, I hit my stuff with a propane flame thrower starting at the cup with a pretty solid flame. Then I start working up the piece. Using sprues made from lower melting temperature wax helps as it clears a path for the wax to leave the shell. By the time I'm done, I've got a shell that is pretty damn vitrified. (meaning its mostly all white) You don't really want to heat the shell to orange or red colors, that would be nearing 2000 degrees me thinks. You know you can stop with the flame thrower when the wax quits dripping out the bottom.

IF you opt to try boil out which is a safer bet to not crack shells, have the water FULL BOIL, securing the shell to a lift out frame and dunk straight in. It only takes 4-5 minutes to have the wax float up out of the shell and you are done. Allow to dry overnight and into the kiln the next day. I ramp up temp kinda slow, say about an hr to prevent any explosions. (That would suck) Watch my boil out experiement videos.. 2 of them for this method. Remember CUP UP!

At the end of the day, a crack in shell is inevitable (except when you boil) and honestly it's not a huge issue as long as you fix them with some slurry and silica before pouring in metal. Zap had a crack recently in his chicken and it was a total failure. If the shell is SUPER complicated and has the risk of having a crack in some hidden location, (not yours in this example) I highly recommend going for another layer of shell AFTER dewax and a final coat of just slurry. It's cheap insurance if you can't see wtf you may or may not have. IN zaps case, it would have been wise. If you want to see what a crack looks like. Watch me dewax this test piece I ran a couple of years ago. This was 1/4" thick wax and that left a thin edge that wasnt wrapped with wire. You'll see the weird flame appear. I patched it before pouring aluminum and all was well.

This was the first shell I ever ran. Lots of learning took place on this.

 

I apologize, by burnout process I meant the whole thing from wax evacuation to pouring (i.e. preheat to 100, hold 2 hours, ramp to 2000, hold 2 hours and how many hours total.) I have a large pressure pot that I used to cleanly steam the wax out. Our hackerspace is small and packed, so just like that lady from the university you talked to, I have to be super careful with pollution because there are people wearing VR headsets and looking at E. coli in the microscope next door.

 

that ramp up, hold stuff is for solid investment. Try that with shell and will surely crack. Did R&R tell you that works with shell?

Shell can be dewaxed, NOT vitrified in a pressure cooker or even an autoclave. I view the process as two steps.... 1st there is Dewax and then there is Burnout (or vitrification) My reasoning for conducting this 2 step, is it gives me an opportunity to inspect for cracks and also to patch relief holes I might have drilling in the shell. After repairs are made to the shell, I conduct burnout right before I pour. That's when I run the shell up to 1700, pull and pour the metal.

 

I am planning to use the DIY autoclave (https://www.amazon.com/dp/B00MCLRFQW) to de-wax and a manual ceramic kiln for vitrifying. Now that you mention it, I reviewed all records I had of the vitrification process and found the only reliable source to be Investment Casting by Beeley & Smart:

"Pores within the loose silica structure still tenaciously hold some water. Indeed this water will not be completely removed until a temperature around 1000°C/1832°F is reached..."
"The silica gel in a dried green mould is the same material as that used as a desiccant. It is capable of absorbing moisture which will, as with a desiccant, be driven off at about 300°C /572°C or above"
"The first requirement of the heating process is to burn off residual wax from the dewaxing operation and to remove free volatile liquids"
"A minimum temperature of 500°C/932°F should be maintained, but it is preferable to increase this to around 800°C/1472°F to ensure rapid removal of residue"
"Firing the mould to 500-800°C [932°F-1472°F] will not by itself be sufficient to sinter the mould and render it inert to molten metal. Many foundries fire within the range 950-1100°C [1742-2012°F] to achieve reasonable inertness and high mould stability"

What this translates to me: "preheat the kiln to 1500°F, insert a de-waxed shell that needs to be vitrified, wait about an hour to enable water to evaporate and any remainders of wax to burn off, then take down to pouring temperature and pour"

 

Fancy DIY autoclave. Hot steam bath could work too if you could generate a lot of steam fast. Brother Bonzai corrected me today and said it's not really vitrification as that would make the shells completely solid and non porous. I do believe I read somewhere at R&R that was the term they used so the jury is out on that one. Your numbers above look right to me too. Again, the final temp of the shell for pour depends on the metal being used. Your 1500 is hot enough to do the job. Once you pull it out, I bet it will lose a couple hundred degrees in a minute and be perfect for aluminum.
Video this autoclave process, I'd be interested to see how that works. 300bucks is cheap if it does the job with no fuss. The big boy foundries have REALLY big autoclaves and they can cost 100k. From what I've read, even that process suffers cracks too. The only thing I've found to be almost 100% is boiling in water. Crazy stuff this shell is. The cheapest method has the best results.

 

The autoclave process using a pressure cooker works amazing for UltraVest, I will video the results for shell casting to see if that still holds.
I know I am lagging on the cast, but this week was rough at work so I took time to recover.

 

We run ultravest in florida at the jewelry shop. No autoclave, we play the ramp up game with wax. We also invest RESIN straight out of the b9c creator. Now there is a goofy ramp up schedule. You HAVE to have a pid or forget it. No worries man, everyone is busy this time of year, a good casting is better than a fast mess.

 

Last couple weeks work was crazy and I am terrible at making quick decisions, so I broke a bunch of equipment and ordered wrong supplies. While I am picking up the pieces and waiting for replacement parts to come in - how does this sprue plan look?

https://github.com/01binary/sprue-planning/blob/master/chest-sprues.stl

More than likely my first shell will be a failure so I am getting a second iteration ready to go.

Thank you!

 

Looks good to me! Should have no problems at all with that. You'll find shell is very forgiving to bad plumbing jobs. Did ya see that last mess I poured? Still worked perfect and there was a lot of crap on that tree.