October Melty 2009: Direct sand casting without foam!

TechNinja's picture

Though I've been waxing high on lost foam casting for some time, I've always revered and looked up to a "higher level" of aluminum casting, green sand split casting. The following recounts my adventure therein.

Using google as our guide, me and "The D" found quite a number of green sand casting resources, namely Foundry101 and Eugene Sargent's Sandcasting Primer. Both excellent resources.. that we probably could have stood to study a little harder before taking on the project.

It's not that we're against reading instructions, or well written detailed how-tos with helpful photos or graphics.. Heavens no! It's more to do with the fact that the learning process so often simply boils down to just doing something, not reading about it, and hoping to try, or matching every single instruction. So we just skip straight to the actual learning part.. which usually means we do more trial by error than we probably could with reading everything extremely well.

But where's the adventure in that?!

The Plan:

  1. Build two strong interlocking hinged frames to hold the sand and mold
  2. Mix the green sand clay together in the right amounts
  3. Pound the green sand into the bottom mold to test
  4. Add the items to be molded (A rubber spatula handle, and a marble egg)
  5. Sprinkle "parting dust" on the top of the molded items and sand, to keep the top sand from sticking to the middle
  6. Add the top frame and pound the rest of the green sand to form the top of the mold
  7. Carefully separate the two frames and remove the items
  8. Then using a pencil, etch the troughs in the sand for the metal to flow from the runner to the cavities
  9. "Drill" the holes for the main sprue to the runner, and vent holes for the steam to escape from the molded cavities
  10. Pour the aluminum, and retrieve the finished product!

The following pictorial is a catalog of mine and "The D"s adventure in green sand casting.

We found some old slat of wood, and guessed that about 12" x 18" x 3" would be quite reasonable for each of the frames.
A quick stop over to my Dad's workshop, yields some amazing helpful framing clamps, some hinges, and self tapping screws.
The idea is that two corners of the frame stay attached, and the two opposite corners are connected with a hasp and a hinge.
The D sketches out an alignment cut to ensure both frames match up when removed.
The finished alignment piece attached to both frames.
The D takes picture of the area for the hasp before a quick trip to the hardware store to buy a couple
The finished and attached hasp and frame. Beautiful!
The D files down the edges of the decidedly overkill alignment teeth which make for quite a snug fit.
Apparently breathing the green sand clay is a -bad- thing, so the D masks up before mixing.
As the green sand mixture is done by weight, the bathroom scale helps out, covered with a high tech scratchproof cover
First the clay is poured into the tub, then the sand, and then the water.
The mixing process. This took 20 minutes of VERY strenuous sitting on the couch watching the D do all the work. Whew!
The sand is poured into the bottom frame. We didn't make enough the first time and had to go back and make a full 50 lbs
Hammer and wood block are your best friends when compressing the sand. We were surprised how compressed 30lbs became
An amazing first test to show that the frame is perfect, and the sand works too (by not falling out)
Another test to see if the drill will work (driven by hand). Success.
With the frame removed, it still holds together! We were even able to lift the sand up .. but not very well or easily.
Round two, and final setup for the items. After filling up the mold as much as I though reasonable, I placed the items in
After a quick sprinkling of parting dust, I put the top mold on and pounded the sand on top of the bottom and the objects
This wasn't flat, but the parting sand worked well, and the top is a proper opposite for all the irregularties.
That thing between the egg and the handle is our runer. In actuality, a piece of rubber tube we found and stuck between
The runner (center) is meant to direct metal flow from the sprue to the troughs. I chipped away the troughs with a pencil
The only "visible" part of the mold, the top of the top, with sprue and vent holes visible
The sprue hole is somewhat visible in the center of the runner, and the vents are visible to the sides of the mold cavities
The frames have been -carefully- put together, the entire unit is then put on some plywood, and moved to the pour location
Expecting so much failure, through the sides, exploding sand, flame and popping molten metal everywhere.. and.. Just perfection
Pouring off the excess into muffin pans. Very tasty...
After an antsy 3.5 minutes, the D begins to chisel away the smoking green sane, eager to see what awaits inside.
The sprue peeks through the sand, the first piece visible
The handle is next to appear.. and WOw! Look at that detail! The hole even came out pretty well
The final "piece", extracted and still steaming. It's pretty pitted and ragged though. One of the vent holes can be seen filled
The underneath. It's all one piece untill we start to chop...
The D makes quick work of our troughs and sprue
It's far shinier than lost foam casting is at the start. It isn't covered with a smelly layer of soot. More rough edges though
The handle in plastic original form at left, and the new and improved handle at right. Woot!
The D works his magic fingers on the grinder to shave off the flashing on the handle