How its done: Resin Bonded Sand Molds
A popular casting method among sculptors is to make a resin bonded sand mold around a wax blank. Today I’ve taken some images to walk through the mold making process here at ECU.
With the Iron Pour coming up soon, I’ve had a ton of work to get through to prepare. Today I packed one of my 4 molds, and here’s how we started.
You take your wax blank, the piece you have tirelessly smoothed, shaped, and formed, and attach a sprue system, a series of supports and channels that will allow for a travel route for the molten metal before it reaches the hollow form of the wax in the mold. Also, make sure you attach small unobtrusive channels, called vents, throughout the piece to allow for trapped gas to travel back up to the top of the mold.
heres the wax blank for "Fafnir's Remains"
Now before we mix the sand we need to decide how we will orient the wax in the mold, you can either place it with the cup, (the section of the sprue system that will form the opening for the metal) facing upwards or with the piece balanced with the cup touching (solidly) the floor beneath it. This is largely a matter of choice or situation, and for this demonstration I’ve oriented the piece with the cup downward.
here we see the beginnings of a casting, a lonely wax inside an empty flask
First we lay down a piece of newsprint, this is to keep the resin in the mold from bonding with the porous concrete beneath. We then build a wooden flask around the piece, if you orient the cup facing downwards you will place your piece inside the flask, making sure to leave at least 1-3 inched between the sides of the flask and your wax. If you want to orient the piece facing upward, you’ll need to pack down a few inches of sand at at the base of the flask.
This muller has been through a lot. Not pictured is his younger and shinier brother.
Now we need to move to the Sand Muller, a heavy duty mixing machine used to mix the resin and catalyst into the sand. This muller has a strict weight limit, so I’ve mixed 100 lbs at a time, usually the most I’ll need for my small-sized castings. We need to be careful with these machines, they can be pretty touchy. You also need to remember to clean the muller out after you finish mixing, the resin in the sand can set over time and make it very difficult to clean mixing material. To get a good surface on from the mold we have to use a very fine sand. Here at the ECU sculpture department we use Unimin Corporation Silica Sand.
First we pour the bags into the muller and form two ditches in the sand. Next measure out the necessary catalyst. This will quicken the time it takes the resin to set and harden the sand. We pour half the measurement into each of the ditches, the brush some more of the sand overtop of the liquid, ensuring that none of the chemical will touch the sides of the muller during mixture, as it would adhere to the metal. After one run with the timer, we repeat the process with the Resin. Once we’ve got our mold material mixed we fill the cart and move over to the flask!
Watch as the mold is swallowed by the rising sand!
Now we start scooping the sand into the flask, making sure pack the sand tightly around the wax, while still being gentle as to not break anything. As your fill the flask you can start moving to larger and larger ramming tools, making sure to keep the sand packed tightly. as you fill the flask you’ll see the mold start to take shape, and once you have 2-3 inches of tightly packed sand on top of the highest point of your wax, you have finished packing your sand mold!
I prepared this mold ahead of time, although it was mostly unessecary, this is the Internet, not a cooking show.
Now that the mold is rammed, we place it in the Low Melt kiln, which will head the mold over an 8 hour period at 400 degrees, melting the wax and leaving a hollow space for the metal to fill.
Next time, after the iron pour, I’ll have pictures of the opening of the mold, as well as cleaning and finishing the piece, until then- Keep working and keep creating, and I’ll see you next time!
-RLP-
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