Ontopic Manly Dudes Doing Manly *porkchop*

Mr. Argumentor

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Sep 27, 2012
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I think I've mentioned that I've been working towards doing cast iron pours. The past three Fridays myself and a couple guys from USF's Art Dept have been working on getting up to speed with pouring bronze. Charles is the young guy, Don is the older guy, I'm the bearded guy. Don basically grew up in a family that did metal casting and general foundry work, so he's been our guide for this.

My goal is to design something in Solidworks, 3D print it, then cast it in metal and be able to put it to use. We did that with this.

The 3D printed parts are the shift-lever selector for a 1954 Goodyear SeaBee 12HP outboard motor, also known as a Gale 12D10. The one that came with the motor was bent just above the curved section at the bottom of the part and fatigued enough that it broke when I tried to shift the motor.
I took measurements, designed it in Solidworks, then printed it. I had a couple clearance issues with the gray piece, so I redesigned it, printed it and went to make a mold of it.

Quick vocab
Sacrificial Positive - Basically exactly what it sounds like, the part that you are trying to make at a much lower melting/burning temperature than anything else in the mold.
Investment - the mold that is the negative of the part you are creating. In this case, a type of plaster of paris that can withstand higher heats than what you'd find in most stores.
Sprues - what the molten metal flows into from the cup
Cup - a reservoir at the top of the mold that holds molten metal so you can pour easily, basically a funnel in the mold.
Gates - Connects various areas of the sacrificial positive to ensure that every part gets an adequate supply of molten metal. If you don't have these you might end up with gaps in your final piece

To make the mold, the first thing to do is make the sprues and gates. These are generally made out of an organic wax that melts away easily, and burns off as CO2 to leave a very clean mold. Once these were made, I turned the piece upside down and melted the wax to a rubber mold that had the cup built in. Slide a stainless steel cylinder into the rubber mold.
The blue webbing you can see is made of that same organic wax that I mentioned earlier. It's purpose is to allow vacuum to reach more of the mold. More on that in a bit.

Mix up the plaster, pour it into the cylinder, put everything under vacuum to remove as much air from the mold as you can. This gives you a better mold, and a better final part. Wait for a day for everything to set and cure, then you're onto the next stage
Tangent: This part worried me a little bit. 3D prints are mostly made of air. There is an outer shell, usually 2-3 layers thick that gives you the appearance of the part, the inside of the part is a honeycomb. The more infill of the inner part, the stronger it is. Default for most 3D prints is 2 outer shells, 10-15% infill. That means that 80-85% of the part is going to be air. If the outer layers are not airtight, you could pull in plaster and have a void in your final part. Happily the plaster was thick enough, and the outer layers tight enough that this didn't happen.

From here, you burn out the sacrificial positive and cure the mold. If you are ready to actually cast at this point, you do a heating pattern that brings the entire mold up to a temperature so there is no thermal shock when the molten metal comes into contact with the mold.
Depending on the size of your mold, you do a slow heat to around 300*F and hold for maybe an hour to burn out all of your sacrificial positive (the wax melts at a fairly low temp, and the ABS plastic is printed at 230 Fahrenheit if I remember correctly,) then you do several step ups to a much higher temperature, I think our final heat temp was 1500*F and it took 5 hours to get there?

While this is happening, you are doing a dry run of your metal melt and pour procedure. Communication is important as you are going to be handling roughly 8-10lbs of metal at around 1800-2000*F, if you drop the crucible from just a couple inches it can splash molten metal up to a couple feet away.

Place the loaded crucible into the furnace, then start the furnace. Wait for roughly an hour, check the level of the molten metal in the crucible. For our purposes we had to add more metal, and a little bit of flux in order to help aid in everything melting. When you do this it's best to turn the flame off. We also placed the additional metal on top of the furnace in order to pre-heat it so that it would not lower the temp of the metal in the crucible too much. As it was, with the furnace off and opened, and adding maybe a pound of additional metal, by the time we added the last piece the metal had cooled to the point that we couldn't put the last piece into molten metal.

Wait maybe another hour for the rest of the metal to heat, check the temperature a couple times till it's where you want it, then get ready to pour.

Bring the mold out of the oven where you've pre-heated it, put it on the vacuum plate and turn on the vacuum. The plaster is porous enough that it will pull vacuum through it, and you've added that blue wax webbing earlier so you have a greater path for the vacuum to reach higher into the investment mold. Pull the crucible out, place it in the yoke, tighten the yoke, then walk over to the mold and pour. Pour your excess metal into a waiting ingot tray (as we did) or pouring it into a waiting bucket, pour it slowly enough so that it is not a stream but individual drops so that it cools as individual beads which allows a quicker melt next time.

Wait for 5-10 minutes or so, then take the mold off the vacuum and carefully dump it into the bucket of water you've prepared. The metal is still orange hot, so is the investment. This causes the water to instantly flash to steam and erode the investment material. After 4 or 5 dunks, the piece should fall out of the metal cylinder. Wait another minute or two, then pull it from the water.


Other than final machining to remove the sprues, gates, and any bubbles caused by air holding onto the positive when the mold is poured, you're good to go.


 
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That is about as manly as it gets. Scary molten metal!

Maybe making some samurai swords or some such, that's gotta be pretty manly.
 
That would be forging, not pouring.
Oh ok yes. I saw a documentary once where they were folding and refolding metal to make hard metal swords. Very interesting. They said that swords are regulated in Japan like guns are elsewhere.
 
Didn't know that. I can believe it, though

And now that I think of it, I think there are some swords that are poured, not forged. Those tend to be more western style swords, though.
 
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Didn't know that. I can believe it, though

And now that I think of it, I think there are some swords that are poured, not forged. Those tend to be more western style swords, though.
Yeah, they said that to get the best swords you have to fold and refold a bunch of times. And heat and cool and heat and cool. It was interesting to watch.
 
I have a friend who makes swords. I have another friend who swallows them.
From what I have heard, the hard part of sword swallowing isn't the gag reflex at the back of the throat, but the secondary one roughly in the middle of the sternum.

I've seen how to make a blade out of a file, I want to do so myself one day.
 
I had a girl work for me some years ago who could do sword swallowing. She announced proudly that she lost her gag reflex when she was working as an 'escort'.