I'm Steve, 66 in 2 weeks. I've been building things and fabricating for a long time but just started casting. I found a Vevor 10kg furnace on facebook marketplace for $50 so I figured I'd give it a shot. Got some petrobond and a flask off ebay and I cast aluminum, copper, and brass skulls on the same day. The aluminum one turned out perfect, but the other two had issues. Today I've been ramming up a rebel flag pattern that a friend wants to make into an air cleaner. I used home made green sand for this with not good results. The aluminum erupts out of the feeder like a volcano. Is my sand too wet or what? I even tried heating it up first on top of the furnace. Still molten aluminum erupting. I poked over a dozen vents in the back side and had an 1 1/4" x 2 1/2" feeder. Kept my pouring basin full to keep air from entering during the pour. What am I doing wrong?
Welcome, the aluminum skull came out great! You have the know-how to build and upgrade your foundry gear already by the sound of it, that's a plus. If the tongs for lifting the crucible that came with your Vevor kit grip the crucible (dangerously) by its rim like the tongs that come with every other hobbyist kit I've seen online lately, that would be the first place I'd start. I think there are a few good threads here about the crucible tools our members have built, if you want to see some examples. Sounds like you have really wet sand to me. You don't want it to feel wet at all, it should feel barely even damp when you squeeze it in your hand, and if anything stays stuck to your hand after doing so it should be just a few loose grains that brush off easily. If you need more water than that to get your sand to hold its shape, you probably need to mull it better. And/or add some more clay. I would try those in that order assuming you began with a reasonable recipe. How much sand, clay and water did you use when you made it? And if you can describe how you mixed/mulled it, that may be helpful. You could start a separate thread about your sand if you have more questions that other newcomers might also want to get answered. You may also find some of the info you need has already been covered if you poke around a bit. Sometimes I find it's easier to find specific info on here with a Google search than with the forum's own search function, but that might just be me. Jeff
Welcome to the forum. Spreading the green sand out on a plastic tarp in the sun and/or in a breeze and raking through it every so often will help dry it.
Jeff, thank you for the quick reply. I agree that the tongs leave a lot to be desired. I have watched several youtube videos about making various types of tongs that will grip the crucible in a much safer way and that is definitely on my to do list. Like I said, I'm new at this and working with a small budget so I made my green sand the same way I saw many other people do it on youtube. I bought 100 lbs of play sand from Lowes, sifted it through screens, then added 11% by weight of kitty litter run through a blender and sifted to the remaining 75 lbs of sifted sand, then mixed it all on the concrete floor and added about 3 quarts of water, and then mixed and mixed until it had the consistency so when you squeeze a handful, it broke into two parts. I mixed it by scraping it up, turning it over and over again for about a half hour. Is there an actual % of moisture content that the sand is supposed to have? I will buy a moisture content meter if that will help me get good, consistent results. I noticed that when I had the flask sitting on top of a stainless steel sheet on the furnace, when I lifted it off, there was a lot of moisture that had come out of the sand. I guess I will start by dumping the sand mixture out on a board and let it bake in the sun for a few hours and see what that will do. I bought a bentonite refresh kit that I could try if that doesn't work. After several failures using sand yesterday, I just wanted a win before I cleaned up the mess, so I casted this spark plug in petrobond. I only have 10 lbs of it, so not enough to cast the flag project, but I've got another 10 lbs on the way. Thanks so much for taking the time to answer my questions.
Tops, thank you for the reply. I will spread the sand out on a board in the sun this afternoon and rake it around to get the moisture out. Is there an actual percentage of moisture that the sand is supposed to have? If so, I'll buy a moisture meter if it will help me get consistent results. I'll post the next pour results one I've dried out this sand a little. Thanks for taking the time to reply.
You are welcome Ezee. I switched from green sand to Petrobond relatively early in my casting journey as it took one large element out of a multi-element learning curve. Not that green sand is bad, I still have a 5 gallon (20L) bucket full, it's just fussier in a way. I got tired of sifting through wet and rocky 3$ big-box store sand, discarding over half, to get something fine enough for casting. Nowadays when I need sand for casting I pay a little more to get it in bags that are clean, dry, and graded. I bought my bentonite clays outright, never did the kitty litter thing. And I also have gotten it too wet to the point where it needed to be dried. Have you seen videos where people take a fistful of green sand, squeeze it into a ball, split it in half, and crumble it back to loose sand as a method to gauge where the sand it at? I don't know if a moisture meter from another discipline would work for this.
Welcome Ezee You're off to a good start, failures notwithstanding. Good score on the furnace. There's a good recent thread about rehabbing and maintaining those fiber lined furnaces. Dig around a bit. Here is a valuable resource. Its the real deal. https://maritime.org/doc/foundry/index.php You'll get useful insights regarding sand in there. As an aside, the chapter on solidification is a great read and gave me a basis of understanding for other topics in the book as well as recognizing the hows and whys of the molding strategies you'll see on this site and elsewhere. As a second aside, beware of some of the methods and techniques you see on YouTube. (The shorts and flipflops should be your first clue). Third aside. Disclaimer: I'm not a safety mother, but the phosgene gas that comes off those teflon muffin pans can make birds fall out of the sky. Rock on. Pete
Letting it dry out and periodically doing a squeeze test will help you dial in how wet your sand as-is has to feel in order to have the strength it needs to act as a mold material. Maybe that's all you need to do. But if that is still enough water to make your molds erupt, there might be a way to get it working with less water. Greensand really should not feel wet at all, just slightly damp. Turning the sand and binder and water over and over should get it quite well mixed, but not necessarily well mulled. When it is properly mulled each grain of sand will have a thin coating of clay on it. This requires some squashing and smearing action while you are mixing it. Mulling should allow your sand to hold its shape (pass the squeeze test) using less water and clay, which should help improve your molten metal volcano problem. The amount of clay you used doesn't seem unreasonable (a bit more than the professional foundry supplier closest to me uses when mechanically mulling sand, but right in line with other hobbyists mulling manually who compromise by using a bit of extra clay to make up for the shortfalls of manual mulling, at the cost of less permeable sand). If it won't hold its shape when it's dried out enough to not erupt your mold, I would keep mulling it and see if that will get it to the point where it will still pass the squeeze test even when it feels barely damp at all and no sand sticks to your hand. The stompy tarp dance this guy does is one way to do it without having a machine called a sand muller: This guy uses his car as a muller: It's also possible to build your own actual sand muller. A machine is a lot less work to use and more effective than manual (possibly even automotive) mulling, but a hobbyist can get by without a dedicated machine for a while. Useful for making molding sand as well as for reconditioning it after each use though... Do not be discouraged, homemade greensand always takes some tweaking to get working right! There's no one right amount of moisture for everyone's sand, there's too many variables to consider that affect it, like the properties of the actual sand you used and the type of bentonite clay. And mulling. Moisture meters that are accurate for molding sand are expensive and hard to find, the cheap ones you stab into a plant pot will give widely varying readings depending on how hard you squeeze the sand around the probe tip. Waste of time. It takes a bit of experience to get a "feel" for it, but that is the only realistic way for a hobby setup. If you really need to put a number on it because it's keeping you up at night not knowing, you could compare the weight of a sample that is tempered just right vs baked dry. Spark plug looks good! Jeff
You could also make the mold this week and pour it next week leaving it uncovered in the meantime if it's warm enough to allow evaporation. Just put a card over the sprue to keep critters out.
What are your skull masters made of, and the white material seems to be some type of plaster. Haven't seen that used in a wooden frame before. Enlighten me. Fredo
