Rotomolded article

Whilst there has been extensive work done on the mechanical properties of rotomolded products and the heat transfer processes occurring during molding, " there has been relatively little work done on the unique microstructures that occur within rotomolded articles. This is surprising in view of the fact that the structures are very amenable to microstructural analysis. They display classic features in terms of spherulite geometries, and it is possible to relate mechanical properties to defects caused by the onset of thermal/oxidative degradation. 

The poor mixing ability of turbo-blending led to the pigment concentrating around the polymer particles and to the development of transciystalline textures in rotomolded articles. ... 

Special Molds. Some molds may require a complicated design, inserts, and special machining. Alignment pins may be used to ensure a perfect fit. If a rotomolded article contains a large section where no resin buildup is desired, the mold can be shielded with an insulating material such as Teflon. 

Rotomolded articles for packaging and durable goods Extruded profiles and sheet... 

In rotational molding, also known as rotomolding, the mold (or cavity) is filled with material, either as a solid powder or liquid. The mold is closed, placed in a heated oven, and then rotated biaxially. The mold is then cooled, opened, and the article recovered. Powders of about 35 mesh (500 pm) are typical though different sizes are also employed. The distribution of particles and additives is determined by the mixing/rotation ratio. 

This paper examines the structures that occur in rotomolded polyethylene and polypropylene produced under a wide range of processing conditions. The effects of pigments are investigated as well as the mechanical and thermal processes that plastic powders typically undergo during preparation for rotomolding. In all cases, the mechanical properties of the molded articles have been related to the microstructure. 

As commented, PVC plastisols are suspensions of emulsion PVC in a plasticizer. Formulations contain components such as pigments and thermal stabilizers, but plasticizers are by far the major component. PVC plastisols are rotomolded to obtain hollow soft articles, mainly in the toy industry. It could be deduced that mechanical properties of these parts are not important, but the finishing operations such as insertion of eyes and hair in dolls heads or mechanisms in arms and bodies, or final assembly, imply big loads apphed to the part, and consequently, the mechanical properties have to be developed to the full. Moreover, the molds used in these apphcations have very intricate shapes, pronounced ribs and comers, and aesthetics and details reproduction is very important in these parts. These complex shapes may involve high tensions in the moldings and corrrphcate the demolding process. To obtain a good thickness distribntion in snch a mold, variables involved in the process have to be at the optimnm. 

The common methods of processing LDPE are blown and cast film extrusion and coextrusion, extrusion coating, blow molding, injection molding, rotomolding, and wire extrusion. Explanations for these processes can he found in other articles in the Encyclopedia. 

In most rotomolding operations the molds or cavities are filled with a certain amount of powder or liquid (charging the molds) the mold halves are pressed together by bolts or clamps, placed in a heated oven, and rotated biaxially. During heating the resin melts, fuses, and densifies into the shape of the mold. The molds are moved into a cooling chamber, where they are slowly cooled by air and water. After removal from the cooling chamber, the molds are opened and the finished articles are released. 

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