can be cast, in either rigid or flexible molds,//// into a variety of shapes (Fig- 18.14a). Typical pans cast are gears, bearings, wheels, thick sheets, and components requiring resistance to abrasive wear.
a. In the conventional casting of thermoplastics, a mixture of monomer, catalyst, and various additives is heated and poured into the mold. The part forms alter polymerization takes place at ambient pressure. Intricate shapes can be produced with flexible molds, which are then peeled off. Degassing may be necessary for product integrity.
b. Centrifugal casting. This process is also used with plastics, including reinforced plastics with short fibers. (See Section 11.13.) Thermosets arc cast in a similar manner; Typical parts produced are similar to those made by thermoplastic castings.
c. Potting and encapsulation. A variation of casting that is important to the electrical and electronics industry is potting and encapsulation This process involves casting the plastic around an electrical component to embed it in the plastic.
Potting (Fig. 1X. 14b) is done in a housing or case, which is an integral pan of the product In encapsulation (Fig. 18.14c), the component is coated with a layer of the solidified plastic. In both applications, the plastic serves as a dielectric (nonconductor). Structural members, such as hooks and studs, may be partly encapsulated.
FIGURE 18.14 Schematic illustration of (a) casting (b) potting, (c) encapsulation of plastics.