yes, Greensand weather its water or opiol bonded is reuseable many
many times..........probably never wear it out in a home shop
environment. When it gets weak in strength, you add more binder and
add oil or water and remull it and use it again.
So its important to not put anything that may screw up your sand in
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I had no input whatsoever.
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IIRC, the "This old house" show was investment casting where the
mold is ceramic. Usually around 1/8" thick. The ceramic is fired
at something like 2000 degrees, comes out of the oven, and is the
pour is done within seconds. I've seen stainless steel done this
way, mold is glowing bright orange, pour in the steel and it
instantly goes incandescent.
Joel Corwith wrote:
I got a personal guided tour of a high volume investment casting
house. Brass, aluminum, stainless, you name it. Pretty nifty
I also found the prices qouted on the TOH segment to be pretty
outlandish. The shop I toured would do them for about 20% of the
price quoted on TOH This would be in quantities of 20 to 50 or so.
Joel Corwith wrote:
That's because they're just a bunch of slobs who do investment casting.
TOH only deals with artistes, who have better marketing -- er --
aesthetic -- skills.
They used plaster of paris, prompting me to do some web research.
Apparently it's a good way to do near-investment quality casting in
aluminum and bronze, but can't be used with steel or iron because the
melt temperature is high enough to fry the plaster before the cast
solidifies. Do an Altavista search on +plaster +aluminum +casting or
some such for links.
I memory serves me,,and sometimes it doesn't,, thought they were
investment casting those doorknobs,, if that were the case they would
have been removing the molds from a burn-out oven after burning off
Dies, I had the privilege of shoveling greensand into a muller as a
night job while in high school oh-so-many years ago. The foundry was in
back of a pattern shop, and 2-3 nights a week and Saturdays, a top
skilled foundryman would work a second job there. He was a magician
with sand, an expert marksman, and had the steadiest hands of any person
I have known. He could draw a cylinder eight inches tall with less than
a half-degree of taper on the sides up out of a mold freehand, and never
disturb the sand at all. I would hold my breath while he did some of
On to some suggestions:
1 Make the sprue larger (1.5"- 2" is not out of the question)
2 Make a big reservoir in the drag (bottom) offset toward the casting
3 Cut wide, thick gates in the cope, (top) from the reservoir to
multiple points in the casting. I saw one thin section cast with a gate
leading more than half way around the casting. At intervals, feeder
gates were cut in the sand from the surrounding gate to the casting.
4 On the farthest corner from the sprue, poke a 3/4 inch diameter riser
up through the cope a short distance away from the casting and gate this
to the casting. You need the air to get out of there fast! It also
serves as a secondary reservoir to reduce shrinkage as the metal cools.
5 Pour as cool as possible. Having said that, the red-almost orange
color mentioned in another post is my best memory of what we poured at.
The molten metal in the pot will be dull on top, stir it a bit to
observe the color. BE SURE THAT EVERYTHING that touches molten aluminum
is DRY! 1200 degree steam has a LOT of power to throw metal in the
wrong directions [first hand experience talking].
6 Work the sand fairly dry if using water bonded greensand. Water
(overly wet sand) rapidly cools the metal.
The theory is kinda like this; you want a lot of molten metal to move
into that hole in the sand very quickly with minimum turbulence. The
cooler it is, the smoother your casting is and the slower it flows so
the metal freezes quicker, with less shrinkage. BUT,you want the metal
hot enough to flow into all corners and pick up the detail, however the
trade-off is... at some point the metal gets hot enough to actually
shape to and bond to the grains of sand. This gives you a nasty casting
covered with silica that will dull your hss tooling very quickly. At
even higher temperatures, you alter the alloy and burn off some
elements, causing ugly castings.
Some alloys just don't flow quickly. If you are using scrap extrusions
for your pour, you may not have as good a luck as with a specific alloy
made for casting (no flames on this, please! I use scrap too).
Good luck! When you are through I might be interested in the patterns...
Rex in Portland in the rain, wishing the forge/furnace was running today.
Wow! Would have loved to see that guy in action. It would make a
wonderful piece for the History Channel.
And a hardy thanks to all! I did a perfect casting of the base today!
I experimented at night to get a feel for the temperature using a
steel rod to check the metal. In one or more of the many suggestions
that I read, someone said the temperature would be correct when the
aluminum stopped sticking to a small steel rod. That seemed to work
I tried bigger vent's than just a small wire and put the sprue
directly in the center of the pour so that the metal would only have
to make one turn to be in the mold. Don't know if that helped but it
seemed to make sense to me.
Anyway, bottom line is I got the base for my lathe! And I feel like
I learned a lot. Well, maybe a little...
If time is the 4th dimension, then money is the 5th dimension.
We are always concerned about dollars per hour for the space we occupy.
- Rod White
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