Sand casting is an ancient technique of using moist and tightly packed sand to press around a model which is then removed leaving a mold cavity to be filled with molten metal.
Which metals can be used to sand cast?
Aluminium, Bronze, Pewter. Silver and Iron.
Two types of sand are used for sand casting:
1: Green sand, a mixture of silica sand, clay, moisture and other additive.
2: Air set sand, a dry sand bonded with other materials than clay using a fast curing adhesive.
Casting sand is commercially available. The finer the sand is the better definition will be achieved on the casting.
The consistency of the sand is very important. If the snad is worked too wet, it will desintegrate once the object is removed to reveal the mold cavity. The consistency of the sand can be evaluated by squeezing the sand into a ball. The sand should then hold itself together in the ball shape.
Sand casting involves a frame wood or metal box called the flask made of two parts ( some more complex casting may require a three or more parts mold). The parts of the frame are called drags( which is the frame without pins) and cope( which is the frame with the locating pins).
Casting an object:
1: Set the drag onto a flat surface such as a sheet of wood.
2: Fill the drag with moist cast sand packing it down tightly with a block of wood.
3: Spray paint the object to be cast if its surface is uneven or use shellac or varnish to seal it.
4: Once the drag is packed up to its surface, level it with a piece of wood by dragging it across its surface in order to remove excess material and create a flat surface.
5: Lay model in the centre of the sand and push gently half way into the sand. Sometimes tools may be used to remove some of the sand in the cavity mold since the packed sand can be difficult to give under the pressure of the object.
6: Sprinkle pounce onto the snad and object. Pounce is a powder used to keep the two frames from sticking together once they are filled with sand. Talc, chalk dust or graphite can be used for this purpose.
7: Use a gauze material to fill the pounce such as muslin.
8: Locate cope and drag using the wooden pins.
9: Sprinkle sand over object and pack frame up to its top surface as previously.
10: Remove cope and carefully take away the object without destroying any of the packed sand.
11: Create a gate with a scalpel (a 3mm channel) which source will be located right at the edge of the object.
12: The channel is created in the drag.
13: Create a pouring cup in the cope using a metal tube and pushing it all the way down the tickness of the frame.
14: Replace cope unto drag.
15: Use a welding rod to create air vents called runners around the object by pushing the wire all the way down the thickness fo the cope.
16: Melt pewter or other metal into a furnace or ladle.
17: Pour molten metal into pouring vent.
18: Let it cool dowm until the metla has solidified.
19: Open the two parts frame and remove the cast object.
20: Rinse the object under clear water to remove any sand particles.
21: Use a metal brush to clean sand away from tiny spaces if necessary.
22: Using a hacksaw cut off excess of metal created by the pouring vent.
23: The object will have inherited the surface of the sand.
24: Finish the object by mashining using files to create a smooth surface.
Sand casting drag and cope.
Sand casting molds.
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Sand casting pour.
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Sand casting diagram 2.
Sand cast cast iron object.
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