Casting involves introducing a liquefied plastic into a mold and allowing it to solidify. In contrast to molding and extrusion, casting relies on atmospheric pressure to fill the mold rather than using significant force to push the plastic into the mold cavity. Some polymers have a viscosity similar to bread dough even when they are at elevated temperature so they are not candidates for the casting process. Examples of this are polymers like POM, PC, PP and many others. Casting includes a number of processes that take a monomer, powder or solvent solution and pur them into a mold. They transition from liquid to solid by either evaporation, chemical action, cooling or external heat. The final product can be removed from the mold once it solidifies.
Casting has several advantages:
-Cost of equipment, tooling and molds are low.
-The process is not complex.
-Products have little or no internal stress.
Casting can have some disadvantages:
-The output rate is slow and has long cycle times.
-Dimensional tolerances are not very good.
-Moisture and air bubbles can be difficult to manage and may cause problems.