Processing rotational casting

In recent years rotational casting methods have made the slush moulding process virtually obsolete. In these processes an amount of material equal to the weight of the finished product is poured into a mould. The mould is then closed and rotated slowly about two axes so that the paste flows easily over the cavity walls in an oven at about 200-250°C. When the compound has gelled, the moulds are cooled and the moulding removed. Compared with the slush moulding process there is no wastage of material, little flash, and more even wall thickness. Completely enclosed hollow articles such as playballs are most conveniently made. 

The fourth class is a miscellaneous collection of shaping processes, such as vacuum forming, calendering, rotation casting, and foaming. 

Anionic polymerization of nylon-based polymer systems to produce finished parts directly from monomers or prepolymers can be carried out by several processes e.g., reaction injection molding, low-pressure casting, resin transfer molding, rotational casting. 

FIGURE 2.43 Plastisol casting processes (a) dip casting (b) slush casting (c) rotational casting. 

PVC plastisols are suspensions of PVC resin in a hquid phase mainly constituted by the plasticizer and the stabilizer. Plastisols can be processed by different techniques, such as rotational casting, slush molding, dip molding, dip coating, or spray coating. In these pro-... 

Roto-molding n. A contraction of the term rotational molding, sometimes used indiscriminately for both the processes of rotational casting and rotational molding. 

Compounded with PVC, plasticizers change the rigid material so it is pliable and elastic across a range of temperature. With emulsion or micro-suspension PVC, the plasticizers form plastisol. The material with plasticizers in turn renders the possibility of room temperature shaping of end products produced by processes such as coating, dipping, and rotational casting. 

Another method for manufacturing polyurethane covers is the moldless rotational casting process (Fig. 6.12). Here the reacting polyurethane mixture is cast as a spiral on the rotating roll, the fast reaction of the polyurethane mixture prevents the material dripping off the roll. Layers of different hardness can be applied easily with this method. 

This form of PVC is called a plastisol or organisol. PVC in the fluid form can be processed by methods such as spread coating, rotational casting, dipping, and spraying. The parts are then dried with heat to remove any solvent and fuse the polymer. Parts such as handles for tools and vinyl gloves are produced by this method. 

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