Sand casting is by far the most important casting process A. sand-casting mold will be used to describe the basic features of a mold. Many off these features and terms are common to
the mold used in other casting processes. Figure 9.2(b) show the cross-sectional view of a typical send-casting mold, indicating some of the terminology. The mold consists of two halves cope and drag. The cope is the upper half of the mold, and the drag is the bottom half. These two mold parts are contained in a box called, a flask, which is also divided into two halves, one for the cope and the other for the drag. The two halves of the mold separate at the parting line.
In sand casting (and other expendable-mold processes) the mold cavity is formed by means of a pattern, which is made of wood, metal, plastic, or other material and has the shape of the part to be cast. The cavity is formed by packing sand aroundthe pattern, about
half each in the cope and drag, so that when the pattern is removed. The the remaining void has the desired shape of the cast part. The pattern is usually made oversized to allow for shrinkage of the metal as it solidifies and cools. The sand for the mold is moist and contains a binder to maintain its shape.
The cavity in the mold provides the external surfaces of the cast part. In addition, a
Casting may have internal surfaces. These surfaces are determined by means of a core, a
Form placed inside the mold cavity to define the interior geometry of the part. In sand casting, cores are generally made of sand, although other materials can be used, such as metals, plaster, and ceramics.
The gating system in a casting mold is the channel, or network of channels. By which molten metal flows into the cavity from outside the mold. As shown in the figure, the gating
System typically consists of a downsprue (also called simply the sprue), through which the metal enters a runner that leads into the main cavity. At the top of the downsprue, a pouring cup is often used to minimize splash and turbulence as the metal flows into the downsprue. It is shown in our diagram as a simple cone-shaped funnel. Some pouring cup are designed in the shape of a bowl, with open channel leading to the downsprue.
In addition to the gating system any casting in which shrinkage is significant requires
A riser connected to the main cavity. The riser reservoir in the mold that serves as a
Source of liquid metal for the casting to compensate for shrinkage during solidification. The
Riser must be designed to freeze after the main casting in order to satisfy its function.
As the metal flows into the mold.The air that previously previously occupied the cavity. As well as hot gases formed by reaction of the molten metal. Must be evacuated so that the metal will completely fill the empty space in sand casting for example the natural porosity of the sandmold permits the air and gasses to escape through the wail of the cavity in permanent metal molds small vent holes are drilled into the mold or machined into the parting line to permit removal of air and gases.