The Home Machinist!

Several members have suggested doing my attempted foam casting with green sand.
So I decided to knock together a batch.
I used a Mini-Carver based on someone else's design, and made a couple of modifications.
If it looks interesting to you, I'll be happy to answer your questions.
The local garden store had 40 lb bags of really fine masonry sand, and I was able to get an 80 lb bag of bentonite at an animal feed store in Kidron, OH.
My formula is based on 10 lb of sand, 22 oz of bentonite, and typically 5 oz of water.
I set up a ratio of sand to bentonite of .1375 -- so I could figure out how much clay I would need for any leftover sand.
I did the stand hand compression and break test, and followed it up with a muffin tin test.
I packed sand in a muffin tin, popped it out, and did the break.
Looks good.
Made a total of 80 lbs in 10 lb batches, which I'm storing in 2 five gallon containers.
The below photos show the process.

Looks good. Now lets see what kind of risers, gating, and sprue you are going to use. If you noticed my pics, I use a rectangular spure, I found over the years that that kind of spue causes less turbulence in the metal. Usually you want the gating and sprue to be a bit larger for Lost Foam.

One thing, when mixing sand, the mixer used is usually called a MULLER by metal casters, but I guess if it gets the job done, you can call it what you want. Mulling the sand is important because it increases its ability to hold together.

I guess I should have described my mixer as a mini-carver muller.
It doesn't use the traditional wheels to compress the sand and clay, but carves the mix together.
The particular design I used will require some additional tweaks for durability, but did a nice job of mixing the first 80 lbs.

Chet: Bravo on the mixer, it takes alot of the work out of mixing the sand. I have a drum cement mixer that I throw a few baseball-softball sized chunks of steel in to mix the sand. Doesnt matter, it beats cutting with a shovel and stompin the pile.

I was concerned when you said masonary sand. It should be noted that beach or bank sand of the #80 to #100 mesh is desirable. The sand used in masonry work is sometimes loaded with small pebbles and are rounded smooth, called Torpedo sand is not suitable for molding sand. The sand should be sharp, and if only damp will form in your hand. It is important to get the right consistancy to avoid problems.

PS. I have never done foam casting, I considered it too dirty and haywire for my needs. Pictures of the successful truck frames and such, now put that opinion in question for me.

Ronald: With your developed foam models, you can easily set them up to bottom pour, rather than top pour. This will go a long way toward having castings without dislodged sand in the bottom of your casting surfaces.

Top pouring directly into a sprue with a capturecup, works well enough, but the rushing metal can grab sand grains eroded from the mold and leave them wherever. By making a 'J' in the foam that gets to the bottom runners of the casting you can mostly eliminate that problem, because the casting will fill from the bottom without all the tubulance induced from the falling metal. While not worth the trouble for small castings, it is more attractive for complex and detailed work, that may be cosmetically or structurally sensative to sand inclusions. You can imagine the casting filling, like a drain filling the bathtub, instead of gurgling in from the top. It can go along way to eliminating laminations, and cold shuts, where a pour begins to freeze and gets overrun by more hot metal. In theory, bottom filling will give a more constistant run, with good gating.

Dave, thanks for the advice. Though I have been into metal casting for many years, it has been as a hobbyist, not a professional. I have learned a lot from those closely associated with metal casting. Yes, my friend Mike, who taught foundry for 25 years, preferred bottom gating. Having at first tried bottom gating, I found, for me, top gating was simpler. So, I rarely bottom gate.

That very first delta trailing truck was bottom gated, with the pattern right-side up. But after that, I mounted the patterns on the molding board, and molded up-side down in the drag. I then put all my gating, etc., in the cope. This saved having to use a larger, heavier flask, and more sand.

I usually use SS/CO-2 sand in the drag, so I get little erosion. For the cope, I have used Petro-Bond sand, or SS/CO-2, and have gotten little erosion.

I also use this method on my non-foam wooden patterns, like my rail joiners (on a Match Plate), or switch frogs.



Getting back to mulling, here is a site on mulling.

http://www.simpsongroup.com/tech/tech.htm