As I remember, the very fine sand--almost like powdered "dirt" in consistency--was a barely moistened mix of sand and water with something added to the water to make it sticky. Then we'd add sand and pound it in place so when the upper mold was taken off the lower, the sand would not fall out [at least after a few tries]. Are you using dry sand or adding something to it to allow it to stick together in the mold? Source for your sand? Did you dust the mold and the separation area with talc or chalk to facilitate separating the mold halves? How did you remove the original model and leave the central sand core intact?
Sand casting is a process that uses a mold made from either metal, wood, or wax to create a negative impression in a special sand that will be the mold for the molten metal. This mold is then filled with a molten metal that is left to cool and solidify. Once the metal has solidified the mold can be hit with a hammer, pipe, or any hard object to crack the sand mold and expose the metal object.
The first step in making a sand casted object is deciding on the object. For this set of instructions I will be using a mug as my object. Once you have decided on the object you want to make you will need to figure out how you can cast said object and still be able to remove the sand mold from the form. This leads me to an important point about sand casting, because you need to be able to remove the sand mold from the form the complexity of the objects that can be molded is limited. It is also important to remember that you will need to leave a hole in the sand cast to pour the molten metal through when it is assembled.
Tools Needed
1) Silica Sand
2) Mold of object
3) Some type of kiln/oven to melt the metal you will be using
4) Ladle to pour molten metal
5) Block of solid metal to melt
6) Hammer or some other object to crack the sand mold after metal solidifies
Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. Over 70% of all metal castings are produced via a sand casting process.
The cavity in the sand is formed by using a pattern (an approximate duplicate of the real part), which are typically made out of wood, sometimes metal. The cavity is contained in an aggregate housed in a box called the flask. Core is a sand shape inserted into the mold to produce the internal features of the part such as holes or internal passages. Cores are placed in the cavity to form holes of the desired shapes. Core print is the region added to the pattern, core, or mold that is used to locate and support the core within the mold. A riser is an extra void created in the mold to contain excessive molten material. The purpose of this is feed the molten metal to the mold cavity as the molten metal solidifies and shrinks, and thereby prevents voids in the main sand casting.
In a two-part mold, which is typical of sand castings, the upper half, including the top half of the pattern, flask, and core is called cope and the lower half is called drag. The parting line or the parting surface is line or surface that separates the cope and drag. The drag is first filled partially with sand, and the core print, the cores, and the gating system are placed near the parting line. The cope is then assembled to the drag, and the sand is poured on the cope half, covering the pattern, core and the gating system. The sand is compacted by vibration and mechanical means. Next, the cope is removed from the drag, and the pattern is carefully removed. The object is to remove the pattern without breaking the mold cavity. This is facilitated by designing a draft, a slight angular offset from the vertical to the vertical surfaces of the pattern. This is usually a minimum of 1° or 1.5 mm (0.060 in), whichever is greater. The rougher the surface of the pattern, the more the draft to be provided.
Precision casting, Sand Casting, EPC Casting
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