Metal Casting Zone Info Blog

Posts Tagged ‘gypsum plaster’

With sand casting the mold is broken up after each casting operation, but with the process known as gravity die casting, the mold also called a ‘die’ is manufactured from metal, and can be utilised a giant number of times. This suggests that the die is far more costly to make, than an expendable ‘one use only’ mold. An intermediate technique gets use from semipermanent molds, which are made of gypsum plaster or fireclay, which may be employed continually for a controlled number of castings. With gravity die casting, the most widely used materials for die-making are cast iron, steel, and heat resisting alloys of iron. For some specific purposes other materials are used to manufacture the dies, and these can include, aluminum. Copper or graphite. A metal die can produce smooth castings with a clean surface, and a very high dimensional accuracy. These castings require awfully little last machining or other finishing treatment. The service life of metal dies can vary in terms of the amount of castings it can produce, and this relies on certain considerations such as the casting material, the thermal metal shock resistance of the die material, the temperature at which it is poured, and the casting technique employed.

Come visit us right here for more Metal Casting Info and get two Metal Casting Ebooks Aluminum Die Castings.

http://www.metalcastingzone.com/

Many different details need to be considered when designing the pattern from that the die is made. For example the pouring-gate system and risers have to be considered so that the walls of mold permit a quenching action upon the molten metal so it van harden more rapidly than in sand casting. Also the die must be supplied with channels at the joints and air vent holes to allow air from the hot metal to escape from the interior of the die. The die must also be built so it won’t restrict the shrinkage that occurs, when the metal cools. Shrinkage can present difficulties when designing the cores which form the casting. Usually the cores are made of steel or special alloys, and sometimes compressible sand or shell cores are used.

To prevent the casting metal from sticking to the die, the die can be given an internal coating of chalk, clay, or bone ash with water glass as a binder. This mixture can be applied to the die by spraying, brushing or immersion.

With straightforward castings the molten metal may be poured in at the top. It should be designed to allow the molten metal to flow quickly without turbulence into all elements of the die. For metals with low melting points the die is frequently heated to stop premature solidification, and for metals with a high melting point, the die may be artificially cooled after each casting operation.

Slowly moving or angling the die while casting can reduce turbulence and enable the metal to flow more smoothly, especially when heavy castings are being produced. For awkwardly formed castings, a vacuum may be applied to help the filling of the die. Slush casting, is a technique used for producing decorative or hollow castings : the molten metal is poured into the die, and when a solid shell of acceptable thickness has formed, the remaining liquid is poured out.

Although die castings are less expensive than sand castings, the die tooling is dearer, and a perfect number of castings have to be produced to make the process cheap.

Come visit us right here for more Metal Casting Info and get two Metal Casting Ebooks Aluminum Die Castings.

http://www.metalcastingzone.com/