Page 19 - Module DMV20173

2.0 CASTING PROCESSES

Figure 2.8 Schematic illustration of the vacuum-casting process. Note that the mould has a

bottom gate. (a) Before and (b) after immersion of the mould into the molten metal.

2.5.2 SLUSH CASTING

1. Slush casting involves with hollow castings with thin walls that made by permanent-
mould casting.
2. This process is suitable for small production runs and generally is used for making

ornamental and decorative objects and toys from low melting-point metals such as
zinc, tin, and lead alloys.
3. The molten metal is poured into the metal mould. After the desired thickness of
solidified skin is obtained, the mould is inverted (or slung) and the remaining liquid

metal is poured out.
4. The mould halves then are opened, and the casting is removed.

2.5.3 PRESSURE CASTING

1. It is also one of the vacuum casting technique.

2. The molten metal flows into the mould cavity by gravity. In pressure casting (also
called pressure pouring or low-pressure casting), the molten metal is forced upward
by gas pressure into a graphite or metal mould as shown in Figure 3.9.
3. The pressure is maintained until the metal has solidified completely in the mould.
4. The molten metal also may be forced upward by a vacuum, which also removes

dissolved gases and produces a casting with lower porosity.

BPLK 51 DMV 20173