Help me make another attempt at shell casting

I'd add several smaller connections between the main sprue and the body of the piece you are casting. Angle them so they start at the main sprue and then travel upwards to the piece. That way metal won't pour down the main shaft and splatter into the different parts but it will rather let the mold fill from the bottom up without having to send all the metal through that small bottom connection.

Also the extra connections add stability. When you are coating it the entire structure is going to be extremely fragile and prone to breaking if you try it like it is.

 

Good idea zap.. it will strengthen the shell. BUT if he dewaxes in boiling water, the piece wont drain properly. I've been spruing upside down for 2 years and never had an issue. Or I have really good aim and pouring speed.

 

Autoclaving didn't work - maybe you have some ideas why. I did go on to try and vitrify the shell that didn't shatter and had a few cracks, but then the kiln burned out.

 

1st thing I notice is your shell is way too thin. You need to keep adding layers until you have a good quarter inch on all the wax parts. This will be 5 or 6 layers. Next the hole at the bottom of the cup is too small. What was the size of that sprue? That center sprue should be at least 1/2", I run 3/4" for bronze. Go fat, ya dont want that freezing before the part fills. I'm glad to see your wetting agent is helping. That might be due to the wax you are using that's not happy with the suspendaslurry. My ugly shit brown wax hasn't had any issues. Was there any chance the boiling water was rocking and rolling your pieces around in the autoclave? Unfired shell has very little strength, after 1700 degrees, it gets very strong. So any knocks inside that thing and they will break. You see me zippy tie shells to a frame to keep them from banging around in boiling water. How long did you run the autoclave? I dont have any idea what kind of time it takes to do this or what pressure is typically reached by the big foundries... You are in uncharted waters pal. I would fill that pot with water, get it boiling hard and submerge the part for 5 minutes. Keep trying. Thanks for showing the video. Carnage is cool!

 

Definitely too thin walled. Not sure if that's why it failed but it wouldn't cast with that wall thickness. There would be too much pressure from the metal and a piece of shell would blow out or crack.

No idea with using an autoclave/pressure cooker.

Jason's right about it rattling and needing to be secured.

 

We went down this road before. It's cheaper to buy them this way. https://m.ebay.com/itm/Kiln-Furnace...HE5RsLa7&_nkw=kiln+coil+5000w&_from=R40&rt=nc Cut to length.

 

I'll change mine out soon. Work has me swamped. They are the same size as what's in my kiln. After I stretch them, I bet I can get 2 out of 1 chinesium fleabay coil. How's that for cheapness?

 

Hey 01.. Read this page. http://www.aschome.com/index.php/en/dewaxing-autoclave

One word jumps out at me.... RAPID. I think the autoclave idea would work if you were using solid block investment. R&R seems to confirm my suspicion. https://docs.wixstatic.com/ugd/cc5f22_ac060636f38049f085c418bbc63a22ac.pdf

Your pressure cooker is too slow. Fatten up your sprues, point everything towards the cup and boil that sucker out.

 

I believe that shell had 7 layers on it (definitely 6 that I remember). Two with small-grain and four+ with large-grain sand.

I will stop using the thinner sprues and do everything with thick sprues. For the main stem, I can spiral 2-3 thickest sprues together. I like the tip with pre-heating the autoclave. It blew out a circuit breaker half an hour after boiling. I turned the power back on, and it was steaming again in 5 minutes. It will probably take longer if I actually open the lid and release the steam while putting the shells in, but maybe in 15 minutes it would start steaming again! I can weld stuff and I watched all of Jason's videos before creating this thread, so I remember the one with the fixture placed inside the pot to keep shells from getting damaged.

Thanks for the tip with the kiln coils. It's too late this time, but they keep burning out so I'm sure I will get to try the custom route in a 2-3 months.

 

I take a set of calipers and measure my wax sprue thickness. Then after I shell it, I measure it again. Keeping in mind you are measure shell on both sides of the sprue. You need at least a quarter of an inch growth of shell on all surfaces. If that takes 10 layers, then so be it. I usually hit my quarter inch at layer 6 or 7. This difference could vary if your slurry is thin or mostly dripped off prior to adding silica. It looks like professional autoclaves have the ability to heat up really fast and the dump a ton of steam in all at once. I know there has got to be a reason they cost upwards of 100k.

I didn't catch how long you tried running these in the autoclave... We talking 5 minutes, 30 minutes or 2 hrs????? Just like boiling, the shell is water soluble and too long and goodbye shell. Ya gotta be fast.

 

Everything you suggested worked - thanks again for sharing your expertise! Looks like we got one final problem with a frozen surface in parts of the cast. Here's a video of this attempt:



Here's the frozen effect. I poured at 950-970 and I skimmed a film of metal off the top, but it filmed over just as I was pouring.





What do you suggest to combat this?

 

I don't cast with aluminum but the hotter you pour it at the more it can shrink when cooling. Those areas look like it had time to crystallize and maybe shrink back a little bit. I'd try pouring cooler. Isn't optimum aluminum pour temp 700-750 C? Someone else will know on the forum for sure.

Also, that section is thicker than the others, so it cools last which means as the thinner outer parts freeze and shrink they pull liquid metal from the thicker parts which causes the thicker parts to shrink more when they eventually cool in turn. Either think out the thick sections so everything is close in thickness over the entire piece or add a thicker feeder sprue at the back of the part where it has the bad surface area. This will let the thick part of your piece pull metal in from the fat feeder sprue and hopefully prevent surface defects.

But I think probably pouring cooler will solve this issue since the shrinkage isn't so bad.

 

I usually pour at 700. Jason mentioned earlier that "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." I decided to pour a couple hundred hotter at least, knowing that he was probably talking about another metal.

 

Uh oh... did I cause that? What was the temp of your shell? I'm going to watch your video now. Looks like we got most of your problems licked. Zap is a bronze weenie like me. Where are all the alluminum experts???? DAVE put the house down and look at this.

 

Couple of questions.. Your dewax looks good. Why didn't you go for another dip and silica BEFORE cooking it? If not, no big deal, but you run the risk of it blowing apart. After you cooked it once, patch or redip and then cook it once right before you want to pour the metal. I have no idea how many times you can cook this stuff, but I've never cooked it more than twice. It shouldn't matter if you cook it 9times, but twice is all you should need.

Next... WTF is that sitting on inside your kiln? Is that steel? I think you would be better off with that thing standing up. Now I know it probably wants to fall over. Use a plinth or two inside to keep it from toppling over. (my thinking is even heat, blah blah blah)

3rd.. Painting or dipping it would not have mattered. You didnt have massive cracks that would have let the slurry inside.... With my 2nd fox, I went for a dip with 3 vents holes open. That was a dumbass mistake I won't do again.

4th.. WHY are you moving this thing around with molten aluminum in it? Notice when we pour bronze we cover the top of the cup with something like kaowool or a block? We are trying to get the metal to solidify slowly. That unique texture you are seeing is what I believe to be the crystalline structure of the aluminum. When I cast dave's buttplug and I'm not kidding here, I over cooked the piss outta the shell. I was at 1700 and I have no idea what the metal temp was. You are in uncharted territory here and a call to R&R might be worth it. I tried to get an answer once from them about pouring aluminum in this stuff and the chick I had on the phone was dumb as a bag of hammers.

If I was you, I would pull the shell from the heat and wrap it in kaowool or bury it in a bucket of sand to help hold the heat. I would then pour the metal and cover with some kaowool. Anything to help this thing cool slowly.

On the plus side, I'm glad to see everything filled nicely. It looks good, just need to nail down a shell and pouring temp. I'd love to know what this magical combination is. I'm sure one day, I'll get crazy and pour that silver stuff again.

 

Oh F, I almost forgot and this is SUPER IMPORTANT. What are you using for aluminum???????????? And you better not say beer cans and window frames. With this level of time, effort and hard work, I'd be using certified ingot or wheelium. NEVER extruded shit. That stuff is for the clowns on youtube making useless swords and junk.