The ultimate play sand

On this fine day, we prepared the sand box and sand mixture used for the molds. After this, we just need a furnace and a crucible with crucible tongs, and then metal will be flowing!

The first order of business was to cover our sandbox with tarp, so as to prevent wood shards from getting into the sand when we use our metal tools. It also gives the box more weather resistance. There are also 3 protecting coatings on it.

Covering the box with the tarp.



Using our staple gun to go around....



cutting and stapling our way through...



and around.



The next order of business was to create the molding sand mixture required. The ingredients list:

• 100 lbs of sand




We purchased the finest sand Home Depot had. "Only your finest sand, madames and sirs!" we proclaimed. This will constitute the majority of the volume of the casting sand.


• 6 lb Bentone 34




Bentone is a very fine, creamy white powder, and wearing masks is necessary or else it will solidify in lungs. Its applications are very diverse from adhesives, automotive finishes, paints, putties, oil industry applications (drilling muds), etc. From the information here, I will attempt to explain its key properties.

It increases viscosity, which means it makes the sand mixture thicker, especially when mixed with the oil.

It provides thixotropy, which makes it thick, but flows when agitated. This lets the sand keep its shape, but breaks apart when crushed. It improves flow and leveling, which is definitely advantageous for molding sand.

One of the most important properties is "[preventing] syneresis in thixotropic systems". A thixotropic system is what we have. See the paragraph above. Syneresis is the separation of a liquid from a gel, like curd formation from milk, to make delicious cheese. In our case, the oil we add should stay evenly distributed in the mixture and the bentone better bonds it to the sand.

Another good idea of how the Benton reacts is to think of kitty litter. It acts like a gelling agent. A purely oil and sand mixture would not have the same properties.

The Bentone powder on top of the sand.



Mix well.




• 2 quarts oil


The oil helps keep the Bentone and sand together. It acts like a glue. We used 2-cycle (for engines with 2 cycles like lawnmowers) because it is cleaner burning and less toxic. Some of the oil will burn and evaporate around where the approximately 1300F molten aluminum hits the sand.




• 2 lbs alcohol




According to the data sheet, alcohol is necessary to chemically activate the Bentone 34. What this exactly means, I am not sure. Nick is saying the alcohol dissolves the Bentone to help distribute it evenly throughout the sand and there is no chemical reaction. It was not an exothermic one, if at all, that is for sure.

The "chemical activators" and amounts are:



Chemical activator	Chemical composition	% based on weight of dry Bentone
Methanol/H2O (95/5)	CH3OH	33 %
Propylene carbonate	C4H6O3	33 %
Ethanol	C2H6O	50 %
Acetone	C3H6O	60 %



We used isopropyl alcohol (C3H8O) at about a 35% mixture. Looking at the table above, it would seem that isopropyl looks more similar to ethanol and acetone, which means we may have wanted to use more.

We mixed the sand in batches of around 10 lb, then mixed it all at the end. Warren was nice to stop by and play with the sand too!

At the end of the day, we powered the Arduino board with one of the batteries. The Tristar controller was set to load mode. In this mode, it controls power being taken out of the battery so as not to damage it. A second Tristar would have to be used for charging the batteries.

Stay tuned.