Vacuum casting attempt

From molding systems to gating, what goes on at the molding bench will make or break a casting.
Rasper
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Re: Vacuum casting attempt

Post by Rasper »

Here where I live, May is the hottest month of the year. A few days ago I put my thermometer outside the front door at 5:30 am. It was 87 degrees. I have a wax ready to invest, floating in the tub of water, but I am too lazy to do it. My sculpture studio is air conditioned and I have a number of pieces in process up there in clay. Most of them I will, at some point, abandon as failures, but two of them are good. I need to go up to Mexico City and buy some polyurethane rubber to make the moulds, along with some foundry supplies, but I have been too lazy to do that. I will be 74 in several months, and I doubt if I will be getting less lazy with age, so I better get off my ass and get to work.

Richard
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Jammer
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Re: Vacuum casting attempt

Post by Jammer »

We're coming into warmer weather. I have a plan this year to get up earlier so I can get some stuff done before it gets too hot. The main problem is that I'm not a morning person. Even after 17 years of swing shift, just get up at 5 o'clock and go to work, didn't matter if it was am or pm. I only messed up one time and showed up to work on my day off.
quando omni flunkus moritati 8-)
Rasper
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Re: Vacuum casting attempt

Post by Rasper »

I get up at 5:30 or 6, but all I do is go for my long walk and then sit and drink coffee until 10 o'clock. In college, after my first semester, I never registered for a class before 10 o'clock. I have always been amazed by people who just pop out of bed and get going. How can they do it?

Richard
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Jammer
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Re: Vacuum casting attempt

Post by Jammer »

I actually got busy yesterday and tried to cast the investments I did up a couple months ago. I'm sure it wasn't a good idea to leave them sit for a long time before burn out. They were showing signs of cracking. I had planned on about 8 hours to burn out since they were small. put them in the kiln early in the day and went on to do other stuff. The kiln is only 20 amp and heats up very slow so I don't think it needs to ramp up. It took 2 hours to get to 1000F. Then it went pretty quickly to 1500F. A lot of smoke and some fire, then it settled down and I let it soak a couple hours while I melted the bronze. I tried to keep them under 1500F but I don't think I trust my pyrometers.
Anyway, the metal sleeves were loose and wouldn't have allowed a vacuum so I just poured some metal in and they came out terrible. It was a learning experience. I wonder if the investment would have stayed in the tubes if I burnt them out shortly after I poured the plaster mix? Or, will I have to buy the real stuff for doing this? I'm a cheapskate but I would buy some if I could find it locally. I just hate to pay as much for shipping as the product costs.

Here's a couple ugly pictures.
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quando omni flunkus moritati 8-)
Rasper
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Re: Vacuum casting attempt

Post by Rasper »

I can't imagine why sitting for a few months would harm a plaster based investment. Plaster statues several thousand years old live in museums now.

Richard
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Jammer
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Re: Vacuum casting attempt

Post by Jammer »

Well, it's been more like 7 months. These were poor invests to start with since the plaster set up to fast. I'll try it again with the citric acid to slow it down. I just hope the metal sleeve doesn't expand and slip off again. It's hard enough to pick up 1200 degree molds without it trying to come apart.
I think the small one would have worked better but I hesitated for just a second while pouring and the bronze froze up. I only melted a couple pounds and didn't realize how fast it would cool off after I took it from the furnace. I shouldn't have stopped to take a picture either.
quando omni flunkus moritati 8-)
Rasper
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Re: Vacuum casting attempt

Post by Rasper »

What exactly was your investment mix?

R
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Jammer
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Re: Vacuum casting attempt

Post by Jammer »

I went with 1 1/2 sand to 1 part plaster by volume.

I wonder if anyone has added Fireclay with the sand and plaster. If it would act as grog or make it stronger or weaker??

I forgot I have another pyrometer, I'll have to get it out and see if it agrees with either of the other two. I think I was a 150 to 200f hotter than the analog said, which was near what the meter said as far as temp. I couldn't use the microvolt because I didn't have the info handy to convert it.
quando omni flunkus moritati 8-)
F.C.
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Re: Vacuum casting attempt

Post by F.C. »

Definitely needs to have a sufficient amount of "grog" in with the mix of sand and plaster. I used broken bits and shards of bisque fired ceramic as grog. I also wrap my investments with chicken wire (as an outer shell wrap within the investment mold) as "all" investments will ultimately crack and allow for leakage of melt if not held together tightly. Also.... I didn't see evidence of any riser vents on either of those molds. Looks to me in the pics that air was trapped inside the mold thereby not allowing for full fill of the voids.
F.C.
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Re: Vacuum casting attempt

Post by F.C. »

A proper pour cup, too, is beneficial (conical shaped, wide at the top, narrow at the bottom) and when you pour a mold "gagging" it will ensure you don't force additive air down into the cavity that may overcome any air vents attached. Gotta ensure the air gets out as the metal goes in. Venting is critical, even if done to excess.
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