Aluminum Rotational Molds

This cast aluminum rotational mold can be modified using inserts so that either a BBQ-Donut Half (Figure 1.175) with steps of invert or a half with motor and umbrella holder can be molded. The mold consists of 10 mold shells. 

Figure 1.178 shows a CNC-machined aluminum rotational mold for a shaft cover (diameter 700 mm) with bent tubular steel frame and hand closures. 

Rotational Molding. Hodow articles and large, complex shapes are made by rotational mol ding, usuady from polyethylene powder of relatively low viscosity (57—59). The resin is in the form of a fine powder. A measured quantity is placed inside an aluminum mold and the mold is heated in an oven and rotated at low speed. The resin sinters and fuses, coating the inside of the mold. The mold is then cooled by water spray and the part solidifies, dupHcating the inside of the mold. 

Focusing collectors are usually cast acrylic Fresnel lenses, or mirrors of aluminized polyester film in frames of aluminum. These reflectors are either enclosed in a bubble of poly(vinyl fluoride) film, or under polycarbonate glazing, which may be covered with a fluorocarbon film to reduce the reflectivity. The absorbers for active systems are copper or aluminum since the temperatures are too high (325—370°C) for plastics. The frames, however, can be molded ABS, high density polyethylene or polyurethane, either solid or structural foam. Polybutylene or chlorinated PVC can be used for piping hot water, and tanks can be made of either reinforced polyester or blow- or rotational-molded, high density polyethylene (12—15). 

ETFE resins in the powder and bead form are rotationally molded into varied structures, such as pump bodies, tanks, and fittings and linings, mostly for the chemical process industries. Inserts can be incorporated to provide attachment points or reinforcement.41 Adhesion to steel, copper, and aluminum can be up to 3 kN/m (5.7 pli) peel force.44... 

The molds are mostly made of steel or aluminum. Since the forces during rotational molding are relatively small, wall thicknesses of 1.5 mm will be sufficient. 

Rotational molding Sheet steel, stainless steel, aluminum, cast aluminum, machined metal, electroformed nickel and copper... 

Molds from aluminum (aluminum casting and CNC-milled) or sheet steel are used today for rotational molds. Electroplated molding has established itself for special rotational molds for PVC plastisols. There are also a couple of other materials that can be used in prototype production. 

If the manufacturing practices show that the walls of the part are uneven, a remedy can be found through the installation of auxiliary panels made from sheet metal, through painting with aluminum colors, or through wall thickness modifications of rotational mold. Inserts made from plastic material or steel can be fixed into the walls of the molded parts, but must be preheated to initial temperature of the mold. It is important that the pins, which are necessary for the acceptance, are properly installed so that no plastic can leak at these points during the rotation. 

Slush molding of plastisols is primarily used to produce rainboots and overshoes, and secondarily for toy and doU parts, and for automotive interior skin coats. The secondary uses are popular where circumstances such as short mns of many variations militate against rotational molding. The molds, typically low-cost aluminum, are preheated to a temperature at which the plastisol will gel rapidly, then filled with plastisol. After a brief gelation time, the molds are emptied of excess plastisol and placed in a fusion oven, then cooled to permit demolding. 

The equipment used in rotational molding is relatively unsophisticated and inexpensive compared to other polyethylene-molding techniques. Molds are subjected to low stresses and can therefore be constructed of relatively lightweight and low cost materials such as sheet steel or cast aluminum, the latter being used for smaller items. Temperature and time regulation are not as critical as in other... 

Applications for extrusion blow molding are often similar to rotational molding. Extrusion blow molding is normally a faster process, but rotational molding can sometimes allow for thicker wall sections. Tools are usually steel, but can also be made of aluminum or other materials. 

The extruder operates at melt temperatures of 360 to -100°F. The temperature is regulated by external cooling, RPM adjustment, or barrel tolerance. Higher melt plastics such as PET and PC, and contaminants such as aluminum and copper become a filler in the melted resins. The molding unit consists of linear molds mounted on a turret that rotate through a... 

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