Rotational casting

Die casting is used to make a solid object, but hollow objects cannot be produced by this method. Hollow objects such as balls and dolls are made by rotational casting. The resin and curative mixture is placed in a hollow mould that can rotate simultaneously along the primary and secondary axes. The resin takes the shape of the mould. The shape is fixed due resin curing under rotation at elevated temperature. The mould is then cooled and opened to remove the product. 

Flat sheets can be made using a rotating cylinder with lips on the ends. The cylinder must be level to ensure even thickness. The polyurethane mixture is added to the bottom of the horizontal drum, which is rotated at a speed of between 2 and 15 revolutions per minute. The thickness of the sheet is controlled by the weight of polyurethane added. The speed of rotation must be adjusted to suit the diameter of the cylinder and the viscosity of the mixture. The cylinder must be fully coated before gelation starts. 

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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. 

Spray ing/bru shing/rolling Resin transfer molding Rotational casting Rotomolding Thermoforming Compounding/vulcani-zation... 

Elastomers come next in order of quantity sold worldwide. Like the previous categories, elastomers cover an extremely broad range of material types and application areas. They include cast elastomers, spray and rotational casting elastomers, thermoplastic elastomers, microcellular elastomers, gels, and elastomeric fibers. Each type is covered separately.13d> 14... 

Rotational casting elastomers, 204 Rubber, urethane, 201 Rubberlike polymers, 18 Rubber-modified blends, 149 Rynite, 21... 

Figure 6 76 inch diameter E. B. Blue Co. rotational casting machine... 

Rotational casting is usually used in making hollow articles such as vessels, dummies, dolls, buoys, floate, etc. The weighed amount of plastisol is given into a metallic sealed mould which then is rotated in three mutually perpendicular directions upon heating in a chamber furnace. Upon gelatination the mould is cooled, stopped, opened, and the article is taken out. 

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

Rotational Casting. Like rotomolding, the plastisol is poured into a cold mold, which is rotated and heated to gel the plastisol onto the walls of the mold. It is then heated to fuse, cooled to solidify, opened, and the product removed. Typical products are volley balls, basketballs, dolls, and auto parts. 

One way which is often used to impart an artificial structure to the dispersion of a carbon black in a composite is to coat the particles of a moulding powder, e.g. 1 mm diameter particles of polyethylene, with a conductive carbon black by mixing them together in a ball-mill. If subsequent moulding does not shear the mixture too much (rotational casting is ideal) the black remains concentrated in a honeycomb-like network, and the overall conductivity is greatly enhanced over that of a uniform dispersion of the same proportion of black. 

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. 

In rotational casting, the reactant mixture is introduced into a closed mold which rotates around one or more axes so as to produce... 

Oxy. [OxyChem] PVC resins for blending, adhesives, flooring, coatings, records, color cones., automotive applies., inj. molded bottles and pipe fittings, calendered and extruded films, rigid foams, pipes, profiles, wire and cable, rotational castings. 

Rotational casting LDPE, LLDPE Melting, flow, and particle coalescence are required particularly flow under little more than gravity, though log times are involved... 

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

In rotational casting a predetermined amount of liquid plastisol is placed in a heated, closed, two-piece mold. The liquid is uniformly distributed against the walls of the mold in a thin uniform layer (Figure 2.43c) by rotating the mold in two planes. The solidified plastisol in the mold is cured in an oven the mold is then opened, and the part is removed. The method is used to make completely enclosed hollow objects. Doll parts, plastic fruits, squeeze bulbs, toilet floats, etc. can be made by rotational casting of plastisols. 

Plasticised suspension PVC is first melt compounded and then extrusion coated onto copper wire to provide electrical insulation. It can be calendered between parallel rolls to produce flexible sheeting for flooring. Emulsion PVC can be converted into a plastisol by mixing it with a high proportion (50-70%) of a plasticiser. The plastisol, containing swollen 1 xm particles suspended in the plasticiser, is a liquid at room temperature with a medium viscosity of 20-50 Nsm . It can be rotationally cast in moulds, coated onto wallpaper or cloth, or used to dip-coat metal products. A subsequent heating to between 150 and 175 °C causes the rest of the plasticiser to be absorbed in the PVC and the particles to fuse into a homogeneous solid. 

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