Discussion in 'Sand Casting' started by Tobho Mott, Jan 15, 2018.
...and this is why the "mic drop" emoticon was developed.
Yep, that the one!!
I havent touched the green sand in years. When I first wanted to try sand casting I made up some green sand from just regular play sand and some ground up kitty litter. Moisture content was wetter than Niagara falls.
I made a "part" but it was not the greatest when it came to the cosmetics. Sand was just too coarse and too wet. I quickly switched to petrobond.
After seeing oldfoundrymans videos of his green sand castings It opened my eyes to how a good greensand should act and the finish it is capable of. Maybe one day I will try it again.... I would like to anyways....
Ill get a picture of the casting up in a minute, I saved it for show and tell.
Keep in mind , this was 15 years or so ago and just an experiment. But I was hooked ever since.
Awww... I took a picture of my first too. Lost foam. Stunk like hell. 1st and last time for me.
I will take the risk of posting some follow up on my prior post reporting surprisingly high moisture content in the green sand I was using starting out in cast iron casting. At that time I had purchased (traded some beer) for sand that a sympathetic local commercial brass and bronze foundry was using. I (erroneously) thought that getting some working sand from them guarantee workable sand and also was an easy local source of foundry sand much more convenient than driving 100 miles and through Seattle to get new raw materials.
While I was able to make that sand work, surface finish left a lot to be desired. So, I ended up buying new southern bentonite, sea coal, and olivine 100 mesh sand.
I mixed that up as 5% clay and 2-3% coal and achieved much much better surface finish and much much easier cleanup of the cast surface. The old sand was baking onto the surface and causing the underlying cast iron surface to be quite rough.
So, now, with my new mix and enough casting sessions under my belt to feel like I am starting to get a handle on mulling the sand effectively, I baked out a 400 gram sample of sand last night, measured the results using a triple beam balance, and got a 3.7% moisture content. This is well within expected results and is somewhat reassuring.
In another thread (http://forums.thehomefoundry.org/index.php?) I posted a couple of times about some useful physical signs I have noted specific to my setup but perhaps similar for other setups and perhaps worth paying attention to. Obviously, though bakeouts provide an objective benchmark, they are cumbersome and not practical to use at the muller on the fly. At the same time, checking one occasionally may help explain unexpected results as it is pretty easy to drift into too moist or too dry mulling.
I think the original sand I got was very tired having had clay added many times over decades and that high clay content needed a lot of water to get the sand to have reasonable green strength. Unfortunately, that high water content also had adverse effects on surface finish. Caveat emptor on getting sand from someone else if you do not know the full history of the sand and its composition.
Is Southern bentonite sodium bentonite or calcium bentonite? Sodium would be nice - S goes with S... but I can never remember which is which. I got some sodium Bentonite and it is from Wyoming I believe. I know there is lots of bentonite in the badlands of Alberta here in Canada and that is out west, but I'm not sure which kind it is or whether it is even considered "western" bentonite for that matter.
Edit - to spell my name right
Southern is calcium bentonite. Now that you have suggested "S" as sodium for Southern, I will never be able to keep it straight ;-)
"Calcium Bentonite (aka Southern Bentonite): The calcium ion concentration in this variety creates a lower swell green sand system with low viscosity, lower water absorption and the resulting quicker water loss. It is generally considered to be easier to mull and provides higher green strengths but lower dry and hot strengths."
Thanks. R=R worked for Rich and Reducing (vs. lean/oxidizing), so S=S was probably just too much to hope for.
Before long you will have your muller finished. And then will begin the "mystery" of trying to figure out how it should behave. Having entered that phase not long ago I am sympathetic to the uncertainties of getting it to work correctly and being able to recognize correct function. To that end I made a few very brief videos to show you what mine looks like when I have the moisture right (I think/guess), way too dry, and just shy of moist enough.
This is just right---note the clumpiness of the sand, partial adherence to the inside bearing surface of the wheel and the general adherence to the non-bearing inner edge of the wheel:
Next way too dry:
Just a tad dry which appears only subtly different than just right:
And here are a few pics of ramming some sand into the corner of my molding beach and then cutting out a cube to test for green strength. This works best as a test of moisture for me---it has a broader apparent spread of results than just squeezing and breaking. May not be great for everyone. And I will be the first to admit that my "correct" moisture level might not actually be optimal. But, when noticeably moister or drier than that point I have had mold failures, so it must be somewhere in the ballpark for my sand mix.
I have no idea if this will be any real help or not. I hope it will help a least a little bit. Sure would be great to hear from some of the experienced folks...
It's a great reference for me, so consider your efforts a win...
Third video is broken though...
I am mystified by the third video link. I just watched it from THF on my iPhone but shows broken link on my PC. I will try reinstalling the link.
OK, I just reinstalled the third video link. It is working fine on my iPhone, but I don't have PC with me to test the link on that platform.
Still no go. Might be set as private not public on Youtube and your iPhone is auto logged in so it plays. -Just a guess.
Sounds sensible. Will have to wait til later to check out settings on that video. I thought I set them all to " unlisted" but probably messed up on that one.
Thanks Melter, the first two videos (and counting) and the photos should be very helpful.
Kelly diagnosed the problem correctly! Not bad!
I accidentally set the video to "private." Now that it is set as "unlisted" all is well, I think. Pls let me know if the link does not work.
What I find most interesting in your videos is the angle the wheel is on...
I'm at the point of developing my wheel apparatus, so I'm currently over analyzing it
I am not sure that the angle is very important. On my setup, the wheel is free to pivot on a vertical axis (and also can move up and down) and finds its own pivot point based on the net direction of resistance it encounters plowing through and rolling over the sand. I did make sure the vertical pivot point (the vertical axis it is mounted on) is well forward of the center of the wheel center of rotation---its axle center. That makes sure you won't get the "shopping cart wheel" chatter so common on poorly designed carts. It is also important that it be able to move up and down as it will encounter hard large lumps of sand when re-mulling sand and will jam if not able to move up and over the lump.
Ever have a forehead smacking moment...? Sometimes it's so easy to make the simplest things difficult. Allowing the wheel to pivot freely is a great idea....
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