Of course, there is no single “right” amount as sand size, angularity, age(fines), type of bentonite, coal, and maybe even other factors could come into play. That said, it turns out that even after many uses, that was the calculated amount of water my mix indicated when first mixed and seems to remain so. I use other clues to also monitor my sand as one complicating factor is that when re-mulling sand I almost never am starting with dry sand. It has some but not all the moisture cooked out of it. So visual clues, packing clues and feel also play into it. I find it tougher to judge my sand when my hands are cold and barn temp is 36 degrees. Here are some vids I made recently for someone trying to get a handle on their greensand. Unfortunately, since my muller is different than theirs and my sand mix is different, the vids are of limited utility. More than showing what is “right” they suggest a method to use in evaluating moisture as you re-mull sand. I really really wish there was a practical way to accurately measure moisture on the fly. It is too bad that garden moisture meters are useless. Very dry sand: Almost moist enough: About right: Handling sand—visual clues: Pack testing: Denis
I was actually wondering about the same thing last night. And even angular sand vs round and how that comes into play. Denis sent me a couple quick videos of his sand and its progression through the mulling process, and I was noting some differences that I could see (I believe his oviline is angular and I know mine is more rounded). Yeah, I've been watching the Tube and comparing a lot of peoples methods (not the kitty litter crowd). The one interesting thing that I realized is the variability in the amount of bentonite that notable people are using. Anywhere from 4.5% all the way to 10.6% and percentages in between (I actually have a little spreadsheet with each Tuber's formula). Not that it's my issue (I don't think) I had plenty of what I consider green strength. Ummm ... is this a Canadian thing or something??
On another point, talc is available in various after-shower powders and even baby powders. Some are cheap and all smell “good.” I buy mine at a local bargain store. Just look up the product and read its data sheet or ingredient label. Denis
Not all bentonites are created equal, ie Western and Southern and the two require dramatically different amounts of water. Like everything opinions will vary on this and their use and none of them really comment on how mesh/grain size might alter the recipe. Here are a few references I collected that may be useful. Here's an opinion from a foundry operator: Just know Southern (Calcium) Bentonite is good for holding dimensional accuracy and sand flowability while Western (Sodium) Bentonite is amazing for mold strength if you are making large molds or deep pockets. It retains water 15x better than southern so it has amazing green & hot strength but at the cost of water and reduced sand flowability. Foundries use different blends of southern and western and it’s the top grade binder for Green Sand Molding. For DIY work a 4/1 ratio Southern/Western bentonite is recommended. Start it at a 90% sand 10% binder. The goal in green sand is to reduce the amount of binder and water needed. The more Western(Sodium) you use the stronger your molds will be but the more moisture you’ll hold since it 15x absorbent. For this reason you want to use as little Western as possible. If you are making molds smaller than 10×10 you can reduce the Western even more. This recommendation is a higher ratio and % then our industrial mix but we also use jolt squeezer machines that compress the molds with 1,000’s of lbs of force. We run our ratios so low that novice molders often have mold collapse when they are ramming. Here's Smelko's take and recommendations....a trusted source of info I'd say: http://smelko.com/?page_id=325 ...and yet another and differing opinion: http://www.hillandgriffith.com/green-sand-metalcasting-foundry-news/green-sand-binders ....and of course some interesting factoids from Wiki. https://en.wikipedia.org/wiki/Bentonite Best, Kelly
Concerning the variation in sand mixes and trouble we all have molding. It is very frustrating that most of work in a “vacuum” all by ourselves without the benefit of being able to hands-on see what the other guy is doing. I think we’d all learn a lot and quickly if that were the case. Sorry for whining... Denis
Reading some of the posts regarding the relative merits of Western and Southern Bentonite and not remembering how I came to use only Southern Bentonite in my sand mix, I decided to add 2% Western to my sand that already has 4-5% Southern Bentonite. I noticed a very definite improvement in green strength. So, now I am wondering how the "improved" sand will cast. I am also pondering how we could develop a simple standardized test that could be by whomever wanted to check the strength of their sand. I know the Navy developed instrumentation for this. But I am trying to think of a practical, repeatable method that would require no expensive or hard-to-obtain components. Any ideas. The advantage would be that we'd each be operating in less of a vacuum of comparative knowledge. One idea that might work would be to use a section of standard pipe into which sand was packed. Then the column of sand could be gradually extruded using a section of all thread and the length of extrusion at breakage would correlate with strength. How to standardize compression of the sand??? Denis
Page 50 of the Navy foundry manual describes a way to make a standardized sample slug. Figure 64 shows a picture of the idea. https://maritime.org/doc/foundry/index.htm#pg49 A standard 1-1/2" schedule 40 PVC pipe, say 8" long would suffice for the packing vessel. A saw kerf the length of the pipe would allow for release. That would at least give a standardized test slug. A simplified version of the mechanism shown in the attached picture could be used to squeeze the slug to failure by attaching a spring scale to the leverage rod and pulling on the other end of the scale to get a measured force. Pete
I guess I am trying to conceive of a very simple setup that could be made with the simplest of tools in a relatively short time at minimal expensive using items available at any hardware store. Since most folks here don’t have a lathe and milling machine at their disposal, the design of both the compression device and strength tester has to be very basic. The schedule 40 pipe is right in line with that. For compression I keep tossing around the use of say 1 foot of 1” round bar dropped into the cylinder from a given height a specified number of times. If the pipe were 3 feet long And a column of sand 1 foot long were to be compressed, sand of a given weight could be poured into the tube followed by say 15 tamps raising the bar to the top of the pipe and then releasing it. (All dimensions and tamps subject to testing). If said pipe had a single full-length kerf, once tamping was complete, it could be placed horizontally and sprung open a bit. Then the column of sand could be slowly pushed out of the tube using a wood dowel until the extruded column broke. The further it could be pushed before breaking, the greater the green strength. Duct tape could be wrapped around the pipe while tamping to prevent spread of the tube due to pressure. The above is the KIND of idea I am thinking of. It would be interesting to hear alternative ideas. Sorry for tangent taken. I’ll start a thread if the idea needs to go further. Denis.
A note, in the Navy Because of limited storage, we used 120 GFN for everything facing, backing, heap, cores, green sand, CO2 and petrobond . 75 GFN is damn course. in green sand and cores this can be overcome with mold wash, and remember as you use sand it accumulated fines, which means used sand well mulled and riddled sand will give a better surface finish. but eventually you will start to loose permiability and begin to have gas issues (OK this is not 100%, because this assumes A LOT of use. casting Aluminum, i dont think you would ever get there without making a mistake... adding too much binders or additives . in cast iron you can get there pretty fast if you are not seperating out burnt sand , brass is middle of the road) V/r HT1
yes, though to the best of my knowldege for foundry use sand really only ranges fron 60-140 GFN we used to use silica powder for washes and as an additive in some cores to get it super fine, but i'm sure that is completely frouwned upon now V/r HT1
That is how I did my first batch, but then I saw this and started adding bentonite AFTER the water... Did I misunderstand the manual? Sorry for the crappy screenshot, its a page from the navy manual you sent me via text about 2 years ago when I was picking your brain about the sand I was making. It says to mix the water and sand first THEN add additives, which I took to include clay. I did let it mull for a fairly long time, maybe that is why it seemed to work about as well as adding water after clay. I definitely lost a lot less bentonite to the air by adding it to the damp sand in the muller though. Jeff
I don't know the official answer, but I find that be it greensand or a bread mix, it is much easier to get a thourough mixing of ingredients if the dry components are blended together before adding liquids.
page 133 of https://www.google.com/books/edition/Molder_3_2/dp7QSpmnI6sC?kptab=editions&gbpv=1 this gives you a much more recent reference then the Foundry manual and it says all dry first, touch of water, mull , then add remainder of water trust me you try to add cereals to wet sand you will have a mess that will take hours of mulling to fix. ( I doubt anyone is using cereal additives, well maybe some of the cast iron guys, cereal aids collapsobility important in cores in cast Fe, aluminum will not even get hot enough to burn out cereal V/r HT1 page 133 of https://www.google.com/books/edition/Molder_3_2/dp7QSpmnI6sC?kptab=editions&gbpv=1
My experience yesterday adding a pound of Western Bentonite to 50 pound batches of moist sand I was re-mulling was that I mulled each of the eight batches for about 3 to 4 minutes and had good mixing and definitely improved strength. I did "riddle" the clay through my fingers as the muller turned in order not to have clumps of clay. But it mixed in just fine. Cereals may be another matter. I also added about 4 to 6 ounces of water to bring the mix back to proper water mix. Denis
Second green sand pour. I made sure I rammed hard.. Same sand. Sand was probably a little wetter. New parting compound. Made sure I brushed with camel hair brush & blew out mold. Different pattern. Results are markedly different. You can run your knuckles over it without skinning them, and maybe that's all my sand will do. drag half is a little smoother than the cope half. I do have some small bubbles into the surface in some areas (sand a tad too wet?).
Those surface bubbles look like hydrogen porosity, It was happening with my castings yesterday due to the aluminium being too hot (increases hydrogen solubility). You could see it in the pools of spilled metal as they solidified.
I think you are right Mark. I was turning one piece on the lathe and I can see a fair number of very small bubbles there.
Most of the time porosity comes from running your burner too rich. If you have flame coming out of your vent, then it's running rich and you need to throttle down your fuel.
Fishbonz - That was most likely my issue. I had a pretty decent flame coming out the vent. I may fire up again tomorrow ... When I was machining that piece, I was taking measurements off the wrong pipe.
In my case I left the furnace run a bit too long and this was 4-5 crucibles into the session and I had orange glowing aluminium (in a dark room) so I pulled it out and let it cool a bit before pouring. As I filled a mould some missed the pouring cup and pooled on the table: a lump 75mm/3" in diameter and 12mm/ 0.5" thick. After I'd put the crucible down and was breaking the pouring cups off with their mostly solid metal I could see this molten blob with it's liquid silver surface had lots of tiny bubbles popping on the surface like champagne or soda.
