Hello me again. Sorry I come too often with askings. Just got a quick note about casting sand. I have read have of this forum after reading Charcoal Foundry book. My mix that I am using is 30% grounded clay from kitty litter. Kitty litter was Natural Litter without any additives. Just natural clay granules. I used cheap coffee grinder. Coffee grinder fixed using wooden frame to the lid of a plastic storage box. Hand drill 14.4 volts fixed above and grinder's bolt goes in drill like a bit. Button fixed with with a vice. I lock battery and it spins non-stop for 30 mins - that is how long battery lasts. I grinded it to fine dust and mixed with Play Pit Sand that was sieved and washed before getting sold. Clay 30% and sand 70% On some videos from members on this site, I can see when frame is used they flip frame 180* and sand mass does fall out. My sand mass starts to slip out when doing that. I will need 2 lids for casting frames. To prevent sand from moving out. Question is simple - do I need to add more clay to the mix? I did several searches here, but could not find any post on the casting sand mix ratio. On some YouTube videos, casting sand is pinking or red. I had a look and it is Delft Petrobond Oil Bounded casting mix. Oil-bounded probably going to smoke. Would anyone please say what I need to add to my Clay/Sand so it be more sticky. Frame size is 23cm wide 44cm long 4.5cm deep. All sizes are from outside. Wood planks are 20mm thick. Perhaps they are too big for flipping them 180*? Thank you in advance.
30% is WAY more clay than should be necessary, 10% would be typical of a normal mix. Tell us about your method of mulling and how much water you are adding to the mix. Here's a video of someone using kitty litter and play sand with frames about the same size as yours, he uses 10-12% clay by weight. Also, notice that his frames have grooves cut into the interior sides, this helps to retain the sand.
I have been using 4 to 5 per cent Bentonite clay ( half southern and half western) in 100 mesh olivine sand. Coarser grain sands like play sand should need less. Moisture in my sand is about 4% as suggested in the US Navy Foundry Manual. A basic reference that is well-tested and well-regarded and available free online is the US Nany Foundry Manual. Here is a relevant page. https://maritime.org/doc/foundry/index.htm#pg43 Denis
If you can post pics of your flasks, please do so. It sounds like they may need to be thicker. I’m thinking 6.5 to 7 cm thick top to bottom for the cope and 6.5 to7cm for the drag. Too thin and the sand will drop out. As Rocco suggested, grooves or keys on the sides can help sand retention as can bars spanning the flasks if needed. Hand turning them at that thickness should not be too much of a problem. If it is, a hoist systems can be rigged. I use a hoist to flip 450 pound molds. Initially I used a chain hoist. Now it is a home-made electric hoist. Molds of the size you are working I flip by hand and I am certainly not a muscular giant—-70kg and 73 years old.... Denis
If I recall correctly, the greensand I bought several years ago from Smelko Foundry Products here in Ontario Canada has 4-7% bentonite, similar to Denis' sand. A sand mulling machine seems to make it a lot easier to mix up workble sand with clay levels below 10%. A lot of people making their first batch by hand seem to end up at around 10% or a little higher. 30% may cause issues with low permeability to steam / mold gases. But at least it should be nice and sticky! Jeff
I was just looking at Opta Minerals' website, they sell a product called premix 46-B, it's mix of Bentonites with a few other additives, they recommend mixing with sand at a rate of 7-9% of the weight of the sand, the actual amount varies with the sand and type of metal being cast. It says finer sands requiresmore Premix and, sand for aluminum casting is at the low end of the range, a little higher for copper based alloys and more still for iron.