Permanent mold casting (gravity die casting)
In gravity die casting, the metal is poured into the mold using only the force of gravity. The mold is typically a two piece mold clamped solidly together.
Molds for casting iron or steel are made of graphite or other refractories. Molds for casting aluminum, magnesium or copper alloy castings are made of iron or die-steel. Molds incorporate the necessary sprues and risers, and also typically have pins for ejecting the castings. Materials:
Materials best suited for gravity die castings are materials with relatively low melting points in order to be fluid in the mold. Typically iron, magnesium alloys, and aluminum alloys are cast using this process. Copper and zinc alloys tend to be insufficiently fluid. Steel and steel alloys require special molds.
Typical applications are:
- pistons/cylinders/rods
- gears
- kitchenware
Advantages:
• the mold can be chilled to speed cooling
• good surface finish
• good dimensional accuracy
• only one mold is required
Disadvantages:
• limited numbers of alloys can be used
• complex shapes cannot be cast
• mold production is time consuming and costly
• mold sizes are limited
