Wednesday, June 10, 2009

The Casting Process...

Some time ago, I had somebody do a 'blog request' about how the casting process works. I agreed to do it, then completely forgot. But now I remembered, so here goes!

Step 1:

Carve your wax. For this example, we will use a round coin with an X carved into it. There are always a few things to keep in mind while carving a wax, as in thickness, angles, etc.

Step 2:

Spru up your wax. A spru is a low melting temperature piece of wax that is attached to the carved wax. This spru creates a path for the metal to low into your carved wax. There shouldn't be any sharp angles in connecting the spru to the wax, because sharp edges could break off and damage the casting. The spru wax should flow smoothly into the carved wax. There are also concerns about the shape of the carved wax, the angle in which it sits for the metal to flow, if multiple sprus are needed... but that is advanced casting work.

Step 3:

Attach your spru to a rubber flask base. The base has a convex dome, in which the spru was is insurted into a hole in the middle. Then you cover the base with wax and soften the edges of where the wax meets the base... again, no sharp angles.

Step 4:

Insert the flask over the wax and into the rubber base. What is a flask, you may ask? Well, a flask is a tube of steel with 2 open ends and perferated around the sides. What is the purpose of this... well, you'll see in a second ;)

Step 5:

Cover the perferated sides with masking tape. Why do this? The next part of this step is pour invenstment into the top of the flask. Investment is similar to plaster, which dries fairly quickly. But to help the investment dry quickly and evenly, the perferations in the metal allows air to flow (even with tape over the holes.)

Step 6:

Remove the tape and the base of the flask. By removing the base, you now have a concave negative space in your investment. Then, you place the flask in a kiln and heat. This melts the wax and it flows out of the investment... leaving a negative space of your carved wax coin.

Step 7:

While flask is good and hot (straight from the kiln) you turn it upside down. The now reveals the concave divot created by the rubber base... which is the perfect place to pour in your metal. The liquid metal flows into the divot, into the spru and finally (if everything goes as planned) into the negative space of the carved wax coin.

You actually need more metal than the weight of the carved wax coin only. This is because the metal cools VERY VERY rapidly and can freeze on even the hottest of surfaces. But if you use more metal that just the carved wax coin, it allows the metal to retain some heat while flowing into the desired area. Also, you should have enough metal to not only fill the spru, but the concave divot created by the rubber base. While the metal cools, it shrinks. And by having this extra amout of metal, it shrinks from into the negative space. Why? I have no clue... I'm just an artist, not a physicist.

But, while it shrinks inward, it takes it from that concave surface... we call this the button.

Step 8:

You break off the investment (in water) and remove the flask. E voila, you have your metal coin... well, attached to a spru and a button. Now the fun begins, saw off the spru and cleaning the metal coin.

1 comment:

Gold said...
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