Permanent mold casting

Other materials include tin, zinc, and lead alloys and iron and steel are also cast in graphite molds.

[1] There are four main types of permanent mold casting: gravity, slush, low-pressure, and vacuum.

Soon after solidification the mold is opened and the casting removed to reduce chances of hot tears.

Because this process is usually carried out on large production run work-pieces automated equipment is used to coat the mold, pour the metal, and remove the casting.

The process is usually used to cast ornamental products, such as candlesticks, lamp bases, and statuary, from low-melting-point materials.

Hollow cast figures generally have a small hole where the excess liquid was poured out.

[citation needed] Similarly, a process called slush molding is used in automotive dashboard manufacture, for soft-panel interiors with artificial leather, where a free-flowing (which behave like a liquid) powder plastic compound, either PVC or TPU, is poured into a hot, hollow mold and a viscous skin forms.

The pressure is applied to the top of the pool of liquid, which forces the molten metal up a refractory pouring tube and finally into the bottom of the mold.

The pouring tube extends to the bottom of the ladle so that the material being pushed into the mold is exceptionally clean.

Yields are usually greater than 85% because there is no riser and any metal in the pouring tube just falls back into the ladle for reuse.

Advantages include very little turbulence when filling the mold because of the constant pressure, which minimizes gas porosity and dross formation.

The fast cooling rates created by using a metal mold results in a finer grain structure than sand casting.

Retractable metal cores can be used to create undercuts while maintaining a quick action mold.

[2][3] There are three main disadvantages: high tooling cost, limited to low-melting-point metals, and short mold life.

A high pouring temperature can also induce shrinkage problems and create longer cycle times.